Kouto Migita

Electron paramagnetic resonance studies of highly anisotropic low-spin states of ferrimyoglobin derivatives

The effects of addition of nitrogenous bases, which gave low-spin ferric porphyrin complexes with highly anisotropic g values, were investigated for ferrimyoglobin by low-temperature EPR measurements. Concomitant denaturation of myoglobin upon addition of the exogenous bases was also of interest. By addition of pyridine-type bases under regulated pH, Mb(Fe3+) complexes showing EPR spectra with highly anisotropic g values were formed. These complexes have the electronic states close to the spin-crossover point but not so close as that of the ferric porphyrin highly anisotropic low-spin (HALS) complexes previously reported. Several types of low-spin species, LSi, LSa and LSb, were produced by the denaturation of myoglobin caused by addition of some exogenous ligands. The LSi was assigned to a complex with histidine-E7 coordinated on the sixth position and LSa to the one with OH- and histidine-F8[Im0].

CdS-Doped Glass as Dosimetric Material with Electron Spin Resonance

Electron spin resonance (ESR) spectra have been measured in X-ray-irradiated CdS-doped glass as functions of X-ray dose and effective X-ray energy. The intensity of the ESR signal is proportional to X-ray dose up to 40 Gy. CdS-doped glass is more sensitive than a commercial alanine dosimeter. The intensity of the ESR signal decreases with decreasing effective X-ray energy for energies lower than 33 keV. Thermal stability was also studied. The ESR signal is relatively stable at room temperature.

The ground electronic state of quadridentate salicylaldehyde Schiff base–cobalt(II) complexes in non- and weakly co-ordinating solvents

The isotropic shifts in the 1H n.m.r. spectra of NN′-o-phenylenebis(salicylideneiminato)cobalt(II) have been observed in solutions of [2H]chloroform, [2H7]dimethylformamide, [2H6]dimethyl sulphoxide, and [2H5]pyridine. The contact shifts derived from the isotropic shifts revealed that the unpaired electron spin is delocalized onto the ligand through the highest-filled π molecular orbital. Formation of more than one species is observed in solutions of [2H7]dimethylformamide and [2H6]dimethyl sulphoxide as evidenced by the electronic absorption spectra in the near-i.r. region and by the large deviation from the Curie law of the temperature dependence of the isotropic shifts. The solvent-dependent isotropic shifts indicate that π-spin delocalization in chloroform solution is an intrinsic property of the planar four-co-ordinate complex and that the ground state of the complex is |2A2, yz〉. Co-ordination of weakly co-ordinating solvent molecules changes the ground state to |2A1, z2〉.

Nuclear magnetic resonance studies of low-spin complexes of cobalt(II) with Schiff bases. NN′-1,1-dimethylethylenebis(salicylideneiminato)cobalt(II) in pyridine

Isotropic paramagnetic proton n.m.r. shifts have been measured for the low-spin title complex in [2H5]pyridine. The temperature dependence of the shifts shows large deviations from the Curie law. The deviation is interpreted in term of the effects of temperature-dependent ligand field on mixing of excited electronic configurations with the ground state. The contact shifts evaluated from the isotropic shifts are shown to arise from spin delocalization through both σ and π orbitals. the latter having a smaller contribution than the former. The pattern of the contact shift is explained by the ground-state configuration of CoII where the unpaired electron is primarily in the dz2 orbital, and by the non-planar structure of the complex.

The high-spin ground state of quadridentate salicylaldehyde Schiff-base complexes of cobalt(II) in N-heterocyclic solvents

Formation of species with a high-spin ground state (S=) has been observed by e.s.r., n.m.r., and magnetic susceptibility measurements for quadridentate salicylaldehyde Schiff-base complexes of cobalt(II) in solution containing N-heterocyclic bases. It was found that a bidentate base, 1,10-phenanthroline, also gave similar high-spin species. The high-spin species were shown to be the base adducts having a six-co-ordinate structure. Magnetic susceptibility measurements revealed that 22% of NN′- ethylenebis(salicylideneiminato)cobalt(II) exists as the high-spin base di-adduct in pyridine at 295 K. The thermodynamic parameter ΔH⊖ for the formation of this high-spin species was found to be –4.25 × 103J mol–1. The amount of the high-spin species increased as the temperature decreased. The analysis of the isotropic shifts in 1H n.m.r. Revealed that the unpaired electron spins in the high-spin species mainly delocalize through σ orbitals.

Electron Spin Resonance of X-ray-Irradiated CdS-Doped Glass before Heat Treatment

The electron spin resonance (ESR) spectrum has been measured in X-ray-irradiated CdS-doped glass before heat treatment to examine the possibility of using such glass as a dosimetric material. No ESR signal is observed before X-ray irradiation, but it was observed after X-ray irradiation. The intensity of the ESR signal of the glass before heat treatment is higher than that after heat treatment. The thermal stability of the ESR signal of the former glass is slightly better than that of the latter. Therefore, the glass before heat treatment has better properties than that after heat treatment.

The first generation of azulenyl-lithium and -magnesium: A novel, versatile method of introducing a substituent at the 2-position of an azulene skeleton

1,3-Dihaloazulenes were effectively transformed into 2-substituted azulenes through lithiation at the 2-position by proton ion. Furthermore, 1,3-dichloro-2-iodoazulene was found to undergo iodine-lithium and -magnesium exchange to generate the corresponding azulenyl-lithium and -magnesium respectively.

Time-resolved e.s.r. study of triplet ketoamines generated by intramolecular proton transfer in free Schiff bases

Non-phosphorescent triplet states of the ketoamine forms of several free Schiff bases generated by intramolecular proton transfer have been observed using a time-resolved e.s.r. method.

High-spin quadridentate salicylaldehyde Schiff base complexes of cobalt(II) in N-heterocyclic solvents

E.s.r. and magnetic susceptibility studies of the title complexes show that an appreciable amount of the high-spin base di-adduct is formed in N-heterocyclic solvents such as pyridine and its methyl derivatives.