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United States Department of Agriculture

Agricultural Research Service

Title: A Dft/ab Initio Study of Hydrogen Bonding and Conformational Preference in Model Cellobiose Analogs Using B3lyp/6-311++g**

Authors
item Strati, Gina - FORMER USDA-ARS
item Willett, Julious
item Momany, Frank

Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 30, 2002
Publication Date: September 30, 2002
Citation: STRATI, G., WILLETT, J.L., MOMANY, F.A. A DFT/AB INITIO STUDY OF HYDROGEN BONDING AND CONFORMATIONAL PREFERENCE IN MODEL CELLOBIOSE ANALOGS USING B3LYP/6-311++G**. CARBOHYDRATE RESEARCH. 2002. v. 337. p. 1851-1859.

Interpretive Summary: Cellulose is one of the most important biological carbohydrate molecules known, in addition to being one of the largest renewable materials on the planet. Cellobiose is the disaccharide building unit of cellulose with two glucose rings linked through an ether bridge. The 3-dimensional structures of eight new forms of cellobiose were studied computationally at the electronic level in order to explain some anomalous conformational features of cellobiose that were found in previous studies. For example, our scientific investigations into the electronic nature of cellobiose led to the realization that in vacuo this molecule energetically prefers a new structure different from that observed experimentally. In this paper we present results on this subject using powerful ab initio computer methods utilized in our laboratory for carbohydrate studies. With these computational tools, we can relate previous experimental information obtained by other researchers to details on the basic structure of many different carbohydrates whose commercial utility is well known. This work has allowed us to better understand the flexibility and electronic organization of the D-glucose components of cellobiose analogs and thus cellulose and will lead to the design of new chemical modifications of cellulose materials. Such chemical modifications will result in the production of biodegradable polymers with new physical properties useful for commercial applications.

Technical Abstract: A series of beta-D-cellobiose analogs were studied at the B3LYP/6-311++G** level of theory to isolate and understand how the various electronic components of the beta-(1->4)-linked disaccharide, cellobiose, contribute to the energetic stability of the molecule in vacuo. Previous studies on beta-D-cellobiose {1} showed that the most energetically stable conformation was that in which the dihedral angle phi was "flipped" by 180 degrees relative to the "normal" form. From our examination of eight sets of structures in which different combinations of functional hydroxyl and hydroxymethyl groups were removed, it was determined that only beta-D-cellobiose and one other analog (analog 7, beta-xylobioside), an analog in which both hydroxymethyl groups were removed but the exocyclic hydroxyl groups retained, can form a "cooperative" hydrogen-bonding network. Only in these two molecules did we find continuous synergistic "communication" through hydrogen bonding from one sugar moiety to the other. This "cooperative" hydrogen bonding energetically stabilizes the "flipped" conformation of beta-D-cellobiose and beta-xylobioside, while the other analogs studied were unable to form a "cooperative" grouping of hydrogen bonds and thus were more stable in their "normal" conformational state.

Last Modified: 9/10/2014
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