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Unformatted text preview: Subpicosecond Transient Signal Spectroscopy of Prodan in Dimethylformamide Solution J ANOS E ROSTY AK , a P ASI M YLLYPERKI O , b A NDREA B UZ ADY , a AND J OUKO K ORPPI-T OMMOLA b a Department of Experimental Physics, University of Pecs, Pecs, Hungary b Nanoscience Center/Department of Chemistry, University of Jyvaskyla, Jyvaskyla, Finland We report a pumpprobe experiment revealing the temporal evolution of subpicosecond evolution of Prodans excited-state absorption in dimethylformamide. Also, we present calculation of the first spectral moment of this spectral band and estimation of different relaxation components on the subpicosecond time scale. Key words: Prodan; dimethylformamide; dynamics; relaxation; time-resolved; transient signal Introduction Fluorescent probes are widely used in studying ul- trafast unfolding and hydration dynamics of proteins. Knowledge of their electronic states and of the details of their ultrafast relaxations is a key to their successful application in biophysical and biological studies. 6-Propionyl-2-dimethylaminonaphthalene (Prodan), first designed and synthesized by Weber and Farris in 1979, 1 is a frequently used probe attached to human serum albumin and other proteins. 2 With human serum albumin, it occupies the warfarin binding site (hydrophobic and electrostatic mode of binding) in domain II. Its steady-state fluorescence spectrum depends very sensitively on the polarity of its environment. It was used to measure simultaneously the environments polarity and the probe partitioning between the aqueous and the lipid phases, 3 role of cholesterol in membrane structure, 4 polarity and packing of lipid molecules in bilayers, 5 and structure of interdigitated bilayers. 6 There are different models describing Prodans ex- cited electronic states. In the simplest model there are two emitting states: the locally excited (LE) and charge transfer (CT) states. 7 First, absorption occurs from the ground state S in the LE state. Then, the CT state is fed by this LE state. This process is also a radiation-less deactivation pathway from the LE state. The equilib- Address for correspondence: Janos Erostyak, Department of Experi- mental Physics, University of Pecs, H-7624 Pecs, Ifjusag. u. 6, Pecs, Hun- gary. Voice: + 36-72-503600, ext. 4488; fax: + 36-72-501571. email@example.com rium of the LE and CT states strongly depends on solvent parameters, because the solvent is responsible for stabilizing the excited-state dipole. Numerical studies have been carried out to de- scribe the possible conformational changes of Prodan in the excited states. Ilich and Prendergast analyzed the molecular orbital structure of the levels and consid- ered what possible structural changes might be induced upon electron excitation....
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This note was uploaded on 07/11/2010 for the course SPECTOGRAP 545 taught by Professor Gdf during the Spring '10 term at AIB College of Business.
- Spring '10