Electrochemical Investigations of L-Cysteine Interactions with Bismuth Ions

Abstract

The use of bismuth compounds as medicinal treatments has prompted the electrochemical investigation of bismuth(III) salicylate, bismuth(III) citrate and bismuth(III) nitrate with L-cysteine in 0.1M HNO3 and 0.1M HCl using cyclic and square wave voltammetry. This level of acidity is meant to approximate the proton levels in gastric fluids. Platinum and gold electrodes were not used in order to avoid the reduction of protons to hydrogen gas at these high proton levels. At boron-doped diamond (BDD) and glassy carbon (GC) electrodes, significant voltammetric changes were observed upon incremental additions of L-cysteine even at pH 1.00. For example, additions of L-cysteine to bismuth(III) salicylate in 0.1M HNO3 at GC caused the Bi(III) reduction process to became narrower with an initial negative potential shift. Upon further additions of L-cysteine, the reduction curve displayed a positive potential shift and became even narrower as the complex exhibited faster electron transfer than the original Bi(III) species. A positive peak potential shift of the corresponding bismuth stripping peaks was also observed upon L-cysteine additions. These results show that L-cysteine, even in its most protonated state, is capable of acting as a complexing agent for Bi(III) species at pH 1.00. The results for other Bi(III) compounds under similar conditions are also planned for presentation.