Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy

Area of Science:

• Biophysics
• Photosynthesis research
• Molecular mechanisms

Background:

• Bacterial reaction centers (BRCs) are crucial models for understanding photosynthesis.
• Efficient solar energy conversion relies on charge separation within BRCs.
• Previous studies have probed BRC structure-function relationships.

Purpose of the Study:

• To investigate the mechanisms of photosynthetic charge separation in BRCs.
• To analyze 2D electronic spectroscopy (2DES) data from Rhodobacter capsulatus mutants.
• To resolve exciton energies and identify charge separation pathways.

Main Methods:

• Utilized 2D electronic spectroscopy (2DES) on BRCs from Rhodobacter capsulatus mutants.
• Employed a multiexcitation global-fitting approach with common basis spectra.
• Incorporated linear absorption spectra and BRC structural data for analysis.

Main Results:

• Resolved previously hidden upper exciton state of the special pair.
• Demonstrated a two-step sequential reaction scheme for charge separation (P* to P+HA- via P+BA-).
• Showed that 2DES data can be explained without a second charge-separation pathway from the monomeric bacteriochlorophyll B*.

Conclusions:

• The study elucidates the primary charge separation mechanism in BRCs.
• A two-step sequential pathway accurately describes energy transfer and charge separation.
• 2DES is a powerful tool for dissecting ultrafast processes in photosynthesis.