Antioxidative Triplet Excitation Energy Transfer in Bacterial Reaction Center Using a Screened Range Separated Hybrid...

Area of Science:

• Photosynthesis research
• Computational biophysics
• Molecular mechanisms of energy transfer

Background:

• Photosystems (PSs) can suffer oxidative damage from excess absorbed energy.
• Triplet excitation energy transfer (TEET) within reaction center pigments is crucial for PS functionality.
• In bacterial reaction centers (BRC), the special pair (P) initiates charge separation via the photoactive branch A.

Purpose of the Study:

• To computationally investigate triplet excitation energy transfer (TEET) in BRC.
• To elucidate the roles of dielectric environment and interpigment orientations in TEET.
• To understand the asymmetry of TEET pathways in BRC.

Main Methods:

• Utilized a computational approach to study TEET in BRC.
• Employed a polarization-consistent framework combining screened range-separated hybrid functional and polarizable continuum model.
• Calculated electronic excitation energies and couplings, then parametrized a quantum mechanical approach using Fermi's golden rule for TEET rates.

Main Results:

• TEET in BRC was confirmed to proceed through branch B, aligning with experimental data.
• TEET to branch B pigments is significantly faster (ps timescale) than to hypothetical branch A pigments (ms timescale).
• Conformational differences were identified as the primary driver of branch asymmetry in TEET, with dielectric asymmetry playing a secondary role.

Conclusions:

• TEET asymmetry in BRC is predominantly governed by conformational factors rather than the dielectric environment.
• The study supports the role of carotenoids as the ultimate triplet energy acceptor in BRC.
• Investigated TEET in a mutant BRC, highlighting the importance of specific pigment arrangements.