Hydrolysis of phosphodiester catalyzed by metallomicelles with histidine residue: Kinetics and mechanism

A new 2-amino-N-dodecyl-3-(1H-imidazole-4-yl)propanamide (L2) surfactant was synthesized and its metallomicelles made of La(III), Cu(II), Co(II) and Zn(II) complexes were used as hydrolytic metalloenzyme mimics to catalyze the hydrolysis of phosphodiester bis(p-nitrophenyl) phosphate (BNPP) in buffer solution at 35 °C. The effects of long alkyl ligand, metal ions, temperature and pH on the catalytic hydrolysis of phosphodiester were investigated. The ternary complex kinetic model for metallomicellar catalysis was suggested to analyze the experimental data. The kinetic and thermodynamic parameters k ′ N , KM, KT, Km and pKa were obtained. The effect of pH was especially analyzed. The pH-independent rate constant of the reaction catalyzed by metallomicelles LaL2, CuL2, CoL2 and ZnL2 was evaluated as 7.03 × 10−4, 6.51 × 10−5, 4.28 × 10−5 and 1.78 × 10−5 s−1, respectively. The different association manners between metallomicelles and substrate were proposed. A hydroxide ion OH− associated metallomicelle, which was detected by ESI-MS spectral analysis, was suggested as the real active species to catalyze the hydrolysis of phosphodiester. Imidazole group might accelerate the hydrolysis by activating H2O associated the metal into metal-OH−. Effect of microenvironment of micelle on the catalysis hydrolysis of BNPP was also discussed.