NMR experiments on solid or semi-solid samples can provide important information for numerous biological systems. Unfortunately, unless specific measures are taken, these samples tend to yield very broad signals that limit the information that can be extracted. In general, there are two main approaches to address this problem:
Magic Angle Spinning (MAS) NMR
One approach is to partially emulate the motional avaraging effects that produce the narrow lines seen in solution NMR by rapidly spinning the solid NMR sample. This is done in one particular orientation, with a 54.7 degree angle (the 'magic angle') between the axis of spinning and the external magnetic field. This approach is a very general method and allows the measurement of narrow signals in a wide range of samples, ranging from small molecule powders to large biomolecules. Examples of biological interest include the study of microcrystalline as well as fibrillar protein structures, discussed on this page. Improved resolution and sensitivity allow the development and application of sensitive structural measurements (see also here).
Oriented solid state NMR
For membrane samples: lipid bilayers have a natural tendency to self assemble and align themselves. When one aligns the material of interest in a single specific orientation (rather than the normal random distribution found in powder samples), one can eliminate much of the broadening typical of solid powders. This approach allows structural measurements in an environment that closely resembles the biological membrane. Here I describe some previous research where this approach has allowed detailed examination of some basic aspects of protein-lipid interactions. Alignment of membrane can involve the use of glass slides (see right), or in form of bicelles.