Kinetic study on the singlet oxygen quenching activity of nordihydroguaiaretic acid (NDGA) using methylene blue sensitized photooxidation of α-terpinene.

Singlet oxygen is highly reactive and can therefore induce rapid oxidation of a range of biological molecules, causing cell damages. The effects of nordihydroguaiaretic acid (NDGA) on the photochemical singlet oxygen oxidation of α-terpinene in methanol were studied. NDGA showed strong protective activity on the singlet oxygen oxidation of α-terpinene in methanol in a dose dependent manner. The protective activity of NDGA was considerably higher than that of butylated hydroxytoluene and 1,4-diazabicyclo[2.2.2]octane. Total singlet oxygen quenching rate constant (k r +k q ) of NDGA was determined by a steady state kinetic equation. The total singlet oxygen quenching rate constant of NDGA was 9.81×107 M-1 sec-1. The result showed that NDGA possessed strong singlet oxygen quenching activity, indicating its potential for the protection of molecules, cells and nutrients from the highly reactive singlet oxygen. To the best of our knowledge, this is the first report on the singlet oxygen quenching rate constant of NDGA.