Cyclic silylated onium ions of group 15 elements.

Five- and six-membered cyclic silylated onium ions of group 15 elements I were synthesized by intramolecular cyclization of transient silylium ions II. Silylium ions II were prepared by the hydride transfer reaction from silanes III using trityl cation as hydride acceptor. It was found that smaller ring systems could not be obtained by this approach.

The calculation of (29)Si NMR chemical shifts of tetracoordinated silicon compounds in the gas phase and in solution.

Aiming at the identification of an efficient computational protocol for the accurate NMR assessment of organosilanes in low-polarity organic solvents, (29)Si NMR chemical shifts of a selected set of such species relevant in organic synthesis have been calculated relative to tetramethylsilane (TMS, 1) using selected density functional and perturbation theory methods. Satisfactory results are obtained when using triple zeta quality basis sets such as IGLO-III. Solvent effects impact the calculated results through both, changes in substrate geometry as well as changes in the actual shieldings.

Design, synthesis, and biological testing of novel naphthoquinones as substrate-based inhibitors of the quinol/fumarate reductase from Wolinella succinogenes.

Novel naphthoquinones were designed, synthesized, and tested as substrate-based inhibitors against the membrane-embedded protein quinol/fumarate reductase (QFR) from Wolinella succinogenes, a target closely related to QFRs from the human pathogens Helicobacter pylori and Campylobacter jejuni. For a better understanding of the hitherto structurally unexplored substrate binding pocket, a structure-activity relationship (SAR) study was carried out. Analogues of lawsone (2-hydroxy-1,4-naphthoquinone 3a) were synthesized that vary in length and size of the alkyl side chains (3b-k).

The correlation of cathodic peak potentials of vitamin K(3) derivatives and their calculated electron affinities. The role of hydrogen bonding and conformational changes.

2-methyl-1,4-naphtoquinone 1 (vitamin K(3), menadione) derivatives with different substituents at the 3-position were synthesized to tune their electrochemical properties. The thermodynamic midpoint potential (E(1/2)) of the naphthoquinone derivatives yielding a semi radical naphthoquinone anion were measured by cyclic voltammetry in the aprotic solvent dimethoxyethane (DME). Using quantum chemical methods, a clear correlation was found between the thermodynamic midpoint potentials and the calculated electron affinities (E(A)).

Hydrogen- and fluorine-bridged disilyl cations and their use in catalytic C-F activation.

The hydrogen-bridged disilyl cation 6 with an 1,8-naphthalenediyl backbone was synthesized and was characterized by NMR spectroscopy and X-ray crystallography, supported by quantum mechanical computations. The SiHSi linkage is symmetrical, corresponding to a single minimum potential, and the structural parameters are in agreement with the presence of a two electron-three center bond in 6. Treatment of disilyl cation 6 with alkyl fluorides yields the disilylfluoronium ion 10.

Magnetic properties of two double-layer structures built from hydroxynaphthoic acids and manganese.

Double-layer structures consisting of alternating polar and non-polar layers have been prepared using Mn2+ ions and o-hydroxynaphthoic acids. The polar layers contain the Mn2+ ions, carboxylate groups, hydroxy groups and water molecules. The non-polar layers are built up from the naphthalene moieties.