Chemical reduction of Ag+ to Ag employing organic electron donors: evaluation of the effect of Ag+-mediated cytosine–cytosine base pairing on the aggregation of Ag nanoparticles

Abstract

Ag⁺-mediated base pairing is valuable for synthesising DNA-based silver nanoparticles (AgNPs) and nanoclusters (AgNCs). Recently, we reported the formation of a [Ag(cytidine)₂]⁺ complex in dimethyl sulfoxide (DMSO), which facilitated the evaluation of the effect of cytosine–Ag⁺–cytosine (C–Ag⁺–C) base pairing on the degree of AgNP aggregation in solution. As an aprotic solvent, DMSO was expected to dissolve the [Ag(cytidine)₂]⁺ complex, and powerful reducing agents, such as organic electron donors. In this study, the chemical reduction of a cytidine/Ag⁺ system using a powerful reducing agent tetrakis(dimethylamino)ethylene (TDAE) was investigated. ¹H/¹³C/¹⁵N NMR spectroscopic evidence was obtained to identify the iminium dication (TDAE²⁺), which is an oxidised form of TDAE. The results were compared with those obtained using another organic electron donor, tetrathiafulvalene (TTF), which exhibits a relatively lower reduction activity than TDAE. AgNPs prepared via redox reaction between [Ag(cytidine)₂]⁺ and organic electron donors (TDAE and TTF) were characterised using UV–Vis spectroscopy and nanoparticle tracking analysis. It was found that the formation of C–Ag⁺–C base pairing inhibited the aggregation of AgNPs in solution. In addition, in the presence of cytidine, the total concentration of the AgNP solution was affected by the reduction activity of the reducing agent.