Coherence in carotenoid-to-chlorophyll energy transfer

Abstract

The subtle details of the mechanism of energy flow from carotenoids to chlorophylls in biological light-harvesting complexes are still not fully understood, especially in the ultrafast regime. Here we focus on the antenna complex peridinin–chlorophyll a–protein (PCP), known for its remarkable efficiency of excitation energy transfer from carotenoids—peridinins—to chlorophylls. PCP solutions are studied by means of 2D electronic spectroscopy in different experimental conditions. Together with a global kinetic analysis and multiscale quantum chemical calculations, these data allow us to comprehensively address the contribution of the potential pathways of energy flow in PCP. These data support dominant energy transfer from peridinin S2 to chlorophyll Qy state via an ultrafast coherent mechanism. The coherent superposition of the two states is functional to drive population to the final acceptor state, adding an important piece of information in the quest for connections between coherent phenomena and biological functions.

Carotenoid-Chlorophyll Interactions in a Photosynthetic Antenna Protein: A Supramolecular QM/MM Approach

“…We present in Table 4 the inter-chromophore coupling constants greater than 100 cm −1 . The obtained pairwise inter-pigment coupling strengths are in general agreement with previous reports [ 13 , 14 , 15 , 21 , 26 , 31 ]. Per-Per interactions within the same cofactor cluster tend to be the strongest, with coupling constants of 194–619 cm −1 .…”

“…Recent theoretical [ 14 , 15 ] and experimental [ 15 , 16 , 17 ] work has identified an ultrafast quantum coherent mechanism in the Per-to-Chl a energy transduction process. While it is now well established that Per-to-Chl a energy transfer represents a fundamental event in light harvesting by PCP, it is still unknown if energy transfer paths among Pers, and from multiple Pers to Chl a , help funnel the transfer of energy.…”

Successes & challenges in the atomistic modeling of light-harvesting and its photoregulation

“…Moreover, it allows computing the SD using only the crystal structure of the complex. On the other hand, this method does not account for protein fluctuations, whose effect has still to be included a posteriori, for example with a simplified atomic charge scheme [85] or with a phenomenological approach [43,92]. Several groups have sought to overcome the force-field issue and to refine the MD sampling of nuclear fluctuations, for example, by computing the trajectories using multiscale QM/MM molecular dynamics [93,94,95,96], which combines the ability of MD to account for the environment with the accuracy of the quantum chemical potentials.…”

Optimization and selection of time-frequency transforms for wave-packet analysis in ultrafast spectroscopy

“…Whatever the nature of the studied material or the particular technique and time resolution used, the analysis of the frequency and time behavior of the beatings is a key ingredient to extract information about the system dynamics. To this aim, methodologies based on linear and bilinear time-frequency transforms (TFT) have been already proposed and applied to ultrafast 1D [14][15][16][17][18][19] and 2D spectroscopy measurements [20][21][22][23][24][25][26]. The advantage of TFTs is that they analyze a non-stationary oscillating signal providing both time and frequency resolution, spreading out the information content along the two dimensions of the time-frequency plane [27].…”