TY - JOUR A1 - Aeschlimann, Martin A1 - Brixner, Tobias A1 - Cinchetti, Mirko A1 - Frisch, Benjamin A1 - Hecht, Bert A1 - Hensen, Matthias A1 - Huber, Bernhard A1 - Kramer, Christian A1 - Krauss, Enno A1 - Loeber, Thomas H. A1 - Pfeiffer, Walter A1 - Piecuch, Martin A1 - Thielen, Philip T1 - Cavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennas JF - Light: Science & Applications N2 - Radiationless energy transfer is at the core of diverse phenomena, such as light harvesting in photosynthesis\(^1\), energy-transfer-based microspectroscopies\(^2\), nanoscale quantum entanglement\(^3\) and photonic-mode hybridization\(^4\). Typically, the transfer is efficient only for separations that are much shorter than the diffraction limit. This hampers its application in optical communication and quantum information processing, which require spatially selective addressing. Here, we demonstrate highly efficient radiationless coherent energy transfer over a distance of twice the excitation wavelength by combining localized and delocalized\(^5\) plasmonic modes. Analogous to the Tavis-Cummings model, two whispering-gallery-mode antennas\(^6\) placed in the foci of an elliptical plasmonic cavity\(^7\) fabricated from single-crystal gold plates act as a pair of oscillators coupled to a common cavity mode. Time-resolved two-photon photoemission electron microscopy (TR 2P-PEEM) reveals an ultrafast long-range periodic energy transfer in accordance with the simulations. Our observations open perspectives for the optimization and tailoring of mesoscopic energy transfer and long-range quantum emitter coupling. KW - chemistry KW - nanocavities KW - nanophotonics and plasmonics KW - photonic devices Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-173265 VL - 6 ER - TY - JOUR A1 - Ahmed, Bilal A1 - Ojha, Animesh K. A1 - Hirsch, Florian A1 - Fischer, Ingo A1 - Patrice, Donfack A1 - Materny, Arnulf T1 - Tailoring of enhanced interfacial polarization in WO\(_3\) nanorods grown over reduced graphene oxide synthesized by a one-step hydrothermal method JF - RSC Advances N2 - In the present report, well-defined WO3 nanorods (NRs) and a rGO–WO\(_3\) composite were successfully synthesized using a one-pot hydrothermal method. The crystal phase, structural morphology, shape, and size of the as-synthesized samples were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The optical properties of the synthesized samples were investigated by Raman, ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy. Raman spectroscopy and TEM results validate the formation of WO\(_3\) (NRs) on the rGO sheet. The value of the dielectric constant (ε′) of WO3 NRs and rGO–WO\(_3\) composite is decreased with an increase in frequency. At low frequency (2.5 to 3.5 Hz), the value of ε′ for the rGO–WO3 composite is greater than that of pure WO\(_3\) NRs. This could be due to the fact that the induced charges follow the ac signal. However, at higher frequency (3.4 to 6.0), the value of ε′ for the rGO–WO\(_3\) composite is less compared to that of the pure WO3 NRs. The overall decrease in the value of ε′ could be due to the occurrence of a polarization process at the interface of the rGO sheet and WO3 NRs. Enhanced interfacial polarization in the rGO–WO\(_3\) composite is observed, which may be attributed to the presence of polar functional groups on the rGO sheet. These functional groups trap charge carriers at the interface, resulting in an enhancement of the interfacial polarization. The value of the dielectric modulus is also calculated to further confirm this enhancement. The values of the ac conductivity of the WO\(_3\) NRs and rGO–WO\(_3\) composite were calculated as a function of the frequency. The greater value of the ac conductivity in the rGO–WO\(_3\) composite compared to that of the WO\(_3\) NRs confirms the restoration of the sp:\(^{++}\) network during the in situ synthesis of the rGO–WO\(_3\) composite, which is well supported by the results obtained by Raman spectroscopy. KW - chemistry Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-181829 VL - 7 IS - 23 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 - Fayez, Shaimaa A1 - Feineis, Doris A1 - Mudogo, Virima A1 - Awale, Suresh A1 - Bringmann, Gerhard T1 - Ancistrolikokines E-H and related 5,8\('\)-coupled naphthylisoquinoline alkaloids from the Congolese liana \(Ancistrocladus\) \(likoko\) with antiausterity activities against PANC-1 human pancreatic cancer cells JF - RSC Advances N2 - A striking feature of the metabolite profile of \(Ancistrocladus\) \(likoko\) (Ancistrocladaceae) is the exclusive production of 5,8\('\)-linked naphthylisoquinoline alkaloids varying in their OMe/OH substitution patterns and in the hydrogenation degree in their isoquinoline portions. Here we present nine new compounds of this coupling type isolated from the twigs of this remarkable Central African liana. Three of them, the ancistrolikokines E (9), E\(_2\) (10), and F (11), are the first 5,8\('\)-linked naphthyldihydroisoquinolines found in nature with \(R\)-configuration at C-3. The fourth new metabolite, ancistrolikokine G (12), is so far the only representative of the 5,8\('\)-coupling type that belongs to the very rare group of alkaloids with a fully dehydrogenated isoquinoline portion. Moreover, five new \(N\)-methylated naphthyltetrahydroisoquinolines, named ancistrolikokines A\(_2\) (13), A\(_3\) (14), C\(_2\) (5), H (15), and H\(_2\) (16) are presented, along with six known 5,8\('\)-linked alkaloids, previously identified in related African \(Ancistrocladus\) species, now found for the first time in \(A.\) \(likoko\). The structural elucidation was achieved by spectroscopic analysis (HRESIMS, 1D and 2D NMR) and by chemical (oxidative degradation) and chiroptical (electronic circular dichroism) methods. The new ancistrolikokines showed moderate to good preferential cytotoxic activities towards pancreatic PANC-1 cells in nutrient-deprived medium (NDM), without causing toxicity under normal, nutrient-rich conditions, with ancistrolikokine H\(_2\) (16) being the most potent compound. KW - chemistry KW - Ancistrocladus likoko KW - alkaloids KW - bioactive compound KW - anti-cancer-agent KW - pancreatic cancer KW - naphthylisoquinoline alkaloid KW - spectroscopic analysis Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172008 VL - 7 IS - 85 ER - TY - JOUR A1 - Hanft, Anna A1 - Lichtenberg, Crispin T1 - Dimerization of 2-[(2-((2-aminophenyl)thio)phenyl)amino]-cyclohepta-2,4,6-trien-1-one through hydrogen bonding, C\(_{19}\)H\(_{16}\)N\(_2\)OS JF - Zeitschrift für Kristallographie - New Crystal Structures N2 - C\(_{19}\)H\(_{16}\)N\(_2\)OS, triclinic, P (1) over bar (no. 2), a= 8.1510(3) angstrom, b = 8.8021(3) angstrom, c =11.3953(5) angstrom, alpha =72.546(2)degrees, beta=84.568(2)degrees, gamma =80.760(2)degrees, V =768.86(5) angstrom(3), Z =2, R\(_{gt}\)(F) = 0.0491, WR\(_{ref}\)(F-2) = 0.1494, T =100 K. KW - crystal structure KW - complexes KW - ligands KW - tropocoronands KW - mononuclear KW - chemistry Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-229482 VL - 235 IS - 4 ER - TY - JOUR A1 - Hartung, Andreas A1 - Seufert, Florian A1 - Berges, Carsten A1 - Gessner, Viktoria H. A1 - Holzgrabe, Ulrike T1 - One-Pot Ugi/Aza-Michael Synthesis of Highly Substituted 2,5-Diketopiperazines with Anti-Proliferative Properties JF - Molecules N2 - The well-known Ugi reaction of aldehydes with amines, carboxylic acids and isocyanides leads to the formation of acyclic alpha-acylaminocarboxamides. Replacement of the carboxylic acid derivatives with beta-acyl substituted acrylic acids gives access to highly substituted 2,5-diketopiperazines in one single reaction-step without additives or complex reaction procedures. The obtained diketopiperazines show anti-proliferative effects on activated T cells and represent therefore potential candidates for targeting unwanted T cell-mediated immune responses. KW - multicomponent Ugi-type reaction KW - intramolecular Michael addition KW - strategy KW - derivates KW - diketopiperazines KW - chemistry KW - T cell KW - 2,5-diketopiperazines KW - anti-proliferative effects Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-130423 VL - 17 IS - 12 ER - TY - THES A1 - Herok, Christoph T1 - Quantum Chemical Exploration of Potential Energy Surfaces: Reaction Cycles and Luminescence Phenomena T1 - Quantenchemische Erforschung von Energiehyperflächen: Reaktionszyklen und Lumineszenzphänomene N2 - This work aims at elucidating chemical processes involving homogeneous catalysis and photo–physical relaxation of excited molecules in the solid state. Furthermore, compounds with supposedly small singlet–triplet gaps and therefore biradicaloid character are investigated with respect to their electro–chemical behavior. The work on hydroboration catalysis via a reduced 9,10–diboraanthracene (DBA) was preformed in collaboration with the Wagner group in Frankfurt, more specifically Dr. Sven Prey, who performed all laboratory experiments. The investigation of delayed luminescence properties in arylboronic esters in their solid state was conducted in collaboration with the Marder group in Würzburg. The author of this work took part in the synthesis of the investigated compounds while being supervised by Dr. Zhu Wu. The final project was a collaboration with the group of Anukul Jana from Hyderabad, India who provided the experimental data. N2 - Ziel dieser Arbeit ist die Aufklärung chemischer Prozesse, die homogene Katalyse und photophysikalische Relaxation angeregter Moleküle im Festkörper beinhalten. Darüber hinaus werden Verbindungen mit vermeintlich kleinen Singulett-Triplett-Lücken und damit biradikaloidem Charakter auf ihr elektrochemisches Verhalten hin untersucht. Die Arbeiten zur Hydroborierungskatalyse mit einem reduzierten 9,10-Diboraanthracen (DBA) wurden in Zusammenarbeit mit der Wagner-Gruppe in Frankfurt durchgeführt, genauer gesagt mit Dr. Sven Prey, der alle Laborexperimente durchführte. Die Untersuchung der verzögerten Lumineszenzeigenschaften von Arylborsäureestern im Festkörper wurde in Zusammenarbeit mit der Marder Gruppe in Würzburg durchgeführt. Der Autor dieser Arbeit war an der Synthese der untersuchten Verbindungen beteiligt und wurde dabei von Dr. Zhu Wu betreut. Das abschließende Projekt war eine Zusammenarbeit mit der Gruppe von Anukul Jana aus Hyderabad, Indien, die die experimentellen Daten zur Verfügung stellte. KW - Simulation KW - Quantum Chemistry KW - Reaction Mechanism KW - Fluorescence KW - Phosphoresence KW - Chemie KW - Katalyse KW - Lumineszenz KW - chemistry KW - simulation KW - catalysis KW - mechanism KW - luminescence KW - Energiehyperfläche Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-352185 ER - TY - JOUR A1 - Koch, Oliver A1 - Cappel, Daniel A1 - Nocker, Monika A1 - Jaeger, Timo A1 - Flohé, Leopold A1 - Sotriffer, Christoph A1 - Selzer, Paul T1 - Virtual screening using structure-based consensus pharmacophore models and ensemble docking based on MD-generated conformations : [From 6th German Conference on Chemoinformatics, GCC 2010, Goslar, Germany. 7-9 November 2010] JF - Journal of Cheminformatics N2 - No abstract available. KW - chemistry Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-142830 VL - 3 IS - Suppl. 1 ER - TY - JOUR A1 - Kraft, Andreas A1 - Stangl, Johannes A1 - Krause, Ana-Maria A1 - Müller-Buschbaum, Klaus A1 - Beuerle, Florian T1 - Supramolecular frameworks based on [60]fullerene hexakisadducts JF - Beilstein Journal of Organic Chemistry N2 - [60]Fullerene hexakisadducts possessing 12 carboxylic acid side chains form crystalline hydrogen-bonding frameworks in the solid state. Depending on the length of the linker between the reactive sites and the malonate units, the distance of the [60]fullerene nodes and thereby the spacing of the frameworks can be controlled and for the most elongated derivative, continuous channels are obtained within the structure. Stability, structural integrity and porosity of the material were investigated by powder X-ray diffraction, thermogravimetry and sorption measurements. KW - chemistry KW - fullerenes KW - hexakisadducts KW - hydrogen bonding KW - porous materials KW - structure elucidation Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-171996 VL - 13 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 -