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 - 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 - Mühlhäuser, M.
A1 - Engels, Bernd
A1 - Marian, C. M.
A1 - Peyerimhoff, S. D.
A1 - Bruna, P. J.
A1 - Jansen, M.
T1 - Einfluß der Ladungsverteilung auf die Bindungslängen im P\(_4\)O\(_6\) Gerüst bei Verbindungen des Typs P\(_4\)O\(_6\)X
N2 - No abstract available
KW - Organische Chemie
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59034
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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - Weiser, Jonas
A1 - Cui, Jingjing
A1 - Dewhurst, Rian D.
A1 - Braunschweig, Holger
A1 - Engels, Bernd
A1 - Fantuzzi, Felipe
T1 - Structure and bonding of proximity‐enforced main‐group dimers stabilized by a rigid naphthyridine diimine ligand
JF - Journal of Computational Chemistry
N2 - The development of ligands capable of effectively stabilizing highly reactive main‐group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity‐enforced group 13–15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8‐naphthyridine (napy) core. We show that the redox‐active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element‐element interaction modes, the latter ranging from isolated, element‐centered lone pairs (e.g., E = Si, Ge) to cases where through‐space π bonds (E = Pb), element‐element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI‐E2 species as viable synthetic targets, highlighting the versatility and potential applications of napy‐based ligands in main‐group chemistry.
KW - bond theory
KW - computational chemistry
KW - density functional calculations
KW - main group elements
KW - N ligands
Y1 - 2023
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-312586
VL - 44
IS - 3
SP - 456
EP - 467
ER -
TY - JOUR
A1 - Müller, Patrick
A1 - Meta, Mergim
A1 - Meidner, Jan Laurenz
A1 - Schwickert, Marvin
A1 - Meyr, Jessica
A1 - Schwickert, Kevin
A1 - Kersten, Christian
A1 - Zimmer, Collin
A1 - Hammerschmidt, Stefan Josef
A1 - Frey, Ariane
A1 - Lahu, Albin
A1 - de la Hoz-Rodríguez, Sergio
A1 - Agost-Beltrán, Laura
A1 - Rodríguez, Santiago
A1 - Diemer, Kira
A1 - Neumann, Wilhelm
A1 - Gonzàlez, Florenci V.
A1 - Engels, Bernd
A1 - Schirmeister, Tanja
T1 - Investigation of the compatibility between warheads and peptidomimetic sequences of protease inhibitors — a comprehensive reactivity and selectivity study
JF - International Journal of Molecular Sciences
N2 - Covalent peptidomimetic protease inhibitors have gained a lot of attention in drug development in recent years. They are designed to covalently bind the catalytically active amino acids through electrophilic groups called warheads. Covalent inhibition has an advantage in terms of pharmacodynamic properties but can also bear toxicity risks due to non-selective off-target protein binding. Therefore, the right combination of a reactive warhead with a well-suited peptidomimetic sequence is of great importance. Herein, the selectivities of well-known warheads combined with peptidomimetic sequences suited for five different proteases were investigated, highlighting the impact of both structure parts (warhead and peptidomimetic sequence) for affinity and selectivity. Molecular docking gave insights into the predicted binding modes of the inhibitors inside the binding pockets of the different enzymes. Moreover, the warheads were investigated by NMR and LC-MS reactivity assays against serine/threonine and cysteine nucleophile models, as well as by quantum mechanics simulations.
KW - covalent inhibitors
KW - in vitro study
KW - protease inhibitors
KW - peptidomimetic sequence
KW - warhead
KW - reactivity and selectivity study
Y1 - 2023
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-313596
SN - 1422-0067
VL - 24
IS - 8
ER -
TY - JOUR
A1 - Schmidt, Paul
A1 - Fantuzzi, Felipe
A1 - Klopf, Jonas
A1 - Schröder, Niklas B.
A1 - Dewhurst, Rian D.
A1 - Braunschweig, Holger
A1 - Engel, Volker
A1 - Engels, Bernd
T1 - Twisting versus delocalization in CAAC- and NHC-stabilized boron-based biradicals: the roles of sterics and electronics
JF - Chemistry - A European Journal
N2 - Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.
KW - chemistry
KW - radicals
KW - ab initio calculations
KW - boron
KW - carbene ligands
KW - density functional calculations
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256636
VL - 27
IS - 16
ER -
TY - JOUR
A1 - Roy, Dipak Kumar
A1 - Tröster, Tobias
A1 - Fantuzzi, Felipe
A1 - Dewhurst, Rian D.
A1 - Lenczyk, Carsten
A1 - Radacki, Krzysztof
A1 - Pranckevicius, Conor
A1 - Engels, Bernd
A1 - Braunschweig, Holger
T1 - Isolation and Reactivity of an Antiaromatic s‐Block Metal Compound
JF - Angewandte Chemie International Edition
N2 - The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation‐state flexibility of the s‐block metals has long stood in the way of their participation in sophisticated π‐bonding arrangements, and truly antiaromatic systems containing s‐block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis‐base‐coordination chemistry.
KW - antiaromaticity
KW - aromaticity
KW - beryllium
KW - heterocycles
KW - s-block metals
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224447
VL - 60
IS - 7
SP - 3812
EP - 3819
ER -
TY - JOUR
A1 - Dietschreit, Johannes C. B.
A1 - Wagner, Annika
A1 - Le, T. Anh
A1 - Klein, Philipp
A1 - Schindelin, Hermann
A1 - Opatz, Till
A1 - Engels, Bernd
A1 - Hellmich, Ute A.
A1 - Ochsenfeld, Christian
T1 - Predicting \(^{19}\)F NMR Chemical Shifts: A Combined Computational and Experimental Study of a Trypanosomal Oxidoreductase–Inhibitor Complex
JF - Angewandte Chemie International Edition
N2 - The absence of fluorine from most biomolecules renders it an excellent probe for NMR spectroscopy to monitor inhibitor–protein interactions. However, predicting the binding mode of a fluorinated ligand from a chemical shift (or vice versa) has been challenging due to the high electron density of the fluorine atom. Nonetheless, reliable \(^{19}\)F chemical‐shift predictions to deduce ligand‐binding modes hold great potential for in silico drug design. Herein, we present a systematic QM/MM study to predict the \(^{19}\)F NMR chemical shifts of a covalently bound fluorinated inhibitor to the essential oxidoreductase tryparedoxin (Tpx) from African trypanosomes, the causative agent of African sleeping sickness. We include many protein–inhibitor conformations as well as monomeric and dimeric inhibitor–protein complexes, thus rendering it the largest computational study on chemical shifts of \(^{19}\)F nuclei in a biological context to date. Our predicted shifts agree well with those obtained experimentally and pave the way for future work in this area.
KW - African sleeping sickness
KW - covalent inhibitors
KW - NMR spectroscopy
KW - quantum chemistry
KW - structural biology
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-214879
VL - 59
IS - 31
SP - 12669
EP - 12673
ER -
TY - JOUR
A1 - Saalfrank, Christian
A1 - Fantuzzi, Felipe
A1 - Kupfer, Thomas
A1 - Ritschel, Benedikt
A1 - Hammond, Kai
A1 - Krummenacher, Ivo
A1 - Bertermann, Rüdiger
A1 - Wirthensohn, Raphael
A1 - Finze, Maik
A1 - Schmid, Paul
A1 - Engel, Volker
A1 - Engels, Bernd
A1 - Braunschweig, Holger
T1 - cAAC‐Stabilized 9,10‐diboraanthracenes—Acenes with Open‐Shell Singlet Biradical Ground States
JF - Angewandte Chemie International Edition
N2 - Narrow HOMO–LUMO gaps and high charge‐carrier mobilities make larger acenes potentially high‐efficient materials for organic electronic applications. The performance of such molecules was shown to significantly increase with increasing number of fused benzene rings. Bulk quantities, however, can only be obtained reliably for acenes up to heptacene. Theoretically, (oligo)acenes and (poly)acenes are predicted to have open‐shell singlet biradical and polyradical ground states, respectively, for which experimental evidence is still scarce. We have now been able to dramatically lower the HOMO–LUMO gap of acenes without the necessity of unfavorable elongation of their conjugated π system, by incorporating two boron atoms into the anthracene skeleton. Stabilizing the boron centers with cyclic (alkyl)(amino)carbenes gives neutral 9,10‐diboraanthracenes, which are shown to feature disjointed, open‐shell singlet biradical ground states.
KW - acenes
KW - biradicals
KW - bond Activation
KW - boron
KW - heterocycles
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-217795
VL - 59
IS - 43
SP - 19338
EP - 19343
ER -
TY - JOUR
A1 - Klein, Philipp
A1 - Johe, Patrick
A1 - Wagner, Annika
A1 - Jung, Sascha
A1 - Kühlborn, Jonas
A1 - Barthels, Fabian
A1 - Tenzer, Stefan
A1 - Distler, Ute
A1 - Waigel, Waldemar
A1 - Engels, Bernd
A1 - Hellmich, Ute A.
A1 - Opatz, Till
A1 - Schirmeister, Tanja
T1 - New cysteine protease inhibitors: electrophilic (het)arenes and unexpected prodrug identification for the Trypanosoma protease rhodesain
JF - Molecules
N2 - Electrophilic (het)arenes can undergo reactions with nucleophiles yielding π- or Meisenheimer (σ-) complexes or the products of the S\(_N\)Ar addition/elimination reactions. Such building blocks have only rarely been employed for the design of enzyme inhibitors. Herein, we demonstrate the combination of a peptidic recognition sequence with such electrophilic (het)arenes to generate highly active inhibitors of disease-relevant proteases. We further elucidate an unexpected mode of action for the trypanosomal protease rhodesain using NMR spectroscopy and mass spectrometry, enzyme kinetics and various types of simulations. After hydrolysis of an ester function in the recognition sequence of a weakly active prodrug inhibitor, the liberated carboxylic acid represents a highly potent inhibitor of rhodesain (K\(_i\) = 4.0 nM). The simulations indicate that, after the cleavage of the ester, the carboxylic acid leaves the active site and re-binds to the enzyme in an orientation that allows the formation of a very stable π-complex between the catalytic dyad (Cys-25/His-162) of rhodesain and the electrophilic aromatic moiety. The reversible inhibition mode results because the S\(_N\)Ar reaction, which is found in an alkaline solvent containing a low molecular weight thiol, is hindered within the enzyme due to the presence of the positively charged imidazolium ring of His-162. Comparisons between measured and calculated NMR shifts support this interpretation
KW - cysteine protease
KW - rhodesain
KW - electrophilic (het)arene
KW - nucleophilic aromatic substitution
KW - Meisenheimer complex
KW - π-complex
KW - prodrug
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-203380
SN - 1420-3049
VL - 25
IS - 6
ER -
TY - JOUR
A1 - Klein, Philipp
A1 - Barthels, Fabian
A1 - Johe, Patrick
A1 - Wagner, Annika
A1 - Tenzer, Stefan
A1 - Distler, Ute
A1 - Le, Thien Anh
A1 - Schmid, Paul
A1 - Engel, Volker
A1 - Engels, Bernd
A1 - Hellmich, Ute A.
A1 - Opatz, Till
A1 - Schirmeister, Tanja
T1 - Naphthoquinones as covalent reversible inhibitors of cysteine proteases — studies on inhibition mechanism and kinetics
JF - Molecules
N2 - The facile synthesis and detailed investigation of a class of highly potent protease inhibitors based on 1,4-naphthoquinones with a dipeptidic recognition motif (HN-l-Phe-l-Leu-OR) in the 2-position and an electron-withdrawing group (EWG) in the 3-position is presented. One of the compound representatives, namely the acid with EWG = CN and with R = H proved to be a highly potent rhodesain inhibitor with nanomolar affinity. The respective benzyl ester (R = Bn) was found to be hydrolyzed by the target enzyme itself yielding the free acid. Detailed kinetic and mass spectrometry studies revealed a reversible covalent binding mode. Theoretical calculations with different density functionals (DFT) as well as wavefunction-based approaches were performed to elucidate the mode of action.
KW - protease
KW - rhodesain
KW - covalent reversible inhibition
KW - 1,4-naphthoquinone
KW - nucleophilic addition
KW - prodrug
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-203791
SN - 1420-3049
VL - 25
IS - 9
ER -
TY - JOUR
A1 - Brunecker, Carina
A1 - Müssig, Jonas H.
A1 - Arrowsmith, Merle
A1 - Fantuzzi, Felipe
A1 - Stoy, Andreas
A1 - Böhnke, Julian
A1 - Hofmann, Alexander
A1 - Bertermann, Rüdiger
A1 - Engels, Bernd
A1 - Braunschweig, Holger
T1 - Boranediyl‐ and Diborane(4)‐1,2‐diyl‐Bridged Platinum A‐Frame Complexes
JF - Chemistry – A European Journal
N2 - Diplatinum A‐frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)‐bridged Pt\(^{0}\)\(_{2}\) complex. While structurally analogous to well‐known μ‐borylene complexes, in which delocalized dative three‐center‐two‐electron M‐B‐M bonding prevails, theoretical investigations into the nature of Pt−B bonding in these A‐frame complexes show them to be rare dimetalla(di)boranes displaying two electron‐sharing Pt−B σ‐bonds. This is experimentally reflected in the low kinetic stability of these compounds, which are prone to loss of the (di)boron bridgehead unit.
KW - boron
KW - bonding
KW - EDA-NOCV
KW - oxidative addition
KW - platinum
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-214707
VL - 26
IS - 39
SP - 8518
EP - 8523
ER -
TY - JOUR
A1 - Saalfrank, Christian
A1 - Fantuzzi, Felipe
A1 - Kupfer, Thomas
A1 - Ritschel, Benedikt
A1 - Hammond, Kai
A1 - Krummenacher, Ivo
A1 - Bertermann, Rüdiger
A1 - Wirthensohn, Raphael
A1 - Finze, Maik
A1 - Schmid, Paul
A1 - Engel, Volker
A1 - Engels, Bernd
A1 - Braunschweig, Holger
T1 - cAAC‐stabilisierte 9,10‐Diboraanthracene – offenschalige Singulettbiradikale
JF - Angewandte Chemie
N2 - Geringe HOMO-LUMO-Abstände und eine hohe Ladungsträgermobilität prädestinieren die höheren Acene für Anwendungen im Bereich der Organoelektronik. Die Leistungsfähigkeit derartiger Verbindungen steigt hierbei dramatisch mit der Anzahl anellierter Benzolringe. Größere Acenmengen sind synthetisch bisher jedoch nur für Acene bis Heptacen verlässlich zugänglich. Theoretischen Studien zufolge besitzen (Oligo)acene offenschalige Singulettbiradikal- und (Poly)acene polyradikalische Grundzustände. Eindeutige experimentelle Belege für diese Vorhersagen sind hingegen äußerst selten. Durch den Einbau von zwei Boratomen in das Anthracengrundgerüst konnten wir den HOMO-LUMO-Abstand von Acenen dramatisch verringern und zwar ohne die Notwendigkeit einer Ausweitung des konjugierten π-Systems. Stabilisierung der Borzentren durch cyclische (Alkyl)(amino)carbene lieferte hierbei neutrale 9,10-Diboraanthracene mit disjunkten, offenschaligen Singulettbiradikal-Grundzuständen.
KW - Acene
KW - Bindungsaktivierung
KW - Biradikale
KW - Bor
KW - Heterocyclen
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218582
VL - 132
IS - 43
SP - 19502
EP - 19507
ER -
TY - JOUR
A1 - Rang, Maximilian
A1 - Fantuzzi, Felipe
A1 - Arrowsmith, Merle
A1 - Krummenacher, Ivo
A1 - Beck, Eva
A1 - Witte, Robert
A1 - Matler, Alexander
A1 - Rempel, Anna
A1 - Bischof, Tobias
A1 - Radacki, Krzysztof
A1 - Engels, Bernd
A1 - Braunschweig, Holger
T1 - Reduktion und Umlagerung eines Bor(I)‐Carbonylkomplexes
JF - Angewandte Chemie
N2 - Bei der Einelektronenreduktion eines durch eine cyclisches (Alkyl)(amino)carben (CAAC) stabilisierten Arylborylen-Carbonylkomplexes erfolgt die Bildung eines dimeren Borylketyl-Radikalanions, bedingt durch eine intramolekulare Arylmigration zum CO Kohlenstoffatom. Computergestützte Analyse liefert Hinweise auf eine radikalanionische [(CAAC)B(CO)Ar]\(^{.-}\) Zwischenstufe. Weiterführende Reduktion des entstandenen Komplexes liefert ein hoch nukleophiles (Boranyliden)methanolat.
KW - Biradikale
KW - Bor-Carbonylkomplexe
KW - Dichtefunktionalrechnungen
KW - Reduktionen
KW - Umlagerungen
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224409
VL - 133
IS - 6
SP - 3000
EP - 3005
ER -