Vibrational-exciton couplings for the amide I, II, III, and A modes of peptides.
The couplings between all amide fundamentals and their overtones and combination vibrational states are calculated. Combined with the level energies reported previously (Hayashi, T.; Zhuang, W.; Mukamel, S. J. Phys. Chem. A 2005, 109, 9747), we obtain a complete effective vibrational Hamiltonian for the entire amide system. Couplings between neighboring peptide units are obtained using the anharmonic vibrational Hamiltonian of glycine dipeptide (GLDP) at the BPW91/6-31G(d,p) level. Electrostatic couplings between non-neighboring units are calculated by the fourth rank transition multipole coupling (TMC) expansion, including 1/R3 (dipole-dipole), 1/R4 (quadrupole-dipole), and 1/R5 (quadrupole-quadrupole and octapole-dipole) interactions. Exciton delocalization length and its variation with frequency in the various amide bands are calculated. The simulated infrared amide I and II absorptions and CD spectra of 24 residue alpha-helical motifs (SPE3) are in good agreement with experiment.
Hayashi
Tomoyuki
T
Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
Mukamel
Shaul
S
D000042:Absorption; D000577:Amides / Q000737:chemistry*; D002942:Circular Dichroism; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D014732:Vibration
D000577:Amides; D010455:Peptides