Lehrstuhl für Physikalische Chemie I
Am Hubland, 97074 Würzburg
Research foci (and basic equipment-based research projects):
The measurement of time resolved fluorescence represents a suitable method to investigate photoinduced energy transfer processes in proteins, polymers and small molecules, since it is very sensitive towards intramolecular distances and to the local molecular environment of the fluorophor. The following systems were investigated using time resoved fluoorescence: conformational changes occuring in proteins of the blood coagulation cascade, solvation processes of polymers interaction in selective Na+and K+ inclusion compounds involving cryptant macromolecules and the dual fluorescence of electrically excited states of small molecules,
In cooperation with Dr.habil. M.Hof, Heyrovsky Institute of Physical Chemistry, Czech Academy of Sciences of the Czech Republic,Prague, a conformational change could be demonstrated which was induced by Calcium ions in a protein fragment of FactorX of the blood coagulation cascade using tryptophane(41)-fluorescence through synchrotron radiation. In the absence of Ca -ions three lifetimes were observed whereas in the presence of Ca- ions four fluorescence decay times could be resolved and assigned on the basis of the X-ray structure of the protein. In further fluorescence work the solvation and solvent relaxation in two copolymer systems were investigated using a covalently bound fluorophor. The environment of the fluorophor becomes strongly polar - as verified from our fluorescence polarization measurements - when the copolymers are allowed to swell in solvents of high dielectric constants (acetone, water).
Together with the research group of Dr. E.Grell, Max Planck Institute of Biophysics, Frankfurt, the dynamics of the formation of selective Na -and K- ion inclusion compounds in certain cryptands were investigated by the fluorescence behavior of covalently bound coumarin chromophors. The protonation of the cryptands at two positions leads to a relatively tight conformation of the macromolecule as seen - among other things - from the large differences in the fluorescence quantum yields and lifetimes of the singly and doubly protonated forms of the cryptands.
The dual fluorescence of the N_ethyl iso quinolinium cation was demonstrated and characterized in methanol below 190 K. On the basis of the time resolved fluorescence spectra, rotation polarization measurements and semi-classical computer calculations (self- consistent reaction field including solute-solvent interactions) good agreement was achieved with theory when we assumed that at least three methanol molecules take part in the electronic excitation and emission process from a S2 and/or S1 excited states . Publications see above.
Fluorescence measurements were done mainly with our AMINCO Bowman Series 2 Fluorimeter. Fluorescenc lifetimes were measured with our Single Photon Lifetime Fluorimeter 199 by Edinburgh Instruments or with the synchrotron source in Orsay, A confocal microscope (Confocor) by Zeiss was also available.