Energy transfer in photosynthesis: Pigment concentration effects and fluorescent lifetimes

Shapiro, S. L.; Kollman, V.H.; Campillo, A. J.

doi:10.1016/0014-5793(75)80939-2

Cited by 55 publications

(16 citation statements)

References 24 publications

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“…The density of bacteriochlorophyll singlets in the Si state, n, as a function of time is given by dn/dt =-kn -yn2 + CI(t) [3] where k = 1/r (r is the fluorescence lifetime at low flash intensities), -y is a bimolecular rate constant for singlet-singlet annihilation, C is a constant, and I(t) is the photon density of the excitation pulse (with units of photons cm-2) (6,36). This equation makes the simplifying assumption that the saturation of the reaction centers at high flash intensity causes only negligible changes in k, compared to the changes resulting from exciton annihilation.…”

Section: Resultsmentioning

confidence: 99%

Light collection and harvesting processes in bacterial photosynthesis investigated on a picosecond time scale

Campillo

Hyer

Monger

et al. 1977

Proc. Natl. Acad. Sci. U.S.A.

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Fluorescence lifetimes have been determined for four strains of Rhodopseudomonas sphaeroides. Chromatophore samples were excited with a single picosecond flash, and the fluorescence was detected with a streak camera. The decay times are 100 psec in strains 2.4.1 and Ga, and 300 psec in the carotenoidless strain R-26. These times are related to the transfer of energy from the light-harvesting antenna pigment molecules to the photochemical reaction center. In strain PM-8 dpl, which lacks reaction centers, the lifetime is 1.1 nsec. In addition, we have obtained curves relating the quantum yield of fluorescence to the photon density of the excitation pulse. These curves can be fit with a simple model that relates excitonic processes to properties of the photosynthetic unit and that qualitatively describes differences between the mutant strains. Picosecond laser techniques are now being widely applied in this field of biophysics, especially in the area of photosynthesis. Picosecond flash-photolysis techniques have identified transitions occurring in the primary photochemical reaction in photosynthetic bacteria (1, 2), and streak-camera measurement techniques have been used to measure rapid transfer of excitations between chlorophyll molecules in vivo (3-6). Other recent biophysical applications of picosecond or subnanosecond techniques include measurements on hemoglobin (7), visual pigments (8), and DNA (9-11).This paper is concerned with a determination by picosecond techniques of the kinetics with which the light-harvesting antenna pigment molecules of photosynthetic bacteria transfer energy to the photochemical reaction center. We have used two approaches to this problem. In the first approach, the sample is excited with a 20-psec pulse of low intensity and the fluorescence lifetime is measured. This time reflects the rate of depopulation of excited singlet states of bacteriochlorophyll in the antenna, mainly due to their capture by the reaction center. In the second approach, high-intensity pulses are used to generate nonlinear optical effects. High intensities produce a high density of excited states, leading to exciton annihilation processes, as Mauzerall (12) has demonstrated with nanosecond pulses and Campillo et al. (13) with picosecond pulses. Such processes have now been studied by several groups (6, 12-18). When two or more singlet excitations are simultaneously present in the photosynthetic unit (or within a certain diffusion radius), they can migrate into the vicinity of one another, and singlet-singlet annihilation can take place by the reactions Si +Si Sn + SO [1] Sn -"Si + heat [21 Eq. 1 represents a bimolecular fusion process in which a molecule in the first excited singlet state SI transfers its energy to a similarly excited neighboring molecule, promoting it to a higher singlet state S,. Because higher excited singlet states in large molecules such as bacteriochlorophyll almost always decay nonradiatively to the S1 state, as shown in Eq. 2, the net result is the loss of one excited singlet...

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Section: Resultsmentioning

confidence: 99%

Light collection and harvesting processes in bacterial photosynthesis investigated on a picosecond time scale

Campillo

Hyer

Monger

et al. 1977

Proc. Natl. Acad. Sci. U.S.A.

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“…The bulk of the pigment in both plants and bacteria fu nctions as antennae, reaction-center (bacterio)chlorophyll making up about 1 % of the total in bacteria, and less than 1 % in plants. The detailed mechanism of excitation energy transfer is still not well understood (176,177). Recently, there has been considerable progress in describing the reaction center photochemistry, and we refer the reader to reviews on the subject (178-180).…”

Section: Heme Proteinsmentioning

confidence: 99%

Linear Dichroism of Biological Chromophores

Hofrichter¹,

Eaton²

1976

Annu. Rev. Biophys. Bioeng.

113

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“…629 work (tJ = 41 i 5 ps) [117]. These authors attribute the anomalously short lifetimes previously reported for in ~ioo systems to be a result of the utilization of full mode-locked pulse trains causing high intensity effects due to exciton-exciton annihilation processes.…”

mentioning

confidence: 74%

Excited States of Biomolecules—iv

Fugate

Song

1976

Photochem & Photobiology

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The electronic excited states of biomolecules are selectively reviewed from approximately mid 1975 through mid 1976. The inclusion of all papers has not been attempted and exclusion does not necessarily reflect the pertinence of a paper. We urge authors to send us their reprints for future series of this Yearly Review. Porphyrins and chlorophyllsThe CND0/2 calculations have been performed for chlorophyll a (chl a), chlorophyll b (chl b) and their Be analogs [65]. Results indicate that the 3d atomic orbitals of the metal contribute significantly to the CJ and n bonding energies. The molecule is stabilized by 167 kJ . mol-' (40 kcal mol-I) when MgZf is replaced by Be2+. Shipman et al. [ 12 11 have discussed

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Energy transfer in photosynthesis: Pigment concentration effects and fluorescent lifetimes

Cited by 55 publications

References 24 publications

Light collection and harvesting processes in bacterial photosynthesis investigated on a picosecond time scale

Light collection and harvesting processes in bacterial photosynthesis investigated on a picosecond time scale

Linear Dichroism of Biological Chromophores

Excited States of Biomolecules—iv

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