Exploring Architecture of Xyloglucan Cellulose Nanocrystal Complexes through Enzyme Susceptibility at Different Adsorption Regimes

Abstract

Xyloglucan (XG) is believed to act as a cementing material that contributes to the cross-linking and mechanical properties of the cellulose framework in plant cell walls. XG can adsorb to the cellulose nanocrystal (CNC) surface in vitro in order to simulate this in vivo relationship. The target of our work was to investigate the sorption behavior of tamarind seed XG on CNC extracted from cotton linters at different XG/CNC concentration ratios, that is, different adsorption regimes regarding the XG-CNC complex organization and the enzymatic susceptibility of XG. First, we determined the adsorption isotherm. Second, XG-CNC complexes were enzymatically hydrolyzed using a xyloglucan-specific endoglucanase in order to quantify the different XG fractions involved in binding to CNC and to determine adsorption regimes, that is, presence of loops, tails, and trains. Finally, the architecture of the XG-CNC complex was investigated by transmission electron microscopy imaging of negatively stained XG-CNC suspensions and XG immunolabeled suspensions at different XG/CNC concentration ratios, both before and after xyloglucanase hydrolysis process. This study revealed that an increasing XG/CNC concentration ratio led to a change in the XG binding organization to CNC. At low XG/CNC concentration ratios, almost all XG chains were bound as trains to the CNC surface. In contrast, at increasing XG/CNC concentration ratios, the proportion of loops and tails increases. The organization change induces CNC aggregation to form a cellulose/XG network at low XG/CNC regimes, whereas CNC remains in the form of individual particles at higher XG/CNC regimes. Results are discussed both regarding the biological role of XG in plant cell walls and in the perspective of designing new biobased materials.

Revision of adsorption models of xyloglucan on microcrystalline cellulose

“…The two-step adsorption mechanism of xyloglucan on cellulose was previously proposed by some authors (Pirich et al 2015;Villares et al 2015;Dammak et al 2015). Moreover, Winter et al (Winter et al 2010) showed that the stability of the bacterial cellulose nanocrystal suspension increases above a certain concentration ratio of xyloglucan, which may be due to a change in the dominant molecule conformation on the surface.…”

“…It is also worth noticing that some authors (Pirich et al 2015) compared the Freundlich and Langmuir model when describing the adsorption of xyloglucan on cellulose. However, none of these two models is able to include lateral interactions in the adsorbed layer, which were proposed in the literature (Pirich et al 2015;Dammak et al 2015). Therefore, in future analysis, the FowlerGuggenheim model and its parameters may help in the qualitative and quantitative description of the adsorption of xyloglucan on cellulose.…”

Kinetic aspects of the adsorption of xyloglucan onto cellulose nanocrystals

“…The negligible variation in CNC surface suggested a strong interaction and affinity of XG to the CNC surface 32 and minute modification of the rigid layer structure. [35][36][37][38][39] However, other authors have pointed out that the Freundlich model is more appropriate to describe the binding of xyloglucan onto cellulose surfaces. 33 Possible unspecific adsorption of XG onto PAH pre-coated gold substrates or bare gold surfaces was discarded since the injection of XG resulted in negligible changes in frequency and dissipation regarding to changes observed for the CNC surfaces, which again suggested the specificity of XG to cellulosic surfaces.…”

Biomimetic adsorption of zwitterionic–xyloglucan block copolymers to CNF: towards tailored super-absorbing cellulose materials

“…Cathala and coworkers have performed several investigations of the adsorption behaviour of XG to CNC in concentrated and dilute regimes, 15,21 and have prepared XG-CNC multi-layer lms. 22,23 Likewise, the adsorption of XG to CNF has also been studied byÖsterberg and colleagues, showing that XG binds efficiently and has a positive inuence on the dispersibility of the CNF.…”