No abstract

In their various incarnations oligosaccharides have roles that are oftentimes conformationally dependent, where this dependency can be dictated by the anomeric configuration, glycosidic linkage, and/or hydrogen bonding (H-bonding) of the sugar molecules. Examples of this phenomenon are linkage- and configuration-selective aptameric binding to oligosaccharides and taste responses that appear to depend on the H-bonding-controlled shape of sugars. Differences in the behavior and use of oligosaccharides as a function of degree of polymerization are also well-known, a classic example being the case of cyclodextrins (CDs) and the different uses and properties of α-, β-, and γ-CD. Here, we have measured the solution conformational entropy of three homologous series of oligosaccharides, linear malto- and cellooligosaccharides and cyclodextrins, using high-resolution oligomeric size-exclusion chromatography (SEC), an entropically controlled separation method. We measured the change in ΔS of the malto- and cello- series as a function of degree of polymerization (DP) and compared the effects of α vs β anomeric configuration at each DP. By comparing select maltooligosaccharides with CDs, we also measured the effect of linearity vs cyclicity on ΔS. Additionally, by performing all of these studies under both hydrogen-bond-accepting and non-hydrogen-bond-accepting conditions, we were able to isolate the effects of H-bonding on the ΔS of the malto- and cellooligosaccharides and cyclodextrins as well.

Carbohydrate flexibility can influence a variety of recognition, processing, and end-use properties, at both the polymeric and oligomeric levels. The influence of glycosidic linkage, in particular, on carbohydrate flexibility is manifested in properties such as bacterial selectivity, solution viscosity, and the ability to regulate the spread of disease. Here, we apply size-exclusion chromatography, an entropically controlled technique, to determine the solution conformational entropy (ΔS) of various oligosaccharide series. The aim of the present study is to highlight how, for a given anomeric configuration, glycosidic linkage affects ΔS, and to do so quantitatively as a function of degree of polymerization (DP). To this end, we compare ΔS values for DP 1-7 for malto- and isomaltooligosaccharides, and for DP 1-5 for cello- and laminarioligosaccharides. To do so, we realize previously unattainable separations of disaccharides via a strict size-exclusion mechanism. Also given here are the requirements for extending our method to other oligomers, as well as to biopolymers