Singlet Oxygen에 의한 Oxygenation 반응에 미치는 Keto-carotenoids의 Quenching Activities

Abstract

The singlet oxygen quenching activites of various carotenoids obtained from natural products were studied. The 102 quenching rate constants (Kq) of β-carotene, capsanthin, capsanthin monoester, capsanthin diester and fucoxanthin were determined and compared quantitatively. The relationship between the structures of carotenoids and its 102 quenching activities were discussed in the light of the substituent effects on the structure. In methanolic solution, the Kqs of capsanthin, capsanthin monoester and fucoxanthin ￦ere shown to be 2.29×10¹⁰, 2.23×10¹⁰ and 0.96×10¹⁰ M⁻¹ sec⁻¹ respectively, while the Kq of βcarotene was determined as 2.36 × 10¹⁰ M⁻¹ sec⁻¹, And the Kq/Kd values of capsanthin monoester, diester and lycopene in benzene-methanol (3 : 5) solution were 1.33×10⁵, 1.26×10⁵ and 2.06×10⁵, respectively. Under the experimental condition, there was no pronounced differences in 102 quenching activity between capsanthin and capsanthin esters. The 102 quenching activity of fucoxanthin was shown to be two-fifth of the β-carotene's These results indicated that the activity of quenching decreased as the introduction of hydroxy or carbonyl group. Carotenoid-fatty acid esters showed lower quenching activity than corresponding free carotenoids, and diester was less active than monoester. These results implied that the existance of long fatty acid chain in carotenoid ester molecules might reduce the quenching actitvity by the reduction of the effective cross-secion of the reaction.