Triplet states in the reaction center of Photosystem II

Abstract

In oxygenic photosynthesis sunlight is harvested and funneled as excitation energy into the reaction center (RC) of Photosystem II (PSII), the site of primary charge separation that initiates the photosynthetic...

Excitation landscape of the CP43 photosynthetic antenna complex from multiscale simulations

“…Most importantly, local protein electrostatics are known to be predominantly responsible for fine-tuning the excitation energies of photosynthetic pigments. 62,63,92 Here we consider all the above factors by employing multiscale modeling techniques within the QM/MM framework to determine the site energies of all CP43 chlorophylls embedded in the “native” PSII system.…”

“…S1†). 35,62,63 The detailed protocols for equilibration and production dynamics are discussed in the ESI †. We consider the entire PSII monomer and a water layer (7 Å around the protein), including all the waters present in the protein cavity and various channels.…”

“…The first 8 excited states (roots) were computed, thus covering the entire Q-band range and further low-lying excited states for individual chlorophylls as well as for dimers. 26,63,80 The electrostatic effects of the protein environment were included through MM point charges. The RIJCOSX approximation 81 and the corresponding auxiliary basis sets were used throughout.…”

“…, H-bonding to the keto group), and pigment–pigment interactions ( e.g. in Chl dimers) are known to directly influence excited state properties of chlorophylls, 32,62,63 it is therefore crucial to treat these interactions at the QM level along with the chromophore, an aspect which has been overlooked in several past studies.…”

Reaction Center Excitation in Photosystem II: From Multiscale Modeling to Functional Principles

“…In light-harvesting complexes and reaction centers, pigments are diversified by their unique environment within the protein scaffold, such as axial ligation to the central Mg ion, hydrogen bonding, steric effects, and electrostatics. Since intrinsic photophysical properties of bare pigments of the same chemical type are almost identical in the absence of substantial structural distortions, it is the protein environment electrostatics (anisotropic charge distribution) that tunes the spectral properties to enable function, such as directed excitation energy transfer and charge separation. ,,− Therefore, accurate computation of excited state properties of pigments requires explicit consideration of the protein environment and of protein–pigment interactions. Hybrid quantum-mechanics/molecular-mechanics (QM/MM) approaches allow this to be achieved effectively.…”