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Issue 5, 2013
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Palette of lipophilic bioconjugatable bacteriochlorins for construction of biohybrid light-harvesting architectures

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Abstract

The challenge of creating both pigment building blocks and scaffolding to organize a large number of such pigments has long constituted a central impediment to the construction of artificial light-harvesting architectures. Light-harvesting (LH) antennas in photosynthetic bacteria are formed in a two-tiered self-assembly process wherein (1) a peptide dyad containing two bacteriochlorophyll a molecules forms, and (2) the dyads associate to form cyclic oligomers composed of 8 or 9 dyads in LH2 and 15 or 16 in LH1 of purple photosynthetic bacteria. While such antenna systems generally have near-quantitative transfer of excitation energy among pigments, only a fraction of the solar spectrum is typically absorbed. A platform architecture for study of light-harvesting phenomena has been developed that employs native photosynthetic peptide analogs, native bacteriochlorophyll a, and synthetic near-infrared-absorbing bacteriochlorins. Herein, the syntheses of 10 lipophilic bacteriochlorins are reported, of which 7 contain bioconjugatable handles (maleimide, iodoacetamide, formyl, carboxylic acid) for attachment to the peptide chassis. The bioconjugatable bacteriochlorins typically exhibit a long-wavelength absorption band in the range 710 to 820 nm, fluorescence yield of 0.1–0.2, and lifetime of the lowest singlet excited state of 2–5 ns. The α-helical structure of the native-like peptide is retained upon conjugation with a synthetic bacteriochlorin, as judged by single-reflection infrared studies. Static and time-resolved optical studies of the oligomeric biohybrid architectures in aqueous detergent solution reveal efficient (∼90%) excitation energy transfer from the attached bacteriochlorin to the native-like bacteriochlorophyll a sites. The biohybrid light-harvesting architectures thus exploit the self-constituting features of the natural systems yet enable versatile incorporation of members from a palette of synthetic chromophores, thereby opening the door to a wide variety of studies in artificial photosynthesis.

Graphical abstract: Palette of lipophilic bioconjugatable bacteriochlorins for construction of biohybrid light-harvesting architectures

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Publication details

The article was received on 22 Dec 2012, accepted on 18 Feb 2013 and first published on 05 Mar 2013


Article type: Edge Article
DOI: 10.1039/C3SC22317E
Citation: Chem. Sci., 2013,4, 2036-2053
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    Palette of lipophilic bioconjugatable bacteriochlorins for construction of biohybrid light-harvesting architectures

    K. R. Reddy, J. Jiang, M. Krayer, M. A. Harris, J. W. Springer, E. Yang, J. Jiao, D. M. Niedzwiedzki, D. Pandithavidana, P. S. Parkes-Loach, C. Kirmaier, P. A. Loach, D. F. Bocian, D. Holten and J. S. Lindsey, Chem. Sci., 2013, 4, 2036
    DOI: 10.1039/C3SC22317E

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