薬品のポーラログラフ的研究 (第13報)
プテリジン類のポーラログラフィー (iii), キサントプテリン
1959 年 79 巻 12 号 p. 1559-1564
詳細
1959 年 79 巻 12 号 p. 1559-1564
Xanthopterin undergoes two-electron reduction to form dihydroxanthopterin and its reduction wave is split into several steps by dissociation of the hydroxyls. The apparent pK' obtained from its wave height-pH curve are 11.25 and 11.9, which are larger than pK 6.84 and 9.46. This is explained as the kinetic current due to recombination reaction of proton. The reduction wave of non-dissociating molecule obtained at pH below 8 is accompanied with an adsorption wave and its wave height is not proportional to the concentration but to mercury pressure, decreasing in an organic solvent. Adsorption phenomenon was also confirmed from AC polarography and electrocapillary curve. From the adsorption wave height, the area of electrode occupied by adsorbed molecule was calculated as 55Å2 and the ring plane was assumed to be oriented parallel to the mercury surface. Transition from alkalinity to acidity results in decrease of total wave height, lowering of the degree of fluores-cence, and increase of oxidation wave observed in rotating platinum electrode. It is assumed from these facts that 2-amino-4, 6-dihydroxypteridine takes the phenoxide form in alkaline medium and about one-half is present as 2-amino-7-hydroxy-7, 8-dihydropteridine-4(3H), 6(5H)-dione in acid medium. Velocity of transition from the former to the latter is proportional to the concentration of hydrogen ion and is calcul-ated as ΔH 11, 000 calories and ΔS -37 calories. Inverse reaction is proportional to [OH-].
