KINETIC-STUDY OF QUENCHING REACTION OF SINGLET OXYGEN AND SCAVENGING REACTION OF FREE-RADICAL BY SQUALENE IN N-BUTANOL

The rate constant of quenching of singlet oxygen (k(Q)) by squalene (SQ) is found to be much larger than those of the lipids in human skin surface. SQ is the first target lipid in human skin surface by oxidative stresses such as sun light exposure. k(Q) of SQ is similar to that of 3,5-di-t-butyl-4-hydroxytoluene (BHT). The large k(Q) of SQ is due to the small ionization potential. SQ consists of six 2-methyl-2-pentene units and k(Q) of SQ is about 6-times as large as that of 2-methyl-2-pentene. The electron donating property of methyl groups bonded to quaternary carbons of SQ is essential to the large k(Q). SQ is not very susceptible to peroxidation and is stable for attacks by peroxide radicals. The chain reaction of lipid peroxidation is unlikely to be propagated with SQ in human skin surface. it is concluded that SQ functions as an efficient quencher of singlet oxygen and prevents the corresponding part of lipid peroxidation in human skin surface.