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.     

Poly(L‐histidine) with several aminoethyl groups for a new pH‐sensitive DNA carrier

In this study, poly(L ‐histidine) with several aminoethyl groups, i.e. aminated poly(L ‐histidine), is reported to be able to make complexes with DNA and to transfect cells in vitro in the presence of serum. The present study was performed to determine whether the pH of the medium had an influence on the complex formation with DNA, on the cell membrane fusion activity and on the transfection efficiency. Agarose gel retardation assays proved that the polyion complex formation of the aminated poly(L ‐histidine) with DNA was affected by pH of the medium, owing to the basicity (protonation–deprotonation) of the imidazole groups with a pK_a value around 6.0. Hemolysis assay showed that the resulting DNA complex enhanced membrane disruptive ability at endosomal pH. The aminated poly(L ‐histidine) gene carrier demonstrated significant transfection efficacy which was decreased by the inclusion of chloroquine as an endosomolytic agent. These results suggest that the aminated poly(L ‐histidine) promises to be a new pH‐sensitive DNA carrier for endosomal escape. Copyright © 2005 John Wiley & Sons, Ltd.     

Spherical turbulent flame propagation of pulverized coal particle clouds in an O2/N2 atmosphere

The present study aims to clarify the effects of turbulence intensity and coal concentration on the spherical turbulent flame propagation of a pulverized coal particle cloud. A unique experimental apparatus was developed in which coal particles can be dispersed homogeneously in a turbulent flow field generated by two fans. Experiments on spherical turbulent flame propagation of pulverized coal particle clouds in a constant volume spherical chamber in various turbulence intensities and coal concentrations were conducted. A common bituminous coal was used in the present study. The flame propagation velocity was obtained from an analysis of flame propagation images taken using a high-speed camera. It was found that the flame propagation velocity increased with increasing flame radius. The flame propagation velocity increases as the turbulence intensity increases. Similar trends were observed in spherical flames using gaseous fuel. The coal concentration has a weak effect on the flame propagation velocity, which is unique to pulverized coal combustions in a turbulent field. These are the first reports of experimental results for the spherical turbulent flame propagation behavior of pulverized coal particle clouds. The results obtained in the present study are obviously different from those of previous pulverized coal combustion studies and any other results of gaseous fuel combustion research.     

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.     

Thermoreversible Contraction and Extension of Layer Spacing in Smectic Phase of Side Chain Liquid Crystal Poly(fumarate)s

Two types of liquid crystal poly(fumarate)s having cyanobiphenyl mesogen in side chain were prepared by radical polymerization of disubstituted fumarate monomers in bulk. The mesogen is thus connected via alkyl spacer to every carbon atom in the main chain. The liquid crystalline temperature range expands with an increase in the molecular weight and with alkyl chain spacer length. The poly(fumarate)s form a smectic A_d phase whose layer spacing decreases and increases on heating and cooling, respectively. The contraction ratio is up to 15.2%. This significantly large change in the layer spacing corresponds to temperature dependence of the orientational order parameter. It may be connected to high density of the mesogen hanging from the main chain.