Insights into the structure of cutin and cutan from Agave americana leaf cuticle using HRMAS NMR spectroscopy

The structure of cutan, and a cutin/cutan mixture from the Agave americana leaf cuticle is herein described by use of the technique of one and two-dimensional high-resolution magic angle spinning (HRMAS) NMR spectroscopy, with added information from solid-state 13C cross-polarization magic angle spinning (CPMAS) and Bloch decay NMR spectroscopy. Cutin in the cutin/cutan mixture is found to contain ester functionalities, in line with previous degradative approaches. Furthermore, epoxy groups, free primary alcohols and carboxylic acid groups are also observed in cutin. A significant new finding is the evidence for α-branched fatty acids/esters in cutin. Cutan has mainly free primary hydroxyls, as well as long-chain carboxylic acids, which have been previously predicted to form ester linkages with trihydroxylated benzene units. Another significant finding in cutan is the evidence for benzenecarboxylic acids that are ester linked with fatty alcohols. The long-chain polymethylenic groups in cutan are shown to express a high degree of crystallinity similar to that observed in soil organic matter.