Nitróxidos com potencial antioxidante: caracterização, desenvolvimento de método indicativo de estabilidade e degradação forçada

Abstract

Nitroxides are a class of substances with promising potential in the cosmetic industry due to their antioxidant actions that allow their use in the treatment of skin aging by inhibiting the action of free radicals and, consequently, reducing the effects of aging on the skin. In this work, three examples of this class: TEMPOL, BZTEMPOL, and TSTEMPOL were characterized using different analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), paramagnetic resonance spectroscopy (EPR), X-ray diffraction ( XRD), Differential Scanning Calorimetry (DSC), Thermogravimetry (TG), Mass Spectrometry (LC-MS) and Ultra Performance Liquid Chromatography (UHPLC), in addition to an indicative method of stability by ultra-performance liquid chromatography (UHPLC) was developed and used for forced degradation studies of the compounds in question. With the results of the DRX, FTIR, EPR, and LC-MS techniques, it was possible to identify the crystalline nature of these molecules, confirm the presence of functional groups and the radical nature expected for the structure of these compounds, in addition to guaranteeing the molecular identity and purity of the samples studied. The thermoanalytical techniques, on the other hand, make it possible to know the thermal behavior of these three nitroxides and for this four heating ratios (5, 10, 15, and 20 °C.min-1) were used, under nitrogen atmosphere. TEMPOL, BZTEMPOL, and TSTEMPOL had a melting point of 72.2, 121, and 108.4 ºC, respectively, with TEMPOL being the most thermally stable nitroxide (152 °C). With the thermogravimetric curves, it was also possible to carry out the kinetic study of the dynamic type through the Ozawa method and as a result, BZTEMPOL presented higher activation energy. As for the analytical method, it was properly developed based on a Box-Behnken factorial design for individual quantification of these molecules and was later applied in the study of forced degradation, showing its efficiency. Thus, this study provides useful support for the development of possible cosmetic formulations with these substances in a safe, effective, and quality manner.