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Ab initio‐based vibrational analysis of α‐poly( L ‐alanine)
Author(s) -
Lee SangHo,
Krimm Samuel
Publication year - 1998
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(19981015)46:5<283::aid-bip2>3.0.co;2-l
Subject(s) - chemistry , ab initio , raman spectroscopy , dipole , force field (fiction) , alanine , deuterium , spectral line , amide , ab initio quantum chemistry methods , computational chemistry , molecular physics , normal mode , perturbation theory (quantum mechanics) , nuclear magnetic resonance , molecule , atomic physics , vibration , amino acid , physics , organic chemistry , quantum mechanics , biochemistry
Polarized ir and Raman spectra have been obtained on oriented films of α‐helical poly( L ‐alanine) (α‐PLA) and its N‐deuterated derivative. These improved spectra permit a more complete assignment of observed bands to A‐, E 1 ‐, and E 2 ‐species modes. A new empirical force field has been refined, based on ab initio force fields of N‐methylacetamide and L ‐alanyl‐ L ‐alanine, which reproduces observed frequencies above 200 cm −1 to less than 5 cm −1 . A new transition dipole coupling treatment avoids the weak coupling and perturbation approximations, and can now account for the newly observed and reassigned amide I (E 2 ) mode. As a result of this improved force field, several other observed bands have also been reassigned. © 1998 John Wiley & Sons, Inc. Biopoly 46: 283–317, 1998
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