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Structural Complexity and Fluorescence Heterogeneous Decays in Proteins

100%
Di Venere A., Mei G., Rosato N., Finazzi Agro A., Gilardi G.
Acta Physica Polonica A
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1997
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vol. 91
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issue 4
731-737
EN
Optical spectroscopy is a suitable technique to study the functional and structural properties of large biomolecules in solution without damaging the samples. In particular, measurements of time-resolved fluorescence may give important information on the tertiary structure of proteins. Furthermore, the study of fluorescence depolarization as a function of time is a very common method to follow the dynamics of the local domains and subunits which form the quaternary structure of oligomeric enzyme. The analysis of fluorescence decays in terms of continuous distribution of lifetimes seems to be an appropriate approach to describe the dynamics of proteins which ranges over an enormous time scale (from 10 ps to 10 ns). The results obtained for several proteins are reported and discussed. The data provide further confirmation of the correlation which exist between heterogeneous fluorescence decays and a hierarchy of many conformational substates in proteins.
2
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Circular Dichroism Spectra of Axially Oriented Rhodospirillum rubrum Cells and Their Fragments Immobilized in Polymer Film

63%
Cegielski R., Frąckowiak D., Liang J.
Acta Physica Polonica A
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1991
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vol. 79
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issue 4
479-491
EN
Circular Dichroism (CD) spectra of Rhodospirillum rubrum cells, and their fragments embedded in isotropic and uniaxially oriented by stretching polyvinyl alcohol films were measured. Effects responsible for CD signal generation such as assymetry of chromophores itself, the helical organisation of lamellar system, the helical texture of stretched PVA matrix, the contribution from circular and linear birefringence, as well as from exciton splitting resulting from pigments mutual interactions are discussed.
3
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Synchrotron Radiation Induced X-Ray Emission - SRIXE

63%
Kwiatek W.
Acta Physica Polonica A
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1992
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vol. 82
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issue 2
263-271
EN
The synchrotron radiation induced X-ray emission (SRIXE) technique was found very useful and sensitive for determination of trace elements content and distribution in different types of materials. Due to properties of synchrotron radiation the SRIXE technique became very unique and powerful for trace elements analysis. This paper describes the phenomena related to production of characteristic X-rays and principles of the method. The properties of SRIXE such as minimum detectable limit, spatial resolution, radiation damage, and depth sensitivity are also discussed. Selected applications are given to emphasize the usefulness of the technique.
4
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The Light Harvesting Process in Purple Bacteria

51%
Krueger B., Scholes G., Yu J., Fleming G.
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vol. 95
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issue 1
63-83
EN
We present and review the results of fluorescence upconversion and photon echo experiments, and $ab initio$ calculations performed in our group within the last few years with respect to the light harvesting process in purple bacteria. Carotenoids transfer energy to bacteriochlorophyll (BChl) mainly via the carotenoid S_{2} → BChl Q_{x} pathway on a ~100 fs timescale. This transfer is reasonably reproduced by considering the Coulombic coupling calculated using the transition density cube method which is valid at all molecular separations. Carotenoids may also serve a role in mediating B800 → B850 energy transfer in LH2 by perturbing the transition density of the B850 as shown by ab initio calculations on a supermolecule of two B850 BChls, one carotenoid and one B800 BChl. Further calculations on dimers of B850 BChl estimate the intra- and interpolypeptide coupling to be 315 and 245 cm^{-1}, respectively. These interactions are dominated by Coulombic coupling, while the orbital overlap dependent coupling is ~20% of the total. Photon echo peak shift experiments (3PEPS) on LH1 and the B820 subunit are quantitatively simulated with identical parameters aside from an energy transfer time of 90 fs in LH1 and ∞ in B820, suggesting that excitation is delocalized over roughly two pigments in LH1. 3PEPS data taken at room and low temperature (34 K) on the B800-B820 suggest that static disorder is the dominant mechanism localizing excitation in LH1 and LH2. We suggest that the competition between the delocalizing effects of strong electronic coupling and the localizing effects of disorder and nuclear motion results in excitation in the B850 and B875 rings being localized on 2-4 pigments within approximately 60 fs.
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