Synthesis of gold nanoparticles in aqueous solutions not containing additional interfering components using sulfite method: the effect of thiol-containing acid additives

Stable solutions of gold nanoparticles with an average diameter of 13 nm and C_Au = 5×10^–4 M were obtained by the reduction of HAuCl₄ with an equivalent amount of sodium sulfite at 80–100 °C in the presence of 2% PEG 6000 as a stabilizer: AuCl₄^– + 3/2 SO₃^2– + 3/2 H₂O → Au⁰ + 3/2 SO₄^2– + 3 H⁺ + 4 Cl^–. The resulting solutions of nanoparticles do not contain additional components capable of complexation, redox, and acid-based interactions. The effect of additives of thiourea, cysteine, thiomalate, and glutathione at various pH on the stability of such solutions to the aggregation has been studied. It was shown that the values of the protonation constants and charges of species of a thiol-containing component are not the only factors determining stability. Using thiomalate (HTM^2–) as an example, it was shown also that at pH 7–8, the chemisorption is not followed by the release of H⁺ ions into the solution.