TEM study on the pore structures of wide-pore silica and polymer gels

Internal structures of wide-pore packing materials for HPLC were studied by transmission electron microscopy (TEM). TEM gave information about the size, shape, and location of the pores as well as the size of primary structures in corpuscular systems. Visualization of the three dimensional internal structures of wide-pore materials was attempted by scanning the TEM photographs with a densitometer.     

Sulfoxidation on a SiO2-supported Ru complex using O2/aldehyde system

A site-isolated SiO(2)-supported Ru-monomer complex, whose structure was characterized by means of solid-state NMR, XPS, UV/vis, and Ru K-edge EXAFS, was found to be efficient for sulfoxidation using an O(2)/aldehyde system. Significant enhancement of sulfoxidation rates was observed on the SiO(2)-supported Ru complex for various sulfide derivatives.     

G protein subtype specificity of rhodopsin intermediates metarhodopsin Ib and metarhodopsin II

Rhodopsin is one of the members of the G protein-coupled receptor family that can catalyze a GDP–GTP exchange reaction on the retinal G protein transducin (Gt) upon photon absorption. There are at least two intermediate states, meta-Ib and meta-II, which exhibit direct interaction with Gt. Meta-Ib binds to GDP-bound Gt, while meta-II forms a complex with Gt having no nucleotide, suggesting that meta-Ib is a state that initially interacts with Gt. Here we investigated whether or not meta-Ib exhibits specific interaction with G protein similar to meta-II, by examining the binding efficiencies of meta-Ib and meta-II to Giα and its mutants whose C-terminal 11 amino acids were replaced with those of Goα, Gqα and Gsα. The affinity of meta-Ib to the C-terminal 11 amino acids of Gtα was similar to those of Giα and its mutant with Goα's C-terminal 11 amino acids, whereas meta-II exhibited affinity to the C-terminal 11 amino acids of Giα mutant with Goα's C-terminal 11 amino acids about half of what was seen for Gtα and Giα. Both intermediates exhibited no affinity to the Giα mutants containing the C-terminal 11 amino acids of Gqα and Gsα. These results suggested that meta-Ib is the state that exhibits specific interaction with G protein as meta-II does, although meta-Ib exhibits a slightly lenient binding selectivity compared to that of meta-II.     

Electrooxidative simulation of stereoselectivity in microsomal allylic hydroxylation

A comparison of the stereochemistry of liver microsomal γ-hydroxylation of some cyclic α, β-unsaturated ketones with that of electrochemical γ-acetoxylation of the corresponding dienol esters and with that of peracid oxidation of the dienol esters has been carried out.     

Water dependence of the HO2 self reaction: kinetics of the HO2-H2O complex

Transient absorption spectra and decay profiles of HO2 have been measured using cw near-IR two-tone frequency modulation absorption spectroscopy at 297 K and 50 Torr in diluent of N2 in the presence of water. From the depletion of the HO2 absorption peak area following the addition of water, the equilibrium constant of the reaction HO2 + H2O <--> HO2-H2O was determined to be K2 = (5.2 +/- 3.2) x 10(-19) cm3 molecule(-1) at 297 K. Substituting K2 into the water dependence of the HO2 decay rate, the rate coefficient of the reaction HO2 + HO2-H2O was estimated to be (1.5 +/- 0.1) x 10(-11) cm3 molecule(-1) s(-1) at 297 K and 50 Torr with N2 as the diluent. This reaction is much faster than the HO2 self-reaction without water. It is suggested that the apparent rate of the HO2 self-reaction is enhanced by the formation of the HO2-H2O complex and its subsequent reaction. Results are discussed with respect to the kinetics and atmospheric chemistry of the HO2-H2O complex. At 297 K and 50% humidity, the concentration ratio of [HO2-H2O]/[HO2] was estimated from the value of K2 to be 0.19 +/- 0.11.     

Determination of low-pressure crystalline--liquid phase boundary of SnI(4)

The location of the liquidus in the low-pressure crystalline phase of SnI(4) was determined utilizing in situ x-ray diffraction measurements under pressures up to approximately 3.5 GPa. The liquidus is not well fitted to a monotonically increasing curve such as Simon's equation, but breaks near 1.5 GPa and then becomes almost flat. The results are compared to those from molecular dynamics simulations. Ways to improve the model potential adopted in the simulations are discussed.     

Stationary phase structures enhancing electroosmotic flow in capillary electrochromatography

Several chemically bonded silicas with C18 groups were examined with respect to electroosmotic flow (EOF) velocities under CEC conditions. Stationary phases with low hydrophobic selectivity generally provided high EOFs. The stationary phases prepared by using octadecyltrichlorosilane showed greater EOF than those from octadecyldimethylchlorosilane. Restricted-access reversed-phase (RARP) packing materials having C18 groups inside the pores and silanols on the external surfaces showed higher EOF than monomeric C18 phases with similarly high hydrophobic selectivity. The RARP-type structure having silanols at the external surface seems to be effective for increasing EOF while maintaining the hydrophobic character of the solute binding sites.     

Development of the reaction time accelerating molecular dynamics method for simulation of chemical reaction

We present a novel and efficient method to integrate chemical reactions into molecular dynamics to simulate chemical reaction systems. We have dubbed this method RTAMD, an acronym for reaction time accelerating molecular dynamics. The methodology we propose here requires no more than the knowledge of the empirical intermolecular potentials for the species at play as well as the elementary reaction path among them. Bond formation during the simulation is performed by changing the inter-atomic potentials from those of the non-bonded species to those of the bonded ones, and a reaction is deemed to occur by the distance separating the bond forming atoms. In this way the energy barrier for a reaction is no longer considered; the estimation of the reaction rate, however, is possible by introducing the principles of the transition state theory. The simplicity of the present scheme to simulate chemical reactions enables it to be used in large-scale MD simulations involving a large number of simultaneous chemical reactions and to evaluate kinetic parameters. In this paper, the basic theory of the method is presented and application to simple equiatomic reaction system where the reaction rates were estimated was illustrated.