固体状態における合成ポリペプチドの骨格と側鎖構造

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The α-helix is one of the most typical conformations of the synthetic polypeptide in the solid state. In most cases, the deviation from the 18 residues 5 turns α-helix which was first proposed by Pauling and Corely has been reported. Several reflections unexpected from a regular α-helix appear on the meridian in diffraction diagrams of many polypeptides. Two different explanations have been presented, one is due to a regular distortion of the backbone α-helix, and the other due to a regular side-chain structure which is independent of the backbone structure.<BR>In a mixture of equimoles of poly (γ-benzyl L-glutamate) and poly (γ-benzyl D-glutα-mate) regular stacks of benzyl groups occur. This mixture shows the first order phase transition in the vicinity of 90°C characterized by a sudden increase in inter-helix distance and a disappearance of the 10.6A meridional reflection, suggesting the disruption of the regular stacks of benzyl groups.<BR>Poly (β-benzyl L-aspartate) can exist in a helix with 4 residues in a turn (ω-helix) as well as the left-handed α-helix. Poly [β- (p-chlorobenzyl) L-aspartate] is, however, the right-handed α-helix, which transforms into the ω-helix by heat treatment at 190°C. Poly (γ- (<I>p</I>-chlorobenzyl) L-glutamate) is found to be a helix with 7 residues in 2 turns which slightly deviates from the α-helix. The variation of the backbone conformation and side-chain structure are discussed in terms of intra- and inter-molecular side chain interactions.
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固体状態における合成ポリペプチドの骨格と側鎖構造

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