Akira Hanaki

Spin-trapping of sulfite radical anion, SO3-., by a water-soluble, nitroso-aromatic spin-trap.

Sulfite radical anion, SO3-., which is generated either by non-enzymatic reaction of hydrogen peroxide (H2O2-) with sulfite (SO3(2-)) or by the oxidation of bisulfite (HSO3) with Ce4+ ion, can be trapped with a water-soluble, nitroso-aromatic spin-trap, sodium 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS, 1), yielding an ESR spectrum with coupling constants [aN (1) = 12.9 G, aH (2) = 0.8 G] and a g-value of 2.0063. The SO3- radical adduct (spin adduct) was observed even in the presence of the very low concentration of H2O2 (1.21 X 10(-2) mumol).

On a spectrally well-defined and stable source of superoxide ion, O−2

It has been shown that superoxide ion, O;, is an endogenic species produced in oxygen-metabolizing organisms and may be related to the toxicity of oxygen and to the bactericidal action in leukocytes [l-lo]. This free radical is also produced enzymatically [ 111, photochemically [12] and chemically [ 131, but the preparation involves reactive intermediates which would interfere with the chemical and biological reactions of superoxide ion. In order to investigate the chemical and biochemical reactivities of O;, it is necessary to have reliable and simple methods for the preparation of well-defined radical species. The ideal source of 0; would have no associated reactive substances and allow spectrophotometric observation of 0;. Ionizing radiation of oxygenated water, in particular by the technique of pulse radiolysis, provides high concentrations of 0; [ 141. However, since O;, being a short-lived species in an aqueous solution, is decomposed immediately after pulse radiolysis, this method could not be used for the study of reactivities of 0;. Electrochemical method also provides a welldefined source of 0;. Maricle and Hodgson [ 151 conducted the electrolytic reduction of oxygen in aprotic solvents and established the method of the generation of 0; which was identified with ESR spectroscopy. The solution containing 0, prepared by electrolysis is stable for several hours at room temperature [ 111. Recently, Fee and Hildenbrand [ 161 prepared 0, by electrolysis in some water-miscible solvents and record-

Spin-trapping of superoxide ion by a water-soluble, nitroso-aromatic spin-trap

Spin-trapping of superoxide ion, O2-, which is produced from two different sources (OH(-)-DMSO and xanthine-xanthine oxidase systems), was investigated by use of a water-soluble, notroso-aromatic spin trap, sodium 3,5-dibromo-4-nitrosobenzene-sulfonate (DBNBS). It was found that O2- from all sources was easily trapped by DBNBS to yield the stable O2- adduct showing the ESR spectrum consisting of a triplet of a triplet [aN (1) = 12.63 G and aH (2) = 0.71 G]. Hydroperoxy radical (HO2.), which can be generated from the oxidation of hydrogen peroxide with Ce4+ ion, was not trapped by DBNBS. These results indicate that the trapped radical is O2-, but not HO2..

Copper(II) complexes of l-histidylglycyl-l-histidylglycine and l-histidyl-l-histidylglycylglycine: Coordination mode of histidyl residues

Abstract The complex formations of L-histidylglycyl-L- histidylglycine (His-Gly-His-Gly) and L-histidyl-L- histidylglycylglycine (His-His-Gly-Gly) with copper- (II) ion were studied in a slightly alkaline medium by visible absorption, circular dichroism and electron spin resonance spectroscopies. His-Gly-His-Gly coordinates to copper(II) ion via a terminal amino nitrogen, two deprotonated peptide nitrogens and an imidazole nitrogen of the histidyl residue in the third position. The copper(II) ion in the His-His- Gly-Gly complex is coordinated by three nitrogen donors; i.e. , a terminal amino nitrogen, an adjacent deprotonated peptide nitrogen and an imidazole nitrogen of the histidyl residue in the second position. The imidazole nitrogen at the N-terminal does not participate in the chelate formation with the copper(II) ion, but it bridges between the two monomeric complexes so that a broad ESR spectrum without the hyperfine structure is observed.

Spectroscopic studies on the reaction of superoxide ion with non-redox metalloporphyrins

Abstract The reactions of superoxide ion, O − 2 , with some non-redox metalloporphyrins were investigated at room temperature by spectroscopic methods (UV/vis, ESR) in dimethyl sulfoxide (DMSO). Addition of the O − 2 solutions prepared from KO 2 to DMSO solutions of the meso -tetraphenylporphyrin which is complexed with group II metals such as Zn(II), Mg(II) and Cd(II), caused the visible spectra to shift to the red and made the g ∥ component of the ESR spectrum due to O − 2 at 77 K shift to the higher field. Addition of methanol decomposed the superoxo complexes to the corresponding metalloporphyrins. These results suggest that the reaction products between these metalloporphyrins and O − 2 are the O − 2 adducts. Other non-redox metalloporphyrins containing group VIII metals such as Ni(II) and Pd(II) do not produce the O − 2 adducts under the experimental conditions. The reasons for the red shifts caused by the formation of the O − 2 adducts and for the difference in the reactivities of metalloporphyrins towards O − 2 are discussed.

Spectroscopic studies on the production of hydroxyl radicals from the reactions of copper(II)polyamine-n-polycarboxylate complexes with hydrogen peroxide

Abstract Reactions of copper(II)-polyamine-N-polycarboxylate complexes such as Cu II (edta) (edta: ethylenediamenetetraacetic acid) and Cu II (dtpa) (dtpa: diethylenetriaminepentaacetic acid) with hydrogen peroxide (H 2 O 2 ) were investigated spectroscopically in the presence or absence of biological reductants. In the absence of biological reductants such as L -cysteine, N-acetyl- L -cysteine, L -ascorbic acid, NADH and glutathione, no reaction occurred between Cu II (edta) and H 2 O 2 ; but, in the presence of these biological reductants, Cu II (edta) was reduced to Cu I and then the subsequent redox reaction (Fenton-type reaction) between Cu I and H 2 O 2 occurred to yield hydroxyl radicals (·.OH). From these results, it is concluded that copper(II)-polyamine-N-polycarboxylate complexes cannot directly be reduced to Cu I by H 2 O 2 , because the redox potentials of CU 2 + ions towards H 2 O 2 have been changed by ligation with these polyamine-N-polycarboxylate ligands.

Spectroscopic studies on the reaction of superoxide ion with tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman

The reaction of superoxide ion, O2-, with alpha-tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman (1b), was investigated spectrophotometrically in acetonitirle. The transient absorption (lambda max = 330 nm) observed at the initial stage of the reaction was ascribed to the chromanoxyl-type radical, one-elecron oxidation product of compound 1b, on the basis of the spectroscopic [ultraviolet (UV)/visible and electron spin resonance (ESR)] data. Further, the final product observed was ascribable to the tocopherol quinone (3).

Axial ligation of nitrogenous bases to five-coordinate chloro-meso-tetraphenylporphyrinatochromium(III)

Abstract The axial ligations of nitrogenous bases to the five-coordinate chloro- meso -tetraphenylporphyrinatochromium(III) [Cr(III)(TPP)(Cl)] were studied in a non-coordinating solvent, dichloromethane (CH 2 Cl 2 ), by spectrophotometric methods. A correlation exists between log K for the axial ligation: and p K a for the N-donor ligand. This correlation suggests that ligand to metal σ bonding contributes to the complex formation, rather than does metal to ligand π back-donation.

ESR evidence of the formation of a new superoxide complex of tetra-p-tolyporphyrinatocobalt(II) in aprotic solvents

Abstract The reactions of the superoxide ion (O 2 − ) with tetra- p -tolyporphyrinatocobalt(II) [Co(II)TTP] in dimethyl sulfoxide(DMSO) have been investigated by use of electron spin resonance (ESR) spectroscopy. In the absence of oxygen, Co(II)TTP in DMSO gives the DMSO adduct, Co(II)(TPP)(DMSO). When this DMSO adduct is exposed to air, an oxygen complex, Co(II)(TTP)(DMSO)(O 2 ), is formed in which the binding state between Co(II) and O 2 has been considered formally as Co(III)ue5f8O 2 − . When the superoxide ion (O 2 − is added to this oxygen complex, a new superoxide complex, Co(II)(TTP)(O 2 − ) 2 , is formed. The same superoxide adduct is formed by the reaction of O 2 − with Co(II)TTP in the absence of oxygen.

Free radicals of tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman which are produced from the reaction with superoxide ion, O2−: studies by high-performance liquid chromatography

Reaction of superoxide ion, O2-, with alpha-tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman (lb), was investigated by high-performance liquid chromatography (HPLC). Chromatogram of the reaction mixture showed three peaks with retention times of 2.5, 1.8 and 1.5 min, and each peak height was dependent on the concentration of O2. Chemical species having the retention time of 1.5 min was ascribed to chromanoxyl radical (3), and the other chemical species having the retention times of 2.5 and 1.8 min were identified with the model compound (lb) and 2-hydroxy-2-methyl-4-(3, 5, 6-tri-methylbenzoquinone-2-yl) butane (2), respectively. This is a first evidence that the free radicals from tocopherol model compounds was separated by HPLC.