Analysis of Solid State ¹³C NMR Spectra of Biologically Active Compounds

The characteristic features of ¹³C solid state NMR applications are discussed. The spectra are routinely measured with cross-polarisation (CP) pulse sequence and fast spinning under magic angle (MAS). Additional techniques (dipolar dephase, variation of cross-polarisation contact time) influence the signal intensities and enable selective observation of nonprotonated or protonated carbons. Solid state NMR is complementary to X-ray diffraction and provides structural information about solids when the attempts to grow suitable single crystals have failed. However the combination of both methods is more successful in characterisation of solid state conformations and dynamic processes. Many medium sized molecules such as: saccharides, amino acids, peptides, steroids, polyphenols (flavonoids), and tocopherol derivatives have been studied. Samples that are insoluble in commonly used solvents or easily decompose in solution should be investigated by solid state NMR. Since the method can be applied to crystalline as well as to amorphous powders it is especially interesting tool in the studies of macromolecules. Numerous results concerning peptides, proteins and polysaccharides are reported.