High-Resolution Magic-Angle-Spinning Nuclear Magnetic Resonance Spectrocopy

NMR Studies of Gels and Immobilized Structures in Solutions

Solution NMR spectroscopy provides in most cases good spectral resolution for chemical shifts and splittings due to through bond (J-) couplings. When the rotational correlation time of larger and larger molecules, aggregating or gelating molecules becomes longer  and longer, however, T2 relaxation times become shorter and shorter and the spectral resolution of the chemical structure is lost. Here magic angle spinning, similar to the solid-state NMR measurements, can help to average the broadening influence of incoming dipolar interations and recover the full chemical shift resolution and the possibility utilize weak trough bond couplings as source of information. 

 Most solution NMR techniques can be transfered to HR-MAS, but in some cases a carful synchronization to the sample spinning frequency is needed in order to obtain reliable, artefact free  results. In contrast to solid-state NMR, where faster spinning is in most cases beneficial, the sample spinning of gels, aggregates and large molecules should be done at moderate spinning frequencies, as fast spinning of dissolved or swollen samples may cause a separation from the solvent, which leads to a loss of spectral resolution.