Structural characterization of suberan isolated from river birch (Betula nigra) bark

Suberan is a biopolymer located in the periderm (cork) of above ground parts of plants or the endoderm of roots. It acts as a protective barrier between plants and the environment and is commonly associated with another suberinic biopolymer, suberin. The structure of suberan has not been suggested, but is believed to have structural components similar to suberin. With the use of destructive and non-destructive techniques, including Fourier transform infrared (FTIR) spectroscopy, flash pyrolysis–gas chromatography–mass spectrometry (py–GC–MS), one and two-dimensional high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy, the structure of suberan from the Betula nigra bark, is now described. Based on data obtained from B. nigra bark, the non-saponifiable residue, considered to be suberan, is a polymethylenic biopolymer with alkyl chain length consisting mainly of 22 carbons, which is consistent with previous degradative studies. Furthermore, esters, acids and primary alcohols were also observed in suberan, which contribute to a glyceryl structural entity. The long-chain polymethylenic structures demonstrate a high degree of crystallinity, providing a primary structural difference between suberan and suberin.