Hydration structure of 1,2-dimethoxyethane (C1E1C1): OH Raman band studies

Raman spectroscopic study of the hydration of short-chain poly(oxyethylene)s C 1EnC 1 (n=1−4)

“…In this conformation the distances between the oxygen atoms of the O-CH 2 −CH 2 −O groups (2.9Å) coincide essentially with those between the oxygen atoms of neighboring water molecules in bulk water (2.85Å), allowing proper incorporation of POE chains into the structure of liquid water [6]. The idea of a partially hydrophobic-like hydration of POE in dilute aqueous solutions is supported by the observed slightly increased partial molar volumes of water [7][8][9], the reduced rotational mobility of hydration water [10][11][12] and the improved tetrahedral coordination [3,4] of hydration water in dilute aqueous solutions of short-chain POEs compared to the case of pure water. There are, however, differences between the hydration of POE in dilute solutions and hydrophobic hydration.…”

“…There are, however, differences between the hydration of POE in dilute solutions and hydrophobic hydration. Generally, the hydrophobic hydration preserves or slightly increases the strength of hydrogen bonding between water molecules, while the opposite behavior is observed in the hydration of short-chain POEs, namely the strength of hydrogen bonding decreases gradually accompanied by improved tetrahedral coordination [3,4,13]. For low concentrations of POE, the weakening of the hydrogen bonds can be explained by the expansion of the inherent cavities in the water structure, required to accommodate the hydrophobic ethylene and terminal methyl groups of the polymer.…”

“…Raman and infrared spectroscopic studies have shown that the hydration of POE at higher concentrations gradually loses its hydrophobic nature, which suggests that another mechanism of hydration arises [3,4]. The most developed network of hydrogen-bonded and tetrahedrally coordinated water molecules in aqueous solutions of POE is formed for a mole ratio of water molecules to oxyethylene monomer units around 2:1.…”

“…The Raman and infrared O-H stretching spectra of aqueous solutions of POE indicate, however, that there still exist tetrahedral structures of water molecules having hydrogen bonding similar to that in bulk water [3,4,13]. Therefore, a tendency for the formation of relatively small and homogeneously distributed clusters of water molecules in the region of moderately concentrated solutions can be accepted.…”

“…In our recent studies [3,4], we have explored the hydration of short-chain POE compounds, CH 3 OCH 2 CH 2 OCH 3 and CH 3 (OCH 2 CH 2 ) 2 OCH 3 , in aqueous solutions. The aim of the present study is to investigate the hydration of a series of short-chain POEs in aqueous solutions in an attempt to generalize the results from the previous studies and to establish an empirical relation between the number of water molecules hydrating one POE molecule and the number of oxygen atoms in it.…”