Linear Aliphatic Dimeric Esters from Cork Suberin

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Abstract
Cork suberin was partially depolymerized by methanolysis catalyzed by calcium hydroxide. Analysis by GC-MS of the methanolysate showed suberin monomers, including glycerol and long-chain α,ω-diacids and ω-hydroxyacids. ESI-MS analysis of the methanolysate showed, besides the aliphatic monomers, suberin oligomers, including linear dimeric esters of α,ω-diacids and ω-hydroxyacids. Two types of dimeric esters were identified: a α,ω-diacid linked to a ω-hydroxyacid and two inter-linked ω-hydroxyacids. The α,ω-diacids and ω-hydroxyacids found as monomer residues in the dimeric esters were mainly the C18 monomers with midchain substituents. The identification of these dimeric esters was based in their CID-MS/MS spectra and confirmed after synthesis of model compounds. The occurrence of inter-esterified long-chain monomers in suberin brings a new insight in the understanding of the polyester structure of this biopolymer.