CONFORMATIONAL ENERGY MAPPING OF XYLOBIOSE WITH QUANTUM MECHANICS

摘要

Xylobiose is the shortest xylan, a hemicellulose that closely interacts with cellulose in woody plants. Those interactions are important in plant growth and utilization. Conformations of ss-xylobiose were studied with a method previously used for cellobiose.[1] Vacuum and continuum solvation efforts found a profound difference, i.e., the optimal Φ torsion angles differed by about 150°. Our vacuum results agreed with other theoretical [2] and vacuum experimental results. [3] The solvated map accommodated the many crystal structures for cellobiose as well as cellulose. The difference in preferred conformations was attributed to dominant inter-residue O-H...O-H hydrogen bonding in the vacuum phase, whereas the condensed-phase structure involved the less attractive 0-5' atom in one of its two hydrogen bonds. The stronger hydrogen bonding in the vacuum phase apparently overcomes the intrinsic preference for anti conformation in a tetrahydropyran analog of cellobiose. Thus it was of interest to study the energy surface of xylobiose, which can only make one inter-residue hydrogen bond.