Complexation of asparagine and glutamine by dioxovanadium

The complexation of pervanadyl ion (VO2+) with L-asparagine and L-glutamine has been investigated by spectrophotometric measurements in aqueous soluti on at an ionic strength of 0.15 mol l(-1) (NaClO4) and 25 +/- 0.1 degreesC in the pH range 1.3-10.3 with high ligand-to-metal ratios. The stability co nstants of the formed complexes and their stoichiometries are given and int erpreted. The logarithms of the cumulative stability constant beta (xyz) of the [(H)(x)(oxometal)(y)(amino acid)(z)] complex are log beta (101) = 8.80 +/- 0.08, log beta (011) = 9.47 +/- 0.10, and log beta (012) = 14.57 +/- 0 .15 for asparagine and log beta (101) = 9.05 +/- 0.10, log beta (011) = 9.5 4 +/- 0.10, and log beta (012) = 14.81 +/- 0.15 for glutamine. The coordina tion mode of the ligands in their protonated and deprotonated complexes is discussed on the basis of these parameters.