On the exciton coupling between two chlorophyll pigments in the absence of a protein environment: Intrinsic effects revealed by theory and experiment

Bruce F. Milne, Christina Kjær, Jørgen Houmøller, Mark H. Stockett, Yoni Toker, Angel Rubio, Steen Brøndsted Nielsen

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Exciton coupling between two or more chlorophyll (Chl) pigments is a key mechanism associated with the color tuning of photosynthetic proteins but it is difficult to disentangle this effect from shifts that are due to the protein microenvironment. Herein, we report the formation of the simplest coupled system, the Chl a dimer, tagged with a quaternary ammonium ion by electrospray ionization. Based on action spectroscopic studies in vacuo, the dimer complexes were found to absorb 50-70 meV to the red of the monomers under the same conditions. First-principles calculations predict shifts that somewhat depend on the relative orientation of the two Chl units, namely 50 and 30 meV for structures where the Chl rings are stacked and unstacked, respectively. Our work demonstrates that Chl association alone can produce a large portion of the color shift observed in photosynthetic macromolecular assemblies. How strong is the coupling between two adjacent chlorophyll molecules in the absence of a protein environment? Mass spectrometry experiments now provide an answer to this question as chlorophyll a dimers tagged by quaternary ammonium ions could be produced in the gas phase by electrospray ionization.

Original languageEnglish
Pages (from-to)6248-6251
Number of pages4
JournalAngewandte Chemie - International Edition
Volume55
Issue number21
DOIs
StatePublished - 17 May 2016

Bibliographical note

Publisher Copyright:
© 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Funding

FundersFunder number
Horizon 2020 Framework Programme646259, 267374

    Keywords

    • absorption spectroscopy
    • chlorophyll
    • density functional calculations
    • mass spectrometry
    • photosynthesis

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