Measurements and Modeling To Determine the Reduction Potential of Uncomplexed Bi(III) in Nitrate Solutions for Application in Bi(III)-Ligand Equilibria Studies by Voltammetry

Abstract

The free metal ion potential, E(M), is a critical parameter in the calculation of formation constants when using voltammetry. When studying complex formation of Bi(III), however, E(Bi) cannot be directly measured. In this work a nitrate background electrolyte was employed to obtain reversible reduction waves. In order to determine E(Bi), measurements have to be made below pH 2 before the bismuth-oxy-nitrate species precipitates and thus corrections for the diffusion junction potential (monitored using Tl(I) as an internal reference ion) must be made.

Effect of Basicity on the Hydrolysis of the Bi(III) Aqua Ion in Solution: An Ab Initio Molecular Dynamics Study

“…Although ion hydration is a central topic of solution chemistry, the description of highly charged ion–water interactions remains a challenge, particularly for some multivalent cations involved in a series of hydrolysis reactions and polynucleation processes. − This is the case of Bi­(III) in water, which plays important roles in chemistry and medicine, for example, as an antimicrobial and anticancer agent or in radio-therapy, to name just a few. ,,− The aqua ion, [Bi­(H 2 O) n ] 3+ , was characterized by Näslund et al from acidic solutions of its triflate salt. These authors emphasized the importance of hydrolysis in its solution chemistry.…”

Application of Protocols Devised to Study Bi(III) Complex Formation by Voltammetry: The Bi(III)–Picolinic Acid System

“…Stock solutions of 0.100 M Tl(I) nitrate in 0.5 M HNO 3 and 0.100 M Bi(III) nitrate in 1 M HNO 3 were made as before. (25) Picolinic acid (PA) was supplied by Aldrich (99%, Milwaukee, USA).…”

“…The DC reduction waves for Bi(III) and Tl(I) were fitted separately, as before, (25) to determine the half-wave potentials (E 1/2 ) and diffusion-limited currents (I d ) at each pH step. The reduction waves showed reversible behavior in the presence of picolinic acid (as was previously found in the absence of ligand in a 0.5 M nitrate solution (25)).…”

“…The methodology whereby E(Bi) was determined by correcting for shifts in potential due to the formation of these species was also developed. (25) This paper presents the investigation of the Bi(III)-picolinic acid system. Picolinic acid is endogenously produced as an intermediate during the degradation of L-tryptophan, an essential amino acid, and has been shown to have a wide range of immunological, neuro-protective, and antiproliferative effects in the human body.…”

“…(30) Their work, however, uses less rigorous methodologies and the role of the Bi(III) nitrates was not yet realized. (30) The work presented here is the culmination of various studies done up to this point, (22)(23)(24)(25) as it illustrates how the protocols that were designed to ultimately study Bi(III)-ligand systems are applied.…”