Mechanistic Details\nof the Organizer-Assisted Nucleation\nof Gold Nanoparticles by the Turkevich Method

Turkevich’s method for synthesizing citrate-stabilized\nAuNPs\nis the most popular method because of its straightforward methodology\nand reliability in producing highly stabilized AuNPs ranging from\n5 to 150 nm. The mechanism involves the reduction of auric Au<sup>3+</sup> species to aurous Au<sup>+</sup> species using trisodium\ncitrate and disproportionation of the aurous Au<sup>+</sup> species\nto metallic gold (Au) atoms. Several studies have been conducted in\nthe last 20 years to understand the mechanism of the Turkevich method.\nIt has been hypothesized that the disproportionation of aurous Au<sup>+</sup> species is aided by the formation of a complex between aurous\nAu<sup>+</sup> species and dicarboxy acetone (DCA), which is a byproduct\nof the first reaction involving the reduction of auric Au<sup>3+</sup> species. However, there has been no direct evidence through experiments\nor molecular simulation of the existence of such a complex. In this\nwork, we use molecular simulations to study the nucleation of AuNPs\nfrom the aurous Au<sup>+</sup> species with a specific focus on the\nrole of DCA as an organizer. The simulations are able to give detailed\ninsights into the mechanism of AuNP formation, including the structure\nof the complex between Au<sup>+</sup> and DCA. The simulations reveal\na probable two-step nucleation mechanism consisting of (i) nucleation\nof the DCA–Au<sup>+</sup> complex into a cluster and (ii) nucleation\nof metallic gold within this cluster. The nucleation mechanism proposed\nin this work can serve as a prototype in other organizer-assisted\nnucleation of metallic nanoparticles.