Expanding the antioxidant activity into higher temperatures - Fullerene C60 conjugated with α-Tocopherol analogue as a hybrid antioxidant in saturated lipid systems

Oxidative stability of two fatty acids: stearic acid (STA) as a model of saturated lipid and linolenic acid (LNA) as model of polyunsaturated lipid containing C60 derivative with covalently bonded hydroxychromanyl moiety as analogue of α-Tocopherol (F-1) was monitored by differential scanning calorimetry. The overall Arrhenius kinetic parameters (activation energy Ea, pre-exponential factor Z, and rate constants k) of non-isothermal oxidative decomposition indicate that in saturated hydrocarbons the hybrid C60+hydroxychromane derivative is effective antioxidant acting at temperatures above 120°C, expressed as 9 kJ/mol increase of Ea and values of k twice smaller than for oxidation of noninhibited pure STA. However, experiments with LNA oxidized at temperatures above 80°C indicated that the hybrid derivative did not improve the oxidative stability of polyunsaturated lipids at higher temperatures (Ea, Z and k's are almost the same as for oxidation of pure LNA). We suggest that C60 is able to inhibit STA autoxidation due to formation of thermally stable adducts with alkoxyl radicals whereas autoxidation LNA is mediated by peroxyl radicals that are not effectively scavenged by C60.