Structural effects of oxidation on sugars: glucose as a precursor of gluconolactone and glucuronolactone.

Although structural information on sugars is wide, experimental studies on the oxidation products of sugars in the gas phase, free from solvent interactions, have been rarely reported. We present an experimental work on the changes in the structure and interactions of two products of glucose oxidation (D-glucono-1,5-lactone (GlcL) and D-glucurono-6,3-lactone (GlcurL)) with respect to their precursor. Features such as intramolecular interactions, ring puckering and tautomerism were observed.

A Competition between Relative Stability and Binding Energy in Caffeine Phenyl-Glucose Aggregates: Implications in Biological Mechanisms.

Hydrogen bonds and stacking interactions are pivotal in biological mechanisms, although their proper characterisation within a molecular complex remains a difficult task. We used quantum mechanical calculations to characterise the complex between caffeine and phenyl-ß-D-glucopyranoside, in which several functional groups of the sugar derivative compete with each other to attract caffeine. Calculations at different levels of theory (M06-2X/6-311++G(d,p) and B3LYP-ED=GD3BJ/def2TZVP) agree to predict several structures similar in stability (relative energy) but with different affinity (binding energy). These computational results were experimentally verified by laser infrared spectroscopy, through which the caffeine·phenyl-ß-D-glucopyranoside complex was identified in an isolated environment, produced under supersonic expansion conditions. The experimental observations correlate with the computational results. Caffeine shows intermolecular interaction preferences that combine both hydrogen bonding and stacking interactions. This dual behaviour had already been observed with phenol, and now with phenyl-ß-D-glucopyranoside, it is confirmed and maximised. In fact, the size of the complex's counterparts affects the maximisation of the intermolecular bond strength because of the conformational adaptability given by the stacking interaction. Comparison with the binding of caffeine within the orthosteric site of the A2A adenosine receptor shows that the more strongly bound caffeine·phenyl-ß-D-glucopyranoside conformer mimics the interactions occurring within the receptor.