Quantum tunneling in biological reactions: the interplay between theory and experiments

José N. Onuchic Chigusa Kobayashi Kim K. Baldridge About the authors

Ricardo Ferreira was the first Brazilian scientist to understand the need of solid theoretical approaches to obtain quantitative understanding mechanisms governing the life sciences. Therefore, in this issue in his honor, we decided to describe how theory has been able to guide the understanding of electron tunneling in biology. During almost twenth years, our Pathway model has been the most powerful model in terms of predicting the tunneling mechanism for electron transfer in biological systems, particularly proteins. Recently, we have generalized the conventional Pathway models to understand how protein dynamics modulate not only the Franck-Condon Factor but also the tunneling matrix element. The interference among pathways modulates the electron tunneling interactions in proteins (particularly destructive interference), and dynamical effects are of critical importance. Tunneling can be controlled by protein conformations from equilibrium, which may be needed to minimize the effect of destructive interference during tunneling. In contrast, when equilibrium configurations have small destructive interference, electron tunneling is mediated by one (or a few) constructively interfering pathway tubes and dynamical effects are modest. This new mechanism has predicted several experimental rates that were later confirmed by experiments.

electron transfer; protein dynamics; quantum interference


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