Supported Au nanoparticles (NPs) prepared by colloid deposition method were well characterized, and their catalytic performance was tested for chemoselective reduction of a nitro group of substituted nitroaromatics by H 2 . Systematic studies on the effects of NPs size and support show small size of Au NPs, and acid-base sites of supports are required for high activity. The Au/Al 2 O 3 catalyst with Au particle size of 2.5 nm selectively hydrogenates a nitro group in the presence of various other reducible functional groups, and it shows higher intrinsic activity than the state-of-the-art catalyst (Au NPs on TiO 2 ). In situ FTIR studies provide a reaction mechanism, which explains fundamental reasons of the observed structure-activity relationship. Cooperation of the acid-base pair site on Al 2 O 3 and the coordinatively unsaturated Au atoms on the Au NPs are responsible for the H 2 dissociation to yield a H + /Hpair at the metal/support interface. High chemoselectivity could be attributed to a preferential transfer of the H + /Hpair to the polar bonds in the nitro group as well as a preferential adsorption of nitroaromatics on the catalyst through the nitro group.

An NAD(P)H-dependent Cr(VI) reductase (molecular weight = 65,000) was purified from a Cr(VI)-resistant bacterium, Pseudomonas ambigua G-1. Stoichiometric analysis of the enzymatic reaction showed that the enzyme catalyzed the reduction of 1 mol of Cr(VI) to Cr(III) while consuming 3 mol of NADH as an electron donor. Chromium(VI) was reduced to Cr(V) by one equivalent NADH molecule in the absence of the enzyme.Electron spin resonance analysis showed that Cr(V) species (g = 1.979) was formed during the enzymatic reduction. The amount of Cr(V) species formed was about 10 times larger than that of the nonenzymatic reduction. These findings show that the Cr(VI) reductase reduced Cr(VI) to Cr(HI) (14) found NAD(P)H-dependent Cr(VI)-reducing activity in the cell-free supernatant fluids from Pseudomonas putida. Das and Chandra (6) have reported that Cr(VI) was reduced to Cr(III) in the presence of NAD(P)H in the cell extract of Streptomyces species. A membrane-associated chromate reduction system was also reported. Ohtake and coworkers (20) and Wang and coworkers (26)(27)(28) have shown that Cr(VI) was reduced to Cr(III) under anaerobic conditions by Enterobacter cloacae and its reduction was caused by the respiratory chain system of the cell membrane. We considered that these bacterial Cr(VI) reduction systems contribute to its detoxification by Cr(VI)-resistant bacteria. However, the Cr(VI) reductase has not yet been purified, and the details of the reaction mechanism are still unclear.P. ambigua G-1 was able to grow in medium containing up to 20 mM K2CrO4 (13). The Cr(VI)-reducing activity (11) of this strain was more thermostable than that of other pseudomonads (14). The Cr(VI)-sensitive mutants of this strain lost the reducing activity (12). These results indicate that this strain is a good source to investigate the Cr(VI) reduction mechanism which contributes to Cr(VI) detoxication.In the present paper, we report the purification of NAD(P)H-dependent Cr(VI) reductases of P. ambigua G-1 and the analysis of the catalytic mechanism of Cr(VI) reduction by the enzymes. Preparation of Cr(VI) reductase. Cells grown in 4 liters of L broth at 37°C were harvested at the late logarithmic phase, washed twice with 20 mM Tris-HCl, pH 7.2, suspended in 100 ml of the same buffer, and disrupted by sonication. After removal of the unbroken cells by centrifugation (1,500 x g, 30 min), the supernatant fluid was heat treated at 60°C for 2 min and centrifuged (1,500 x g, 30 min). The supernatant fluid was separated on a DE32 column (3.5 by 6 cm; Whatman Ltd., Maidstone, England) previously equilibrated with buffer A (50 mM glucose in 20 mM Tris-HCl, pH 7.2), and proteins were eluted with 0.4 M NaCl in buffer A at a flow rate of 100 ml/h. The fractions carrying the Cr(VI)-reducing activity were concentrated and separated by Cu2" chelate affinity chromatography using an AF-chelate Toyopearl 650M column (2.6 by 4 cm; Toso Ltd., Tokyo, Japan) which was sequentially equilibrated with 200 PM CUSO4 solution and buffer B (0.5 M NaCl in buf...

In this paper report on the synthesis of copper and zinc sulfide nanocrystals (NCs) via the formation of polymetallic thiolate cages. Cu 2 S NCs derived from Cu-dodecanethiol complex formed well-defined spherers, which were sufficiently monodisperse (with a size distribution of w10% standard deviation of approximately 4.7 nm diameter on average) to generate ordered self-assemblies. An electron diffraction pattern and UV-vis spectrum of Cu 2 S NCs indicate that this process can provide pure b-chalcocite (Cu 2 S). Nearly monodisperse ZnS NCs with a size ranging from 3 to 7 nm were obtained by thermolysis of the S-Zn-dodecanethiol precursor. The electron diffraction pattern indicates that zinc sulfide NCs are either wurtzite or a mixture of wurtzite and zincblende. TEM observation and UV-vis spectra revealed that the growth rate of ZnS NCs depends strongly on the annealing temperature. UV-vis spectra of 3 nm ZnS NCs show sharp excitonic features and a large blue shift from the bulk material. The photoluminescence spectra exhibit a large red shift from the absorption band edges. These shifts could be attributed to recombination from the surface traps. The narrow size distribution of Cu 2 S and ZnS NCs led to the formation of ordered self-assemblies with various well-defined but nonclosed-packing. q

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