A WISE NMR Approach to Heterogeneous Biopolymer Mixtures: Dynamics and Domains in Wounded Potato Tissues

Two-dimensional 1H−13C wide-line separation (WISE) NMR, a technique developed for the characterization of synthetic copolymers and blends in the solid state, has been used to study the dynamic behavior and domain structure of the biopolymer suberin deposited within the wound periderm of potato tubers. This blend consists of cell-wall polysaccharides and cross-linked aromatic−aliphatic polyesters that regulate water transport and protect the plant tissue from pathogenic attack. Though most of the suberin chemical moieties are rigid, about 20% of its chain-methylene groups exhibit surprising flexibility on the 50-kHz frequency scale. The resulting motional narrowing is propagated rapidly by spin diffusion to other residues within the suberin domain, but much more slowly to the spatially separated cell-wall region. Using a selective spin-diffusion experiment with a dipolar filter, the suberin domain size has been estimated as 50 nm and compared with prior results from electron microscopy. Finally, the resist...