Speciation in the vanadate-alanylhistidine-peroxide system.
The speciation in the quaternary aqueous H+-H2VO4(-)-H2O2-L-alpha-alanyl-L-histidine (Ah) system has been determined from quantitative 51V NMR measurements and potentiometric data (glass electrode). The study was performed in 0.150 M Na(Cl) medium at 25 degrees C. Data were evaluated with the computer program LAKE, which is able to treat combined potentiometric and NMR data. In the ternary H+-H2VO4(-)-Ah system, two complexes, (H+)p(H2VO4-)q(Ah)r, having (p, q, r) values (0, 1, 1) and (1, 1, 1) (pKa = 6.88) explain all data. In the quaternary H+-H2VO4(-)-H2O2-Ah system, seven complexes were determined in addition to all binary and ternary complexes, four with a V/X/Ah ratio 1:1:1 and three with a ratio 1:2:1 (X = peroxo ligand). VX2Ah2- and VX2Ah- (pKa = 8.26) are the main quaternary complexes and predominate in the pH range 5 to 9. Chemical shifts, compositions and formation constants for all the quaternary complexes are given, and equilibrium conditions are illustrated in distribution diagrams.
Schmidt
H
H
Department of Chemistry, Umeå University, Sweden.
Andersson
I
I
Rehder
D
D
Pettersson
L
L
D000409:Alanine / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010545:Peroxides / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*
D004151:Dipeptides; D010545:Peroxides; D014638:Vanadates; D006639:Histidine; D000409:Alanine