Exploring Biological Quantum Effects in Photosynthesis across Varied Spatial Scales

The utilization of quantum effects by nature to enhance photosynthetic efficiency has emerged as a subject of intense scientific inquiry. However, fundamental questions remain unresolved, most notably, whether coherent energy transfer occurs in the primary photochemical events. This featured article summarizes recent work from our group and collaborators, addressing several manifestations of biological quantum effects in photosynthesis across varied spatial scales. These include: (1) Coherent energy transfer in allophycocyanin (inter-pigment distance of 21 Å) and phycoerythrin 545 (15 Å). An exciton-vibrational coherence time of up to 500 fs and a 220 fs coherent energy transfer time have been observed in allophycocyanin. In contrast, in the structurally similar phycocyanin 620, which possesses an identical pigment pair and separation distance, energy transfer follows an incoherent way with a time constant of 460 fs. (2) Quantum switch in the light-harvesting complex of photosystem II of higher plants, which is driven by a dynamical protein structure. The antenna reversibly regulates light harvesting (Förster energy transfer, classical) and excess energy dissipation (Dexter energy transfer, quantum mechanical) states in response to dynamic changes in sunlight intensity. This switch is achieved by dynamic modulation of the distance between the main quenching pair, lutein 1 and chlorophyll a 612 (∼5.6 to 6 Å). (3) Macroscale quantum design in membrane architecture. The optimal size of intracytoplasmic membrane vesicles is regulated by quantum design principles in the LH2 structure, where the structural robustness and excitonic coherence of LH2 are preserved only within an evolutionarily optimized vesicle size range (50-80 nm).