Modulation of the antioxidant activity of HO^. scavengers by albumin binding: A ¹⁹F-NMR study

The interaction between different HO^. radical scavengers in a three-component antioxidant system has been investigated by means of ¹⁹F-NMR spectroscopy. This system is composed of bovine serum albumin (BSA), trolox, and N-(4-hydroxyphenyl)-trifluoroacetamide (CF₃PAF). The antioxidant capacity of BSA and trolox has been assessed by measuring the amount of trifluoroacetamide (TFAM) arising from the radical mediated decomposition of CF₃PAF. When assayed separately, both trolox and BSA behaved as antioxidants, as they were effective to protect CF₃PAF from HO^. radical-mediated decomposition. By contrast, trolox enhanced the production of TFAM in the presence of BSA, thus behaving as a pro-oxidant. Urate, carnosine, glucose, and propylgallate showed antioxidant properties both with or without BSA. CF₃PAF and trolox were found to bind to BSA with association constants in the order of 5×10³M^-1 and to compete for the same binding sites. These results have been discussed in terms of BSA-catalysed cross-reactions between trolox-derived secondary radicals and CF₃PAF.