The glycosidic linkage flexibility and time-scale similarity hypotheses

Abstract

In this paper, the framework surrounding two hypotheses is described: 1. (1) that glycosidic linkages of carbohydrates can be inherently flexible and thus undergo significant torsional motions in solution; 2. (2) that internal and overall motions of disaccharides occur on similar time-scales. A brief summary is provided of the current position of the experimental and theoretical data with respect to these hypotheses. An analysis of glycosidic linkage conformational flexibility in terms of linkage density functions is presented. Statistical indices for the evaluation and ranking of linkage flexibility are developed. Conformational sampling of glycosidic linkages using Monte Carlo sampling based on linkage distributions is described. Time-scale similarity is examined by comparing interproton correlation functions with respect to the laboratory frame and different internal coordinate frames, and the relative dependence of the time-scales on the system temperature is analysed. Finally, it is suggested that, instead of the traditional “lock-and-key” viewpoint, we should consider the paradigm that carbohydrates may be viewed as a “bunch of keys”.