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Abstract  

The aqueous solutions of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) containing various amount of (-)-epigallocatechin gallate (EGCg) were mixed with tritiated water, then frozen and β-ray irradiatedin situ for 90 days at −80°C. ESR spectra were measured as a function of time after melting the sample at room temperature. The intensity of the hydroxyl (OH)_ radical adduct, DMPO-OH, was obtained by the extrapolation to zero time. The ratio of the reaction rate constants of the OH radical with EGCg and DMPO,k EGCg/k DMPO, was obtained kinetically. The result was compared with the case of DNA and EGCg in tritiated water, in order to make clear the mechanism of the protection of DNA from the radiation-induced scission with EGCg.

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Abstract  

The values of Sb(III), Tl(I), Te(IV), and biological substance, DNA determined by sub- and super-equivalence method of isotope dilution analysis (SSE-IDA) and substoichiometric isotope dilution analysis (Subst-IDA) under the same condition were compared. From the results, it was proved that SEE-IDA did not need the strict condition necessary for Subst-IDA and the determination by SEE-IDA was possible within the error of a few percent, and the range of determination was wider than that of Subst-IDA. The various variants of SSE-IDA reported so far were classified into SEE-Reverse-IDA and SEE-Direct-IDA. Finally, the characteristics of SEE-IDA allowing accurate determination were discussed and summarized.

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Abstract  

Reaction rate constants of (−)-epigallocatechin gallate (EGCG) and (+)-catechin with the hydroxyl radical (·OH) were measured using the rapid flow ESR method. The rate constant of EGCG was larger twice than that of the pyrogallol or gallic acid, they are the model compounds of the B ring of EGCG. It was explained by the quantum-chemical calculation of the bond dissociation energy (BDE) of the phenolic hydroxyl group (ϕ-OH) and the spin densities of EGCG radical. The energy of the EGCG radical was lowered by the hydrogen bonding between the radical part on the B ring and the hydroxyl group on the gallate group, leading to the lowering of BDE. Linear relationship between the relative activation energy and BDE of all the polyphenols measured was observed (Evans-Polanyi equation), showing that the reaction with ·OH occurs in the same manner.

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Abstract  

A new sub-superequivalence method of radiometric analysis is proposed, which is derived by combining the sub-superequivalence method of isotope dilution analysis with substoichiometric radiometric analysis. This method using redox reaction is applied for the determination of trace amount of antimony and was proved to be an excellent technique. The fundamental problems of this method are discussed analytically.

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Abstract  

The redox titration of antimony(III), labeled with125Sb(III), by potassium iodate was radiometrically investigated using the burette method and the standard series method. The stoichiometry of the redox process was determined. The redox valence (the number of equivalents per mol) of potassium iodate for the oxidation of antimony(III) to antimony(V) was found to be 6, differing from the results obtained using the usual visual indicator method, where the value was shown to be 4. This disagreement in the equivalents of potassium iodate for the oxidation of antimony(III) is discussed.

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Abstract  

Inhibiting effect of four tea catechins, (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCG), on the lipid peroxidation induced by β-ray in tritiated water was examined using a spin probe method. 16-Doxylstearic acid (16NS) was incorporated into the liposome prepared from egg yolk phosphatidylcholine and the rate of the decrease of ESR intensity of 16NS was used as a measure of the inhibiting effect. In the low concentration region below 10−5M, catechins showed their inhibitions on the lipid peroxidation according to the order of ECG>EGCG>EC>EGC. This result was explained by a model that the initiator of the peroxidation is the hydroxyl radical (·OH) and the catechins adsorbed on the lipid membrane surface acting as scavengers of ·OH. In the high concentration range, however, the effect was diverse and it decreased with the increase of it in the case of EGCG. EGCG in this range was considered to enter into the interior of the membrane and break the structure, which causes the decrease of 16NS. Observation with transmission electron microscope (TEM) revealed that the size of the liposome became larger with the increasing concentration of EGCG and finally it was broken into fragments, showing that EGCG broadened the area of the liposome as expected from the result of ESR.

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Redox substoichiometry in isotope dilution analysis

V. The use of potassium bromate as the oxidizing agent in the analysis of metallic zinc for antimony

Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Kambara, J. Suzuki, H. Yoshioka, and Y. Watanabe

Abstract  

Radiometric titration of antimony(III) with potassium bromate in hydrochloric acid media using the standard series method provided much valuable informations on the titration errors which depended on the concentrations of the acid and antimony(III). The hydrochloric acid concentrations between 2.5 and 3.0M were found to be optimum for the oxidation of antimony(III) amounts of 4 μg or less. Under these optimum reaction conditions the redox substoichiometric isotope dilution analysis was applied to the determination of antimony in metallic zinc and the satisfactory results were obtained, without the separation of matrix element. Also, the merits of various oxidizing agents hitherto studied for the quantitative oxidation of antimony(III) were compared and discussed.

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Abstract  

The reduction reaction mechanism of carrier-free125Sb in HCl solution was studied kinetically. Sb(III) and Sb(v) were separated by solvent extraction using n-benzoyl-n-phenylhydroxylamine(BPHA) in chloroform at different constant time in interval and the reaction rate was determined by measuring the radioactivities of125Sb in both organic and aqueous phases. Plot of log[125Sb(V)/ [125Sb(III)+125Sb(V)] against the elasped time do not give straight lines. The curves can be solved to be ABC type reactions by a non-linear squares. On the basis of dependence of the reactions, overall reactions can be expressed as follows;

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Redox substoichiometry in isotope dilution analysis

IV. Determination of antimony content in metallic tin

Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Kambara, J. Suzuki, H. Yoshioka, and Y. Ugai

Abstract  

The oxidation reaction of antimony(III) with potassium dichromate has been investigated radiometrically. The quantitative oxidation of antimony(III) was found to be not disturbed even in large amounts of tin(IV). On the basis of these results the redox substoichiometric isotope dilution analysis using potassium dichromate as the oxidizing agent was proposed for the determination of antimony in metallic tin. The antimony content of 1.22±0.05 μg in metallic tin (10 mg) was determined without separation of the matrix element.

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Redox substoichiometry in isotope dilution analysis

II. Determination of antimony content in metallic zinc

Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Kambara, J. Suzuki, H. Yoshioka, and N. Nakajima

Abstract  

Isotope dilution analysis using the redox substoichiometric principle has been applied to the determination of antimony content in metallic zinc. As the substoichiometric reaction, the oxidation of trivalent to pentavalent antimony with potassium permanganate was used, followed by separation of these species by the BPHA extraction of trivalent antimony. Determination of antimony contents less than 0.5 μg was found to be possible with good accuracy, without separation of zinc ions. The antimony content in metallic zinc was determined to be 19.7±0.8 ppm, in good agreement with the results obtained by the other analytical methods.

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