High Time Resolution Electron Paramagnetic Resonance of Light-Induced Radical Pairs in Photosynthetic Bacterial Reaction Centers: Observation of Quantum Beats

Light-induced radical pairs in fully deuterated photosynthetic reaction centers of purple bacteria Rhodobacter sphaeroides have been studied by high time resolution electron paramagnetic resonance. Quantum beat oscillations are detected at early times after laser excitation for native and iron-removed reaction center preparations. Due to their spin-correlated generation, the secondary radical pairs P super(+)[QFe super(2+)] super(-) and P super(+)Q super(-) are expected to start out in a coherent superposition of eigenstates, as observed experimentally. Analysis of the quantum beats as a function of the static magnetic field can ultimately provide detailed information on the molecular structure of the short-lived intermediates in the primary steps of bacterial photosynthesis.