The bibliographic search in the Cambridge Structural Database: problems arising with Asiatic names

A bibliographic search for a Chinese author in the Cambridge Structural Database using the option SURNAME or AUTHOR does not result in all entries published by this author. This can be due to the order in which surname and first name were written in the original publication and/or writing the first name with or without a hyphen. The most efficient way to retrieve all entries consists of the translation of the Chinese characters of the author's name into two or three parts and then use the TEXT option. Attention is paid to the fact that this problem can also occur in other (scientific) databases and with authors from other nationalities.     

(S,S)-2,3-Dihydroxy-2,3-dihydrobenzoic acid: microbial access with engineered cells of Escherichia coli and application as starting material in natural-product synthesis

Cyclohexadiene-trans-5,6-diols such as (S,S)-2,3-dihydroxy-2,3-dihydrobenzoic acid (2,3-trans-CHD) have been shown to be of importance as chiral starting materials for the syntheses of bioactive substances, especially for the syntheses of carbasugars. By using methods of metabolic-pathway engineering, the Escherichia coli genes entB and entC, which encode isochorismatase and isochorismate synthase, were cloned and over-expressed in E. coli strains with a deficiency of entA, which encodes 2,3-dihydroxybenzoate synthase. A 30-fold increase in the corresponding EntB/EntC enzyme activities affects the accumulation of 2,3-trans-CHD in the cultivation medium. Although the strains did not contain deletions in chorismate-utilising pathways towards aromatic amino acids, neither chorismate nor any other metabolic intermediates were found as by-products. Fermentation of these strains in a 30 L pH-controlled stirred tank reactor showed that 2,3-trans-CHD could be obtained in concentrations of up to 4.6 g L(-1). This demonstrates that post-chorismate metabolites are accessible on a preparative scale by using techniques of metabolic-pathway engineering. Isolation and separation from fermentation salts could be performed economically in one step through anion-exchange chromatography or, alternatively, by reactive extraction. Starting from 2,3-trans-CHD as an example, we established short syntheses towards new carbasugar derivatives.     

Electrostatic complexation and photoinduced electron transfer between Zn-cytochrome c and [olyanionic fullerene dendrimers

Two dendritic fullerene (DF) monoadducts, 2 and 3, which can carry up to 9 and 18 negative charges, respectively, were examined with respect to electrostatic complexation with Cytochrome c (Cytc). To facilitate comprehensive photophysical investigations, the zinc analogue of Cytc (ZnCytc) was prepared according to a novel, modified procedure. The association of ZnCytc and DF, and consequential photoinduced electron transfer within ZnCytc-DF from the photoexcited protein to the fullerene, was proven by fluorescence spectroscopy and transient absorption spectroscopy. These findings were also supported by circular dichroism as well as by extensive molecular dynamics (MD) simulations.     

Synthese,Kristallstruktur und Magnetismus von Natriumtetrachlorotitanat(II), Na2TiCl4

Synthesis, Crystal Structure and Magnetism of Sodium Tetrachlorotitanate(II), Na₂TiCl₄ Na₂TiCl₄ is obtained as single crystals by metallothermic reduction of TiCl₃ with sodium (525°C, 90 d, Ta container). Pure powder samples may be prepared by synproportionation of TiCl₃ with Ti in the presence of NaCl (950–520°C, 21 d). The structure refinement from four-circle diffractometer data confirms that Na₂TiCl₄ is isotypic with Sr₂PbO₄ (orthorhombic, space group Pbam (No. 55), Z = 2 a = 694.2(1), b = 1 198.9(2), c = 385.6(1) pm, R = 0.055, R_w = 0,038). Ti²⁺ is surrounded by a distorted octahedron of Cl^?. The octahedra are connected via common edges to chains, [TiCl_2/1Cl_4/2]^2?, that run in the [001] direction. Magnetic susceptibility data were recorded in the 2 to 300 K temperature range at various field strengths. The interpretation of the data was carried out with the aid of crystal-field calculations taking magnetic interactions into account. The non-Curie behaviour of the reciprocal magnetic susceptibility of Ti²⁺ in Na₂TiCl₄ is due to the influence of spin-obit coupling.     

Thermally reversible C60-based donor-acceptor ensembles

Diels-Alder cycloaddition of anthracene derivatives--bearing fused pi-extended TTFs--to C60 yielded thermally reversible donor-acceptor materials which function as fluorescence switches.     

Triorganophosphine–dithiomonometaphosphoryl halides

The title compounds, ethyldiphenylphosphine–dithiomono­metaphosphoryl chloride, EtPh₂PPS₂Cl, C₁₄H₁₅ClP₂S₂, (I), and tris‐n‐propyl­phosphine–di­thio­monometa­phospho­ryl chloride and bromide, ⁿPr₃PPS₂Cl, C₉H₂₁ClP₂S₂, (II), and ⁿPr₃PPS₂Br, C₉H₂₁BrP₂S₂, (III), respectively, are the first phosphine‐stabilized di­thio­monometa­phospho­ryl halides to be structurally characterized. In the tris‐n‐propyl­phosphine derivatives, the central PP donor–acceptor bond becomes longer in the order bromo < chloro < fluoro. Substitution of the tris‐n‐propyl­phosphine group in (II) by the more bulky ethyl­di­phenyl­phosphine group also leads to a longer PP bond. These structural features agree with the observed ³¹P NMR data. In (II) and (III), the central P—P bond coincides with the crystallographic threefold axis, entailing site‐occupational disorder for the S₂Y group.     

The alphaM1 transmembrane segment of the nicotinic acetylcholine receptor interacts strongly with model membranes

The transmembrane domain of the nicotinic acetylcholine receptor (nAChR) plays a role in the regulation of the activity of this important ligand-gated ion channel. The lipid composition of the host membrane affects conformational equilibria of the nAChR and several classes of inhibitors, most notably anaesthetics, interact directly or indirectly with the four transmembrane M-segments, M1-M4, of the nAChR subunits. It has proven difficult to gain insight into structure-function relationships of the M-segments in the context of the entire receptor and the biomembrane environment. However, model membrane systems are well suited to obtain detailed information about protein-lipid interactions. In this solid-state NMR study, we characterized interactions between a synthetic alphaM1 segment of the T. californica nAChR and model membranes of different phosphatidylcholine (PC) lipids. The results indicate that alphaM1 interacts strongly with PC bilayers: the peptide orders the lipid acyl chains and induces the formation of small vesicles, possibly through modification of the lateral pressure profile in the bilayer. The multilamellar vesicle morphology was stabilized by the presence of cholesterol, implying that either the rigidity or the bilayer thickness is a relevant parameter for alphaM1-membrane interactions, which also has been suggested for the entire nAChR. Our results suggest that the model systems are to a certain extent sensitive to peptide-bilayer hydrophobic matching requirements, but that the lipid response to hydrophobic mismatch alone is not the explanation. The effect of alphaM1 on different PC bilayers may indicate that the peptide is conformationally flexible, which in turn would support a membrane-mediated modulation of the conformation of transmembrane segments of the nAChR.     

Eine einfache Synthese von Tetrabromsilan

A Simple Synthesis of Tetrabromosilane We report on a synthesis of SiBr₄ by reacting C₆H₅SiBr₃ with HBr/AlBr₃ to give a nearly quantitative yield. We start from C₆H₅SiCl₃ which gives C₆H₅SiH₃ with LiAlH₄ and further on C₆H₅SiBr₃ with Br₂.     

Ring-closing metathesis for the synthesis of side chain knotted pentapeptides inspired by vancomycin

A versatile method for the synthesis of bicyclic side chain knotted peptides inspired by vancomycin is described. The synthetic approach is based on the incorporation of a central amino acid derivative having two allylic groups-introduced by a Stille coupling-into pentapeptide 8 containing two allylated serine residues. Treatment of this bis-ring-closing metathesis precursor with 2nd generation Grubbs catalyst results in the formation of a bicyclic pentapeptide with the correct side chain to side chain connectivity pattern as observed in vancomycin: i- 2 --> i, i --> i + 2. Modelling studies using MacroModel hint at a cavity-like structure of the bicyclic pentapeptide which may bind suitable ligands.