Insights into colour-tuning of chlorophyll optical response in green plants

Abstract

First–principles calculations within the framework of real–space time–dependent density functional theory have been performed for the complete chlorophyll (Chl) network of the light–harvesting complex from green plants, LHC–II. A local-dipole analysis method developed for this work has made possible studies of the optical response of individual Chl molecules subject to the influence of the remainder of the chromophore network. The spectra calculated with our real–space TDDFT method agree with previous suggestions that weak interaction with the protein microenvironment should produce only minor changes in the absorption spectrum of Chl chromophores in LHC–II. In addition, relative shifting of Chl absorption energies leads the stromal and lumenal sides of LHC–II to absorb in slightly different parts of the visible spectrum providing greater coverage of available light frequencies. The site-specific alterations in Chl excitation energies support the existence of intrinsic energy transfer pathways within the LHC–II complex.

On the Exciton Coupling between Two Chlorophyll Pigments in the Absence of a Protein Environment: Intrinsic Effects Revealed by Theory and Experiment

“…The highly complex nature of the macromolecular systems involved has, however, always served to complicate such attempts. In recent years, experimental approaches have been joined by theoretical/computational methods, and this has permitted studies at levels of detail that were previously unattainable …”

Ultranonlocality and accurate band gaps from a meta-generalized gradient approximation

“…This restriction can have serious consequences because often the interesting features of real-world systems, especially in the realm of nanomolecular and supramolecular science, stem from an intrinsic complexity that requires the explicit treatment of a large number of particles. Understanding light-harvesting systems [33][34][35] is a paradigm example: it requires calculating energy and charge transfer through arrays of dozens of chromophores, where each chromophore typically has hundreds of electrons. The chromophores in turn are typically embedded in a protein matrix, at least parts of which should also be taken into account explicitly [33,[35][36][37].…”

Applications of large-scale density functional theory in biology

“…Improvements in accuracy are expected when employing a time-dependent Hamiltonian, and towards this goal, researchers have started to apply TDDFT calculations to study natural photosynthesis. Indeed, a recent study performed real-space time-propagation TDDFT calculations of the electronic absorption spectrum of the chlorophyll network of the light-harvesting antenna complex from green plants (LHC-II) [171]. The trimeric pigment-protein complex comprises over 17000 atoms and contains 14 chlorophyll molecules per monomer.…”

“…Recently, however, there has been increasing availability of methodology for large-scale TDDFT calculations. Real space methods including Octopus [53] can be used for calculations of very large systems such as chlorophyll networks in pigment-protein complexes [171], as will be discussed in more detail in Section 4.4. Zuehlsdorff et al developed an approach to enable linear-response TDDFT within the ONETEP large-scale DFT code [172,173,174], and demonstrated application to solvated chromophores and dye molecules embedded in explicit solvent [21].…”