科研之友
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摘要
The fundamental property of biological systems is photostability. Without photostability no life would be possible. Molecular structures responsible for harvesting of the solar energy must be photostable and resistant to photo-induced chemical changes or must find a way for a recovery. To answer the questions about the photostability we have to understand mechanisms of relaxation and energy dissipation upon an optical excitation. There is a common agreement that such channels are provided by some special features of the potential energy surfaces including the conical intersections. The mechanism that leads to decrease in the energy gap between the excited-state potential and the ground state energy surfaces is related to the coupling between the excited state (electronic or vibrational) and the intramolecular and intermolecular vibrational modes. When the potential energy surfaces approach each other nonadiabatic transitions are facilitated by their close proximity and the rate of radiationless transitions increases. The mechanism seems to be universal both for simple species such as H-bond systems, solvated electrons, and biologically important photoreceptor proteins such as bacteriorhodopsin. In order to study energy dissipation and dynamical alterations in the structure, a system is triggered with laser and monitored with excellent time-resolution. Ultrafast spectroscopies have played an important role in the study of a number of biological processes and have provided unique information about primary events and the mechanism of energy relaxation. Biological activity of molecules is frequently initiated by elementary chemical reactions such as energy and electron transfer, cis-trans isomerizations, or proton transfer. Many of these reactions are usually very fast and efficient and occur on picosecond and femtosecond timescales. This paper reviews recent progress of understanding light-energy collection and dissipation, with a special emphasis on the role of the vibronic coupling in H-bonded systems, solvated electrons and light-initiated biological photoreceptors. We will concentrate on the spectroscopic methods based on the linear and nonlinear responses such as the time resolved coherent anti-Stokes Raman spectroscopy (CARS) and the pump-probe transient femtosecond absorption spectroscopy. Detailed understanding the paths of energy dissipation will reveal mechanisms that mediate light-induced signal transduction as well as the role of photoreceptors in photostability protection and reparation mechanisms in living cells.
- 出版日期2012-1
