Effects of electron beam preirradiation on the γ radiolysis of polyethylene

The γ radiolysis of polyethylene preirradiated with electron beams to 3 Mrad was carried out at 30–100°C in vacuo with a dose rate of 6.35 × 10⁵ rad/hr. The hydrogen formation in the γ radiolysis was little affected by the preirradiation of electron beams, whereas the formation of trans-vinylene unsaturation and gel was somewhat retarded. The rates of the formation of hydrogen and trans-vinylene unsaturation were described by the zero-order formation kinetics with respect to each concentration combined with the first-order disappearance. The apparent rate constants and activation energies for the formation and disappearance of hydrogen and trans-vinylene unsaturation were almost independent of the preirradiation. The gel fraction was analyzed by using the Charlesby–Pinner equation. The G values of crosslinking and main chain scission were increased by the preirradiation, whereas their activation energies remained unaltered. On the basis of these results the effects of preirradiation on the reactions induced by γ rays in polyethylene were discussed.     

Optimal control of ultrafast cis-trans photoisomerization of retinal in rhodopsin via a conical intersection

Optimal control simulation is applied to the cis-trans photoisomerization of retinal in rhodopsin within a two-dimensional, two-electronic-state model with a conical intersection [S. Hahn and G. Stock, J. Phys. Chem. B 104, 1146 (2000)]. For this case study, we investigate coherent control mechanisms, in which laser pulses work cooperatively with a conical intersection that acts as a "wave-packet cannon." Optimally designed pulses largely consist of shaping subpulses that prepare a wave packet, which is localized along a reaction coordinate and has little energy in the coupling mode, through multiple electronic transitions. This shaping process is shown to be essential for achieving a high target yield although the envelopes of the calculated pulses depend on the local topography of the potential-energy surfaces around the conical intersection and the choice of target. The control mechanisms are analyzed by considering the motion of reduced wave packets in a nuclear configuration space as well as by snapshots of probability current-density maps.     

Crystal structure of cobalt molybdate hydrate CoMoO4·nH2O

We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of , , , α=76.617°, β=84.188°, γ=74.510° and space group . The crystal structure suggests the chemical formula CoMoO₄·3/4H₂O. The structure consists of MoO₄ tetrahedra and CoO₆ octahedra, confirming the earlier X-ray absorption near-edge spectroscopic (XANES) investigation on the hydrate. The comparison of the crystal structures of the hydrate and the α-,β-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the β-phase, but had arrangements of CoO₆ and MoO_n polyhedra similar to those of the hp-phase.     

Development of novel chiral urea catalysts for the hetero-Michael reaction

Chiral urea compounds 10a-g were synthesized as catalysts for conjugate addition of pyrrolidine (2) to gamma-crotonolactone (3). In the presence of a catalytic amount of the chiral ureas, this hetero-Michael reaction was greatly accelerated. Asymmetric induction was observed with the catalysts 10e, 10f, and 10g.     

Hydrophobic indicators for two-phase titrations and their application to the determination of silver and pentachlorophenol

The hydrophobic dyes tetrabromophenolphthalein ethyl ester and 2,6-dichlorophenolindo-phenol are proposed as visual indicators for two-phase titrations. The aqueous phase is colourless throughout the titration and these indicators make it possible to detect the end-point of the titration by the colour of one or the other phase. The indicators allow the two-phase titration of the silver(I)-1,10-phenanthroline complex with tetraphenylborate and of pentachlorophenol with tetraphenylphosphonium chloride.