Chiral Anomaly in Contorted Spacetimes

The Dirac equation in Riemann-Cartan spacetimeswith torsion is reconsidered. As is well-known, only theaxial covector torsion A, a oneform, couples to massiveDirac fields. Using diagrammatic techniques, we show that besides the familiar Riemannianterm only the Pontrjagin type four-form dA dA doesarise additionally in the chiral anomaly, but not theNieh-Yan term d * A, as has been claimed recently.Implications for Ashtekar's canonical approach to quantumgravity are discussed.     

Redox inversion of helicity in propeller-shaped molecules derived from s-methyl cysteine and methioninol

One-electron reduction inverts the helicity of copper complexes formed from derivatives of S-methylcysteine and methioninol. The change in conformation of the organic ligand is followed in the exciton-coupled circular dichroism (ECCD) spectra of the complexes.     

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.     

Zum Reaktionsmechanismus von Glutaraldehyd mit Proteinen

The interaction of glutaraldehyde with model aliphatic amines was studied in order to understand the crosslinking reaction of glutaraldehyde with proteins. The reaction in organic solvents gave N-alkyl-1,4-dihydropyridines and N,N-dialkyl-1,5-diiminopentanes. The isolated products are new or were previously described by us for the first time¹. Hydration of the reaction products led to stable N-alkylpiperidines and N,N-dialkyl-1,5-diaminopentanes. In aqueous solution the reaction depends on thepH: at apH above 7, N-alkyl-1,4-dihydropyridines and at apH below 7, polymers were obtained. For the crosslinking reaction of proteins with glutaraldehyde the following mechanism is proposed: Monomeric glutaraldehyde reacts with the protein to give intermediate N-alkyl-2,6-dihydroxypiperidines. Intramolecular dehydration leads to the corresponding N-alkyl-1,4-dihydropyridines. Condensation of the cyclic monohydrate of glutaraldehyde and N-alkyl-2,6-dihydroxypiperidines gives linear polymeric crosslinks containing -oxo-N-alkylpiperidine units.

Lubig R., Dissertation, RWTH Aachen, 1974.     

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.