Hilty Research Group

Hyperpolarization

In many cases, membrane protiens involved in important cellular processes, such as signaling, can only be obtained in very dilute or heterogeneous samples. Conventional experimental techniques do not allow studying such systems due to a lack of signal intensity or selectivity of the observation. We are working on fundamentally new ways of overcoming such problems by using and developing hyperpolarization techniques.
Hyperpolarization of nuclear spins is the most powerful method of signal enhancement in NMR, in those cases where we can find ways to apply it. In hyperpolarization, a physical means is used to repopulate the Zeeman energy levels of the nuclear spin system before an NMR experiment. Because the NMR sensitivity is proportional to the population, this enhances the detectable signal up to 10,000 fold.

Dynamic nuclear polarization (DNP) is a newly available technology[1] for providing hyperpolarization of various classes of molecules. It makes use of the high polarizability of electron spins. Even at a moderate magnetic field of 1T, and at a temperature of 1K, electron spins are almost completely polarized. At the same temperature, the polarization of nuclear spins is still small even at the highest magnetic fields available. In DNP, polarization is transferred from the electron spins of free radicals to nuclear spins by means of microwave irradiation. After polarization in a DNP polarizer, the sample is thawed and injected into the NMR spectrometer.

Ligand Binding and Transient Processes
DNP polarization is ideal for the determination of the binding of ligands to proteins. This can be used for example in drug discovery, or for the investigation of processes such as signaling. Examples include the interaction of signal peptides with the membrane translocation and insertion machinery, as well as hormones binding to receptor proteins. In addition to investigating systems at equilibrium, as when determining ligand binding, DNP polarization allows the fast observation of transient processes. We are developing methods to obtain structural information down to a time resolution of 10 ms, a time scale for wich currently very few experimental methods are available. Of particular interest is the study of the folding of protiens, as well as the lipid association and insertion of membrane proteins.

[1] J.H. Ardenkjaer-Larsen et al., Proc. Natl. Acad. Sci. USA 2003, 100, 10158-10163