Unveiling the dual role of the cholinium hexanoate ionic liquid as solvent and catalyst in suberin depolymerisation

Abstract

Disruption of the three-dimensional network of suberin in cork by cholinium hexanoate leads to its efficient and selective isolation. The reaction mechanism, which likely involves selective cleavage of some intermonomeric bonds in suberin, was still unanswered. To address this question, the role of the ionic liquid during suberin depolymerisation and during cleavage of standard compounds carrying key chemical functionalities was herein investigated. A clear demonstration that the ionic liquid catalyses the hydrolysis of acylglycerol ester bonds was attained herein, both experimentally and computationally (DFT calculations). This behaviour is related to cholinium hexanoate capacity to activate the nucleophilic attack of water. The data showed also that the most favourable reaction is the hydrolysis of acylglycerol ester bonds, with the C2 position reporting the faster kinetics, whilst most of the linear aliphatic esters remained intact. The study emphasises that the ionic liquid plays the dual role of solvent and catalyst and leads to suberin efficient extraction through a mild depolymerisation. It is also one of the few reports of ionic liquids as efficient catalysts in the hydrolysis of esters.

Effect of anion structures on cholinium ionic liquids pretreatment of rice straw and the subsequent enzymatic hydrolysis

“…It was reported that lignin dissolution in ILs generally accompanied its structural modifications such as the cleavage of β‐O‐4 bonds, in which the IL anions played a primary role (George et al, ). Therefore, multiple functional groups in the anions may exert antagonistic effects on the dissolution of lignin, in which the ILs act as the dual roles of solvents and catalysts (Ferreira et al, ).…”

Suberin: the biopolyester at the frontier of plants

“…trees harvesting (outer bark) (Pinto et al, 2009 ). In the perspective of its industrial use, the extraction of suberin from the suberized matrices has been made by conventional hydrolytic means, and more recently, was achieved using ionic liquids, specifically targeting the acylglycerol linkages (Ferreira et al, 2014 ).…”

Effect of choline carboxylate ionic liquids on biological membranes

“…Sodium alkyl-benzene sulfonates and sodium butyl monoglycolsulfate (NaBMGS) are used to extract non-polar, water insoluble phyto-constituents selectively due to permeabilization of the cell. Also choline hexanoate is able to dissolve suberin out of cork by cleavage of the ester bonds in suberin [14]. …”