The interaction between different HO. radical scavengers in a three-component antioxidant system has been investigated by means of F-19-NMR spectroscopy. This system is composed of bovine serum albumin (BSA), trolox, and N-(4-hydroxyphenyl)trifluoroacetamide (CF(3)PAF). The antioxidant capacity of BSA and trolox has been assessed by measuring the amount of trifluoroacetamide (TFAM) arising from the radical mediated decomposition of CF(3)PAF. When assayed separately, both trolox and BSA behaved as antioxidants, as they were effective to protect CF(3)PAF from HO. radical-mediated decomposition. By contrast, trolox enhanced the production of TEAM in the presence of BSA, thus behaving as a pro-oxidant. Urate, carnosine, glucose, and propylgallate showed antioxidant properties both with or without BSA. CF(3)PAF and trolox were found to bind to BSA with association constants in the order of 5 x 10(3) M-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 CF(3)PAF. (C) 2003 Elsevier Inc. All rights reserved.