Probing the Catalytically Active Species in POM-Catalyzed DNAmodel Hydrolysis

Phosphoester hydrolysis is an important chemical step in DNA repair. One archetypal molecular model of phosphoesters is para-nitrophenylphosphate (pNPP). It has been shown previously that the presence of molecular metal oxide [Mo7O24]6– may catalyse the hydrolysis of pNPP through the partial decomposition of polyoxomolybdate framework resulting in a [(PO4)2Mo5O15]6– product. Real-time monitoring of the catalytic system using electrospray ionisation mass spectrometry (ESI-MS) provided a glance into the species present in the reaction mixture. Following up on the obtained spectrometric data, Density Functional Theory (DFT) calculations were carried out to characterise the hypothetical intermediate [Mo5O15(pNPP)2(H2O)6]6– that would be required to form under the hypothesised transformation. Surprisingly, our results point to the dimeric [Mo2O8]4- anion resulting from the decomposition of [Mo7O24]6– as the active catalytic species involved in the hydrolysis of pNPP rather than the originally assumed {Mo5O15} skeleton. A similar study was carried out involving the same species but substituting Mo by W. The mechanism involving W species showed a higher barrier and less stable products in agreement with the non-catalytic effect found in experimental results.