Kinetics and equilibrium study of nickel(II) complexation by pterin and 6-carboxypterin

VICTOR D. MONÓPOLI; ANDRÉS H. THOMAS; ALBERTO L. CAPPARELLI

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS

Wiley-VCH

Año: 2000 vol. 32 p. 231 - 237

0538-8066

The kinetics of complexation of Ni(II) by pterin was studied in aqueous solutions with a stopped-flow apparatus under conditions of pseudo-first order in the temperature range 5-45°C, pH between 4.0 and 6.5, and ionic strength 0.4 M. The equilibrium constants, stoichiometry, and pKa of the ligand and complex were also determined using a spectrophotometric technique. The results are consistent with the formation of a 1:1 complex between the metal ion and pterin. The first-order experimental rate constant kapp is pH independent and shows the following dependence with the ion metal concentration at 25°C: kapp/s-1 = 3.8 × 10-3 + 1.6 × 10-4 × [Ni(II)]-1. A global activation energy of 57 ± 2 kJ/mol associated with the formation of a 1:1 chelate was measured.