Effect of citrate substitution by various α-hydroxycarboxylate anions on properties of gold nanoparticles synthesized by Turkevich method

The Turkevich method, in which citrate reduces chloroauric acid, is one of the most popular and standard protocols for the synthesis of gold nanoparticles. Mechanistic studies for this reduction have shown that reducing and capping capabilities of citrate are associated with its structure and particularly with the hydroxyl group attached to the alpha-position of the carboxyl group. Hence, it should be possible to synthesize gold nanoparticles with similar characteristics upon substitution of citrate by the other alpha-hydroxycarboxylates. Various alpha-and beta-hydroxycarboxylates have been used to investigate the effect of citrate substitution on reaction outcome. The shape, size distribution, stability and optical properties of gold nanoparticles were characterized by scanning and transmission electron microscopy, differential centrifugal sedimentation and UV-vis spectroscopy. The citrate can be substituted in the Turkevich method by other alpha-hydroxycarboxylates, however, their structure and the first product of their oxidation strongly influence shape, size and size distribution of synthesized gold nanoparticles. The alpha-position of the hydroxyl group with respect to the carboxyl group is critical for the reduction to occur. These comprehensive studies provide new insights into the reaction mechanism governing the Turkevich method.