Structural studies of amino acids, polypeptides and proteins in the solid state by 1H cramps NMR

Abstract

This chapter presents a study on the solid structure of α -amino acid, polypeptide, and a protein to introduce the basis of the chemical shift of proton nuclear magnetic resonance (NMR). Some of the issues discussed in the chapter, include the discrimination of amino acid crystal polymorphism, conformational analysis of polypeptides and fibrous proteins, and the determination of the N–H bond length in polypeptides. The chapter introduces research results from recent proton Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR of α -amino acids, polypeptides, and proteins. At present, NMR spectrometers such as the Chemagnetics CMX and Bruker DSX are sufficient for CRAMPS, as the adjustment procedure for CRAMPS experiments has been simplified. Even a standard CP-MAS probe is sometimes used for CRAMPS measurements on the Bruker machines. The most important process for CRAMPS measurement is to generate nearly ideal rectangular pulses and to cancel out pulse imperfections. The probe adjustments of magic angle and the shim are matters of common knowledge. The chapter discusses a recent research example application to crystal structure analysis of polymorphic forms of some typical α -amino acids to test the power of 1 H CRAMPS NMR, compared with 13 C and 15 N NMR methods.