Location: Plant Polymer Research
Title: DFT studies of the conformation and relative energies of alpha-maltotetraose (DP-4): An amylose fragment at atomic resolution Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 12, 2008
Publication Date: August 19, 2008
Citation: Momany, F.A., Willett, J.L., Schnupf, U. 2008. DFT studies of the conformation and relative energies of alpha-maltotetraose (DP-4): An amylose fragment at atomic resolution. Meeting Abstract. xx. Technical Abstract: DFT optimization studies of more than one hundred conformations of a-maltotetraose have been carried out at the B3LYP/6-311++G** level of theory. The DP-4 fragments of predominately 4C1 chair residues include tightly bent forms, helix, band-flips, kinks, boat, and some 1C4 conformers. The three dominant hydroxymethyl conformations (gg, gt, tg) were included at different positions in the sequence and their influence on the bridging conformations described. Hydroxyl groups were considered in both the clockwise (c) and counterclockwise (r) directions, with some complex mixing of the hydroxyl directions to examine hydrogen bond flipping. Energetic differences between conformations are examined to assess the stability and positions in the sequence of different conformer states. Band-flip conformations reproduce experimentally observed structural elements in large amylose fragments and are of modest relative energy when compared to the lowest energy conformations. Kink conformations are of higher energy but only stable when hydroxyl groups across the bridge are in the ‘r’ forms. In vacuo the ‘c’ forms are generally of lower energy than the ‘r’ forms, while upon addition of solvent using COSMO, the ‘r’ forms become favored. The large number of conformers allows the analysis of fragmentation energies, and these suggest strongly that maltose is not a particularly good model for amylose polymer analysis.