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Issue 6, 2012
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Self-organization of tetrapyrrole constituents to give a photoactive protocell

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A tandem combinatorial reaction of four acyclic, colorless compounds (two α-aminoketones and two diones; one polar and one nonpolar for each) in aqueous solution (30 mM each, 60 °C, pH 7, 24 h) containing lipid vesicles and with or without quinones and solar illumination affords a distribution of up to 538 porphyrins in 1.6–3.9% overall yield. The reactions leading to the porphyrins can occur in either or both the aqueous phase and the hydrophobic membrane of the vesicles. The porphyrins encompass a broad range of polarity and partition in the aqueous-lipid medium. Two fractions obtained by size-exclusion chromatography include porphyrins associated with the lipid vesicles and porphyrins in the aqueous phase. The porphyrins in both phases are photoactive as demonstrated by fluorescence quantum yield measurements (Φf ∼ 0.07–0.08) and by the Krasnovsky reaction (a photosynthetic-like process). The constituents of the Krasnovsky reaction employed here are methyl red, ascorbic acid, and 2,6-dichlorophenolindophenol. Illumination of the two porphyrin-containing samples (aqueous phase or vesicles) in the presence of the Krasnovsky constituents results in the reduction of methyl red and oxidation of ascorbic acid. Thus, the overall process transforms a colorless aqueous suspension via four stages (two combinatorial reactions, oxidation, physical partitioning) to photoactive porphyrins in distinct venues. The process may provide a model for the origin of pigments that enable proto-photosynthesis.

Graphical abstract: Self-organization of tetrapyrrole constituents to give a photoactive protocell

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The article was received on 26 Dec 2011, accepted on 28 Feb 2012 and first published on 22 Mar 2012

Article type: Edge Article
DOI: 10.1039/C2SC01120D
Citation: Chem. Sci., 2012,3, 1963-1974
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    Self-organization of tetrapyrrole constituents to give a photoactive protocell

    A. R. M. Soares, M. Taniguchi, V. Chandrashaker and J. S. Lindsey, Chem. Sci., 2012, 3, 1963
    DOI: 10.1039/C2SC01120D

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