Henrike M. Müller-Werkmeister

Structural Dynamics upon Photoexcitation in a Spin Crossover Crystal Probed with Femtosecond Electron Diffraction

Photoexcitation of spin crossover (SCO) complexes can trigger extensive electronic spin transitions and transformation of molecular structure. However, the precise nature of the associated ultrafast structural dynamics remains elusive, especially in the solid state. Here, we studied a single-crystal SCO material with femtosecond electron diffraction (FED). The unique capability of FED allows us to directly probe atomic motions and to track ultrafast structural changes within a crystal lattice. By monitoring the time-dependent changes of the Bragg reflections, we observed the formation of a photoinduced structure similar to the thermally induced high-spin state. The data and refinement calculations indicate the global structural reorganization within 2.3 ps, as the metal-ligand bond distribution narrows during intramolecular vibrational energy redistribution (IVR) driving the intermolecular rearrangement. Three independent dynamical group are identified to model the structural dynamics upon photoinduced SCO.

Femtosecond Electron Diffraction Study of the Spin Crossover Dynamics of Single Crystal [Fe(PM-AzA)2](NCS)2

The atomic motions involved in spin crossover photo-switching dynamics of single crystal [Fe(PM-AzA)2](NCS)2 are investigated by femtosecond electron diffraction (FED). The experiment was performed with an ultrabright femtosecond electron source using 8.5 × 104 electrons per pulse with 400 fs temporal instrument response function.

Impact of Azidohomoalanine Incorporation on Protein Structure and Ligand Binding

The impact of the incorporation of a non‐natural amino acid (NNAA) on protein structure, dynamics, and ligand binding has not been studied rigorously so far. NNAAs are regularly used to modify proteins post‐translationally in vivo and in vitro through click chemistry. Herein, structural characterisation of the impact of the incorporation of azidohomoalanine (AZH) into the model protein domain PDZ3 is examined by means of NMR spectroscopy and X‐ray crystallography. The structure and dynamics of the apo state of AZH‐modified PDZ3 remain mostly unperturbed. Furthermore, the binding of two PDZ3 binding peptides are unchanged upon incorporation of AZH. The interface of the AZH‐modified PDZ3 and an azulene‐linked peptide for vibrational energy transfer studies has been mapped by means of chemical shift perturbations and NOEs between the unlabelled azulene‐linked peptide and the isotopically labelled protein. Co‐crystallisation and soaking failed for the peptide‐bound holo complex. NMR spectroscopy, however, allowed determination of the protein–ligand interface. Although the incorporation of AZH was minimally invasive for PDZ3, structural analysis of NNAA‐modified proteins through the methodology presented herein should be performed to ensure structural integrity of the studied target.

Towards Direct Measurement of Ultrafast Vibrational Energy Flow in Proteins

Vibrational energy transfer (VET) within a molecule can be investigated in great detail with ultrafast IR spectroscopy. We report on progress towards mapping of VET pathways in proteins using unnatural amino acids as site-specific probes.