EmeryStar Research Archive

Abstract

The observation of long-lived electronic coherence in a photosynthetic pigment–protein complex, the Fenna–Matthews–Olson (FMO) complex, is suggestive that quantum coherence might play a significant role in achieving the remarkable efficiency of photosynthetic electronic energy transfer (EET), although the data were acquired at cryogenic temperature [Engel GS, et al. (2007) Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems. Nature 446:782–786]. In this paper, the spatial and temporal dynamics of EET through the FMO complex at physiological temperature are investigated theoretically. The numerical results reveal that quantum wave-like motion persists for several hundred femtoseconds even at physiological temperature, and suggest that the FMO complex may work as a rectifier for unidirectional energy flow from the peripheral light-harvesting antenna to the reaction center complex by taking advantage of quantum coherence and the energy landscape of pigments tuned by the protein scaffold. A potential role of quantum coherence is to overcome local energetic traps and aid efficient trapping of electronic energy by the pigments facing the reaction center complex.

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 play. Intriguingly, recent work has documented that light-absorbing molecules in some photosynthetic proteins capture and transfer energy according to quantum-mechanical probability laws instead of classical laws 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 spectroscopy 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.

Abstract

Hydrophilic materials such as Nafion can nucleate the buildup of interfacial water, which shows features different from bulk water. We investigated the effect of infrared (IR) light on a negatively charged, interfacial exclusion zone (EZ) and a positively charged proton zone (PZ) formed in the vicinity of Nafion. After irradiation for 5 min by mid-IR light, EZ size increased with an expansion ratio of 1.41. A significant expansion was also found in the size of PZ, equivalent to an increment of about 1.39 × 10¹⁶ molecules of hydronium ions. Thus, IR radiation not only builds EZ, but at the same time drives release of protons from the growing EZ to bulk water. Near-IR illumination also showed expansion of EZ and PZ water. These results imply that incident IR light not only promotes the build-up of interfacial water at the hydrophilic surface, but also provides a driving force for charge separation.