(533f) Optimization of An All-Atom Additive Charmm Force Field for Glycosyl Linked Hexo-Pyranoses
AIChE Annual Meeting
Wednesday, November 19, 2008 - 4:51pm to 5:09pm
The force field parameters developed for hexo-pyranoses is extended to disaccharides. The partial charge on the glycosidic oxygen was determined based on reproduction of the scaled energetics and hydrogen bond distances from QM while the LJ parameters were transferred from the ring ether oxygen. The (φ,ψ ) rotations around the glycosidic bonds are the fingerprints for the conformations in the disaccharides. Extensive dihedral phase space conformations were explored on model compound 2H-Pyran, 2,2'- oxybis[tetrahydro], to optimize the (φ,ψ ) dihedral parameters that governs the rotation around the glycosyl bond. 1875 MP2/cc-pvtz//MP2-6-31g(d) conformations were used to optimize the force constants for φ=O5-C1-O1-C1' , ψ=C1-O1-C1'-O5' dihedrals in 1-1 linkage using a Monte Carlo simulated annealing algorithm while 3750 conformations were used to determine the φ=O5-C1-O1-Cn' and ψ=C1-O1-Cn'-Cn-1' (n=2,3,4) dihedral parameters in 1-2, 1-3 and 1-4 linkages. A total of 2090 MP2/cc-pvtz//MP2-6-31g(d) conformations were used to determine the dihedrals φ=O5-C1-O1-CH2 ,ψ=O1-CH2-Cn'-O5' and ω=C1-O16-CH2-Cn' in 1-6 linkage (Cn'=C5'). The dihedral parameters developed for the model compound were then transferred to disaccharides which have a hydroxyl group attached to the different carbons instead of two hydrogens for the model compound. Crystal and aqueous phase simulations performed for disaccharides showed good agreement with experiment. The average φ and ψ obtained from 5 ns simulations for trehalose+water, maltose+water and cellobiose+water, and the coupling constants Jφ and Jψ derived using Karplus equation were in good agreement with experimental NMR results.