HR: 1330h
AN: B12C-0790    [PDF]
TI: Effect of Calcite Surfaces on Chiral Separtion of Amino Acids
AU: * Kwon, K
EM: kkwon@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, University Park, PA 16802 United States
AU: Kubicki, J D
EM: kubicki@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, University Park, PA 16802 United States
AB: Studies have suggested that mineral surfaces break chirality of biomolecules by selective adsorption of amino acids to mineral surfaces and mineral surfaces catalyze amino acid polymerization. Recently, a plausible chiral-separation of amino acids was proposed by showing aspartic acids adsorb selectively on chiral calcite surfaces (Hazen et al., 2001, P NATL ACAD SCI USA). However, the selective adsorption is still phenomenal observation without a theoretical model. We have applied molecular modeling tools to explain the selective adsorption in terms of structures and energetics of interactions between aspartic acids and calcite surfaces. Molecular dynamics (MD) simulations were used to obtain structures of L- and D-aspartic acids and calcite surfaces. The Universal Force Field with Ewald sum and canonical ensemble at 300K were used. Simulations were run with a time step of 1 fs for 100,000 steps. The charges of each atom were calculated every 300 steps using the charge equilibration method (QEq). The interactions between one type of aspartic acid (D or L) and a calcite surface ((21\~{3}1) or (3\~{1}\~{2}1)) were simulated in a 3-D periodic box model. Gas-phase MD simulations predicted that D-aspartic acid has stronger binding energy (averaged internal energy of a system) than L-aspartic acid to calcite (21\~{3}1) surface, while L-aspartic acid has stronger binding energy than D-aspartic acid to calcite (3\~{1}\~{2}1) surface. The gas-phase simulations are in a good agreement with the experimental observation of aspartic acids­_ preferential adsorption in that lager binding energy corresponds to more adsorption. Because the adsorption occurs in solution, we simulated the interactions in solution by adding 451 water molecules in the lowest-energy configurations obtained from gas phase simulations. The solution simulations predicted a similar trend to the gas phase simulations, but the averaged binding-energy differences between D/L amino acids with calcite surfaces were within the range of energy deviation of each simulation. Therefore, molecular orbital calculations were carried out using the program GAMESS to calculate more accurate interaction-energies from minimum-energy configurations of solution-phase MD simulations. Molecular orbital calculations combined with MD simulations are expected to give a theoretical basis to understand the selective adsorption.
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
DE: 3620 Crystal chemistry
DE: 3947 Surfaces and interfaces
SC: Biogeosciences [B]
MN: 2003 Fall Meeting