Kinetics of the release of hydrogen sulfide from cysteine and glutathione during thermal treatment
1994
Zheng, Y. | Ho, C.T.
0.1M of cysteine or glutathione solutions with a pH of 3.0, 5.0, 7.0 or 9.0 were incubated at 80 degrees C, 90 degrees C, 100 degrees C or 110 degrees C for a certain period of time. The amount of hydrogen sulfide released during the thermal treatment was determined using a sulfide/silver electrode. The results showed that both reactions followed first order kinetics. The rate constants of the reactions increased with the pH value. The release of hydrogen sulfide from these two compounds was catalyzed by the hydroxide ion, while the beta-elimination was favored at higher pH. The activation energies for both reactions were calculated using the Arrhenius equation; 31.3, 31.8, 32.2 and 29.4 kcal/mol for cysteine and 18.8, 30.8, 22.8 and 19.9 kcal/mol for glutathione at pH 3.0, 5.0, 7.0 and 9.0, and respectively. The lower activation energies for glutathione implies that the molecular structure and micro-environmental condition of the amino compound plays a significant role in the release of hydrogen sulfide.
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