In an ongoing investigation of the interaction of bismuth(III) compounds with L-cysteiene¹, recent work has involved more complete characterization of these interactions at lower pH levels in various aqueous media. Pharmaceutical medications² such as bismuth subsalicylate (BSS) and bismuth citrate (BC) have now been investigated at pH 1.00 and 3.00 by both cyclic voltammetric and UV-VIS methods. Electrochemical methods have been used to evaluate the interaction of L-cysteine with bismuth compounds by observing shifts in the potential for bismuth reduction, and UV-VIS methods have allowed the observation of an absorbance peak at approximately 340 nm due to the bismuth(III) ion interaction with the L-cysteine thiol group.

Results and Discussion

Recent work has involved investigation of bismuth(III) nitrate (BN), BSS, and BC with L-cysteine at pH 1.00 and 3.00 in both HNO₃ and HCl solutions. In general, complexation of BN is not quite as favorable at lower pH levels as in pH 7.00 MOPS (3-N-morpholino)propanesulfonic acid)³ buffer solution.¹ This conclusion was based on the need for higher mole ratios of L-cysteine to BN to achieve the final state of the voltammograms. The UV-VIS behavior was also not as well-defined as in our previous work¹, with higher molar ratios of L-cysteine needed to produce the 340 nm absorbance peak. These results support the competition of protons with bismuth(III) for the L-cysteine ligand, there being much higher proton levels at pH 1.00 and pH 3.00 than at pH 7.00. The behaviors of BC and BSS at pH 1.00 and pH 3.00 are in many ways similar to that of BN. Finally, some preliminary work on glutathione (cysteine-containing tripeptide) interactions with bismuth compounds is also planned for presentation.

References

1. T. Cheek and D. Peña, J. Electrochem. Soc., 167, 155522 (2020)
2. Li, R. Wang, and H. Sun, Acc. Chem. Res., 52, 216 (2019).
3. M. H. Ferreira, I. S. S. Pinto, E. V. Soares, and H. M. V. M. Soares, RSC Advances, 5(39), 30989 (2015).