Palladium complexes of 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phosphaadamantane: synthesis, crystal structure and use in the Suzuki and Sonogashira reactions and the alpha-arylation of ketones

Palladium complexes of 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phosphaadamantane were prepared and characterized with Pd[1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phosphaadamantane](2).dba shown to be an effective catalyst for use in the Suzuki and Sonogashira reactions and the alpha-arylation of ketones. Couplings using this versatile complex proceeded in excellent yields under mild conditions.     

Hard amorphous (diamond-like) carbons

The hard forms of amorphous carbon and hydrogenated amorphous carbon, also known as diamond-like carbon, have recently aroused considerable interest as coating materials. This paper reviews their preparation, structure and properties. These carbons contain both sp² and sp³ sites. A chemical bonding model is developed which describes the arrangement of these sites and which accounts for many of the electronic and mechanical properties. The review covers the various deposition methods and the deposition mechanisms, the characterisation of amorphous carbons by techniques such as diffraction, electron energy loss, Raman, infra-red, nuclear magnetic resonance, and thermal stability, their electronic structure, optical properties and electronic spectra, and their mechanical properties such as elastic modulus, hardness, wear rate, friction and film adhesion. The dependence of electronic and mechanical properties on deposition methods and conditions is studied, to assess which methods are most valuable for applications.     

ROLE OF CAROTENOIDS IN PROTECTING CHLOROPHYLL FROM PHOTODESTRUCTION—II. STUDIES ON THE EFFECT OF FOUR MODIFIERS OF THE ALBINO cl1 MUTANT OF MAIZE*

Abstract— By combining independent, dominant, niodifier genes of the albino cl₁ mutant it is possible to produce a spectrum of phenotypes ranging from normal green to albino. Analysis of plastid pigments reveals that the albino possesses the ability to produce as much or more chlorophyll than normal siblings and that this ability is not impaired by the presence of the modifier genes. The modifiers do influence, however, the amount of carotene and xanthophyll the plants produced. The level of the three plastid pigments (chlorophyll, carotene and xanthophyll) vary simultaneously and, in most modified phenotypes, occur in approximately the same concentrations relative to their normal siblings. Since chlorophyll production appears to be normal in these mutants, it is suggested that the modifier genes do not directly influence the concentration of this pigment. Rather, the ultimate amount of chlorophyll will not rise above that which can be protected from photodestruction by the carotenoid levels determined by the various modifier genotypes.     

Dissociation of 2,4-bis(2,4,6-tri-tert-butylphenyl)-cyclo-1,3-dipnicta-2,4-diazanes (pnict = P, As, Sb) imposed by substituent steric strain: a cyclobutane/olefin analogy

Three 2,4-bis(Mes)-cyclo-1,3-dipnicta-2,4-diazanes, 2PnX, have been synthesized as 1,3-dichloro- (Pn = As; X = Cl) or 1,3-bis(triflato)- (Pn = P, Sb; X = OTf) derivatives (Mes = 2,4,6-tri-tert-butylphenyl; OTf = triflato = trifluoromethanesulfonoxy). The compounds have been structurally characterized as cyclodimers, but spectroscopic characterization of melts and solutions indicates facile dissociation of the diphosphadiazane 2POTf derivative to give the corresponding iminophosphine 1POTf and of the diarsadiazane 2AsCl derivative to give the corresponding iminoarsine 1AsCl. 1,3-Bis(triflato)-2,4-bis(Mes)-cyclo-1,3-distiba-2,4-diazane (2SbOTf) does not dissociate in the melt or in solution. The presence of the sterically bulky Mes substituent does not preclude association of N-Pn olefin analogues to give single bonded cyclobutane analogues. The facile dissociation of 2POTf and isolation of 1POTf implicates a relatively high degree of substituent steric strain in the dimer. In comparison, dissociation of 2AsCl is only apparent in the melt and in solution, likely the result of the lower substituent strain in the larger N(2)As(2) framework. The largest N(2)Pn(2) framework in 2SbOTf provides sufficient space for the Mes substituents, and the monomer is not observed under the conditions examined.     

Instrumental and radiochemical neutron activation analysis techniques for protein bound trace metals in human serum

Gel filtration and neutron activation analysis methods were combined in work aimed at the development of methods for the determination of metals firmly bound to protein in human blood serum. The values obtained are semiquantative. A purely instrumental technique afforded data on Cu, Fe, Zn, Al and Mn but values for the latter two only were determined since Cu, Fe and Zn are already well known. The concentrations for Al and Mn were found to be 300 ppb and 0.4 ppb, respectively. Despite the high resolution of Ge(Li) detectors, no other metals were found. For the determination of any others, radiochemical separations are necessary and were used to obtain data on the following elements: As 3 ppb, Ag 3 ppb, Au 0.003 ppb, Cr 1 ppb, Sb 1 ppb, Co, Cd, Mo and Sn could not be detected and upper limits were estimated to be 0.1 ppb, 2 ppb, 2 ppb, and 1 ppb, respectively.     

PIXE analysis of the hydrothermal leaching of trace elements in coal

The minor and trace element content in coal is of great interest due to the potential impact on the environment from the release of these elements during combustion. Reducing the concentrations of potentially hazardous elements in coal prior to combustion is one way of dealing with this issue. In this research particle induced X-ray emission (PIXE) was used to investigate a hydrothermal leaching process for the removal of trace elements from a bituminous coal. The leaching agents HNO₃ and NaOH were evaluated along with the effects of process parameters (temperature, pressure, and time) on the method's effectiveness. The variable with the greatest influence was the leaching agent itself. HNO₃ was determined to be more effective than NaOH in reducing elemental concentrations for nearly all the elements determined. Increasing the temperature did result in greater reductions for some elements (Cl, Br, Zn) whereas increasing the pressure and duration of the leaching process had minimal impact on reductions, in elemental concentrations.     

Ene cyclisations of alpha-(prenyl)dialkylsilyloxy aldehydes: formation and oxidative cleavage of oxasilacyclohexanols

A variety of routes are described for the synthesis of a-silyloxy aldehydes in which the silicon atom bears a prenyl side chain. These compounds are shown to undergo stereoselective carbonyl ene cyclisation under mildly Lewis acidic conditions and the derived silacycles are cleaved to afford single diastereomers of functionalised triols.     

Zeolite-confined Nano-RuO(2): A green,selective, and efficient catalyst for aerobic alcohol oxidation

The development of green, selective, and efficient catalysts, which can aerobically oxidize a variety of alcohols to their corresponding aldehydes and ketones, is of both economic and environmental significance. We report here the synthesis of a novel aerobic oxidation catalyst, a zeolite-confined nanometer-sized RuO(2) (RuO(2)-FAU), by a one-step hydrothermal method. Using the spatial constraints of the rigid zeolitic framework, we sucessfully incorporated RuO(2) nanoparticles (1.3 +/- 0.2 nm) into the supercages of faujasite zeolite. Ru K-edge X-ray absorption fine structure results indicate that the RuO(2) nanoclusters anchored in the zeolite are structurally similar to highly hydrous RuO(2); that is, there is a two-dimensional structure of independent chains, in which RuO(6) octahedra are connected together by two shared oxygen atoms. In our preliminary catalytic studies, we find that the RuO(2) nanoclusters exhibit extraordinarily high activity and selectivity in the aerobic oxidation of alcohols under mild conditions, for example, air and ambient pressure. The physically trapped RuO(2) nanoclusters cannot diffuse out of the relatively narrow channels/pores of the zeolite during the catalytic process, making the catalyst both stable and reusable.