Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 5, 2004
Publication Date: October 18, 2004
Citation: Momany, F.A., Willett, J.L. 2004. Molecular dynamics simulations of amylose fragments with cross-linking reagents:glass transition temperatures of epichlorohydrin bridged complexes [abstract]. American Chemical Society. 190:416. Technical Abstract: Molecular dynamics simulations using AMB99C (NPT ensembles, 1 atm.) were carried out on a periodic cell that contained three DP-30 amylose fragments, epichlorohydrin (ECH), or covalent cross-links of ECH, and TIP3P water molecules. Solvent diffusion and molecular motion of the cross-linked complexes are examined at temperatures above and below the glass transition temperature. The amorphous cell was constructed as described previously, through successive dynamic equilibrium steps at temperatures above the Tg value and the temperature successively lowered until several points of reduced slope (exm. 1/T v.s. volume) were obtained at temperatures below Tg. Each dynamics simulation was continued at a given temperature until the volume drift stopped and remained constant for at least 100 ps. Final Tg values were found by noting the discontinuity in slope of the volume (V), potential energy (PE), or density (p)versus 1/T. After equilibrium was reached at a particular level of hydration and a Tg profile established, a free ECH molecule was inserted into the cell replacing three water molecules. Upon equilibrium, a covalent linkage was created to two sugar hydroxyl groups, one nearest to the chlorine atom on ECH and a second near the opened active carbon atom of the ECH epoxy three-membered ring. These linkages create a glycerine bridging group between different sections of the amylose chains. The simulations at different temperatures were again carried out to obtain Tg, and a second bridge added and the procedure repeated.