The kinetics of the photolysis of formylmethylflavin, a major intermediate product in the aerobic and anaerobic photolysis of riboflavin, was studied in the pH range 2.0–11.0. Formylmethylflavin and its photoproducts, lumichrome and lumiflavin, were determined in degraded solutions using a specific multicomponent spectrophotometric method. The photolysis of formylmethylflavin in alkaline medium takes place by first-order kinetics and the rate constants (kobs) at pH 7.5–11.0 range from 0.27 × 10–4 to 3.88 × 10–4 and 0.36 × 10–4 to 5.63 × 10–4 s–1 under aerobic and anaerobic conditions respectively. In acid medium, the photolysis involves a second-order mechanism and the rate constants at pH 2.0–7.0 range from 1.37 to 2.11 and 2.03 to 2.94 M–1 s–1 under aerobic and anaerobic conditions respectively. The rate–pH profiles for the photolysis reactions indicate the highest rate of formylmethylflavin degradation is at ~pH 4 and above pH 10. In the alkaline region, the increase in rate with pH is due to higher reactivity of the flavin triplet state. The photolysis of formylmethylflavin is catalyzed by phosphate ions and is affected by the solvent viscosity.
研究了核黄素在有氧和无氧光解过程中的主要中间产物甲酰甲基黄素在 pH 值为 2.0-11.0 范围内的光解动力学。采用一种特定的多组分分光光度法测定了降解溶液中的甲酰甲基黄素及其光反应产物--发光黄素和发光黄素。甲酰甲基黄素在碱性介质中的光解是通过一阶动力学进行的,在 pH 值为 7.5-11.0 时,有氧和厌氧条件下的速率常数(kobs)分别为 0.27 × 10-4 至 3.88 × 10-4 和 0.36 × 10-4 至 5.63 × 10-4 s-1。在酸性介质中,光解涉及二阶机制,pH 值为 2.0-7.0 时,有氧和厌氧条件下的速率常数分别为 1.37 至 2.11 和 2.03 至 2.94 M-1 s-1。光解反应的速率-pH 曲线表明,甲酰甲基黄素降解的最高速率出现在 ~pH 4 和 pH 10 以上的条件下。在碱性区域,速率随 pH 值的增加而增加,这是由于黄素三重态的反应活性较高。甲酰甲基黄素的光解由磷酸离子催化,并受溶剂粘度的影响。