Nuclear Magnetic Resonance (NMR) spectroscopy provides precise structural and dynamic information of chemical compounds at atomic resolution and has thus become an essential analytical tool for catalysis research. This method can be used to solve structures and dynamics of new catalysts and of catalytic products and intermediates, differentiate stereochemistries, follow reaction kinetic in real-time, and decipher reaction mechanisms.
The NMR department at the MPI für Kohlenforschung supplies the expertise for the implementation of standard and advanced NMR experiments and their analytic interpretation as well as the development of novel methodologies for the different research groups. We are dedicated as well to teaching and research.
Residual dipolar couplings (RDC) are orientation restraints which are rapidly becoming standard in NMR of small compounds. They are used to determine stereochemistries, to differentiate enantiomers and to provide complementary conformational and dynamic information. Developments are ongoing in sample preparation (orienting media), measurement and analysis.
The way spin magnetisation returns to equilibrium depends on the fluctuation of local fields and can reveal details of dynamic and exchange processes. We are developing the use relaxation dispersion to identify of low-populated intermediate states in catalytic reactions.
Rapid-injection NMR applications are being used to track species in catalytic transformations immediately after mixing with a time resolution of as little as 0.25 s. Such real-time experiments help characterise important key intermediates in very fast reactions.
Basic NMR measurements in liquid state are carried out in high throughput mode on two NMR spectrometers with 1H frequencies of 400- and 300-MHz at room temperature. With minimal setup, scientific personnel from the institute can access these instruments round the clock and obtain NMR data which are acquired and processed fully automatically. The selection of available experiments is limited to those with high sensitivity, high information content and rapid execution with predefined parameters. These include experiments for 1D spectra of 1H, 13C, 31P and 11B as well as for 2D correlation experiments such as 1H/1H COSY and 1H/13C HSQC.
Liquid samples requiring special setup or treatment are submitted for measurement to our operators on 400- and 500-MHz spectrometers. The most common requests are for(a) experiments or nuclear frequencies not available in the automatic mode, (b) experiments at high or low temperature, (c) techniques requiring adjustment of acquisition parameters to optimise the spectra, and (d) spectroscopy of chemical reactions and kinetics followed in real time directly in the NMR tube.
Particularly challenging NMR studies of solution compounds are submitted to advanced analysis. For these samples, our technical staff members provide full measurement, analysis and interpretation assistance in close collaboration with the chemical research groups. The advanced techniques are carried out on our dedicated 600- and 500-MHz NMR spectrometers. The 600-MHz spectrometer is implemented with a cryogenically cooled probehead, which considerably enhances signal-to-noise ratio up to a factor of 8 compared to conventional equipment. A large part of the analytical work is dedicated to determine or confirm structures, stereochemistries, conformations and dynamics.
Solid-state NMR spectroscopy remains one of the most important techniques for the characterisation of complex solid catalyst support and other insoluble materials studied in the institute such as mesoporous silicas, aluminium hydrides, alanates, coals and organometallic compounds. Both dedicated 300- and 500-MHz spectrometers are equipped with magic-angle spinning (MAS) probeheads to obtain high resolution signals from a wide range of NMR active nuclei.
Dr. Farès, Christophe
M.Sc. Lingnau, Julia
Dr. Rufinska, Anna
Dr. Zibrowius, Bodo