The complex species formed in aqueous solution (25degreesC, I=0.15 mol dm(-3) KCl ionic medium) between VO2+ cation and carnosine (HL) have been studied potentiometrically and spectrophotometrically. The application of the least-squares computer program LETAGROP to the experimental emf and UV-Vis data, taking into account the hydrolytic species of VO2+ ion, indicates that under the employed experimental conditions (carnosine-oxovanadium(IV) ratios ranging from 6/1 to 25/1; pH range 2.5-5 and 7-9) only the species in the ligand-metal ratio 2: 1, [VO(H3L)(H2L)](5+), [VO(H2L)(2)](4+) and [VO(H2L)(HL)](3+) (acid zone, pH 2.5-5), and [VO(HL)L](+), [VOL2] and [VOL2H-1](-) (basic zone, pH 7-9), are formed in significant amounts. At pH 5-7 VO(OH)(2) precipitates. With ratio ligand-metal greater than or equal to 60:1, the hydrolysis is repressed and precipitation is not observed. In the pH range 2.5-9, the same species and moreover the species [VO(HL)(2)](2+) is also found. This model is confirmed at 25degreesC and I=1.5 mol dm(-3) ionic medium. The stability constants and ionization constants of the complexes formed were determined. The species distribution diagrams as a function of pH and electronic spectra are jointly discussed. Theoretical calculations of protonation constants of carnosine have also been made using PALLAs 3.0 program. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 56]
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