A library approach to the generation of bisubstrate analogue sulfotransferase inhibitors

[reaction: see text]. A library of potential bisubstrate analogue inhibitors (1) targeting sulfotransferase enzymes was generated by the chemoselective ligation of the PAPS mimic 2 with a panel of 447 aldehydes. Preliminary screening has identified compounds that inhibit estrogen sulfotransferase (EST), an enzyme relevant to breast cancer.     

Spontaneous Stepwise Self‐Assembly of a Polyoxometalate–Organic Hybrid into Catalytically Active One‐Dimensional Anisotropic Structures

An inorganic–organic hybrid surfactant with a hexavanadate cluster as the polar head group was designed and observed to assemble into micelle structures, which further spontaneously coagulate into a 1D anisotropic structure in aqueous solutions. Such a hierarchical self‐assembly process is driven by the cooperation of varied noncovalent interactions, including hydrophobic, electrostatic, and hydrogen‐bonding interactions. The hydrophobic interaction drives the quick formation of the micelle structure; electrostatic interactions involving counterions leads to the further coagulation of the micelles into larger assemblies. This process is similar to the crystallization process, but the specific counterions and the directional hydrogen bonding lead to the 1D growth of the final assemblies. Since most of the hexavanadates are exposed to the surface, the 1D assembly with nanoscale thickness is a highly efficient heterogeneous catalyst for the oxidation of organic sulfides with appreciable recyclability.     

Piano hammers and their force compression characteristics: does a power law make sense?

We have studied the force characteristics of a collection of piano hammers, through studies of the acceleration of the hammer head, the force due to the compression of the hammer felt, Fh, and the associated bending of the hammer shank which occurs when a hammer strikes a rigid object. By integration of the acceleration one can estimate the compression of the felt, and thus obtain a force-compression Fh(z) relationship; our results for this function are compared with previous experiments and theoretical models. Close examination of our findings suggests that bending of the hammer shank, and also the time required for the force to be transmitted from the outer edge of the hammer to its core, play significant roles in the hammer dynamics. The data are used to estimate the quantitative impact of these effects on the derived Fh(z) relation. The implications for physical modeling of a piano tone are briefly discussed.     

Oxidative dehydrogenation of cyclohexene on size selected subnanometer cobalt clusters: improved catalytic performance via evolution of cluster-assembled nanostructures

The catalytic activity of oxide-supported metal nanoclusters strongly depends on their size and support. In this study, the origin of morphology transformation and chemical state changes during the oxidative dehydrogenation of cyclohexene was investigated in terms of metal-support interactions. Model catalyst systems were prepared by deposition of size selected subnanometer Co(27±4) clusters on various metal oxide supports (Al(2)O(3), ZnO and TiO(2) and MgO). The oxidation state and reactivity of the supported cobalt clusters were investigated by temperature programmed reaction (TPRx) and in situ grazing incidence X-ray absorption (GIXAS) during oxidative dehydrogenation of cyclohexene, while the sintering resistance monitored with grazing incidence small angle X-ray scattering (GISAXS). The activity and selectivity of cobalt clusters shows strong dependence on the support. GIXAS reveals that metal-support interaction plays a key role in the reaction. The most pronounced support effect is observed for MgO, where during the course of the reaction in its activity, composition and size dynamically evolving nanoassembly is formed from subnanometer cobalt clusters.     

速度算符和电子的颤动

指出了国外某些量子力学教材中关于速度算符的概念错误和相对论自由电子进行颤动的错误,分析了错误的原因.     

Solvent venting interface for capillary gas chromatography and a microwave-induced plasma

A solvent venting system for capillary gas chromatography coupled with a microwave-induced plasma detector was constructed and evaluated. The solvent vent is based on a fluid logic system within the plasma containment tube. During solvent elution, the column effluent is routed to waste and does not pass through the plasma. During analyte elution, the fluid logic system is used to direct the analytes through the plasma for detection. Because the system has no transfer line, problems associated with interface dead volume and analyte degradation reaction due to reactive sites in the transfer line are eliminated. Switching from the vent-on to the vent-off mode is rapid and does not affect plasma stability or flow through the chromatographic column. The baseline shift during switching is negligible. The solvent venting system is simple and easily constructed. Design details are presented and chromatographic results are evaluated.     

Small molecule inhibitors of mucin-type O-linked glycosylation from a uridine-based library

The polypeptide N-acetyl-alpha-galactosaminyltransferases (ppGalNAcTs, also abbreviated ppGaNTases) initiate mucin-type O-linked glycosylation and therefore play pivotal roles in cell-cell communication and protection of tissues. In order to develop new tools for studying mucin-type O-linked glycosylation, we screened a 1338 member uridine-based library to identify small molecule inhibitors of ppGalNAcTs. Using a high-throughput enzyme-linked lectin assay (ELLA), two inhibitors of murine ppGalNAcT-1 (K(I) approximately 8 microM) were identified that also inhibit several other members of the family. The compounds did not inhibit other mammalian glycosyltransferases or nucleotide sugar utilizing enzymes, suggesting selectivity for the ppGalNAcTs. Treatment of cells with the compounds abrogated mucin-type O-linked glycosylation but not N-linked glycosylation and also induced apoptosis. These uridine analogs represent the first generation of chemical tools to study the functions of mucin-type O-linked glycosylation.     

Small-angle X-ray studies of soot inception and growth

The high spectral intensity of X-rays produced by the undulator at the Basic Energy Sciences Synchrotron Radiation Center of Argonne's Advanced Photon Source has allowed us to perform small-angle X-ray scattering (SAXS) studies of the initial distribution of soot particles formed by various fuels. SAXS provides an in situ probe of the morphology of soot in the region between 1 and 100 nm and complements the ex situ technique of electron microscopy. The basic aspects of SAXS and its potential are illustrated with measurement on a laminar flame of acetylene in air. The more complex fuel toluene has been studied in a flat-flame burner that supports a CH4/H2/air or CO/H2/air diffusion flame stabilized by N2 co-flow. This burner produces a nearly constant temperature region above the flame where the pyrolysis and combustion of the heavier fuels occurs. Kinetic information is obtained by performing measurements of the scattered intensity profile as a function of the height above the burner. These profiles have been reduced to give the mean radius and dispersion of a distribution of spherical particles. Mean radii between 0.8 and 18 nm have been observed. The smallest of these is a factor of ten smaller than previously detected with Lorentz-Mie scattering. Near 1550 K, the soot distribution found in toluene shows a distinct step behavior that is consistent with model calculations.