Ultrafast Spectroscopy and Photosynthesis

Warren Beck

Associate Professor

3 CEM

517-353-1137


Research webpage


Primary Research Area

Physical (Ph)

Other Area(s) of Interest

Biological (Bi)

Chemical Physics (CP)

Inorganic (In)

Research

(Research Description PDF)

The Beck group uses femtosecond nonlinear spectroscopy to study photophysical and photochemical processes in photosynthetic light-harvesting proteins. The current focus is on how carotenoids function in energy transfer and photoprotection mechanisms in lightharvesting proteins. The long-range goal is to learn the principles that can be used to design and optimize materials for light capture and excitation energy conversion to fuels. Two-dimensional electronic spectroscopy (2DES) allows us to characterize the formation and decay of electronic coherences and intermediate states or to discern the motion of the surrounding protein or solvent medium. We conduct this work with a structural biological perspective; a goal of the research is to understand how the structure of a chromophore and the electrostatic environment derived from the binding site in a protein results in optimal function in energy transfer or photoprotection.

In one project, we are studying the peridinin–chlorophyll a protein (PCP, Figure 1), a light-harvesting protein from marine dinoflagellates that incorporates a carbonylsubstituted carotenoid, peridinin, as its main light-absorbing chromophore. Energy absorbed from the mid-visible part of the solar spectrum by peridinin is transferred efficiently to chlorophyll a on the < 3 ps timescale. PCP represents an important system in which the energy transfer function is optmized by the protein environment and by chemical modification of the active chromophore. An intramolecular charge-transfer (ICT) character is produced in peridinin by the electronwithdrawing character of the carotenoid substituent and the distorted conformation of the conjugated polyene backbone derived from its binding site. The result is a very long lifetime for the S2 (1 1Bu +) excited state and improved yields of excitation energy transfer to the chlorophyll a acceptors via quantum coherent and Förster mechanisms.

Figure 1. Peridinin–chlorophyll a protein from Amphidinium carterae (1PPR.pdb).

 

In a new collaboration with Professor Cheryl Kerfeld (MSU–DOE PRL and LBNL), we are studying the photochemistry and structural dynamics associated with the photoactivation of the orange carotenoid protein (OCP, Figure 2) from cyanobacteria. OCP uses another carbonyl-substituted carotenoid, 3'-hydroxyechinenone, as a light sensor and as a quencher of excited states in the cyanobacterial phycobilisome. We are also interested in the mechanism with which OCP serves as a quencher of singlet oxygen, a reactive oxygen species that is produced as a byproduct in photosynthesis by recombination of charge-separated states in the photosystem II reaction center. Here the ability of OCP to stabilize low-lying triplet states of 3'-hydroxyechinenone is likely to be very important.

Figure 2. Orange carotenoid protein from Synechocystis PCC 6803 (3MG1.pdb).

 

Selected Publications

Excited state conformational dynamics in carotenoids: dark intermediates and excitation energy transfer, Beck, W. F.; Bishop, M. M.; Roscioli, J. D.; Ghosh, S.; Frank, H. A., Arch. Biochem. Biophys. 2015, 572, 175-183.

Vibrationally coherent preparation of the transition state for photoisomerization of the cyanine dye Cy5 in water, Bishop, M. M.; Roscioli, J. D.; Ghosh, S.; Mueller, J. J.; Shepherd, N. C.; Beck, W. F., J. Phys. Chem. B 2015, 119, 6905-6915.

Femtosecond heterodyne transient-grating studies of nonradiative decay of the S2 (1 1Bu+) state of β-carotene: Contributions from dark intermediates and double-quantum coherences, Ghosh, S.; Bishop, M. M.; Roscioli, J. D.; Mueller, J. J.; Shepherd, N. C.; LaFountain, A. M.; Frank, H. A.; Beck, W. F., J. Phys. Chem. B 2015, 119, 14905-14924.

Femtosecond heterodyne transient grating studies of nonradiative deactivation of the S2 (1 1Bu+) state of peridinin: detection and spectroscopic assignment of an intermediate in the decay pathway, Ghosh, S.; Bishop, M. M.; Roscioli, J. D.; LaFountain, A. M.; Frank, H. A.; Beck, W. F., J. Phys. Chem. B 2016, 120, 3601-3614.

Torsional dynamics and intramolecular charge transfer in the S2 (1 1Bu +) excited state of peridinin: a mechanism for enhanced mid-visible light harvesting, Ghosh, S.; Roscioli, J. D.; Bishop, M. M.; Gurchiek, J. K.; LaFountain, A. M.; Frank, H. A.; Beck, W. F., J. Phys. Chem. Lett. 2016, 7, 3621-3626.

Excitation energy transfer by coherent and incoherent mechanisms in the peridinin– chlorophyll a protein, Ghosh, S.; Bishop, M. M.; Roscioli, J. D.; LaFountain, A. M.; Frank, H. A.; Beck, W. F., J. Phys. Chem. Lett. 2017, 8, 463-469.

CV

B.S., 1982, Davidson College

Ph.D., 1988, Yale Univ.

Miller Institute Postdoctoral Fellowship, 1989–91, Univ. of California, Berkeley

Awards/Honors

2015 Natsci Teaching Prize Michigan State University (College of Natural Science)
1994 Cottrell Scholars Award Research Corporation
1993 - 1994 Teaching Fellowship Lilly Endowment
1992 - 1995 Searle Scholarship Chicago Community Trust/Searle Scholars Program
1989 - 1991 Miller Institute Postdoctoral Fellowship University of California, Berkeley
1988 Ph.D. Yale University
1988 Richard Wolfgang Dissertation Prize Yale University Department of Chemistry
1982 - 1986 Kent Fellowship Yale University Department of Chemistry
1982 Phi Beta Kappa Phi Beta Kappa
1982 - 1985 Graduate Fellowship National Science Foundation
1982 Bachelor of Science Cum Laude Davidson College