J Solution Chem (2010) 39: 639–653 DOI 10.1007/s10953-010-9535-8 Complex Formation Equilibria Between Zinc(II), Nitrilo-tris(Methyl Phosphonic Acid) and Some Bio-relevant Ligands. The Kinetics and Mechanism for Zinc(II) Ion Promoted Hydrolysis of Glycine Methyl Ester Mahmoud M.A. Mohamed · Ahmed A. El-Sherif Received: 6 August 2009 / Accepted: 24 November 2009 / Published online: 11 May 2010 © Springer Science+Business Media, LLC 2010 Abstract Binary and ternary complexes of zinc(II) involving nitrilo-tris(methyl phospho- nic acid (H 6 A) and amino acids, peptides (HL), or DNA constituents have been investi- gated. The stoichiometry and stability constants for the complexes formed are reported. The results show that ternary complexes are formed in a stepwise manner whereby nitrilo- tris(methylphosphonic acid) binds to zinc(II), which is then followed by coordination of an amino acid, peptide or DNA. Zinc(II) was found to form ZnA and ZnAH n complex species where n = 3, 2 or 1. The stabilities of the ternary complexes are compared with the stabilities of their corresponding binary complexes. The concentration distributions of the various complex species have been evaluated. The kinetics of the base hydrolysis of glycine methyl ester in the presence of Zn(II)-NTP complexes was studied in aqueous solution us- ing a pH-stat technique. The pK a for ionization of the coordinated water molecule is 9.14 as determined from the kinetic results, while direct potentiometric titration of the complex [Zn(NTP)(H 2 O)] gave 9.98 (±0.02). The rate constant for the intramolecular attack of co- ordinated hydroxide on the ester is k = (2.65 × 10 −4 ± 0.003) dm 3 ·mol −1 ·s −1 . Keywords Zinc(II) formation equilibria · Nitrilo-tris(methylphosphonic acid) · Bio-relevant ligands · Kinetics of hydrolysis · Glycine methyl ester 1 Introduction The study of ternary complexes of transition metal ions with amino acids, peptides or DNA constituents has become the focus of increasing research effort [1–4], which is revealing M.M.A. Mohamed ( ) Department of Sciences and Mathematics, New-Valley Faculty of Education, Assiut University, Assiut, Egypt e-mail: mmhm802004@yahoo.com A.A. El-Sherif Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt e-mail: aelsherif72@yahoo.com