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Forde A, Maity S, Freixas VM, Fernandez-Alberti S, Neukirch AJ, Kleinekathöfer U, Tretiak S. Stabilization of Charge-Transfer Excited States in Biological Systems: A Computational Focus on the Special Pair in Photosystem II Reaction Centers. J Phys Chem Lett 2024; 15:4142-4150. [PMID: 38593451 DOI: 10.1021/acs.jpclett.4c00362] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2024]
Abstract
Charge-transfer (CT) excited states play an important role in many biological processes. However, many computational approaches often inadequately address the equilibration effects of nuclear and environmental degrees of freedom on these states. One prominent example of systems in which CT states are of utmost importance is reaction centers (RC) in photosystems. Here we use a multiscale approach combined with time-dependent density functional theory to explore the lowest CT excited state of the special pair PD1-PD2 in the Photosystem II-RC of a cyanobacterium. We find that the nonequilibrium CT excited state resides near the Soret band, making an exciton the lowest-energy excited state. However, accounting for nuclear and state-specific dielectric equilibration along the CT potential energy surface (PES), the CT state PD1--PD2+ stabilizes energetically below the excitonic state. This underscores the crucial role of state-specific solvation in mapping the PES of CT states, as demonstrated in a simplified dimer model.
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Affiliation(s)
- Aaron Forde
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Sayan Maity
- School of Science, Constructor University, Campus Ring 1, 28759 Bremen, Germany
| | - Victor M Freixas
- Departamento de Ciencia y Tecnologiia, Univresidad Nacional de Quilmes/CONICET, B1876BXD Bernal, Argentina
| | | | - Amanda J Neukirch
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | | | - Sergei Tretiak
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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Gemeinhardt FG, Lahav Y, Schapiro I, Noy D, Müh F, Lindorfer D, Renger T. Short-Range Effects in the Special Pair of Photosystem II Reaction Centers: The Nonconservative Nature of Circular Dichroism. J Phys Chem Lett 2023; 14:11758-11767. [PMID: 38117270 PMCID: PMC10758115 DOI: 10.1021/acs.jpclett.3c02693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 11/29/2023] [Accepted: 12/04/2023] [Indexed: 12/21/2023]
Abstract
Photosystem II reaction centers extract electrons from water, providing the basis of oxygenic life on earth. Among the light-sensitive pigments of the reaction center, a central chlorophyll a dimer, known as the special pair, so far has escaped a complete theoretical characterization of its excited state properties. The close proximity of the special pair pigments gives rise to short-range effects that comprise a coupling between local and charge transfer (CT) excited states as well as other intermolecular quantum effects. Using a multiscale simulation and a diabatization technique, we show that the coupling to CT states is responsible for 45% of the excitonic coupling in the special pair. The other short-range effects cause a nonconservative nature of the circular dichroism spectrum of the reaction center by effectively rotating the electric transition dipole moments of the special pair pigments inverting and strongly enhancing their intrinsic rotational strength.
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Affiliation(s)
- Felix G. Gemeinhardt
- Institut
für Theoretische Physik, Johannes
Kepler Universität Linz, Altenberger Strasse 69, 4040 Linz, Austria
| | - Yigal Lahav
- Fritz
Haber Center for Molecular Dynamics Research, Institute of Chemistry, Hebrew University of Jerusalem, 9190401 Jerusalem, Israel
- MIGAL
- Galilee Research Institute, S. Industrial Zone, 1101602 Kiryat Shmona, Israel
| | - Igor Schapiro
- Fritz
Haber Center for Molecular Dynamics Research, Institute of Chemistry, Hebrew University of Jerusalem, 9190401 Jerusalem, Israel
| | - Dror Noy
- MIGAL
- Galilee Research Institute, S. Industrial Zone, 1101602 Kiryat Shmona, Israel
- Faculty
of Sciences and Technology, Tel-Hai Academic
College, 1220800 Upper Galilee, Israel
| | - Frank Müh
- Institut
für Theoretische Physik, Johannes
Kepler Universität Linz, Altenberger Strasse 69, 4040 Linz, Austria
| | - Dominik Lindorfer
- Institut
für Theoretische Physik, Johannes
Kepler Universität Linz, Altenberger Strasse 69, 4040 Linz, Austria
| | - Thomas Renger
- Institut
für Theoretische Physik, Johannes
Kepler Universität Linz, Altenberger Strasse 69, 4040 Linz, Austria
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Seibt J, Lindorfer D, Renger T. Signatures of intramolecular vibrational and vibronic Q[Formula: see text]-Q[Formula: see text] coupling effects in absorption and CD spectra of chlorophyll dimers. PHOTOSYNTHESIS RESEARCH 2023; 156:19-37. [PMID: 36040654 PMCID: PMC10070234 DOI: 10.1007/s11120-022-00946-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 07/25/2022] [Indexed: 06/15/2023]
Abstract
An electron-vibrational coupling model that includes the vibronic (non-adiabatic) coupling between the Q[Formula: see text] and Q[Formula: see text] transitions of chlorophyll (Chl), created by Reimers and coworkers (Scientific Rep. 3, 2761, 2013) is extended here to chlorophyll dimers with interchlorophyll excitonic coupling. The model is applied to a Chl a dimer of the water-soluble chlorophyll binding protein (WSCP). As for isolated chlorophyll, the vibronic coupling is found to have a strong influence on the high-frequency vibrational sideband in the absorption spectrum, giving rise to a band splitting. In contrast, in the CD spectrum the interplay of vibronic coupling and static disorder leads to a strong suppression of the vibrational sideband in excellent agreement with the experimental data. The conservative nature of the CD spectrum in the low-energy region is found to be caused by a delicate balance of the intermonomer excitonic coupling between the purely electronic Q[Formula: see text] transition and the Q[Formula: see text] transition involving intramolecular vibrational excitations on one hand and the coupling to higher-energy electronic transitions on the other hand.
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Affiliation(s)
- Joachim Seibt
- Institut für Theoretische Physik, Johannes Kepler Universität Linz, Altenberger Str. 69, 4040, Linz, Austria.
| | - Dominik Lindorfer
- Institut für Theoretische Physik, Johannes Kepler Universität Linz, Altenberger Str. 69, 4040, Linz, Austria
| | - Thomas Renger
- Institut für Theoretische Physik, Johannes Kepler Universität Linz, Altenberger Str. 69, 4040, Linz, Austria
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Friedl C, Fedorov DG, Renger T. Towards a quantitative description of excitonic couplings in photosynthetic pigment-protein complexes: quantum chemistry driven multiscale approaches. Phys Chem Chem Phys 2022; 24:5014-5038. [PMID: 35142765 PMCID: PMC8865841 DOI: 10.1039/d1cp03566e] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 12/31/2021] [Indexed: 01/18/2023]
Abstract
A structure-based quantitative calculation of excitonic couplings between photosynthetic pigments has to describe the dynamical polarization of the protein/solvent environment of the pigments, giving rise to reaction field and screening effects. Here, this challenging problem is approached by combining the fragment molecular orbital (FMO) method with the polarizable continuum model (PCM). The method is applied to compute excitonic couplings between chlorophyll a (Chl a) pigments of the water-soluble chlorophyll-binding protein (WSCP). By calibrating the vacuum dipole strength of the 0-0 transition of the Chl a chromophores according to experimental data, an excellent agreement between calculated and experimental linear absorption and circular dichroism spectra of WSCP is obtained. The effect of the mutual polarization of the pigment ground states is calculated to be very small. The simple Poisson-Transition-charge-from-Electrostatic-potential (Poisson-TrEsp) method is found to accurately describe the screening part of the excitonic coupling, obtained with FMO/PCM. Taking into account that the reaction field effects of the latter method can be described by a scalar constant leads to an improvement of Poisson-TrEsp that is expected to provide the basis for simple and realistic calculations of optical spectra and energy transfer in photosynthetic light-harvesting complexes. In addition, we present an expression for the estimation of Huang-Rhys factors of high-frequency pigment vibrations from experimental fluorescence line-narrowing spectra that takes into account the redistribution of oscillator strength by the interpigment excitonic coupling. Application to WSCP results in corrected Huang-Rhys factors that are less than one third of the original values obtained by the standard electronic two-state analysis that neglects the above redistribution. These factors are important for the estimation of the dipole strength of the 0-0 transition of the chromophores and for the development of calculation schemes for the spectral density of the exciton-vibrational coupling.
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Affiliation(s)
- Christian Friedl
- Institut für Theoretische Physik, Johannes Kepler Universität Linz, Altenberger Str. 69, 4040 Linz, Austria.
| | - Dmitri G Fedorov
- Research Center for Computational Design of Advanced Functional Materials (CD-FMat), National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Umezono 1-1-1, Tsukuba, 305-8568, Japan.
| | - Thomas Renger
- Institut für Theoretische Physik, Johannes Kepler Universität Linz, Altenberger Str. 69, 4040 Linz, Austria.
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