Abstract
X-Ray structure studies of poly(L-valine), poly(L-isoleucine), and poly(L-phenylalanine) have been carried out. Poly(L-valine) has two structural forms. One is an α-helical conformation packed in the hexagonal lattice with a dimension of a=11.43 Å, though this conformation is unfavorable for poly(L-valine). The other is a β pleated sheet structure with the crystal data: P212121, a=4.80 Å, b=19.14 Å, c=6.59 Å (fiber axis). The β poly(L-valine) gave an X-ray fiber photograph of high quality and a detailed structural study was carried out. Poly(L-isoleucine) also crystallizes in a β pleated sheet structure with a=4.8 Å, b=23 Å, c=6.6 Å, orthorhombic. Contraction of fiber axes in both β structures are observed. The X-ray fiber photograph of poly(L-phenylalanine) suggests the coexistence of ω- and α-helix. This specimen may be the third example of an ω-helix. The significance of the hydrophobic interaction of the side chains in the structures is discussed.
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Yamashita, O., Yamane, T., Ashida, T. et al. X-Ray Structural Studies of Some Poly(α-amino acid)s with Hydrophobic Side Chains: Poly(L-valine), Poly(L-isoleucine), and Poly(L-phenylalanine). Polym J 11, 763–774 (1979). https://doi.org/10.1295/polymj.11.763
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DOI: https://doi.org/10.1295/polymj.11.763