PH-Dependent Effects of L-Cysteine on Mercury Dissolution of α-HgS and β-HgS.

Abstract

Mercury sulfide is an insoluble inorganic mercury compound, and it is the main chemical form in traditional oral mercury-containing medicines. Hg2+ has a high affinity for thiols, and small molecule thiols in the gastrointestinal tract may promote mercury dissolution of mercury sulfide by binding to Hg2+. L-cysteine is the only amino acid that possesses a reducing sulfhydryl group (-SH), out of the 20 amino acids. This study investigates the effect of L-cysteine on mercury dissolution of mercury sulfide at pHs ranging from 1.2 to 7.2. The results showed that L-cysteine had different pH-dependent effects on the mercury dissolution of α-HgS and β-HgS. For α-HgS, the dissolved mercury concentration increased from 5.47 ± 0.97ng/mL to 12.49 ± 0.54ng/mL when the pH rose from 1.2 to 4.2, and decreased to 3.37 ± 0.70ng/mL at pH6.0 and then increased to 9.36 ± 0.79ng/mL at pH7.2. For β-HgS, the dissolved mercury concentration increased from 151.09 ± 2.25ng/mL to 2346.71 ± 62.62ng/mL when the pH increased from 1.2 to 7.2. In conclusion, L-Cys was distinctly enhanced upon mercury dissolution of α-HgS and β-HgS with increasing pH. These results may contribute to our understanding of the mercury absorption mechanism of traditional oral mercury-containing medicines.