Engineering Excitonically-Coupled Dimers in an Artificial Protein for Light Harvesting via Molecular Dynamics Simulations

Abstract

In photosynthesis, pigment – protein complexes achieve outstanding photoinduced charge separation efficiencies through a set of strategies in which excited states delocalisation over multiple pigments (‘excitons’) and charge-transfer states play key roles. These concepts, and their implementation in bioinspired artificial systems, are attracting increasing attention due to the vast potential that could be tapped by realising efficient photochemical reactions. In particular, de novo designed proteins provide a diverse structural toolbox that can be used to manipulate the geometric and electronic properties of bound chromophore molecules. However, achieving excitonic and charge-transfer states requires closely spaced chromophores, a non-trivial aspect since a strong binding with the protein matrix needs to be maintained. Here, we show how a general-purpose artificial protein can be optimised via molecular dynamics simulations to improve its binding capacity of a chlorophyll derivative, achieving complexes in which chromophores form two closely spaced and strongly interacting dimers. Based on spectroscopy results and computational modelling, we propose each dimer is excitonically coupled, and displays signatures of charge-transfer state mixing. This work could open new avenues for the rational design of chromophore – protein complexes with advanced functionalities.

Bioexcitons by Design: How Do We Get There?

“…Fortunately, critical progress has been made on both fronts in the last few years. Indeed, the recent de novo design of a variety of model proteins that bind Chl-like pigments − gives reason to hope that this side of the bioexciton design problem will in the coming years be “solved” to some workable degree of accuracy. The focus of this Perspective will instead be on the structure–spectrum problem: the challenge of accurately predicting optical spectra from structural data, allowing for a priori screening of design models for desired optical properties.…”