On the use of (TMS)3CH as novel tin-free radical reducing agent

(TMS)₃CH is an efficient free radical reducing agent. Debromination, deiodation, dechlorination as well as decarboxylation of Barton and Kim esters can proceed smoothly using this tin-free reducing agent. Rate constants for hydrogen atom abstraction from TMS₃CH by primary radicals were also determined.     

A construction of thec<1 modular invariant partition functions

Decomposition theorems for certain representations of Kac-Moody algebras which are needed for the construction of modular invariant unitary conformal models are proved. It is shown that allc<1 modular invariant models can then be recovered from gauged free fermionic models, including the exceptional cases.This work was supported in part by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Division of High Energy Physics of the U.S. Department of Energy under Contract DE-AC03-76SF00098 and in part by the National Science Foundation under grant PHY85-15857Supported by the Swiss National Science FoundationSupported in part by the American-Israeli Binational Science Foundation and the Israeli Academy of Sciences     

The first AMPA receptor negative modulators based on the tetrahydroquinazoline scaffold

A convenient approach to novel symmetric bispyrimidine diamines comprises S_NAr reactions of 4-fluoropyrimidine N-oxide with alkane-α,ω-diamines with subsequent reduction of N-oxide function. The obtained substances were tested in patch-clamp experiments for the influence on the kainateinduced currents in Purkinje neurons and showed negative modulating effect.

     

The structure of a tetrabromotetrahydrodibenzocyclooctene

5, 6, 11, 12-Tetrabromo-5, 6, 11, 12-tetrahydrodibenzo[a, e]cyclooctene, C₁₆H₁₂Br₄, crystallizes in monoclinic space group P2₁/c witha=8.6917(7),b=15.135(2),c=12.892(2) Å, =101.836(8)°, V=1660.0(7) ų,Z=4. The structure was refined toR=0.058 for 3137 observed reflections. The molecule has approximate C₂ symmetry, with the eight-membered ring adopting the twist-boat conformation. The planes of the two phenyl rings form a dihedral angle of 117.3(2)°, C–Br distances range 1.965(5)–1.981(5) Å.     

Study of stressed hard coatings and of their abrasive particles by AES and REM

Chromium nitride and chromium oxide were deposited by arc PVD and APS on steel substrates to be worn in a testing set up simulating the abrasion process of a screw rotor compressor. The damage of Cr _x N is more severe than that of Cr₂O₃. The abrasive particles were collected on glassy carbon with a Batelle impactor and analyzed by AES and REM. Particles from the Cr _x N coating are totally oxidized, in contrast to particles from Cr₂O₃ which are not chemically influenced. No oxidation can be detected on the surface of the treated Cr _x N coating. The Cr₂O₃ coating is not affected either.Dedicated to Professor Dr. rer. nat. Dr.h.c. Hubertus Nickel on the occasion of his 65th birthday     

Regio- and stereospecific addition of phosphines to cyanoacetylenes

Primary and secondary phosphines add regio- and stereospecifically to phenylcyanoacetylene and 4-hydroxy-4-methylpent-2-ynenitrile under mild conditions to form corresponding functionalized secondary and tertiary phosphines of Z-configuration in 70-91% yield. According to ESR and UV data, the addition of primary phosphines to phenylcyanoacetylene involves a single electron transfer process.     

Isolation and properties of a thermostable endoglucanase from a thermophilic mutant strain ofTielavia terrestris

A heat-stable enzyme was isolated from the cellulase complex of a thermophilic strain of the micromyceteThielavia terrestris. The purified enzyme exhibited both endoglucanase and xylanase activities and had a mol mass of 69,000 Daltons and an isoelectric point of 6.4. When the cells were grown at 48°C, the initial activity of the purified enzyme using carboxymethylcellulose as a substrate was 150 nkat/mg and the Michaelis constant was 6.6 g/L. The heat stability of the enzyme was high, losing only 20% of the initial activity after a 6-h incubation at 65 °C. When cultures were grown on microcrystalline cellulose and xylose was added after 48 h of growth, endoglucanase and xylanase activities were more than doubled. Similar increases in these activities were observed by growing the cultures on straw.     

Thermostable amperometric lactate biosensor with Clostridium thermocelluml-LDH for the measurement of blood lactate

The gene for Clostridium thermocelluml-lactate dehydrogenase enzyme was cloned into pGEX-4T-2 purification vector to supply a source for a thermostable enzyme in order to produce a stable lactate biosensor working at relatively high temperatures. The purified thermostable enzyme (t-LDH) was then immobilized on a gold electrode via polymerization of polygluteraldehyde and pyrrol resulting in a conductive co-polymer. t-LDH working electrode (t-LDHE) was used for determination of lactate in CHES buffer. Amperometric response of the produced electrodes was measured as a function of lactate concentration, at a fixed bias voltage of 200 mV in a three-electrode system. The linear range and sensitivity of the biosensor was investigated at various temperatures in the range of 25-60 °C. The sensitivity t-LDHE increased with increasing the temperature and reached its highest value at 60 °C. The calculated value was nearly 70 times higher as compared to the sensitivity value of the same electrode tested at 25 °C. The sensing parameters of t-LDHE were compared with the electrodes produced by commercially available rabbit muscle LDH (m-LDH). The sensitivity of t-LDHE was nearly 8 times higher than that of m-LDHE. t-LDHE was found to retain its activity for a week incubation at refrigerator (+5 °C), while m-LDHE lost its activity in this period. t-LDHE was also tested in the presence of human blood serum. The results showed that the current increased with increasing concentrations of lactate in the human blood serum and the biosensor is more sensitive to serum lactate as well as the commercial lactate dissolved in serum as compared to the commercial lactate dissolved in CHES buffer.     

Investigations in the systems Sr–As–O–X (X = H,Cl): Preparation and crystal structure refinements of the anhydrous arsenates(V) Sr3(AsO4)2, Sr2As2O7, α- and β-SrAs2O6, and of the apatite-type phases Sr5(AsO4)3OH and Sr5(AsO4)3Cl

The previously uninvestigated atomic arrangements of six strontium arsenate(V) phases in the systems Sr-As-O-X (X = H, Cl) have been determined. Single crystals of Sr₃(AsO₄)₂ and Sr₅(AsO₄)₃Cl were grown from a borate and NaCl melt, respectively, whereas single crystals of α- and β-SrAs₂O₆ and of Sr₅-(AsO₄)₃OH were obtained under hydrothermal conditions. Microcrystalline samples of Sr₂As₂O₇ were prepared by solid-state reaction of As₂O₅ with SrCO₃ and, alternatively, by thermolysis of SrHAsO₄. Crystal structure determinations based on powder X-ray diffraction data using the Rietveld method (Sr₂As₂O₇), and from single-crystal X-ray diffraction data (all other phases) revealed isotypism with known structure types (except β-SrAs₂O₆ which represents a new structure type). Sr₃(AsO₄)₂ crystallizes in the K₂Pb(SO₄)₂ structure type; Sr₂As₂O₇ is isotypic with the high-temperature polymorphs of Ca₂P₂O₇ and Sr₂V₂O₇, but itself shows no polymorphism; Sr₅(AsO₄)₃OH and Sr₅(AsO₄)₃Cl crystallize with the hydroxylapatite and chloroapatite structure, respectively; SrAs₂O₆ is dimorphic. Like all other known M^IIAs₂O₆ metaarsenates (M = Mn, Co, Ni, Sr, Pd, Cd, Hg, Pb), the α-polymorph crystallizes in the PbSb₂O₆ structure type, whereas the novel β-polymorph is the first example of a M^IIAs₂O₆ superstructure with a doubled c-axis. Additional analytical methods using Raman spectroscopy and thermal analyses support the results of the X-ray structure work.