Octa-O-propanoyl-beta-maltose: crystal structure, acyl stacking, related structures, and conformational analysis.
The crystal structure of beta-maltose octapropanoate (1) was solved to improve understanding of di-, oligo-, and polysaccharide conformations. The O6 and O6' atoms are in gg and gt orientations, respectively. Extrapolation of the coordinates of the non-reducing residue and observed linkage bond and torsion angles of 1 [Formula: see text] yields a left-handed helix similar to amylose triacetate I. The phi and psi values of 1 are also similar to those of other crystalline, acylated maltose compounds as well as some hydroxyl-bearing molecules. Acylated maltose moieties are often stabilized by stacking of the carbonyl groups and alpha-carbons on O3 and O2' as well as by the exo-anomeric effect. The conformation of 1 is within the 1-kcal/mol contour on a hybrid energy map built with a dielectric constant of 7.5, but corresponds to higher energies on maps made with lower dielectric constants. In one region of phi,psi space, both hydroxyl-bearing and derivatized maltose moieties are found but no inter-residue, intramolecular hydrogen-bonding occurs. In another region, only hydroxyl-bearing molecules crystallize and O2'...O3 hydrogen bonds are always found. In agreement with the energy surfaces, amylose helices extrapolated from available linkage geometries were almost all left-handed.
Johnson
Glenn P
GP
Southern Regional Research Center, US Department of Agriculture, 1100 Robert E. Lee Blvd., New Orleans, LA 70124, United States.
Stevens
Edwin D
ED
French
Alfred D
AD
D002236:Carbohydrate Conformation; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D006860:Hydrogen Bonding; D008320:Maltose / Q000031:analogs & derivatives / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure
D008320:Maltose