Fluorescence photosynthetic reaction centers

Stanley R J and Boxer S G 1995 Oscillations in the spontaneous fluorescence from photosynthetic reaction centers J. Phys. Chem. 99 859-63... 

As mentioned above, the natural photosynthetic reaction center uses chlorophyll derivatives rather than porphyrins in the initial electron transfer events. Synthetic triads have also been prepared from chlorophylls [62]. For example, triad 11 features both a naphthoquinone-type acceptor and a carotenoid donor linked to a pyropheophorbide (Phe) which was prepared from chlorophyll-a. The fluorescence of the pyropheophorbide moiety was strongly quenched in dichloromethane, and this suggested rapid electron transfer to the attached quinone to yield C-Phe+-Q r. Transient absorption studies at 207 K detected the carotenoid radical cation (kmax = 990 nm) and thus confirmed formation of a C+-Phe-QT charge separated state analogous to those formed in the porphyrin-based triads. This state had a lifetime of 120 ns, and was formed with a quantum yield of about 0.04. The lifetime was 50 ns at ambient temperatures, and this precluded accurate determination of the quantum yield at this temperature with the apparatus employed. 

King, B. A. (2001) Ultrafast dynamics in the photosynthetic reaction center and green fluorescent proteins. 172 pp. AN 2001 914004... 

Phytochrome, Photosynthetic Reaction Center, Electron Transfer, Color-tuning Mechanism, Retinal Protein, Green Fluorescent Protein, Firefly Luciferase... 

Van Brederode, M. E., Jones, M. R., and Van Grondelle, R., 1997a, Fluorescence excitation spech a of membrane bound photosynthetic reaction centers of Rhodobacter sphaeroides in which tyrosine M210 is replaced by byptophan evidence for a new pathway of charge separation. Chem. Phys. Letts., 268 143nl49. 

Woodbury, N. W. T., and Parson, W. W., 1984, Nanosecond fluorescence from isolated photosynthetic reaction centers of Rhodopseudomonas sphaeroides. Biochim. Biophys. Acta, 767 345n361. 

As demonstrated in this chapter, the binding of metal ions to maclocyclic ligands (e.g., porphyrins) results in the change in both the thermodynamic and dynamic properties of ET reactions of metalloporphyrins. Excellent models of the photosynthetic reaction center were developed by the appropriate choice of combination of metal ions and macrocyclic ligands. The lifetimes of the CS states in models of photosynthetic reaction center composed of electron donors and acceptors also were controlled by binding of metal ions to radical anions of electron acceptor moieties in the electron donor-acceptor hnked molecules. The control of ET processes by coordination of metal ions to the dyads led us to develop a unique fluorescence sensor for the ion. The binding of metal ions to radical anions of electron acceptors results in acceleration of thermal ET reactions, which would otherwise be impossible to occur. Such effects of metal ions to enhance the ET... 

The lack of energy transfer in 24 is in marked contrast to the results for a variety of other bichromophoric molecules where singlet energy transfer occurs over many tens of angstroms via the Forster dipole-dipole mechanism. Since the effidency of Forster energy transfer depends upon the fluorescence quantum yield of the donor, we postulated that the lack of energy transfer in 24 was due to the very low fluorescence quantum yield of the carotenoid, and further concluded that energy transfer from carotenoid polyenes to chlorophyll in photosynthetic reaction centers could therefore not occur by the dipole-dipole mechanism [72]. 

M. E. (1991) Excitation dichroism of electric field modulated fluorescence yield for the identification of primary electron acceptor in photosynthetic reaction center. /. Phys. Chem., 95, 2036-2041. 

Figure 25. (A) Structure of an artificial photosynthetic reaction center, the molecular triad C-P-Q, and the proton-shuttling quinone, Qsl (B) Schematic diagram showing orientation of the triad In the liposome and the sequence of events after photoexcitation (see table at right and text for details) (C) Fluorescence excitation spectra of the pH-indicator dye pyraninetrisulphonate as a measure of the concentration of the protonated form of the indicator dye (D) Fluorescence excitation-band intensity as a function of irradiation time in the absence and in the presence of FCCP. Figures adapted from Steinberg-Yfrach, Liddeii, Hung, (AL) Moore, Gust and (TA) Moore (1997) Conversion of light energy to proton potential in liposomes by artificial photosynthetic reaction centres. Natu re 385 239-241.

Kleima FJ, Gradinaru CC, Calkoen F, Van Stokkum IHM, Van Grondelle Rand Van Amerongen H (1997) Energy transfer in LHCH monomers at 77K studied by sub-picosecond transient absorption spectroscopy. Biochemistry 36 15262-15268 Kleinherenbrink FAM, Hastings G, Wittmershaus BP and Blankenship RE (1994) Delayed fluorescence from Fe-S type photosynthetic reaction centers at low redox potential. Biochemistry 33 3096-3105... 

There is some evidence that the collective modes are coupled to the electronic transitions in proteins, although these measurements are somewhat indirect since no one has yet seen direct Debye-Waller factors in the ZPL fluorescence work. The main evidence has come from the work of Vos et al. involving electron transfer studies in photosynthetic reaction centers. Martin and collaborators have engineered a mutant of the photo-... 

Phycobilisomes are large complex assemblies of phyco> biliproteins designed to collect light and transfer the energy to the photosynthetic reaction centers of cyanobacteria. Phy> cobilipFOteins and phycobilisomes contain several fluorescent species and are known to display complex intensity decays. While these complex decays can be analyzed in terms of the muitiexponential model, it is equally probable... 

The intensity of fluorescence from an immobilized, isotropic sample of photosynthetic reaction centers (RCs) increases upon application of an electric field at 77 K [IJ. The change in fluorescence was found to be quadratic with the applied field strength, and the fluorescence in the field was found to become polarized [2]. The fluorescence increase is ascribed to a net decrease in the rate of the forward electron transfer reaction which competes with fluorescence from P. The field alters the free energy change for electron transfer, AG, and thus the rate because the energy of the dipolar product state... 

Zankel KL, Reed DW and Clayton RK. Fluorescence and photochemical quenching in photosynthetic reaction centers. Proc. Natl. Acad. Sci. USA 1968 61 1243. 

Delayed fluorescence also can report on the energies and dynamics of metastable states that are created photochemically by electron transfer or other processes. In photosynthetic reaction centers of purple bacteria or plant photosystem 11, the amplitude of delayed fluorescence from an early ion-pair state decreases on picosecond and nanosecond time scales, while the population of the state remains essentially constant [290-293]. Both structural heterogeneity and relaxations of the protein around the ion-pair probably contribute to the complex time dependence of the delayed fluorescence. 

Stanley, R.J., Boxer, S.G. Oscillations in spontaneous fluorescence fi om photosynthetic reaction centers. J. Phys. Chem. 99, 859-863 (1995)... 

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