Quantum Chemical Study of the Interaction of the Short-Chain Poly(oxyethylene)s CH_3(OCH_2CH_2)_mOCH_3(C_1E_mC_1;m = 1 and 2)with a Water Molecule in the Gas Phase and in Solutions

摘要

It is well-known that the role of the oxygen atom of the hydrophilic unit of poly(oxyethylene)(POE)is one of the important factors of the high solubility of POE in water.In the present study,we focused on the hydration of the oxyethylene OCH_2CH_2O unit of POE,CH_3(OCH_2CH_2)_mOCH_3(C_1E_mC_1),and theoretically examined the role of the water molecule on the stability of POE using the short-chain POE,1,2-dimethoxyethane(DME)CH_3(OCH_2CH_2)OCH_3(C_1E_1C_1)and diglyme CH_3(OCH_2CH_2)_2OCH_3(C_1E_2C_1).The relative energies of the important conformers of the model POE with and without a water molecule in the gas phase and the solvent have been calculated by the second-order Moller-Plesset perturbation(MP2)method using the 6-311G* * basis set.We found three types of H-bonding of a water molecule with the POE chain for the TTT and the TGT conformers of C_1E_1C_1 and for the TTTTTT,the TGTTGT,and the TGTTG'T conformers of C_1E_2C_1,which are classified into the monodentate and the bidentate H-bonding.The conformers including the gauche form of the OCH_2CH_2O unit without the intramolecular electrostatic interaction are less stable in energy than the trans conformers in the gas phase for both C_1E_1C_1 and C_1E_2C_1.However,this order in the stability is reversed by the hydration.It is also found that the H-bond between POE and a water molecule is strengthened in the solvent.The stability of the conformers of POE in the gas phase and in the solvent is discussed in detail.