Energy transport in carbohydrates. Part I. Molecular aggregation effects

Abstract

Acid production from solid anhydrous α-D-glucose on γ-irradiation is dependent on the physical state in which the solid is prepared. From linear yield–dose curves, G(acid) for the normal polycrystalline form is 13·2, for the syrup 6·5, and for the freeze-dried state 2–4 according to the method of freeze-drying; α-D-glucose monohydrate shows initial G(acid) 5·0. From infrared evidence it is probable that acid formation is a primary process occurring directly in the solid state. Reverse isotope-dilution analysis was used to estimate –G for the hexose when irradiated in the freeze-dried state. Electron spin resonance spectra indicate that the free-redical concentration is initially the same for the polycrystalline and freeze-dried forms, but that the decay is more rapid in the latter. For the long-lived free radicals, initial G(radical) is ca. 4.

X-Ray crystallography demonstrates that the polycrystalline and freeze-dried samples have indistinguishable chemical and crystallographic forms. Optical and electron microscopic examination revealed that a highly strained and imperfect lattice is produced on freeze-drying. The observations provide evidence for the existence of a mechanism of energy transport which is facilitated by a highly ordered crystal system. Lattice imperfections appear to act as exciton traps, resulting in appreciably less radiation decomposition.