Tobias Borrmann

Theoretical study of flavonoids and proline interactions. Aqueous and gas phases

Abstract Flavonoids are polyphenolic compounds found in all land plants and in plant-related foods. These compounds have many positive effects, and the interaction with proline aminoacid is one of the most important characteristics. The present work shows the results of the application of the multiple minima hypersurfaces procedures, in the study of the interactions of flavonoid monomers (catechin and robinetinidin) with proline. These results are compared with experimental and classical theoretical results reported in the available literature. The most important results of this work are related with the conformations of monomers in these interactions, the preferential position of interactions and the thermodynamic stability of these complexes. All the results are successfully compared in both, gas and aqueous phases.

Arylthiazylamides: syntheses, structures, and bonding properties.

Air-sensitive, thermally unstable tris(dimethylamino)sulfonium (TAS) salts (3) of the title anions [ArNSN]- have been prepared from corresponding sulfurdiimides Ar-N=S=N-SiMe3 (2) by Si-N bond cleavage with [(Me2N)3S]-[Me3SiF2]- (TASF). They are characterized by low-temperature X-ray crystallography as Z isomers. Because of the very short terminal S-N distance (144.2 (3h)-147.9 (3i)pm) and the relatively long internal S-N distance (158.3 (3i)-160.3 (3c) pm) the [ArNSN]- ions should be regarded as thiazylamides 1b, rare species containing a S triple bond N triple bond. A bonding model is developed and the experimental results are compared with those of restricted Hartree-Fock (RHF), density functional theory (DFT), and Møller-Plesset second-order (MP2) calculations.

Azanonaborane-pyridine derivatives [(R′C5H4N)B8H11NHR″]: synthesis, structure and some molecular-orbital calculations

The molecular structure of hypho -type [(RNH2)B8H11NHR] is based on a {B8} cluster with one nitrogen bridge and one exo amine ligand. In general these azanonaboranes are synthesized by the reaction of [B9H13(SMe2)] with primary amines. Modifications of these azanonaboranes are possible by ligand-exchange reactions. Necessary conditions for ligand-exchange reactions of the azanonaboranes [(RNH2)B8H11NHR], in which the exo -{NH2R} group is replaced by other nitrogen-donor ligands, are reported. The nitrogen-donor ligands that have been examined include primary, secondary and tertiary amines as well as a series of substituted pyridines. The structures of the pyridine-containing azanonaboranes [(C5H5N)B8H11NHR] where R� /methyl, ethyl, iso propyl or tertiary butyl, have been determined crystallographically, and are compared with the aliphatic azanonaboranes [(RNH2)B8H11NHR]. The reactions of the various [(RNH2)B8H11NHR] species with pyridine or the substituted pyridines give coloured products, contrasting with the colourless nature of the starting alkylamine species. The electronic interaction between the {B8} hypho -type unit and the bonded pyridine units has been investigated by UV � /vis spectroscopy and by AM-1 molecular-orbital calculations. # 2002 Elsevier Science B.V. All rights reserved.

Synthesis of a cofacial chlorin dimer of defined symmetry

Special pair chlorophylls arranged in a cofacial dimeric structure play an important role in the initial step of light induced electron transfer of photosynthetic reaction centers of bacteria and plants. For mimicking the natural photosynthetic reaction center we aimed on synthesis of an artificial special pair 13 constructed from two chlorin subunits 5a, b and a rigid biphenylene spacer moiety 11. Due to the reduced C2h symmetry of the chlorin units compared with so far used D4h porphyrins and due to the rigid spacer a cofacial dimer of defined symmetry and distance was obtained.

Synthesis of an amide-linked chlorin-anthraquinone dyad and its structural and spectroscopic properties

An enantiomerically pure chlorin-anthraquinone dyad 6 was synthesized in respect to a model compound for light-induced electron transfer in the photosynthetic center. Therefore, the enantiomerically pure chlorin 4 was linked with the anthraquinone amine 5 to form a peptide-like dyad. The conformation of the dyad follows NMR investigations and a PM3 calculation. Observed quenching of the fluorescence indicates an intramolecular energy and/or electron transfer from the chlorin donor moiety to the anthraquinone subunit of the dyad.

F3CCN5S3, A BICYCLIC MULTIFUNCTIONAL SULFUR-NITROGEN LIGAND

The bicyclic sulfur-nitrogen heterocycle F3CCN5S3 (1) was investigated as a donor and acceptor toward H+, metal cations, and F−. Whereas the protonated species F3CCN5S3H+ AsF6 − (2) can be isolated, the product of the reaction with F− is unstable and decomposes among other products to TAS+ F3CCN5S3NC(NH2)CF3 − (3), which is isolated from this reaction in small amounts.

Acetone and the precursor ligand acetylacetone

In focused electron beam induced deposition (FEBID) acetylacetone plays a role as a ligand in metal acetylacetonate complexes. As part of a larger effort to understand the chemical processes in FEBID, the electron-induced reactions of acetylacetone were studied both in condensed layers and in the gas phase and compared to those of acetone. X-ray photoelectron spectroscopy (XPS) shows that the electron-induced decomposition of condensed acetone layers yields a non-volatile hydrocarbon residue while electron irradiation of acetylacetone films produces a non-volatile residue that contains not only much larger amounts of carbon but also significant amounts of oxygen. Electron-stimulated desorption (ESD) and thermal desorption spectrometry (TDS) measurements reveal striking differences in the decay kinetics of the layers. In particular, intact acetylacetone suppresses the desorption of volatile products. Gas-phase studies of dissociative electron attachment and electron impact ionization suggest that this effect cannot be traced back to differences in the initial fragmentation reactions of the isolated molecules but is due to subsequent dissociation processes and to an efficient reaction of released methyl radicals with adjacent acetylacetone molecules. These results could explain the incorporation of large amounts of ligand material in deposits fabricated by FEBID processes using acetylacetonate complexes.