There is considerable structural homology between PSAO and ECAO. A combination of evidence from both structures indicates that the TPQ side chain is sufficiently flexible to permit the aromatic grouf to rotate about the Cbeta-Cgamma bond, and to move between bonding and non-bonding positions with respect to the Cu atom. Conformational flexibility is also required at the surface of the molecule to allow the substrates access to the active site, which is inaccessible to solvent, as expected for an enzyme that uses radical chemistry.

The heterogeneously catalyzed aerobic selective oxidation of hydrocarbons offers new, environmentally benign routes to a diverse range of valuable intermediates for the pharmaceutical, fine chemical, and agrochemical sectors.[1] Such powerful catalytic technologies circumvent the use of stoichiometric reagents and expensive homogeneous complexes along with the associated process disadvantages and safety issues. [2] While there has been recent interest in the potential of gold as a partial oxidation catalyst, [3] such systems typically offer low oxygenate yields and require either radical initiators, [4] high temperatures, or high O 2 partial pressures.[5] Supported ruthenium, [6] palladium, and platinum clusters are also promising candidates to catalyze the selective oxidation (selox) of primary alcohols to their corresponding aldehydes under mild conditions. [7] These reactions are highly regioselective in the presence of diverse functionalities, including allylic groups. Most studies in this area employing Pd and Pt have utilized commercial formulations based upon amorphous carbon or oxide supports. However, the poor intrinsic performance of these materials relative to their homogeneous counterparts has often necessitated ad hoc promotion of the reaction by non-noble metals to achieve even moderate yields.[8] Two factors presently constrain the wider adoption of heterogeneous Pd selox catalysts amongst both academic and industrial communities: first, uncertainty over the active site responsible for the rate-limiting oxidative dehydrogenation step, [9] and second, the use of conventional supports with restrictive pore dimensions that inhibit efficient mass and heat transfer to and from reaction sites and limit the range of viable solvents and substrates. [10] Recent studies have implicated surface palladium oxide as the active center in allylic alcohol selox.[11] Since the energetics of metal clusters increasingly favor oxide-terminated surfaces with decreasing cluster size, [12] we hypothesized that a mesoporous high-area support would serve to both stabilize highly dispersed palladium oxide nanoparticles and would facilitate efficient alcohol and aldehyde diffusion. Herein, we report the successful synthesis of tailored PdAl 2 O 3 catalysts and demonstrate that extremely low palladium loadings generate atomically dispersed Pd II surface species that confer exceptional selox activity of allylic alcohols.Mesoporous alumina-supported palladium catalysts (Pd/ meso-Al 2 O 3 ) were prepared by a modified surfactant-templated route through hydrolysis of aluminum sec-butoxide and subsequent aging in the presence of lauric acid.[13] The organic template was removed by calcination prior to incipient wetness impregnation with tetraammine palladium(II) nitrate solution (see the Supporting Information). Samples were then calcined, reduced, and stored in air. Porosimetry and powder X-ray diffraction confirmed that the final processed materials possessed well-defined, hexagonal pore structures, with surface areas of 35...

The heterogeneously catalyzed aerobic selective oxidation of hydrocarbons offers new, environmentally benign routes to a diverse range of valuable intermediates for the pharmaceutical, fine chemical, and agrochemical sectors.[1] Such powerful catalytic technologies circumvent the use of stoichiometric reagents and expensive homogeneous complexes along with the associated process disadvantages and safety issues. [2] While there has been recent interest in the potential of gold as a partial oxidation catalyst, [3] such systems typically offer low oxygenate yields and require either radical initiators, [4] high temperatures, or high O 2 partial pressures.[5] Supported ruthenium, [6] palladium, and platinum clusters are also promising candidates to catalyze the selective oxidation (selox) of primary alcohols to their corresponding aldehydes under mild conditions. [7] These reactions are highly regioselective in the presence of diverse functionalities, including allylic groups. Most studies in this area employing Pd and Pt have utilized commercial formulations based upon amorphous carbon or oxide supports. However, the poor intrinsic performance of these materials relative to their homogeneous counterparts has often necessitated ad hoc promotion of the reaction by non-noble metals to achieve even moderate yields.[8] Two factors presently constrain the wider adoption of heterogeneous Pd selox catalysts amongst both academic and industrial communities: first, uncertainty over the active site responsible for the rate-limiting oxidative dehydrogenation step, [9] and second, the use of conventional supports with restrictive pore dimensions that inhibit efficient mass and heat transfer to and from reaction sites and limit the range of viable solvents and substrates. [10] Recent studies have implicated surface palladium oxide as the active center in allylic alcohol selox.[11] Since the energetics of metal clusters increasingly favor oxide-terminated surfaces with decreasing cluster size, [12] we hypothesized that a mesoporous high-area support would serve to both stabilize highly dispersed palladium oxide nanoparticles and would facilitate efficient alcohol and aldehyde diffusion. Herein, we report the successful synthesis of tailored PdAl 2 O 3 catalysts and demonstrate that extremely low palladium loadings generate atomically dispersed Pd II surface species that confer exceptional selox activity of allylic alcohols.Mesoporous alumina-supported palladium catalysts (Pd/ meso-Al 2 O 3 ) were prepared by a modified surfactant-templated route through hydrolysis of aluminum sec-butoxide and subsequent aging in the presence of lauric acid.[13] The organic template was removed by calcination prior to incipient wetness impregnation with tetraammine palladium(II) nitrate solution (see the Supporting Information). Samples were then calcined, reduced, and stored in air. Porosimetry and powder X-ray diffraction confirmed that the final processed materials possessed well-defined, hexagonal pore structures, with surface areas of 35...

The tripeptide glutathione (y-~-Gl~-~-Cys-Gly, GSH) is an important intracellular reducing agent for Cu(I1) and complexation agent for Cu(1). We have studied the complexation of Cu(1) to GSH in aqueous solution at a range of pH values and Cu(1):GSH molar ratios by 'H-NMR and 'IC-NMR spectroscopy and X-ray absorption spectroscopy. The NMR data are consistent with formation of a complex with approximate 1 : 1 stoichiometry [Cu(SG)] as the major species with only thiolate sulfur of GSH binding to Cu(1). The rate of exchange of GSH with GS-Cu was determined to be 13 s-' at 283 K, pH 6.8. X-ray absorption spectroscopic measurements showed that Cu(1) is coordinated to 3.1 +-0.3 sulfur atoms at approximately 0.222 nm in solutions (and solids) containing GSH:Cu in 1 : 1 and 2: 1 mol ratios. The possible structures of polymeric Cu(1)-glutathione complexes are discussed. The high thermodynamic stability of Cu(1)-S bonds in Cu(1)-glutathione complexes coupled with their kinetic lability may provide efficient and specific pathways for the transport of copper in cells.Keywords: glutathione ; copper; NMR ; X-ray absorption near-edge structure ; extended X-ray absorption fine structure.Glutathione (GSH) is present in all living cells and is frequently the most abundant cytosolic thiol compound with concentrations in the range 0.1-10 mM. Usually the ratio between the oxidised (GSSG) and the reduced (GSH) forms in the body is maintained at a low value of approximately 0.1 [l].-0,c c0,- SH 0 GSHGSH is a tlexible peptide, the X-ray structure showing no internal H-bonds [ 21, and has several potential metal-binding groups : two peptide bonds, two carboxylic acid groups, one amino group and one thiol group. However, its structure is such that few of these functional groups are likely to coordinate simultaneously to the same metal ion.In cells, one of the roles of GSH is as a substrate for GSHperoxidase, an enzyme capable of both removing hydrogen peroxide from cells and repairing peroxidativel y damaged membranes 131. It is also involved in metal detoxification, and an Correspondence to P. J. Sadler,

. Metallothionein (MT)1 is an intriguing, low molecular mass (ϳ7 kDa), cysteine-and metal-rich protein. It was first isolated from equine renal cortex 40 years ago (1) and contains 61 amino acids, of which 20 are cysteine residues. Since then, similar proteins have been isolated from the kidney, liver, and intestines of a variety of animal species (2), fungi (3, 4), plants (5), and metal-resistant bacteria (6 -8). The two major isoforms of mammalian MT (MT(I) and MT(II)) differ only in minor sequence changes and overall charge. Recently, the discovery of a growth inhibitory factor (GIF) from human brain tissue and nerve and its characterization as a metallothionein (MT-III) has stimulated new interests in studying this small protein (9, 10).The functions of metallothionein are still not fully understood. It appears to play a fundamental role in the metabolism of copper and zinc ions under various physiological conditions (11, 12), including its ability to donate metal ions to apo-Zn 2ϩ enzymes (13,14 (18,19), thereby preventing reactions with other cellular targets in mammals and other higher organisms (20). Metallothionein also appears to play a role in radical scavenging, stress response, and the pharmacology of metallodrugs and alkylating agents (12,21,22).The best characterized mammalian metallothioneins contain a single polypeptide chain with seven bound metal ions (either Zn 2ϩ or Cd 2ϩ ). The x-ray crystal structure of rat liver Zn 2 Cd 5 -MT(II) (23) and NMR solution structures of rabbit liver Cd 7 -MT(II) (24), rat liver Cd 7 -MT(II) (25), and human liver Cd 7 -MT (26) show that metallothionein contains two structurally independent ␣ (C-terminal) and ␤ (N-terminal) domains, which are linked in the protein via two amino acids. The seven metal ions are present in clusters of four and three metals bound to bridging and terminal cysteine thiolate ligands, with metal-tothiolate ratios of M 4 S 11 and M 3 S 9 for the ␣-and ␤-domains, respectively (23). When both Zn 2ϩ and Cd 2ϩ are present, Cd 2ϩ binds preferentially to the ␣-domain, whereas Zn 2ϩ is found preferentially in the ␤-domain (23, 28). A Zn 2 Cd three-metal cluster (␤ domain) in MT has the same structure as a Cd 3 cluster (23). The ␣-domain binds Cd 2ϩ ions cooperatively (29). All 20-cysteine residues participate in metal binding, and each of the seven Zn 2ϩ or Cd 2ϩ ions is tetrahedrally coordinated to four cysteine thiolate sulfur atoms (30,31).Bismuth is known to induce the synthesis of renal metallothionein (32), and it has been shown that pretreatment with bismuth complexes can prevent the toxic side effects of the anti-cancer drug cisplatin without compromising its anti-tumor activity (33)(34)(35)(36)