Solids NMR is a noninvasive analytical method that can be used to investigate the chemical compositions and covalent interactions that occur in biological samples intractable to conventional analytical approaches. Solids NMR techniques such as cross polarization, dipolar decoupling, magic angle spinning, magnetization dephasing, and isotopic enrichment have been used to obtain high resolution spectra that provided information about the relative concentrations and internuclear distances between atoms in complex biological solids. Levels of proteins, chitin, catechols, lipids, pigments, and other organic constituents in composite materials were estimated. Covalent interactions between specific carbons and nitrogens have been detected by isotopic enrichment with labeled precursor molecules. We have used solids NMR in studies of polymeric and analytically intractable samples such as insect cuticular exoskeletons, egg cases, egg shells, silk cocoons, and marine coral skeletons. Evidence was obtained for stabilization mechanisms occurring primarily when quinones derived from catechol-containing compounds including catecholamines and o-diphenols with acid, aldehyde and alcohol side chains form adducts with functional groups of
structural proteins and perhaps chitin. Solids N M R can be utilized for probing the compositions and covalent interactions of many other types of biological samples found in the biosphere and geosphere and, when combined with other analytical techniques, provides a powerful approach for elucidating the complex structures of biopolymeric materials. |
