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Echizen T, Ibrahim MM, Nakata K, Izumi M, Ichikawa K, Shiro M: Nucleophilic reaction by carbonic anhydrase model zinc compound: characterization of intermediates for CO2 hydration and phosphoester hydrolysis. J Inorg Biochem. 2004 Aug;98(8):1347-60.
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 (-). |
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