The peridinin chlorophyll-a protein (PCP) of dinoflagellates differs from the well-studied light-harvesting complexes of purple bacteria and green plants in its large (4:1) carotenoid to chlorophyll ratio and the unusual properties of its primary pigment, the carotenoid peridinin. We utilized ultrafast polarized transient absorption spectroscopy to examine the flow of energy in PCP after initial excitation into the strongly allowed peridinin S2 state. Global and target analysis of the isotropic and anisotropic decays reveals that significant excitation (25-50%) is transferred to chlorophyll-a directly from the peridinin S2 state. Because of overlapping positive and negative features, this pathway was unseen in earlier single-wavelength experiments. In addition, the anisotropy remains constant and high in the peridinin population, indicating that energy transfer from peridinin to peridinin represents a minor or negligible pathway. The carotenoids are also coupled directly to chlorophyll-a via a low-lying singlet state S1 or the recently identified SCT. We model this energy transfer time scale as 2.3 +/- 0.2 ps, driven by a coupling of approximately 47 cm(-1). This coupling strength allows us to estimate that the peridinin S1/SCT donor state transition moment is approximately 3 D.

We present laser flash-induced triplet-minus-singlet (TmS(flash)) and absorbance-detected-magnetic-resonance (TmS(ADMR)) measurements on the light-harvesting chlorophyll a/b pigment-protein complex (LHCII) from pea. We investigated the influence of LHCII aggregation on xanthophyll triplet formation. The effect of aggregation was previously studied using TmS(ADMR) [van der Vos et al. (1994) Biochim. Biophys. Acta 1208, 243-250] for LHCII from spinach, and it was concluded that aggregation leads to a large increase of the amount of intertrimer triplet transfer. However, a similar study on LHCII from pea with the use of TmS(flash) measurements [Barzda et al. (1998) Biochemistry 37, 546-561] showed much smaller effects. To resolve this apparent discrepancy and to compare the results of TmS(ADMR) and TmS(flash) measurements, we used both techniques to study LHCII from pea, applying an identical aggregation procedure in both cases. It appears that aggregation does not lead to an increase of intertrimer triplet transfer as thought before but to a redistribution of the triplets over the two central xanthophylls (mainly lutein) that are present in each monomeric subunit of LHCII. Moreover, it is argued that the TmS band at 525 nm is due to lutein instead of violaxanthin as was reported in earlier studies. It is concluded that aggregation leads to a change in chlorophyll-xanthophyll interactions, which might explain the large change in excited-state lifetime of chlorophyll a in LHCII upon aggregation. This change in lifetime is possibly related to the phenomenon of nonphotochemical quenching in green plants, which is an important protective regulatory mechanism, that lowers the probability of photoinhibition.

The Optical Dynamics of Excitons in Cylindrical J-Aggregates Lampoura, S.S.; Spitz, C.; Dähne, S.; Knoester, Jasper; Duppen, K.; Dahne, S. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Research and Testing, Richard-Willstaetter-Strasse 11, D-12489 Berlin, Germany. ReceiVed: September 12, 2001; In Final Form: NoVember 28, 2001 The optical dynamics of excitons in cylindrical 5,5′,6,6′-tetrachloro-1,1′-diethyl-3,3′-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC)/C8O3 aggregates have been investigated by ultrafast pump-probe spectroscopy and accumulated photon echo experiments. In the nonlinear optical interactions, both the oneexciton band and the two-exciton band are excited. The interpretation of the results involves the separation of the two-exciton states into two types: those that have predominantly "ring"-character, with energy separations determined by the circumference of the cylinder, and those that have predominantly "longitudinal"-character, with energy separations determined by the coherence length of the excitons along the length of the cylinder. At 1.5 K, the excitons were found to be delocalized over an area of, on average, 95 molecules. These excitons can move incoherently to other localized regions on the cylinder, leading to rapid relaxation within the oneexciton band.

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Exciton dynamics in the B850 and B875 bands of isolated complexes of Rhodopseudomonas acidophila (strain 10 050 and 7050) and in the B875 band of isolated complexes of Rhodobium marinum were investigated by means of accumulated photon echo and pump-probe techniques at different temperatures and wavelengths. For all three systems, the optical dephasing time T 2 was found to be very similar: at 4.2 K, T 2 is 116 and 106 ps for the B850 and B875 bands of Rhodopseudomonas acidophila, respectively, and 93 ps for the B875 band of Rhodobium marinum. The rapid dephasing, which displays glassy character, is a consequence of the strong pigment-protein interactions that arise through the rather short distances in these complexes. The observed dephasing time at the red edge of the B850 band of Rhodopseudomonas acidophila at 4.2 K reveals the existence of spectral diffusion in this system. From the wavelength dependence of the pump-probe signal in the B875 LH1 band of Rhodopseudomonas acidophila at 3 K it is concluded that energy transfer between energetically inequivalent LH1 rings occurs on a time scale of several tens picoseconds, while energy trapping takes place in about 250 ps.