Group Leader

Dr Johannes Hunger
Dr Johannes Hunger
Group Leader
Phone:+49 6131 379-765Fax:+49 6131 379-360

Liquid Dynamics Group - Research

Current research topics

Fundamentals of Asymmetric Organo-Catalysis

In recent years asymmetric organo-catalysis has emerged as a powerful, metal-free route in enantioselective catalysis, where a chiral organic catalyst is used to control the chirality of a reacting substrate. To date there is little known about the molecular level details of the interaction between the catalyst and the substrate in solution, like binding lifetime and geometry. Due to this lack of fundamental knowledge, optimization of reaction conditions (e.g. solvent, temperature, catalyst, concentrations) is largely based on trial and error. As a consequence, a few hundred different conditions have to be tested in order to optimize the enantiomeric excess of a given catalytic process.
Our current work focuses on determining such fundamental binding parameters (strength of attraction, lifetime of binding, and steric repulsion) in solution. We obtain real-time information on association and binding strength from ultrafast infrared and dielectric spectroscopies. Via systematic correlation of the binding parameters to the enantiomeric excess in a catalytic process, we aim at elucidating the key ingredients for efficient stereocontrol. Such knowledge has the potential to guide optimization of existing catalytic routes and to design of novel catalyses.

Interaction of Osmolytes and Ions with Biopolymers

Different solutes can have tremendously different effects on the stability of proteins. For instance, simple inorganic cations follow an important rule of thumb: the higher the surface charge density of the cation the stronger the ion destabilizes proteins in solution. Interestingly, the opposite trend is observed for anions. Similarly, the small molecules tert-butanol and trimethylamine-N-oxide are structurally very similar, however they destabilize and stabilize proteins, respectively. Despite such effects on biomolecules are well established, the molecular level details are not fully understood.
We are currently studying the effect of osmolytes and ions on the mobility of protein model building blocks in solution. Thus, we aim at unravelling the underlying molecular-level interaction between these solutes and proteins, with a strong focus on the guanidinium cation – a prominent outlier in the Hofmeister series. In our present work we use the coupling of the ions’ translation to the rotation of the model proteins as a measure for their interaction. This allows us to study very weak ion-protein interaction with high sensitivity.

Dynamics of Ionic Liquids

In recent years, computer simulations have changed the general perception of room temperature ionic liquids. These simulations revealed that these macroscopically homogeneous ionic liquids segregate on a molecular level into ionic and hydrophobic sub-phases, which opens new opportunities for material science. However, insight into dynamical aspects of this heterogeneity, which plays a key role for the performance of ionic liquids as reaction media, has remained elusive. We study the dynamics of different molecular entities of the constituting ions using time-resolved infrared spectroscopy. In particular we focus on the dynamics of protic ionic liquids. This subclass of ionic liquids exhibit properties similar to liquid water due to the formation of directional hydrogen-bonds.
Our seminal study showed that the directional hydrogen-bonds also lead to a jump-like reorientation of the constituting ions, reminiscent of liquid water. Comparison of the dynamics in the ionic domains and the hydrophobic domains evidenced that – despite being connected via covalent bonds – the dynamics in the hydrophobic domains are decoupled from the ionic domains.

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