Nanocrystalline gold and gold palladium alloy catalysts for chemical synthesis

Catalysis by gold has become one of the most studied new topics in chemistry in recent years, and yet for many gold acting as a catalyst is, perhaps, a most unlikely possibility since bulk gold is a relatively non-reactive, immutable, ductile metal that is prized for its great beauty and value rather than for the depth of its chemistry. However, when prepared in nanocrystalline form, as a collection of a few hundreds of atoms, it displays remarkable activity as a heterogeneous catalyst for a broad range of redox reactions. Of particular note is the ability of gold, either alone or alloyed with palladium, to catalyse selective oxidation reactions, e.g. alkene epoxidation, alcohol oxidation, and the direct synthesis of hydrogen peroxide by the hydrogenation of molecular oxygen. In this article the recent advances in this exciting new field are explored.     

The preparation, characterization, and X-ray structural analysis of dichlorobis[1-methyl-3-(2-propyl) -2(3H)-imidazolethione]mercury(II)

A new compound of mercury(II) chloride complexed to 1-methyl-3-(2-propyl) -2(3H)-imidazolethione (mipit) has been prepared and characterized via standard methods and X-ray crystallography. The structural significance of this study is that it shows one of the few monomeric examples of a mercury(II) chloride thione complex reported to date. The compound crystallizes in space group P2₁/c with a = 17.143(6) Å, b = 17.047(6) Å, c = 14.759(5) Å, = 105.899(5)°, V = 4148(2) ų, Z = 8. The coordination sphere is distorted tetrahedral with Hg–S bonds and Hg–Cl bond distances falling within the normally expected ranges. Bond angles ranged from 108.11(4)° to 115.51(4)° with the widest angle being observed for the S–Hg–S linkage. Ligand bond distances and angles including the C=S distance are within the normally expected values observed for this compound.     

Interface development in polycarbonate/poly(methyl methacrylate) bilayer films

We report the effect of annealing over a range of temperatures and times on the mixing, stability, and interfacial width in thin bilayer films of bisphenol A–polycarbonate (PC) on deuterated poly(methyl methacrylate) (dPMMA). These bilayer films were highly stable when annealed at temperatures of up to 438 K, the temperature at which the degradation of the blends of these materials was first detectable by thermogravimetric analysis. At higher temperatures, dewetting of the PC upper layer of the film occurred at an increasing rate. Nuclear reaction analysis showed that the PC and dPMMA layers remained segregated. Neutron reflectometry data showed that the interfacial width between the two polymer layers grew rapidly from 0.5 nm for an unannealed sample to approximately 4.0 nm, the latter value being in good agreement with the predicted value for the interfacial width in the absence of any reaction. Extended annealing at 438 K and lower temperatures had no effect on the interfacial width, whereas at higher temperatures, the interfacial width increased to approximately 5.5 nm before the films became unstable. The broadening of the interface found at higher annealing temperatures was attributed to an increase in the miscibility of the polymers induced by the monomer from the unzipping of the dPMMA chains. There was no evidence of a thermally induced chemical reaction between the two polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2351–2362, 2001     

Surface modification of polyethylene with multi-end-functional polyethylene additives

We have prepared and characterized a series of multifluorocarbon end-functional polyethylene additives, which when blended with polyethylene matrices increase surface hydrophobicity and lipophobicity. Water contact angles of >112° were observed on spin-cast blended film surfaces containing less than 1% fluorocarbon in the bulk, compared to ~98° in the absence of any additive. Crystallinity in these films gives rise to surface roughness that is an order of magnitude greater than is typical for amorphous spin-cast films but is too little to give rise to superhydrophobicity. X-ray photoelectron spectroscopy (XPS) confirms the enrichment of the multifluorocarbon additives at the air surface by up to 80 times the bulk concentration. Ion beam analysis was used to quantify the surface excess of the additives as a function of composition, functionality, and molecular weight of either blend component. In some cases, an excess of the additives was also found at the substrate interface, indicating phase separation into self-stratified layers. The combination of neutron reflectometry and ion beam analysis allowed the surface excess to be quantified above and below the melting point of the blended films. In these films, where the melting temperatures of the additive and matrix components are relatively similar (within 15 °C), the surface excess is almost independent of whether the blended film is semicrystalline or molten, suggesting that the additive undergoes cocrystallization with the matrix when the blended films are allowed to cool below the melting point.     

Influence of counterions on the structure of bis(oxazoline)copper(ii) complexes; an EPR and ENDOR investigation

X- and Q-band EPR and ENDOR spectroscopy was used to study the structure of a series of heteroleptic and homoleptic copper bis(oxazoline) complexes, based on the (-)-2,2'-isopropylidenebis[(4S)-4-phenyl-2-oxazoline] ligand and bearing different counterions (chloride versus triflate); labelled [Cu(II)()]. The geometry of the two heteroleptic complexes, [Cu(II)()] and [Cu(II)()], depended on the choice of counterion. Formation of the homoleptic complex was only evident when the Cu(II)(OTf)(2) salt was used (Cu(II)(Cl)(2) inhibited the transformation from heteroleptic to homoleptic complexes). The hyperfine and quadrupole parameters for the surrounding ligand nuclei were determined by ENDOR. Well resolved (19)F and (1)H couplings confirmed the presence of both coordinated water and TfO(-) counterions in [Cu()].     

Chiral inversion of 2-arylpropionyl-CoA esters by human α-methylacyl-CoA racemase 1A (P504S)--a potential mechanism for the anti-cancer effects of ibuprofen

Metabolic chiral inversion of 2-arylpropanoic acids (2-APAs;'profens'), such as ibuprofen, is important for pharmacological activity. Several 2-APA-CoA esters were good racemisation substrates for human AMACR 1A, suggesting a common chiral inversion pathway for all 2-APAs and an additional mechanism for their anti-cancer properties.