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A quantitative anharmonic analysis of the amide A band in α‐helical poly( L ‐alanine)
Author(s) -
Lee SangHo,
Mirkin Noemi G.,
Krimm Samuel
Publication year - 1999
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/(sici)1097-0282(199903)49:3<195::aid-bip1>3.0.co;2-g
Subject(s) - dichloroacetic acid , chemistry , anharmonicity , overtone , amide , fermi resonance , alanine , residual , crystallography , spectral line , analytical chemistry (journal) , amino acid , infrared spectroscopy , physics , condensed matter physics , organic chemistry , quantum mechanics , biochemistry , computer science , algorithm
Polarized ir spectra of oriented films of α‐helical poly( l ‐alanine) (α‐PLA) have been obtained as a function of residual solvent dichloroacetic acid (DCA). The amide A, B, II, and V regions exhibit multiple bands whose structure depends on the residual DCA content, and those associated with the α I ‐PLA structure have been identified. A calculation of the relevant cubic anharmonic force constants indicates that, contrary to previous assignments, the overtone of amide II(A) is in Fermi resonance with the NH stretch fundamental, whose unperturbed frequency we now find to be at 3314 cm −1 , significantly higher than the previously suggested 3279 cm −1 . The presence of a structure in addition to the standard α I ‐PLA is indicated by our analysis. © 1999 John Wiley & Sons, Inc. Biopoly 49: 195–207, 1999