N-ヘテロ芳香族の電子的性状 : 第24報 発ガン性物質4-Nitroquinoline 1-Oxideとチアミシとの相互作用 錯体形成および置換反応

Abstract

Interaction between carcinogenic 4-nitroquinoline 1-oxide (4-NQO) and thiamine has been investigated. When required, we used a model compound which contained a thiazolium or a pyrimidine as part of the thaimine molecule and we found out that either molecular complexation or substitution reaction between 4-NQO and thiamine took place in acid or alkaline region, respectively. The difference spectra of acid mixtures of 4-NQO and thiamine exhibited an absorption maximum in the vicinity of 400 mμ. Spectrophotometric examinations were made on the effects of pH and polarity of solvents upon the complex formation, the molar ratio (1 : 1) and ε, K, and ΔH values of the complex. It was found that the interaction was best explainable in terms of n-π type charge transfer between thiamine and 4-NQO, wherein the pyrimidine moiety of the former acts as electron donor and the latter as electron acceptor. The substitution reaction between 4-NQO and thiamine in alkaline solution was exhibited by the appearance of a new absorption band around 360 mμ region of the spectrum of the mixture as well as by the liberation of nitrite ion from the reaction mixture. Quantitative examination was made on the nitrite ion liberation reaction, and the involvement of thiol group of thiamine and nitro group of 4-NQO was presumed. A chemical structure is proposed for the reaction product, which was separated by paper chromatography. Non-carcinogenic 4-nitropyridine 1-oxide also formed a molecular complex with thiamine in acid medium, but it gave no detectable reaction with the vitamin in alkaline medium.