Structure and properties of copolyaspartate. III. Dielectric studies of copoly(butyl-L-aspartate-benzyl-L-aspartate)
作者:
Yoshiharu Tsujita,
Noboru Satomi,
Akira Takizawa,
期刊:
Journal of Macromolecular Science, Part B
(Taylor Available online 1983)
卷期:
Volume 22,
issue 5-6
页码: 619-632
ISSN:0022-2348
年代: 1983
DOI:10.1080/00222348308245746
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
The side-chain molecular motion of the α helix, ω helix, and β form of copoly(butyl-L-aspartate-benzyl-L-aspartate) with degrees of butylation 0%, 25%, and 43% was investigated by means of dielectric relaxation. Copoly(butyl-L-aspartate-benzyl-L-aspartate) with butylation 0% and 25% has a left-handed α helix, and, on the contrary, that of the 43% copolymer is a right-handed α helix. These two a helices transformed into the left-handed ω helix, with stacking between the benzyl groups, or between benzyl and butyl groups, or between butyl groups when heated to 140°C. The dielectric constant decreased at the α-ω transition temperature, irrespective of frequency. In particular, a remarkable decrease of dielectric constant was observed to accompany the reversal in helix sense. The ω-β transformation was observed at about 180°C by further heating, accompanied by an abrupt increase in dielectric constant. The side-chain dispersion temperature was in the following order: T(ω) ≲ T(β) < T(α). Relatively free rotation of the side chain for the ω helix is possible, although the side-chain molecular motion, the side-chain dispersion, is restricted by the stacking of the side chain in the ω helix. The side-chain molecular motion of the α helix, rotation of the benzene ring, is hindered by the presence of δ O and ϵ CH2atoms of the residue above and below the benzene ring.
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