Molecular Dynamics Simulations of 1,2-Dimethoxyethane/Water Solutions. 1. Conformational and Structural Properties

Abstract

Molecular dynamics simulations of solutions of 1,2-dimethoxyethane (DME) and water have been performed in order to investigate the conformations of DME and the local solution structure as a function of solution composition and temperature. The simulations employ a previously developed force field based upon ab initio quantum chemistry calculations of DME/water interactions. The DME conformer populations show a strong dependence on temperature and solution composition and are quite different in aqueous solutions from those found in the gas phase or neat liquid. An analysis of the dependence of the conformer population distribution on temperature allows us to estimate the relative free energies of solvation for different conformers in water solution, which are found to be primarily energetic in origin for dilute solutions. The conformation dependence of the solvation free energy, resulting in "hydrophilic" and "hydrophobic" conformers, is explained in terms of differences in polar interactions between DME and neighboring water molecules. Analysis of the local structure of water around different DME conformers reveals that the degree of DME/water hydrogen bonding is nearly independent of the DME conformer for dilute solutions. The extent of water/water hydrogen bonding is also found to be nearly independent of composition over a wide composition range. To maintain a nearly constant level of water-water hydrogen bonding with increasing DME concentration, water is not randomly distributed in the system on a nearest-neighbor length scale but rather tends to form clusters of 4-5 molecules. The entropic penalty associated with this water structure increases with increasing DME concentration and temperature, thereby increasing the free energy of hydrophilic conformers relative to hydrophobic conformers.

Effect of Cross-Linking on the Diffusion of Water, Ions, and Small Molecules in Hydrogels

“…Water is divided into regions I, II, III and IV according to the distance from the polymer. number shown here is similar to the phenomenon observed in 1,2-Dimethoxyethane/water solutions with varying polymer concentration [69].…”

“…The electrostatic interaction energy components were subtracted from the total binding energies by the Coulomb potential using the partial changes on PEG and water molecules shown in Table 3.2 and 3.8. The remaining binding energy components were fitted to the LJ potential using least square fitting method to obtain the LJ parameters [69,70,68]. In order to verify the interaction parameters between PEG and water, we simulated a system composed only of DME chains and water (the mole fraction of DME is 0.04) and calculated the radial distribution function of the oxygen of the DME with the oxygen of water and obtained good agreement with the results of Borodin et al [68], as shown in Figure 3.4.…”

Molecular Dynamics Simulation of 1,2-Dimethoxyethane/Water Solutions. 2. Dynamical Properties

“…The increase in the C-O;C-C t state and O-C;C-O g state populations with increasing water content indicate a stabilization of these states by water. 4 This stabilization results in an increase in the t_g rotational energy barrier for the C-O;C-C bond and the g_t barrier for the O-C;C-O bond, consistent with the decrease in average transition rates for these bonds with increasing water content.…”

Concentration Dependence of Water Dynamics in Poly(Ethylene Oxide)/Water Solutions from Molecular Dynamics Simulations

“…10 Because of the widespread importance of PEO in aqueous solutions, we [11][12][13][14][15] and other groups [16][17][18][19][20] have conducted molecular dynamics (MD) simulation studies in order to gain atomistic level insight into the thermodynamics and dynamics of PEO and its oligomers in aqueous solutions. This paper is the third in a series dealing with the dynamic properties of PEO/water solutions from MD simulations.…”