We are looking for structure-function relationships in biological macromolecules.
We develope theories of optical spectra and charge-, excitation energy and matter transport in biomolecules using methods of non-equilibrium statistics. The parameters of the theories are calculated from the crystal structures by combining quantum chemical, elctrostatic and molecular dynamics calculations.
An important topic in our research is the investigation of primary processes in photosynthesis
Calculations of the parameters
For the calculation of parameters we combine quantum chemical with electrostatic methods and molecular dynamics simulations. The example below illustrates the calculation of shifts in optical transiton energies of pigments (site energies) by their local protein environments and the calculation of resonance energy transfer couplings (excitonic couplings) between the pigments.
In the calculation of site energy shifts, the electrostatic potential of the electronic ground and excited state of the pigments is first obtained by an ab-initio quantum chemical calculation in vacuum. This potential is fitted by atomic partial charges that are used afterwards in electrostatic calculations of site energy shifts, solving a Poisson Boltzmann equation, including the whole protein in atomic detail. The polarizability of the protein and the solvent and membrane environments are described by three different dielectric constants. In essence, the site energy shifts are obtained from the difference of the charge density coupling of the excited and the ground state of a pigment with the protein. An average is performed with respect to the possible protonation states of the titratable amino acid residues of the protein.
In the calculation of excitonic couplings, the transition density of the relevant optical transition of the pigments is calculated by an ab-initio method. The electrostatic potential of this transition density is fitted by atomic partial charges. The values of the latter are rescaled by a constant factor in order to reproduce the vacuum transition dipole moment estimated from experiments in different solvent environments. The partial charges are then placed into molecule shaped vacuum cavities representing the pigments. The protein and solvent environment are approximated by a homogeneous dielectric with an optical dielectri constant of two. The Coulomb coupling between transition partial charges is obtained by solving a Poisson equation.
Development of dynamic theories
The challenge is to include the interactions between various electronic and vibrational degrees of freedoms as well as the coupling to external electromagnetic fields into a theory of, e.g., excitation energy transfer and optical spectra. In the case of excitation energy transfer there are standard theories if one of the two types of couplings, the excitonic or the exciton-vibrational coupling, dominates. In the first case delocalized states of several pigments are excited and Redfield theory can be used to study relaxation between these states. If the exciton-vibrational coupling is much stronger than the excitonic coupling, stndard Förster theory applies. However, in most pigment-protein complexes both types of couplings are of similiar magnitude. We are working on theories to describe this situation (Renger and Marcus J. Phys. Chem. B 2002, Renger and Marcus J. Chem. Phys. 2003, Renger Phys. Rev. Lett. 2004, Raszewski and Renger JACS 2008).
- Identification of functional states in photosystem II reaction centers (Raszewski et al. Biophys. J. 2008)
- Solvatochromic shifts in nonpolar solvents do not depend on the oscillator strength of the solute transition (Renger et al. PNAS 2008)
- Identity of chlorophylls in photosystem II reaction center of A. marina (Renger and Schlodder J. Phys. Chem. B 2008)
- Thermally activated superradiance and intersystem crossing in water-soluble chlorophyll protein (Renger et al. J. Phys. Chem. B 2009)
- Short-range effects create excitation energy sink in the special pair of photosystem I (Madjet, Müh, Renger, J. Phys. Chem. B 2009)
- Univ.-Prof. Dr. Thomas Renger
- Brigitte Wagner
- Dr. Frank Müh
- Dr. Julian Alexander Adolphs
- DI Thanh-Chung Dinh
- Dipl.-Phys. Florimond Collette
- Dr. Marcel Schmidt am Busch
- Christian Friedl
- DI Johannes Haslmayr
- Johannes ROSINA
Please see our Team page for more information.