Study on kinetics and mechanism of mononuclear rare earth metal complexes in promoting the hydrolysis of p-nitrophenyl phosphate (NPP)

Two novel tripodal ligands, N,N ',N ''-tri-(3 '-phenylpropionic acid-2 '-yl-)-1,3,5-triaminomethylbenzene (L1), N,N ',N '',ff'-tri-(4 '-methylvaleric acid-2 '-yl-)-1,3,5-triaminomethylbenzene (L2) have been synthesized. The hydrolytic kinetics of p-nitrophenyl phosphate (NPP) catalyzed by complexes of L1, and L2 with La(III) and Gd(III) have been studied in aqueous solution at 298 K, I = 0.10 mol dm(-3) KNO3 at pH 6.7-8.2, respectively. In the study it is found that the catalytic effect of GdL2 was the best in the four complexes for hydrolysis of HPNP. Its k(LnLH-1), k(LnL) and pK(a), are 0.0198 mol(-1) dm(3) s(-1), 0.0000187 mol(-1) dm(3) s(-1) and 7.76, respectively. This paper expounds the result from the structure of the ligands and the properties of the metal ions, and deduces the catalysis mechanism. (c) 2006 Published by Elsevier.