The Electronic Origin of Far‐Red‐Light‐Driven Oxygenic Photosynthesis

Sirohiwal, Abhishek; Pantazis, Dimitrios A.

doi:10.1002/ange.202200356

Cited by 5 publications

(13 citation statements)

References 40 publications

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“…The data further establish that there is no appreciable competition from P D1 —independent of excitation wavelength—indicating that the initial electron acceptor is Phe as supported by the observed vibrational structure at early waiting times. These results are entirely in agreement with the recent theoretical work of Sirohiwal et al where the Chl D1 + Phe CT state was found to be the lowest energy excitation within the PSII-RC with reasonable oscillator strength 41 , 52 . Further, no similarly low energy CT states involving P D1 P D2 were found 41 , thus theoretically excluding the special pair as a candidate for initial CS as our experimental data support.…”

Section: Resultssupporting

confidence: 93%

“…Such a result is consistent with a recent QM/MM calculation, utilizing range-separated TD-DFT theory and the coupled-cluster theory with single and double excitations (CCSD), which proposed that the lowest CT state was Chl D1 + Phe − 41 . Recent theoretical studies suggest that the lowest CT state among the RC pigments is composed of P + Phe − 51 , 52 and that state, which has very low oscillator strength, can be directly excited by far-red light (in the red tail of, or beyond our laser spectrum) 52 . Our spectra show similar frequencies for Chl D1 + and P + , thus it is possible that there is a small contribution from P + to the signal even at early time.…”

Section: Resultsmentioning

confidence: 99%

“…Our spectra show similar frequencies for Chl D1 + and P + , thus it is possible that there is a small contribution from P + to the signal even at early time. It is clear, however, that the majority of the initial signal at 1716 cm −1 and 1677 cm −1 arises from Chl D1 because of the significant oscillator strength of Chl D1 + Pheo − transition 52 in addition to indicating that the initial electron acceptor is Phe. A previous transient IR study also suggested that the initial electron acceptor is Phe 11 , however, this study relied on an extrinsic deconvolution of the vibrational spectrum as opposed to the intrinsic ability of 2DEV spectroscopy to separate excitonic and CT contributions along the ω exc.…”

Section: Resultsmentioning

confidence: 99%

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The initial charge separation step in oxygenic photosynthesis

Yoneda¹,

Arsenault²,

Orcutt³

et al. 2022

Nat Commun

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Photosystem II is crucial for life on Earth as it provides oxygen as a result of photoinduced electron transfer and water splitting reactions. The excited state dynamics of the photosystem II-reaction center (PSII-RC) has been a matter of vivid debate because the absorption spectra of the embedded chromophores significantly overlap and hence it is extremely difficult to distinguish transients. Here, we report the two-dimensional electronic-vibrational spectroscopic study of the PSII-RC. The simultaneous resolution along both the visible excitation and infrared detection axis is crucial in allowing for the character of the excitonic states and interplay between them to be clearly distinguished. In particular, this work demonstrates that the mixed exciton-charge transfer state, previously proposed to be responsible for the far-red light operation of photosynthesis, is characterized by the ChlD1+Phe radical pair and can be directly prepared upon photoexcitation. Further, we find that the initial electron acceptor in the PSII-RC is Phe, rather than PD1, regardless of excitation wavelength.

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Section: Resultssupporting

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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The initial charge separation step in oxygenic photosynthesis

Yoneda¹,

Arsenault²,

Orcutt³

et al. 2022

Nat Commun

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show abstract

“…Lastly, the RSH kernels CAMY-B3LYP and ωB97-X, which are typically used in computational studies of the PSII RC − , give very different results. CAMY-B3LYP is actually in excellent agreement with the experiment and the GW -BSE calculations, while ωB97-X gives much too high excitation energies and also massively overestimates .…”

Section: Resultsmentioning

confidence: 99%

“…In agreement with previous results and our own calculations on the TD-DFT/RSH level for the full hexameric complex also ev GW -BSE and qs GW -BSE only predict states with predominantly local characters in the absence of the protein environment. These states can therefore not be linked to the experimentally observed CT processes. − Recent computational studies have established that the environmental electrostatics are responsible for this type of CT. ,, Along the lines of previous GW -BSE implementations, ,, future research needs to focus on ways to explicitly account for the environmental electrostatics in large-scale GW -BSE calculations.…”

Section: Discussionmentioning

confidence: 99%

Quasiparticle Self-Consistent GW-Bethe–Salpeter Equation Calculations for Large Chromophoric Systems

Förster

Visscher

2022

J. Chem. Theory Comput.

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The GW-Bethe−Salpeter equation (BSE) method is promising for calculating the low-lying excitonic states of molecular systems. However, so far it has only been applied to rather small molecules and in the commonly implemented diagonal approximations to the electronic self-energy, it depends on a mean-field starting point. We describe here an implementation of the self-consistent and starting-point-independent quasiparticle self-consistent (qsGW)-BSE approach, which is suitable for calculations on large molecules. We herein show that eigenvalue-only self-consistency can lead to an unfaithful description of some excitonic states for chlorophyll dimers while the qsGW-BSE vertical excitation energies (VEEs) are in excellent agreement with spectroscopic experiments for chlorophyll monomers and dimers measured in the gas phase. Furthermore, VEEs from time-dependent density functional theory calculations tend to disagree with experimental values and using different range-separated hybrid (RSH) kernels does change the VEEs by up to 0.5 eV. We use the new qsGW-BSE implementation to calculate the lowest excitation energies of the six chromophores of the photosystem II (PSII) reaction center (RC) with nearly 2000 correlated electrons. Using more than 11,000 (6000) basis functions, the calculation could be completed in less than 5 (2) days on a single modern compute node. In agreement with previous TD-DFT calculations using RSH kernels on models that also do not include environmental effects, our qsGW-BSE calculations only yield states with local characters in the low-energy spectrum of the hexameric complex. Earlier works with RSH kernels have demonstrated that the protein environment facilitates the experimentally observed interchromophoric charge transfer. Therefore, future research will need to combine correlation effects beyond TD-DFT with an explicit treatment of environmental electrostatics.

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Alternative Fast and Slow Primary Charge‐Separation Pathways in Photosystem II

et al. 2023

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Photosystem-II (PSII) is a multi-subunit protein complex that harvests sunlight to perform oxygenic photosynthesis. Initial light-activated charge separation takes place at a reaction centre consisting of four chlorophylls and two pheophytins. Understanding the processes following light excitation remains elusive due to spectral congestion, the ultrafast nature, and multicomponent behaviour of the charge-separation process.Here, using advanced computational multiscale approaches which take into account the large-scale configurational flexibility of the system, we identify two possible primary pathways to radical-pair formation that differ by three orders of magnitude in their kinetics. The fast (short-range) pathway is dominant, but the existence of an alternative slow (long-range) charge-separation pathway hints at the evolution of redundancy that may serve other purposes, adaptive or protective, related to formation of the unique oxidative species that drives water oxidation in PSII.

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The Electronic Origin of Far‐Red‐Light‐Driven Oxygenic Photosynthesis

Cited by 5 publications

References 40 publications

The initial charge separation step in oxygenic photosynthesis

The initial charge separation step in oxygenic photosynthesis

Quasiparticle Self-Consistent GW-Bethe–Salpeter Equation Calculations for Large Chromophoric Systems

Alternative Fast and Slow Primary Charge‐Separation Pathways in Photosystem II

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