APPLICATIONS OF SOLIDS NMR TO THE ANALYSIS OF INSECT SCLEROTIZED STRUCTURES

This article reviews the solids NMR research conducted on insect scler otized structures in the last 10 years and previews some of the experi ments that will be conducted in the future, Solids MMR has been used a s a noninvasive approach to investigate the chemical compositions of, and some covalent interactions that occur in, several types of sclerot ized structures that are otherwise highly intractable to conventional chemical analyses, Sclerotization is a complex process used by insects to confer stability and mechanical versatility to their cuticular exo skeletons and certain other proteinaceous structures; Samples analyzed include cuticular exoskeletons, egg cases, egg shells, cocoons and pe ritrophic membranes, Cross polarization, dipolar decoupling, magic ang le spinning, magnetization dephasing, and isotropic enrichment were us ed to obtain high resolution spectra that provide information about th e types and relative concentrations of carbon atoms as well as internu clear distances and covalent bonds between carbon and nitrogen atoms, Relative amounts of protein, chitin, catechols, lipids, pigment, and o xalate were estimated, Covalent interactions between protein nitrogens and catechol carbons were detected in the stiff brown pupal cuticle o f the tobacco hornworm, Manduca sexta, The results of these solids NMR studies support the hypothesis that sclerotization of insect structur es occurs primarily when quinones derived from N-acylcatecholamines fo rm cross-links and adducts with functional groups of proteins deposite d in the structures, Future applications of solids NMR will utilize ad vanced techniques for further probing the covalent interactions of(13) C, N-15 and O-17-labeled catechols, chitin and protein in sclerotized structures.