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Theoretical CD studies of polypeptide helices: Examination of important electronic and geometric factors
Author(s) -
Manning Mark C.,
Woody Robert W.
Publication year - 1991
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.360310511
Subject(s) - chemistry , cndo/2 , excited state , helix (gastropod) , spectral line , crystallography , wave function , exciton , ground state , peptide , molecular physics , atomic physics , molecule , physics , condensed matter physics , quantum mechanics , ecology , biochemistry , organic chemistry , snail , biology
An improved model for calculating the CD of polypeptides has been developed. Excited state wavefunctions were derived from CNDO/S (complete neglect of differential overlap, spectroscopic) calculations on N‐methylacetamide. Four discrete peptide‐localized transitions were employed: π 0 π*(NV 1 ), π+π* (NV 2 ), n π*, and n ′π*. Inclusion of the π+π*transition (λ 0 = 140 nm) significantly improves the accuracy of the calculated CD spectra in the 180‐250‐nm region. Spectra were computed for various helical structures, including right‐handed α‐, α II ‐, ω‐, π‐, 3 10 ‐, and poly(proline)I‐helices, and the left‐handed poly(proline)II‐helix. Sensitivity to changes in the peptide backbone geometry and chain length are examined. Electronic factors such as ground‐state charge distribution, hybridization effects, and basis set deorthogonalization have been investigated. The nonconservative nature of the poly (Pro) I and II CD spectra is reproduced, and the helix band present in earlier exciton calculations on the α‐helix has been diminished.