BIOPHYSICAL THEORY AND MODELING |
Photoinduced conformational dynamics of a photoswitchable peptide: A nonequilibrium molecular dynamics simulation study
Phuong H Nguyen 1, Roman D Gorbunov 1 and Gerhard Stock 2*
1 University Frankfurt
2 University of Frankfurt
* To whom correspondence should be addressed. E-mail: stock{at}theochem.uni-frankfurt.de.
Submitted on March 13, 2006
Revised on May 5, 2006
Accepted on 9 May 2006
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Abstract |
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Employing nonequilibrium molecular dynamics simulations, a comprehensive computational study of the photoinduced conformational dynamics of a photoswitchable bicyclic azobenzene octapeptide is presented. The calculation of time-dependent probability distributions along various global and local reaction coordinates reveals that the conformational rearrangement of the peptide is rather complex and occurs on at least four time scales: (i) Following photoexcitation, the azobenzene unit of the molecule undergoes nonadiabatic photoisomerization within 0.2 ps. (ii) On the picosecond time scale, the cooling (13 ps) and the stretching (14 ps) of the photoexcited peptide is observed. (iii) Most reaction coordinates exhibit a 50-100 ps component reflecting a fast conformational rearrangement. (iv) The 500-1000 ps component observed in the simulation accounts for the slow diffusion-controlled conformational equilibration of the system. The simulation of the photoinduced molecular processes is in remarkable agreement with time-resolved optical and infrared experiments, although the calculated cooling as well as the initial conformational rearrangements of the peptide appear to be somewhat too slow. Based on an ab initio parameterized vibrational Hamiltonian, the time-dependent amide I frequency shift is calculated. Both intramolecular and solvent-induced contributions to the frequency shift were found to change by <2 cm-1, in reasonable agreement with experiment. The potential of transient infrared spectra to characterize the conformational dynamics of peptides is discussed in some detail.
Key Words:
Photoinduced conformational dynamics, amide I infrared specrum, energy tranfer in peptides, nonequilibrium molecular dynamics simulation, photoswitchable peptides
