Novel gold dendritic nanoflowers deposited on titanium nitride for photoelectrochemical cells

This study demonstrates the elaboration of a novel composite comprising gold dendritic nanoflowers (Au DNFs)/titanium nitride (TiN)/silicon (Si); this composite can be used for methanol oxidation reactions in alkaline electrolytes. Cyclic voltammograms showed that a thick (650 nm) Au DNFs/TiN/Si (L-DNFs-TiN) composite had double the oxidation current density of a thick (800 nm) Au DNFs/Si (L-DNFs-Si) composite in the presence of light illumination, whereas the oxidation current density for a thin (250 nm) Au DNFs/Si (S-DNFs-Si) composite and Au nanoparticles could not be determined. Chronoamperometry (CA) testing indicated that the L-DNFs-TiN could absorb light illumination more effectively than the L-DNFs-Si did. These results correspond to the broadband light absorption of TiN. Testing with continuous cyclic on/off light illumination showed a repeatable performance in CA, indicating that the proposed L-DNFs-TiN composite can be applied in photoelectrochemical cells in the future.     

An Improved Synthesis for Novel Hexaruthenium Cluster Compound Bearing Two Quadruply-Bridging CO Ligands: Synthesis, Characterization, and X-Ray Structural Analysis of Ru6(CO)12(μ3-H)(μ-CO) (μ4-η2-CO)2[η5-C5H4(SiMe3)]

The hexaruthenium cluster compound Ru₆(₃-H)(CO)₁₅[C₅H₄(SiMe₃)] (2), possessing two ₄-²-CO ligands and with the Ru[C₅H₄(SiMe₃)] fragment located at the apex of the central tetrahedral framework, was prepared in low yield by refluxing a toluene solution of C₅H₅(SiMe₃) with excess Ru₃(CO)₁₂. This unique complex was characterized by spectroscopic methods and by X-ray structural analysis. The possible mechanism leading to its formation is discussed.     

Grignard reagent-promoted selective ring expansion and alkylation of formyl borneol and isoborneol: a new route to highly substituted cyclopentanes

Formyl borneol, a [2.2.1]-bicyclic carbinol, reacts with various Grignard reagents to produce corresponding alkyl [3.2.1]-bicyclic diols, which can be converted to new highly substituted cyclopentanes, and further to 3-acyl-bornylenes. These ring expansion-alkylation reactions are highly selective. Reaction of formyl isoborneol with methyl magnesium bromide gave ring expansion-only and alkylation-only products.     

Control of particle size distribution of CdS quantum dots in gel matrix

A novel sol-gel process has been developed to prepare nano-sized CdS quantum dots to improve the nonlinear optical properties. A bifunctional ligand, 3-aminopropyl triethoxysilane H₂N(CH₂)₃Si(OC₂H₅)₃, was used to disperse the Cd²⁺ ions in the gel solution. The CdO and CdS particles were observed by transmission electron microscope (TEM). The size of CdS microcrystallites with concentrations up to 13 wt.% in SiO₂ gel matrix was found to be in the range of 2–4 nm with a very sharp size distribution. A well-defined absorption edge was observed in the absorption spectrum.     

Molecular shuttles based on tetrathiafulvalene units and 1,5-dioxynaphthalene ring systems

Six different degenerate [2]rotaxanes were synthesized and characterized. The rotaxanes contained either two tetrathiafulvalene (TTF) units or two 1,5-dioxynaphthalene (DNP) ring systems, both of which serve as recognition sites for a cyclobis(paraquat-p-phenylene) (CBPQT4+) ring. Three different spacer units were incorporated into the dumbbell components of the [2]rotaxanes between the recognition sites. They include a polyether chain, a terphenyl unit, and a diphenyl ether linker, all of which were investigated in order to probe the effect of the spacers on the rate of the shuttling process. Data from dynamic 1H NMR spectroscopy revealed a relatively small difference in the DeltaG++ values for the shuttling process in the [2]rotaxanes containing the three different spacers, in contrast to a large difference between the TTF-containing rotaxanes (18 kcal mol(-1)) and the DNP-containing rotaxanes (15 kcal mol(-1)). This 3 kcal mol(-1) difference is predominantly a result of a ground-state effect, reflecting the much stronger binding of TTF units to the CBPQT4+ ring in comparison with DNP ring systems. An examination of the enthalpic (DeltaH++) and entropic (DeltaS++) components for the shuttling process in the DNP-containing rotaxanes revealed significant differences between the three spacers, a property which could be important in designing new molecules for incorporation into molecular electronic and nanoelectromechanical (NEMs) devices.     

Phosphoproteomic analysis with a solid-phase capture-release-tag approach

A comprehensive study of global phosphorylation events in biological systems is critical. We report a chemistry-based capture-release-tag method for isolation of complex phospho-Ser/Thr-containing peptides by liquid beta-elimination combined with solid-phase Michael addition. The free thiol groups of 6-(mercapto-acetylamino)-hexanoic acid functionalized resin are used as immobilized Michael donors to capture dehydro-serine/threonine peptides. After an acid-mediated release step, phospho-peptides are labeled with a 6-(2-mercapto-acetylamine)-hexanoic amide tag at phosphorylated sites. We applied this method to analyze the phosphorylation status of microtubule-associated proteins. We find that a CDK5 substrate microtubule-associated protein 2 (MAP2) is phosphorylated on residues that are within a homologous region of Tau. The chemical method corroborates previous results and suggests that Tau and MAP2 may contain a CDK5 phosphorylation motif.     

DpgC is a metal- and cofactor-free 3,5-dihydroxyphenylacetyl-CoA 1,2-dioxygenase in the vancomycin biosynthetic pathway

3,5-Dihydroxyphenylglycine is a crucial amino acid monomer in the nonribosomal glycopeptide antibiotic vancomycin. This nonproteinogenic amino acid is constructed from malonyl-CoA by a set of four enzymes, DpgA-D, in the biosynthetic cluster. DpgC is an unusual metal-free, cofactor-free enzyme that consumes O(2) during the conversion of 3,5-dihydroxyphenylacetyl-CoA (DPA-CoA) to the penultimate intermediate 3,5-dihydroxyphenylglyoxylate (DPGx). We show that in anaerobic incubations, DpgC catalyzes the exchange of the C(2)-methylene hydrogens of DPA-CoA at unequal rates, consistent with enzyme-mediated formation of the substrate-derived C(2)-carbanion as an early intermediate. Incubations with (18)O(2) reveal that DpgC transfers both atoms of an O(2) molecule to DPGx product. This establishes DpgC as a 1,2-dioxygenase that mediates thioester cleavage by the oxygen transfer process. These results are consistent with a DPA-CoA C(2)-peroxy intermediate, followed by enzyme-directed alpha-peroxylactone formation and collapse by O-O bond cleavage.     

Derivation of analytical expressions for the electrical potential distribution in lipid structures

The electrical potential inside a lipid structure, which is described by a modified Poisson-Boltzmann equation in the literature (Borukhov et al. Electrochim. Acta 2000, 46, 221), is solved, taking into account the effects of ionic sizes. Here, a micelle comprises an ionic surfactant layer and an aqueous core; the dissociation of the former yields a charged surface. The governing equation, which was solved numerically in a previous study for spherical geometry (Hsu et al. J. Phys. Chem. B 2003, 107, 14429), is solved analytically in this study for planar, cylindrical, and spherical geometries. The analytical results obtained are readily applicable for the evaluation of the spatial distributions of counterions inside a lipid structure. We show that if the linear size of a reverse micelle is fixed, the degree of dissociation of the surfactant layer follows the order planar > cylindrical > spherical.