Radiation chemistry of carbohydrates. Part XVIII. The extreme and variable susceptibility of crystalline lactose to ionising radiations

Abstract

Acid production (G=ca. 45) and overall decomposition (–G=ca. 55) of α-lactose monohydrate after γ-irradiation is considerably higher than for the anhydrous α- and β-anomers, which behave similarly (G_acid=ca. 3·2; –G=ca. 22). Production of stable radicals is the same for all the anomers (G_radical=ca. 3·9). Diffuse reflectance and i.r. spectroscopy confirm that the enhanced yield of acid products for the monohydrate occurs directly in the solid state. It is suggested that the remarkable radiation susceptibility of the monohydrate could be a function of the crystal structure in which one water molecule is hydrogen-bonded to four lactose molecules. The presence of water promotes acid production and this is manifested in a high radiation decomposition. When water is absent the acid yield is low and irradiation leads to an enhanced neutral product formation but an overall lower degree of destruction.