Shigenobu Yamanaka

Gelation of tamarind seed polysaccharide xyloglucan in the presence of ethanol

Abstract Tamarind seed polysaccharide xyloglucan undergoes thermoreversible gelation in the presence of ethanol. Its gel–sol transition process was observed by time-resolved small-angle X-ray scattering, and the results were analyzed by assuming two phases composed of random aggregates and of single chains. The analysis has revealed that the complete dissolution of aggregates corresponds to the gel–sol transition. Here the cross-linking domain seems to be composed of random aggregates and has no ordered structure.

Photophysics and photochemistry of nitroanthracenes. Part 2. Primary process in the photochemical reaction of 9-nitroanthracene studied by steady-state photolysis and laser photolysis

From measurements of phosphorescence and triplet–triplet absorption spectra of the lowest excited triplet ππ* state of 9-nitroanthracene (NA) together with the absorption spectrum of 9-anthryloxy radical, it is concluded that photolysis of 9-nitroanthracene gives rise to the nitro → nitrite rearrangement for a higher excited triplet state of nπ* character, followed by the cleavage of 9-anthryl nitrite to 9-anthryloxy radical and nitrogen(II) oxide, yielding 9-anthrol (and anthrone), 10,10′-bianthrone and 9-nitrosoanthrone in ethanol; and 10,10′-bianthrone and 9-nitrosoanthrone in benzene. Hence, the primary process in the photochemical reaction of NA is essentially identical with those of 9-benzoyl-10-nitroanthracene and 9-cyano-10-nitroanthracene except that no 10,10′-bianthrone derivatives are formed.

Photophysics and photochemistry of nitroanthracenes. Part 1.—Primary processes in the photochemical reactions of 9-benzoyl-10-nitroanthracene and 9-cyano-10-nitroanthracene studied by steady-state photolysis and nanosecond laser photolysis

The genuine phosphorescence spectra of the title compounds (XNA) have been clearly observed at 77 K in EPA (diethyl ether–isopentane–ethanol 5 : 5 : 2 volume ratio). Also, the time-resolved absorption spectra obtained at the end of nanosecond laser pulse at 77 K (in EPA) and at room temperature (in ethanol and benzene) have been ascribed to the superposition of the absorptions of the lowest triplet XNA [3XNA(T1)] on those of the corresponding anthryloxy radicals (XAO˙). The decay of 3XNA(T1) is not accompanied by the formation of XAO˙ and the following results are obtained. (1) In ethanol at room temperature, the first-order decay of XAO˙ corresponds to hydrogen-atom abstraction by XAO˙ from the solvent, giving rise to the formation of corresponding anthrols (XAOH), while the second-order reaction of XAO˙ with nitrogen(II) oxide (NO˙) yields the corresponding nitrosoanthrones (XNSAN) which decompose very slowly into XAO˙ and NO˙ followed by the rapid formation of XAOH. (2) In benzene at room temperature no formation of XAOH is observed, but there exists an equilibrium between XAO˙(+NO˙) and XNSAN. All these results support our previous conclusion that the nitro → nitrite rearrangement of XNA does not occur for the lowest triplet states of ππ* character but does occur for the higher triplet states of nπ* character, followed by the cleavage of the nitrites to XAO˙ and NO˙.

Polysiloxane network formation observed by time-resolved small-angle X-ray scattering

Abstract Time-resolved small-angle X-ray scattering was observed on systems undergoing gelation. A polysiloxane network was used as a model system, where the polysiloxane network was formed by hydrosylation of VT-M with F4-C. The Flory-Stockmayer model for gelation was found to be satisfactory to describe the polysiloxane network formation. No inhomogeneous distribution of densely crosslinked region exists, and in this respect the gel formed by the polysiloxane network is homogeneous. The invariance of the correlation length ξ evaluated from the Lorenzian term suggests that the local network architecture would not change by gelation.

Temperature dependence of single particle dynamics of flexible liquid tetrachloromethane using molecular dynamics simulation

Abstract A molecular dynamics (MD) simulation, which includes all degrees of freedom of atomic motion, has been carried out in order to investigate the temperature dependence of single particle dynamics such as translational and reorientational motions of liquid tetrachloromethane (CCl 4 ). The translational diffusion coefficients D and first and second rank reorientational correlation times τ lR ( l = 1, 2) of liquid CCl 4 are simulated at three temperatures. Both motions are characteristics of the typical molecular liquids, and these simulated D and τ lR values and their activation energies are close to the experimental ones. The Stokes-Einstein-Debye (SED) equations, which are based on a hydrodynamics model, have also been checked for the D and τ lR values with changing the temperatures. It has been found that the SED equations hold for both values, and the hydrodynamical model is effective for the simulated liquid CCl 4 .