X-ray absorption spectroscopy of selenate reductase

The metal sites of selenate reductase from Thauera selenatis have been characterized by Mo, Se, and Fe K-edge X-ray absorption spectroscopy. The Mo site of the oxidized enzyme has 3 to 4 sulfur ligands at 2.33 A from two molybdopterin cofactors, one Mo=O group at 1.68 A and one Mo-O with an intermediate bond length of 1.81 A. The reduced enzyme has a des-oxo active site, again with about four Mo-S ligands (at 2.32 A) and possibly one oxygen ligand at 2.22 A. The enzyme was found to contain Se in a reduced form (probably organic) although the sequence does not indicate the presence of selenocysteine. The Se is coordinated to both a metal (probably Fe) and a lighter scatterer such as carbon.     

Photochromism of fulgides and stereoelectronic factors: Synthesis of (E)-4(3)-adamantyhdene-(5)-dicyanomethylene-3(4)-[1-(2,5-dimethylfuryl)ethylidene]tetrahydrofuran-2-one 4 and 4a and (E)-4-adamantylidene-3-[2,6-dimethyl-3,5-bis(p-diethyl-aminostyryl)benzylidene]tetrahydrofuran-2,5-dione 10

In the search for fulgides with potential semiconductor laser compatibility, 4-adamantylidene-5-dicyanomemylene-3-[1-(2,5-dimethyl-3-furyl)ethylidene]tetrahydrofuran-2-one ( 4 ), along with its regioisomer 4a , have been synthesized from the corresponding fulgide 6 containing a succinic anhydride ring by reaction with malononitrile in the presence of diethylamine. Upon irradiation with a uv light at λ_max 350 run, a mixture of 4 and 4a revealed a considerably enhanced bathochromic shift to the visible region, λ_max 605 nm as compared with the starting fulgide 6 which, upon analogous uv irradiation, absorbed at λ_max 515 nm. In the search for semiconductor-laser-compatible fulgides with increased efficiency for the reverse bleaching reaction, another fulgide (E)–adamantylidene-3-[2,6-dimethyl-3,5-bis(p-diethylaminostyryl)-benzylidene]tetrahydrofuran-2,5-dione ( 10 ) was synthesized in seven steps starting from 2-bromo-m-xylene. However, 10 failed to undergo electrocyclic ring-closure upon irradiation with a uv light at λ_max 350 nm. The analogous fulgide 8 , which contains an isopropylidene functionality in place of the adamantyl group of 10 , was resynthesized for comparison, and showed two absorption maxima, one at 545 nm and the other at 620 nm. The missing physico-chemical data for 8 have also been provided.     

Rapid detection and characterization of minor reactive metabolites using stable-isotope trapping in combination with tandem mass spectrometry

Stable-isotope trapping combined with mass spectrometry (MS) neutral loss scanning has recently been developed as a high-throughput method for the in vitro screening of major reactive metabolites. In fact, detection and identification of minor reactive metabolites are equally important since the minor metabolites, even though at low levels, may be highly reactive and also play an important role in drug-induced adverse reactions. In this study, 2-acetylthiophene, clozapine, troglitazone and 7-methylindole were selected as model compounds to further validate the advantages of this method for rapid detection and structural characterization of minor glutathione (GSH) adducts derived from reactive metabolites. The utility of the current method was clearly demonstrated by successful identification of novel reactive metabolites at low levels and also minor ones either masked by non-specific responses or co-eluted with other conjugates. In comparison with existing methods, this method is sensitive, efficient, and suitable for rapid screening and more complete profiling of reactive metabolites.     

Mixing study of the induction plasma reactor: Part I. Axial injection mode

A systematic study of the gas-mixing pattern in an induction plasma reactor under atmospheric and low pressure conditions is reported. Different reactor configurations were investigated in which nitrogen is injected as an auxiliary gas either axially into an Ar/H₂, discharge in the center of the induction coil region, or radially through multiple orifices, into the plasma jet at tire exit nozzle of the torch. Concentration mapping in the mixing zone was carried out, using a VG-Microniass-PC 300 D mass spectrometer at plasma power levels and reactor pressures, in the range of 13–24 k 6V and 35–93 kPa, respectively. Comparison of these results with cold-flow measurements underlined the substantial difference in the mixing pattern in each of these two cases. A considerably faster mixing of the gases is noted under cold flow conditions compared to that in the presence of the discharge. The results are discussed from the viewpoint of their use for optimum reactor design applied to tire vapor-phase synthesis of ultrafine ceramic powders, using induction plasma technology.     

Spectroscopic studies on some complexes of nickel(II) and palladium(II) with thiosemicarbazides

Summary The electronic absorption spectra of the complexes M(L)Cl₂ and M(L)₂Cl₂ [M=Ni^II or Pd^II; L=thiosemicarbazide (tsc), 1-phenylthiosemicarbazide (1-phtsc), or 4-phenylthiosemicarbazide (4-phtsc)] were investigated in a number of solvents. The complexes Ni(tsc)Cl₂, Ni(tsc)₂Cl₂, Ni(4-phtsc)Cl₂ and Ni(4-phtsc)₂Cl₂ exist in a distorted O_h geometry when dissolved in any of the solvents used. On the other hand, the complex Ni(1-phtsc)₂Cl₂, although weakly paramagnetic, proved to be planar. Theoretical and experimental results proved that the complex has neither O_h nor T_d geometry. Molecular orbital calculations were performed on some selected complex ions assuming a local point group symmetry of D_2h.