8,873 Matching Results

Search Results

Excitation energy transfer in natural photosynthetic complexes and chlorophyll trefoils: hole-burning and single complex/trefoil spectroscopic studies

Description: In this project we studied both natural photosynthetic antenna complexes and various artificial systems (e.g. chlorophyll (Chl) trefoils) using high resolution hole-burning (HB) spectroscopy and excitonic calculations. Results obtained provided more insight into the electronic (excitonic) structure, inhomogeneity, electron-phonon coupling strength, vibrational frequencies, and excitation energy (or electron) transfer (EET) processes in several antennas and reaction centers. For example, our recent work provided important constraints and parameters for more advanced excitonic calculations of CP43, CP47, and PSII core complexes. Improved theoretical description of HB spectra for various model systems offers new insight into the excitonic structure and composition of low-energy absorption traps in very several antenna protein complexes and reaction centers. We anticipate that better understanding of HB spectra obtained for various photosynthetic complexes and their simultaneous fits with other optical spectra (i.e. absorption, emission, and circular dichroism spectra) provides more insight into the underlying electronic structures of these important biological systems. Our recent progress provides a necessary framework for probing the electronic structure of these systems via Hole Burning Spectroscopy. For example, we have shown that the theoretical description of non-resonant holes is more restrictive (in terms of possible site energies) than those of absorption and emission spectra. We have demonstrated that simultaneous description of linear optical spectra along with HB spectra provides more realistic site energies. We have also developed new algorithms to describe both nonresonant and resonant hole-burn spectra using more advanced Redfield theory. Simultaneous description of various optical spectra for complex biological system, e.g. artificial antenna systems, FMO protein complexes, water soluble protein complexes, and various mutants of reaction centers continues; this work is supported by the new DOE BES grant.
Date: September 12, 2012
Creator: Ryszard Jankowiak, Kansas State University, Department of Chemistry, CBC Bldg., Manhattan KS, 66505 & 532-6785, Phone: (785)
Partner: UNT Libraries Government Documents Department

Visualization of Excitonic Structure in the Fenna-Matthews-OlsonPhotosynthetic Complex by Polarization-Dependent Two-DimensionalElectronic Spectroscopy

Description: Photosynthetic light-harvesting proceeds by the collection and highly efficient transfer of energy through a network of pigment-protein complexes. Inter-chromophore electronic couplings and interactions between pigments and the surrounding protein determine energy levels of excitonic states and dictate the mechanism of energy flow. The excitonic structure (orientation of excitonic transition dipoles) of pigment-protein complexes is generally deduced indirectly from x-ray crystallography in combination with predictions of transition energies and couplings in the chromophore site basis. Here, we demonstrate that coarse-grained excitonic structural information in the form of projection angles between transition dipole moments can be obtained from polarization-dependent two-dimensional electronic spectroscopy of an isotropic sample, particularly when the nonrephasing or free polarization decay signal rather than the photon echo signal is considered. The method provides an experimental link between atomic and electronic structure and accesses dynamical information with femtosecond time resolution. In an investigation of the Fenna-Matthews-Olson complex from green sulfur bacteria, energy transfer connecting two particular exciton states in the protein is isolated as being the primary contributor to a cross peak in the nonrephasing 2D spectrum at 400 fs under a specific sequence of polarized excitation pulses. The results suggest the possibility of designing experiments using combinations of tailored polarization sequencesto separate and monitor individual relaxation pathways.
Date: May 26, 2008
Creator: Department of Chemistry, The University of Chicago; Department of Biology, Department of Chemistry, Washington University; Fleming, Graham; Read, Elizabeth L.; Schlau-Cohen, Gabriela S.; Engel, Gregory S. et al.
Partner: UNT Libraries Government Documents Department

Production of hydrogen in non oxygen-evolving systems: co-produced hydrogen as a bonus in the photodegradation of organic pollutants and hydrogen sulfide

Description: This report was prepared as part of the documentation of Annex 10 (Photoproduction of Hydrogen) of the IEA Hydrogen Agreement. Subtask A of this Annex concerned photo-electrochemical hydrogen production, with an emphasis on direct water splitting. However, studies of non oxygen-evolving systems were also included in view of their interesting potential for combined hydrogen production and waste degradation. Annex 10 was operative from 1 March 1995 until 1 October 1998. One of the collaborative projects involved scientists from the Universities of Geneva and Bern, and the Federal Institute of Technology in Laussane, Switzerland. A device consisting of a photoelectrochemical cell (PEC) with a WO{sub 3} photoanode connected in series with a so-called Grazel cell (a dye sensitized liquid junction photovoltaic cell) was developed and studied in this project. Part of these studies concerned the combination of hydrogen production with degradation of organic pollutants, as described in Chapter 3 of this report. For completeness, a review of the state of the art of organic waste treatment is included in Chapter 2. Most of the work at the University of Geneva, under the supervision of Prof. J. Augustynski, was focused on the development and testing of efficient WO{sub 3} photoanodes for the photoelectrochemical degradation of organic waste solutions. Two types of WO{sub 3} anodes were developed: non transparent bulk photoanodes and non-particle-based transparent film photoanodes. Both types were tested for degradation and proved to be very efficient in dilute solutions. For instance, a solar-to-chemical energy conversion efficiency of 9% was obtained by operating the device in a 0.01M solution of methanol (as compared to about 4% obtained for direct water splitting with the same device). These organic compounds are oxidized to CO{sub 2} by the photocurrent produced by the photoanode. The advantages of this procedure over conventional electrolytic degradation are that much ...
Date: January 1, 2000
Creator: Sartoretti, C. Jorand; Ulmann, M.; Augustynski, J. (Electrochemistry Laboratory, Department of Chemistry, University of Geneva (CH)) & Linkous, C.A. (Florida Solar Energy Center, University of Central Florida (US))
Partner: UNT Libraries Government Documents Department

[Administrators at an event]

Description: Photograph of three unidentified people, possibly part of the North Texas Administration, standing in an interior. One older woman holding a fur wrap/jacket, and two older men. All three wear name-tags. The man to far right tentatively identified as Dr. J.J. Spurlock (North Texas State Teachers College 1935), professor of Chemistry 1940-1976, and Vice President 1959-1971. Probably taken between 1955 and 1968.
Date: 19uu
Partner: UNT Libraries Special Collections

[Alumni Awards Luncheon, April 26, 1975]

Description: Photograph from the Alumni Awards Luncheon, Saturday April 26, 1975 at the Denton Country Club. Seen are (left) Dr. Henry Kamp of the Department of Political Science, and (right) Dr. William Glaze, of the Department of Chemistry, Associate Dean of the College of Arts & Sciences, and Director of Institute of Environmental Studies, each of whom were awarded a Distinguished Teaching Award by the Alumni Association.
Date: April 26, 1975
Partner: UNT Libraries Special Collections

[Alumni Awards Luncheon, April 26, 1975]

Description: Photograph from the Alumni Awards Luncheon, Saturday April 26, 1975 at the Denton Country Club. Dr. William Glaze (standing, right), of the Department of Chemistry, Associate Dean of the College of Arts & Sciences, and Director of Institute of Environmental Studies, is seen receiving the Distinguished Teaching Award by the Alumni Association from Tom Harpool (North Texas State Teachers College 1939), President of the North Texas State University Alumni Association. Seated at far left is Edwina Granberry, to the right of Mrs.Granberry is Dr. Jim Granberry (North Texas State College 1958), Master of Ceremonies for the luncheon.
Date: April 26, 1975
Partner: UNT Libraries Special Collections