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Infrared absorption spectrum of keratin. I. Spectra of α‐, β‐, and supercontracted keratin
Author(s) -
Bendit E. G.
Publication year - 1966
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1966.360040506
Subject(s) - chemistry , amide , keratin , phase (matter) , infrared , spectral line , absorption band , absorption (acoustics) , infrared spectroscopy , crystallography , analytical chemistry (journal) , organic chemistry , optics , materials science , composite material , medicine , physics , pathology , astronomy
A number of basic features of the infrared spectrum of keratin have been confirmed and some new features have been found. In the 3‐μ region, the amide A frequency of helical material in α‐keratin at 3286 cm. −1 is close to the expected value, but that of the crystalline phase in α‐keratin, near 3270 cm. −1 , is lower than had previously been reported. The noncrystalline phase absorbs in the vicinity of 3300 cm. −1 or above, and this causes the low‐intensity component of the amide A band in both α‐ and β‐keratin to occur at higher frequencies than those of the high‐intensity component. In the 6‐μ region, the amide II frequency of noncrystalline material is below 1525 cm. −1 . Keratin denatured in lithium bromide, after washing out the reagent, appears to have a considerable helix content, possibly as much as that of the original protein. Hydration causes significant spectral changes. In the 6‐mu; region, the frequency of the amide I band of crystalline material is lowered, while that of the amide II band is increased, both by a few wavenumbers; the amide II frequency of noncrystaline material is also increased by a few wavenumbers. In the 3‐μ region, no significant change is observed in the amide A frequency of crystalline material, while the frequency of the noncrystaline material is reduced. These spectral changes are interpreted in terms of a weak association of water with main‐chain carbonyl groups in the crystalline phase, while in the noncrystaline phase it is thought likely that water molecules form hydrogen‐bond bridges between polypetide chains. The absorption coefficient of the amide A band and the integrated absorption intensities of the amide A, I, and II bands do not vary appreciably in the three forms of keratin investigated.