Shin-ichi Nagaoka

KINETIC STUDY OF QUENCHING REACTION OF SINGLET OXYGEN AND SCAVENGING REACTION OF FREE RADICAL BY SQUALENE IN N-BUTANOL

The rate constant of quenching of singlet oxygen (kQ) by squalene (SQ) is found to be much larger than those of the lipids in human skin surface. SQ is the first target lipid in human skin surface by oxidative stresses such as sun light exposure. kQ of SQ is similar to that of 3,5-di-t-butyl-4-hydroxytoluene (BHT). The large kQ of SQ is due to the small ionization potential. SQ consists of six 2-methyl-2-pentene units and kQ of SQ is about 6-times as large as that of 2-methyl-2-pentene. The electron donating property of methyl groups bonded to quaternary carbons of SQ is essential to the large kQ. SQ is not very susceptible to peroxidation and is stable for attacks by peroxide radicals. The chain reaction of lipid peroxidation is unlikely to be propagated with SQ in human skin surface. It is concluded that SQ functions as an efficient quencher of singlet oxygen and prevents the corresponding part of lipid peroxidation in human skin surface.

An NMR relaxation study on the proton transfer in the hydrogen bonded carboxylic acid dimers

We have studied the proton spin‐lattice relaxation times (T1) of a series of benzoic acid (BAC) derivatives and decanoic acid (DAC) over a wide range of temperature and analyzed the results in terms of the double proton switching along the hydrogen bonds. The proton T1 in the high temperature region are analyzed using the classical jump model and the barrier heights for the proton transfer are determined. The thermodynamic parameters for the equilibria between the two configurations in the solid state are also determined by the FT–IR measurements. It is shown that the energetics and dynamics of the proton transfer in DAC and the para‐ and meta‐substituted BAC are all similar, but they are very different in the ortho‐substituted ones. It is suggested that the low temperature behavior of the proton T1 of the dimers of carboxylic acid is due to the tunneling and the asymmetry of the potential brings in a small activation energy.

Intramolecular proton transfer in various electronic states of o-hydroxybenzaldehyde

Abstract Intramolecular proton transfer in various electronic states of o -hydroxybenzaldehyde (OHBA) has been investigated experimentally and theoretically. The stable molecular structure in the ground state of OHBA is an intramolecularly hydrogen-bonded closed conformer. The potential surface of the ground state has only one minimum, and no S 0 -state tautomer exists as a metastable state. In the first excited 1 (π, π*) state of OHBA, the intramolecular proton transfer takes place and an enol tautomer is formed. The deformation of the benzene skeleton plays an important role in the dynamic process in the first excited 1 (π, π*) state. In the second excited 1 (π, π*) state and the first and second ionic states of OHBA, the intramolecular proton transfer to yield the enol tautomer does not take place. These results are consistent with the explanation that the nodal plane of the wavefunction stabilizes the enol tautomer only in the first excited (π, π*) state. The observed behavior concerning proton transfer of various hydrogen-bonded molecules also can be explained similarly.

Monochromator for a soft X-ray photochemistry beamline BL27SU of SPring-8

A high-resolution monochromator with varied line space plane gratings (VLSG) and spherical focusing mirrors was installed in one of three branches of BL27SU in SPring-8. The performance of the monochromator was roughly evaluated from the photo ion yield of nitrogen molecule. Furthermore, the kinetic energy of the photoelectron from Xe 5p3/2 orbit was also measured at the same photon energy with the N2 to avoid the influence of natural width. The resolving power over 104 has been confirmed at the N K-edge.

A study on the proton transfer in the benzoic acid dimer by 13C high-resolution solid-state NMR and proton T1 measurements

Abstract By a solid-state 13 C and proton NMR study of the hydrogen bonded dimer of benzoic acid, the rate of proton transfer, the height of the potential barrier for the transfer and the relative population of two different configurations were determined.

Kinetic study of free-radical-scavenging action of biological hydroquinones (reduced forms of ubiquinone, vitamin K and tocopherol quinone) in solution

Kinetic study of free-radical-scavenging (FRS) action of eight kinds of biologically important hydroquinones (HQs) (ubiquinol-10 (UQ10H2 1), ubiquinol-0 (UQ0H2 2), vitamin K1 HQ (VK1H2 3), vitamin K3 HQ (VK3H2 4), alpha-, beta-, gamma-tocopherol HQs (alpha-, beta-, gamma-TQH2 5, 6, 7), and 2,3,5-trimethyl-1,4-HQ (TMQH2 8)) has been performed. The second-order rate constants, k3, for the reaction of HQs 1-8 with substituted phenoxyl radical (PhO.) in ethanol, diethyl ether, benzene, and n-hexane have been measured with a stopped-flow spectrophotometer, as a model reaction of HQs with unstable free radicals (LOO., LO., and HO.) in biological systems. The rate constant of UQ10H2 1 is similar to that of alpha-tocopherol in ethanol. The HQs 3-8 showed higher reactivity than alpha-tocopherol in ethanol. Especially, the rate constants of VK1H2 3 and VK3H2 4 were found to be 31- and 21-fold larger than that of alpha-tocopherol, respectively, which has the highest reactivity among natural tocopherols. The rate constant of these HQs increased by decreasing the polarity of solvents. The approximate order of magnitude of k3 value was (i) VK1H2 and VK3H2 > (ii) alpha-, beta-, and gamma-TQH2s and TMQH2 > (iii) alpha-tocopherol > (iv) UQ10H2 and UQ0H2 in solution. The result suggests that these biological HQs also scavenge the active oxygen free radicals and prevent lipid peroxidation in various tissues and membranes. On the other hand, the reaction between substituted phenoxyl and biological quinones has not been observed.

Kinetic study of reactions between tocopheroxyl radicals and fatty acids

A kinetic study on the prooxidant effect of vitamin E derivatives has been carried out. Rates of hydrogen abstraction from various fatty acids and egg yolk lecithin by tocopheroxyl radicals were determined spectrophotometrically. The rate constants measured in micellar dispersion were compared with those obtained in homogeneous solutions. The effects of structural variations of the vitamin E derivatives on their prooxidant activities were examined. The formation of lecithin reverse micelles in benzene appears to prevent the tocopheroxyl radicals from reacting with the phospholipid fatty acid moieties.

Nodal-plane model of the excited-state intramolecular proton transfer of 2-(o-hydroxyaryl)benzazoles

The excited-state intramolecular proton transfer of 2-(o-hydroxyaryl)benzazoles has been studied by emission spectroscopy. Although both 2-(2-hydroxy-3-aryl)benzazole and 2-(1-hydroxy-2-aryl)benzazole consist of an aryl moiety, a benzazol-2-yl group and an OH group, their emission properties are very different for the reasons that can be explained in terms of our previously offered nodal-plane model.

Nodal-plane model for excited-state intramolecular proton transfer of o-hydroxybenzaldehyde: substituent effect

The excited-state intramolecular proton transfer (ESIPT) of o-hydroxybenzaldehyde (OHBA) and related molecules in solution has been studied by emission spectroscopy. The substituent effects on the fluorescence quantum yield for the lowest excited 1 (, ∗ ) state can be explained by considering the nodal pattern of the wave function along with the delocalization of the electrons in the excited state. The substituent effect in 5-substituted salicylaldehydes is much less than that in o-(substituted-formyl)phenols.

An ab initio calculation on proton transfer in the benzoic acid dimer

Abstract We have made an ab initio calculation of the barriers for proton transfer in the hydrogen-bonded dimers of benzoic acid and acetic acid. Geometrical optimization values which are closer to the experiment one.