Gas-phase reactivity of heterobinuclear oxometalate anions [CrMoO6(OR)]-, [CrWO6(OR)]-, and [MoWO6(OR)]- (R = H, nBu)

Heterobinuclear oxometalate anions based upon [CrMoO7]2-, [CrWO7]2-, and [MoWO7]2- were generated and transferred to the gas phase by the electrospray process from acetonitrile solutions containing two of the salts (Bu4N)2[MO4] (M = Cr, Mo, W). Their reactivities were examined and compared with those of the related homobinuclear anions based upon [M2O7]2- (M = Cr, Mo, W). Particular emphasis was placed upon reactions relevant to gas-phase catalytic cycles described previously for oxidation of alcohols by [Mo2O6(OH)]- (Waters, T.; O'Hair, R. A. J.; Wedd, A. G. J. Am. Chem. Soc. 2003, 125, 3384-3396). The protonated anions [MM'O6(OH)]- each reacted with methanol with loss of water to form [MM'O6(OCH3)]- at a rate that was intermediate between those of [M2O6(OH)]- and [M'2O6(OH)]-. The butylated anions [MM'O6(OBu)]- were generated by collisional activation of the ion-pairs {Bu4N+ [MM'O7]2-}-. Collisional activation of [MM'O6(OBu)]- resulted in either the loss of butanal (redox reaction) or the loss of butene (elimination reaction), with the detailed nature of the observations depending on the nature of both M and M'. Selective 18O labeling indicated that the butoxo ligands of [CrMoO6(OBu)]- and [CrWO6(OBu)]- were located on molybdenum and tungsten, respectively. This structural insight allowed a more detailed comparison of reactivity with the homobinuclear species, and highlighted the importance of the neighboring metal center in these reactions.     

Ultraviolet radiation, vitamin D and risk of prostate cancer and other diseases

Most common diseases appear to result from complex, poorly understood interactions between genetic and environmental factors. Relatively few factors have been unequivocally linked with disease risk or outcome. Evidence from various studies using different experimental approaches has been interpreted as showing that, apart from its harmful effects on the pathogenesis of the common skin cancers, ultraviolet radiation (UVR) may exert a beneficial effect on development of various internal cancers and other pathologies. This concept is supported by parallel studies showing that hypovitaminosis D is linked with increased risk of various diseases including insulin resistance and multiple sclerosis. These findings suggest that, first, host factors such as skin pigmentation that affect UVR-induced synthesis of vitamin D and, second, polymorphism in genes that mediate the effectiveness of vitamin D action are susceptibility candidates for a variety of diseases. Collectively, these data suggest the hypothesis that, via effects on vitamin D synthesis, UVR exposure has beneficial effects on susceptibility and outcome to a variety of complex diseases. We describe evidence from studies in various diseases, but mainly from prostate cancer patients, that supports this hypothesis, but we emphasize that, although supportive data are available, the concept is unproven. Indeed, other explanations are possible. However, given the potentially important public health implications of the hypothesis and the potential for the development of novel therapeutic modalities, we believe the concept is worthy of further investigation.     

Metabonomics: the use of electrospray mass spectrometry coupled to reversed-phase liquid chromatography shows potential for the screening of rat urine in drug development

The application of liquid chromatography/mass spectrometry (LC/MS) followed by principal components analysis (PCA) has been successfully applied to the screening of rat urine following the administration of three candidate pharmaceuticals. With this methodology it was possible to differentiate the control samples from the dosed samples and to identify the components of the mass spectrum responsible for the separation. These data clearly show that LC/MS is a viable alternative, or complementary, technique to proton NMR for metabonomics applications in drug discovery and development.     

One‐Dimensional,Cofacial Porphyrin Polymers Formed by Self‐Assembly of meso‐Tetrakis(ERE Donor) Zinc(II) Porphyrins

A series of meso‐tetrakis‐(ERE donor) zinc(II) porphyrins n Zn (ERE donor=4‐R‐3,5‐bis[(E)‐methyl]phenyl; 1 Zn: E=NMe₂, R=Br; 2 Zn: E=NMe₂, R=H; 3 Zn: E=OMe, R=Br; 4 Zn: E=OMe, R=H) have been synthesized in excellent yields. As a result of the combination of a Lewis acidic site and eight Lewis basic sites within one molecule, monomeric molecules of n Zn self‐assemble to form one‐dimensional porphyrin polymers [ n Zn]_∞ in the solid state, as confirmed for 1 Zn and 3 Zn by X‐ray crystallography. The coordination environment around the zinc(II) ions in these polymers is octahedral. They are ligated by four equatorial nitrogen atoms of the porphyrin and two apical E atoms (E=N, O) provided by the EBrE donor groups of adjacent n Zn molecules. Complexes 2 Zn and 4 Zn did not form single crystals, but solid‐state UV/Vis analysis points to the formation of similar structures. Solution UV/Vis and ¹H NMR spectroscopy indicated that interactions between 1 Zn and 2 Zn monomers in the polymers are stronger than between 3 Zn and 4 Zn monomers. Interestingly, they also revealed that the presence of a neighboring bromine atom in the EBrE donor groups has a considerable influence on the coordination properties of the benzylic N or O atoms. The zinc(II) ions of the porphyrins most likely adopt only hexacoordination in the solid state, owing to the unique predisposition of Lewis acidic and basic sites in the n Zn molecules. Several parameters of the aggregates, for example, the interplanar separation between porphyrins and the zinc–zinc distances, change as a function of the coordinating E groups. The high degree of modularity in their synthesis makes these zinc(II) porphyrins an interesting new entry in noncovalent multiporphyrin assemblies.     

Matrix elements of the Coulomb Green function between Slater orbitals

Analytic expressions are given for integrals of the Coulomb Green function with Slater type atomic orbitals. The results involve hypergeometric functions.Supported by the National Institutes of Health, Grant No. GM23223.     

Preparation of polymer colloids by chemical reactions in aerosols. I. Poly(p-tertiarybutylstyrene)

A procedure was developed by which polymer colloids can be prepared by polymerizing aerosol droplets of monomers with an initiator in the vapor state. This work describes the formation of poly(p-tertiarybutylstyrene) particles by exposing the corresponding monomer droplets to trifluoromethanesulfonic acid. It was found that the monomer-to-initiator mass ratio is the critical factor in determining the uniformity and morphology of the particles. Under ideal conditions spheres of narrow size distribution are obtained. Otherwise porous particles or soft particles with whiskers may develop. The aerosol was prepared in a falling film generator, but other procedures for producing monomer droplets may be used.     

An NMR study of the rotational barriers in cobalt-stabilized carbocations: X-ray crystal structures of (η-C4Ph4)Co-(η-C5H4R), where R is CH3CO, CHO, CH(Bu)OH

Treatment of the aldehyde (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-CHO) (4b) with tert-butyllithium or phenyllithium yields the secondary alcohols (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-CH(R)OH), where R=tert-butyl (5) or phenyl (6). Protonation of 5 and 6 at −80 °C furnishes the deep purple, cobalt-stabilized cations, 7 and 8, respectively, both of which exhibit restricted rotation about the external C₅H₄-CHR⁺ linkage on the NMR time-scale. These data indicate a minimum value for the barrier to rotation of 15 kcal mol⁻¹, but it is certainly much higher, indicating a considerable degree of C-C double bond character. X-ray crystal structures of 4b, 5 and also of the ketone (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-C(O)CH₃ (4a) are reported. The secondary alcohol 5 exhibits disorder in the solid state because of the presence of diastereomers as a consequence of the stereogenic center at the α-carbon and the clockwise or anticlockwise propeller orientations of the tetraphenylcyclobutadiene ligand.     

Photophysical properties of a C6 hydrocarbon linked porphyrin dimer

The synthesis and characterisation of a C₆ hydrocarbon linked porphyrin dimer and its zinc complex is described. From fluorescence quantum yields and excited singlet and triplet state lifetimes, recorded for the dimers and the corresponding monomer species, it is suggested that the dimeric porphyrins exist in solution in open and closed conformations. The open conformations retain photophysical properties similar to those of the relevant monomeric species but the closed conformations do not fluoresce.     

Mediated amperometric biosensors for d-galactose,glycolate and l-amino acids based on a ferrocene-modified carbon paste electrode

Direct-current cyclic voltammetry is used to investigate the suitability of a ferrocene derivative as a mediator with galactose, glycolate and l-amino acid oxidases. The three enzymes coupled catalytically to ferrocene monocarboxylic acid exhibiting homogeneous second-order rate constants in the range 0.4 × 10⁵ to 8.5 × 10⁵ l mol^?1 s^?1. Enzyme electrodes which responded to d-galactose, glycolate or l-amino acids were constructed. The appropriate oxidase was retained behind a dialysis membrane at a carbon paste electrode containing the poorly soluble derivative 1,1′-dimethylferrocene. All the electrodes responded rapidly to millimolar concentrations of their respective substrates producing 95% of the steady-state current response in <2 min. This general method of biosensor construction should be widely applicable to oxidases and other oxidoreductase enzymes.     

Bismuth-catalyzed benzylic oxidations with tert-butyl hydroperoxide

[reaction: see text] Oxidation of alkyl and cycloalkyl arenes with tert-butyl hydroperoxide catalyzed by bismuth and picolinic acid in pyridine and acetic acid gave the corresponding benzylic ketones (48-99%). Alternatively, oxidation of methyl arenes gave the corresponding substituted benzoic acids (50-95%). Preliminary mechanistic studies were consistent with a radical mechanism rather than a bismuth(III)-bismuth(V) cycle.