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Amphiphilic,hydrophilic, or hydrophobic synthetic bacteriochlorins in biohybrid light-harvesting architectures: consideration of molecular designs |
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| Authors: | Jianbing Jiang Kanumuri Ramesh Reddy M. Phani Pavan Elisa Lubian Michelle A. Harris Jieying Jiao Dariusz M. Niedzwiedzki Christine Kirmaier Pamela S. Parkes-Loach Paul A. Loach David F. Bocian Dewey Holten Jonathan S. Lindsey |
| Affiliation: | 1. Department of Chemistry, North Carolina State University, Raleigh, NC, 27695-8204, USA 2. Department of Chemistry, Washington University, St. Louis, MO, 63130-4889, USA 3. Department of Chemistry, University of California, Riverside, CA, 92521-0403, USA 5. Photosynthetic Antenna Research Center, Washington University, St. Louis, MO, 63130-4889, USA 4. Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208-3500, USA |
| Abstract: | Biohybrid light-harvesting architectures can be constructed that employ native-like bacterial photosynthetic antenna peptides as a scaffold to which synthetic chromophores are attached to augment overall spectral coverage. Synthetic bacteriochlorins are attractive to enhance capture of solar radiation in the photon-rich near-infrared spectral region. The effect of the polarity of the bacteriochlorin substituents on the antenna self-assembly process was explored by the preparation of a bacteriochlorin–peptide conjugate using a synthetic amphiphilic bacteriochlorin (B1) to complement prior studies using hydrophilic (B2, four carboxylic acids) or hydrophobic (B3) bacteriochlorins. The amphiphilic bioconjugatable bacteriochlorin B1 with a polar ammonium-terminated tail was synthesized by sequential Pd-mediated reactions of a 3,13-dibromo-5-methoxybacteriochlorin. Each bacteriochlorin bears a maleimido-terminated tether for attachment to a cysteine-containing analog of the Rhodobacter sphaeroides antenna β-peptide to give conjugates β-B1, β-B2, and β-B3. Given the hydrophobic nature of the β-peptide, the polarity of B1 and B2 facilitated purification of the respective conjugate compared to the hydrophobic B3. Bacteriochlorophyll a (BChl a) associates with each conjugate in aqueous micellar media to form a dyad containing two β-peptides, two covalently attached synthetic bacteriochlorins, and a datively bonded BChl-a pair, albeit to a limited extent for β-B2. The reversible assembly/disassembly of dyad (β-B2/BChl)2 was examined in aqueous detergent (octyl glucoside) solution by temperature variation (15–35 °C). The energy-transfer efficiency from the synthetic bacteriochlorin to the BChl-a dimer was found to be 0.85 for (β-B1/BChl)2, 0.40 for (β-B2/BChl)2, and 0.85 for (β-B3/BChl)2. Thus, in terms of handling, assembly and energy-transfer efficiency taken together, the amphiphilic design examined herein is more attractive than the prior hydrophilic or hydrophobic designs. |
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