Quantification of Structure–Property Relationships for Plant Polyesters Reveals Suberin and Cutin Idiosyncrasies

Abstract

Polyesters, as they exist in planta , are promising materials with which to begin the development of “green” replacements. Cutin and suberin, polyesters found ubiquitously in plants, are prime candidates. Samples enriched for plant polyesters, and in which their native backbones were largely preserved, were studied to identify “natural” structural features; features that influence critical physical properties. Quantitative nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and X-ray scattering methods were used to quantify structure–property relationships in these polymeric materials. The degree of esterification, namely, the presence of acylglycerol linkages in suberin and of secondary esters in cutin, and the existence of mid-chain epoxide groups defining the packing of the aliphatic chains were observed. This packing determines polymer crystallinity, the resulting crystal structure, and the melting temperature. To evaluate the strength of this rule, tomato cutin from the same genotype, studying wild-type plants and two well-characterized mutants, was analyzed. The results show that cutin’s material properties are influenced by the amount of unbound aliphatic hydroxyl groups and by the length of the aliphatic chain. Collectively, the acquired data can be used as a tool to guide the selection of plant polyesters with precise structural features, and hence physicochemical properties.

Finding a Needle in a Haystack: Producing Antimicrobial Cutin-Derived Oligomers from Tomato Pomace

“…This strategy has been successfully applied to solubilize cork suberin directly from cork residues, 29 and to solubilize cutin from tomato peels. 22 , 28 The high-resolution 1 H NMR spectra of either pomace depict many overlapping signals ( Figure S1 ), which are typically found in cutin isolated from peels. 22 , 28 The assignment of the NMR signals was attained through a combination of 2D spectra ( 1 H– 1 H COSY, 1 H– 13 C HSQC, and 1 H– 13 C HMBC; Figures S2–S7 ), using as reference previous assignments in oligomeric/polymeric structures of cutin, 22 , 28 , 29 , 33 suberin, 28 , 29 and lignin.…”

“… 22 , 28 The high-resolution 1 H NMR spectra of either pomace depict many overlapping signals ( Figure S1 ), which are typically found in cutin isolated from peels. 22 , 28 The assignment of the NMR signals was attained through a combination of 2D spectra ( 1 H– 1 H COSY, 1 H– 13 C HSQC, and 1 H– 13 C HMBC; Figures S2–S7 ), using as reference previous assignments in oligomeric/polymeric structures of cutin, 22 , 28 , 29 , 33 suberin, 28 , 29 and lignin. 34 − 36 The acquired HSQC spectra are shown in Figure 1 , detailing the aliphatic and CH/CH 2 -X aliphatics (A) and glycerol CH-acyl (B) regions, highlighting cutin signature signals (e.g., primary aliphatic esters, PAE).…”

“… 4 , 15 , 23 − 27 The extractant cholinium hexanoate preserves cutin esterification, while it washes out efficiently polysaccharides and soluble components of the cuticle (e.g., waxes), resulting in the isolation of an insoluble cutin continuum. 22 , 28 Studies on a related plant polyester—suberin—showed that particles can be obtained through a catalysis that partially preserves its esterified network. These particles display per se antimicrobial activity 29 and can spontaneously self-assemble forming antimicrobial films, 30 contrarily to the composing monomeric hydrolysates that do not.…”

“…Cutin, can however, be isolated from tomato peel using a one-pot reaction with an ionic liquid extractant; this method is simpler and faster compared to those frequently used to isolate cutin that combine enzymatic digestion of polysaccharides with organic solvent removal of waxes. ,,− The extractant cholinium hexanoate preserves cutin esterification, while it washes out efficiently polysaccharides and soluble components of the cuticle (e.g., waxes), resulting in the isolation of an insoluble cutin continuum. , Studies on a related plant polyestersuberinshowed that particles can be obtained through a catalysis that partially preserves its esterified network. These particles display per se antimicrobial activity and can spontaneously self-assemble forming antimicrobial films, contrarily to the composing monomeric hydrolysates that do not.…”

The making of suberin

“…Suberin types with less bifunctional oxygenated aliphatics (CYP86A33-RNAi) or esterified ferulic acid (FHT-RNAi) are enriched in the mobile aliphatic fraction (Serra et al, 2014). Recently, 2D-NMR, able to determine proton-carbon bond correlations, has been applied to cork and potato suberised phellems, providing resolution on overlapping NMR signals of similar molecular moieties and revealing covalent linkages in suberin and lignin (Marques et al, 2016;Correia et al, 2020;Bento et al, 2021). These analyses may be highly informative for revealing the molecular structure of suberin but are still limited for the relatively high amount of purified ligno-suberised material needed (c. 50 mg).…”