Regulated light harvesting in natural and artificial photosynthesis

 
I have a long-standing interest in the physical mechanisms of photosynthesis since the start of my Ph. D. in Leiden in 1992. Presently I participate in the Biophysics of Photosynthesis research program at the Biophysics group.

My studies are focused on light harvesting, photoprotection and regulatory phenomena in photosynthesis and the role of carotenoids therein. Carotenoids are polyene-like molecules with a complex excited-state manifold that act as accessory light harvesters by absorbing blue-green light and transferring the excited-state energy to chlorophylls. Moreover, they protect the photosynthetic apparatus against oxidative damage by quenching chlorophyll triplet states and singlet oxygen radicals. Importantly, carotenoids are involved in complex regulatory feedback mechanisms that prevent over-excitation of the photosynthetic apparatus through a set of phenomena collectively known as nonphotochemical quenching. The goal of the research program is to assess the physical mechanisms by which these processes occur. In essence, this question condenses to a molecular understanding of controlled energy and electron transfer flows in confined geometries of Chls and carotenoids, and the role played by symmetry-forbidden excited states and intra- and intermolecular charge-transfer states.

Natural photosystems are studied in varying degrees of complexity and cooperativity, from isolated light-harvesting complexes to native membranes and even intact plant leaves. A separate research line involves the study of artificial light-harvesting systems, by which carotenoids and Chl-like tetrapyrroles or electron acceptors such as fullerenes are covalently linked in well-defined geometries.

The photophysical and –chemical phenomena in the natural and artificial photosystems are investigated with advanced ultrafast methods. Foremost is a novel technique known as femtosecond stimulated Raman spectroscopy (FSRS), which is presently being developed by myself at the VU LaserCenter. With FSRS, resonant Raman spectra can be obtained on a femtosecond timescale with high spectral resolution and sensitivity and affords detailed molecular information of the dynamic processes under study.

Presently the program is supported by grants from NWO-ALW: an ALW open competition grant (250 kEur, with R. van Grondelle) and an investment grant to construct an advanced multi-pulse spectrometer (672 kEur, with R. van Grondelle). Close collaborations exist with profs. T.A. Moore, A.L. Moore and D. Gust from Arizona State University, prof. A. Ruban from Queen Mary College, London, prof. P. Horton, Sheffield and prof H.A. Frank, Connecticut.

Key publications:

R. Berera, C. Herrero, I.H.M. van Stokkum, M. Vengris, G. Kodis, R.E. Palacios, H. van Amerongen, R. van Grondelle, D. Gust, T.A. Moore, A.L. Moore, J.T.M. Kennis, A simple artificial light-harvesting dyad as a model for excess energy dissipation in oxygenic photosynthesis Proc. Natl. Acad. Sci. USA, 2006, 103, p. 5343-5348

G. Kodis, C. Herrero, R. Palacios, E. Mariño-Ochoa, S. Gould, L. de la Garza, R. van Grondelle, D. Gust, T.A. Moore, A.L. Moore, J.T.M. Kennis, Light harvesting and photoprotective functions of carotenoids in compact artificial photosynthetic antenna designs J. Phys. Chem. B 108, 2004, p. 414-425

E. Papagiannakis, S.K. Das, A. Gall, I.H.M. van Stokkum, B. Robert, R. van Grondelle, H.A. Frank, J.T.M. Kennis, Light harvesting by carotenoids incorporated into the B850 light-harvesting complex from Rhodobacter sphaeroides R-26.1: Excited-state relaxation, ultrafast triplet formation and energy transfer to bacteriochlorophyll J. Phys. Chem. B 107, 2003, p. 5642-5649

E. Papagiannakis, J.T.M. Kennis, I.H.M. van Stokkum, R.J. Cogdell, R. van Grondelle, An alternative carotenoid-to-bacteriochlorophyll energy transfer pathway in photosynthetic light harvesting Proc. Natl. Acad. Sci. USA 99, 2002, p. 6017-6022

C.C. Gradinaru, J.T.M. Kennis, E. Papagiannakis, I.H.M. van Stokkum, R.J. Cogdell, G.R. Fleming, R.A. Niederman, R. van Grondelle, An unusual pathway of excitation energy deactivation in carotenoids: Singlet-to-triplet conversion on an ultrafast timescale in a photosynthetic antenna Proc. Natl. Acad. Sci. USA 98, 2001, p. 2364-2369