The X-Ray-Induced Damage to the p-Aminobenzoic Acid Moiety of Folic Acid and Some Other p-Aminobenzoic Acid Conjugates Irradiated in Solution

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Abstract
In aerated solutions the radiation damage to N-(p-aminobenzoyl) glutamic acid and N-(p-aminobenzoyl)glycine was found to be preferentially localized to the p-aminobenzoic acid moiety which was degraded with a slightly higher yield (G = 1.08) than was free p-aminobenzoic acid (G = 0.99). The results indicate that the aliphatic residues of the conjugates studied are unable to compete effectively for the radicals degrading p-aminobenzoic acid. Folic acid was degraded with a total yield of G = 1.20. The main part of the degradation involved the p-aminobenzoic acid moiety which was hydroxylated in the o-amine position with a yield of G = 0.61. N-(p-aminobenzoyl) glutamic acid and N-(3-hydroxy-4-aminobenzoyl)glutamic acid were liberated with yields of G = 0.33 and G = 0.22, respectively, demonstrating that the 9,10 linkage was split with a G-value of 0.55. The results indicate that folic acid is degraded by OH radicals which attack selectively the benzene ring and the 9,10 linkage. The results reflect the high rate of interaction of OH radicals with benzene rings activated by amino groups. The mechanism of the degradation is discussed.