Raman Spectroscopic Study on the Conformation of 1,2-Dimethoxyethane in the Liquid Phase and in Aqueous Solutions

Abstract

The conformation of 1,2-dimethoxyethane in the liquid phase and in aqueous solutions was studied by Raman spectroscopy. The conformation-sensitive Raman bands of 1,2-dimethoxyethane, located in the wavenumber region 300−600 cm-1, were analyzed by means of the band decomposition based on normal coordinate analysis. The populations of the conformers of 1,2-dimethoxyethane, their relative energies, and their relative entropies in the liquid phase were estimated and compared with the relevant data for the gas phase of 1,2-dimethoxyethane. The condensed phase effects on the conformation of 1,2-dimethoxyethane were discussed on the basis of the experimental data. The populations of the conformers at 318 K in aqueous solutions with different concentrations were estimated. It was revealed that the populations of the TTT and TGG‘ conformers of 1,2-dimethoxyethane decrease on increasing concentration of water, while the populations of the TGT and TGG conformers increase. The entropies of the less hydrophilic TTT and TGG‘ conformers are higher than the entropies of the more hydrophilic TGT and TGG conformers. This experimental observation suggests that the inverse temperature solubility of poly(oxyethylene) in water originates from the conformational changes of the polymer chain.

Modeling of Aqueous Poly(oxyethylene) Solutions: 1. Atomistic simulations

“…The population of the TGT conformer is almost identical for both force fields and rather close to the experimental value. 8 Using TraPPE-UA, the TGG population is overestimated while the TGG′ population is underestimated compared with the modified TraPPE-UA. We conclude that the TraPPE-UA force field with correct 1-4 interactions performs significantly better than the TraPPE-UA model with erroneous use of OPLS-like 1-4 scaling.…”

“…Note that "T" always refers to a dihedral angle of 180°, whereas " G + " refers to an angle corresponding to the position of the first minimum shown in panel b, which is slightly varying with the force field. We compare data obtained from Raman measurements 8 (black) with data from MD simulation using different force field models: TraPPE-UA 3 (green), TraPPE-UA with modified dihedral potentials 5 (red), and TraPPE-UA with erroneous use of OPLS-like 1-4 scaling (orange). Absolute standard deviations for all simulation results is lower or equal to 2.5%.…”

Density, sound velocity and refractive index in the water + 1,2-dimethoxyethane system

“…Moreover, the hydrophobic part of the molecule favours the arrangement of water (W) molecules around DME, further compacting than in the pure water. In this respect, Raman spectroscopy studies performed by Goutev, Matsuura et al [24][25][26] on water + DME mixtures have shown that, at low DME content, hydration structures are observed in which water clusters are coordinated by hydrogen bonds on the oxygen atoms of the ether groups and, simultaneously, the methyl groups act as Physics and Chemistry of Liquids 13 hydrophobic centres. This leads to an increase in local order of the hydration structure around each conformer type of DME molecules which are of course surrounded by an environment of water clusters.…”

Structural Aspects of Nucleosides: Protonated and Complexed Adenosines

“…3). The strong preference of the conformers with À sc orientations about the C(5')ÀC(4') bond found in the X-ray structures is reminiscent of the structure of 1,2-dimethoxyethane in the liquid phase, where the gauche conformation for C(1)ÀC(2) has the lowest energy, and in the crystalline phase, where only the gauche conformation is observed [7]. This preference is interpreted in terms of the anomeric effect, part of which may be associated with a hyperconjugative stabilization via a s(CÀH)/s*(CÀO) interaction.…”