Kristallstruktur und elektrische Leitfähigkeit von Li2–2xMn1+xCl4-Spinelltyp-Mischkristallen

Crystal Structure and Electric Conductivity of Spinel-Type Li_2–2xMn_1+xCl₄ Solid Solutions The electric conductivity of the fast lithium ion conductors Li_2–2xMn_1+xCl₄ was measured by impedance spectroscopic methods. The conductivities obtained, e.g. ～ 4 × 10^?1 Ω^?2 cm^?1 at 570 K, depend only little on the lithium content. The crystal structure of Li_1.6Mn_1.2Cl₄ was determined by neutron powder and X-ray single crystal diffraction (space group Fd3 m, Z = 8, a = 1 049.39(6) pm, R_w = 1.4% on the basis of 170 reflections). The lithium deficient chloride crystallizes in an inverse spinel structure like the stoichiometric compound Li₂MnCl₄ according to the formula (Li_0,8)[Li_0,4Mn_0,6]₂Cl₄ with vacancies ( ) at the tetrahedral sites. The decrease of the M_oct? Cl distances with the increase of x reveals that the ionic radius of Mn²⁺ in chlorides is equal or even smaller than that of Li⁺ opposite to fluorides and oxides. The ? Cl distances of spinel type chlorides are 237 ( _tet) and 274 pm ( _oct), respectively. The mechanism of the ionic conductivity is discussed.     

Cephalosporines a chaines amino-2 thiazolyl-4 acetyles: Influence de la presence et de la configuration d'un groupe oxyimino sur l'activite antibacterienne

The syntheses of 2-(2-amino-4-thiazolyl) 2-(hydroxy or alkoxy)-imino acetic acid derivatives, with the anti (E) and syn (Z) configurations, are described. By means of these compounds, the acylation of the amino-group of 7β-amino cephalosporanic acid (7-ACA) has been achieved. The two resulting series of cephalosporin derivatives-anti and syn-are markedly different with respect to their antibiotic activity. Some of the syn compounds possess an antibacterial activity which is the highest ever observed.     

Combinatorial docking and combinatorial chemistry: Design of potent non-peptide thrombin inhibitors

A computational algorithm was used to design automatically novel thrombin inhibitors that are available from a single-step chemical reaction. The compounds do not contain amide bonds, are achiral and have a molecular weight below 400. Of the 10 compounds that were synthesized, five bind to thrombin with a Ki in the nanomolar range. Subsequent X-ray structure determination of the thrombin-inhibitor complex for the best compound (Ki=95 nM) confirms the predicted binding mode. The novel algorithm is applicable to a broad range of chemical reactions.     

Biomimetic silica formation: analysis of the phosphate-induced self-assembly of polyamines

The highly siliceous cell walls of diatoms are probably the most outstanding examples of nanostructured materials in nature. Previous in vitro experiments have shown that the biomolecules found in the cell walls of diatoms, namely polyamines and silaffins, are capable of catalysing the formation of silica nanospheres from silicic/oligosilicic acid solutions. In a previous publication, silica precipitation was found to be strictly correlated with a phosphate-induced microscopic phase separation of the polyamines. The present contribution further characterises the phase separation behaviour of polyamines in aqueous solutions. In particular, a pronounced pH-dependence of the average particle diameter is found. It is, furthermore, shown that the ability of phosphate ions to form polyamine aggregates in aqueous solutions cannot be a purely electrostatic effect. Instead, a defined hydrogen-bonded network stabilised by properly balanced electrostatic interactions should be considered. Finally, solid-state 31P NMR studies on phase-separated polyamines, synthetic silica precipitates, and diatom cell walls from the species Coscinodicus granii support the assumption of a phosphate-induced phase separation process taking place during cell wall formation.     

Mößbauer- und Neutronenbeugungs-Messungen an Li6FeCl8

Mößbauer and Neutron Diffraction Studies on Li₆FeCl₈ On Suzuki-Type Li₆FeCl₈ Mößbauer spectra and neutron powder diffraction data are presented. The Suzuki-type structure (space group Fm3 m, Z = 4, 1 031.11(1) pm) was supported refining by the Rietveld method (program PROFIL) to a final R₁ = 6.8%. The Mößbauer spectra confirm the ideal octahedral coordination of the Fe²⁺ ions (no quadrupole splitting). The isomer shift of 1.097(1) mm s^?1 at 295 K resembles those of other ferrous chlorides. At temperatures above the phase transition to deficient NaCl-type solid solution the half-width of the Mößbauer signal strongly increases.     

Synthesis of 5,6-carbonyldioxyindole,a melanogenic cyclic carbonate ester of 5,6-dihydroxyindole

5,6-Carbonyldioxyindole ( 4 ), a melanogenic derivative of 5,6-dihydroxyindole ( 1 ), was synthesized by a procedure starting with 3,4-methylenedioxycinnamic acid ( 5 ). Compound 4 is a stable crystalline solid which is readily hydrolyzed to 1 , a key intermediate on the biosynthetic pathway from tyrosine to melanin.     

Photoelectron spectroscopy of above-threshold ionization of xenon with circularly and linearly polarized light

Above-threshold multiphoton ionization (photon energy 1.17 eV and 2.33 eV) of xenon was studied with circularly and linearly polarized light. Pronounced differences in shape have been observed for photoelectron spectra taken with linearly and circularly polarized light. With circularly polarized light a strong suppression of low-energy electrons was observed; the total electron yield was reduced by factors of approximately 4 (photon energy 2.33 eV) and, depending on the laser intensity, between 13 and 80 (photon energy 1.17 eV).     

C-H bond arylations and benzylations on oxazol(in)es with a palladium catalyst of a secondary phosphine oxide

An air-stable, well-defined palladium complex derived from secondary phosphine oxide (SPO) (1-Ad)(2)P(O)H enabled efficient C-H bond functionalizations with ample scope, which set the stage for direct arylations and benzylations of (benz)oxazoles, as well as unprecedented palladium-catalyzed C-H bond arylations on nonaromatic oxazolines.