Ultrafast Spectroscopy on Biologically Relevant Systems:
Ultrafast protonation processes
Protonation and deprotonation processes are essential in proteins for proton and ion transport within proteins and membrane proteins. Ion transport is the basis for fundamental processes such as photosynthesis, and pain sensation (https://www.nobelprize.org/prizes/medicine/2021/press-release/). In 2021 the nobel prize for medicine or physiology was awarded for the discoveries of receptors for temperature and touch. The protein responsible for sensing capsaicin was encoded as a novel ion channel protein the capsaicin receptor later named TRPV1. Also in 2021, the Albert Lasker Basic Medical Research Award honors three scientists for the discovery of light-sensitive microbial proteins that can activate or silence individual brain cells. These proteins are also ion channels or ion pumps that can be used in developing optogenetics, and applications in neuroscience (https://laskerfoundation.org/winners/light-sensitive-microbial-proteins-optogenetics/).
The light active ion channels and ion pumps are triggered on a time-scale of femto- and picoseconds. The activation develops within the protein in time and space leading to new protein conformations with altered ion configurations. The functional conformations are active on a microsecond to milisecond time-scale, but how the interaction cascade transforms the initial light activated state to the functional state is still not understood.
Recent fs x-ray experiments display structural changes in the protein already on a femtosecond time-scale, supported by femtosecond visible and vibrational studies of AG Heyne. Infrared spectroscopy is very sensitive to hydrogen bonds and protonation changes that can occur on a femtosecond time scale reflecting the very first changes in proteins upon photoexcitation.
With polarization resolved femtosecond vibrational spectroscopy we aim to unravel interactions and reaction mechanisms on the ultrafast time-scale in proteins. Here, the perturbation of the protein initiates an ultrafast change of the system followed by relaxation processes guided by the protein structure and interactions to the desired functional conformation.
AG Heyne investigates proteins and model systems to elucidate the reaction mechanism and energy relaxation pathways upon electronic, and vibrational excitation, as well as upon electric field changes.
Acceleration of ground state reactions
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).