Sviluppo di un metodo elettrochimico per la determinazione della capacità antiossidante

The aim of the present thesis, carried out at the Analytical Group of the Faculty of Industrial Chemistry in Bologna, is to develop a new electrochemical method for the determination of the Antioxidant Capacity (AOC). The approach is based on the deposition of a non-conducting polymeric film on the working electrode surface and the following exposition to the radicals OH· produced by H2O2 photolysis. The strongly oxidant action of hydroxyl radicals degrades, causing an increase of the Faradic current, relevant to the redox couple [Ru(NH3)6]2+/3+ monitored by cyclic voltammetry(CV); the presence of an antioxidant compound in solution slows down the radical action, thus protecting the polymeric film and blocking the charge transfer. The parameter adopted for the quantification of the AOC, was the induction time, called also lag phase, which is the time when the degradation of the film starts. Five pure compounds, among most commonly antioxidant, were investigated : Trolox®(an analogue water-soluble of vitamin E), (L)-ascorbic acid, gallic acid, pyrogallol and (-)- epicatechin. The AOC of each antioxidant was expressed by TEAC index (Trolox® Equivalent Antioxidant Capacity), calculated from the ratio between the slope of the calibration curve of the target compound and the slope of the calibration curve of Trolox®. The results from the electrochemical method, have been compared with those obtained from some other standardized methods, widely employed. The assays used for the comparison, have been: ORAC, a spectrofluorimetric method based on the decrease of fluorescein emission after the attack of alkylperoxide radicals, ABTS and DPPH that exploit the decoloration of stable nitrogen radicals when they are reduced in presence of an antioxidant compound and, finally, a potentiometric method based on the response of the redox couple [Fe(CN)6]3-/ [Fe(CN)6]4-. From the results obtained from pure compounds, it has been found that ORAC is the methodology showing the best correlation with the developed electrochemical method, maybe since similar radical species are involved. The comparison between the considered assays, was also extended to the analysis of a real sample of fruit juice. In such a case the TEAC value resulting from the electrochemical method is higher than those from standardized assays.

Main characteristics of the emission from elliptical galaxies

Elliptical galaxies are one of the most characteristic objects we can find in the sky. In order to unveil their properties, such as their structure or chemical composition, one must study their spectral emission. In fact they seem to behave rather differently when observed with different eyes. This is because their light is mainly brought by two different components: optical radiation arises from its stars, while the X emission is primarly due to a halo of extremely hot gas in which ellipticals seem to be embedded. After a brief classification, the two main processes linked to these phenomena will be described, together with the informations we can collect thanks to them. Eventually, we will take a quick look at the other regions of the electromagnetic spectrum.