Size effect of gold nanoparticles supported on carbon nanotube as catalysts in selected organic reactions

Carbon nanotube-supported gold nanoparticles of different sizes (diameter of 3 or 20 nm) were evaluated as catalysts in four selected organic transformations. The nanohybrids were shown to efficiently catalyze the investigated reactions, regardless of the size of the supported gold nanoparticles. However, some differences were observed as regards turnover frequency values although size effect turned out to be less significant when only gold surface atoms were considered.     

Automated quantum mechanical total line shape fitting model for quantitative NMR-based profiling of human serum metabolites

An automated quantum mechanical total line shape (QMTLS) fitting model was implemented for quantitative nuclear magnetic resonance (NMR)-based profiling of 42 metabolites in ultrafiltrated human serum samples. Each metabolite was described by a set of chemical shifts, J-couplings, and line widths. These parameters were optimized for each metabolite in each sample by iteratively minimizing the difference between the calculated and the experimental spectrum. In total, 92.0 to 98.1 % of the signal intensities in the experimental spectrum could be explained by the calculated spectrum. The model was validated by comparison to signal integration of metabolites with isolated signals and by means of standard additions. Metabolites present at average concentration higher than 50 μM were quantified with average absolute relative error less than 10 % when using different initial parameters for the fitting procedure. Furthermore, the biological applicability of the QMTLS model was demonstrated on 287 samples from an intervention study in 37 human volunteers undergoing an exercise challenge. Our automated QMTLS model was able to cope with the large dynamic range of metabolite concentrations in serum and proved to be suitable for high-throughput analysis.

N2 hydrogenation from activated end-on bis(indenyl) zirconium dinitrogen complexes

Sodium amalgam reduction of the bis(indenyl)zirconium dihalide complexes, (eta5-C9H5-1-iPr-3-Me)2ZrX2 (X = Cl, Br, I), yielded the corresponding end-on dinitrogen complexes, [(eta5-C9H5-1-iPr-3-Me)2Zr(NaX)]2(mu2, eta1, eta1-N2), with inclusion of 1 equiv of salt per zirconocene. The solid state structures of the chloro and iodo congeners establish short Zr N and elongated N N bonds, consistent with modest to strong activation of the coordinated dinitrogen molecule. Exposure of the N2 compounds to 1 atm of dihydrogen resulted in rapid N H bond formation to yield a hydrido zirconocene hydrazido compound concomitant with salt elimination. These studies establish a new structural type of zirconocene dinitrogen complex and demonstrate that side-on coordination of the N2 ligand in the ground state is not a prerequisite for dinitrogen hydrogenation.     

Self-assembled zinc chlorin rod antennae powered by peripheral light-harvesting chromophores

The multichromophoric dyads 1, 2 and triad 3 have been synthesized by coupling of the appropriately functionalized chlorin derivative with naphthalene diimide dyes through esterification, and subsequent metalation of the chlorin center with zinc acetate. The self-assembly properties of naphthalene diimide (NDI)-zinc chlorin (ZnChl) dyads 1, 2 and triad 3 have been studied in nonpolar, aprotic solvents by UV-vis, CD, and steady-state emission spectroscopy, revealing formation of rod-like structures by noncovalent interactions of zinc chlorin units, while the appended naphthalene diimide dyes do not aggregate at the periphery of the rod antennae. In all these systems, photoexcitation of the enveloping naphthalene diimides at 540 and 620 nm, respectively, leads to highly efficient energy-transfer processes (FRET; phiET > or = 0.99) to the inner zinc chlorin backbone, as explored by time-resolved fluorescence spectroscopy on the picosecond time scale. The efficiencies of zinc chlorin rod aggregates for the harvesting of solar light are markedly increased from 26% for dyad 2 up to 63% for triad 3, compared to the LH capacity of the monochromophoric aggregates of model system ZnChl 6a. Thus, with the self-assembled zinc chlorin rod antenna based on triad 3, a highly efficient artificial LH system has been achieved.     

Supramolecular self-assembly of amphiphiles on carbon nanotubes: a versatile strategy for the construction of CNT/metal nanohybrids, application to electrocatalysis

Homogeneous coating of carbon nanotubes with metallic nanoparticles was achieved using supramolecular auto-organization of amphiphilic molecules as template. The resulting Pd nanoparticles/carbon nanotube nanohybrids were then evaluated in electrocatalysis experiments, showing superior activity in ethanol oxidation compared to analogous systems.     

Synthesis and properties of propene copolymers with ether comonomers

The direct copolymerization of propene with polar comonomers using metallocene catalysts in solution was investigated. As comonomers, two ether compounds were used in comparison to 10-undecene-1-ol as well-investigated comonomer. The ether comonomers were diethylene glycol mono-10-undecenyl ether (DEGUE) and octaethylene glycol-10-undecenyl methyl ether (OEGUME). The influence of the different comonomers on the copolymerization behavior was studied. The copolymers were characterized with respect to their comonomer contents, molar masses, and thermal properties. The incorporation rate of DEGUE and OEGUME into the propene copolymers did not exceed 1.6 mol% for DEGUE and 0.31 mol% for OEGUME and was thus considerably lower than in the reference propene copolymerization with 10-undecene-1-ol. An uncompleted shielding of the oxygen atoms of the ether groups by triisobutyl aluminum (TIBA) to the metallocene catalyst is assumed to be responsible for this behavior. The crystallization kinetics in the copolymers with comparable molar masses is mainly influenced by the side chain density per 1000 propene units, n₁₀₀₀.The incorporation of hydrophilic comonomers into polypropene was expected to alter the surface properties. The slightly lowered water contact angles found on films of copolymers with higher comonomer content indicated the enhanced hydrophilicity of the polypropene copolymer surfaces compared to polypropene (PP).     

Enzymatic synthesis of tumor-associated carbohydrate antigen Globo-H hexasaccharide

We report the enzymatic synthesis of an important tumor-associated carbohydrate antigen, Globo-H hexasaccharide. Starting with Lac-OBn as the initial acceptor, this approach employs three glycosyltransferases: LgtC, an alpha1,4-galactosyltransferase; LgtD, a bifunctional beta1,3-galactosyl/beta1,3-N-acetylgalactosaminyltransferase; and WbsJ, an alpha1,2-fucosyltransferase. In addition, two epimerases, GalE and WbgU, were also employed for the generation of more expensive sugar nucleotides, UDP-Gal and UDP-GalNAc, from their corresponding inexpensive C4 epimers. This study represents a facile enzymatic synthesis of the Globo-H antigen.