Femtosecond Biology Coherent Nuclear Dynamics Studied in Populations of Proteins

Femtosecond Biology Coherent Nuclear Dynamics Studied in Populations of Proteins 

A number of experiments measuring the decay of the P state have revealed complicating factors in addition to the multi-exponential decay of the state described above. In measurements monitoring the decay of P using short (SOnlOOfs) laser pulses conducted by Vos and co-workers, oscillations were observed superimposed on the resulting kinetic traces (Vos et al., 1994a,b,c 1993,1991). These oscillations have been attributed to coherent nuclear motion associated with the P state (Vos and Martin, 1999  

Stanley and Boxer, 1995 Vos et ah, 1993). Under conditions where the excitation pulse is long relative to the period of this nuclear motion, this phenomenon is not observed. 

The experiments of Vos and eo-workers raise the question of whether the coherent nuclear motion associated with the P state that persists on the time-scale of eleetron transfer is coupled to the primary electron transfer reaction. In particular, do any of the nuclear vibrations coupled to the P state facilitate the transfer of electrons from P to Ba The observation of coherent nuclear motion that persists on the time-scale of primary electron transfer raises the possibility that this nuclear motion may be an important parameter that governs the characteristics of this reaction, which would place this process in a near-adiabatic regime. Of obvious importance is the question of whether it is possible to observe coherence in the formation of a produet state such as P Ba . A number of recent studies have addressed this difficult problem with conflicting conclusions (Sp rlein et al., 1998 Streltsov et al., 1998 Vos et al., 1998 Streltsov et al., 1996) and, as discussed in reeent review (Vos and Martin, 1999) at present this question remains to be answered. 

Modulation of the Time Constant for Primary Electron Transfer between 200fs and SOOps throngh Site-Directed Mntagenesis 

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