TY - JOUR
A1 - Grande, Vincenzo
A1 - Soberats, Bartolome
A1 - Herbst, Stefanie
A1 - Stepanenko, Vladimir
A1 - Würthner, Frank
T1 - Hydrogen-bonded perylene bisimide J-aggregate aqua material
N2 - A new twelvefold methoxy-triethyleneglycol-jacketed tetraphenoxy-perylene bisimide (MEG-PBI) amphiphile was synthesized that self-assembles into two types of supramolecular aggregates in water: red-coloured aggregates of low order and with weak exciton coupling among the PBIs and blue-coloured strongly coupled J-aggregates consisting of a highly ordered hydrogen-bonded triple helix of PBIs. At room temperature this PBI is miscible with water at any proportions which enables the development of robust dye aggregates in solution, in hydrogel states and in lyotropic liquid crystalline states. In the presence of 60–95 wt% water, self-standing coloured hydrogels exhibit colour changes from red to blue accompanied by a fluorescence light-up in the far-red region upon heating in the range of 30–50 °C. This phenomenon is triggered by an entropically driven temperature-induced hydrogen-bond-directed slipped stacking arrangement of the MEG-PBI chromophores within structurally well-defined J-aggregates. This versatile aqua material is the first example of a stable PBI J-aggregate in water. We anticipate that this study will open a new avenue for the development of biocompatible functional materials based on self-assembled dyes and inspire the construction of other hydrogen-bonded supramolecular materials in the highly competitive solvent water.
KW - self-assembly
KW - dyes
KW - aqua material
Y1 - 2018
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-204715
UR - https://doi.org/10.1039/C8SC02409J
SN - 2041-6539
VL - 9
ER -
TY - JOUR
A1 - Renner, Rebecca
A1 - Stolte, Matthias
A1 - Würthner, Frank
T1 - Self-Assembly of bowl-shaped naphthalimide-annulated
corannulene
JF - ChemistryOpen
N2 - The self-assembly of a bowl-shaped naphthalimide-annulated corannulene of high solubility has been studied in a variety of solvents by NMR and UV/Vis spectroscopy. Evaluation by the anti-cooperative K\(_2\)-K model revealed the formation of supramolecular dimers of outstanding thermodynamic stability. Further structural proof for the almost exclusive formation of dimers over extended aggregates is demonstrated by atomic force microscopy (AFM) and diffusion ordered spectroscopy (DOSY) measurements as well as by theoretical calculations. Thus, herein we present the first report of a supramolecular dimer of an annulated corannulene derivative in solution and discuss its extraordinarily high thermodynamic stability with association constants up to > 10\(^6\)M\(^-\) \(^1\) in methylcyclohexane, which is comparable to the association constants given for planar phthalocyanine and perylene bisimide dyes.
KW - corannulene
KW - π-π-interactions
KW - aelf-assembly
KW - aggregation
KW - supramolecular chemistry
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-204396
VL - 9
IS - 1
ER -
TY - JOUR
A1 - Mueller, Stefan
A1 - Lüttig, Julian
A1 - Malý, Pavel
A1 - Ji, Lei
A1 - Han, Jie
A1 - Moos, Michael
A1 - Marder, Todd B.
A1 - Bunz, Uwe H. F.
A1 - Dreuw, Andreas
A1 - Lambert, Christoph
A1 - Brixner, Tobias
T1 - Rapid multiple-quantum three-dimensional fluorescence spectroscopy disentangles quantum pathways
JF - Nature Communications
N2 - Coherent two-dimensional spectroscopy is a powerful tool for probing ultrafast quantum dynamics in complex systems. Several variants offer different types of information but typically require distinct beam geometries. Here we introduce population-based three-dimensional (3D) electronic spectroscopy and demonstrate the extraction of all fourth- and multiple sixth-order nonlinear signal contributions by employing 125-fold (1⨯5⨯5⨯5) phase cycling of a four-pulse sequence. Utilizing fluorescence detection and shot-to-shot pulse shaping in single-beam geometry, we obtain various 3D spectra of the dianion of TIPS-tetraazapentacene, a fluorophore with limited stability at ambient conditions. From this, we recover previously unknown characteristics of its electronic two-photon state. Rephasing and nonrephasing sixth-order contributions are measured without additional phasing that hampered previous attempts using noncollinear geometries. We systematically resolve all nonlinear signals from the same dataset that can be acquired in 8 min. The approach is generalizable to other incoherent observables such as external photoelectrons, photocurrents, or photoions.
KW - Atomic and molecular interactions with photons
KW - Optical spectroscopy
Y1 - 2019
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-202529
VL - 10
ER -
TY - JOUR
A1 - Fayez, Shaimaa
A1 - Feineis, Doris
A1 - Aké Assi, Laurent
A1 - Seo, Ean-Jeong
A1 - Efferth, Thomas
A1 - Bringmann, Gerhard
T1 - Ancistrobreveines A–D and related dehydrogenated naphthylisoquinoline alkaloids with antiproliferative activities against leukemia cells, from the West African liana Ancistrocladus abbreviatus
JF - RSC Advances
N2 - A unique series of six biaryl natural products displaying four different coupling types (5,10 , 7,10 , 7,80 , and 5,80) were isolated from the roots of the West African liana Ancistrocladus abbreviatus (Ancistrocladaceae). Although at first sight structurally diverse, these secondary metabolites all have in common that they belong to the rare group of naphthylisoquinoline alkaloids with a fully dehydrogenated isoquinoline portion. Among the African Ancistrocladus species, A. abbreviatus is so far only the second one that was found to produce compounds with such a molecular entity. Here, we report on four new representatives, named ancistrobreveines A–D (12–14, and 6). They were identified along with the two known alkaloids 6-O-methylhamateine (4) and entdioncophylleine A (10). The two latter naphthylisoquinolines had so far only been detected in Ancistrocladus species from Southeast Asia. All of these fully dehydrogenated alkaloids have in common being optically active despite the absence of stereogenic centers, due to the presence of the rotationally hindered biaryl axis as the only element of chirality. Except for ent-dioncophylleine A (10), which lacks an oxygen function at C-6, the ancistrobreveines A–D (12–14, and 6) and 6-O-methylhamateine (4) are 6-oxygenated alkaloids, and are, thus, typical ‘Ancistrocladaceae-type’ compounds. Ancistrobreveine C (14), is the first – and so far only – example of a 7,80-linked fully dehydrogenated naphthylisoquinoline discovered in nature that is configurationally stable at the biaryl axis. The stereostructures of the new alkaloids were established by spectroscopic (in particular HRESIMS, 1D and 2D NMR) and chiroptical (electronic circular dichroism) methods. Ancistrobreveine C (14) and 6-O-methylhamateine (4) exhibited strong antiproliferative activities against drug-sensitive acute lymphoblastic CCRF-CEM leukemia cells and their multidrugresistant subline, CEM/ADR5000.
KW - chemistry
Y1 - 2019
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201686
VL - 9
IS - 28
ER -
TY - JOUR
A1 - Mufusama, Jean-Pierre
A1 - Feineis, Doris
A1 - Mudogo, Virima
A1 - Kaiser, Marcel
A1 - Brun, Reto
A1 - Bringmann, Gerhard
T1 - Antiprotozoal dimeric naphthylisoquinolines, mbandakamines B\(_3\) and B\(_4\), and related 5,8′-coupled monomeric alkaloids, ikelacongolines A–D, from a Congolese Ancistrocladus liana
JF - RSC Advances
N2 - From the leaves of a botanically and phytochemically as yet unexplored Ancistrocladus liana discovered in the rainforests of the Central region of the Democratic Republic of the Congo in the vicinity of the town of Ikela, six new naphthylisoquinoline alkaloids were isolated, viz., two constitutionally unsymmetric dimers, the mbandakamines B\(_3\) (3) and B\(_4\) (4), and four related 5,8′-linked monomeric alkaloids, named ikelacongolines A–D (5a, 5b, 6, and 7). The dimers 3 and 4 are structurally unusual quateraryls comprising two 5,8′-coupled monomers linked via a sterically strongly constrained 6′,1′′-connection between their naphthalene units. These compounds contain seven elements of chirality, four stereogenic centers and three consecutive chiral axes. They were identified along with two known related compounds, the mbandakamines A (1) and B\(_2\) (2), which had so far only been detected in two Ancistrocladus species indigenous to the Northwestern Congo Basin. In addition, five known monomeric alkaloids, previously found in related Central African Ancistrocladus species, were isolated from the here investigated Congolese liana, three of them belonging to the subclass of 5,8′-coupled naphthylisoquinoline alkaloids, whereas two compounds exhibited a less frequently occurring 7,8′-biaryl linkage. The stereostructures of the new alkaloids were established by spectroscopic (in particular HRESIMS, 1D and 2D NMR), chemical (oxidative degradation), and chiroptical (electronic circular dichroism) methods. The mbandakamines B\(_3\) (3) and B\(_4\) (4) displayed pronounced activities in vitro against the malaria parasite Plasmodium falciparum and the pathogen of African sleeping sickness, Trypanosoma brucei rhodesiense.
KW - chemistry
Y1 - 2019
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201141
VL - 9
IS - 21
ER -
TY - JOUR
A1 - Tshitenge Tshitenge, Dieudonné
A1 - Bruhn, Torsten
A1 - Feineis, Doris
A1 - Mudogo, Virima
A1 - Kaiser, Marcel
A1 - Brun, Reto
A1 - Bringmann, Gerhard
T1 - An unusually broad series of seven cyclombandakamines, bridged dimeric naphthylisoquinoline alkaloids from the Congolese liana Ancistrocladus ealaensis
JF - Scientific Reports
N2 - A series of seven unusual dimeric naphthylisoquinoline alkaloids was isolated from the leaves of the tropical liana Ancistrocladus ealaensis J. Léonard, named cyclombandakamine A (1), 1-epi-cyclombandakamine A (2), and cyclombandakamines A3–7 (3–7). These alkaloids have a chemically thrilling structural array consisting of a twisted dihydrofuran-cyclohexenone-isochromene system. The 1′″-epimer of 4, cyclombandakamine A1 (8), had previously been discovered in an unidentified Ancistrocladus species related to A. ealaensis. Both lianas produce the potential parent precursor, mbandakamine A (9), but only A. ealaensis synthesizes the corresponding cyclized form, along with a broad series of slightly modified analogs. The challenging isolation required, besides multi-dimensional chromatography, the use of a pentafluorophenyl stationary phase. Featuring up to six stereocenters and two types of chiral axes, their structures were elucidated by means of 1D and 2D NMR, HRESIMS, in combination with oxidative chemical degradation experiments as well as chiroptical (electronic circular dichroism spectroscopy) and quantum chemical calculations. Compared to the ‘open-chain’ parent compound 9, these dimers displayed rather moderate antiplasmodial activities.
KW - Screening
KW - Solution-state NMR
KW - Stereochemistry
KW - Structure elucidation
Y1 - 2019
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-200759
VL - 9
ER -
TY - JOUR
A1 - Steinmetzger, Christian
A1 - Bäuerlein, Carmen
A1 - Höbartner, Claudia
T1 - Supramolecular fluorescence resonance energy transfer in nucleobase-modified fluorogenic RNA aptamers
JF - Angewandte Chemie, International Edition
N2 - RNA aptamers form compact tertiary structures and bind their ligands in specific binding sites. Fluorescence-based strategies reveal information on structure and dynamics of RNA aptamers. Here we report the incorporation of the universal emissive nucleobase analog 4-cyanoindole into the fluorogenic RNA aptamer Chili, and its application as a donor for supramolecular FRET to bound ligands DMHBI+ or DMHBO+. The photophysical properties of the new nucleobase-ligand-FRET pair revealed structural restraints for the overall RNA aptamer organization and identified nucleotide positions suitable for FRET-based readout of ligand binding. This strategy is generally suitable for binding site mapping and may also be applied for responsive aptamer devices.
KW - RNA aptamers
KW - fluorescence resonance energy transfer
KW - large stokes shift
KW - isomorphic nucleobase analog
KW - structure probing
KW - structure probes
KW - stokes shift
KW - Fluoreszenzresonanz-Energietransfer
KW - Isomorphe Nukleobasen-Analoga
KW - RNA-Aptamere
KW - Stokes-Verschiebung
KW - Struktursonden
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-203084
N1 - Parallel erschienen in Angewandte Chemie 2020,132, 6826–6830. DOI: 10.1002/ange.201916707 (Deutsche Ausgabe).
VL - 59
ER -
TY - JOUR
A1 - Hollmann, Claudia
A1 - Wiese, Teresa
A1 - Dennstädt, Fabio
A1 - Fink, Julian
A1 - Schneider-Schaulies, Jürgen
A1 - Beyersdorf, Niklas
T1 - Translational approaches targeting ceramide generation from sphingomyelin in T cells to modulate immunity in humans
JF - Frontiers in Immunology
N2 - In T cells, as in all other cells of the body, sphingolipids form important structural components of membranes. Due to metabolic modifications, sphingolipids additionally play an active part in the signaling of cell surface receptors of T cells like the T cell receptor or the co-stimulatory molecule CD28. Moreover, the sphingolipid composition of their membranes crucially affects the integrity and function of subcellular compartments such as the lysosome. Previously, studying sphingolipid metabolism has been severely hampered by the limited number of analytical methods/model systems available. Besides well-established high resolution mass spectrometry new tools are now available like novel minimally modified sphingolipid subspecies for click chemistry as well as recently generated mouse mutants with deficiencies/overexpression of sphingolipid-modifying enzymes. Making use of these tools we and others discovered that the sphingolipid sphingomyelin is metabolized to ceramide to different degrees in distinct T cell subpopulations of mice and humans. This knowledge has already been translated into novel immunomodulatory approaches in mice and will in the future hopefully also be applicable to humans. In this paper we are, thus, summarizing the most recent findings on the impact of sphingolipid metabolism on T cell activation, differentiation, and effector functions. Moreover, we are discussing the therapeutic concepts arising from these insights and drugs or drug candidates which are already in clinical use or could be developed for clinical use in patients with diseases as distant as major depression and chronic viral infection.
KW - sphingolipids
KW - CD4+ T cells
KW - regulatory T cells (Treg)
KW - CD8+ T cells
KW - anti-depressant drug
Y1 - 2019
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198806
SN - 1664-3224
VL - 10
IS - 2363
ER -
TY - JOUR
A1 - Steinmetzger, Christian
A1 - Bessi, Irene
A1 - Lenz, Ann-Kathrin
A1 - Höbartner, Claudia
T1 - Structure-fluorescence activation relationships of a large Stokes shift fluorogenic RNA aptamer
JF - Nucleic Acids Research
N2 - The Chili RNA aptamer is a 52 nt long fluorogen-activating RNA aptamer (FLAP) that confers fluorescence to structurally diverse derivatives of fluorescent protein chromophores. A key feature of Chili is the formation of highly stable complexes with different ligands, which exhibit bright, highly Stokes-shifted fluorescence emission. In this work, we have analyzed the interactions between the Chili RNA and a family of conditionally fluorescent ligands using a variety of spectroscopic, calorimetric and biochemical techniques to reveal key structure - fluorescence activation relationships (SFARs). The ligands under investigation form two categories with emission maxima of ~540 nm or ~590 nm, respectively, and bind with affinities in the nanomolar to low-micromolar range. Isothermal titration calorimetry was used to elucidate the enthalpic and entropic contributions to binding affinity for a cationic ligand that is unique to the Chili aptamer. In addition to fluorescence activation, ligand binding was also observed by NMR spectroscopy, revealing characteristic signals for the formation of a G-quadruplex only upon ligand binding. These data shed light on the molecular features required and responsible for the large Stokes shift and the strong fluorescence enhancement of red and green emitting RNA-chromophore complexes.
KW - Chili RNA Aptamer
KW - fluorogen-activating RNA aptamer (FLAP)
KW - Stokes-shifted fluorescence emission
KW - key structure - fluorescence activation relationships (SFARs)
KW - ligand binding
Y1 - 2019
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-192340
ER -
TY - JOUR
A1 - Tshitenge, Dieudonné Tshitenge
A1 - Feineis, Doris
A1 - Mudogo, Virima
A1 - Kaiser, Marcel
A1 - Brun, Reto
A1 - Bringmann, Gerhard
T1 - Antiplasmodial Ealapasamines A-C,'Mixed' Naphthylisoquinoline Dimers from the Central African Liana Ancistrocladus ealaensis
JF - Scientific Reports
N2 - Three unusual heterodimeric naphthylisoquinoline alkaloids, named ealapasamines A-C (1–3), were isolated from the leaves of the tropical plant Ancistrocladus ealaensis J. Léonard. These ‘mixed’, constitutionally unsymmetric dimers are the first stereochemically fully assigned cross-coupling products of a 5,8′- and a 7,8′-coupled naphthylisoquinoline linked via C-6′ in both naphthalene portions. So far, only two other West and Central Ancistrocladus species were known to produce dimers with a central 6,6″-axis, yet, in contrast to the ealapasamines, usually consisting of two 5,8′-coupled monomers, like e.g., in michellamine B. The new dimers 1–3 contain six elements of chirality, four stereogenic centers and the two outer axes, while the central biaryl axis is configurationally unstable. The elucidation of the complete stereostructures of the ealapasamines was achieved by the interplay of spectroscopic methods including HRESIMS, 1D and 2D NMR (in particular ROESY measurements), in combination with chemical (oxidative degradation) and chiroptical (electronic circular dichroism) investigations. The ealapasamines A-C display high antiplasmodial activities with excellent half-maximum inhibition concentration values in the low nanomolar range.
KW - structure elucidation
KW - stereochemistry
KW - Ancistrocladus ealaensis
KW - dimers
Y1 - 2017
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170645
VL - 7
IS - 5767
ER -
TY - JOUR
A1 - Pimentel-Elardo, Sheila M.
A1 - Buback, Verena
A1 - Gulder, Tobias A. M.
A1 - Bugni, Tim S.
A1 - Reppart, Jason
A1 - Bringmann, Gerhard
A1 - Ireland, Chris M.
A1 - Schirmeister, Tanja
A1 - Hentschel, Ute
T1 - New Tetromycin Derivatives with Anti-Trypanosomal and Protease Inhibitory Activities
JF - Marine drugs
N2 - Four new tetromycin derivatives, tetromycins 1-4 and a previously known one, tetromycin B (5) were isolated from Streptomyces axinellae Pol001(T) cultivated from the Mediterranean sponge Axinella polypoides. Structures were assigned using extensive 1D and 2D NMR spectroscopy as well as HRESIMS analysis. The compounds were tested for antiparasitic activities against Leishmania major and Trypanosoma brucei, and for protease inhibition against several cysteine proteases such as falcipain, rhodesain, cathepsin L, cathepsin B, and viral proteases SARS-CoV M(pro), and PL(pro). The compounds showed antiparasitic activities against T. brucei and time-dependent inhibition of cathepsin L-like proteases with K(i) values in the low micromolar range.
KW - cysteine protease
KW - drugs
KW - streptomyces
KW - discovery
KW - anti-trypanosomal
KW - protease inhibition
KW - Streptomyces axinellae
KW - marine sponge
KW - tetromycin
Y1 - 2011
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-141171
VL - 9
IS - 10
ER -
TY - JOUR
A1 - He, Tao
A1 - Stolte, Matthias
A1 - Burschka, Christian
A1 - Hansen, Nis Hauke
A1 - Musiol, Thomas
A1 - Kälblein, Daniel
A1 - Pflaum, Jens
A1 - Tao, Xutang
A1 - Brill, Jochen
A1 - Würthner, Frank
T1 - Single-crystal field-effect transistors of new Cl\(_{2}\)-NDI polymorph processed by sublimation in air
JF - Nature Communications
N2 - Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (\(\beta\)-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (\(\alpha\)-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\alpha\)-phase) and up to 3.5 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\beta\)-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on \(\beta\)-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\). The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.
KW - thin-film transistors
KW - carrier transport
KW - \(\beta\)-phase
KW - organic semiconductors
KW - induced phase transition
KW - charge transport
KW - materials design
KW - \(\alpha\)-phase
KW - mobility
KW - pentacene
Y1 - 2015
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149255
VL - 6
IS - 5954
ER -
TY - JOUR
A1 - Görl, Daniel
A1 - Zhang, Xin
A1 - Stepanenko, Vladimir
A1 - Würthner, Frank
T1 - Supramolecular block copolymers by kinetically controlled co-self-assembly of planar and core-twisted perylene bisimides
JF - Nature Communications
N2 - New synthetic methodologies for the formation of block copolymers have revolutionized polymer science within the last two decades. However, the formation of supramolecular block copolymers composed of alternating sequences of larger block segments has not been realized yet. Here we show by transmission electron microscopy (TEM), 2D NMR and optical spectroscopy that two different perylene bisimide dyes bearing either a flat (A) or a twisted (B) core self-assemble in water into supramolecular block copolymers with an alternating sequence of (A\(_{m}\)BB)\(_{n}\). The highly defined ultralong nanowire structure of these supramolecular copolymers is entirely different from those formed upon self-assembly of the individual counterparts, that is, stiff nanorods (A) and irregular nanoworms (B), respectively. Our studies further reveal that the as-formed supramolecular block copolymer constitutes a kinetic self-assembly product that transforms into thermodynamically more stable self-sorted homopolymers upon heating.
KW - cylindrical micelles
KW - water
KW - amplification
KW - association
KW - emission
KW - organization
KW - polymerization
KW - dyes
KW - fluorescent
KW - aqueous medium
Y1 - 2015
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148657
VL - 6
IS - 7009
ER -
TY - JOUR
A1 - Sung, Jooyoung
A1 - Kim, Pyosang
A1 - Fimmel, Benjamin
A1 - Würthner, Frank
A1 - Kim, Dongho
T1 - Direct observation of ultrafast coherent exciton dynamics in helical π-stacks of self-assembled perylene bisimides
JF - Nature Communications
N2 - Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with pi-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π-π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process.
KW - systems
KW - molecules
KW - J-aggregate behavior
KW - absorption
KW - spectroscopy
KW - photoluminescence
KW - diffusion
KW - fluorescence
KW - excimer formation
KW - organic semiconductors
Y1 - 2015
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148157
VL - 6
IS - 8646
ER -
TY - JOUR
A1 - Görl, Daniel
A1 - Soberats, Bartolome
A1 - Herbst, Stefanie
A1 - Stepanenko, Vladimir
A1 - Würthner, Frank
T1 - Perylene bisimide hydrogels and lyotropic liquid crystals with temperature-responsive color change
JF - Chemical Science
N2 - The self-assembly of perylene bisimide (PBI) dyes bearing oligo ethylene glycol (OEG) units in water affords responsive functional nanostructures characterized by their lower critical solution temperature (LCST). Tuning of the LCST is realized by a supramolecular approach that relies on two structurally closely related PBI–OEG molecules. The two PBIs socially co-assemble in water and the resulting nanostructures exhibit a single LCST in between the transition temperatures of the aggregates formed by single components. This permits to precisely tune the transition from a hydrogel to a lyotropic liquid crystal state at temperatures between 26 and 51 °C by adjusting the molar fraction of the two PBIs. Owing to concomitant changes in PBI–PBI interactions this phase transition affords a pronounced color change with “fluorescence-on” response that can be utilized as a smart temperature sensory system.
KW - perylene bisimide hydrogels
Y1 - 2016
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-162459
VL - 7
IS - 11
ER -
TY - JOUR
A1 - Becam, Jérôme
A1 - Walter, Tim
A1 - Burgert, Anne
A1 - Schlegel, Jan
A1 - Sauer, Markus
A1 - Seibel, Jürgen
A1 - Schubert-Unkmeir, Alexandra
T1 - Antibacterial activity of ceramide and ceramide analogs against pathogenic Neisseria
JF - Scientific Reports
N2 - Certain fatty acids and sphingoid bases found at mucosal surfaces are known to have antibacterial activity and are thought to play a more direct role in innate immunity against bacterial infections. Herein, we analysed the antibacterial activity of sphingolipids, including the sphingoid base sphingosine as well as short-chain C\(_{6}\) and long-chain C\(_{16}\)-ceramides and azido-functionalized ceramide analogs against pathogenic Neisseriae. Determination of the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) demonstrated that short-chain ceramides and a ω-azido-functionalized C\(_{6}\)-ceramide were active against Neisseria meningitidis and N. gonorrhoeae, whereas they were inactive against Escherichia coli and Staphylococcus aureus. Kinetic assays showed that killing of N. meningitidis occurred within 2 h with ω–azido-C\(_{6}\)-ceramide at 1 X the MIC. Of note, at a bactericidal concentration, ω–azido-C\(_{6}\)-ceramide had no significant toxic effect on host cells. Moreover, lipid uptake and localization was studied by flow cytometry and confocal laser scanning microscopy (CLSM) and revealed a rapid uptake by bacteria within 5 min. CLSM and super-resolution fluorescence imaging by direct stochastic optical reconstruction microscopy demonstrated homogeneous distribution of ceramide analogs in the bacterial membrane. Taken together, these data demonstrate the potent bactericidal activity of sphingosine and synthetic short-chain ceramide analogs against pathogenic Neisseriae.
KW - ceramide analogs
KW - Neisseria
KW - ceramide
Y1 - 2017
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-159367
VL - 7
ER -
TY - JOUR
A1 - Wolter, Steffen
A1 - Aizezers, Janis
A1 - Fennel, Franziska
A1 - Seidel, Marcus
A1 - Würthner, Frank
A1 - Kühn, Oliver
A1 - Lochbrunner, Stefan
T1 - Size-dependent exciton dynamics in one-dimensional perylene bisimide aggregates
JF - New Journal of Physics
N2 - The size-dependent exciton dynamics of one-dimensional aggregates of substituted perylene bisimides are studied by ultrafast transient absorption spectroscopy and kinetic Monte-Carlo simulations as a function of the excitation density and the temperature in the range of 25-90 degrees C. For low temperatures, the aggregates can be treated as infinite chains and the dynamics is dominated by diffusion-driven exciton-exciton annihilation. With increasing temperature the aggregates dissociate into small fragments consisting of very few monomers. This scenario is also supported by the time-dependent anisotropy deduced from polarization-dependent experiments.
KW - rotational diffusion
KW - spectroscopy
KW - dyes
KW - annihilation
KW - migration
KW - films
Y1 - 2012
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-135190
VL - 14
IS - 105027
ER -
TY - JOUR
A1 - Messi, Bernadette Biloa
A1 - Ndjoko-Ioset, Karine
A1 - Hertlein-Amslinger, Barbara
A1 - Lannang, Alain Meli
A1 - Nkengfack, Augustin E.
A1 - Wolfender, Jean-Luc
A1 - Hostettmann, Kurt
A1 - Bringmann, Gerhard
T1 - Preussianone, a New Flavanone-Chromone Biflavonoid from Garcinia preussii Engl.
JF - Molecules
N2 - A new flavanone-chromone biflavonoid, preussianone (1), has been isolated from the leaves of Garcinia preussii, along with four known biflavonoids. The absolute stereostructures were elucidated by chemical, spectroscopic, and chiroptical methods. The biological properties of the new biflavonoid against several bacterial strains were evaluated.
KW - multiflora
KW - minimal inhibitory concentration
KW - absolute configuration
KW - circular dichroism
KW - C-13 NMR
KW - guttiferae
KW - flavenoids
KW - extractives
KW - biflavanoids
KW - livingstonei
KW - high-temperature NMR
KW - antibacterial activity
KW - Garcinia biflavonoids
Y1 - 2012
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-130881
VL - 17
IS - 5
ER -
TY - JOUR
A1 - Jansen, Nils
A1 - Ohlendorf, Birgit
A1 - Erhard, Arlette
A1 - Bruhn, Torsten
A1 - Bringmann, Gerhard
A1 - Imhoff, Johannes F.
T1 - Helicusin E, Isochromophilone X and Isochromophilone XI: New Chloroazaphilones Produced by the Fungus Bartalinia robillardoides Strain LF550
JF - Marine Drugs
N2 - Microbial studies of the Mediterranean sponge Tethya aurantium led to the isolation of the fungus Bartalinia robillardoides strain LF550. The strain produced a number of secondary metabolites belonging to the chloroazaphilones. This is the first report on the isolation of chloroazaphilones of a fungal strain belonging to the genus Bartalinia. Besides some known compounds (helicusin A (1) and deacetylsclerotiorin (2)), three new chloroazaphilones (helicusin E (3); isochromophilone X (4) and isochromophilone XI (5)) and one new pentaketide (bartanolide (6)) were isolated. The structure elucidations were based on spectroscopic analyses. All isolated compounds revealed different biological activity spectra against a test panel of four bacteria: three fungi; two tumor cell lines and two enzymes.
KW - tethya aurantium
KW - marine natural product
KW - azaphilone
KW - pentaketide
KW - bartalinia robillardoides
Y1 - 2013
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129649
VL - 11
IS - 3
ER -
TY - JOUR
A1 - Rest, Christina
A1 - Mayoral, María José
A1 - Fernández, Gustavo
T1 - Aqueous Self-Sorting in Extended Supramolecular Aggregates
JF - International Journal of Molecular Sciences
N2 - Self-organization and self-sorting processes are responsible for the regulation and control of the vast majority of biological processes that eventually sustain life on our planet. Attempts to unveil the complexity of these systems have been devoted to the investigation of the binding processes between artificial molecules, complexes or aggregates within multicomponent mixtures, which has facilitated the emergence of the field of self-sorting in the last decade. Since, artificial systems involving discrete supramolecular structures, extended supramolecular aggregates or gel-phase materials in organic solvents or—to a lesser extent—in water have been investigated. In this review, we have collected diverse strategies employed in recent years to construct extended supramolecular aggregates in water upon self-sorting of small synthetic molecules. We have made particular emphasis on co-assembly processes in binary mixtures leading to supramolecular structures of remarkable complexity and the influence of different external variables such as solvent and concentration to direct recognition or discrimination processes between these species. The comprehension of such recognition phenomena will be crucial for the organization and evolution of complex matter.
KW - co-aggregation
KW - self-sorting
KW - supramolecular chemistry
KW - self-assembly
Y1 - 2013
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129435
VL - 14
IS - 1
ER -
TY - JOUR
A1 - Wang, Hui
A1 - Li, Min-Yi
A1 - Katele, Félix Zongwe
A1 - Satyanandamurty, Tirumani
A1 - Wu, Jun
A1 - Bringmann, Gerhard
T1 - Decandrinin, an unprecedented \(C_9\)-spiro-fused 7,8-\( seco-ent\)-abietane from the Godavari mangrove \(Ceriops\ decandra\)
JF - Beilstein Journal of Organic Chemistry
N2 - Decandrinin (1), an unprecedented \(C_9\)-spiro-fused 7,8-\(seco-ent\)-abietane, was obtained from the bark of an Indian mangrove, \(Ceriops\ decandra\), collected in the estuary of Godavari, Andhra Pradesh. The constitution and the relative configuration of 1 were determined by HRMS (ESI) and extensive NMR investigations, and the absolute configuration by circular dichroism (CD) and optical-rotatory dispersion (ORD) spectroscopy in combination with quantum-chemical calculations. Decandrinin is the first 7,8-\(seco-ent\)-abietane.
KW - ceriops decandra
KW - abietane
KW - absolute configuration
KW - circular dichroism
KW - decandrinin
KW - rhizophoraceae
Y1 - 2014
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119983
SN - 1860-5397
VL - 10
ER -
TY - JOUR
A1 - Kunz, Anna Lena
A1 - Labes, Antje
A1 - Wiese, Jutta
A1 - Bruhn, Torsten
A1 - Bringmann, Gerhard
A1 - Imhoff, Johannes F.
T1 - Nature's Lab for Derivatization: New and Revised Structures of a Variety of Streptophenazines Produced by a Sponge-Derived Streptomyces Strain
JF - Marine Drugs
N2 - Eight streptophenazines (A-H) have been identified so far as products of Streptomyces strain HB202, which was isolated from the sponge Halichondria panicea from the Baltic Sea. The variation of bioactivities based on small structural changes initiated further studies on new derivatives. Three new streptophenazines (I-K) were identified after fermentation in the present study. In addition, revised molecular structures of streptophenazines C, D, F and H are proposed. Streptophenazines G and K exhibited moderate antibacterial activity against the facultative pathogenic bacterium Staphylococcus epidermidis and against Bacillus subtilis. All tested compounds (streptophenazines G, I-K) also showed moderate activities against PDE 4B.
KW - marine natural product
KW - phenazine
KW - Baltic Sea
KW - streptomyces
KW - halichondria panicea
KW - obstructive pulmonary disease
KW - phosphodiesterase-4 inhibitor
KW - absolute configuration
KW - biosynthesis
KW - rofumilast
Y1 - 2014
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-116816
SN - 1660-3397
VL - 12
IS - 4
ER -
TY - JOUR
A1 - Epe, Bernd
A1 - Häring, Martin
A1 - Ramaiah, Danaboyina
A1 - Stopper, Helga
A1 - Abou-Elzahab, Mohamed M.
A1 - Adam, Waldemar
A1 - Saha-Möller, Chantu R.
T1 - DNA damage induced by furocoumarin hydroperoxides plus UV (360 nm)
N2 - Wben irradiated at 360 nm, furocoumarins with a hydroperoxide group in a side chain effciently give rise to a type of DNA damage that can best be explained by a photoinduced generation of hydroxyl radicals from the excited pbotosensitizers. The observed DNA damage profiles, i.e. the ratios of single-strand breaks, sites of base loss (AP sites) and base modifications sensitive to fonnamidopyrimidine-DNA glycosylase (FPG protein) and endonuclease m, are similar to the DNA damage profile produced by hydroxyl radicals generated by lonizing radiation or by xanthine and xanthine oxidase in the presence of Fe(III)-EDTA. No such damage is observed with the corresponding furocoumarin alcohols or in the absence of near-UV radiation. The damage caused by the photo-excited hydroperoxides is not influenced by superoxide dismutase (SOD) or catalase or by D2O as solvent. The presence of t-butanol, however, reduces both the formation of single-strand breaks and of base odifications sensitive to FPG protein. The cytotoxicity caused by one of the hydroperoxides in L5178Y mome lymphoma cells is found to be dependent on the near-UV irradiation and to be much higher than that of the corresponding alcohol. Therefore the new type of photoinduced damage occurs inside cells. Intercalating photosensitizers with an attached hydroperoxide group might represent a novel and versatile class of DNA damaging agents, e.g. for phototherapy.
KW - DNS-Schädigung
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-86870
ER -
TY - JOUR
A1 - Brixner, Tobias
A1 - Koch, Federico
A1 - Kullmann, Martin
A1 - Selig, Ulrike
A1 - Nuernberger, Patrick
A1 - Götz, Daniel C. G.
A1 - Bringmann, Gerhard
T1 - Coherent two-dimensional electronic spectroscopy in the Soret band of a chiral porphyrin dimer
JF - New Journal of Physics
N2 - Using coherent two-dimensional (2D) electronic spectroscopy in fully noncollinear geometry, we observe the excitonic coupling of β,β'-linked bis[tetraphenylporphyrinato-zinc(II)] on an ultrafast timescale in the excited state. The results for two states in the Soret band originating from an excitonic splitting are explained by population transfer with approximately 100 fs from the energetically higher to the lower excitonic state. This interpretation is consistent with exemplary calculations of 2D spectra for a model four-level system with coupling.
KW - optics
KW - quantum optics
KW - laser
Y1 - 2013
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-96139
ER -
TY - JOUR
A1 - Homann, Arne
A1 - Timm, Malte
A1 - Seibel, Jürgen
T1 - Chemo-enzymatic synthesis and in vitro cytokine profiling of tailor-made oligofructosides
N2 - Background It is well known that carbohydrates play fundamental roles in cell signaling and infection processes as well as tumor formation and progression. However, the interaction pathways and cellular receptors targeted by carbohydrates and glycoconjugates remain poorly examined and understood. This lack of research stems, at least to a major part, from accessibility problems of large, branched oligosaccharides. Results To test glycan - cell interactions in vitro, a variety of tailored oligosaccharides was synthesized chemo-enzymatically. Glycosyltransferases from the GRAS organisms Bacillus megaterium (SacB) and Aspergillus niger (Suc1) were used in this study. Substrate engineering of these glycosyltransferases generally acting on sucrose leads to the controlled formation of novel tailored di-, tri- and tetrasaccharides. Already industrially used as prebiotics in functional food, the immunogenic potential of novel oligosaccharides was characterized in this study. A differential secretion of CXCL8 and CCL2 was observed upon oligosaccharide co-cultivation with colorectal epithelial Caco-2 cells. Conclusion Pure carbohydrates are able to stimulate a cytokine response in human endothelial cells in vitro. The type and amount of cytokine secretion depends on the type of co-cultivated oligosaccharide.
KW - Chemie
KW - Oligofructoside
KW - Glycosyltransferase
KW - Suc1
KW - Aspergillus niger
KW - SacB
KW - Bacillus megaterium
KW - CXCL8 (IL-8)
KW - CCL2 (MCP-1)
KW - Caco-2
Y1 - 2012
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-76393
ER -
TY - JOUR
A1 - Cecil, Alexander
A1 - Rikanovic, Carina
A1 - Ohlsen, Knut
A1 - Liang, Chunguang
A1 - Bernhardt, Jorg
A1 - Oelschlaeger, Tobias A.
A1 - Gulder, Tanja
A1 - Bringmann, Gerd
A1 - Holzgrabe, Ulrike
A1 - Unger, Matthias
A1 - Dandekar, Thomas
T1 - Modeling antibiotic and cytotoxic effects of the dimeric isoquinoline IQ-143 on metabolism and its regulation in Staphylococcus aureus, Staphylococcus epidermidis and human cells
N2 - Background: Xenobiotics represent an environmental stress and as such are a source for antibiotics, including the isoquinoline (IQ) compound IQ-143. Here, we demonstrate the utility of complementary analysis of both host and pathogen datasets in assessing bacterial adaptation to IQ-143, a synthetic analog of the novel type N,C-coupled naphthyl-isoquinoline alkaloid ancisheynine. Results: Metabolite measurements, gene expression data and functional assays were combined with metabolic modeling to assess the effects of IQ-143 on Staphylococcus aureus, Staphylococcus epidermidis and human cell lines, as a potential paradigm for novel antibiotics. Genome annotation and PCR validation identified novel enzymes in the primary metabolism of staphylococci. Gene expression response analysis and metabolic modeling demonstrated the adaptation of enzymes to IQ-143, including those not affected by significant gene expression changes. At lower concentrations, IQ-143 was bacteriostatic, and at higher concentrations bactericidal, while the analysis suggested that the mode of action was a direct interference in nucleotide and energy metabolism. Experiments in human cell lines supported the conclusions from pathway modeling and found that IQ-143 had low cytotoxicity. Conclusions: The data suggest that IQ-143 is a promising lead compound for antibiotic therapy against staphylococci. The combination of gene expression and metabolite analyses with in silico modeling of metabolite pathways allowed us to study metabolic adaptations in detail and can be used for the evaluation of metabolic effects of other xenobiotics.
KW - Staphylococcus aureus
Y1 - 2011
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-68802
ER -
TY - JOUR
A1 - Pratihar, Pampa
A1 - Ghosh, Suhrit
A1 - Stepanenko, Vladimir
A1 - Patwardhan, Sameer
A1 - Grozema, Ferdinand C.
A1 - Siebbeles, Laurens D. A.
A1 - Würthner, Frank
T1 - Self-assembly and semiconductivity of an oligothiophene supergelator
N2 - A bis(trialkoxybenzamide)-functionalized quaterthiophene derivative was synthesized and its self-assembly properties in solution were studied. In non-polar solvents such as cyclohexane, this quaterthiophene π-system formed fibril aggregates with an H-type molecular arrangement due to synergistic effect of hydrogen bonding and π-stacking. The self-assembled fibres were found to gelate numerous organic solvents of diverse polarity. The charge transport ability of such elongated fibres of quaterthiophene π-system was explored by the pulse radiolysis time resolved microwave conductivity (PR-TRMC) technique and moderate mobility values were obtained. Furthermore, initial AFM and UV-vis spectroscopic studies of a mixture of our electron-rich quaterthiophene derivative with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) revealed a nanoscale segregated assembly of the individual building blocks in the blend.
KW - Organische Chemie
KW - charge transport; hydrogen bonding; oligothiophene; organogel; self-assembly
Y1 - 2010
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-67817
ER -
TY - JOUR
A1 - Homann, Arne
A1 - Qamar, Riaz-ul
A1 - Serim, Sevnur
A1 - Dersch, Petra
A1 - Seibel, Juergen
T1 - Bioorthogonal metabolic glycoengineering of human larynx carcinoma (HEp-2) cells targeting sialic acid
N2 - Sialic acids are located at the termini of mammalian cell-surface glycostructures, which participate in essential interaction processes including adhesion of pathogens prior to infection and immunogenicity. Here we present the synthesis and bioorthogonal metabolic incorporation of the sialic acid analogue N-(1-oxohex-5-ynyl)neuraminic acid (Neu5Hex) into the cell-surface glycocalyx of a human larynx carcinoma cell line (HEp-2) and its fluorescence labelling by click chemistry.
KW - Organische Chemie
KW - bioorthogonal metabolic glycoengineering; click chemistry; sialic acid
Y1 - 2010
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-67806
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Brüntrup, Gisela
T1 - Diimine Reduction and Ozonolysis of Benzvalene
N2 - Via reduction of benzvalene (1) with diirnine tricyclo[3.1.0.02•6]hexane is obtained in good yield. The procedure renders 3, which has already been synthesized by Lemal and Shim, accessible much easier and in larger quantities. IH and 13C n.m.r. spectroscopic data are discussed. Both the thermal and the AgBF4-catalyzed rearrangernent of 3 yield 1,3-cyclohexadiene (8). - The ozonolysis of 1 with subsequent LiAIH4-reduction results in cis-I,3- bis(hydroxyrnethyl)cyclobutane (13a).
N2 - Durch Reduktion von Benzvalen (1) mit Diimin wird das Tricyc1o[3.1.0.02•6]hexan (3) in guter Ausbeute erhalten. Das Verfahren macht das bereits von Lemal und Shim dargestellte 3 erheblich leichter und in größeren Mengen zugänglich. IH- und 13C-NMR-spektroskopische Daten werden diskutiert. Sowohl die thermische als auch die AgBF4-katalysierte Umlagerung von 3 führt zu 1,3-Cyclohexadien (8). - Die Ozonolyse von 1 mit anschließender LiAlH4-Reduktion ergibt das cis-l,3-Bis(hydroxymethyl)cyclobutan (13a).
KW - Organische Chemie
Y1 - 1974
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-57953
ER -
TY - JOUR
A1 - Kaupp, Martin
A1 - Schleyer, Paul von Rague
T1 - Do Low-Coordinated Group 1-3 cations M\(^n\) \(^+\)L\(_m\) (Mn\(^+\) = K\(^+\), Rb\(^+\), Cs\(^+\), Ca\(^{2+}\), Sr\(^{2+}\), Ba\(^{2+}\), Sc\(^{3+}\), Y\(^{3+}\), La\(^{3+}\); L = NH\(_3\), H\(_2\)0, HF; m = 1-3) with a Formal Noble-Gas Electron Configuration Favor Regular or "Abnormal" Shapes?
N2 - No abstract available
KW - Anorganische Chemie
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60111
ER -
TY - JOUR
A1 - Wissing, Elmo
A1 - Kaupp, Martin
A1 - Boersma, Jaap
A1 - Spek, Anthony L.
A1 - Koten, Gerard van
T1 - Alkylation Reactions of Dialkylzinc Compounds with 1,4- Diaza- 1,3-butadienes: Cationic and radical Anionic Organozinc Intermediates. Molecular Structure of the Cationic Organozinc Species [MeZn(t-BuN=CHCH=N-t-Bu)]O\(_3\)SCF\(_3\) and Me\(_2\)Zn(bpy)(bpy = 2,2' -Bipyridine)
N2 - No abstract available
KW - Anorganische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60008
ER -
TY - JOUR
A1 - Suter, H. U.
A1 - Pleß, V.
A1 - Ernzerhof, M.
A1 - Engels, Bernd
T1 - Difficulties in the Calculation of Electron Spin Resonance Parameters using Density Functional Methods
N2 - Density functional theory is applied to the calculation ofthe isotropic byperfine coupJing constants in some small molecules. Various functionals are tested. The agreement of the calculated values to experimental data and values obtained from sophisticated ab initio methods depends on the functionals used and the system under consideration. With respect to spin density calculations the functional of Lee, Yang and Parr with Becke's excbange functional (BLYP) is found to give good results for tbe heavier center of the CH and the NH molecule, while the spin densities of other molecules such as OH, H\(_2\)CN, H\(_2\)CO\(^+\), NO and O\(_2\) deviate considerably from experimental and/or other theoretical results (30%-60%). In cases where the singly occupied orbital can contribute to the isotropic hyperfine coupling constants, accurate results are obtained. The reason fortbis is analyzed.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59113
ER -
TY - JOUR
A1 - Suter, H. U.
A1 - Huang, M.-B.
A1 - Engels, Bernd
T1 - A Multireference Configuration Interaction Study of the Hyperfine Structure of the Molecules CCO, CNN and NCN in their triplet ground states
N2 - The hyperfine structures of the isoelectronic molecules CCO. CNN, and NCN in their triplet ground states (X\(^3 \sum ^-\)) are investigated by means of ab initio methods. The infrared frequencies and geometries are detennined and compared with experiment. Configuration selected multireference configuration interaction calculations in combination with perturbation theory to correct the wave function (MRD-CI/B\(_K\)) employing extended atomic orbital (AO) basis sets yielded very accurate hyperfine properties. The theoretical values for CCO are in excellent agreement with the experimental values determined by Smith and Weltner [J. Chem. Phys. 62,4592 (1975)]. For CNN, the first assignment of Smith and Weltner for the two nitrogen atoms has to be changed. A qualitative discussion of the electronic structure discloses no simple relation between the structure of the singly occupied orbitals and the measured hyperfine coupling constants. Vibrational effects were found to be of little importance.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59108
ER -
TY - JOUR
A1 - Froudakis, G.
A1 - Zdetsis, A.
A1 - Mühlhäuser, M.
A1 - Engels, Bernd
A1 - Peyerimhoff, S. D.
T1 - A comparative ab initio study of the Si\(_2\)C\(_4\), Si\(_3\)C\(_3\), Si\(_4\)C\(_2\) clusters
N2 - Various structural possibilities for the Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order M0ller-Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si\(_3\)C\(_3\) clusters is found to be fully operative for Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters. A comparison of the structure and stability of various geometrical arrangements in the series C\(_6\) , Si\(_2\)C\(_4\) , Si\(_3\)C\(_3\) , Si\(_4\)C\(_2\), and Si\(_6\) shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent Si\(_6\) structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59097
ER -
TY - JOUR
A1 - Staikova, M.
A1 - Peric, M.
A1 - Engels, Bernd
A1 - Peyerimhoff, S. D.
T1 - Ab initio Investigation of the Structure of the X\(^2\)A', A\(^2\)A'' (1\(^2\)Π) Spectral System of HCO: Investigation of the Magnetic Hyperfine Effects
N2 - Results ofan ab initio study ofthe hyperfine structure of the X\(^2\)A', A\(^2\) A" ( 1\(^2 \Pi\)) system ofthe formyl radical are presented. Special attention is paid to the analysis of the interplay between the vibronic and magnetic hyperfine etfects. The results of computations are in very good agreement with the available experimental findings. The values for the hyperfine coupling constants in lower bending Ievels of both electronic species are predicted.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59089
ER -
TY - JOUR
A1 - Wortmann-Saleh, D.
A1 - Engels, Bernd
A1 - Peyerimhoff, S. D.
T1 - Theoretical Study of the Reaction O(\(^3\)P) + C\(_2\)H\(_4\) and comparison with the \(^3\)CH\(_3\) + C\(_2\)H\(_4\) Reaction
N2 - The minimum energy path for the reaction O(\(^3\)P\(_g\)) + C\(_2\)H\(_4\)(\(^1\)A\(_g\)) has been calculated by optimizing all relevant geometrical parameters along the approach of oxygen to ethene. A barrier of 4.7 kcal/mol in the \(^3\)A"( ... 9a'\(^2\)- 10a'3a") potential energy surface and an energy difference of 14.4 kcal/mol between the product and the fragments is found at the multireference-configuration interaction level. The corresponding values at the lower-level treatment CASSCF are 9 kcal/mol for the barrier and 9 kcal/mol for the depth of the potential; this shows the importance of inclusion of electron correlation. The barrier for CH\(_2\) rotation for the lowestenergy structure (asymmetric OC\(_2\)H\(_4\)) is around 5 kcal/mol. The energy gap to the first excited state \(^3\)A'( ... 9a'l0a'3a'12) is found tobe 3.6 kcal/mol in MRD-CI calculations at the ground-state minimum. Comparison with \(^3\)CH\(_2\) + C\(_2\)H\(_4\) shows that in this system the lowest-energy surface is \(^3\)A', i.e., the state which is the excited state in 0 + C\(_2\)H\(_4\). This difference in energy ordering of \(^3\)A' and \(^3\)A" states results from the fact that the p\(_x\), p\(_y\), p\(_z\) degeneracy of oxygen orbitals is lifted in \(^3\)CH\(_2\)leading to b\(_1\), b\(_2\). and a\(_1\) MOs whereby the lowest b\(_2\) (a") remains doubly occupied; as a consequence, the reaction pattem between the oxygen and \(^3\)CH\(_2\) approach is different, which is also quite apparent in the calculated charge transfer.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59076
ER -
TY - JOUR
A1 - Mühlhäuser, M.
A1 - Froudakis, G.
A1 - Zdetsis, A.
A1 - Engels, Bernd
A1 - Flytzanis, N.
A1 - Peyerimhoff, S. D.
T1 - Ab initio investigation of the stability of Si\(_3\)C<\(_3\) clusters and their structural and bonding features
N2 - Various structural possibilities for Si\(_3\)C\(_3\) clusters are investigated by ab initio calculations employing basis sets of double- and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Piesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A "pyramidlike" structure with various multicenter bonds, followed by a es symmetric isomer closely related to the ground state Si6 structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si - C-C-C-Si -Si structure, which is calculated to lie about 38 kcalfmole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59060
ER -
TY - JOUR
A1 - Pleß, V.
A1 - Suter, H. U.
A1 - Engels, Bernd
T1 - Ab initio study of the energy difference between the benzene and the cumulene form of the C\(_6\) molecule
N2 - The energy difference between the three lowest-lying isomers of C\(_6\) the linear \(^3 \sum ^-\) state and the two ring forms,the benzene structure (\(^1\)A\(_{18}\)) possessing D\(_{6h}\) symmetry and a distorted cyclic form ( \(^1\)A'\(_1\), D\(_{3h}\) symmetry) have been calculated using various ab initio methods. Variational methods such as multireference configuration interaction (MR-CI) and complete active space second order perturbatiOn treatment (CASPT2) have been applied, as weil as perturbational treatments and coupled cluster calculations (CCD). The correlation of all valence shell electrons is found to be important for a balanced description of the isomers of C\(_6\) . Methods which do not account for higher-order effects appropriately proved to be unsuitable for calculating the energy difference correctly. The results from multireference configuration interaction methods show that the isomers are close in energy with the cyclic forms somewhat lower than the linear form. The ring form possessing D\(_{3h}\) symmetry (\(^1\)A'\(_1\)} is found tobe the lowest-lying structure.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59059
ER -
TY - JOUR
A1 - Huang, M.-B.
A1 - Suter, H. U.
A1 - Engels, Bernd
T1 - Theoretical Study of the Dimethylamino Radical (CH\(_3\))\(_2\)N and its protonated cation (CH\(_3\))\(_2\)NH\(^+\)
N2 - In the present work the dimethylamino radical ( ( CH\(_3\)) \(_2\)N) and its protonated cation ( ( CH\(_3\))\(_2\)NH\(^+\)) are investigated by means of ab initio methods. The geometries of various conformations of both compounds are obtained with UMP2/6·31 G** calculations, while the hyperfine structure and its dependence on the geometry is studied using the MRD-Cl/B\(_K\) method. The two molecules are compared to study the inftuence of the protonation on geometry and hyperfine structure. The effects of the rotational barriers on the hyperfine structures of (CH\(_3\))\(_2\)N, (CH\(_3\)CH\(_2\))\(_2\)N and ( (CH\(_3\))\(_2\)CH)\(_2\)N will be discussed.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59047
ER -
TY - JOUR
A1 - Suter, H. U.
A1 - Engels, Bernd
T1 - Theoretical investigation of ESR parameters: H\(_2\)CN and H\(_2\)CO\(^+\)
N2 - The hyperfine structure of the two isoelectronic molecules H\(_2\)CN and H\(_2\)CO\(^+\) in their electronic ground state (X\(^2\)B\(_2\)) is studied. The influence of the atomic orbital (AO), basis sets, of the correlation treatment, and of the. equilibrium geometry on the obtained hyperfine propertles 1s - investigated. It is found that the multireference double excitation-configuration interaction (MRD-CI)/ BK treatment in which an MRD-CI wave function is corrected by a modified B\(_K\) method yields equivalent results to quadratic CI [QCISD(T)], coupled cluster single doubles [CCSD(T)), or Brueckner doubled [BD(T)]. Uncertainties in the equilibrium geometries are found to be the major source for discrepancies between theoretically and experimentally determined isotropic hyperfine coupling constants (hfccs). For the heavier centers, the calculated values of the isotropic hfccs agrees nearly perfectly with experimental values (\(\approx\) 1%-2%). The calculated values for the hydrogens are too low, but using the equilibrium structure suggested by Yamamoto and Sato [J. Chem. Phys. 96, 4157 ( 1992)], the best estimate deviates by less than 3%.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59029
ER -
TY - JOUR
A1 - Engels, Bernd
T1 - Detailed study of the configuration selected multi-reference configuration interaction method combined with perturbation theory to correct the wave function
N2 - A reliable prediction of the isotropic hyperfine coupling constant A\(_{iso}\) is still a difficult task for ab initio calculations. In previous studies, the configuration selected multireference configuration interaction method in combination with perturbation theory to correct the wave function (MRCI/ B\(_K\)) yielded accurate isotropic hyperfine coupling constants very economically. The present study gives a detailed analysis of the MRCI/ B\(_K\) method based on the X\(^2 \pi\) state of CH as a test case. Furthermore, a comparison to various other methods such as Maller-Ptesset perturbation theory and the coupled cluster approach is made. The success of the MRCI/ B\(_K\) method in predicting isotropic hyperfine coupling constants is explained in terms of the inßuence of higher than double excitations.
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59019
ER -
TY - JOUR
A1 - Staikova, M.
A1 - Engels, Bernd
A1 - Peric, M.
T1 - Ab initio investigation of the hyperfine structure in the 1\(^2\)Π\(_u\)(X\(^2\)A\(_1\), A\(^2\)B\(_1\) system of BH\(_2\))
N2 - No abstract available
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59000
ER -
TY - JOUR
A1 - Staikova, M.
A1 - Engels, Bernd
A1 - Peric, M.
A1 - Peyerimhoff, S. D.
T1 - Ab initio calculation of the vibronically averaged hyperfine coupling constants in the two lowest electronic states of H\(_2\)O\(^+\)
N2 - No abstract available
T2 - Ab initio calculations of the vibronically averaged hyperfine coupling constants in the 1\(^2\)Π\(_u\)(X\(^2\)B\(_1\),A\(^2\)A\(_1\)) state of the water cation
KW - Organische Chemie
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58998
ER -
TY - JOUR
A1 - Gittins, C. M.
A1 - Harris, N. A.
A1 - Field, R. W.
A1 - Verges, J.
A1 - Ernst, W. E.
A1 - Bündgen, P.
A1 - Engels, Bernd
T1 - Analysis and Depertubation of the C\(^2\)Π and D\(^2\)Σ\(^+\) states of CaF
N2 - No abstract available
KW - Organische Chemie
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58980
ER -
TY - JOUR
A1 - Engels, Bernd
T1 - Study of influences of various excitation classes on ab initio calculated isotropic hyperfine coupling constants
N2 - Reliable prediction of the isotropic hyperfine coupling constant A\(_{iso}\) is still a difficult task for ab initio calculations. Strang dependence on the method employed for its ca1culation has been found. Within a CI ansatz A\(_{iso}\) is considerably affected by the excitation classes taken into account within the CI calculation. In the present work the influence of various excitation classes on A\(_{iso}\) is examined. Calculations including all single, double, triple and a large part of the quadruple excitations are performed and the individual effects of the excitation classes are studied. It is found that the surprisingly good agreement found for S-CI treatments is due to large error cancellations. The importance of higher than double excitations arises from their indirect influence on the single excitations.
KW - Organische Chemie
KW - Spin density
KW - Hyperfine coupling constants
KW - Influence of excitation classes
KW - Indirect and direct contributions to Aiso
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58973
ER -
TY - JOUR
A1 - Metropoulos, B.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - On the chemi-ionization reaction O + CH ----> HCO\(^+\)+ e\(^-\). Coollinear O-CH Approach
N2 - We have investigated theoretically the importance of the O(\(^3\)P)+CH(a\(^4\sum^-\)) and the O(\(^3\)P)+CH(X\(^2\Pi\)) channels in the collinear chemi-ionization reaction O+CH->HCO\(^+\) +e\(^-\). We have found that both channels may lead to chemi-ionization via favorable Franck-Condon overlaps with the states ofthe ionic species.
KW - Organische Chemie
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58963
ER -
TY - JOUR
A1 - Peric, M.
A1 - Engels, Bernd
T1 - Ab initio calculation of the vibronically averaged hyperfine coupling constants in the 1\(^2\)Π\(_u\) electronic state of CH\(_2 ^+\)
N2 - The results of pure ab initio calculations of the hyperfine coupling constants for the 1 \(^2 \pi _u\) electronic state for various isotopomers of CHi in the energy range between 0 and 20 000 cm\(^{-1}\) are presented. Effects of vibronic and spin-orbit coupling are discussed.
KW - Organische Chemie
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58951
ER -
TY - JOUR
A1 - Peric, M.
A1 - Engels, Bernd
T1 - Ab initio calculations of the vibronically averaged values for the hyperfine coupling constants in NH\(_2\), NHD and ND\(_2\)
N2 - Vibronically averaged values for K =0 and K = 1 bending levels in the energy range between 0 and 25 000 cm\(^{-1}\) are computed for the \(^{14}\)N, H, and D atoms in NH\(_2\), NHD, and ND\(_2\) The pure ab initio electronic potentials, as well as those derived by fitting of experimentally observed band positions are employed. Effects of vibronic coupling and local perturbations of close-lying levels belanging to different electronic states are discussed.
KW - Organische Chemie
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58941
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peric, M.
A1 - Reuter, W.
A1 - Peyerimhoff, S.D.
A1 - Grein, F.
T1 - Study of the hyperfine coupling constants \(^{14}\)N and \(^1\)H) of the NH\(_2\) molecule in the X\(^2\)B\(_1\) ground state and the A\(^2\)A\(_1\) excited state
N2 - The hyperfine coupling constants (hfcc) A\(_{iso}\) and A\(_{ij}\) are calculated for the atoms of NH\(_2\) in its, two lowest-lying electronk states at various molecular geometries by means of the ab initio multireference configuration interaction .method. The vibronically averaged values of the hfccs for the K = 0 and 1 levels in \(^{14}\)N \(^1\)H\(_2\) in the energy range up to 20 000 cm\(^{-1}\) are computed. Polarization elfects which determine A\(_{iso}\) as well as a simple model to describe the dipolar hfccs are discussed. All resrilts are in excellent agreement with experimental data.
KW - Organische Chemie
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58937
ER -
TY - JOUR
A1 - Reuter, W.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - The Reaction of Singlet and Triplet Methylen with Ethene - A Multi-Reference CI Study
N2 - Large-scale multireference configuration interaction (MRD-CI) calculations in a flexible atomic orbital (AO) basis are employed to study the reaction of C\(_2\)H\(_4\) with CH\(_2\) in its firSt triplet and singlet state. The minimum energy path (MEP) of both reactions is calculated, and different mechanisms are discussed. To examine the possible participation of the singlet state in the overall reaction starting from the triplet channel and terminating in the singlet-state c-C\(_3\)H\(_6\), various cuts through both hypersurfaces are calculated. lt is found that favorable interconversion from the trip1et to the singlet surface can only occur at !arge separations of the two fragments of CH2 and C\(_2\)H\(_4\). Experimental data considering the vibrational motion of CH\(_2\) in connection with the relative position of both surfaces are used to obtain an estimate for the overall barrier of the reaction. The height of the barrier is about 6 kcal/mol, while the barrier of the pure triplet reaction is calculated to be 7-9 kcal/mol.
KW - Organische Chemie
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58923
ER -
TY - JOUR
A1 - Peric, M.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - Ab initio investigation of the vibronic structure of the C\(_2\)H spectrum Computation of the vibronically-averaged values for the Hyperfine Coupling Constants
N2 - The vibronically averaged values for tbe hyperfine coupling constants in the X\(^2 \sum\)-A\(^2 \Pi\) system of the ethynyl radical are computed by means of tbe ab initio metbod calculations. The results point at tbe importance of taking into account the coupling of a1l tbree electronic states in question ( I\(^2\)A', 2\(^2\)A', and 1\(^2\)A") for a reliable explanation of the available experimental findings. The mean values of the hfcc's for K = 0 and 1 levels in \(^{13}\)C\(_2\)H and \(^{13}\)C\(_2\)D in the energy range up to 6000 cm\(^{-1}\) are predicted.
KW - Organische Chemie
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58915
ER -
TY - JOUR
A1 - Peric, M.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - Ab initio investigation of the vibronic structure of the C\(_2\)H spectrum Calculation of the hyperfine coupling constants for the three lowest lying electronic states
N2 - The hyperfine coupling constants (isotropic hfcc and four Cartesian components of the ani~ tropic tensor) are calculated for all three atoms of C\(_2\)H in its three lowest-lying electronic states at various molecu)ar geometries by means of the ab initio configuration interaction ( MRO.CI) method. The off-diagonal electronic matrix elements involving the two species ofthe A' symmetry are also computed. A diabatic transforrnation is perforrned Jeading to simple geometrical depen· dences of the hyperline coupling constants.
KW - Organische Chemie
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58901
ER -
TY - JOUR
A1 - Engels, Bernd
T1 - Estimation of the influence of the configurations neglected within truncated MR-CI wavefunctions on molecular properties
N2 - Reliable prediction of the isotropic hyperfine coupling constant, a\(_{iso}\), is still a difficult task for ab initio calculations. Strong dependence on the method used for its calculation is found. Within a truncated multi-referencc ansatz a\(_{iso}\) is strongly affected by the size ofthe reference space and the nurober of terms in the truncated Cl expansion. In the present paperdifferent effects of the neglected Cl space are discussed. Modified B\(_K\) and A\(_K\) methods are used to estimate the contributions ofthe neglected configurations. lt can be shown that a combination of both methods is able to recover about 90-9 S% of the total error in a\(_{iso}\)· Furthermore, it was found that to obtain about 90% of the B\(_K\) correction only about I 0-20% ofthe configurations within H0 have to be corrected.
KW - Organische Chemie
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58890
ER -
TY - JOUR
A1 - Bündgen, P.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - An MRD-CI study of low-lying electronic states in CaF
N2 - Dipole moments and various spectroscopic constants of some low-lying electronic states of the CaF molecule have been calculated using the multireference single· and double-excitation configuration-interaction (MRD-CI) method. The electronic structure of the highly ionic molecule in various excited states can be explained in tenns of different polarisations of the mainly Cacentered valence electron in the field of the F\(^-\) anion. Plots of natural orbitals occupied by the valence electron in the different states give a qualitative picture of the charge distribution and provide a visualisation of the different polarisations of the valence electron in the various states. Comparisons with the electrostatic polarisation model ofTörring, Ernstand Kändler (TEK model) are made. The unknown A' \(^2 \Delta\) state is predicted to lie about 21200 cm\(^{-1}\) above the ground state.
KW - Organische Chemie
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58880
ER -
TY - JOUR
A1 - Funken, K.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
A1 - Grein, F.
T1 - Study of the hyperfine coupling constants of the moleculs NH2, NHD and ND2
N2 - In the present paper we c:alculate tbe magnetic hyperfine couplina constants (hfcc) ai.ID and A11 of the ground states of the isotopes NH2, NHD and ND2 using truncated MR..CI methods. Differences from other theoretical methocls and shortoominp of the truncated Cl approach in calculating tlj10 are studied. Polarization effects wbich detennirae ailo. as weU as a simple model to describe the dipolar hfcc's, are discussed. All results are in. excellent aareement with experimental data. lt is shown that ab initio methods are able to obtain reliable values for otf-diaaonal values of A41 which are difficult to measure experimentaDy.
KW - Organische Chemie
Y1 - 1990
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58875
ER -
TY - JOUR
A1 - Karna, S.P.
A1 - Grein, F.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - Ab initio configuration-interaction studies of the ground state potential energy and hyperfine coupling constants of \(^{35}\)Cl\(_2^-\)
N2 - Potential energy and spectroscopic constants for the X\(^2 \sum^+ _\mu\) ground state of a;, were calculated by configuration-interaction (Cl) methods, using large basis sets with polarization and diffuse functions. From these CI wavefunctions, the isotropic (a\(_{iso}\)) and dipolar (A\(_{dip}\)) components of the hyperfine coupling constant were obtained. The effects of various s, p basis sets, polarization and diffuse functions, as well as the influence of reference configurations and configuration selection thresholds were investigated. The best values obtained are 35·31 G for a\(_{iso}\) and 29·440 for A\(_{dip}\)• tobe compared with experimental values of 37 ± 1 G and 32 ± 1 G, respectively. It is shown that the contributions to a1so of the K and L shells are opposite in sign, differing by about 4 G. Upon vibrational averaging, both a\(_{iso}\) and A\(_{dip}\) move towards smaller values as v increases. An adiabatic electron affinity of 2·46eV was obtained for CL\(_2\) , and a vertical electron detachment energy of 3·71 eV for Cl;.
KW - Organische Chemie
Y1 - 1990
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58869
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
A1 - Skell, P.S.
T1 - Theoretical study of the potential energy surface governing the stereochemistry in ClC\(_2\)H\(_4\) reactions
N2 - Large-scale multireference configuration interaction calculations in a double·t·type AO basis including polarization functions are carried out for the potential surface of the ClC\(_2\)H\(_4\9 system. The charge distribution for various extreme points of the surface is discussed. The absolute minimum is found for an asymmetric ClC2H4 structure. The symmetrical bridged nuclear conformation is also found to be stable with respect to dissociation into Cl + C\(_2\)H\(_4\)• The activation energy for rotation about the C-C axis is calculated tobe around 18 kJ/mol, which is comparable tothat for the 1,2 migration {around 26 kJ/mol). The stereochemistry is governed by the fact that addition of CI to C\(_2\)H\(_4\) (or dissociation) is a two-step reaction proceeding through a symmetrica1 intermediate. The direct addition pathway possesses a small barrier of about 8 kJ jmol.
KW - Organische Chemie
Y1 - 1990
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58851
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - Study of orbital transformations in configurational interaction calculation of hyperfine coupling in nitrogen and CH molecule
N2 - Multi-reference configuration interaction calculations employing various orbital transformations are undertaken to obtain the isotropic hyperfine coupling constant a\(_{iso\) in nitrogen and a\(_{iso\) (H) in the CH molecule. The natural orbital (NO) basis is found to be more effective than the simple RHF-MO basis; the most obvious is a basis of spin natural orbitals (SNO). It is found that a\(_{iso\) is approached from opposite sides in the NO and 2s shell SNO basis if the CI expansion is increased. Both results are within a few percent of the full CI Iimit for the nitrogen atorn (in the given AO basis) and the experimental value for Hin the CH radical. Various features ofthe SNO are discussed.
KW - Organische Chemie
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58847
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - The hyperfine coupling constants of the X\(^3\)Σ\(^-\) state of NH : Influence of polarization functions and configuration space on the description of spin polarization
N2 - The hyperfine coupling constants for the \(^3\)Σ\(-\) ground state of the NH molecule are determined by configuration interaction calculations whereby the infl.uence of polarization functions as weil as of the configuration space on the spin polarization mechanism is analysed. The dipolar part Au(N) and Au(H) can be obtained very reliably without much computational effort (A .. (N) == -45·3 MHz and A"(H) = -62·3 MHz). The value for the isotropic contribution a1.., in the best AO basis and MRD-CI treatment is - 64·5 MHz for H and 16·6 MHz for nitrogen compared to the corresponding experimental quantities of -66 MHz and 19 MHz respectively. Their determination depends on a subtle balance of the lu, 2u and 3u shell correlation description, whereby the dominant contribution to a1..,(H) results from the 2u shell. It is shown that the often good agreement of a110 values with experiment in a small basis singledouble configuration interaction treatment results from a cancellation of two errors.
KW - Organische Chemie
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58832
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - Theoretical study of FC\(_2\)H\(_4\)
N2 - Large-scale multireference configuration interaction (MRD-CI) calculations in a quite flexible AO basis are employed to study the energy hypersurface for the reaction intermediate FC\(_2\)H\(_4\) • The reaction F + C\(_2\)H\(_4\) -> FC\(_2\)H\(_4\) as weil as the 1,2 migration of the fluorine atom in FC\(_2\)H\(_4\) is investigated. In addition the rotation around the CC bond in the optimum conformation is studied. The absolute minimum in the potential energy is found for the asymmetric structure but the symmetric structure is also found to be stable with respect to the dissociation, so that a shuttling of the fluorine atom is in principle possible but highly unlikely because ( l) the activation energy is high ( II 5-130 kJ fmol) and the saddle point lies only 4(}-50 kJ jmol below the dissociation Iimit of F + C\(_2\)H\(_4\) and (2) the competitive motion, i.e., rotation around the CC axis, is nearly free (I 1-17 kJ/mol).
KW - Organische Chemie
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58824
ER -
TY - JOUR
A1 - Karna, S.
A1 - Grein, F.
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - The hyperfine coupling constants of \(^{19}\)F\(_2\)
N2 - The isotropic (a\(_{iso}\)) and dipolar (A\(_{dip}\)) hyperfine coupling constants of 19F2 were obtained from MRD-CI wave functions using a variety of basis sets. In series I, increasing numbers of d functions were added to a 5s4p contracted Huzinaga!Dunning basis. In series II, the 5s3p basis set was uncontracted in several steps until 9s5p was reached, to which were added from one to three d-polarization functions. Cl parameters (selectioo threshoids and the number of reference coofiguratioos) were also varied. A study of the R dependence of aiso and Adip was perfonned. The best values obtained at R\(_e\) are 260 G for a\(_{iso}\) and 308 G for A\(_{dip}\)• compared with experimental values of about 280 G for a;10 and 320 G for A\(_{dip}\)·
KW - Organische Chemie
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58817
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
A1 - Karna, S.P.
A1 - Grein, F.
T1 - The hyperfine coupling constants of the five lowest states of CH : An ab initio MRD-CI study
N2 - No abstract available
KW - Organische Chemie
Y1 - 1988
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58807
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
T1 - Study of the 1s and 2s shell contributions to the isotropic hyperfine coupling constant in nitrogen
N2 - The istropic part of the hyperfine coupling constant is investigated by means of multireference configuration interaction calculations employing Gaussian basis sets. A detailed study of the 1s and 2s spin polarisation in the nitrogen atom and the NH molecule shows that the structure of the lower-energy space of the unoccupied orbitals is essential for the results. A contraction of the Gaussian basis is possible without loss of accuracy if enough flexibility is retained to describe the main features of the original space of unoccupied functions. Higher than double excitations are found to be non-negligible for the description of α\(_{iso}\).
KW - Organische Chemie
Y1 - 1988
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58793
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S.D.
A1 - Davidson, E.R.
T1 - Calculation of hyperfine coupling constants : An ab initio MRD-CI study for nitrogen to analyse the effects of the basis sets and CI parameter
N2 - The hyperfine coupling constant for the nitrogen atom is evaluated by large-scale MRD-CI calculations. A detailed analysis of the charge density at the nucleus and the spin polarization in the ls and 2s shell as a function of various technical parameters is undertaken. Various (s, p) AO basis sets and the inftuence of correlation orbitals is investigated as weil as selection threshold and other properlies in CI calculations. The best value, obtained for the isotropic hyperfine coupling constant in an s, p, d basis, based on theoretical judgment of' best' quantities, is 9·9 MHz compared to 10·4509 MHz.
KW - Organische Chemie
Y1 - 1987
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58784
ER -
TY - JOUR
A1 - Engels, Bernd
A1 - Peyerimhoff, S. D.
T1 - Theoretical study of the bridging in β-Halo Ethyl
N2 - Large-acale multi-reference configuration interaction (MRD-CI) calculations in a quite flexible AO basis are employed to study the energy hypersurface for the reaction intermediates XC\(_3\)H\(_4\) with X = Cl, Br and F. Particular emphasis is therby placed on determining the equilibrium conformations, the CH\(_2\) rotation barrier and the energy surface for a possible bridging (shuttling motion (1a] of X between the two carbon centers). The absolute minimum in the potential energy surface is found in all three cases for the asymmetric ß-halo radical in general agreement with ESR data at an XCC angle of ca. 110°, a c-c separation somewhat shorter than a single bond and an approximate sp3 type hybridization (\(\alpha _2 \approx \) 135-140°). In FC\(_2\)H\(_4\) the energy difference between the minimum in the symmetric conformation and the absolute minimum is found to be more than 30 kcal so that shuttling seems impossible in agreement with experimental findings. In BrC\(_2\)H\(_4\) the difference between these two potential minima is only between 1-2 kcal, i.e., smaller than the barrier to CH\(_2\), rotation, so that· shuttling is favored, while ClC\(_2\)H\(_4\) takes an intermediate position between these extremes. The use of correlated wavefunctions is found to be quite important for such a study; the results are related to various kinetic studies of these radicals.
KW - Organische Chemie
Y1 - 1986
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58779
ER -
TY - JOUR
A1 - Bentley, T. W.
A1 - Christl, Manfred
A1 - Kemmer, R.
A1 - Llewellyn, G.
A1 - Oakley, J. E.
T1 - Kinetic and Spectroscopic Characterisation of Highly Reactive Methanesulfonates. Leaving Group Effects for Solvolyses and Comments on Geminal Electronic Effects Influencing S\(_N\)1 Reactivity
N2 - Highly reactive methanesulfonates (mesylates, ROMs) have been prepared from 1-phenylethanol. cyclohex-2-en-1-ol, diphenylmethanol and p-methoxybenzyl alcohol by treatment with methanesulfonyl chloride and triethylamine in dichloro- or trichloro-methane at - 20 to 0 °C. The mesylates. characterised in solution by \(^1\)H and \(^{13}\)C NMR at -20 °C, were obtained in satisfactory purity (ca. 95%) in cold solutions but they decomposed by reaction with chloride, triethylamine or the parent alcohol. Rate constants for solvolyses in aqueous acetone and aqueous ethanol have been determined by a fast response conductimetric method. Product selectivities for solvolyses of pmethoxybenzyl mesylate in aqueous ethanol and methanol at 0 °C have been determined by HPLC. From additional new or Iiterature kinetic data for solvolyses of corresponding bromides. chlorides and p-nitrobenzoates (OPNB). Br/CI. OMs/Br and OMs/OPNB rate ratios were calculated; the results are consistent with electronic effects stabilising the carbocationic transition states and increasing OMs/Br rate ratios for these SN 1 solvolyses; none of the evidence supports a geminal electronic effect on Br/CI rate ratios (e.g. caused by stabilisation of the initial state in pmethoxybenzyl chloride). Steric effects on ester /halide rate ratios for solvolyses of tertiary substrates are confirmed. Relative rates over a 10\(^{16}\) range for ester and halide leaving groups are evaluated for solvolyses of 1-phenylethyl substrates in 80% ethanol-water. updating previous work by Noyce et al. (1972).
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58748
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Türk, M.
A1 - Peters, K.
A1 - Peters, E.-M.
A1 - Schnering, H. G. von
T1 - Octahydro-1,2,3:4,5,6-dimethenopentalene-2-carbonitrile, the First Derivative of a Yet-Unknown (CH)\(_{10}\)-Hydrocarbon
N2 - No abstract available
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58731
ER -
TY - JOUR
A1 - Bentley, T. W.
A1 - Norman, S. J.
A1 - Gerstner, E.
A1 - Kemmer, R.
A1 - Christl, Manfred
T1 - Solvolysis of Tricyclo[3.1.0.0\(^{2,6}\)]hex-3-yl and Bicyclo[2.1.1]hex-2-yl Sulfonates
N2 - No abstract available
KW - Organische Chemie
KW - Bicyclo[1.1.0]butylcarbinyl sulfonates
KW - solvolysis of
KW - Cyclobutylcarbinyl sulfonates
KW - Anchimeric assistance in solvolysis
KW - Rearrangement of carbocations
KW - Electron demand in ditosylates
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58689
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Braun, Martin
A1 - Müller, Germar
T1 - 1,2,4-Cyclohexatriene, an Isobenzene, and Bicyclo[4.4.0)deca-1,3,5,7,8-pentaene, an Isonaphthalene: Generation and Trapping Reactions
N2 - No abstract available
KW - Organische Chemie
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58639
ER -
TY - JOUR
A1 - Bentley, T. W.
A1 - Christl, Manfred
A1 - Norman, S. J.
T1 - Methanesulfonate/p-Nitrobenzoate and p-Toluenesulfonate/p-Nitrobenzoate Rate Ratios. Solvolyses of 1-Adamantyl and Benzhydryl Substrates
N2 - No abstract available
KW - Organische Chemie
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58599
ER -
TY - JOUR
A1 - Markgraf, J. H.
A1 - Cort, J. R.
A1 - Davis, H. A.
A1 - Lindeman, N. I.
A1 - Myers, C. R.
A1 - Kraft, A.
A1 - Christl, Manfred
T1 - Strained Heterocyclic Systems. 20. Basicities of Bicyclic Quinoxalines
N2 - No abstract available
KW - Organische Chemie
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58584
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Reuchlein, H.
T1 - Synthesis and NMR Spectra of 2,3-Dihydro-1,3-methanoindene Derivatives and 1,2,3,5-Tetrahydro-1,3-methanopentalene
N2 - No abstract available
KW - Organische Chemie
Y1 - 1990
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58557
ER -
TY - JOUR
A1 - Kim, E.
A1 - Christl, Manfred
A1 - Kochl, J. K.
T1 - Charge-Transfer Cycloaddition of Homobenzvalene with Tetracyanoethylene
N2 - The transient yellow color observed in the cycloaddition of homobenzvalene (HB) with tetracyanoethylene (TCNE) is associated with the charge-transfer complex [HB, TCNE). The deliberate photoexcitation of [HB,TCNE) affords a mixture of charge-transfer cycloadducts (1, 2, and 3) that differs from that obtained in thermal cycloaddition. The relationship of {HB t TCNE•) radical-ion pair (as the critical reactive intermediate in charge-transfer cycloaddition) to the activation process for thermal cycloaddition is discussed.
KW - Organische Chemie
KW - Electron transfer
KW - photochemical
KW - Radical-ion pair
KW - Photochemistry
Y1 - 1990
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58537
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Braun, Max
T1 - Photocycloadditions of Benzvalene
N2 - No abstract available
KW - Organische Chemie
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58506
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Brunn, E.
A1 - Roth, W. R.
A1 - Lennartz, H.-W.
T1 - 7-Methyl- and 7-Phenylcyclohepta-1,3,5-trienes from Benzvalene Via 3,3a,4,5,6,6a-Hexahydro-4,5,6-methenocyclopentapyrazoles and Tetracyclo[4.1.0.0\(^{2,4}\).0\(^{3,5}\)]heptanes
N2 - No abstract available
KW - Organische Chemie
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58471
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Kraft, A.
T1 - Tricyclo[3.1.1.0\(^{2,6}\)]hexandion (the Valen of o-Benzochinons), Bicyclo[2.1.1]hexan-2,3-dion and Valene of a Chinoxalins, of Phenazins and of a Benzophenazine
N2 - No abstract available
KW - Organische Chemie
Y1 - 1988
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58462
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Freund, S.
A1 - Henneberger, H.
A1 - Kraft, A.
A1 - Hauck, J.
A1 - Irngartinger, H.
T1 - Several Polycyclic Valence Isomers of Dimethyl [14]Annulene-1,8-dicarboxylate. Reactivity of a "Nonconjugated" Bis(bicyclo[1.1.0]butane)
N2 - Diels-Alder reaction of dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate (5) with benzvalene (4), norbornene, and norbornadiene afforded the azo compounds 7 and 8. Theseare derivatives of 2,3-diazabicyclo[2.2.2]oct-2-ene as is azo compound 3, which had been obtained previously from 5 and 2 equiv of benzvalene (4). The photochemical extrusion of nitrogen from 3, 7, and 8 has been studied. Whereas 7 and 8 on direct irradiation in benzene gave rise exclusively to the bicyclo[2.2.0]hexane derivatives 9 and 10, respectively, from 3 in addition to the bicyclo[2.2.0]hexane 11, the diolefin 1l was formed. Diolefin 12 has cisdouble bonds in the nine-membered ring and is fixed in a boat conformation in a manner so that the two bicyclobutane systems approach each other very closely. This geometry suggests the unusual ring opening of the intermediate 1,4-cyclohexanediyl diradical from a boat conformation, which arises by inversion of the primarily generated boat conformation. Sensitized photolysis of 3 as weilasthat of ll produced the saturated isomer 13 of 11 and 12. The proximity of the bicyclobutane systems in 1l causes unprecedented reactions leading to cage compounds. When ll was heated at 90 °C, a rearrangement to the pentacyclic product 10 took place. Utilization of tetradeuteriated substrate ll-d4 supported a pathway with two diradical intermediates. Behaving in a convcntional manncr, bicyclobutane 9 and bis(bicyclobutane) 11 took up 1 and 2 equiv of thiophenol most probably in a radical-chain addition to give the thioethers 28 and 19, respectively. In contrast, bis(bicyclobutane) ll was converted by 1 equiv of thiophenol into cagc compound 30 in a process involving both the strained a systems. Heating at 80 °C subjected 30 to a reversible Copc rearrangement, resulting in a 6:1 mixture of 31 and 30. When it was treated with bromine, 11 was transformed to cage compound 38. This addition is believed to proceed via a cationic intermediate. The structure of cage compound 10 was established by a singlc-crystal X-ray analysis of dialcohol 11 prepared from 20 and methyllithium.
KW - Organische Chemie
Y1 - 1988
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58413
ER -
TY - JOUR
A1 - Korth, H.-G.
A1 - Müller, W.
A1 - Sustmann, R.
A1 - Christl, Manfred
T1 - Rearrangement of Free Radicals, XII. ESR Spectroscopic Study of the Ring Opening of the Homobenzvalenyl Radical
N2 - Abstraction of an allylic hydrogen atom in homobenzvalene (4) either in solurion by photolyticaßy generated tert-butoxyl radicals or in an adamantane matrix by X-rays produces the homobcnzvalenyl radical (5). which tbennally rearranps · to tbe tropylium ndical (1). In solution tbe activation cnergy for the rate determined step of the reaction sequence was detennined· to be 13.4 ± O.S kcal/mol.
KW - Organische Chemie
Y1 - 1987
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58376
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Lang, R.
A1 - Herzog, C.
T1 - The Synthesis of Octavalene (Tricyclo[5.1.0.0\(^{2,8}\)]octa-3,5-diene) and Several Substituted Octavalenes
N2 - No abstract available
KW - Organische Chemie
Y1 - 1986
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58254
ER -
TY - JOUR
A1 - Leininger, H.
A1 - Lanzendörfer, F.
A1 - Christl, Manfred
T1 - Über die Reduktion des Benzvalenozonids zum cis-1,3-Cyclobutandimethanol mit LiAlH\(_4\)
N2 - No abstract available
KW - Organische Chemie
Y1 - 1983
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58130
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Lang, R.
T1 - Tricyclo[5.1.0.0\(^{2,8}\)]octa-3,5-diene (Octavalene)
N2 - No abstract available
KW - Organische Chemie
Y1 - 1982
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58124
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Herbert, R.
T1 - Unusual Carbon Shielding Effects of Cyclopropanes and Double Bonds in Strained Bicyclo[3.1.0]hexanes and Cyclopentenes
N2 - Carbon-13 shieldings and one-bond \(^{13}\)C-H coupling constants of bicydo[2.1.1]hexane, bicydo[2.l.l]hex- 2-ene, tricydo[3.1.1.0\(^{2.4}\)]heptane and benzvalene are presented and compared. to the data of related. compounds. H a bicydo[3.1.0]hexane system is part of a rigid skeleton, the cydopropane ring exerts spedfk: 'Y substituent eflects of two ldnds. In the case of the bicyclobexane boat form an upfield shift of the C-3 signal is observed and in tbe esse of the chair form a downfield shift of 15-20 ppm. Compared to the corresponding cydopentanes the double bond in strained cydopentenes causes downfield shifts of the C-4 absorption. 1bis eftect increases witb increasing strain, reaching 8 45.9 ppm maximum in benzvalene. Hence it is tbe only known bicydo[l.l.O]butane baving 8 reversed order of carbon shieldings. The downfield shifts are e:xplained by means of simple orbital interaction schemes.
KW - Organische Chemie
Y1 - 1979
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58038
ER -
TY - JOUR
A1 - Volz, H.
A1 - Shin, J.-H.
A1 - Prinzbach, H.
A1 - Babsch, H.
A1 - Christl, Manfred
T1 - Stability of Tricyclo[4.1.0.0\(^{2,7}\)]heptenyl-Cations
N2 - No abstract available
KW - Organische Chemie
Y1 - 1978
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58001
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Heinemann, U.
A1 - Kristof, W.
T1 - Thermal Rearrangement of Some Endo-Endo'-Bridged Bicyclo[1.1.0]butanes
N2 - No abstract available
KW - Organische Chemie
Y1 - 1975
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-57967
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Warren, J. D.
A1 - Hawkins, B. L.
A1 - Roberts, J. D.
T1 - \(^{13}\)C and \(^{15}\)N Nuclear Magnetic Resonance Spectroscopy of Nitrile Oxides and Related Reaction Products : Unexpected \(^{13}\)C and \(^{15}\)N Nuclear Magnetic Resonance Parameters of 2,4,6-Trimethylbenzonitrile Oxide
N2 - No abstract available
KW - Organische Chemie
Y1 - 1973
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-57894
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Roberts, J. D.
T1 - Nuclear Magnetic Resonance Spectroscopy : Carbon-13 Chemical Shifts of Small Peptides as a Function of pH
N2 - No abstract available
KW - Organische Chemie
Y1 - 1972
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-57885
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Reich, H. J.
A1 - Roberts, J. D.
T1 - Nuclear Magnetic Resonance Spectroscopy. Carbon-13 Chemical Shifts of Methylcyclopentanes, Cyclopentanols, and Cyclopentyl Acetates
N2 - No abstract available
KW - Organische Chemie
Y1 - 1971
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-57862
ER -
TY - JOUR
A1 - Gleiter, Rolf
A1 - Bischof, Peter
A1 - Gubernator, Klaus
A1 - Christl, Manfred
A1 - Schwager, Luis
A1 - Vogel, Pierre
T1 - 2,3-Bis(methylene)bicyclo[2.1.1]hexane and 3,4-Bis(methylene)tricyclo[3.1.0.0\(^{2,6}\)]hexane : Interaction between a π System and a Cyclobutane or Bicyclobutane Moiety
N2 - The He (I) photoelectron spectra of 2-bicyclo[2.1.l]hexene (1), 2,3-bis(methylene)bicyclo[2.1.l]hexane (3), and 3,4-bis(methylene)tricyclo[3.l.O.0\(^{2.6}\)]hexane (4) have been investigated. The assignment given is based on a ZDO model and semiempirical calculations. Tagether with the PE data of benzvalene (2), the reported data allow a comparison between 1-2 and 3-4. This yields a measure of the interactions between 8 cyclobutane or 8 bicyclobutane moiety and a double bond system within a ZDO model. The resonance integral found in the case of 1 and 3 amounts to -1.9 eV, that for 2 and 4, to -2.3 eV. The investigations furthermore reveal that the electronic factors which contribute to the higher reactivity of the bicyclobutane compounds amount to 5 kcal/mol.
KW - Chemie
Y1 - 1985
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31845
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Schreck, Michael
T1 - 1,2,3,5,8,8a-Hexahydronaphthalin aus 1,2-Cyclohexadien
N2 - Reaktionen von 1,3-Butadien und einigen seiner Methylderivate mit 1a und 1- Methyl-1,2-cyclohexadien 1b sowie den Übergang der [2 + 2]-Cycloaddukte 2 und 3 in das bisher unbekannte 1,2,3,5,8,8a-HexahydronaphthaJin 4a und einige seiner Methylderivate
KW - Chemie
KW - Butadien
Y1 - 1987
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31656
ER -
TY - JOUR
A1 - Gleiter, Rolf
A1 - Bischof, Peter
A1 - Christl, Manfred
T1 - Electronic Structure of Octavalene : Photoelectron Spectroscopic Investigations
N2 - The He I photoelectron (PE) spectra of octavalene (5) as weil as its hydrogenated products 6-8 have been investigated. The assignment given is based on an empirical comparison of 5-8 with related compounds, a ZDO model, and semiempirical and ab initio calculations. Within the ZDO model the interaction between the buta.diene moiety and the bicyclobutane fragment of 5 is described by a resonance integral of -2.3 eV. The orbitalsequence of 5 is found tobe 2a\(_2\) (\(\pi\)-\(\sigma\)), 9a\(_1\) (\(\sigma\)), 3b1 (\(\pi\) - \(\sigma\)), 1a\(_2\) (\(\sigma\) + \(\pi\)), 2b\(_1\) (\(\sigma\) + \(\pi\)).
KW - Chemie
KW - Octavalen
KW - Photoelektron
Y1 - 1986
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31588
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Braun, Martin
T1 - Generation and interception of 1-OXA-2,3-Cyclohexadiene and 1,2,4-Cyclohexatriene
N2 - The cycloadducts 6 and 7 of tricyc1o[4.1.0.0 2 ,7)hepta- 3,4-diene (~) with styrene and 1,3-butadiene rearrange to unusual products on thermolysis, namely the cycloheptatriene derivatives ~ and 10. 1-0xa-3,4-cyclohexadiene (20) is generated smoothly from 6,6-dichloro-3-oxabicyclo[3.1.0]hexane (22) and n-butyllithium. 1-0xa-2,3-cyclohexadiene (11) is formed from 6-exo-bromo-6-endo-fluoro-2-oxabicyclo[ 3.1.0]hexane (30) and methyllithium. In the presence of activated olefins, this reaction provides an efficient route to 28 and 33 - 38, the trapping products of 21. Interestingly, [2+2]-cycloadditions do not take place at the same double bond of 21 as [4+2]-cycloadditions. The reactions of 1,3-cyclopentadiene and indene with bromofluorocarbene afford 6-exo-bromo-6-endo-fluorobicyclo[3.1.0]hex-2-ene (50) and its benzo derivative ~, respectively. On treatment of these compounds with methyl lithium in the presence of styrene, the interception products 53 and 47 of 1,2,4-cyc10- hexatriene (44) and its benzo derivative 43, respectively, are formed in good yields.
KW - Chemie
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-56566
ER -
TY - JOUR
A1 - Schreck, Michael
A1 - Christl, Manfred
T1 - Generation and Interception of 1-Oxa-3,4-cyclohexadiene
N2 - No abstract available
KW - Chemie
Y1 - 1987
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31601
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Roberts, John D.
T1 - Carbon-13 Nuclear Magnetic Resonance Spectroscopy : Conformational Analysis of Methyl-Substituted Cycloheptanes, Cycloheptanols, and Cycloheptanones
N2 - The 130 chemical shifts were determined of the carbons in 12 cycloheptanes, 21 cycloheptanols, and 8 cycloheptanones. In some cyc1oheptanols and cyc1oheptanones, the assignments have been obtained unambiguously by the synthesis of deuterated derivatives and the use of paramagnetic-shift reagents. Substituent effects for the different types of groups have been calculated. The most informative data about the cyc10heptane conformations were provided by the relatively well understood I' effects. The results are generally in,good agreement with predictions based on the twist-chair form, which has been predicted by Hendrickson to be the most stable conformation. Pairs of cis-trans isomers are found to have rather characteristic differences in their 130 spectra. This fact was used to assign the resonances found for cis-trans mixtures of methyl-substituted cyc1oheptanols to specific isomers.
Y1 - 1972
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41663
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Leß, Roland
A1 - Müller, Heinrich
T1 - 6,7-Dimethylene-2,4-diphenylbicyclo[3.2.l]oct-3-en-2-yl Anion : A Test for the Origin of the Unusual Properties of the Bicyclo[3.2.l]octa-3,6-dien-2-yl Anion
N2 - No abstract available
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31547
ER -
TY - JOUR
A1 - Gigstad, Kenneth M.
A1 - Ricci JR., John S.
A1 - Markgraf, J. Hodge
A1 - Christl, Manfred
A1 - Kraft, Arno
T1 - Strained Heterocyclic Systems : 18. Structure of 1,2,3-Methylidyne-2,3-dihydro-1H-cyclopenta[b]quinoxaline
N2 - No abstract available
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41645
SN - 0108-2701
ER -
TY - JOUR
A1 - Irngartinger, H.
A1 - Reimann, W.
A1 - Lang, R.
A1 - Christl, Manfred
T1 - Electron Density Distribution in a Bicyclo[l.l.0]butane
N2 - No abstract available
Y1 - 1990
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31576
ER -
TY - JOUR
A1 - Christl, Manfred
A1 - Leininger, Hartmut
A1 - Mattauch, Brigitte
T1 - The 13C NMR Spectra of Some Tricyclo[2.2.0.02,6]hexane Derivatives : Unexpected High Field Absorptions Due to Additive gamma-anti Subsituent Effects
N2 - By means of the BC NMR spectra of tricyclo{2.2.0~rfJ6Jhexane and thirteen of its derivatives the effects of substituents in endo-3- and endo-5-positions on the HC chemical shifts have been determined. The y-anti effects are at least as Jarge as in monosubstituted cyc1obutanes, where the shielding values of second-row hetero substituents exceed those in unstrained systems by far, and higher-row and carbon substituents still cause substantial upfield shifts. In the title system the y-anti effect of a substituent in the endo-3- and endo-5-position are operative additively, and thus shift the absorption of C-J upfieJd by a maximum of 27 ppm with respect to the unsubstituted hydrocarbon.
Y1 - 1983
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41620
SN - x
ER -
TY - JOUR
A1 - Hegmann, Joachim
A1 - Christl, Manfred
A1 - Peters, Karl
A1 - Peters, Eva-Maria
A1 - Schnering, Hans Georg
T1 - Conjugated and Nonconjugated Cyclopentenones by a Reaction Cascade from Methyl 6-0xo-5-phenyl-1,3,4-oxadiazine-2-carboxylate and 1,3-Butadienes
N2 - No abstract available
Y1 - 1988
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30207
ER -
TY - JOUR
A1 - Lanzendörfer, Franz
A1 - Christl, Manfred
T1 - 3,4-Bismethylentricyclo[3.1.0.02,6]hexan - Synthese und Diels-Alder-Addition an Tetracyanethylen
N2 - No abstract available
Y1 - 1983
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30263
ER -
TY - JOUR
A1 - Brüntrup, Gisela
A1 - Christl, Manfred
T1 - Darstellung und Thermolyse der Hexamethyldewarbenzol-Cycloaddukte aromatischer Nitriloxide und des Diphenylnitrilimins
N2 - No abstract available
Y1 - 1973
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30257
ER -