Radiation chemistry of carbohydrates. Part 14. Hydroxyl radical induced oxidation of D-glucose in oxygenated aqueous solution

Abstract

D-Glucose (5 × 10^–3M) has been γ-irradiated in N₂O–O₂(80 : 20 v/v) saturated aqueous solutions (dose rate 1.1 × 10¹⁵ eV g^–1 s^–1), and the G values of 22 products determined. Major products (G values in parentheses) are : D-gluconic acid (1)(0.9). D-arabino-hexosulose (2)(0.9). D-ribo-hexos-3-ulose (3)(0.57), D-xylo-hexos-4-ulose (4)(0.50), D-xylo-hexos-5-ulose (5)(0.60). D-gluco-hexodialdose (6)(1.55), and L-threo-tetrodialdose (12)(0.20). Products (1)–(6) are thought to be formed by OH attack at C-1–C-6, followed by oxygen addition and and HO₂ elimination. In competition, reactions between the glucose peroxyl radicals and HO₂·(O₂^–·) give rise to fragmentation of C–C bonds. The major product from these fragmentation reactions is (12)(precursor. radical at C-5). From a dose rate study using electron pulses from a van de Graaff generator it has been shown that the rates of HO₂· elimination are in the order: C-1 C-2, C-3, C-4 > C-6 C-5. Furthermore, it has been calculated that OH radicals abstract a hydrogen atom from C-1 and C-2 with a probability of ca. 20%. from C-3 and C-4 of ca. 10% from C-5 of ca. 15%, and from C-6 ca. 30%.