Vanadium(V)-substituted Keggin-type heteropolyoxotungstophosphates as electron transfer and antimicrobial agents: oxidation of glutathione and sensitization of MRSA towards β-lactam antibiotics

Abstract

Glutathione (GSH) undergoes facile electron transfer with vanadium(V)-substituted Keggin-type heteropolyoxometalates, ½PV V W 11 O 40 4À (HPA1) and ½PV V -V V W 10 O 40 5À (HPA2). The kinetics of these reactions have been investigated in phthalate buffers spectrophotometrically at 25°C in aqueous medium. One mole of HPA1 consumes one mole of GSH and the product is the oneelectron reduced heteropoly blue, ½PV IV W 11 O 40 5À . But in the GSH-HPA2 reaction, one mole of HPA2 consumes two moles of GSH and gives the two-electron reduced heteropoly blue ½PV IV V IV W 10 O 40 7À . Both reactions show overall third-order kinetics. At constant pH, the order with respect to both [HPA] species is one and order with respect to [GSH] is two. At constant [GSH], the rate shows inverse dependence on [H ? ], suggesting participation of the deprotonated thiol group of GSH in the reaction. A suitable mechanism has been proposed and a rate law for the title reaction is derived. The antimicrobial activities of HPA1, HPA2 and ½PV V V V V V W 9 O 40 6À (HPA3) against MRSA were tested in vitro in combination with vancomycin and penicillin G. The HPAs sensitize MRSA towards penicillin G.

Chitosan-Polyoxometalate Nanocomposites: Synthesis, Characterization and Application as Antimicrobial Agents

“…Among several mechanisms proposed for antimicrobial activities of metal/metal oxides, impairment of membrane architecture through electrostatic repulsion [13] and oxidative degradation have been commonly acknowledged [68]. As a matter of fact, POMs have already been used to promote electron transfer (ET) reactions with biologically relevant substrates, highlighting their major role as electron acceptors [6]. The oxidative power of the POMs under investigation is thus expected to be a key factor for better performances.…”

“…Several different classes of POMs have been reported as efficient antimicrobial agents in a number of different formulations: polyoxotungstates were used to inhibit the growth of methicillin-resistant Staphylococcus aureus, since they depress the formation of a penicillin-binding protein with low affinity for b-lactams [6][7][8][9]. Then organoantimony(III)-containing heteropolytungstates were used against Escherichia coli and Bacillus subtilis, showing a slightly stronger activity against the latter gram-positive bacterium [10].…”

“…This work reports the synthesis and characterization of novel nanocomposites derived from commercially available low molecular weight CS and different POMs, namely (NH 4 ) 6 (Fig. 1).…”

Studies on electron transfer reactions: oxidation of phenol and ring-substituted phenols by heteropoly 11-tungstophosphovanadate(V) in aqueous acidic medium

“…The oxidant K 4 ½PV V W 11 O 40 Á 2H 2 O was prepared by the method described by Domaille [21] and characterized by elemental analysis and IR spectrum as reported in our previous papers [17,20]. All the phenols were purchased from Aldrich.…”

“…The electron transfer reactions of V(V)-substituted heteropolyoxotungstates with NADH, thiourea, thioglycolicacid L-cysteine, and glutathione have been reported [15][16][17][18][19][20].…”