Conformational analysis for hydrated ethylene oxide oligomer models by quantum chemical calculations |
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Authors: | Minoru Kobayashi Makoto Takahashi Hisaya Sato |
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Affiliation: | (1) Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan;(2) Graduate School of Technical Management, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan |
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Abstract: | Hydrate effects on the conformations of ethylene oxide oligomers (EO-x, x = 1–8 mers) were examined using quantum chemical calculations (QCC). Conformational analyses were carried out by RHF/6-31G.
The models were constructed by locating a water molecule to each ether–oxygen in the structures optimized for non-hydrate
oligomers. Hydrate ratio, h (h = H2Omol/Omol in oligomer), was set from 0 to 1.0. The six type conformations with repeated units of O–C, C–C and C–O bonds were examined. Conformational
energy, E
c (HF), was calculated as difference between the energy of oligomer with water molecules and that of non-hydrogen and/or hydrogen
bonding water molecules. Hydrate energies for each conformer, ∆μ
h
(kcal/m.u., based on E
c in non-hydrate state), were negative and linearly decreased with the increase of h values, and such effects with the increase of h values were weaken with increasing x values. These results were consistent with our previous results calculated using the permittivity, ε (ε = 0–80.1), by QCC. In non-hydrate (h = 0), the (ttt)
x
conformers were the most stable independent of x. However, in hydrate states (h = 0.44–0.67), the (tg+t)
x
conformers were the most stable independent of x values, and in h = 1, the (tg+t)8 conformer (8-mer) was most stable ∆E
c(g) = −1.3 kcal/m.u., ∆E
c(g): energy difference between a given oligomer and the (ttt)
x
oligomer]. These results supported the experimental those based on NMR analyses using dimethoxyethane and triglyme solutions.
Molecular lengths (l) of (tg+t)
x
, (tg+g−)
x
and (g+g+g+)
x
conformers having higher x values significantly decreased with increasing h values. Such contraction with hydration, however, was independent of ΔE
c(g) values of each conformer. |
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Keywords: | Conformation Poly(ethylene oxide) Oligomer Hydrate effect Quantum chemical calculation |
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