Single crystals of a random copolypeptide composed of γ-benzyl l-glutamate and l-phenylalanine |
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Authors: | Y. Tajima M. Anderson P.H. Geil |
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Affiliation: | Department of Macromlecular science, Case Western Reserve University, Cleveland, Ohio 44106, USA |
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Abstract: | Lamellar single crystals were formed from a random copolypeptide composed of γ-benzyl l-glutamate and l-phenylalanine at the ratio of 4 to 1. The copolypeptide takes the αhelical structure. The crystals were formed by casting dilute solutions at room temperature from a solvent consisting of a 1 to 1 mixture of chloroform and trifluoroacetic acid and were observed by electron microscopy. The average crystal thickness was 670 a in the as-polymerized sample, and 580 a in a fractionated sample. The thickness was decreased by annealing at temperatures above 110 C. A hexagonal form, a group of three orthorhombic forms (group 1), and a group of an orthorhombic form and two monoclinic forms (group II) were observed by electron diffraction. The diversity of the crystal structures is suggested to be caused by a variation in crystallization conditions during evaporation of the solvent. The hexagonal form and the structures of group I are changed into the structures of group II by annealing. The crystal structures other than the hexagonal form indicate on ordered arrangements of side chains in the crystals. |
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