Nucleophilic reaction by carbonic anhydrase model zinc compound: characterization of intermediates for CO2 hydration and phosphoester hydrolysis.
The partially hydrophilic and hydrophobic tripodal ligands, tris(hydroxy-2-benzimidazolylmethyl)amine L1h and tris(2-benzimidazolyl)amine L1 were used for the preparation of biomimetic complex of carbonic anhydrase. The CO(2) hydration using [L1hZn(OH)]ClO(4).1.5H(2)O provided the zinc-bound and free HCO(3)(-)s, which were formed by nucleophilic attack of Zn-OH toward CO(2) in dimethyl sulfoxide (DMSO). The phenolic OH in L1h can recognize water molecules through hydrogen bonds to facilitate the collection of the water molecules around a biomimetic zinc compound; the molecular structure of [L1hZn(OH)](+) was revealed. The packing diagram has demonstrated the all the water molecules are hydrogen bonded to each phenolic OH. The nucleophilic attack of zinc-bound OH(-) to substrate is used to catalyze the CO(2) hydration and phosphoester hydrolysis. The carbonic anhydrase model compound [L1Zn(OH(2))](2+) was applied for the hydrolysis of phosphoesters, parathion and bis(p-nitrophenyl)phosphate (BNPP(-)). The low reactivity of [L1Zn(OH)](+) for parathion hydrolysis is attributed to the stability of the intermediate [L1Zn(OP(S)(OEt)(2))](+). Since the structures of the intermediates [L1Zn(OH(2))](BNPP)(2) (1) and [L1Zn(OP(S)(OEt)(2))]ClO(4) (2) formed on the way of hydrolysis are too stable to realize the catalytic cycle and are not active for hydrolysis, carbonic anhydrase model compound [L1Zn(OH(2))](2+) was not suitable for phosphoester hydrolysis; the zinc model compound surrounded by three benzimidazolyl groups is used to have the steric hindrance for bulky substrate, such as parathion and BNPP(-).
Division of Material Science, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan.
Tsuneo
T
Echizen
M M
MM
Ibrahim
Kou
K
Nakata
Mitsunori
M
Izumi
Kazuhiko
K
Ichikawa
Motoo
M
Shiro
D001665:Binding Sites; D002245:Carbon Dioxide / Q000737:chemistry*; D002256:Carbonic Anhydrases / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D014867:Water / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry*
D017967:Zinc Compounds; D014867:Water; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases