ENERGY TRANSFER IN THE PRIMARY STAGES OF THE PHOTOSYNTHETIC PROCESS INVESTIGATED BY PICOSECOND TIME-RESOLVED FLUORESCENCE SPECTROSCOPY.
Item
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Title
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ENERGY TRANSFER IN THE PRIMARY STAGES OF THE PHOTOSYNTHETIC PROCESS INVESTIGATED BY PICOSECOND TIME-RESOLVED FLUORESCENCE SPECTROSCOPY.
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Identifier
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AAI8119756
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identifier
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8119756
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Creator
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PELLEGRINO, FRANCESCO.
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Contributor
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Prof. Robert R. Alfano
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Date
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1981
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter
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Abstract
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The aim of this research has been to understand the fate of the absorbed light energy in the primary stages of the photosynthetic process. In particular, the energy transfer in the accessory pigment complex consisting of carotenoids, Chl. a and Chl. b in higher green plants and phycobiliproteins in blue-green algae have been investigated. These accessory pigments are responsible for the highly efficient transfer of the excitation energy to the photochemically active reaction center traps. In this study I have directly measured the risetime, decay time, fluorescence depolarization, temperature and intensity dependence of the fluorescence emission from higher green plant and algal photosystems. Excitation was provided by single picosecond laser pulses, as well as a train of pulses at 530 nm, within an intensity range of 10('12)-10('16) photons/cm('2) per pulse.;The energy transfer in the light harvesting pigment complex of Phycobilisomes from the blue-green alga Nostoc sp. were measured by isolating the phycobiliproteins Phycoerythrin (C-PE), Phycocyanin (C-PC), and Allophycocyanin (APC) forms I,II,III and B. These phycobiliproteins were studied singly, as well as in intact phycobilisomes. A study of the effects of the intensity of a single 6 ps excitation pulse on the decay kinetics and yield of fluorescence in the individual isolated phycobiliproteins at pH 7 and 23(DEGREES)C has revealed an exponential fluorescence decay for intensities < 10('14) photons/cm('2) per pulse in all the phycobiliproteins. At higher intensities the fluorescence decay was found to be non-exponential only in C-PE.;The fluorescence risetime and decay kinetics of C-PE and the C-PC+APC emission from intact phycobilisomes of the blue-green alga Nostoc sp. were studied as a function of the intensity of a single 6 ps laser pulse over the range 10('13) to 10('15) photons/cm('2) per pulse. A risetime of 34 (+OR-) 13 ps was observed for the C-PC+APC emission in PBS's. Since the fluorescence decay for C-PE in PBS was measured to be 31 (+OR-) 4 ps, energy transfer from C-PE to C-PC is interpreted to occur in this time.;The fluorescence kinetics from the alga Scenedesmus obliquus, Wild Type and Mutants 8 and 11 were measured. Although the Wild Type is known to possess both active PS I and PS II components, Mutant 8 has an inactive PS I reaction center, while Mutant 11 has an active PS II reaction center trap. It was found that while the fluorescence decay kinetics in the Wild Type form is comparable to that observed for other photosynthetic systems, the lifetimes measured in the mutant 8 and 11 forms are considerably longer. This is interpreted in terms of the destroyed cooperation between PS I and PS II, which gives rise to increased flourescence when one or the other photosystem trap is inactivated.;Depolarization kinetics from the naturally ordered chloroplast arrangement found in the alga Nitella as well as spinach chloroplast and anthocyanin pigments in vivo and in vitro were measured with a novel beam splitter optical delay technique allowing for the simultaneous measurement of both I(,(PARLL)) and I(,(PERP)), the fluorescence intensity measured parallel to and perpendicular to the incident polarization direction respectively, in a single shot experiment.;The fluorescence kinetics of Photosynthetic green Norway maple leaves (Acer platenoides), and non-photosynthetic autumnal (yellow) Norway maple leaves at both room temperature and 90(DEGREES)K have been measured. The lifetime at low intensities ((TURN)10('13) photons/cm('2) per pulse) has been found to be nearly identical in both cases, though shifted in wavelength. The findings of this study with respect to energy transfer in the carotenoid pigment complex of Norway maple questions the traditional interpretation of fluorescence kinetics as directly indicative of photosynthetic energy trapping.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Physics
