The Self-Assembly of Cationic Metal Complexes on Gold Nanoparticle Surface.

This work aims to study the interaction between cationic metal complexes (M ) and gold nanoparticles (AuNPs ). The M complexes were chosen from previous works described in the literature and were synthesized as defined. For example, they are as follows: = RuCl(dppb)(bipy)(py); = RuCl(dppb)(bipy)(vpy); = RuCl(dppb)(bipy)(mepy); = RuCl(dppb)(bipy)(bpy); = RuCl(dppb)(bipy); = [Fe(bipy)]Cl; = Ru(bipy); = TPyP{RuCl(dppb)(bipy)}; and = RuCl(-cymene)(Dipmp). The interactions between M and AuNPs were carried out using conductometry and UV-vis spectroscopy. These experiments allowed determination of kinetic parameters, revealing three different steps in the interaction process: induction time, flocculation, and agglomeration. The self-assembly between M and AuNPs was investigated using three different models of binding site, namely, Langmuir or direct plot, Benesi-Hildebrand, and Scatchard. These models provide the fraction of total binding sites occupied (θ), the formation constant ( ), which is dependent on the temperature and geometric structure of each group of M , and the Gibbs free energy of reaction (Δ ), which was negative for each pair of M and AuNPs , revealing a spontaneous agglomeration process. The Hill coefficient () was 1 for almost all complexes, indicating that agglomeration is an independent process, except for , where = 2, suggesting a positive propensity to bind onto the AuNPs surface. The models have confirmed a noncovalent interaction between these species. The relative error in site binding does not show any variation with changes in the temperature, but a fine-tuning of the value to 1.00 was observed with the increase of the temperature. Finally, the reduction reaction of the 4-nitrophenolate anion (4-NP) by NaBH catalyzed by AuNPs was used in the presence of M as an evaluation test to show how the M species will disturb the 4-NP binding site on the surface of gold nanoparticles.