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Protein dynamics and electron transfer: electronic decoherence and non-Condon effects - PubMed

️Sat Jan 01 2005

Protein dynamics and electron transfer: electronic decoherence and non-Condon effects

Spiros S Skourtis et al. Proc Natl Acad Sci U S A. 2005.

Abstract

We compute the autocorrelation function of the donor-acceptor tunneling matrix element <T(DA)(t)T(DA)(0)> for six Ru-azurin derivatives. Comparison of this decay time to the decay time of the time-dependent Franck-Condon factor {computed by Rossky and coworkers [Lockwood, D. M., Cheng, Y.-K. & Rossky, P. J. (2001) Chem. Phys. Lett. 345, 159-165]} reveals the extent to which non-Condon effects influence the electron-transfer rate. <T(DA)(t)T(DA)(0)> is studied as a function of donor-acceptor distance, tunneling pathway structure, tunneling energy, and temperature to explore the structural and dynamical origins of non-Condon effects. For azurin, the correlation function is remarkably insensitive to tunneling pathway structure. The decay time is only slightly shorter than it is for solvent-mediated electron transfer in small organic molecules and originates, largely, from fluctuations of valence angles rather than bond lengths.

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Figures

**Fig. 1.**
Structures of the Ru-modified WT azurin 1BEX and its mutants, H83G Q107H, H83G M109H, H83G K122H, H83G T124H, and H83G T126H, used in the calculations of the *T_DA* correlation functions.

**Fig. 2.**
for the WT computed from a trajectory of 5,000 × 1 fsec MD snapshots at 310 K. The donor is the Cu-S(Cys-112) orbital described in *T_DA Calculations*, and the acceptor is a *d_x²-y²* ruthenium orbital. The tunneling energy is -10.8 eV. The coherence parameter is the long-time limit of , and τ_coh is approximately the amount of time it takes for to drop to 1/e of its initial value.

formula image — **Fig. 2.**
for the WT computed from a trajectory of 5,000 × 1 fsec MD snapshots at 310 K. The donor is the Cu-S(Cys-112) orbital described in *T_DA Calculations*, and the acceptor is a *d_x²-y²* ruthenium orbital. The tunneling energy is -10.8 eV. The coherence parameter is the long-time limit of , and τ_coh is approximately the amount of time it takes for to drop to 1/e of its initial value.

**Fig. 3.**
The dependence of 〈*T_DA*〉 (*Upper*) and (*Lower*) on the number (N) of MD conformations used to compute the averages. All conformations were chosen from the same MD trajectory of the WT structure (0.5-nsec total length). The temperature is 310 K, and *T_DA* was computed with E_tun =-10.8 eV. The donor and acceptor orbitals are the same as in Fig. 2. The first point N = 10 on the horizontal axis denotes 10 MD conformations separated by 50 psec, the second point is 25 conformations separated by 20 psec, and the final point is 5,000 conformations separated by 100 fsec. In all cases, the block renormalization method was used to compute the errors.

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Protein dynamics and electron transfer: electronic decoherence and non-Condon effects - PubMed