Mikio Hoshino

Detection of 1270 nm emission from singlet oxygen and photocytotoxic property of sugar-pendant 60 fullerenes.

Sugar-pendant [60] fullerene derivatives have been prepared from carbohydrate-linked azides 1a-e. Both monosugar (4a-e) and bissugar derivatives (5a-e) produce singlet oxygen ((1)O(2)) under laser irradiation (355 nm) proved by the direct observation of (1)O(2) emission at 1270 nm. Monosugar derivatives exhibit photocytotoxicity varying by the attached sugar molecule.

Oxidative DNA damage following exposure to dimethylarsinous iodide: the formation of cis-thymine glycol.

The purpose of the present study was to elucidate the genotoxic mechanism of trivalent dimethylated arsenic, particularly the induction mechanism of oxidative stress in nuclear bases. Cis-thymine glycol was used as a biomarker of DNA oxidation damage. The treatment of thymine with dimethylarsinous iodide (DMI), a model compound of dimethylarsinous acid, induced the formation of cis-thymine glycol. This oxidative damage was induced via the production of dimethylated arsenic peroxide, but not via the production of superoxide anion or hydrogen peroxide. Trivalent dimethylated arsenic may thus play an important role in arsenic carcinogenesis through the induction of oxidative base damage.

Photoreduction of iron(III) tetraphenylporphyrin in ethanol studied by laser flash photolysis: effects of concentration on quantum yields

Chloroiron(III) tetraphenylporphyrin, CIFeIIITPP, in deaerated ethanol is photoreduced to yield iron(II) tetraphenylporphyrin, FeIITPP, upon irradiation with UV light. The 355 nm laser photolysis studies have confirmed that the initial yields for the formation of FeIITPP are markedly decreased with an increase in the concentration of CIFeIIITPP: ϕ= 0.015 at 5.35 × 10–6 mol dm–3 CIFeIIITPP and ϕ= 0.01 at 1.0 × 10–4 mol dm–3 CIFeIIITPP. The effects of the concentration on the quantum yields were interpreted in terms of the formation of photoreactive iron(III) porphyrin at low concentrations of CIFeIIITPP.

OPTICAL ABSORPTION AND ELECTRON SPIN RESONANCE SPECTRA OF CATION RADICALS OF DIMERIC CHLOROPHYLL a IN LOW‐TEMPERATURE MATRICES

Abstract— A chlorophyll (Chl) a solution in 3‐methylpentane at 77 K exhibits an absorption spectrum with a distinct peak at 706 nm in the red‐band region. The formation of the 706 nm absorbing species (S706) was reversible with respect to temperature change; no chemical change was observed. γ‐Irradiation of the rigid 3‐methylpentane solution at 77 K yields an absorption spectrum which can be ascribed to S706+ and S706−. When carbon tetrachloride, an electron scavenger, was added to the solution, the absorption of S706+ survived, which has peaks at 850 and 956 nm. It is assumed that the S706 is hydrogen‐bonded dimeric Chi a, which may be regarded as a model of P700 in photosynthesis. Cation radicals of monomeric Chi a were formed in a γ‐irradiated sec‐butyl chloride solution at 77 K, and an absorption spectrum with peaks at 730 and 813 nm was recorded. ESR spectra of the cation radicals of S706 and monomeric Chi a are of a similar shape but their linewidths are 7.5 and 11.0 Gauss, respectively. The linewidth narrowing observed for S706+ is clear evidence for the assumption that S706 is dimeric Chi a. Comparison was made of the absorption spectrum of S706+ with the light‐induced spectrum of P700 reported earlier.

Photodissociation of monopyridinate of chlorochromium(III) tetraphenylporphyrin in acetone. Studies on the reactive state and ligand exchange reaction by laser photolysis

Abstract The title compound, ClCr(III)TPP-Py (Py = pyridine), in acetone photodissociates the axial pyridine, probably from the 4 S 1 state, to give ClCr(III)TPP as an initial product with yield of ≈ 0.16 upon 532 and 355 nm excitation. The initial product, ClCr(III)TPP, reacts with both pyridine and acetone to yield ClCr(III)TPP-Py and ClCr(III)TPP-Ac (Ac = acetone). The monoacetonate complex, ClCr(III)TPP-Ac, further exchanges the axial acetone for pyridine to regenerate ClCr(III)TPP-Py.

Luminescence of the copper porphyrin aggregate

Abstract Copper(II) mesoporphyrin IX dimethyl ester in methylcyclohexane solution shows at 77 K a single-line ESR spectrum ascribable to an aggregated species. The luminescence of the aggregate is confirmed by the absorption, emission, and excitation spectra and also its yield and lifetime are compared with those of the monomer.

Low-temperature laser photolysis of benzophenone in neat diethylaniline: Optical detection of an excited triplet state with a strong charge-transfer structure at 77 K

Abstract Benzophenone forms a weak complex with diethylaniline in the ground state at 77 K . Laser photolysis studies carried out for a neat diethylaniline solution of benzophenone at 77 K reveal that the excited triplet state of the weak complex has a strong charge-transfer structure and exhibits a transient spectrum composed of the benzophenone anion radical and the cation radical of diethylaniline.

Photo-induced dissociation of oxygen from dioxygen adduct of cobalt(II) tetraphenylporphyrinn studied by laser photolysis at low temperature

Abstract Optical absorption and laser photolysis studies of cobalt(II) tetraphenylporphyrin in oxygen-saturated 2-methyltetrahydrofuran solutions reveal that the dioxygen adduct of cobalt(II) tetraphenylporphyrin undergoes facile photo-induced dissociation of oxygen.

Luminescence of dimeric copper(II) porphyrin

Abstract The ESR spectra or Cu(II) mesoporphyrin IX dimethyl ester in toluene solution at 77 K revealed the formation of the triplet state dimer. The luminescence of the dimer was confirmed by the absorption, emission, and excitation spectra.

Laser photolysis studies on CuI complexes of thia-calix[3]pyridine. Phosphorescence from the intramolecular charge-transfer excited state

Abstract Copper(I) complexes of thia-calix[3]pyridine in dichloromethane exhibit phosphorescence from the MLCT triplet states at room temperature. The phosphorescence spectrum shifts to red on going from 300 to 180 K. The laser photolysis study carried out in the temperature range 300–180 K reveals that phosphorescence originates from the two triplet states, T H and T L , which are in thermal equilibrium with the energy difference of ca. 5 kcal mol −1 .