Integration of multiple chromophores with native photosynthetic antennas to enhance solar energy capture and delivery

Abstract

Native length bacterial light-harvesting peptides carrying covalently attached designer chromophores have been created that self-assemble with native bacteriochlorophyll a (BChl a) to afford stable antennas with enhanced spectral coverage. Native (or native-like) α- and β-peptides interact with each other and BChl a to form a heterodimeric (αβ-dyad) unit that can then oligomerize to form biohybrid analogs of the bacterial core light-harvesting complex (LH1). Pairs of distinct synthetic chromophores were incorporated in αβ-dyads at selected distances from the BChl a target site (position 0). Two designs were explored. One design used green-yellow absorbing/emitting Oregon Green at the −34 position (toward the N-terminus relative to the BChl a coordination site) of β and orange-red absorbing/emitting Rhodamine Red at the −20 position of α, which combine with BChl a to give homogeneous oligomers. A second design used two different β-peptide conjugates, one with Oregon Green at the −34 position and the second with a near-infrared absorbing/emitting synthetic bacteriochlorin at the −14 position, which combine with α and BChl a to give a heterogeneous mixture of oligomers. The designs afford antennas with ∼45 to ∼60 pigments, provide enhanced spectral coverage across the visible and near-infrared regions relative to native antennas, and accommodate pigments at remote sites that contribute to solar light harvesting via an energy-transfer cascade. The efficiencies of energy-transfer to the BChl a target in the biohybrid antennas are comparable to native antennas, as revealed by static and time-resolved absorption and emission studies. The results show that the biohybrid approach, where designer chromophores are integrated via semisynthesis with native-like scaffolding, constitutes a versatile platform technology for rapid prototyping of antennas for solar energy capture without the laborious synthesis typically required for creating artificial photosynthetic light-harvesting architectures.