TY - JOUR A1 - Kleinpeter, Erich A1 - Stohß, S. A1 - Schroth, W. T1 - Stereochemistry and complexational behaviour of dibenzo-crown ethers Y1 - 1992 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Hartmann, Jürgen A1 - Schroth, W. A1 - Hofer, O. A1 - Kalchhauser, H. A1 - Wurz, G. T1 - Synthesis and conformational behaviour of Ditosyldiaza[2.2]orthometacyclophanes Y1 - 1992 ER - TY - JOUR A1 - Haufe, G. A1 - Rolle, U. A1 - Kleinpeter, Erich A1 - Kivikoski, J. A1 - Rissanen, K. T1 - N-Heterocyclization in electrophilic haloamination reactions of 1,5-cyclooctadiene : formation of the granatanine and homotropane skeletons Y1 - 1993 ER - TY - JOUR A1 - Lehmann, J. A1 - Kleinpeter, Erich T1 - 1H NMR Lanthanideinduced Shift (LIS) investigations of highly flexible molecules : a new approach Y1 - 1993 ER - TY - JOUR A1 - Lehmann, J. A1 - Kleinpeter, Erich T1 - 1H NMR Lanthanideinduced Shift (LIS) investigations of highly flexible molecules : a new approach ; Part II Y1 - 1993 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Thomas, Steffen A1 - Uhlig, G. A1 - Rudorf, Wolf-Dieter T1 - Study of the distribution of pi-Electrons in Push-Pull Alkenes by 1H an 13C NMR spectroscopy Y1 - 1993 ER - TY - BOOK A1 - Pihlaja, Kalevi A1 - Kleinpeter, Erich T1 - 13C NMR chemical shifts in structural and stereochemical analysis T3 - Methods in stereochemical analysis Y1 - 1994 PB - VCH CY - New York ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Chatterjee, S. K. A1 - Rudorf, Wolf-Dieter T1 - Study of the pi-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy, III : the conformation of 3,4-Dihydro-4-oxo-2H-thiins Y1 - 1994 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Chatterjee, S. K. A1 - Rudorf, Wolf-Dieter T1 - Study of the pi-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy Y1 - 1994 ER - TY - JOUR A1 - Mäki, E. A1 - Pihlaja, Kalevi A1 - Kleinpeter, Erich A1 - Hartmann, Jürgen A1 - Schroth, W. T1 - Electron impact ionization mass spectrometry of some 4,9-Dihetro-(X,X)-cyclodeca-1,6-dienes : mono- and dibenzo analogues Y1 - 1994 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas A1 - Heydenreich, Matthias A1 - Chatterjee, S. K. A1 - Rudorf, Wolf-Dieter T1 - Study of the pi-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy, IV : the conformation and dynamic behaviour of substituted N-Phenyl-2,3-dihydro-4(1H)-pyridones Y1 - 1995 ER - TY - JOUR A1 - Oszczapowicz, J. A1 - Wawer, I. A1 - Dargatz, M. A1 - Kleinpeter, Erich T1 - Amidines .34. N-15 NMR spectra of trisubstituted amidines - substituent effects Y1 - 1995 ER - TY - JOUR A1 - Starke, Ines A1 - Koch, Andreas A1 - Uhlemann, Erhard A1 - Kleinpeter, Erich T1 - Nuclear-magnetic-resonance studies and molecular modelling of the solution structure of some dibenzo crown- ethers and their complexes Y1 - 1995 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Thomas, Steffen A1 - Fischer, G. T1 - 13C and 15N NMR study of 1,2,4-Triazolo[1,5-a]pyrimidines with one tautomerism-introducing substituent Y1 - 1995 ER - TY - JOUR A1 - Kleinpeter, Erich T1 - Conformational analysis of six-membered sulfur-containing heterocycles Y1 - 1995 ER - TY - JOUR A1 - Kleinpeter, Erich T1 - Effect of the variation of ring size of cyclic NR2 substituents on the barrier to rotation in amides, thioamides and related compounds Y1 - 1995 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Pihlaja, Kalevi T1 - Functions containing a thiocarbonyl group and at least one halogen, also at least one chalcogen and no halogen Y1 - 1995 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Ströhl, D. A1 - Peinze, S. T1 - Solution conformation of tripeptides by NMR spectroscopy and force field calculations Y1 - 1995 ER - TY - JOUR A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Ab-initio study and semiempirical calculations of keto-enol tautomerism of triazolopyrimidines Y1 - 1995 ER - TY - JOUR A1 - Koch, Andreas A1 - Starke, Ines A1 - Kleinpeter, Erich T1 - Conformational study of Dibenzo crown ethers and their complexation with Li+ and Na+ Y1 - 1995 ER - TY - JOUR A1 - Lehmann, J. A1 - Kleinpeter, Erich T1 - 1H NMR lanthanide-induced shift investigations of highly flexible molecules, part III. Applications to alcohols, aldehydes, esters and amines Y1 - 1995 ER - TY - JOUR A1 - Starke, Ines A1 - Koch, Andreas A1 - Holdt, Hans-Jürgen A1 - Kleinpeter, Erich T1 - 1H, 13C, and 15N NMR study of the solution structure of metabridged bis(benzo-15-crown-5-ether)s Y1 - 1995 ER - TY - JOUR A1 - Pihlaja, Kalevi A1 - Lehmann, S. A1 - Schroth, W. A1 - Gäber, M. A1 - Kleinpeter, Erich T1 - Electron impact induced fragmentation of dibenzo crown ethers Y1 - 1996 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Ströhl, D. A1 - Peinze, S. A1 - Brandt, W. A1 - Schmidt, R. A1 - Neubert, K. T1 - The solution conformation of cyclic ß-casomorphine-5 analogues Y1 - 1996 ER - TY - JOUR A1 - Kleinpeter, Erich T1 - The structure of hydantoins in solution and in the solid state Y1 - 1996 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Starke, Ines A1 - Ströhl, D. A1 - Holdt, Hans-Jürgen T1 - NMR spectroscopic study of the solution structure and complexational behaviour of bis-benzocrown ethers Y1 - 1996 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Kalder, L. A1 - Koch, Andreas A1 - Henning, Dietrich A1 - Kempter, Gerhard T1 - NMR spectroscopic and theoretical structural analysis of 5,5-disubstituted hydantoins in solution Y1 - 1997 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas A1 - Fischer, G. A1 - Askolin, C.-P. T1 - 13 C NMR, 15 N NMR and quantum-chemical study of the tautomerism of 2-substituted 5-ME-7-OH-1,2,4-triazolo[1,5- a]pyrimidines Y1 - 1997 ER - TY - JOUR A1 - Kleinpeter, Erich T1 - The Structure of hydantions in solution and in the solid state Y1 - 1997 ER - TY - JOUR A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Restricted rotation about particial C, N Double Bond Y1 - 1997 ER - TY - JOUR A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Zimmermann, Thomas T1 - Dynamic NMR study of the flexibility of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts Y1 - 1997 UR - http://www.springerlink.com/content/110258 U6 - https://doi.org/10.1007/s002160050205 SN - 0937-0633 ER - TY - JOUR A1 - Thomas, Steffen A1 - Brühl, Iris A1 - Heilmann, Dieter A1 - Kleinpeter, Erich T1 - 13 C NMR Chemical shift calculations for some substituted pyridines - a comparative consideration Y1 - 1997 ER - TY - JOUR A1 - Sarodnick, Gerhard A1 - Hilfert, Liane A1 - Kempter, Gerhard A1 - Kleinpeter, Erich T1 - Reactin of 2-(halogenomethyl)-quinoxalines and quinolines with hydroxybenzoic acids and their esters Y1 - 1997 ER - TY - JOUR A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Study of the tautomerism by experimentally and theoretically estimated 13C and 15N chemical shifts Y1 - 1997 ER - TY - JOUR A1 - Koch, Andreas A1 - Thomas, Steffen A1 - Kleinpeter, Erich T1 - Ab-initio study, semi-empirical calculation and NMR spectroscopy of keto-enol tautomerism of triazolopyrimidines Y1 - 1997 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Kalder, L. A1 - Koch, Andreas A1 - Henning, Dietrich A1 - Kempter, Gerhard A1 - Benassi, Rois A1 - Taddei, F. T1 - NMR spectroscopic and theoretical structural analysis of 5,5-disubstituted hydantoins in solution Y1 - 1997 ER - TY - JOUR A1 - Grotjahn, Manuela A1 - Drexler, Hans-Joachim A1 - Jäger, Norbert A1 - Kleinpeter, Erich A1 - Holdt, Hans-Jürgen T1 - Molecular dynamic and conformational study of an unsaturated 12-crown-S202 ether and its AgI complexes Y1 - 1997 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Starke, Ines A1 - Ströhl, D. A1 - Holdt, Hans-Jürgen T1 - NMR spectroscopic study of the solution structure and complexational behaviour of bis-benzocrown ethers Y1 - 1997 ER - TY - JOUR A1 - Benassi, Rois A1 - Bregulla, Antje A1 - Friedrich, Alwin A1 - Henning, Dietrich A1 - Heydenreich, Matthias A1 - Mickler, Wulfhard A1 - Kleinpeter, Erich A1 - Kempter, Gerhard A1 - Schilde, Uwe A1 - Taddei, F. T1 - NMR spectroscopic and theoretical structural study of 5-exo-methylene-substituted hydantoins Y1 - 1998 ER - TY - JOUR A1 - Hilfert, Liane A1 - Sarodnick, Gerhard A1 - Kempter, Gerhard A1 - Kleinpeter, Erich T1 - 1H, 13C and 15 N NMR study and molecular modelling of 2,3- disubstituted quinoxalines with sterically hinderered aromatic and heteroaromatic substituents Y1 - 1998 ER - TY - JOUR A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Ristau, Thomas A1 - Knoll, Susanne A1 - Heinicke, Jochen A1 - Sieler, Joachim A1 - Niemitz, Matthias A1 - Mühlstädt, Manfred A1 - Kleinpeter, Erich T1 - Conformational analysis of sulfur-containing heterocycles ; part I: synthesis and structural determination of diastereomerically pure 4,6-bis(phenoxymethyl)-1,2,5-trithiepanes Y1 - 1998 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Woller, Jochen A1 - Wolf, Gunter A1 - Koch, Andreas A1 - Kempter, Gerhard A1 - Pihlaja, Kalevi T1 - Configuration and stereodynamics of exo/endoisomeric push-pull alkenes of pentadiene structure Y1 - 1998 ER - TY - JOUR A1 - Kleinpeter, Erich T1 - Conformational analysis of saturated six-membered oxygen-containing heterocyclic rings Y1 - 1998 ER - TY - JOUR A1 - Reiche, K. B. A1 - Starke, Ines A1 - Kleinpeter, Erich A1 - Holdt, Hans-Jürgen T1 - Host-guest complexation of imine-type meta-bridged bis(benzo crown ether)s with alkali cations in the gas phase under FAB conditions Y1 - 1998 ER - TY - JOUR A1 - Benassi, Rois A1 - Bregulla, Antje A1 - Henning, Dietrich A1 - Heydenreich, Matthias A1 - Kempter, Gerhard A1 - Kleinpeter, Erich A1 - Taddei, F. T1 - NMR-spectroscopic and theoretical structural analysis of 5-benzyl subtituted hydantoins in solutions Y1 - 1999 ER - TY - JOUR A1 - Zucchi, Claudia A1 - Cornia, Andrea A1 - Boese, Roland A1 - Kleinpeter, Erich A1 - Alper, Howard A1 - Palyi, Gyula T1 - Preparation and molecular structures of benzyl- and phenyl-acetycobalt-carbonyls Y1 - 1999 ER - TY - JOUR A1 - Scholl, S. A1 - Koch, Andreas A1 - Henning, Dietrich A1 - Kempter, Gerhard A1 - Kleinpeter, Erich T1 - The influence of structure and lipophilicity of hydantoin derivatives on anticonvulsant activity Y1 - 1999 ER - TY - JOUR A1 - Grotjahn, Manuela A1 - Kleinpeter, Erich T1 - Conformational behaviour of N-tosyl-substituted diaza-crown ethers Y1 - 1999 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Hilfert, Liane A1 - Koch, Andreas T1 - NMR spectroscopic and ab-initio MO study of sterically hindered 2,3-disubstituted quinoxalines Y1 - 1999 ER - TY - JOUR A1 - Grotjahn, Manuela A1 - Jäger, Norbert A1 - Drexler, Hans-Joachim A1 - Holdt, Hans-Jürgen A1 - Kleinpeter, Erich T1 - Molecular modeling study of the PtCl2 complexes of unsaturated S2On+1- coronands: dynamic simulations and investigation of the ring interconversion Y1 - 1999 ER - TY - JOUR A1 - Drexler, Hans-Joachim A1 - Starke, Ines A1 - Grojahn, Manuela A1 - Reinke, H. A1 - Kleinpeter, Erich A1 - Holdt, Hans-Jürgen T1 - SbCl3, BiCl3 and Na+ Complexes of maleonitrile-dithiacrown ethers: synthesis, crystal structures and DEP-MS experiments Y1 - 1999 ER - TY - JOUR A1 - Reiche, K. B. A1 - Starke, Ines A1 - Kleinpeter, Erich A1 - Holdt, Hans-Jürgen A1 - Pihlaja, Kalevi A1 - Oksaman, P. A1 - Ovcharenko, V. V. T1 - Fragmentation of imine-type meta-bridged bis(benzo crown ether)s under electron impact Y1 - 1999 ER - TY - JOUR A1 - Drexler, Hans-Joachim A1 - Grotjahn, Manuela A1 - Kleinpeter, Erich A1 - Holdt, Hans-Jürgen T1 - A novel polymeric disilver(I) complex containing both macrocyclic- and linear-coordinate silver(I) centres : [Ag-2(mn-15S(2)O(3))](infinity)(ClO4)(2 infinity) (mn-15S(2)O(3) = maleonitrile-dithia[15]crown-5) Y1 - 1999 ER - TY - JOUR A1 - Benassi, Rois A1 - Bertarini, C. A1 - Kleinpeter, Erich A1 - Taddei, F. T1 - Exocyclic push-pull conjugated compounds, Part 2 : the effect of donor and acceptor substituents on the rotational barrier of push-pull ethylenes Y1 - 2000 ER - TY - JOUR A1 - Benassi, Rois A1 - Bertarini, C. A1 - Kleinpeter, Erich A1 - Taddei, F. A1 - Thomas, Steffen T1 - Exocyclic push-pull conjugated compounds : Part 1 ; theoretical study of the effect of ring size on the structure, electronic properties and rotational barriers of cyclic analogoues of 1,1-diamino-2.2-dicyanoethylene Y1 - 2000 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Hilfert, Liane A1 - Koch, Andreas T1 - GIAO-HF/DFT calculation of C-13 and N-15 chemical shifts for studying tautomerism and intramolecular hydrogen bonding in 2,3-disubstituted quinoxalines Y1 - 2000 ER - TY - JOUR A1 - Starke, Ines A1 - Holzberger, Anja A1 - Kamm, Birgit A1 - Kleinpeter, Erich T1 - Qualitative and quantitative analysis of carbohydrates in green juices (wild mix grass and alfalfa) from a green biorefinery by gas chromatography/mass spectrometry Y1 - 2000 ER - TY - JOUR A1 - Kleinpeter, Erich T1 - Recent advances in studying tautomerism in solution and in solid state Y1 - 2000 ER - TY - JOUR A1 - Benassi, Rois A1 - Bertarini, C. A1 - Hilfert, Liane A1 - Kempter, Gerhard A1 - Kleinpeter, Erich A1 - Spindler, Jürgen A1 - Taddei, F. A1 - Thomas, Steffen T1 - Exocyclic push-pull conjugated compounds : Part 3 Y1 - 2000 ER - TY - JOUR A1 - Beitz, Toralf A1 - Koetz, Joachim A1 - Wolf, Gunter A1 - Kleinpeter, Erich A1 - Friberg, Stig E. T1 - Poly(N-vinyl-2-pyrrolidone) and 1-octyl-2-pyrrolidinone modified ionic microemulsions Y1 - 2001 ER - TY - JOUR A1 - Grotjahn, Manuela A1 - Lehmann, S. A1 - Aurich, Ines A1 - Holdt, Hans-Joachim A1 - Kleinpeter, Erich T1 - NMR spectroscopic and molecular modelling studies of the solution structure and complexational behaviour of some bis(benzocrown ether)s N2 - Structural information about the bis(benzo crown ether)s I-VI and their complexes with alkali metal cations was deduced from the 13C NMR chemical shifts, the salt-induced 1H and 13C chemical shifts and the vicinal 1H,1H coupling constants. Especially the isomerism with respect to the amide O=C - NH bonds and imine fragments were assigned by various useful NMR parameters ( C=O, 1JN,H, 1JC,H) and proved to be E,E-anti,anti. Furthermore, stereochemical information about preferred conformations about flexible bonds was obtained from 2D ROESY NMR experiments. The complex formation (2:1 complexes and sandwich-like 1:1 complexes, respectively) were determined also by 23Na NMR spectroscopy. The conformational study of the crown ethers was accompanied and corroborated by molecular dynamics and quantum chemical calculations. Y1 - 2001 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Grotjahn, Manuela A1 - Klinka, Karel D. A1 - Drexler, Hans-Joachim A1 - Holdt, Hans-Jürgen T1 - Conformational and complexational study of some maleonitrile mixed oxadithia crown ethers by NMR spectroscopy and molecular modelling N2 - The macrocyclic ring interconversion of four maleonitrile mixed oxadithia crown ethers of variable ring size, mn-12-S2O2, mn-15-S2O3, mn-18-S2O4 and fn-12-S2O2, were studied by 1H and 13C NMR spectroscopy and by molecular modelling. The barriers to ring interconversion were estimated using variable temperature NMR spectroscopy and from the calculated activation energies, together with the spin-lattice relaxation times of the CH2 carbon atoms, conclusions were drawn regarding the intramolecular flexibility of the crown ethers in both the free state as well as the complexed state incorporating either AgI, BiIII, SbIII, PdII or PtII metal cations. Furthermore, both the stoichiometry of the complexes and the coordination sites of the crown ethers to the various cations were also clearly implicated. Molecular modelling was also utilised to ascertain the preferred conformers of the four compounds and their corresponding complexes, the results of which corroborated the experimental NMR results to a high degree. Y1 - 2001 ER - TY - JOUR A1 - Holdt, Hans-Jürgen A1 - Drexler, Hans-Joachim A1 - Starke, Ines A1 - Grotjahn, Manuela A1 - Kleinpeter, Erich T1 - Homologous series of the PdCl2 and PtCl2 complexes of maleonitrile-dithiacrown ethers : synthesis, crystal structures, NMR spectroscopy and mass spectrometry Y1 - 2001 ER - TY - JOUR A1 - Germer, Antje A1 - Peter, Martin G. A1 - Kleinpeter, Erich T1 - Solution-state conformational study of the hevamine inhibitor allosamidin and six potential inhibitor analogues by NMR spectroscopy and molecular modeling N2 - The soln.-state conformations of the hevamine inhibitor allosamidin and six potential inhibitor analogs were studied by various NMR spectroscopic techniques and mol. modeling using force field calcns. Detn. solely of the global energy min. conformation was found to be insufficient for consensus with the NMR results, and agreement between the NMR exptl. data and the theor. calcns. was only reached by assessing the structures as population-weighted av. conformers on the basis of Boltzmann distributions derived from the calcd. relative energies. The conformations of the glycosidic linkages in the compds. were found to be similar when the sugar residues were the same, but differences were markedly evident otherwise and also for the various heterocyclic group linkages. The binding of the compds. to hevamine, which may also complex to chitinases in general, was assessed using HMQC, transfer-NOESY, and both 1-D and 2-D satn. transfer difference NMR expts. Under the conditions employed, only allosamidin was implicated to be bound to hevamine, and then only by HMQC with the dipolar coupling-based expts. failing to substantiate the formation of the complex. However, the results are consistent with the biochem. activities of the compds. whereby only allosamidin has been shown to act as a competitive inhibitor. Y1 - 2002 ER - TY - JOUR A1 - Thiele, Gabriela A1 - Rottmann, Antje A1 - Germer, Antje A1 - Kleinpeter, Erich A1 - Spindler, Klaus-Dieter A1 - Synstad, Bjoenar A1 - Eijsink, Vincent G. H. A1 - Peter, Martin G. T1 - Synthesis and conformational analysis of pseudosugar analogues of chitotriose N2 - In this article, the synthesis of analogs of N,N',N''-triacetylchitotriose in which the central sugar residue was replaced by a succinic acid is presented. Mol. modeling calcns. revealed that the pseudotrisaccharides exist in low energy extended conformations which show similar space filling as N,N',N''-triacetylchitotriose. Of the N,N',N''-triacetylchitotriose pseudosugar analogs tested as chitinase inhibitors, none showed any appreciable competition (numerical data not presented). The conformational anal. along with further synthetic efforts will hopefully lead to more efficient pseudosaccharides as chitinase inhibitors. Y1 - 2002 ER - TY - JOUR A1 - Germer, Antje A1 - Klod, Sabrina A1 - Peter, Martin G. A1 - Kleinpeter, Erich T1 - NMR spectroscopic and theoretical study of the complexation of the inhibitor allosamidin in the binding pocket of the plant chitinase hevamine N2 - Based on NMR spectroscopic information about the allosamidin-hevamine complex, ab initio MO calcns. of the ring current effect of the arom. moieties of Trp255, Tyr183 and Tyr6 of hevamine were carried out to investigate the role of these amino acid residues in binding interactions with allosamidin in soln. In addn., the intermol. steric compression effect on the 13C chem. shifts of the allosamizoline carbon atoms and the hydrogen bonding to Glu127 was identified. It can be inferred that the binding forces are strongest in the allosamizoline moiety of allosamidin. Y1 - 2002 ER - TY - JOUR A1 - Germer, Antje A1 - Mugge, Clemens A1 - Peter, Martin G. A1 - Rottmann, Antje A1 - Kleinpeter, Erich T1 - Solution- and bound-state conformational study of N,N',N''-triacetyl chitotriose and other analogous potential inhibitors of hevamine: Application of trNOESY and STD NMR spectroscopy N2 - The soln.-state conformations of N,N',N''-triacetyl chitotriose (1) and other potential chitinase inhibitors 2-4 were studied using a combination of NMR spectroscopy (NOESY) and mol. mechanics calcns. Detn. solely of the global energy min. conformation was found to be insufficient for an agreement with the NMR results. An appropriate consistency between the NMR exptl. data and theor. calcns. was only reached by assessing the structures as population-weighted av. conformers based on Boltzmann distributions derived from the calcd. relative energies. Analogies, but also particular differences, between the synthetic compds. 2-4 and the naturally-occurring N,N',N''-triacetyl chitotriose were found. Furthermore, the conformation of compds. 1 and 2 when bound to hevamine was also studied using transferred NOESY expts. and the binding process was found to impart a level of conformational restriction on the ligands. The preferred conformation as detd. for 1 in the bound state to hevamine belonged to one of the conformational families found for the compd. when free in soln., although full characterization of the bound-state conformations was impeded due to severe signal overlap. Satn. transfer difference NMR expts. were also employed to analyze the binding epitopes of the bound compds. We thus detd. that it is mainly the acetyl amido groups of the trisaccharide and the heterocyclic moiety which are in close contact with hevamine. Y1 - 2003 ER - TY - JOUR A1 - Sarodnick, Gerhard A1 - Heydenreich, Matthias A1 - Linker, Torsten A1 - Kleinpeter, Erich T1 - Quinoxalines : Part 12: Synthesis and structural study of 1-(thiazol-2-yl)-1H-pyrazolo[3,4-b]quinoxalines - the dehydrogenative cyclization with hydroxylamine hydrochloride Y1 - 2003 ER - TY - JOUR A1 - Kovacs, J. A1 - Toth, G. A1 - Kleinpeter, Erich A1 - Schilde, Uwe T1 - Crystal structure of trans, cis-(ñ)-3ï-4-fluorophenyl)-2-phenylspiro[2H-1-benzothiopyran-34H,2ï-oxiran]-4-one 1- oxide, C22H15FO3S Y1 - 2003 UR - ftp://ftp.oldenbourg.de/pub/download/frei/ncs/218-2/1267-1023.pdf SN - 1433-7266 ER - TY - JOUR A1 - Koetz, Joachim A1 - Günther, Claudia A1 - Kosmella, Sabine A1 - Kleinpeter, Erich A1 - Wolf, Gunter T1 - Polyelectrolyte induced structural changes in the isotropic phase of the system sulfobetaine/pentanol/toluene/ water Y1 - 2004 ER - TY - JOUR A1 - Heydenreich, Matthias A1 - Wolf, G. A1 - Woller, Jochen A1 - Kleinpeter, Erich T1 - Restricted rotation of the amino group and ring inversion in highly substituted anilines. A dynamic NMR and computational study N2 - The reaction of cyclic ylidene malononitriles with acetylene (di)carboxylic acid esters led to the production of nine bicyclic systems incorporating highly substituted (5/6) anilines. The free energy of activation (DeltaG(#)) for the restricted rotation about the aniline-NH2 bond was experimentally measured in each case and a correlation was evident between the increase in steric strain in the ground state, the electron withdrawing capabilities of the ring substituents, and a reduction in the rotational barrier. For four of the compounds, the slow ring interconversion (chairreversible arrowchair) for the annelated saturated seven-membered ring that formed part of the bicyclic system was also evident. In these four compounds, both dynamic processes were also studied theoretically using ab initio methods whilst the ring interconversion was additionally studied using molecular dynamic simulations. The interconversion between the two stable chair forms was deemed to occur via a conformation series consisting of chairreversible arrowboatreversible arrowtwist-boatreversible arrowboatreversible arrowchair. (C) 2004 Elsevier Ltd. All rights reserved Y1 - 2004 SN - 0040-4020 ER - TY - JOUR A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Kovacs, J. A1 - Toth, G. A1 - Kleinpeter, Erich T1 - Electronic influences on (3)J(C,H) coupling constants via -S-, -S(O)- and -SO2--: their determination, calculation and comparison of detection methods N2 - (3)J(C,H) coupling constants via a sulfur atom in two series of compounds, both including a sulfide, a sulfoxide and a sulfone, were detected experimentally and calculated by quantum mechanical methods. In the first series (1-3) the coupling between a hydrogen, bonded to an Sp(3) carbon, and an Sp(2) carbon is treated; the second series (4- 6) deals with the coupling between a hydrogen, bonded to an Sp3 carbon, and an Sp3 carbon. Different pulse sequences (broadband HMBC, SelJres, 1D HSQMBC, J-HMBC-2, selective J-resolved long-range experiment and IMPEACH-MBC) proved to be useful in determining the long-range (3)J(C,H) coupling constants. However, the dynamic behaviour of two of the compounds (4 and 6) led to weighted averages of the two coupling constants expected (concerning equatorial and axial positions of the corresponding hydrogens). DFT calculations proved to be useful to calculate not only the (3)J(C,H) coupling constants but also the different contributions of FC, PSO, DSO and SD terms; the calculation of the Fermi contact term (FC) was found to be sufficient for the correct estimation of (3)J(C,H) coupling constants. Copyright (C) 2004 John Wiley Sons, Ltd Y1 - 2004 SN - 0749-1581 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Klod, Sabrina T1 - Separation of anisotropic and steric substituent effects - nuclear chemical shielding analysis of H-4 and C-4 in phenanthrene and 11-ethynylphenanthrene N2 - The anisotropic effect of a proximally introduced ethynyl group on the chemical shifts of H-4 and C-4 of the phenanthrene skeleton was calculated using GIAO-HF/NICS methodology. The anisotropic effect, long considered to be the source of the considerable downfield shift of H-4 in 11-ethynylphenanthrene in comparison to the chemical shift value of the corresponding proton in phenanthrene, was determined to be only negligible in magnitude on the basis of these calculations. Partitioning of the natural chemical shieldings of H-4 and C-4 by the NCS-NBO method into various contributions from the C-C and C-H bonds present in each molecule revealed that steric compression was able to account for the large downfield shifts of both H-4 and C-4 in 11-ethynylphenanthrene relative to phenanthrene. Thus, the substituent effect is almost totally permeated by this latter interaction and not by the aforementioned process, which was previously presumed to be the sole underlying cause Y1 - 2004 ER - TY - JOUR A1 - Holzberger, Anja A1 - Holdt, H. N. A1 - Kleinpeter, Erich T1 - NMR spectroscopic and molecular modelling study of the solution structure and the complexational behavior of maleonitrile tetrathia crown ethers with silver(I) N2 - The flexibility and complex formation of two maleonitrile tetrathia crown ethers were studied in solution using H-1 and C-13 NMR spectroscopy and molecular modelling. Both the stoichiometry and the stability of the complexes that these crown ethers form with Ag(I) were determined by NMR titration measurements. Spin-lattice relaxation time measurements provided information concerning the donor atoms involved in complex formation and also the intramolecular mobility of the free and complexed ligands. Molecular modelling was also used to gain further insight into the conformational space of the free ligands and their silver(I) complexes. Copyright (C) 2004 John Wiley Sons, Ltd Y1 - 2004 ER - TY - JOUR A1 - Holzberger, Anja A1 - Kleinpeter, Erich T1 - Solution structure of the palladium(II) complex of 1,4,7,10-tetrathiacyclododec-2-ene-2,3-dicarbonitrile N2 - The solution structure of the Pd(II) complex of mn-12-S-4 was studied in detail by NMR spectroscopy. The stoichiometry of the complex was determined by H-1 NMR titration experiments. (3)J(H,H) coupling constants were extracted from the 2D J-resolved NMR spectrum of the complex providing information concerning the S-C-C-S torsional angles. Further conclusions about the conformation of [Pd(mn-12-S-4)](BF4)(2) were drawn from experimental NOES. The results of the NMR study were corroborated by molecular modelling. Copyright (C) 2004 John Wiley Sons, Ltd Y1 - 2004 SN - 0749-1581 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Klod, Sabrina T1 - Ab initio calculation of the anisotropic/ring current effects of amino acid residues to locate the position of substrates in the binding site of enzymes N2 - The ring current effects of aromatic moieties and the anisotropic effects of the C=O and C-X (X = C, N, S) bonds and of the NH=C(NH2)-NH- moiety in the side chains of amino acid residues of proteins were ab initio calculated based on nuclear independent chemical shieldings as employed by P.v.R. Schleyer. Hereby, quantitative information about the spatial extension, sign and scope of the corresponding ring current/anisotropic effects was obtained and they were visualized as iso-chemical-shielding-surfaces. Examining this quantitative information compared with experimental NMR chemical shifts, the role of the corresponding amino acid residues in binding substrates in the binding site of enzymes was studied. (C) 2004 Elsevier B.V. All rights reserved Y1 - 2004 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Klod, Sabrina A1 - Rudorf, Wolf-Dieter T1 - Electronic state of push-pull alkenes : an experimental dynamic NMR and theoretical ab initio MO study N2 - The H-1 and C-13 NMR spectra of a number of push-pull alkenes were recorded and the C-13 chemical shifts calculated employing the GIAO perturbation method. Of the various levels of theory tried, MP2 calculations with a triple- zeta-valence basis set were found to be the most effective for providing reliable results. The effect of the solvent was also considered but only by single-point calculations. Generally, the agreement between the experimental and theoretically calculated C-13 chemical shifts was good with only the carbons of the carbonyl, thiocarbonyl, and cyano groups deviating significantly. The substituents on the different sides of the central C=C partial double bond were classified qualitatively with respect to their donor (S,S < S,N < N,N) and acceptor properties (CdropN < C=O < C=S) and according to the ring size on the donor side (6 < 7 < 5). The geometries of both the ground (GS) and transition states (TS) of the restricted rotation about the central C=C partial double bond were also calculated at the HF and MP2 levels of theory and the free energy differences compared with the barriers to rotation determined experimentally by dynamic NMR spectroscopy. Structural differences between the various push-pull alkenes were reproduced well, but the barriers to rotation were generally overestimated theoretically. Nevertheless, by correlating the barriers to rotation and the length of the central C=C partial double bonds, the push-pull alkenes could be classified with respect to the amount of hydrogen bonding present, the extent of donor-acceptor interactions (the push-pull effect), and the level of steric hindrance within the molecules. Finally, by means of NBO analysis of a set of model push-pull alkenes (acceptors: - CdropN, -CH=O, and -CH=S; donors: S, O, and NH), the occupation numbers of the bonding pi orbitals of the central C=C partial double bond were shown to quantitatively describe the acceptor powers of the substituents and the corresponding occupation numbers of the antibonding pi* orbital the donor powers of the substituents. Thus, for the first time an estimation of both the acceptor and the donor properties of the substituents attached to the push-pull double bond have been separately quantified. Furthermore, both the balance between strong donor/weak acceptor substituents (and vice versa) and the additional influences on the barriers to rotation (hydrogen bonding and steric hindrance in the GSs and TSs) could be differentiated Y1 - 2004 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Seidl, Peter Rudolf T1 - The gamma- and the delta-effects in C-13 NMR spectroscopy in terms of nuclear chemical shielding (NCS) analysis N2 - Carbon-13 NMR is widely used in the determination of the stereochemistry of organic compounds. Changes in chemical shifts caused by interactions of groups that are close in space normally result in shielding of the carbon and deshielding of the hydrogen nuclei that are involved. This is not always the case, however, and further work on the origin of these effects would be desirable. Early applications of theoretical methods to the study of NMR shielding parameters were not particularly successful, but in recent years, the calculation of NMR shielding parameters by theoretical methods has developed into a useful and popular tool for structural studies by NMR. A promising approach to the problem of distinguishing and evaluating stereochemical influences on carbon and hydrogen chemical shifts is provided by natural chemical shielding (NCS) analysis. This method allows a partitioning of theoretical NMR shieldings into magnetic contributions from bonds and lone pairs of the molecule using the natural bond orbital (NBO) method. In order to investigate the origins of steric effects, we employed the NCS analysis to axial/equatorial-Me-cyclohexane, norbornane and exo/endo-Me-norbornane, in addition to n-pentane in the anti, gauche and g(P) g(M) conformations. Our results indicate that distortions in molecular structure due to steric effects can result in bond stretching or compression or in angular distortions. Changes in bond lengths result in the predictable shielding or deshielding of the nuclei that are involved. Where the molecular framework may be distorted to alleviate strain, chemical shifts appear to reflect changes in angles. Copyright (C) 2004 John Wiley Sons, Ltd Y1 - 2004 ER - TY - JOUR A1 - Koch, Andreas A1 - Mikhova, Bozhana A1 - Kleinpeter, Erich T1 - Ab initio MP2/GIAO/NBO study of the delta-syn-axial effect in C-13 NMR spectroscopy N2 - The C-13 chemical shifts of 20 rigid bicyclic compounds have been calculated with ab initio HF and MP2 methods. The calculations showed very good reproducibility of the experimental values. The molecular orbital interactions in the rigid, nearly planar delta-syn-axial fragments in the isomeric groups of norbornane derivatives 1.x-4.x were studied in detail and were employed to explain the deshielding delta-syn-axial effect in C-13 NMR spectroscopy. (C) 2004 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0022-2860 ER - TY - JOUR A1 - Miklos, F. A1 - Kanizsai, I. A1 - Thomas, Steffen A1 - Kleinpeter, Erich A1 - Sillanpaa, R. A1 - Stajer, G. T1 - Preparation and structure of diexo-oxanorbornane-fused 1,3-heterocycles N2 - Via the reaction of diexo-oxanorbornanedicarboxylic anhydride with toluene, the diexo-aroylcarboxylic acid (3a) was prepared, which exists partly as the tautomeric lactol (3b). With bifunctional reagents, 3a yields fused heterocycles containing three-six rings. Thus, alkylenediamines result in imidazole- and 1,3-diazepine-fused oxygen- bridged isoindolones (6a,b), alkanolamines form the oxazole- and 1,3-oxazine-fused oxanorbornene derivatives (7a-c), and o-phenylenediamine undergoes cyclization to furnish the condensed benzimidazole (8). The reaction of 3a with diexo- aminonorbornanecarbohydrazide yields a pyrimidopyridazine containing six condensed rings (9). In a similar reaction with diendo-aminonorbornenecarbohydrazide, cyclopentadiene cleaves off to give the tricyclic retro Diels-Alder product (10). The structures, and particulary the configurations at the oxanorbornane ring systems and the position of the aryl substituent, were established by means of 1D- and 2D-NMR spectroscopy and, for 3b and 7c, also by X-Ray measurements Y1 - 2004 SN - 0385-5414 ER - TY - JOUR A1 - Hausmann, J. A1 - Kass, S. A1 - Klod, Sabrina A1 - Kleinpeter, Erich A1 - Kersting, Berthold T1 - Binucleating aza-sulfonate and aza-sulfinate macrocycles : Synthesis and coordination chemistry N2 - The preparation and ligating properties of S-oxygenated derivatives of a macrobinucleating hexaazadithiophenolate macrocycle H2L1 of the Robson type towards nickel(II) and zinc(II) ions are reported. Nickel complexes of the hexaazadiphenylsulfonate ligand (L-2)(2-)[(L-2)Ni-2(II)(mu-L)](+)(L = m-Cl-OBz(-) (3), Cl- (4) and OAc- (6)] are readily obtained in high yields by oxidation of the respective [(L-1)Ni-2(II)(mu-L)](+) parent complexes [L = m- Cl-OBz- (2), Cl- (1), OAc- (5)] with meta-chloroperoxybenzoic acid or hydrogen peroxide. Decomposition of the sulfonate complexes gives the free macrocycle H2L2 which, upon treatment with Zn(OAc)(2)(.)2H(2)O, produces the diamagnetic zinc complex [(L-2)Z(2)(II)(OAc)](+) (8). A dinuclear Cu-II complex of the hexaazadisulfinate derivative (L-3')(2-), [(L-3)CU2II](2+) (9), is formed rather unexpectedly by air oxidation of (L-1)(2-) in the presence of Cu-I. The crystal- structure determinations of the perchlorate or tetraphenylborate salts of 2, 3, and 4 show that the new ligands support the formation of binuclear complexes with bowl-shaped, calixarene-like binding cavities. NMR spectroscopic studies of 8 show that the complexes retain their solid-state structures in solution. A crystal-structure determination of 9 reveals two five-coordinate Cu-II ions bridged by the two sulfinate functions of (L-3)(2-) Y1 - 2004 SN - 1434-1948 ER - TY - JOUR A1 - Starke, I. A1 - Sarodnick, Gerhard A1 - Ovcharenko, V. V. A1 - Pihlaja, Kalevi A1 - Kleinpeter, Erich T1 - Quinoxalines : Part 13: Synthesis and mass spectrometric study of aryloxymethylquinoxalines and benzo[b]furylquinoxalines N2 - A series of new aryloxymethylquinoxalines, benzo[b]- and naphtho[2,1-b] fury] quinoxalines, possessing potential biological activity, was prepared, characterized by IR and NMR spectroscopy and their electron ionization (EI) mass spectra studied in detail. The aryloxymethylquinoxalines were obtained by reacting halogenomethylquinoxalines with bifunctional O-nucleophiles. The benzo[b]furylquinoxalines and naphtho[2, I -b]furylquinoxalines were prepared via two routes, which differed in the order of the two cyclization steps involved in the syntheses. The composition of the ions obtained by El mass spectrometry were determined by accurate mass measurements and the fragmentation pathways clarified by B/E linked scans and collision induced dissociation. The mass spectrometric behaviour of the compounds studied as to the possible loss of OH' radicals proved to be very characteristic. (C) 2004 Elsevier Ltd. All rights reserved Y1 - 2004 SN - 0040-4020 ER - TY - JOUR A1 - Taddei, F. A1 - Kleinpeter, Erich T1 - The anomeric effect in substituted cyclohexanes : I. The role of hyperconjugative interactions and steric effect in monosubstituted cyclohexanes N2 - The relative energy of conformers, DeltaE, of monosubstituted cyclohexanes with OR (R = Me, Et, i-Pr and t-Bu) and R substituents (R = Me, Et, i-Pr and t-Bu) was calculated with MO ab initio theory at RHF, MP2 and QCISD levels with the 6-311G* and 6-311 + G* basis sets. A selected group of delocalizing interactions were calculated with the natural bond orbital method in order to quantify the hyperconjugative contribution, DeltaE(hyp.), to the relative stability of conformers. From the calculated values of DeltaE and DeltaE(hyp.) an estimate of the differential steric effect, DeltaE(ster.), of substituents in cyclohexane was obtained. The values of DeltaE(hyp), and DeltaE(ster.) show that they have a similar magnitude for OR substituents, while for R substituents the values of are greater. The shift in the conformational equilibrium towards the axial conformer, the so-called anomeric effect, takes place when, within a series of substituents, hyperconjugative interactions and steric interactions balance in favour of the stability of this conformer. (C) 2004 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0166-1280 ER - TY - JOUR A1 - Holzberger, Anja A1 - Holdt, Hans-Jürgen A1 - Kleinpeter, Erich T1 - Conformational analysis of mixed oxathia crown ethers and their complexational ability towards Ag(I) and Pd(II) : an experimental solution NMR and theoretical molecular modelling study N2 - Both the conformation and flexibility of four mixed oxathia crown ethers and their Ag(I) and Pd(II) complexes were studied by H-1 NMR (delta, J, NOE, T-1), C-13 NMR, dynamic 1H NMR spectroscopy and molecular modelling. The stoichiometry and stability constants of the complexes were determined from corresponding Job's plots in the case of Ag(I) complexes as the interchange between free and complexed states was fast on the NMR timescale; interchange for the Pd(II) complexes was sufficiently slow such that distinct sub-spectra were observable for the free and complexed states. In all cases where complexation was observed, 1 : 1 complexes were formed. Global minima structures determined from the modelling studies were analysed with respect to the barriers to ring interconversion, the flexibility of the species in solution and the preferred complexation of Ag(I) and Pd(II) to the sulfur atoms of the crown ethers Y1 - 2004 SN - 1477-0520 ER - TY - JOUR A1 - Szatmari, Istvan A1 - Martinek, T. A. A1 - Lazar, L. A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Neuvonen, Kari A1 - Fulop, Ferenc T1 - Stereoelectronic effects in ring-chain tautomerism of 1,3-diarylnaphth[1,2-e][1,3]oxazines and 3-alkyl-1- arylnaphth[1,2-e][1,3]oxazines N2 - The disubstitution effects of X and Y in 1-(Y-phenyl)-3-(X-phenyl)-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines on the ring-chain tautomerism, the delocalization of the nitrogen lone pair (anomeric effect), and the C-13 NMR chemical shifts were analyzed by using multiple linear regression analysis. Study of the three-component equilibrium B reversible arrow A reversible arrow C revealed that the chain reversible arrow trans (A reversible arrow B) equilibrium constants are significantly influenced by the inductive effect (sigma(F)) of substituent Y on the 1-phenyl ring. In contrast, no significant substituent dependence on Y was observed for the chain reversible arrow cis (A reversible arrow C) equilibrium. There was an analogous dependence for the epimerization (C reversible arrow B) constants of 1-(Y-phenyl)-3- alkyl-2,3-dihydro-1H-naphth[1,2-e] [1,3]oxazines. With these model compounds, significant overlapping energies of the nitrogen lone pair was observed by NBO analysis in the trans forms B (to sigma*(C1-C1'), sigma*(C1-C10b), and sigma*(C3-O4)) and in the cis forms C (to sigma*(C1-H), sigma*(C1-C10b), and sigma*(C3-O4)). The effects of disubstitution revealed some characteristic differences between the cis and trans isomers. However, the results do not suggest that the anomeric effect predominates in the preponderance of the trans over the cis isomer. When the C-13 chemical shift changes induced Y by substituents X and Y (SCS) were subjected to multiple linear regression analysis, negative rho(F)(Y) and rho(F)(X) values were observed at C-1 and C-3 for both the cis and trans isomers. In contrast, the positive rho(R)(Y) values at C-1 and the negative rho(R)(X) values at C-3 observed indicated the contribution of resonance structures f (rho(R) > 0) and g (rho(R) < 0), respectively. The classical double bond-no-bond resonance structures proved useful in explaining the substituent sensitivities of the donation energies and the behavior of the SCS values Y1 - 2004 SN - 0022-3263 ER - TY - JOUR A1 - Markovic, Rade A1 - Baranac-Stojanovic, Marija A1 - Steel, Peter J. A1 - Kleinpeter, Erich T1 - Stereocontrolled synthesis of new tetrahydrofuro[2,3-d]thiazole derivatives via activated vinylogous iminium ions N2 - Heterocyclization of (Z)-5-(2-hydroxyethyl)-3-methyl-4-oxothiazolidines, bearing electron-withdrawing groups conjugated to an exocyclic double bond at C(2)-position, afforded under reductive conditions, cis-tetrahydroftiro[2,3- d]thiazole derivatives. The reactions of these functionalized push-pull beta-enamines occur in a stereocontrolled fashion via activated vinylogous N-methyliminium ions, which are trapped by an internal hydroxyethyl group Y1 - 2005 SN - 0385-5414 ER - TY - JOUR A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Sarodnick, Gerhard A1 - Kleinpeter, Erich T1 - Quinoxalines XIV : Synthesis, H-1, C-13, N-15 NMR spectroscopic, and quantum chemical study of 1H-pyrazolo[3,4- b]quinoxalines (flavazoles) N2 - The synthesis of a series of 1H-pyrazolo[3,4-b]quinoxalines (flavazoles) by acylation, alkylation, halogenation, and aminomethylation of the parent compound is reported and their structure is investigated by H-1, C-13 and N-15 NMR spectroscopy. The restricted rotation about the partial C, N double bond of the N-acyl derivatives 7-10 is studied by dynamic NMR spectroscopy and the barriers to rotation are determined. In order to assign unequivocally the 15 N chemical shifts of N-4 and N-9, in case of 3-substituted flavazoles, exemplary the H-1, C-13, and N-15 NMR chemical shifts of 34, 35, and 39 are also theoretically calculated by quantum chemical methods [ab initio at different levels of theory (HF/6-3G* and B3LYP/6-31G*)]. (C) 2005 Elsevier Ltd. All rights reserved Y1 - 2005 SN - 0040-4020 ER - TY - JOUR A1 - Klinka, Karel D. A1 - Imrich, Jan A1 - Danihel, I. A1 - Bohm, Stanislav A1 - Kristian, Pavol A1 - Harnul'akova, S. A1 - Pihlaja, Kalevi A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Configuration and E/Z interconversion mechanism of O(S)-allyl-S(O)-methyl-N-(acridin-9-yl)iminothiocarbonate N2 - The configuration and dynamic behavior of O-allyl-S-methyl-N-(acridin-9-yl)iminothiocarbonate (1) and its S- allyl-O-methyl regioisomer (2) were studied using quantum chemical calculations and by applying a novel graphical method to scatter maps obtained from MD simulations for evaluation of an NOE-weighted internuclear distance (r(NOE)). Energy calculations indicated that the Z configuration was predominant for each compound and, further, this was supported both by the calculated chemical shifts and the rNOE. Both N-inversion- and rotation-type transition-state structures were also calculated for the E/Z isomerization process, the results indicating that the preferred interconversion mechanism for 1 is N-inversion, but contrastingly, interconversion via rotation is equally as probable as N-inversion for 2. This supports the notion that one or the other or both pathways can be active and each system needs to be assessed on a case- by-case basis. Copyright (c) 2005 John Wiley & Sons, Ltd Y1 - 2005 SN - 0749-1581 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas A1 - Pihlaja, Kalevi T1 - Application of (1)J(C,H) coupling constants in conformational analysis N2 - Conformational equilibria for a number of methyl substituted 1,3-dioxanes 1, 1,3-oxathianes 2 and 1,3-dithianes 3 were calculated at the HF and DFT levels of theory. In addition to the chair conformers also the energetically adjacent twist conformers were considered and the positions of the corresponding conformational equilibria estimated. On the basis of the global energy minima of conformers, participating in the conformational equilibria, the 1J(C,Hax,equ) coupling constants were calculated using the GIAO method and compared with the experimental values obtained from C-13, H- 1 coupled C-13 NMR spectra. The Perlin effect, the influence of the solvent and the suitability of this NMR parameter for assigning the conformational equilibria present are critically discussed. (c) 2005 Elsevier Ltd. All rights reserved Y1 - 2005 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Schulenburg, A. T1 - Quantification of the push-pull effect in substituted alkenes N2 - The quotient of the occupation numbers of pi bonding and pi* antibonding orbitals of the central C=C partial double bond, pi*(C=C)/pi(C=C), proved to be a useful parameter to quantify the push-pull effect completely for the first time in substituted alkenes by examination of a comprehensive set of compounds. (c) 2005 Elsevier Ltd. All rights reserved Y1 - 2005 SN - 0040-4039 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Schulenburg, Anja A1 - Zug, Ines A1 - Hartmann, Horst T1 - The interplay of thio(seleno)amide/vinylogous thio(seleno)amide "Resonance" and the anisotropic effect of thiocarbonyl and selenocarbonyl functional groups N2 - [GRAPHICS] Amino-substituted thio(seleno)acrylamides 1-4 were synthesized and their H-1 and C-13 NMR spectra assigned. Both the NMR data and the results of theoretical calculations at the ab initio level of theory were employed to elucidate the adopted structures of the compounds in terms of E/Z isomerism and s-cis/s-trans configuration. In the case of the asymmetrically N(Me)Ph-substituted compounds, ab initio GIAO-calculated ring current effects of the N-phenyl group were applied to successfully determine the preferred conformer bias. The restricted rotations about the two C-N partial double bonds were studied by DNMR and the barriers to rotation (Delta G(c)(double dagger)) determined at the coalescence temperatures, and these were discussed with respect to the structural differences between the compounds. The barriers to rotation were also calculated at the ab initio level of theory where the best results (R-2 = 0.8746) were obtained only with inclusion of the solvent at the SCIPCMHF/6-31G* level of theory. The calculations also provided means of assessing structural influences which were not available due to inaccessible rotation barriers. By means of natural bond orbital (NBO) analysis of 1-4, the occupation numbers of nitrogen lone pairs and bonding/antibonding pi/pi* orbitals were shown to quantitatively describe thio(seleno)amide/vinylogous thio(seleno)amide "resonance". Finally, the thio(seleno)carbonyl anisotropic effect was quantitatively calculated by the GIRO method and visualized by isochemical shielding surfaces (ICSS). Only marginal differences between the two anisotropic effects were calculated and are therefore of questionable utility for previous and future applications with respect to stereochemical assignments Y1 - 2005 SN - 0022-3263 ER - TY - JOUR A1 - Taddei, F. A1 - Kleinpeter, Erich T1 - The anomeric effect in substituted cyclohexanes : II. The role of hyperconjugative interactions and steric effect in 1,4-disubstituted cyclohexanes N2 - The conformational equilibria of the cis/trans isomers of some 1,4-di-substituted cyclohexanes (X = OH, OMe, Me, OCOCH3, OCOC(CH3)(3), OCOCCl3, OCOCF3) were calculated at several levels of theory; the best correlation between calculated and experimentally available Delta G(0)s refers to the MP2/6-311 +G*//MP2/6-311G* results. In addition, the hyperconjugative effect of the substituents was studied with the NBO options included in the GAUSSIAN-98 package; a number of interactions between filled NBOs and antibonding orbitals could be considered as most representative for delocalization along the molecules studied. The effect of the substituents on the molecular geometry of the substituted cyclohexanesas well as the partitioning of both hyperconjugative and steric substituent effects on the present conformational equilibria is critically evaluated. Our model [E. Kleinpeter, F. Taddei, J. Mol. Struct. (THEOCHEM) 683 (2004) 29] for interpreting the relative stability of conformers of substituted cyclohexanes could be further verified and its reliability assessed. (c) 2005 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0166-1280 ER - TY - JOUR A1 - Thomas, Steffen A1 - Kleinpeter, Erich T1 - A novel empirical approach for the structure elucidation of disilanes by empirical estimation of their Si-29 chemical shifts N2 - In C-13 NMR spectroscopy, there are many empirical methods for fast and exact computation of C-13 chemical shifts; comparable procedures for Si-29 NMR chemical shifts are not existing or are older than 20 years. On basis of the largest database of Si-29 chemical shifts available, along this paper a relatively simple procedure for the similarly exact calculation of the Si-29 chemical shifts of disilanes (average margin of error ca. 3.7 ppm) is given. (c) 2005 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0022-2860 ER - TY - JOUR A1 - Seidl, Peter Rudolf A1 - Carneiro, J. W. D. A1 - Tostes, J. G. R. A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Interpretation of conformational effects on 2-endo-norborneol by natural chemical shielding analysis N2 - This paper represents an extension of our work on the H-1 and C-13 NMR chemical shifts of norbornane and 2-endo- norborneol. NCS-NBO analysis was employed to probe contributions of bond orbitals and orbitals of lone pairs to nuclear shielding in conformers of the alcohol generated by rotation of the C-O bond. Variations in H-1 and C-13 chemical shifts with the dihedral angle are discussed in terms of Lewis and non-Lewis partitioning and their respective importance is evaluated. In addition to hyperconjugation of the lone pair in a p orbital of oxygen that was previously reported, a sizable participation of the lone pair which is in an sp orbital is also observed and their combined effect dominates the carbon chemical shifts of the C-1-C-2-OH and C-3-C-2-OH fragments. Both lone pairs on oxygen also contribute to localized, though-space effects on nuclei in the vicinity, these effects answering for the largest deviations in hydrogen chemical shifts on rotation around the C-O bond. On the other hand, for conformers in which nonbonded repulsions lead to distortions in the molecular framework, variations in chemical shifts may be attributed to angular effects Y1 - 2005 SN - 1089-5639 ER - TY - JOUR A1 - Ryppa, C. A1 - Senge, Mathias O. A1 - Hatscher, S. S. A1 - Kleinpeter, Erich A1 - Wacker, Philipp A1 - Schilde, Uwe A1 - Wiehe, A. T1 - Synthesis of mono- and disubstituted porphyrins : A- and 5,10-A(2)-type systems N2 - General syntheses have been developed for meso-substituted porphyrins with one or two substituents in the 5,10- positions and no beta substituents. 5-Substituted porphyrins with only one meso substituent are easily prepared by an acid-catalyzed condensation of dipyrromethane, pyrrole-2-carbaldehyde. and an appropriate aldehyde using a "[2+1+1]" approach. Similarly, 5,10-disubstituted porphyrins are accessible by simple condensation of unsubstituted tripyrrane with pyrrole and various aldehydes using a "[3+1]" approach. The yields for these reactions are low to moderate and additional formation of either di- or mono-substituted porphyrins due to scrambling of the intermediates is observed. However, the reactions can be performed quite easily and the desired target compounds are easily removed due to large differences in solubility. A complementary and more selective synthesis involves the use of organolithium reagents for SNAr reactions. Reaction of in situ generated porphyrin (porphine) with 1.1-8 equivalents of RLi gave the monosubstituted porphyrins, while reaction with 3-6 equivalents of RLi gave the 5,10-disubstituted porphyrins in yields ranging from 43 to 90%. These hitherto almost inaccessible compounds complete the series of different homologues of A-, 5,15-A(2)-, 5,10-A(2)-, A(3)-, and A(4)-type porphyrin's and allow an investigation of the gradual influence of type, number, and regiochemical arrangement of substituents on the properties of meso-substituted porphyrins. They also present important starting materials for the synthesis of ABCD porphyrins and are potential synthons for supramolecular materials requiring specific substituent orientations Y1 - 2005 SN - 0947-6539 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Seidl, Peter Rudolf T1 - The gamma- and the delta-effects in C-13 NMR spectroscopy in terms of nuclear chemical shielding (NCS) analysis Y1 - 2005 SN - 0894-3230 ER - TY - JOUR A1 - Neuvonen, Helmi A1 - Neuvonen, Kari A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Ab initio study of the substituent effects on the relative stability of the E and Z conformers of phenyl esters : Stereoelectronic effects on the reactivity of the carbonyl group N2 - Equilibria between the Z (tau(1) = 0 degrees) and E (tau(1) = 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, Delta E(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mot(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between Delta E of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (n(O) -> pi*(C=O)) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The n(O) -> pi*(C=O) electron donation has a minimum value with tau(1) = 90 degrees and a maximum value with tau(1) = 90 degrees (the Z conformer), the value with tau(1) = 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*(C=O) antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*(C=O) occupancies of the ester series 4 and Y1 - 2005 SN - 1089-5639 ER - TY - JOUR A1 - Wolf, G. A1 - Kleinpeter, Erich T1 - Pulsed field gradient NMR study of anomalous diffusion in a lecithin-based microemulsion N2 - Self-diffusion measurements in microemulsion systems composed of a naturally occurring soybean lecithin mixture, an aqueous phase, either water or a 1% aqueous PDADMAC solution, and isooctane were accomplished by pulsed field gradient (PFG) (HNMR)-H-1 spectroscopy at oil dilution lines of low and intermediate water/lecithin ratios. The concentration-dependent diffusion data reveal water-in-oil (W/O) reverse micellar aggregates with dimensions on the nanometer scale being slightly smaller at low water content. With increasing micellar volume fractions, both hydrodynamic as well as direct interactions between particles significantly slow aggregate diffusion. The surfactant mean square displacements (msd's) in dilute and concentrated polymer-free systems studied as a function of diffusion time (20-1000 ms) are characterized by a crossover from Gaussian diffusion, due to slow aggregate motion, to anomalously enhanced diffusion, due to fast surface-bulk surfactant exchange at intermediate times revealing weak, barrier-controlled adsorption behavior. Upon addition of the polycation PDADMAC, the diffusion characteristics change to exclusively superdiffusive behavior with surfactant msd scaling with time as t(3/2) over the entire time range studied. This is caused by surfactant molecules performing Levy walks along the surface of reverse micelles mediated by the dilute bulk. The bulk-mediated surface diffusion is a consequence of the diffusion-controlled micelle-bulk exchange dynamics induced by interactions of PDADMAC with surfactant headgroups Y1 - 2005 SN - 0743-7463 ER - TY - JOUR A1 - Virta, P. A1 - Koch, Andreas A1 - Roslund, M. U. A1 - Mattjus, P. A1 - Kleinpeter, Erich A1 - Kronberg, L. A1 - Sjoholm, R. A1 - Klika, Karel D. T1 - Synthesis, characterisation and theoretical calculations of 2,6-diaminopurine etheno derivatives N2 - Four derivatives of 2,6-diaminopurine (1) were synthesised and characterised. When 1 was reacted with chloroacetaldehyde, 5-aminoimidazo[2,1- i] purine (2), 9-aminoimidazo[2,1-b]purine (3), 9-aminoimidazo[1,2- a]purine (4) and diimidazo[2,1-b: 2', 1'-i]purine (5) were formed. The purified products (3 - 5) were fully characterised by MS, complete NMR assignments as well as fluorescence and UV spectroscopy. The purified, isolated yields of these products ( 3 - 5) varied from 2.5 to 30%. The relative stability of different tautomers was investigated by theoretical calculations. Fluorescence characteristics are also discussed and compared to the starting material 1 and a reference molecule 2-aminopurine Y1 - 2005 SN - 1477-0520 ER - TY - JOUR A1 - Neuvonen, Kari A1 - Fulop, Ferenc A1 - Neuvonen, Helmi A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Pihlaja, Kalevi T1 - Propagation of polar substituent effects in 1-(substituted phenyl)-6,7-dimethoxy-3,4-dihydro- and -1,2,3,4- tetrahydroisoquinolines as explained by resonance polarization concept N2 - Propagation of inductive and resonance effects of phenyl substituents within 1-(substituted phenyl)-6,7- dimethoxy-3,4-dihydro- and -1,2,3,4-tetrahydroisoquinolines were studied with the aid of C-13 and N-15 NMR chemical shifts and ab initio calculations. The substituent-induced changes in the chemical shift (SCS) were correlated with a dual substituent parameter equation. The contributions of conjugative (rho(R)) and nonconjugative effects (rho(F)) were analyzed, and mapping of the substituent-induced changes is given over the entire isoquinoline moiety for both series. The experimental results can be rationalized with the aid of the resonance polarization concept. This means the consideration of the substituent-sensitive balance of different resonance structures, i.e., electron delocalization, and the effect of the aromatic ring substituents on their relative contributions. With tetrahydroisoquinolines, the delocalization of the nitrogen lone pair (stereoelectronic effect) particularly contributes. Correlation analysis of the Mulliken atomic charges for the dihydroisoquinoline derivatives was also performed. The results support the concept of the substituent-sensitive polarization of the isoquinoline moiety even if the polarization pattern achieved via the NMR approach is not quite the same as that predicted by the computational charges. Previously the concepts of localized pi- polarization and extended polarization have been used to explain polar substituent effects within aromatic side-chain derivatives. We consider that the resonance polarization model effectively contributes to the understanding of the polar substituent effects Y1 - 2005 ER -