Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 21, 2009
Publication Date: October 24, 2009
Citation: Momany, F.A., Schnupf, U., Willett, J.L. 2009. 27ps DFTMD Simulations of Maltose using a Reduced Basis Set. Meeting Abstract #334. Technical Abstract: The disaccharide, a-maltose, has been studied using constant energy density functional molecular dynamics (DFTMD) at the B3LYP/6-31+G*/4-31G+COSMO (solvent) level of theory. Maltose is of particular interest as the variation in glycosidic dihedral angles has been found to be dependent upon the starting hydroxyl and hydroxymethyl conformations. This very long simulation is possible because of the use of a small basis set (4-31G) on the carbon atoms, while maintaining the rigor describing hydrogen bonding of the B3LYP/6-31+G* level on all other atoms. This modification provides an approximate ten fold increase in speed without significant loss of accuracy with respect to the relative energies or structure compared to the use of larger basis sets. The simulation is started from the clockwise, gg-gg-c, form, and quickly converges to the ‘r’ form as the molecule become equilibrated. The ‘r’ conformations with COSMO have lower starting energies (~1 kcal/mol) than the ‘c’ forms, in contrast to the vacuum optimized structures where similar relative energies are found. The H1’---H4 distance is ~2.15Å for the predominate ‘r’ form is in excellent agreement with recent NMR studies. The conformation undergoes numerous transient structural transitions to kinks, skew forms, and transition state conformations. Vibrational spectra were extracted from the dynamics run.