Masao Yamamoto

Fluorescence label studies of thermo-responsive poly(N-isopropylacrylamide) hydrogels

Abstract Temperature-induced phase transitions and microenvironment of poly(N-isopropylacrylamide) (PNIPAM) hydrogels were studied in water using 9-(4-N,N-dimethylaminophenyl)phenanthrene (DP) as an intramolecular fluorescence probe. Fluorescence behavior of the DP-labeled PNIPAM gels depended on the conditions of the gel preparation such as concentrations of monomer and crosslinker. Thermo-responsive behavior of the PNIPAM gel was affected by copolymerization of NIPAM with a hydrophilic monomer N,N-dimethylacrylamide (DMAM) and a hydrophobic monomer methyl methacrylate (MMA). Incorporation of DMAM raised the lower critical solution temperature (LCST) of the PNIPAM gel, and that of MMA lowered it. Obtained results indicate that the NIPAM–DMAM copolymer gels with higher LCST are of a more open, water-swollen nature above their LCST and the NIPAM–MMA copolymer gels with lower LCST are of a less open, water-shrunken nature below their LCST than that of the NIPAM homopolymer gel.

Fluorescence probe studies of thermosensitive N-isopropylacrylamide copolymers in aqueous solutions

Abstract Temperature-induced phase transitions of some N−isopropylacrylamide (NIPAM) copolymers in aqueous solutions were studied with 9-(4-N,N− dimethylaminophenyl)phenanthrene (DP) as an intramolecular fluorescence probe. Lower critical solution temperature (LCST) of DP-labeled NIPAM copolymers depends on the properties and contents of comonomers incorporated in the NIPAM copolymers, i.e., a hydrophobic comonomer such as methyl methacrylate (MMA) lowers the LCST, and a hydrophilic comonomer such as methacrylic acid (MAA) raises it. The higher contents of comonomers, the bigger changes of the LCST. And the micro-environments of the NIPAM copolymers in aqueous solutions also depend on them. The temperature-induced phase transitions of NIPAM copolymers with N-n−propylacrylamide (NNPAM), and N−isopropylmethacrylamide (NIPMAM) appear to be very sharp as well as that of NIPAM homopolymer aqueous solution and their LCST values are good correlated with their copolymer compositions.

Theoretical study of electron impact mass spectrometry. II. ab initio MO study of the fragmentation of ionized 1-propanol

Abstract In order to elucidate qualitatively the fragmentation mechanism of 1-propanol following low energy electron bombardment, the potential energy curves have been calculated using ab initio MO methods (4-31G//ST0-3G), The present study indicates that H 2 O elimination proceeds via the formation of a five-membered ring intermediate/transition state. A hydrogen atom of the methyl group isshifted to form H 2 O, which is in line with the deuterium labelling experiment. In the simple bond cleavage process, it is mainly the C α C β bond which is expected to be broken.

Theoretical study of electron impact mass spectrometry. I. Ab initio MO study of the fragmentation of n-butane

Abstract The fragmentation mechanism of n-butane by low-energy electron bombardment has been studied by means of the ab initio MO method. Optimized geometries of possible n-butane cation conformers, reaction intermediates and fragments have been calculated using the energy gradient technique. The results suggest that the fragmentation to C1 + C3 is more favorable than that to C2 + C2, when the electron impact energy is at most only a few eV above the ionization threshold. The base peak at m/z 43 has been calculated to be due to the 2-propyl cation. In the course of fragmentation to C1 + C3 proton tunneling is expected.

Effect of a high magnetic field on the decay rate of chain-linked intramolecular exciplex fluorescence

Abstract The effect of a high magnetic field ( 1 T) enhances the singlet-triplet intersystem crossing of an intramolecular radical ion pair intervening in the reaction ( Δ g mechanism).

A study of low energy electron impact mass spectra using molecular orbital theory

Abstract The fragmentation mechanism of n-propylalcohol and n-propylamine at low energy electron impact has been studied by means of ab initio MO method. The results suggest that in n-propylalcohol the dehydration process is favorable and that in n-propylamine the process of NH3 loss analogous to the dehydration of n-propyl-alcohol is unfavorable.

An ab initio molecular orbital study of the electron affinity of boron clusters

Abstract The electron affinities of boron clusters were studied using ab initio molecular orbital methods to discuss the phenomenon of clustered boron anions emitted during sputtering. Calculations were performed at the MP4(SDQ)/CBSB5 level. The calculated electron affinities of B, B 2 , and B 3 were found to be 0.214, 3.66, and 3.20 eV, respectively. These values are qualitatively consistent with the experimental data of sputtering yield of B − , B 2 − , and B 3 − .

The charge effects in the low-energy ion depositing processes

Abstract The charge effects in the low-energy carbon ion depositing process on a graphite surface were discussed by using an ab initio molecular orbital calculation with a UHF method and a 3-21G basis set. A positively charged carbon ion is strongly bound on a graphite surface by a covalent bond. A neutral carbon atom is adsorbed by a van der Waals interaction. A negatively charged carbon ion is not bound to a graphite surface and is repulsed. These charge effects are independent of the approach points of the incident carbon ion on a graphite surface.

Effects of charge in ion-surface interactions

A theoretical investigation of the effect of charge in ion-solid interactions was carried out for the first time by ab initio molecular orbital calculations. In the case of a carbon cation interacting with a graphite surface, a strong bond is produced by covalent binding to the π electrons of the substrate. In the case of a neutral carbon, binding is through van der Waals interactions. With an anion, no stable bound state is produced. Ion-solid interactions were thus found to vary in a clear-cut fashion according to ion species.

An ab initio molecular orbital study of ion-solid interaction in carbon deposition processes

The charge effects of incident carbon ions on the chemical bond formation are discussed by using ab initio molecular orbital calculations. There are two kinds of bonds which are formed in the incident carbon and graphite surface; one is a covalent bond of a carbon cation with the surface, and the other is a van der Waals bond of a carbon nonion and the surface. A carbon anion can not have a stable bond to the graphite surface. The calculated results at the MP2 level are qualitatively consistent with the results at the UHF level.