抗氧剂L-半胱氨酸盐酸盐在水溶液中的氧化反应速率常数

Determination of oxidation rate constant of antioxidant L-cysteine hydrochloride in aqueous solution

目的测定抗氧剂L-半胱氨酸盐酸盐在水溶液中与氧反应的速率常数,并评价其抗氧化能力。方法在25℃、35℃、45℃下,向反应液中持续通入空气以维持溶解氧浓度恒定,并用氧电极测定其浓度;用碘量法测定L-半胱氨酸盐酸盐在水溶液中不同时刻的浓度,做出降解曲线,计算各温度下的氧化降解速率常数。结果25℃时,L-半胱氨酸盐酸盐在pH4.0、pH6.8缓冲溶液中与氧的反应均为表观零级反应,而在pH9.0缓冲溶液中为表观一级反应。3个不同pH条件下的表观反应速率常数分别为7.78、30.1μmol.L-1.h-1、5.03×10-2h-1。结论L-半胱氨酸盐酸盐在弱酸性条件下,反应速率较慢,抗氧化能力较弱;在中性和弱碱性条件下反应速率较快,抗氧化能力较强。

OBJECTIVE To determine the oxidation reaction rate constants of L - cysteine hydrochloride in aqueous solutions and to evaluate the antioxygenic property of L - cysteine hydrochloride. METHODS At 25℃, 35℃ and 45℃, sufficient air was inflate into the solution continually to keep the concentration of dissolved oxygen steady. The concentrations of dissolved oxygen were determined by electric potential method, and the residual concentrations of L - cysteine hydrochloride in the solutions were determined by iodimetry. The reaction rate constants were obtained from linear regressions between concentration （or logarithm of concentration ） and time. RESULTS At 25℃, the degradation of L - cysteine hydrochloride obeyed the apparent zero - order kinetics in the pH4.0, pH6. 8 buffer solution, while obeyed the apparent first - order kinetics in pH9.0 buffer solution, The apparent rate constants were 7. 78 μmol·L^-1·h^-1 at pH 4.0, 30. 1 μmol·L^-1·h^-1 at pH6. 8 and 5.03×10^-2 h^-1 at pH9.0, respectively. CONCLUSION The L - cysteine hydrochloride was found to possess stronger antioxidant activity in neutral and weak acid solutions than in weak alkaline one.