The complete microspeciation of ovothiol A, the smallest octafarious antioxidant biomolecule

Abstract

Ovothiol A, a small biomolecule with highly potent antioxidant capacity, and three newly synthesized derivatives were studied by (1)H NMR, (15)N NMR, UV-pH titrations, and a customized evaluation method. The omni-interactive imidazole, amino, carboxylate, and thiolate moieties of ovothiol A are quantified in terms of 32 microscopic protonation constants, the relative concentrations of 16 microspecies, 6 pairwise interactivity parameters, and 8 protonation shifts. The highest and lowest imidazole basicities differ by a record-breaking five orders of magnitude, and the predominant thiolate protonation constant is by far the smallest known thiolate logK value. The latter provides an indication as to why ovothiol A occurs naturally under deep-water circumstances only. Since thiolate basicities are in correlation with thiol-disulfide redox potentials, the eight different, fine-tunable thiolate basicities offer versatile and highly specific antioxidant capacities within one single molecular skeleton. This work is the first complete microspeciation of a tetrabasic, nonsymmetrical natural compound.