Electrochemical and Spectroscopic Studies of Bismuth-Cysteine Interactions

Abstract

IntroductionThe electrochemical behavior of bismuth(III) compounds in various media has been investigated over the past few years in this laboratory.1 More recently, attention has turned to the bismuth compounds which are used in pharmaceutical applications to treat stomach disorders.2 It is apparent from the extensive literature on bismuth pharmaceuticals that interactions of bismuth(III) ions with the sulfhydryl group of L-cysteine and related compounds accounts for much of the chemical fate of bismuth compounds in the human digestive system.2 Electrochemical techniques have been found to provide information about both the redox properties of L-cysteine3 and the complexation of bismuth by sulfur-containing ligands in the body.1 This information complements the results obtained by spectroscopic methods.2 Most investigations of pharmaceutical bismuth compounds have not involved electrochemical techniques, allowing a fuller picture of bismuth(III) interactions with biologically active ligands to be obtained.Results and DiscussionThe results of work with bismuth(III) nitrate in aqueous media at both pH 1.0 and 7.4 at glassy carbon working electrodes is intended for presentation. In brief, the addition of L-cysteine to such solutions produced a shift in the peak potential for bismuth(III) reduction, indicating an extensive interaction of the sulfhydryl group of L-cysteine with bismuth(III) ion. This interaction at pH 1.0 is particularly interesting because these conditions simulate the acid levels found in stomach contents. For pH 7.4 studies, the MOPS (3-N-morpholino)propanesulfonic acid buffer4 system has been chosen in order to minimize interaction of bismuth(III) with the buffer components. At pH 7.4, UV-VIS studies have shown that a new absorbance band at 330 nm appears upon addition of L-cysteine to bismuth(III) nitrate solutions. It is expected that this feature will contribute greatly to further studies of bismuth(III) compounds with sulfur-containing ligands. In other work, the pharmaceutical compounds bismuth(III) citrate and bismuth(III) salicylate have also been investigated and show similar behavior to that of bismuth(III) nitrate. It is expected that the results of investigations involving other sulfur-containing ligands will also be presented.References G. T. Cheek and D. Peña, J. Electrochem. Soc., 167, 155522 (2020)H. Li, R. Wang, and H. Sun, Acc. Chem. Res., 52, 216 (2019).G. T. Cheek and M.A. Worosz, ECS Trans., 164(12), D707 (2016).C. M. H. Ferreira, I. S. S. Pinto, E. V. Soares, and H. M. V. M. Soares, RSC Advances, 5(39), 30989 (2015).