Kinetic study on enzymatic s-oxygenation promoted by a reconstituted system with purified cytochrome P-450

Thioanisole derivatives ($\text{1a–e}$) were found to be oxygenated by a reconstituted system of purified cytochrome P-450 to give sulfoxides ($\text{2a–e}$). Logarithms of Vmax were found to be correlated linearly with one electron oxidation potentials of the sulfides (Ep) suggesting the oxygenation to proceed via one electron transfer from sulfides to the active species of the enzyme.     

Automated autoradiographic grain counting of DNA repair in cultured human fibroblasts after ultraviolet irradiation

Measurement of autoradiographic grains produced by the decay of incorporated radioisotopes is often used for a quantitative assay of the rate of DNA replication and DNA repair in cells or tissues. However, visual grain counting by microscopic observation is time-consuming and tedious process. Recently, Kraemer et al. reported that automated measurement of grains in cultured human cells may be facilitated by using appropriate grain counting instruments. Under their experimental conditions using Kodak NTB-3 emulsion, instrument-determined grain number per nucleus was proportional to visual counts up to 30 grains, and then leveled off at much larger visual counts. The saturation phenomenon was due to counting-loss by the instrument caused by overlapping of neighboring grains. To prevent the counting-loss, we have used in the present study Japanese Sakura NR-M2 emulsion which is less sensitive to radiation exposure than Kodak NTB-3, thereby yielding smaller size of grains per radioactive decay. Samples were prepared from cultured skin fibroblasts derived from normal individuals and xeroderma pigmentosum (XP) patients defective in DNA repair. These cells were irradiated with 254 nm UV incubated for 3 h with culture medium containing 3H-thymidine, and autoradiograms were made by dipping in Sakura NR-M2 emulsion. The number of grains as well as grain surface area per nucleus was measured by using ARTEK CYTO TALLY MODEL 900 counting instrument, and compared with visual counts. The results showed that, under our optimum condition, the instrument-determined number of grains was directly proportional to visual counts, at least up to 150 grains per nucleus, with a correlation coefficient of 0.971.(ABSTRACT TRUNCATED AT 250 WORDS)     

Theoretical study of degree of covalency in some CoF6(n-) complexes (n = 4, 3, and 2)

On the basis of a high-quality LCAO MO SCF calculation, covalency versus ionicity of a Co–F bond in the CoF₆(n-) complexes, where n = 4, 3, and 2, is discussed. The overlap and gross atomic populations, delocalization of certain MOS, and the charge densities in the bond region as well as around F's all indicate that the covalency increases as n decreases or the valency of Co increases in these complexes.     

Synthesis, structure, and bonding properties of 5-carbaphosphatranes: a new class of main group atrane

1-Hydro-5-carbaphosphatrane (1) and 1-methyl-5-carbaphosphatrane (2), the first 5-carbon analogues of phosphatranes, were synthesized by a demethylation reaction of cyclic phosphinate 3. X-ray analysis revealed that 1 has a typical trigonal bipyramidal structure with hydrogen and carbon atoms at the apical position and three oxygen atoms at the equatorial positions, indicating that 1 is a phosphorane in the perfectly "anti-apicophilic" arrangement. Apical P-C and P-H bond lengths were 1.921(2) and 1.38(2) A, respectively. The (1)J(PH) value of 1 and the (1)J(PC)(P-CH(3)) value of 2 were 852 and 215 Hz, respectively, which are extraordinarily large for the apical coupling constants of phosphoranes, but close to those of the reported phosphatranes with a 5-nitrogen atom. IR and Raman spectra are also reported. Force constant calculations indicate the transannular bond in carbaphosphatrane is 3 times stronger than in silatrane, due to its covalent character.     

Reactions of aromatic nitro,nitroso, hydroxylamino azoxy,azo and hydrazo compounds with selenol

Relative reactivities of aromatic nitro, nitroso, hydroxylamino, azoxy, azo and hydrazo compounds in the reduction with RSe^? were found to fall in the following order :

     

Amphiphilic NaY zeolite particles loaded with niobic acid: Materials with applications for catalysis in immiscible liquid-liquid system

The catalytic potential of catalysts for acid-catalyzed reactions has been demonstrated by NaY zeolite loaded with alkylsilane-covered niobic acid in the liquid phase hydration of 1,2-epoxyoctane with water. The catalytic activity of the catalysts was correlated to the amphiphilic character of the solid catalyst particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reduction of diaryl disulfides with 1-benzyl-1,4-dihydronicotinamide

Reduction of diaryl disulfides with 1-benzyl-1,4-dihydronicotinamide (BNAH) proceeded through a radical chain reaction, while dialkyl disulfides were found to be inert to BNAH.     

Characteristic reactions and properties of C-apical O-equatorial (O-cis) spirophosphoranes: effect of the sigma(P)(-)(O) orbital in the equatorial plane and isolation of a hexacoordinate oxaphosphetane as an intermediate of the Wittig type reaction of 10-P-5 phosphoranes

Novel spirophosphoranes (O-cis) that exhibit reversed apicophilicity having an apical carbon-equatorial oxygen array in a five-membered ring showed enhanced reactivity toward nucleophiles such as n-Bu(4)N(+)F(-) or MeLi in comparison with the corresponding stable isomeric spirophosphoranes (O-trans) having an apical oxygen-equatorial carbon configuration. The enhanced reactivity of the O-cis isomer could be explained by the presence of a lower-lying sigma(P)(-)(O(equatorial)) orbital as the reacting orbital in the equatorial plane, whereas the corresponding orbital is a higher-lying sigma(P)(-)(C(equatorial)) in the O-trans isomer. Density functional theory (DFT) calculation on the actual compounds provided theoretical support for this assumption. In addition, we found that the benzylic anion alpha to the phosphorus atom in O-cis benzyl phosphorane is much more stable than that generated from the corresponding O-trans compounds. The experimental results were considered to be due to the n(C) --> sigma(P)(-)(O) interaction in the O-cis anion, and this was confirmed by DFT calculations. Furthermore, the hexacoordinate anionic species derived from the reaction of the benzylic anion from O-cis benzylphosphorane with an aldehyde was also found to be stabilized as compared with analogous species from the corresponding O-trans isomer. The first X-ray structural characterization of a hexacoordinate phosphate intermediate in the Wittig type reaction using pentacoordinate phosphoranes is reported.     

Construction of molecular wires based on a gold(I) bis-sigma-acetylide building block incorporated into ruthenium(II) polypyridyl complexes

An Ru(II)-Au(I)-Ru(II) triad has been synthesized from [Ru(bpy)2(3-ethynylphenanthroline)]2+ with Au(tht)Cl and characterized by spectroscopic means such as NMR and ESI-MS; the Ru(II)-Au(I)-Ru(II) triad shows an intense emission at 620 nm upon excitation at 360 nm, which suggests an efficient energy transfer from the Au site to Ru sites via extended pi-conjugation through the ethynyl units.