Ressonância paramagnética eletrônica de radicais nitróxidos e nanobastões de ouro funcionalizados com marcadores de spin

Abstract

For this work, a novell spin label specific for gold nanostructures was synthesized (ALTEMPOL). Having a nitroxide radical group, it was synthesized by means of an esterification reaction of TEMPOL (1-Oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine) coupled to lipoic acid (AL). AL was chosen because of two sulfur atoms in its structure, which can form thiol groups (-SH) that have high affinity to gold nanostructures. After its synthesis, the molecular structure of the ALTEMPOL was confirmed by Nuclear Magnetic Resonance (NMR) and Infrared Spectroscopy. Following that, a systematic characterization of the TEMPOL, as well as the spin label ALTEMPOL, both in solutions, was done with Electron Paramagnetic Resonance (EPR). Among the several results obtained in this part, the most important were: 1) the dependence on the microwave power that allowed to stablish the saturation behavior of EPR spectrum for these two radicals; 2) the influence of the concentration in EPR spectra, reflected in lineshape, is in accordance with the appearance of an exchange interaction among close molecules; 3) varying the solvent, the spin Hamiltonian parameters showed a correlation with the polarity and viscosity of the solvent and were consistent with the literature; and, 4) the activation energy for rotational diffusion for the TEMPOL radical was calculated from the Arrhenius plot of the temperature-dependent EPR spectra. In the second part of this work, gold nanorods (AuNR) were synthesized via seedless method, with resveratrol acting as reducing agent for gold ions (Au3+ to Au+), and later exposed to ALTEMPOL for the spin labelling. Optical Absorption UV-VIS and Transmission Electron Microscopy (TEM) were used for a preliminary characterization of the ALTEMPOL spin-labeled AuNRs. In the sequence, the EPR investigation of three different ALTEMPOL-labeled AuNR samples revealed the binding of the molecules of the radicals to the surface of the AuNRs