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Pavel A. Kusochek, Victoria I. Nazarova, Sergey A. Kazantsev, Vladislav R. Aslopovsky, Andrei V. Scherbinin, Anastasia V. Bochenkova
Impact
of the protein environment on two-photon absorption cross-sections of type I and
type II retinal-containing proteins
Abstract
Abstract. Predicting and optimizing the
photophysical properties of retinal-containing channel proteins under
two-photon absorption (TPA) conditions are required for their efficient use in
optogenetics. Nonlinear two-photon excitation can also lead to photoactivation
of visual rhodopsins in the IR range of 950–1000 nm. Here, by using high-level
quantum chemistry calculations, we explore the factors that influence the TPA
activity of the type I and type II rhodopsins upon their two-photon resonant
excitation to the first singlet excited state. We show that in the case of the S0
→ S1 transition, the channels through permanent dipole moments,
which are associated with the initial and final states only, make the largest
contribution to the calculated TPA cross-sections. The fast numerical
convergence of the sum-over-states formalism provides direct evidence for the
applicability of the two-level model for calculating TPA cross-sections in
rhodopsins, which are characterized by the large transition dipole moment and a significant
redistribution of the electron density upon the S0 → S1
transition. The calculated TPA cross-sections (340–610 GM) are found to be very sensitive
to changes in the permanent dipole moments between the ground and excited
states and highly tunable by internal electric field of the protein
environment. The high tunability of the nonlinear photophysical properties of
the retinal protonated Schiff-base chromophore can be used for the rational design
of retinal-containing proteins with optimal photoresponse.
Key words: two-photon absorption cross-section,
retinal-containing proteins, bacteriorhodopsin, visual rhodopsin, rhodopsin
KR2, multiconfiguration quasi-degenerate perturbation theory
Copyright (C) Chemistry Dept., Moscow State University, 2002
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