Enhanced Light‐Harvesting Capacity by Micellar Assembly of Free Accessory Chromophores and LH1‐like Antennas

Abstract

Biohybrid light-harvesting antennas are an emerging platform technology with versatile tailorability for solar-energy conversion. These systems combine the proven peptide scaffold unit utilized for light harvesting by purple photosynthetic bacteria with attached synthetic chromophores to extend solar coverage beyond that of the natural systems. Herein, synthetic unattached chromophores are employed that partition into the organized milieu (e.g. detergent micelles) that house the LH1-like biohybrid architectures. The synthetic chromophores include a hydrophobic boron-dipyrrin dye (A1) and an amphiphilic bacteriochlorin (A2), which transfer energy with reasonable efficiency to the bacteriochlorophyll acceptor array (B875) of the LH1-like cyclic oligomers. The energy-transfer efficiencies are markedly increased upon covalent attachment of a bacteriochlorin (B1 or B2) to the peptide scaffold, where the latter likely acts as an energy-transfer relay site for the (potentially diffusing) free chromophores. The efficiencies are consistent with a Förster (through-space) mechanism for energy transfer. The overall energy-transfer efficiency from the free chromophores via the relay to the target site can approach those obtained previously by relay-assisted energy transfer from chromophores attached at distant sites on the peptides. Thus, the use of free accessory chromophores affords a simple design to enhance the overall light-harvesting capacity of biohybrid LH1-like architectures.

Expanding Covalent Attachment Sites of Nonnative Chromophores to Encompass the C‐Terminal Hydrophilic Domain in Biohybrid Light‐Harvesting Architectures

“…In prior studies using this biohybrid approach to create light‐harvesting architectures, we have (1) found efficient energy transfer from an attached bacteriochlorin (including BC1 in Figure D) at a range of sites (−2, −6, −10, −14, −17, −21, −34) toward the N‐terminus of the β‐peptide from the His (position 0) that coordinates BChl a (Figure C and Table ), (2) attached two BC1 to two sites per β‐peptide to give an average of 30 synthetic chromophores per ring to increase absorptivity, (3) incorporated three different peptide‐bacteriochlorin conjugates per ring with different spectral properties to increase solar coverage, making use of a palette of synthetic bacteriochlorins designed for such purposes, (4) demonstrated relay energy transfer using different chromophores and attachment sites to increase the efficiency of energy transfer from distant sites, (5) explored bacteriochlorins with different photophysical and physicochemical properties (hydrophobic, hydrophilic, amphiphilic), and (6) demonstrated effective energy transfer from nonattached chromophores to the BChl a complex in the LH1‐type rings, and enhancement of this process by the attachment of bacteriochlorins with spectral properties complementary to those free in solution …”

Engineering of a calcium-ion binding site into the RC-LH1-PufX complex of Rhodobacter sphaeroides to enable ion-dependent spectral red-shifting

“…Another approach was the fusion of YFP to the RC-H subunit to enhance the light-harvesting ability of the RC-LH1-X complex [33] . Through protein engineering various pigments that extend the range of light absorption have been attached covalently or noncovalently to light-harvesting complexes and shown to efficiently transfer light energy [34] , [35] , [36] , [37] , [38] , [39] .…”

Excitation energy transfer between monomolecular layers of light harvesting LH2 and LH1-reaction centre complexes printed on a glass substrate

“…New bio-hybrid energy transfer and trapping assemblies take many forms, and range from incorporating new chromophores into native [6][7][8][9][10][11][12][13][14] and de novo-designed 15,16 proteins, to using a variety of lithographic patterning methods to precisely position a single type of photosynthetic complex. [17][18][19][20][21][22] In this case, the assembly of extensive twodimensional architectures for energy harvesting, transfer and trapping requires the ability to direct the relative positions of two or more types of photosynthetic complex on the same surface.…”