Estudo cinético e termodinâmico da interação de nanopartículas de ouro com compostos de coordenação

Abstract

This work aims to study the interaction between metallic complexes and gold nanoparticles (AuNPsn−), and the determination of its physicochemical parameters. Earlier studies showed that the interaction between metallic compounds and AuNPsn− coupled to modified sensors were capable of catalyzing the electrochemical oxidation of the acetaminophen. Seeking to better understand the interactions for future applications, we carried out this study. Most of the ruthenium complexes were synthesized by exchanging ligands in their coordination sphere and the addition of a counter-ion, given these a cationic character. The AuNPsn− were synthesized through the encapsulation method citrate giving them an anionic character. The synthesized compounds were characterized by various techniques such as Ultraviolet-visible absorption spectroscopy, infrared absorption spectroscopy, cyclic voltammetry, square wave voltammetry and condutimetry. The monitoring of interactions between the cationic complexes and anionic gold nanoparticles (Mn+/AuNPsn−) were carried out with the aid of two techniques: Conductimetry and Uv-vis. In condutimetry, additions were made aliquots (20 μL to 2200 μL) solutions of metallic compounds of nominal concentration of 10-5 mol/L in 10 mL of AuNPsn− solution. In Uv-vis spectroscopy, was the application of various methods for the thermodynamic and kinetic investigation of Mn+/AuNPsn− interactions. The kinetics approach consists in monitoring the transverse plasmon band of AuNPsn− (Z = 520 nm) and the resulting longitunidal band interaction formed system of AuNPsn− (Z = 625 nm) in function of time after variation of the temperature and concentration of the cationic complexes. These experiments allowed to determination various kinetic parameters of Mn+/AuNPsn− interactions, such as the rate constants (k), activation energy (Ea), and the collision factor (ln A). Activation thermodynamic parameters also were determined: activation enthalpy (ΔH‡), activation entropy (ΔS‡) and activation Gibbs free energy (ΔG‡). In thermodynamic approach, we used the Langmuir isotherm (direct graph), Benesi-Hildebrand model and Sctachard model to obtain thermodynamic parameters, such as: dissociation constant (Kd) and Hill coefficient (n). The relative error was determined where the Kd values are maximum. Posteriorly, this study can be applied in catalysis, improving the studies that are underway.