Computational analysis of side-chain conformations in polyaspartates exhibiting reversible helical sense inversion in the solid state |
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Authors: | Koichi Sakajiri Satoshi Saeki Shinji Ando Susumu Kawauchi Junji Watanabe |
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Institution: | a Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8552, Japan b CREST-JST (Japan Science and Technology Corporation), 4-1-8 Hon-cho, Kawaguchi, Saitama 332-0012, Japan |
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Abstract: | Poly(β-phenylpropyl
-aspartate), poly(β-phenylbutyl
-aspartate), and poly(β-phenylpentyl
-aspartate) exhibit a reversible transformation from a right-handed -helix (R) to a left-handed ω-helix (ωL) in the solid state. During this transition, the infrared (IR) dichroism of the side-chain ester group and the birefringence change drastically, showing that the side-chain conformations are different for these two helices. In the present study, for the purpose of elucidating the preferred side-chain conformation in each helix, we performed the computational analyses. The energy contours, the directions of the IR transition moments and the anisotropies in polarizability as functions of the first two dihedral angles of the side chain, χ1 and χ2 were calculated. Then, comparing them with the experimental IR dichroism and birefringence data, we elucidated the specific side-chain conformation preferred for each R or ωL skeleton. The preferred values of (χ1, χ2) were found to be (?75, ?60°) for R and (180, 45°) for ωL. |
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Keywords: | Polyaspartates Energy contours Dichroism |
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