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Theoretical optical properties of poly‐ L ‐proline
Author(s) -
Tterlikkis L.,
Loxsom F. M.,
Rhodes William
Publication year - 1973
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.1973.360120318
Subject(s) - chemistry , exciton , circular dichroism , absorption spectroscopy , spectral line , gaussian , polyproline helix , crystallography , molecular physics , peptide , computational chemistry , optics , condensed matter physics , physics , quantum mechanics , biochemistry
A non‐perturbational technique is used to calculate the circular dichroism and absorption spectra of polypeptide chains having conformations similar to that of poly‐ L ‐proline II. The method employs a Bogoliubov exciton formalism, from which the various optical terms associated with parallel and perpendicular components of the exciton band are obtained. A simple model for the peptide unit, consisting of three Gaussian absorption bands, leads to reasonable results for the polymer spectra, provided the lowest energy peptide π → π* transition is taken at 207 mμ and the value of the Ramachandran angle Ψ is taken to be 390°. The calculations suggest that the polymer circular dichroism spectrum is the resultant of strong interference among the two Gaussian exciton terms and the non‐Gaussian helix term. Consequently, the CD spectrum is very sensitive to the value of Ψ. It is found that the small positive CD band in the vicinity of 230 mμ arises partly from the effect of the static (crystal) field interactions on the n → π* CD band.