| Abstract
| - It is well-known that the role of the oxygen atom of the hydrophilic unit of poly(oxyethylene) (POE) is oneof the important factors of the high solubility of POE in water. In the present study, we focused on thehydration of the oxyethylene OCH2CH2O unit of POE, CH3(OCH2CH2)mOCH3 (C1EmC1), and theoreticallyexamined the role of the water molecule on the stability of POE using the short-chain POE, 1,2-dimethoxyethane(DME) CH3(OCH2CH2)OCH3 (C1E1C1) and diglyme CH3(OCH2CH2)2OCH3 (C1E2C1). The relative energiesof the important conformers of the model POE with and without a water molecule in the gas phase and thesolvent have been calculated by the second-order Møller−Plesset perturbation (MP2) method using the6-311G** basis set. We found three types of H-bonding of a water molecule with the POE chain for the TTTand the TGT conformers of C1E1C1 and for the TTTTTT, the TGTTGT, and the TGTTG‘T conformers ofC1E2C1, which are classified into the monodentate and the bidentate H-bonding. The conformers includingthe gauche form of the OCH2CH2O unit without the intramolecular electrostatic interaction are less stable inenergy than the trans conformers in the gas phase for both C1E1C1 and C1E2C1. However, this order in thestability is reversed by the hydration. It is also found that the H-bond between POE and a water molecule isstrengthened in the solvent. The stability of the conformers of POE in the gas phase and in the solvent isdiscussed in detail.
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