Potentiometric Investigation on the System Lead(II)-Arginine

Arginine is an amino acid playing an important role in human physiology because it is involved in the production of NO, which is a vasodilatator and is the precursor of urea. Although the effect of arginine on tissue lead(1) mobilization in plumbism has been studied, its property as a ligand toward cations has not been adequately investigated. In this paper the behavior of arginine as a ligand toward lead(II) is studied in two different ionic media: 1.00 mol dm(-3) NaCl and 1.00 mol dm(-3) NaClO4. Galvanic cells involving a lead amalgam and glass electrodes were employed to study the behavior of L-arginine as a ligand toward lead(II). The experimental data, obtained at 25 degrees C and in 1.00 mol dm(-3) NaCl are explained by assuming the presence of the species PbH2L, PbHL, and PbH2L2 with the relative stability constants. The data obtained in NaClO4 are explained by assuming the formation of the species PbH2L, PbHL, PbH2L2, and PbL with the relative stability constants. In all of the above species, the symbol L indicates arginine completely deprotonated. The role played by the ionic medium is discussed.