NMR spectroscopy of solid state and oriented systems has long been an important area of research in the Pines group. NMR spectra of these systems contain plenty of chemical information. However, interpreting these spectra often requires sophisticated manipulation of the spin interactions in order to selectively extract the desired information or to correlate one kind of information to another.
Our recent work in high-resolution solid-state NMR includes a collaboration with the Wemmer lab to investigate the structures of fibril-forming peptides. The major focus in this area is the development of high performance recoupling pulse sequence combined with novel sample labeling strategy, in order to extract structural information of solid peptides with local order. Long-range distance information is the major target of our pursuit.
We are also developing and using novel switched-angle spinning (SAS) and projected magic-angle spinning (p-MAS) experiments. By correlating the information-rich, but hard-to-interpret anisotropic spectrum with the (over)simplified magic angle spinning (MAS) spectrum, we can efficiently obtain structural information. We have applied this principle by using variable angle spinning (VAS) to measure scaled dipolar couplings in a small molecule dissolved in different thermotropic liquid crystals, thus the circumventing experimental errors encountered when changing the order parameter by varying the temperature. For samples such as liquid crystals and other oriented systems, which become unstable when spun at the magic angle, we can reconstruct the hypothetical isotropic spectrum from the appropriate projection in the p-MAS experiment .
For the oriented systems, the information-tailoring can be done not only by manipulating spin interactions, but also by changing the way that the sample is oriented. Different orienting media provide different kinds of spectral information, and different physical methods for molecular alignment can offer new possibilities for NMR methodology and applications.
