Disaccharide conformational maps: adiabaticity in analogs with variable ring shapes

Authors: STORTZ, CARLOS - UNIV OF BUENOS AIRES; French, Alfred - Al

Submitted to: Molecular Simulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2007
Publication Date: 4/1/2008
Citation: Stortz, C., French, A.D. 2008. Disaccharide conformational maps: adiabaticity in analogs with variable ring shapes. Molecular Simulation. 34(4):373-389.

Interpretive Summary: A better knowledge of the structures of cotton fibers and other agricultural substances such as starch should be useful so that knowledge-based proposals can be made for improvements in their properties. Conformational energy maps are valuable tools for the prediction of likely shapes of flexible molecules such as sugars and longer carbohydrate molecules that are composed of individual sugar units. Not only are the longer molecules flexible, but sometimes the sugar units also change from their usual shape. This paper presents methodology for the study of the impact of the changes of the sugar ring shapes on the shapes of the longer molecules of which they are a part. The work is mostly of interest to chemists who are studying models of these molecules.

Technical Abstract: Relaxed MM3 potential energy surfaces (conformational maps) were calculated for analogs of the three trehaloses, maltose, cellobiose and galabiose based on 2-methyltetrahydropyran. Starting structures included not only 4C1 (sugar nomenclature) geometries, but also combinations with 1C4 conformers, and some flexible (boat or skew) forms. These forms were included as part of continuing efforts to eliminate unwarranted assumptions in modeling studies, as well as to account for new experimental findings. Four to nine maps were obtained for each analog, and from them adiabatic maps were produced. Although the minimum energy regions always resulted from 4C1-4C1 geometries, moderate to large parts of most maps had lower energies when one or both rings were in the 1C4 conformation. Only the adiabatic surface for the (diequatorial) analog of beta,beta-trehalose was covered entirely by 4C1-4C1 conformers. For the cellobiose and alpha,beta-trehalose analogs, these conformers covered 74 and 67% of the surfaces, respectively. The remainder of the cellobiose analog surface was covered by conformers having a 1C4 conformation at the “reducing” end, and for the alpha,beta-trehalose analog, by conformers having 1C4 shapes for the '-linked unit. Adiabatic surfaces of the other three analogs were based on all combinations of 4C1 and 1C4 conformers. The “normal” 4C1-4C1 combination only covered 37-41% of those surfaces, whereas each of the other three conformations accounted for 10 to 31%. Although the “normal” conformation accounted for 97.0-99.8% of the total population, adiabaticity in disaccharide maps is not guaranteed unless variable ring shapes are considered.