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CPP: Chemische Physik und Polymerphysik

CPP 16: Electronic Structure and Spectroscopy II

CPP 16.4: Vortrag

Mittwoch, 29. März 2006, 14:45–15:00, ZEU 160

Multiexciton Vibrational States in α-Helical Polypeptides — •Dmitry Tsivlin and Volkhard May — Institut für Physik, Humboldt Universität zu Berlin, Newtonstr. 15, D-12489 Berlin

Studies of amide vibrations in α-helical polypeptides attracted much interest due to the mechanism of self-trapping of vibrational excitation, originally proposed by Davydov. Recently, it became possible to observe the self-trapped states in α-helices by using femtosecond infrared pump-probe spectroscopy [1].

Since for the amide vibrational states the so-called nonadiabatic limit is reached [2], theoretical description of the system requires a quantum treatment of the high-frequency amide mode coordinates as well as the coordinates of the polypeptide lattice. In the present work, by employing a multiexciton expansion of the model Hamiltonian an accurate quantum-dynamical description of vibrational states formed by amide C=O and N-H stretching modes of α-helix is presented [3]. Using the multiconfiguration time-dependent Hartree method, linear and pump-probe infrared absorption spectra are calculated by numerical time-propagation of the exciton-chain vibrational wavefunction. Formation of self-trapped exciton states is discussed within the adiabatic exciton approximation and within the full quantum approach. Interpretation of the infrared pump-probe experiments for α-helical polypeptides and for peptide model crystals is proposed [1,2].

[1] J. Edler et al., Phys. Rev. Lett. 93, 106405 (2004)

[2] D.V. Tsivlin, V. May, and H.-D. Meyer, J. Chem. Phys., submitted

[3] D.V. Tsivlin and V. May, Chem. Phys. Lett. 408, 360 (2004)