Perturbation Treatment of the Characteristic Vibrations of Polypeptide Chains in Various Configurations

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Abstract
A perturbation treatment has been made of localized group vibrations of helical polymer chains. The amide I and II frequencies were derived in terms of adjacent group interactions as well as interchain and intrachain hydrogen bonding interactions. Frequency shifts caused by these interactions depend upon the configuration of polypeptide chains and also upon the chain packing in the crystalline region. Each characteristic vibration of the amide group gives rise to parallel and perpendicular bands. The parallel bands of the α helix of poly‐γ‐benzyl‐L‐glutamate were observed at 1650 cm—1 (amide I) and 1516 cm—1 (amide II) whereas the perpendicular bands were observed at 1652 cm—1 (amide I) and 1546 cm—1 (amide II). Both the parallel‐chain and antiparallel‐chain pleated sheets exhibit the perpendicular amide I band at ca 1630 cm—1. A characteristic band of β configurations at ca 1690 cm—1 was assigned to the parallel amide I band of the antiparallel‐chain pleated sheet.

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