A TEMPO-catalyzed oxidation–reduction method to probe surface and anhydrous crystalline-core domains of cellulose microfibril bundles

Abstract

A modi ed TEMPO-catalyzed oxidation of the solvent-exposed glucosyl units of cellulose to uronic acids, followed by carboxyl reduction with NaBD 4 to 6-deutero-and 6,6-dideuteroglucosyl units, provided a robust method for determining relative proportions of disordered amorphous, ordered surface chains, and anhydrous core-crystalline residues of cellulose micro brils inaccessible to TEMPO. Both glucosyl residues of cellobiose units, digested from amorphous chains of cellulose with a combination of cellulase and cellobiohydrolase, were deuterated, whereas those from anhydrous chains were undeuterated. By contrast, solvent-exposed and anhydrous residues alternate in surface chains, so only one of the two residues of cellobiosyl units was labeled. Although current estimates indicate that each cellulose micro bril comprises only 18 to 24 (1 , 4)-b eta-D-glucan chains, we show here that micro brils of walls of Arabidopsis leaves and maize coleoptiles, and those of secondary wall cellulose of cotton bers and poplar wood, bundle into much larger macro brils, with 67 to 86% of the glucan chains in the anhydrous domain. These results indicate extensive bundling of micro brils into macro brils occurs during both primary and secondary wall formation. We discuss how, beyond lignin, the degree of bundling into macro brils contributes an additional recalcitrance factor to lignocellulosic biomass for enzymatic or chemical catalytic conversion to biofuel substrates.

Lack of xyloglucan in the cell walls of the Arabidopsis xxt1/xxt2 mutant results in specific increases in homogalacturonan and glucomannan

“…Cellulase digestion and electrospray ionization mass spectrometry was modified from Shiga et al. (2021). Ammonium sulfate (3.2 m ) suspensions of Trichoderma longibrachiatum cellulase (endo‐1,4‐β‐ d ‐glucanase EGII; EC 3.2.1.4; Megazyme, Wicklow, Ireland; Cat.…”

Building an extensible cell wall

“…At the newly deposited surface of onion epidermal walls, individual microfibrils are seen to merge into and out of bundle junctions, with most of the microfibril length, on average, aggregated in bundles of two or more microfibrils ( Zhang et al, 2016 ). Such microscopic evidence is supported by estimates of extensive CMF bundling based on chemical oxidation of water-accessible surfaces ( Shiga et al, 2021 ). As elaborated below, bundling enables direct transmission of tensile forces between CMFs without intermediation by the matrix ( Zhang et al, 2021c ).…”

Fiber-reinforced polymer composite: Higher performance with renewable and eco-friendly plant-based fibers

“…91 Bundles of cellulose microfibrils contain both crystalline and amorphous areas and are made up of 3 nm elementary fibrils. 92 At the molecular level, repeating units of D-glucose assemble through covalent bonds as well as intra- and interchain hydrogen bonds to create linear and rigid cellulose chains.…”