Exciton transport in the PE545 complex: insight from atomistic QM/MM-based quantum master equations and elastic network models

Abstract

In this paper, we work out a parameterization of environmental noise within the Haken-Strobl-Reinenker (HSR) model for the PE545 light-harvesting complex, based on atomic-level quantum mechanics/molecular mechanics (QM/MM) simulations. We use this approach to investigate the role of various auto- and cross-correlations in the HSR noise tensor, confirming that site-energy autocorrelations (pure dephasing) terms dominate the noise-induced exciton mobility enhancement, followed by site energy-coupling cross-correlations for specific triplets of pigments. Interestingly, several cross-correlations of the latter kind, together with coupling-coupling cross-correlations, display clear low-frequency signatures in their spectral densities in the 30-70 [Formula: see text] region. These slow components lie at the limits of validity of the HSR approach, which requires that environmental fluctuations be faster than typical exciton transfer time scales. We show that a simple coarse-grained elastic-network-model (ENM) analysis of the PE545 protein naturally spotlights collective normal modes in this frequency range that represent specific concerted motions of the subnetwork of cysteines covalenty linked to the pigments. This analysis strongly suggests that protein scaffolds in light-harvesting complexes are able to express specific collective, low-frequency normal modes providing a fold-rooted blueprint of exciton transport pathways. We speculate that ENM-based mixed quantum classical methods, such as Ehrenfest dynamics, might be promising tools to disentangle the fundamental designing principles of these dynamical processes in natural and artificial light-harvesting structures.

Wavelet imaging of transient energy localization in nonlinear systems at thermal equilibrium: The case study of NaI crystals at high temperature

“…For example, it would be interesting to adopt a tool inspired to our method to characterize the dynamics of energy transfer and exciton-phonon interactions in light-harvesting complexes. [79][80][81] Wavelet-based methods could be used to characterize the dynamics of vibrational energy transfer 82,83 in many complex system, including biomolecules. For example, coupled to pumpprobe molecular dynamics approaches 84 to investigate in a time-resolved manner long-range coupling 85 in frequency space.…”

An investigation into the energy transfer efficiency of a two-pigment photosynthetic system using a macroscopic quantum model

“…In our double-state system the coefficients | χ e 1 (t) and | χ e 2 (t) , using Eqs. ( 4), ( 14) and (15), take the following forms, respectively…”