Formation of a hydroxyl radical from tar dye by photo-illumination

Article abstract of DOI:10.1248/cpb.43.1810

When indigo carmine (B-2) was illuminated in the presence of phenylalanine in 0.1 M citrate buffer (pH 4.0), p-tyrosine, m-tyrosine and o-tyrosine were identified as hydroxylated products. However, ten other food colors did not form tyrosine isomers. The hydroxylation of B-2 was pH-dependent, and the maximum rate was found at around pH 4.0. Replacement of air with nitrogen gas completely prevented the formation of tyrosine isomers and the decomposition of B-2. In contrast, oxygen gas accelerated both the hydroxylation and the decomposition. The addition of superoxide dismutase or catalase to this system prevented hydroxylation. Chemical scavengers of the hydroxyl radical (HO·) prevented the hydroxylation. On the other hand, a singlet oxygen scavenger had no significant effect. The above results suggest that the formation of HO· may occur in the photochemical reaction system in the presence of B-2 under aerobic conditions, and that a superoxide radical and hydrogen peroxide may he involved in the HO· formation.

Full text of DOI:10.1248/cpb.43.1810

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