Light harvesting complex II B850 excitation dynamics.

Area of Science:

• Photosynthesis research
• Biophysics
• Quantum mechanics in biology

Background:

• Light Harvesting Complex 2 (LH2) in Rhodobacter sphaeroides efficiently captures light energy.
• Understanding excitation energy transfer (EET) dynamics is crucial for photosynthesis.
• The B850 ring is a key component of LH2 involved in light capture.

Purpose of the Study:

• To investigate the dynamics of excitation energy transfer within and between B850 rings of LH2.
• To determine the primary pathways and contributing exciton states for inter-ring energy transfer.
• To validate the use of generalized Forster theory with Boltzmann populated donor states for EET calculations.

Main Methods:

• Dissipative quantum mechanics simulations.
• Generalized Forster theory for calculating intercomplex excitation transfer rates.
• Analysis of intracomplex exciton relaxation dynamics.

Main Results:

• Intracomplex exciton relaxation to near-Boltzmann populations occurs within picoseconds.
• The assumption of Boltzmann populated donor states provides accurate intercomplex transfer rates.
• The five lowest-lying exciton states are primary channels for inter-ring EET.
• Non-850 nm exciton states contribute significantly to the total transfer rate.

Conclusions:

• The study provides accurate insights into EET dynamics in LH2 B850 rings.
• Generalized Forster theory with specific assumptions is a valid method for studying intercomplex EET.
• Both low-lying and non-850 nm exciton states play vital roles in efficient energy transfer within photosynthetic systems.