MO-Calculation of the Optical Activity of Oligopeptides. I. Computational Procedure and Application to Small Helices

✍ Scribed by Georges Wagnière; Max Iseli; Rudolf Geiger; Werner Gans

• Publisher: John Wiley and Sons
• Year: 1977
• Tongue: German
• Weight: 661 KB
• Volume: 60
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19770600602

✦ Synopsis

Abstract

All‐valence electron calculations on the chiroptic properties of oligopeptides rapidly become intractable, as the size of the molecule increases. A Frozen Core procedure is here proposed, which is inspired by the PPP method. It takes explicitly into account only the (pseudo) π electrons and oxygen n electrons of the amide moieties, as well as the π electrons of eventual long‐wavelength absorbing sidegroups. Local n‐π interaction is taken into account by an adjustable parameter. Other parameters are calibrated on the isolated amide and carbonyl chromophores. The method then follows the usual SCF‐CI procedure. Rotatory strengths and f‐values for the transitions are computed without further approximations, as previously described. Comparisons with results from exciton calculations and experimental data on polypeptides show the computed quantities to have a consistent and satisfactory order of magnitude.