Mechanism and analyses for extracting photosynthetic electrons using exogenous quinones – what makes a good extraction pathway?

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Mechanism and analyses for extracting photosynthetic electrons using exogenous quinones – what makes a good extraction pathway?, Photochem. Photobiol. Sci., 2016,15, 969-979

 

Extraction of photosynthetic electrons to produce an amenable electric current is a recent and important research topic. Indeed photosynthesis has overall a low yield in vivo (a few % of the total energy available from sunlight is converted into chemical energy). Among its various limitations, such a low yield is related to the saturation of the photochemical conversion (rate limiting electron transfer steps occurring downstream of Photosystem II) but not to the quantum efficiencies of photosystems (close to 100% under optimal conditions). That is why photosynthesis is viewed as a promising and unexploited reservoir to produce electricity by harvesting electrons among the photosynthetic chain. Furthermore, under high light conditions, the saturation of the photochemical conversion can lead to photoinhibition, i.e. formation of reactive species which can induce some biological damage while overwhelming the usual photorepair pathways. Therefore, extracting photosynthetic electrons is expected to alleviate the saturation and thus to limit photoinhibition.

 

 

In this work we used fluorescence measurements to extract the open center ratio within a population of photosynthetic algae. Furthermore, we consider it as a proxy for investigating the extraction of photosynthetic electrons by means of an exogenous quinone, 2,6-DCBQ. A mechanism was suggested and was globally found consistent with the experimentally extracted parameters. Zone diagrams were constructed to identify the most appropriate experimental conditions (quinone concentration and light intensity) depending on the desired usage of the photosynthetic electron harvesting. As a consequence, it stresses the choice to preserve endogenous flow or to minimize photoinhibition and extract high photocurrent.

 

 

Résumé: 

Photochem. Photobiol. Sci., 2016,15, 969-979

 

Plants or algae take many bene!ts from oxygenic photosynthesis by converting solar energy into chemical energy through the synthesis of carbohydrates from carbon dioxide and water. However, the overall yield of this process is rather low (about 4% of the total energy available from sunlight is converted into chemical energy). This is the principal reason why recently many studies have been devoted to extraction of photosynthetic electrons in order to produce a sustainable electric current. Practically, the electron transfer occurs between the photosynthetic organism and an electrode and can be assisted by an exogenous mediator, mainly a quinone. In this regard, we recently reported on a method involving "uorescence measurements to estimate the ability of di#erent quinones to extract photosynthetic electrons from a mutant of Chlamydomonas reinhardtii. In the present work, we used the same kind of methodology to establish a zone diagram for predicting the most suitable experimental conditions to extract photoelectrons from intact algae (quinone concentration and light intensity) as a function of the purpose of the study. This will provide further insights into the extraction mechanism of photosynthetic electrons using exogenous quinones. Indeed "uorescence measurements allowed us to model the capacity of photosynthetic algae to donate electrons to an exogenous quinone by considering a numerical parameter called “open center ratio” which is related to the Photosystem II acceptor redox state. Then, using it as a proxy for investigating the extraction of photosynthetic electrons by means of an exogenous quinone, 2,6-DCBQ, we suggested an extraction mechanism that was globally found consistent with the experimentally extracted parameters.

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Mechanism and analyses for extracting photosynthetic electrons using exogenous quinones – what makes a good extraction pathway?

 

G. Longatte,  F. Rappaport,   F.-A. Wollman,   M. Guille-Collignon and   F. Lemaître

 

Photochem. Photobiol. Sci., 2016,15, 969-979

 

DOI: 10.1039/C6PP00076B