Multinuclear Diffusion NMR Spectroscopy and DFT Modeling: A Powerful Combination for Unraveling the Mechanism of Phosphoester Bond Hydrolysis Catalyzed by Metal-Substituted Polyoxometalates

In this work we propose a detailed reaction mechanism for the hydrolysis of the phosphoester bonds in the DNA model substrate bis-4-nitrophenyl phosphate (BNPP) in the presence of the ZrIV-substituted Keggin type polyoxometalate (Et2NH2)8[{α- PW11O39Zr(µ-OH)(H2O)}2]·7H2O (ZrK 2:2) at pD 6.4. Low temperature 31P DOSY spectra at pD 6.4 give the first experimental evidence for the presence of ZrK 1:1 in fast equilibrium with ZrK 2:2 in pure aqueous solution. Moreover, theoretical calculations identified the ZrK 1:1 form as potentially active species in solution. The reaction intermediates involved in the hydrolysis have been identified based on 1 H/31P NMR studies, including EXSY and DOSY NMR, and are supported by DFT calculations. This combined experimental/theoretical approach enabled us to determine the structures of four intermediate species in which the starting compound BNPP, nitrophenyl phosphate (NPP) or the end product phosphate (P) are coordinated to ZrK 1:1. In the proposed reaction mechanism BNPP initially coordinates to ZrK 1:1 in a monodentate fashion resulting in hydrolysis of the first phophoester bond in BNPP and formation of NPP. EXSY NMR shows that the bidentate complex between NPP and ZrK 1:1 is in equilibrium with monobound and free NPP. Subsequently, hydrolysis of NPP results in P which is in equilibrium with its monobound form.

Publication year:2015

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Authors:International

Authors from:Higher Education

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