Biophysical studies of the mechanisms of charge separation and recombination in bacterial photosynthetic reaction centers

• Applicant: Dr. Miguel Saggu
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2010 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 182537781

• Final Report Year: 2012

Final Report Abstract

The most important results are summarized in the following. 1D solid-state CP/MAS NMR of 13C-labeled reaction center wild-type and mutant I(M204)E indicate that tyrosine M208 is hydrogen-bonded in the mutant and not hydrogen-bonded in the wild-type protein. Picosecond transient absorption spectroscopy displays a very different electron transfer behavior of the mutant (monoexponential decay of P*). These results confirm the functional importance of tyrosine M208 and indicate that its hydroxyl group might act as a switch that stabilizes the initial charged separated intermediate P+BL-. This is a significant result because this particular tyrosine is highly conserved in photosynthetic reaction centers of different organisms. Electric fields in intermolecular interactions could be quantified experimentally for the first time using a combination of vibrational Stark spectroscopy and DFT calculations. It could be shown that weak O-H···π interactions (or π-hydrogen bonds) between phenol and aromatic benzene derivatives are dominated by electrostatics because the obtained electrostatic interaction energies are in very good agreement with experimentally obtained dissociation enthalpies. Bond polarization effects become more important for N-H···π and in particular S-H···π interactions due to the larger atomic polarizabilities in the order O

Publications

• Direct measurements of electric fields in weak OH···π hydrogen bonds, J. Am. Chem. Soc., 133, 17414-17419 (2011)
  Saggu M., Levinson N.M., and Boxer S.G.