TYPE I and TYPE II PHOTOSENSITIZATION BY THE ANTIBACTERIAL DRUG NALIDIXIC ACID. A LASER FLASH PHOTOLYSIS STUDY*

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Abstract
The 355 nm laser flash photolysis of nalidixic acid at pH 9.2 leads to the formation of the nalidixate anion triplet state (absorption Λmax= 620 nm; 5700 ≤εT≤ 9000 M−1cm−1; 0.6 ≤φT≤ 1). The first order triplet state decay (kT= 7.7 times 10−3s−1) is accompanied by a diffusion controlled triplet‐triplet annihilation. Oxygen efficiently quenches the triplet state (k = 3.2 times 109M−1s−1). The nalidixate radical dianion (absorption Λmilx= 650 nm; ε= 3000 M−1cm−1) is produced by the diffusion controlled reductive quenching of the triplet state by tryptophan and tyrosine. The superoxide anion (O−2) is produced by diffusion controlled reaction of the radical dianion with oxygen. The O−2 is characterized by its reactions with ferricytochrome c and superoxide dismutase. The physiological form of nalidixic acid is thus a good Type I and Type II photosensitizer.

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