Estudo da interação entre peptídeos derivados de triptofano e nanopartículas metálicas

Abstract

The adsorption of tryptophan (Trp), his derivatives and 2-mercaptoethanol (MET) on metallic nanoparticle surface had been studied on this thesis. For such investigations it was employed the following tools: ultraviolet and visible absorption spectroscopy (UV-VIS), Raman scattering spectroscopy, surface enhanced Raman spectroscopy (SERS) and density functional theory. The localized surface plasmon resonance (LSPR) band was monitored on UV-VIS spectra to study the electronic properties of metallic nanoparticles involved in the interactions with the adsorbates and the size distributions. Silver nanoplates were synthesized in different conditions of temperature, multiple growing steps and using copper as a stabilizing doping. A small addition of copper, compared to silver, increased the triangular nanoprism yield of the original synthesis. These nanoparticles were used for adsorption study of MET. It was synthesized gold and silver nanospheres for studying Trp adsorption and other peptides on different chemical surroundings. The nanoprisms were utilized for LSPR study in the presence of MET at different concentrations, in addition to SERS spectra of this molecule. It has been observed the molecule concentration has a key role for self-assembled monolayer formation, which changes the most common conformer on the metallic surface. DFT calculation allowed us to simulate MET adsorption on silver surface (111) obtaining results related to the structures and stabilities of the conformers. Theory and experiment showed in agreement in the conditions studied and conclude the hydrogen bond is a key player in the monolayer properties. It was studied the adsorption of the isomers, L-Trp and D-Trp, and the peptides, Ala-Trp, Trp-Gly, pGlu-Lys-Trp-Ala-Pro and Trp-His-Trp-Leu-Gln-Leu, through SERS spectroscopy. In silver, the spectra showed amino acids and dipeptides tend to adsorb by the acid and amine group. In gold, an enhancement and shifting of the bands allowed us to identify the adsorption by the indole ring, specifically by the nitrogen atom. The spectra were obtained at concentration of 10-3mol.L-1 on different metals, however in presence of HCl the molecular concentration was 10-5mol.L-1. When HCl was added, the spectra showed a slightly different pattern, which suggest us that, in this condition, Trp interacts stronger to the surface.