title: Amphiphilic, hydrophilic, or hydrophobic synthetic bacteriochlorins in biohybrid light-harvesting architectures: consideration of molecular designs.
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.
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, NC, 27695-8204, USA.
authors.forename: Jianbing
authors.initials: J
authors.lastname: Jiang
authors.forename: Kanumuri Ramesh
authors.initials: KR
authors.lastname: Reddy
authors.forename: M Phani
authors.initials: MP
authors.lastname: Pavan
authors.forename: Elisa
authors.initials: E
authors.lastname: Lubian
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Harris
authors.forename: Jieying
authors.initials: J
authors.lastname: Jiao
authors.forename: Dariusz M
authors.initials: DM
authors.lastname: Niedzwiedzki
authors.forename: Christine
authors.initials: C
authors.lastname: Kirmaier
authors.forename: Pamela S
authors.initials: PS
authors.lastname: Parkes-Loach
authors.forename: Paul A
authors.initials: PA
authors.lastname: Loach
authors.forename: David F
authors.initials: DF
authors.lastname: Bocian
authors.forename: Dewey
authors.initials: D
authors.lastname: Holten
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Lindsey
mesh_terms: D001674:Bioelectric Energy Sources; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008958:Models, Molecular; D011166:Porphyrins / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D045342:Light-Harvesting Protein Complexes; D011166:Porphyrins; C452433:bacteriochlorin