A simple artificial light-harvesting dyad as a model for excess energy dissipation in oxygenic photosynthesis
- Rudi Berera†,
- Christian Herrero‡,
- Ivo H. M. van Stokkum†,
- Mikas Vengris†,
- Gerdenis Kodis‡,
- Rodrigo E. Palacios‡,
- Herbert van Amerongen§,
- Rienk van Grondelle†,
- Devens Gust‡,
- Thomas A. Moore‡,
- Ana L. Moore‡, and
- John T. M. Kennis†,¶
- †Department of Biophysics, Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, 1081 HV, Amsterdam, The Netherlands;
- ‡Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, AZ 85287; and
- §Laboratory for Biophysics, Wageningen University, 6703 HA, Wageningen, The Netherlands
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Edited by Robin M. Hochstrasser, University of Pennsylvania, Philadelphia, PA, and approved February 10, 2006 (received for review September 29, 2005)
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Fig. 1.Molecular structures and absorption spectra of the compounds. (Upper) Molecular structures of the dyads. A zinc-Pc is covalently linked to a carotenoid with 9 conjugated carbon–carbon double bonds (dyad 1), 10 carbon–carbon double bonds (dyad 2), and 11 carbon–carbon double bonds (dyad 3). Model Pc 4 bears a hexanoyl group instead of a polyene. Model carotenoid 2′ has a terminal ester instead of a Pc. (Lower) Absorption spectrum in THF for dyad 1 (dashed line), dyad 2 (dashed-dotted line), dyad 3 (dotted line), and model Pc 4 (solid line).
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Fig. 2.Kinetic traces and global analysis of the time-resolved data. (A) Kinetic traces with excitation and detection at 680 nm for model Pc 4 (red line), dyad 1 (blue line), dyad 2 (green line), and dyad 3 (magenta line) in THF, along with the result of the global analysis fit (thin solid line). (B) EADS that follow from a global analysis of data for dyad 1. (Inset) An expanded view of the EADS in the spectral region from 475 to 620 nm. (C) The same as for B for dyad 2. (D) The same as for B for dyad 3. The difference spectra corresponding to the vibrationally relaxed, fully solvated Qy state for model Pc 4, as determined from a global analysis, are also shown in B–D as black dashed lines.
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Fig. 3.Kinetic traces with excitation and detection at 680 nm for dyad 1 (solid line), dyad 2 (dotted line), and dyad 3 (dashed line) in acetone. The gray lines denote the result of a global analysis.
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Fig. 4.Target analysis of the time-resolved data. (Upper) Kinetic model used in target analysis of time-resolved data on dyads 2 and 3. (Lower) SADS from the target analysis for dyad 3 in THF. See text for details.
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Fig. 5.Schematic representation of the proposed quenching process: the energy from the Qy state of Pc is transferred to the carotenoid ICT state, which then equilibrates with the carotenoid S1 state before relaxation to the ground state by internal conversion. An increase in solvent polarity leads to a lowering of the ICT energy (gray to black lines).
Footnotes
- ¶To whom correspondence should be addressed. E-mail: j.kennis{at}few.vu.nl
- © 2006 by The National Academy of Sciences of the USA
