- Quantum mechanical effects have been demonstrated in photosynthesis
Recent experiments on photosynthetic ‘Light Harvesting Complexes’ (LHC) and their constituents (e.g., the Fenna–Matthews–Olson (FMO) pigment-protein complex in green sulfur bacteria) have suggested that quantum coherence may play a role in one of the most fundamental and important of biological processes: energy transport and energy conversion. N Lambert – 2012.
Evidence suggests a wavelike characteristic can explain the extreme efficiency of the energy transfer because it enables the system to simultaneously sample all the potential energy pathways and choose the most efficient one. This evidence includes detection of “quantum beating” signals, coherent electronic oscillations in both donor and acceptor molecules, generated by light-induced energy excitations.
There have also been indications of long-lived quantum coherence in the purple bacterium Rhodobacter sphaeroides pigment protein complex. H Lee 2007, P Rebentrost. 2009, Xian-Ting Liang 2010. And quantum beats have been found in various photosynthetic systems LHC2 (in bacteria, spinach and potentially other plant photosystems), and the photosystem of a group of aquatic algae called cryptophytes. S Harrop 2014.
A radical pairs mechanism has been found to operate in photosynthetic reaction centres. The initial charge separation steps of bacterial photosynthetic energy conversion proceed via a series of radical ion pairs formed by sequential electron transfers along a chain of immobilised chlorophyll and quinone cofactors in a reaction centre protein complex. Provided subsequent forward electron transfer is blocked, the recombination of the primary radical pair responses to magnetic fields in excess of ≈1 mT. In unblocked reaction centres, spin correlation can be transferred along the electron transport chain from the primary to the secondary radical pair whose lifetime is also magnetically sensitive. Similar effect occur in plant photosystems. C T Rogers and P J Hore 2008.
During charge separation in photosynthetic reaction centres, triplet states can react with molecular oxygen generating destructive singlet oxygen. The triplet product yield in bacteria and plants is observed to be reduced by weak magnetic fields. It has been suggested that this effect is due to ‘solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP ), which is thought to involve radical pair mechanisms. Read More…