An improved procedure for the preparation of very pure ethanol-OD

Changed molar ratio of starting materials and prolonged reaction times in the deuterolysis of tetraethylorthosilicate gave yields of pure (>99.5%) ethanol-OD (relative to starting D₂O) nearly twice of that of a literature procedure.

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Eine verbesserte Vorschrift zur Herstellung von hochreinem Ethanol-OD (Kurze Mitteilung)

Zusammenfassung Verändertes molares Verhältnis der Ausgangsverbindungen und längere Reaktionszeit bei der Deuterolyse von Orthokieselsäuretetraethylester führt zur nahezu zweifachen Ausbeute einer Literaturmethode an reinem (>99.5%) Ethanol-OD (relativ zu eingesetztem D₂O).

     

Chiral Compounds Synthesized by Biocatalytic Reductions [New Synthetic Methods (51)]

It has been known for many decades that chiral compounds can be obtained by stereospecific biocatalytic reduction. Further significant methodological developments in this field have, however, only been made during the past ten years; they include the application of previously unused microorganisms and electron donors, the discovery of additional substrates for the known reductases, the development of methods for regenerating reduced pyridine nucleotides, and the discovery of new reductases which were sought for specific preparative purposes. Many chiral compounds can now be synthesized by microbial hydrogenation using H₂ and hydrogenase-containing microorganisms as well as by electromicrobial or electroenzymatic reduction. In the two latter methods, anaerobic or aerobic organisms are supplied with electrons from electrochemically reduced, artificial mediators, e.g., methyl viologen. Reductases that do not require pyridine nucleotides and can accept electrons directly from reduced viologens are especially useful. Two examples of this type of enzyme are described which are of preparative interest. Many cells contain methyl viologen-dependent NAD(P) reductases, a large number of which have still not been characterized. A productivity number is proposed which allows different methods of bioconversion with microorganisms to be compared. The productivity numbers of compounds synthesized by the methods described in this review are often 10- to 100-fold higher than those of substances obtained by conventional techniques.     

Automated derivation of reaction rules for the EROS 6.0 system for reaction prediction

The purpose of the EROS 6.0 system is to predict the products of chemical reactions and to model reaction mechanisms. This is accomplished by elementary reaction steps that are selected through the rules that constitute the knowledge base of the EROS 6.0 system. These rules are derived by methods of machine learning. The learning process is based on reaction in data bases. An overview of the EROS 6.0 system is given and the structure of the knowledge as well as the generation of reaction rules are described.     

Alkynyl ruthenium colorimetric sensors: optimizing the selectivity toward fluoride anion

We report on the synthesis of alkynyl ruthenium colorimetric sensors whose receptors are constituted by thiazolidinedione, rhodanine, or barbituric heads as recognition centers for anions. As modifications in the charge density at these recognition centers affect the whole molecule, through the alkynyl ligand acting as a communicating wire, the effects of hydrogen-bonding interactions with the anions were observed with the naked eye and monitored by UV-vis absorption spectrometry. The selectivity of the sensors was improved through electronic modifications of the alkynyl ruthenium subunit: the higher the electron density at the receptor head, the higher the selectivity is. TD-DFT calculations rationalize the long-range electronic communication as a main characteristic of the alkynyl ruthenium species and as a key to improve the selectivity of alkynyl ruthenium-based sensors toward anions.