Structural Studies of Peptides and Polypeptides in the Solid State by Nitrogen-15 NMR

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This chapter describes the structural studies of peptides and polypeptides in the solid state by nitrogen-15 NMR. The investigation of peptides, proteins, and other biopolymers in the solid state is being increasingly pursued by means of NMR studies. This important area of scientific investigation regularly merits mention in three chapters of the Specialist Periodical Reports on NMR—namely, those relating to solid-state NMR, synthetic macromolecules, and natural macromolecules. The chapter focuses on the uses of nitrogen NMR studies in the structural investigations of peptides and similar compounds. Many of the molecules of interest are insufficiently soluble to permit solution-state NMR studies, and thus solid-state measurements are the method of necessity. An additional virtue of solid-state NMR is that it provides the possibility of obtaining special information that the tumbling motion of molecules in a solution would average out. The chapter also covers applications of nitrogen NMR measurements to studies on oligopeptides and synthetic polypeptides, respectively. Majority of the reports mentioned deal with 15N NMR investigations. The additional quadrupolar signal broadening produced by 14N NMR is often counterproductive to the work that forms the focus of this chapter.