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Voltammetric Study of the Influence of Various Phosphate Anions on Silver Nanoparticle Oxidation.

ABSTRACT: The antibacterial properties of silver are strongly controlled by the redox couple of silver/silver(I). This work reports the influence of phosphate anions on silver nanoparticle oxidation, which is important given the abundance of phosphate species in biological systems. The three different species of anions were found to have a varying degree of influence on silver oxidation with the order PO4 (3-)>HPO4 (2-)>H2PO4 (-). It was found that in the presence of phosphate anions, the silver oxidation potential shifts to a less positive value, which indicated the increasing ease of the oxidation reaction of silver. Given that the interplay between silver and its cation is crucial to its antibacterial properties and significant concentrations of the HPO4 (2-) anion are present at biological pH (near neutral), it is essential that the influence of the dibasic anion (HPO4 (2-)) on silver oxidation dynamics be considered for biological systems.

SUBMITTER: Navolotskaya DV

PROVIDER: S-EPMC4608526 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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Voltammetric Study of the Influence of Various Phosphate Anions on Silver Nanoparticle Oxidation.

Navolotskaya Daria V DV Toh Her Shuang HS Batchelor-McAuley Christopher C Compton Richard G RG

ChemistryOpen 20150612 5

The antibacterial properties of silver are strongly controlled by the redox couple of silver/silver(I). This work reports the influence of phosphate anions on silver nanoparticle oxidation, which is important given the abundance of phosphate species in biological systems. The three different species of anions were found to have a varying degree of influence on silver oxidation with the order PO4 (3-)>HPO4 (2-)>H2PO4 (-). It was found that in the presence of phosphate anions, the silver oxidation ...[more]

PMID: 26491638

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Project description:Uracil DNA glycosylase (UNG) is a powerful DNA repair enzyme that has been shown to stabilize a glycosyl cation reaction intermediate and a related tight binding inhibitor using electrostatic interactions with the +1 and -1, but not the +2, phosphodiester group of the single-stranded DNA substrate Ap (2+)Ap (1+)Up (1-)ApA. These experimental results differed considerably from computational findings using duplex DNA, where the +2 phosphate was found to stabilize the transition state by approximately 5 kcal/mol, suggesting that UNG uses different catalytic strategies with single-stranded and double-stranded DNA substrates. In addition, the computational studies indicated that the conserved and positively charged His148 (which hydrogen bonds to the +2 phosphate) destabilized the glycosyl cation intermediate by 6-8 kcal/mol through anticatalytic electrostatic interactions. To evaluate these interesting proposals, we measured the kinetic effects of neutral methylphosphonate (MeP) stereoisomers at the +1 and +2 positions of a 12-mer dsDNA substrate and also the catalytic contribution and ionization state of His148. For MeP substitutions at the +1 position, single-turnover kinetic studies showed that the activation barrier was increased by 9.8 and 3.1 kcal/mol, corresponding to a stereoselectivity of nearly 40000-fold for the respective MeP isomers. Identical to the findings with ssDNA, MeP substitutions at the +2 position resulted in only small changes in the activation barrier (+/-0.3 kcal/mol), with little stereoselectivity ( approximately 4-fold). However, the H148A mutation destabilizes both the ground state and transition states by 2.4 and 4.3 kcal/mol, respectively. Thus, His148 is catalytic because it stabilizes the transition state to a greater extent (1.9 kcal/mol) than the ground state. Heteronuclear NMR studies established that His148 was neutral in the free enzyme at neutral pH, and in conformational exchange in a specific DNA complex containing uracil. We conclude that the +1 and +2 phosphate esters play identical catalytic roles in the reactions of single-stranded and double-stranded DNA substrates, and that His148 serves a catalytic role by positioning the substrate and catalytic water, or by an environmental effect.

Dataset Information

Voltammetric Study of the Influence of Various Phosphate Anions on Silver Nanoparticle Oxidation.

Publications

Voltammetric Study of the Influence of Various Phosphate Anions on Silver Nanoparticle Oxidation.

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