166. Abstract

A context for molecular deformations in crystals was established by reviewing conformational studies of isolated mono- and disaccharides that were carried out with MM3(92). In new work, miniature crystal models of cellulose allomorphs, cellobiose, maltosyl di- and trisaccharides and panose were based on published crystal structures, and the lattice energies were computed after complete optimization. Comparisons of the conformations of molecules in the crystal models with the models of isolated individual molecules indicate the extents of distortion resulting from the crystal field. Ring puckerings, linkage conformations and side group orientations can all be deformed by the crystal field by as much as 2 and even 3 kcal/mol for individual overall characteristics, while the sum of such distortions is typically about 5 kcal/mol/glucose residue, compared to the molecule modeled in isolation. Lattice energies range from about 15 to almost 50 kcal/mol of monomer residues, with larger molecules having lower lattice energies per residue. Contrary to conventional thought, the total van der Waals forces are, overall, stronger than hydrogen bonding, especially in the case of the cellulose models.

For Online Viewing  (3 Mb)                

For Printing (16 Mb)

Up to the 1995 Publications Page

Up to Publication Listing Page