Study on kinetics and mechanism of mononuclear rare earth metal complexes in promoting the hydrolysis of 2-hydroxy-propyl-p-nitrophenyl phosphate (HPNP)

Two novel tripodal ligands, N,N′,N″-tri-(3′-phenylpropionic acid-2′-yl)-1,3,5-tri-aminomethylbenzene (L1), N,N′,N″-tri-(4′-methylvaleric acid-2′-yl)-1,3,5-triamino-methylbenzene (L2) have been synthesized. The hydrolytic kinetics of 2-hydroxy-propyl-p-nitrophenyl phosphate (HPNP) 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. GdL2 has the best catalytic effect in the four complexes for hydrolysis of HPNP. Its kLnLH−1, kLnL and pKa are 0.0927 mol−1 dm3 s−1, 0.000101 mol−1 dm3 s−1 and 7.73, respectively. Due to smaller radius of Gd(III) compared with that of La(III), its complexes have lower pKa and better catalytic ability compared with corresponding La(III) complexes. This paper expounds the result from the structure of the ligands and the properties of the metal ions, and deduces the catalysis mechanism.

Graphical abstractKinetics and mechanism of promoted hydrolysis of 2-hydroxy-propyl-p-nitrophenyl phosphate (HPNP) by complexes of tripodal ligands L1 and L2 with La(III) and Gd(III).Figure optionsDownload full-size imageDownload as PowerPoint slide