Veranstaltungen

The human medial temporal lobe contains neurons that respond selectively to the semantic contents of a presented stimulus. These "concept cells" may respond to very different pictures of a given person and even to their written and spoken name. Their response latency is far longer than necessary for object recognition, they follow subjective, conscious perception, and they are found in brain regions that are crucial for declarative memory formation. It has thus been hypothesized that they may represent the semantic "building blocks" of episodic memories. In this talk I will present data from single unit recordings in the hippocampus, entorhinal cortex, parahippocampal cortex, and amygdala during paradigms involving object recognition as well as encoding and consolidation of episodic memories in order to characterize the role of concept cells in these cognitive functions.

Chemists often treat gaseous fragment ions as esoteric chemical species only of interest to analytical mass spectrometry and gas phase ion chemistry. Meanwhile, their potential as building blocks for designing new compounds in the condensed phase remained largely unexplored until recently. In this presentation, preparative mass spectrometry (ion soft-landing) is introduced as a method for small-scale chemical synthesis using gaseous ions. The preparation of new compounds and surface layers using fragment ions deposited from the gas phase is demonstrated. This includes binding of inorganic fragment ions to (bio-)molecules, covalent binding of cluster ions of same polarity on surfaces and binding of unreactive molecules like N2 to reactive fragment ions, which are subsequently “taken out” of the mass spectrometer for further conventional analytics and applications.

Electrostatic effects are a major factor that drive and tune molecular processes in chemistry and biology. Examples include solvent dependence in chemical reactivity, the electric double layer at (bio)interfaces, or, most notably, the “mechanism“ of electrostatic catalysis that contributes to the acceleration of chemical reactions by up to 1018 times in enzyme active sites. In this talk, I will present how we develop and utilize advanced infrared (IR) spectroscopic approaches to quantify relevant electrostatic forces in condensed matter as well as to apply electrostatic perturbations to monitor the consequences on molecular processes. On the one hand, we explore the vibrational Stark effect (VSE), which utilizes the electric field-sensitivity of C=O or C≡N vibrations to measure electric fields at the single bond level. On the other hand, we develop surface-enhanced infrared absorption (SEIRA) spectroscopic approaches, which are based on a plasmonic Au surface.

The methods of magnetic resonance (NMR, EPR and MRI) offer fantastic analytical and diagnostic possibilities. As the radiation used is of very low energy, these methods also have the advantage of being non-invasive. Unfortunately, the low energy is also associated with low sensitivity, which means that sample volumes in NMR have to be quite large and measurement times in MRI quite long. So- called hyperpolarization techniques offer one way of increasing sensitivity. The best known is called "dynamic nuclear polarization" (DNP) and uses electron spins to "pump" nuclear spins. To do this, the sample must be irradiated with microwaves. Of course, one would prefer to "pump" with light. This is possible with the help of "photo-CIDNP" (photochemically induced dynamic nuclear polarization). The lecture will explain the origin, applications and possibilities of photo-CIDNP NMR.

Dr. Rössler’s lab makes use of chemical principles to understand fundamentally important reactions in biology. Reduction-oxidation (redox) reactions underpin innumerable chemical reactions and much of the chemistry of life. Many redox reactions proceed via radical intermediates and these are often located in mechanistically key locations. She investigates how oxidation-state changes govern respiration in the respiratory complex I and photosynthesis in photosynthetic complex I and how nature has fine-tuned the redox properties of its many intricate molecular machines. Membranes play a fundamentally important role for many proteins and she is investigating the role of membranes on protein activity and function through spin labels and protein-intrinsic paramagnetic centres.