Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature

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Abstract

Photosynthesis makes use of sunlight to convert carbon dioxide into useful biomass and is vital for life on Earth. Crucial components for the photosynthetic process are antenna proteins, which absorb light and transmit the resultant excitation energy between molecules to a reaction centre. The efficiency of these electronic energy transfers has inspired much work on antenna proteins isolated from photosynthetic organisms to uncover the basic mechanisms at play1,2,3,4,5. Intriguingly, recent work has documented6,7,8 that light-absorbing molecules in some photosynthetic proteins capture and transfer energy according to quantum-mechanical probability laws instead of classical laws9 at temperatures up to 180 K. This contrasts with the long-held view that long-range quantum coherence between molecules cannot be sustained in complex biological systems, even at low temperatures. Here we present two-dimensional photon echo spectroscopy10,11,12,13 measurements on two evolutionarily related light-harvesting proteins isolated from marine cryptophyte algae, which reveal exceptionally long-lasting excitation oscillations with distinct correlations and anti-correlations even at ambient temperature. These observations provide compelling evidence for quantum-coherent sharing of electronic excitation across the 5-nm-wide proteins under biologically relevant conditions, suggesting that distant molecules within the photosynthetic proteins are ‘wired’ together by quantum coherence for more efficient light-harvesting in cryptophyte marine algae.

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Figure 1: Structure and spectroscopy of cryptophyte antenna proteins.
Figure 2: Two-dimensional photon echo data for PC645.
Figure 3: Two-dimensional photon echo data for PE545.

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Acknowledgements

This work was supported by the Natural Sciences and Engineering Research Council of Canada and the Australian Research Council. G.D.S. acknowledges the support of an EWR Steacie Memorial Fellowship.

Author Contributions E.C. performed the experiments on PC645 and analysed those data. C.Y.W. performed the experiments on PE545 and analysed those data. K.E.W. prepared the samples. P.M.G.C. and G.D.S. designed the research. P.B. and G.D.S. examined the interpretation of the results. G.D.S. wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Gregory D. Scholes.

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This file contains a Supplementary Data, Supplementary Figures S1- S9 with Legends, Supplementary Tables S1- S9 and Supplementary References. (PDF 10391 kb)

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