An Extended Fano-DeVoe Polarizability Theory Similar to the Bayley-Nielsen-Schellman Secular Matrix Method: CD Calculations of Polypeptides Having (alpha)-Helix, (beta) -Sheet, and (beta) -Turn Structures

We have expanded the previous Bayley-Nielsen-Schellman type polarizability theory so as to involve a new diagonal type of CAE (Condon, Alter, Eyring) interaction energy as {(the previous diagonal type of CAE interaction energy) - (the electrostatically corrected ground state energy)}, which corresponds to the term pointed out by Misra in his review article. For the CD and UV band shape functions which were previously derived in a different way, we have newly rederived the polymer CD and UV band shape functions by making use of the Green’s function method, starting from the well-known text book by Eyring et al. For a monomer polarizability tensor, the two most often used Lorentzian and Gaussian band approximations will be studied together with practically necessary relationships on the bandwidths. The theory has been applied to the CD and UV absorption calculations on polypeptides. Previously, unless one scaled the earlier diagonal type of CAE interaction energy, poor predictions were then obtained, especially for the (beta)-sheet polypeptides as well as the small (alpha)-helix and (beta)-turn tripeptides. Now, using the new diagonal type of CAE interaction energies, promising CD results have been obtained together with reasonable UV spectral shifts.