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Research

Methods

 Processes and systems

Ultrafast Spectroscopy on Biologically Relevant Systems:


 

Analysis of light-induced vibrational structural changes of photoreceptors and antenna pigments (Sfb 498 / Heyne B11)

In this project we investigate interactions between cofactor and its protein environment by ultrafast polarization-resolved spectroscopy in the mid-infrared and visible spectral range.
We mainly focus on two issues:

(a) Chromophore geometry and its interactions with the protein-binding pocket in phytochrome
Structural information on the chromophore geometry of the ground state can be obtained by ultrafast polarization-resolved nonlinear infrared (IR) spectroscopy. The measured angles between the electronic transition-dipole moment and the transition-dipole moments of vibrational modes are directly connected to the chromophore geometry. Especially, the pure N-H in-plane bending marker modes (at 1570 cm-1) of the tetrapyrrole rings B and C of the chromophore can provide direct insight into the orientation of the ring planes with respect to the electronic transition-dipole moment. Analysis of chromophore and protein vibrational changes in the fingerprint region in response to chromophore excitation reveals dynamical and structural information on the chromophore and the protein-binding pocket, in the ground state, the electronic excited state, and the first product state. Combining polarization-resolved IR spectroscopy with density-functional calculations will improve knowledge on the chromophore geometry inside the phytochrome binding-pocket, resulting in a better understanding of the essential interactions for the initial reaction steps of phytochrome.

(b) Chlorophyll-protein and chlorophyll-chlorophyll interactions
We study the properties of chlorophyll molecules in the ground state and the electronic excited state in different solvents, which is a prerequisite for understanding the photophysical properties of protein-bound chlorophylls. Questions on ligand binding and specific solute-solvent interactions in ground and excited states will be addressed, using ultrafast VIS-pump / IR-probe spectroscopy. The chlorophyll-protein interaction in an intact protein will be explored for the cytochrome b6f complex, which binds a single chlorophyll molecule. By probing the vibrational dynamics of the chromophore and the protein surroundings we are able to determine which amino-acid residues and other cofactors directly interact with the chlorophyll. Chlorophyll-chlorophyll interactions are of fundamental importance for excitation-energy transfer in natural photosynthesis. The main problem in photosystems is usually to isolate a subset of chlorophylls and to study their interactions. A subset of so-called "red-absorbing" chlorophylls can selectively be excited in photosystem I. We apply time-resolved Vis pump / IR probe spectroscopy  to analyze the dynamics of these "red-absorbing" chlorophylls.

 

 

Analysis and control of structural changes in biological relevant systems in the condensed phase (Sfb 450 / Heyne B9)
 

Ziel des Projektes ist die Charakterisierung der primären Photoreaktionsdynamik schaltbarer Medikamente, die nach Lichtanregung reaktive Gruppen erzeugen und von Molekülen, deren Eigenschaften (z.B. die Chiralität) biologisch von Bedeutung sind. Mit Kenntnis der Reaktionsdynamik sollen funktionale Reaktionskanäle dieser Moleküle mit Zwei-Photonen Anregung und mit geformten Lichtimpulsen kontrolliert werden.  Zur umfassenden Charakterisierung der primären Photoreaktion werden sowohl die elektronischen als auch die Schwingungsübergänge untersucht. Wichtige Informationen liefert hierbei die polarisationsaufgelöste nichtlineare Schwingungsspektroskopie, die es ermöglicht strukturelle Änderungen auf der Femtosekundenzeitskala zu verfolgen. Neben caged compounds werden Photosensitizer und Moleküle mit Endoperoxidgruppen wie Anthracene-9,10-endoperoxid

(APO) und Artemisinin untersucht. In Molekülen mit Endoperoxidgruppe soll durch UV-Anrege-IR-Abtast-Experimente die strukturelle Dynamik, die zur homolytischen Trennung der Endoperoxidgruppe oder zur Abspaltung von Singlettsauerstoff führt in Echtzeit nachgewiesen werden. Weitere zentrale Fragestellungen sind die Aktivierung von Photosensitizern durch Zwei-Photonen-Prozesse und der Einfluss der chiralen Eigenschaften von Aminosäuren (z.B. von Tyrosin) auf die Reaktionsdynamik.

Hierbei werden auch die Wechselwirkungen zwischen Aminosäuren in kurzen Peptiden untersucht, um ein besseres Verständnis der anharmonischen Kopplung zu gewinnen. Durch Lichtanregung sollen einzelne Wechselwirkungen gezielt aufgehoben und Strukturänderungen induziert werden. Die experimentellen Untersuchungen sind eng mit den theoretischen Arbeiten der Teilprojekte C9, C5 und C2 verknüpft.

 


Electron and energy transfer systems

 

We investigate the influence of the core metal ion and axial ligands on photophysical and photochemical processes in the metallocorroles, and corrole donor-acceptor complexes. The focus will be on metallocorroles with Al(III), Ga(III), Sb(III), or Sb(V) as the central metal ion, covering the range from light to fairly heavy metal ions, and allowing the study of the influence of the oxidation state. The kinetics and structural dynamics of newly synthesized metallocorroles will be characterized, from femtosecond to millisecond timescales, using polarization-resolved femtosecond visible and infrared spectroscopy, nanosecond electron paramagnetic resonance (EPR), and laser flash photolysis. The impact of the core metal ion, and its oxidation state, on the 3-dimensional structure of the various electronic states, and the efficiency of the triplet generation, will be studied. The results on isolated metallocorroles will be implemented in studies of electron and energy transfer in corrole based donor- acceptor complexes. Particular emphasis will be devoted to the dependence of the electron and energy transfer on the donor-acceptor distance, their mutual orientation, and the nature of their linkage such as covalent, electrostatic, coordinative, and hydrogen bonding. The information gained will enhance the development of advanced catalytic processes and the design of efficient biomimetic systems.



Vibrational energy relaxation processes

Femtosecond two-colour pump-probe experiments in the mid-infrared demonstrate that excitation energy of the hydrogen-bonded O-H stretching oscillator of phthalic acid monomethyl ester is redistributed on a sub-picosecond time scale along the O-H bending vibration. The O-H stretching and O-H bending lifetimes are 220 and 800 fs, respectively. Quantum dynamical model calculations of the energy flow induced by O-H stretching excitation reveal a relaxation mechanism involving cascaded energy redistribution along the O-H bending vibration and two O-H out-of-plane deformation modes at about 700 and 800 cm-1. (Journal of Physical Chemistry A, 108, (2004), 6083).

 

Entwicklung eines gepulsten Infrarotmessgerätes zur Messung der Leberfunktion (BMBF EXIST)

 

Die Entwicklung einer Messmethode zur Leberfunktionsmessungen an Patienten wird in Zusammenarbeit mit Dr. Martin Stockmann, Charité Berlin, durchgeführt. Hierzu wird die Absolutkonzentration des vom Patienten ausgeatmeten 13CO2 nach Verabreichung eines 13C-angereicherten Medikamentes mittels zeitaufgelöster Infrarotspektroskopie bestimmt. Aus der abgeatmeten 13CO2Menge im Maximum der Metabolisierung kann auf die   Menge der aktiven Cytochrom P450 CYP1A2 Isoenzyme geschlossen werden. Diese Menge ist ein direktes Maß für die maximale Leberfunktionskapazität. 

 

Inter- and intramolecular couplings of peptides and amino acids