@article{BalciKochKleinpeter2006, author = {Balci, Kubilay and Koch, Andreas and Kleinpeter, Erich}, title = {A comparative vibrational spectroscopic investigation of free mn-12S(2)O(2) and fn-12S(2)O(2) dithiacrown ethers based on DFT calculations}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2005.10.048}, year = {2006}, abstract = {A successful assignment for the fundamental bands observed in the experimental IR spectra of mn-12S(2)O(2) and fn-12S(2)O(2) dithiacrown ethers was achieved by the aid of the density functional theory (DFT) based quantum mechanical calculations carried out at the 133LYP/6-31G(d) and B3LYP/6-31 + G(d) level of theory. Two different scaling approaches, '(i) scaled quantum mechanics force field (SQM FF) methodology', and (ii) the 'scaling frequencies with dual empirical scale factors', were used in order to fit the calculated harmonic frequencies to the experimental ones. Potential energy distribution (PED) calculations were carried out to define the internal coordinate contributions to each normal mode and to define the corresponding normal modes of the molecules. The effects of the conformational differences onto the IR active normal modes of the two isomeric molecules and their corresponding experimental frequencies were discussed in the light of the calculated spectral data.}, language = {en} } @article{HeydenreichKochKlodetal.2006, author = {Heydenreich, Matthias and Koch, Andreas and Klod, Sabrina and Szatmari, Istvan and Fulop, Ferenc and Kleinpeter, Erich}, title = {Synthesis and conformational analysis of naphth[1', 2':5,6][1,3]oxazino[3,2-c][1,3]benzoxazine and naphth[1', 2':5,6][1,3]oxazino[3,4-c][1,3]benzoxazine derivatives}, series = {Tetrahedron}, volume = {62}, journal = {Tetrahedron}, number = {48}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0040-4020}, doi = {10.1016/j.tet.2006.09.037}, pages = {11081 -- 11089}, year = {2006}, abstract = {A new functional group, the hydroxy group, was inserted into a Betti base by reaction with salicylaldehyde, and the naphthoxazine derivatives thus obtained were converted by ring-closure reactions with formaldehyde, acetaldehyde, propionaldehyde or phosgene to the corresponding naphth[1',2':5,6][1,3]oxazino[3,2-c][1,3]benzoxazine derivatives. Further, the conformational analysis of these polycyclic compounds by NMR spectroscopy and an accompanying molecular modelling are reported; especially, both quantitative anisotropic ring current effects of the aromatic moieties in these compounds and steric substituent effects were employed to determine the stereochemistry of the naphthoxazinobenzoxazine derivatives.}, language = {en} } @article{HoldtMuellerPotteretal.2006, author = {Holdt, Hans-J{\"u}rgen and M{\"u}ller, Holger and Potter, Matthias and Kelling, Alexandra and Schilde, Uwe and Starke, Ines and Heydenreich, Matthias and Kleinpeter, Erich}, title = {The first sandwich complex with an octa(thioether) coordination sphere : Bis(maleonitrile-tetrathia-12-crown- 4)silver(I)}, issn = {1434-1948}, doi = {10.1002/ejic.200501109}, year = {2006}, abstract = {The new tetrathiacrown ethers maleonitrile-tetrathia-12-crown-4 (mn12S(4)) and maleonitrile-tetrathia-13-crown- 4 (mn13S(4)) have been prepared and characterised by X-ray crystallographic analysis. These crown ethers form 2:1, 3:2 and 1: 1 complexes with AgY (Y = BF4, PF6). The crystal structures of [Ag(mn12S(4))(2)]BF4 (3a), [Ag(mn13S(4))(2)]BF4 (4a) and [Ag-2(mn13S(4))(3)](PF6)(2) (6b) have been determined. Compound 3a contains the centrosymmetric sandwich complex cation [Ag(mn12S(4))(2)](+) where each mn12S(4) ligand is coordinated to the Ag centre in an endo manner through all four S atoms. The 2:1 complex [Ag(mn12S(4))(2)](+) is the first sandwich complex with a tetrathiacrown ether and the first complex with an octa(thioether) coordination sphere. The crystal structure of compound 4a also reveals a 2:1 complex. This complex, [Ag(mnl3S(4))(2)](+), exhibits a half-sandwich structure. One mn13S(4) ligand coordinates to Ag+ by all four S donor atoms and the other 13S(4) crown by only one S atom. Compound 6b contains a dinuclear Ag complex. The Ag complexes 3a,b-8a,b were also studied by electrospray ionisation mass spectrometry. Collision-induced dissociation (CID) was used to compare the relative stability of 2:1 complexes [AgL2]+ and 1:1 complexes [AgL](+) (L = mn12S(4), mn13S(4)). The C-13 NMR chemical shifts of 2:1 and 1:1 Ag complexes and their corresponding free ligands were also estimated and compared. The free energy of the barrier of ring inversion (Delta G(double dagger)) for [Ag(mn12S(4))(2)](+) was determined to be 64 kJmol(-1).}, language = {en} } @article{KammKammSchmidtetal.2006, author = {Kamm, Birgit and Kamm, Michael and Schmidt, Matthias and Starke, Ines and Kleinpeter, Erich}, title = {Chemical and biochemical generation of carbohydrates from lignocellulose-feedstock (Lupinus nootkatensis) : quantification of glucose}, issn = {0045-6535}, doi = {10.1016/j.chemosphere.2005.03.073}, year = {2006}, abstract = {Different chemical and enzymatic methods were applied for the hydrolysis of main stems from Lupinus nootkatensis (harvest November 2002). The whole process (all steps) is based on the lignocellulose-feedstock biorefinery regime. The acid hydrolysis of L. was performed with concentrated hydrochloric acid; advantages in this process are exothermic hydrolysis and the possibility of acid recovery. Enzymatic hydrolysis achieved high yields of fermentable carbohydrates (regarding to input cellulose) with high selectivity. However, this way requires the generation of cellulose from L. by chemical pulping. Monosaccharide derivatives thus obtained were identified by their GC retention times and the corresponding MS fragmentation. Hexamethyldisilazane was used as derivatization reagent to prepare the trimethylsilyl derivatives of the carbohydrates and of the degradations products of cellulose from the different fractions. The glucose content was quantified by GC peak integration with respect to an internal standard.}, language = {en} } @article{Kleinpeter2006, author = {Kleinpeter, Erich}, title = {Push-pull alkenes : structure and pi-electron distribution}, doi = {10.2298/Jsc0601001k}, year = {2006}, abstract = {Push-pull alkenes are substituted alkenes with one or two electron-donating substituents on one end of C=C double bond and with one or two electron-accepting substituents at the other end. Allowance for pi-electron delocalization leads to the central C=C double bond becoming ever more polarized and with rising push-pull character, the pi-bond order of this double bond is reduced and, conversely, the corresponding pi-bond orders of the C-Don and C- Ace bonds are accordingly increased. This push-pull effect is of decisive influence on both the dynamic behavior and the chemical reactivity of this class of compounds and thus it is Of Considerable interest to both determine and to quantify the inherent push-pull effect. previously, the barriers to rotation about the C=C, C-Don and/or C-Acc partial double bonds (Delta G(not equal), as determined by dynamic NMR spectroscopy) or the C-13 chemical shift difference of the polarized C=C partial double bond (Delta delta(C=C)) were employed for this purpose, However, these parameters can have serious limitations, viz. the barriers can be immeasurable on the NMR timescale (either by being too high or too low-, heavily-biased conformers are present, etc.) or Delta delta(C=C) behaves in a non-additive manner with respect to the combination of the four substituents. Hence, a general parameter to quantify the push-pull effect is not yet available. Ab initio MO calculations on a collection of compounds, together with NBO analysis, provided valuable information on the structure, bond energies, electron occupancies and bonding/antibonding interactions. In addition to Delta G(C=C)(not equal) (either experimentally determined or theoretically calculated) and Delta delta(C=C), the bond length of the C=C partial double bond was also examined and it proved to be a reliable parameter to quantify the push-pull effect. Equally so, the quotient of the occupation numbers of the antibonding and bonding pi orbitals of the central C=C partial double bond ( pi*(C=C)/pi(C=C) ) could also be employed for this purpose}, language = {en} } @article{KleinpeterHolzberger2006, author = {Kleinpeter, Erich and Holzberger, Anja}, title = {Structure, intramolecular flexibility, and complexation of aza crown ethers to anions H2PO4- and HSO4- in nonprotic solvents}, series = {Tetrahedron}, volume = {62}, journal = {Tetrahedron}, number = {43}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0040-4020}, doi = {10.1016/j.tet.2006.07.074}, pages = {10237 -- 10247}, year = {2006}, abstract = {Both the structure and intramolecular flexibility of a series of aza crown ethers were studied by experimental NMR and theoretical molecular modeling. The stoichiometries of complexation to the anions H2PO4- and resulting complex stabilities were determined by experimental NMR (1H, 31P) titration and, in addition, the structure and mobility changes of the aza crown ethers upon complexation were also examined.}, language = {en} } @article{KleinpeterRollaKochetal.2006, author = {Kleinpeter, Erich and Rolla, Nadja and Koch, Andreas and Taddei, Fernando}, title = {Hyperconjugation and the increasing bulk of OCOCX3 substituents in trans-1,4-disubstituted cyclohexanes destabilize the diequatorial conformer}, issn = {4393-4399}, doi = {10.1021/Jo0600858}, year = {2006}, abstract = {The trans diesters of 1,4-cyclohexanediol with a number of acetic acid analogues, CX3COOH, of varying steric hindrance and polarity (CX3 = Me, Et, iso-Pr, tert-Bu, CF3, CH2Cl, CHCl2, CCl3, CH2Br, CHBr2, CBr3) were synthesized, and the axial, axial/equatorial, equatorial conformational equilibria were studied by low-temperature H-1 NMR spectroscopy in CD2Cl2. The structures and relative energies of the axial, axial and equatorial, equatorial conformers were calculated at both the MP2/6-311G* and the MP2/6-311+G* levels of theory, and it was only by including diffuse functions that a good correlation of Delta G degrees(calcd) vs Delta G(exptl) could be obtained. Both the structures and the energy differences of the axial, axial and equatorial, equatorial conformers are discussed with respect to the established models of conformational analysis, viz., steric 1,3-diaxial and hyperconjugative interactions. Interestingly, the hyperconjugative interactions sigma(C-C)/sigma(C-H)->sigma*(C-O), together with a steric effect which also destabilizes the equatorial, equatorial conformers on increasing bulk of the substituents, proved to dominate the position of the conformational equilibria. In addition, the preference of the axial, axial conformers with respect to their equatorial, equatorial analogues was greater than expected from the conformational energies of the corresponding substituents in the monosubstituted cyclohexyl esters. The reason for this very interesting and unexpected result is also discussed}, language = {en} } @article{KleinpeterSchulenburg2006, author = {Kleinpeter, Erich and Schulenburg, Anja}, title = {Quantification of the push-pull effect in tolanes and a revaluation of the factors affecting the C-13 chemical shifts of the carbon atoms of the C=C triple bond}, issn = {0022-3263}, doi = {10.1021/Jo060199j}, year = {2006}, abstract = {Variously substituted tolanes were employed to show that the push-pull effect is also active in C equivalent to C triple bonds by the successful correlation of the occupation quotient pi*/pi of the pi orbital in resonance with the substituted phenyl moieties of tolanes versus the bond length of the C equivalent to C triple bond. In addition, the influences of the ortho phenyl ring substituents on the C-13 chemical shifts of the triple bond carbon atoms, which were estimated by Rubin et al.(4) to be "inapplicable for describing triple bond polarization", were re-evaluated, leading to the conclusion that, while anisotropic effects of ortho substituents are negligible, the steric ortho-substituent effects do in fact dominate the deviations obtained. A detailed theoretical NBO/NCS study has been employed to illuminate the facts of this case}, language = {en} } @article{KlinkaBalentovaBernatetal.2006, author = {Klinka, Karel D. and Balentova, Eva and Bern{\´a}t, Juraj and Imrich, Jan and Vavrusova, Martina and Kleinpeter, Erich and Pihlaja, Kalevi and Koch, Andreas}, title = {Tautomerism, regioisomerism, and cyclization reactions of acridinyl thiosemicarbazides}, issn = {0022-152X}, doi = {10.1002/jhet.5570430317}, year = {2006}, abstract = {The regioselectivities of methyl- and phenylhydrazine with acridin-9-yl isothiocyanate (thus yielding thiosemicarbazides with acridine substituted on the urea-type side) were examined. Methythydrazine regioselectivity was high with the alpha-nitrogen atom overwhelmingly more nucleophilic than the beta-nitrogen atom; phenylhydrazine regioselectivity was poor but varied with the solvent and only in the case of ethanol was nucleophilic predominance of the alpha-nitrogen atom pronounced. Of note, whilst both phenyl thiosemicarbazides were present in solution only as spiro forms, the methyl product was present as an equilibrium mixture of open-chain and spiro thiosemicarbazides. Reactions on the NH2 blocked analogue of methyl acridin-9-ylthiosemicarbazide (1-isopropylidene-2- methylthiosemicarbazide) were also examined. Interestingly, present in the starting material itself was a structural motif of novelty wherein a triazolethione represented the major species of an equilibrium between cyclic and open-chain forms}, language = {en} } @article{KlinkaBalentovaBernatetal.2006, author = {Klinka, Karel D. and Balentova, Eva and Bern{\´a}t, Juraj and Imrich, J{\´a}n and Vavrusov{\´a}, Martina and Pihlaja, Kalevi and Koch, Andreas and Kleinpeter, Erich and Kelling, Alexandra and Schilde, Uwe}, title = {Structural revision of products resulting from the reaction of methylhydrazine with acridin-9-yl isothiocyanate due to unexpected acridinyl migration And further reactions}, issn = {1551-7004}, year = {2006}, abstract = {The reaction of methyl acridin-9-ylthiosemicarbazide under basic conditions with methyl bromoacetate resulted in a 1,3-thiazolin-4-one structure as provided by X-ray crystallography. The structure forced a re-evaluation of the reactant methyl acridin-9-ylthiosemicarbazide, originally thought to be 2-methyl 4-acridin-9-ylthiosemicarbazide based on synthetic expectations, but which when examined by X-ray crystallography was found to be in fact the isomeric 2- methyl 1-acridin-9-ylthiosemicarbazide resulting from rearrangement via a spiro form which it is in equilibrium with in solution. The product resulting from reaction with methyl iodide was also studied and the previously reported semicarbazide produced by reaction with MNO was re-examined. In both cases, the 1,2 isomer rather than the 2,4 isomer was found to be present based on the sign of the 3JCH3,N11 coupling. Full characterization of the compounds was rendered by 1H, 13C, and 15N solution-state NMR, and in the solid state, by both 13C and 15N NMR.}, language = {en} }