Time-resolved spectroscopy, photosynthetic

So far we have exclusively discussed time-resolved absorption spectroscopy with visible femtosecond pulses. It has become recently feasible to perfomi time-resolved spectroscopy with femtosecond IR pulses. Flochstrasser and co-workers [M, 150. 151. 152. 153. 154. 155. 156 and 157] have worked out methods to employ IR pulses to monitor chemical reactions following electronic excitation by visible pump pulses these methods were applied in work on the light-initiated charge-transfer reactions that occur in the photosynthetic reaction centre [156. 157] and on the excited-state isomerization of tlie retinal pigment in bacteriorhodopsin [155]. Walker and co-workers [158] have recently used femtosecond IR spectroscopy to study vibrational dynamics associated with intramolecular charge transfer these studies are complementary to those perfomied by Barbara and co-workers [159. 160], in which ground-state RISRS wavepackets were monitored using a dynamic-absorption technique with visible pulses. 

Schmidt, S., Arlt, T., Hamm, P., Lauterwasser, C., Finkele, U., Drews, G., and Zinth, W., 1993, Time-resolved spectroscopy of the primary photosynthetic processes of membrane-bound reaction centers from an antenna-deficient mutant of Rhodobacter capsulatus. Biochim. 

Zinth, W., and Kaiser, W., 1993, Time-resolved spectroscopy of the primary electron transfer in reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis. In The Photosynthetic Reaction Center, (J. Deisenhofer and J. R. Norris, eds.) Volume 2, 71988, Academic Press, San Diego, USA. 

Fig. 9. (A) Absorption spectrum of Rb. sphaeroides used as a reference to show the Qx and Qy bands of the primary donor (P), BChl [B] and bacteriopheophytin [BO] (B) Femtosecond absorption changes at 920 (a), 785 (b) and 545 nm (c) vs. the delay time of the monitoring pulse measured at room temperature, and (C) absorption changes at 920 (a) and 794 nm (b) measured at 25 K. Figure source (A) see Fig. 7 (B) Holzapfel, Finkele, Kaiser, Oesterheldt, Scheer, Stilz and Zinth (1990) Initial electron transferin the reaction center from Rhodobacter sphaeroides. Proc Nat Acad Sci, USA 87 5170 (C) Zinth and Kaiser (1993) Time-resolved spectroscopy of the primary electron transfer in reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis. I n JR Norris and J Deisenhofer (eds) The Photosynthetic Reaction Center, Voi il, p 82. Acad Press.

Robert B, Nabedryk E and Lutz M (1989) Vibrational spectroscopy of transient states in photosynthetic bacterial reaction centers. In Clark RJH and Hester RE (eds) Time-resolved spectroscopy, pp 301-333. John Wiley and Sons, New York... 

In this chapter we have shown that the dynamics and spectroscopy of the initial events taking place in bacterial photosynthetic RCs can be described by the model shown in Table I and Fig. 19. Using these physical constants we can calculate the absorption spectra, ET rate constants, and fs time-resolved spectra. It should be noted that for processes taking place in sub-ps range, it is more reasonable not to use rate constant because the concept of rate constant requires the validity of the Markoff approximation [82,88]. Instead the... 

Dau H, Haumann M. Time-resolved X-ray spectroscopy leads to an extension of the classical S-state cycle model of photosynthetic oxygen evolution. Photosynth Res 2007 92 327-43. 

Raman and Infrared Spectroscopy. Two reviews deal with resonance Raman spectroscopy of carotenoid-containing biomolecules and micro-organisms152 and of carotenoids and chlorophylls in photosynthetic bacteria.153 The resonance Raman excitation profile of lycopene in acetone has been determined.154 Calculations previously used for (3-carotene do not explain the lycopene data. Several papers report detailed studies of the time-resolved resonance Raman spectra of... 

There continues to be an enormous amount of activity in the area of PET, much of it directed towards the development of systems capable of delivering artificial photosynthesis. Many of these systems involve porphyrin units as electron-donors and thus it is appropriate to consider them in this section of the review. A number of new fullerene-porphyrin dyads have been reported. A pyrazolinofullerene (155) has been constructed which facilitates efficient PET when strong donors such as iV,Ar-diethylaniline or ferrocene are linked to the pyrazoline ring. A photosynthetic multi-step ET model (156) based on a triad consisting of a meso,meso- inked porphyrin dimer connected to ferrocene and Ceo as electron-donor and electron-acceptor, respectively, has been synthesized and its ET dynamics (Scheme 38) have been investigated using time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. ... 

H. Lemetyinen, J. Andreasson, and many others have studied other large x-systems including the Cgo molecule. After excitation, electrons or excitations can be seen in time-resolved transient spectroscopy jumping between the connected molecules. This type of work is useful in understanding natural photosynthetic processes. It deserves to be mentioned that ET or conductivity cannot occur without excitation. 

Fluorescence spectroscopy has been used for a long time to investigate energy transfer in photosynthetic membranes. Spectral and time-resolved properties can be studied. Fluorescence is still of interest in many cases (e.g., for the screening of photosynthetic mutants), but its impact is especially important in the study of Photosystem II, because the fluorescence yield of chlorophyll a in photosynthetic membranes... 

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