Synthesis and characterization of peroxotungsten(vi) complexes bound to water soluble macromolecules and their interaction with acid and alkaline phosphatases

Abstract

A set of peroxotungsten(VI) complexes in a macroligand environment has been prepared and characterized by elemental analysis (CHN and energy dispersive X-ray spectroscopy), spectral studies (UV–vis, IR, ¹³C NMR) and thermal gravimetric analysis (TGA), as well as SEM studies. The compounds were obtained by anchoring of peroxotungsten species to the pendant functional groups of water soluble polymers, such as poly(vinyl sulfonate) (PVS), poly(acrylate) (PA), poly(methylacrylate) (PMA) and poly(acrylamide) (PAm). The stability of the compounds in solutions of pH values ranging between 1.2 to 8.0 has been ascertained. The polymeric compounds, as well as a pair of previously reported monomeric and dinuclear pW complexes, were screened for their effect on two different membrane bound phosphatases viz., wheat thylakoid membrane acid phosphatase (ACP) and rabbit intestine alkaline phosphatase (ALP). Each of the tested complexes behaved as active inhibitors of the enzymatic function of the model enzymes. The two classes of enzymes exhibited significantly different sensitivity towards the inhibitors. The IC₅₀ and K_i values were more than 50 orders of magnitude lower for ACP than for ALP, which shows the greater affinity of the complexes for the enzyme binding site of ACP compared to ALP. The kinetic data enabled us to group the complexes into two classes on the basis of their mechanistic preferences. The group comprised of polymeric pW complexes behave as classic non-competitive inhibitors of ACP and ALP, while the free heteroligand pW compounds show mixed inhibition, combining competitive and non-competitive pathways.