α-Alkyl cysteine-coated gold nanoparticles: effect of Cα-tetrasubstitution on colloidal stability

In this work, we report the synthesis of new α-methyl l-cysteine-coated gold nanoparticles (average core diameter ca. 3 nm) and the remarkable enhancement of their aqueous stability against aggregation in comparison with the nanoparticles capped with unmodified l-cysteine under the same experimental conditions. Atomistic molecular dynamics simulations of model gold surfaces capped with l-cysteine or α-methyl l-cysteine revealed important differences in both the organization of the amino acids with respect to the surface and their spontaneous assembly with neighboring molecules. These differences, which are originated by the introduction of the α-methyl group in the amino acid, could be associated with the observed increase in stability and dispersibility of the composites in aqueous solutions at different pH values and ionic concentrations.