Anomalous conformational behavior of poly(ethylene oxide) oligomers in aqueous solutions. A molecular dynamics study

摘要

Molecular dynamics simulations of 1,2-dimethoxyethane (DME) CH3(OCH2CH2)OCH3 and diglyme CH3(OCH2CH2)(2)OCH3 in aqueous solution have been performed for several solution compositions. Conformational analysis of these systems shows that the g population of the G-CC-G dihedral increases with increasing water content. For DME solutions, this increase is monotonic with a tendency to saturate in the extremely dilute (water-rich) regime. For diglyme solutions a distinct maximum in the g population of the O-C-C-O dihedral was observed at mole fraction X-diglyme = 0.03. More detailed analysis of the composition dependence of diglyme conformational populations reveals that the decrease in the G-C-C-G g population in extremely dilute solutions is due to a decrease in the tgt population of the C-O-C-C-O-C conformational triad. This in turn can be related to a decrease in a single conformer of diglyme, namely tgttgt. This conformer is unique in its nearly perfect antiparallel alignment of large triad dipoles. Finally, the anomalous conformational behavior of diglyme at extreme dilution is found to disappear at higher temperature. (C) 1998 American Institute of Physics. [S0021-9606(98)50742-8] [References: 18]