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Kemifaglige foredrag 2012

08.11.2012 Helmuth Cölfen

Organic inorganic hybrid materials and mechanisms of nonclassical crystallization

Biominerals teach excellent lessons about advanced materials design. Their structural design is optimized for the specific materials purpose and often, the beneficial properties are generated on several hierarchy levels. Consequently, Biominerals are an intense subject of research to reveal the design principles. This led to the discovery of amorphous or even liquid precursors to single crystals in Biomineralization and additive controlled crystallization events. Non classical particle mediated crystallization pathways were found to be important besides the classical crystallization path.

Vært: Henrik Birkedal

18.10.2012 Michael Robb

Michael Robb

Mechanisms of Photochemistry and Photobiological reactivity: Studies using Quantum Chemistry and Quantum Dynamics.

A photochemical reaction begins with the absorption of light, which promotes the system to an excited state.   In order to understand photochemistry from a mechanistic point of view, we need to study 1) how the bonding in an excited state differs from that in the ground state, since this determines the forces which govern the initial reaction path on an excited state and 2) the mechanism through which the photoexcited system  returns to the ground state by changing from the excited state potential surface to the ground state potential surface at a conical intersection (where the bonding in excited state and the ground state balance each other). We have studied these two aspects of photochemical mechanisms using quantum chemistry and  quantum dynamics.  Our purpose in this lecture is to discuss some new theoretical and mechanistic ideas that have emerged. We shall choose examples from organic photochemistry and photobiology.

Vært: Peter R. Ogilby 

11.10.2012 Johan Hofkens

The power of one: what can we learn by looking at single molecules?

Over the last 15 years, single molecule spectroscopy (SMS) has been established as a new tool in the ever expanding range of spectroscopic methods. SMS is especially useful to study inhomogeneous systems. Biological systems are by their nature highly heterogeneous and as such perfect targets for SMS. From this it is clear that, next to biological samples, material science (polymers, catalyst nano-particles) can benefit from single molecule measurements as materials are very often heterogeneous in their behavior. Furthermore, many theories that describe material properties are based on a microscopic picture that now can be evaluated experimentally by applying single molecule techniques. In this contribution, I will give an overview of how we study polymers (reptation, dynamics near glass transition, molecular motors), catalyst particles (heterogeneous catalysis and the problem of diffusion limitations) and biophysical processes (recent work on rafts, viruses and DNA mapping) with different single molecule techniques.

Vært: Peter R. Ogilby

27.09.2012 John Sutherland

John Sutherland

Origins of life chemistry – reconciling the iron-sulfur and the RNA worlds

A true understanding of biology must include knowledge of its chemical origin, and comprehending
the chemical events that gave biology its foundations - cellular format, the central dogma, the genetic
code - is therefore a fundamental aspect of natural science. We are interested in uncovering
prebiotically plausible syntheses of the informational, catalytic and compartment-forming molecules
necessary for the emergence of life. We have previously demonstrated the constitutional self-assembly
of pyrimidine ribonucleotides from mixtures of simple building blocks, and we are now exploring
similar ‘systems chemistry’ approaches to these building blocks and the purine ribonucleotides, as well as ways of assembling RNA from these ribonucleotides with regiocontrol of the internucleotide phosphodiester linkage.

Vært: Thomas B. Poulsen

13.09.2012 Peter Hamm

Peter Hamm

Towards understanding allosteric dynamics by ultrafast IR spectroscopy

Allostery is a fundamental concept Nature uses to regulate the affinity of a certain substrate to an active site of a protein by binding a ligand to a distant allosteric site. Although there are many well-developed models of allosteric interactions and networks, little is known about the dynamics of allosteric conformational transitions on an atomistic level. In order to better the nature of the free energy landscape governing this dynamics, we cross-linked two amino acid side chains of the PDZ2 domain, a single-domain allosteric protein, with a photo-switchable azobenzene-moiety in a such a way that we can mimic the conformational transition upon ligand binding. Upon photo-initiation, the protein responds in a highly non-exponential manner stretching from picoseconds to 100’s of nanoseconds. All-atom molecular dynamics (MD) simulations suggest that this behavior reflects the friction of mostly the water surrounding the protein.

Vært: Ove Christiansen