Wood cellulose microfibrils have a 24-chain core–shell nanostructure in seed plants

• Published in: Nature plants Vol. 9; no. 7; pp. 1154 - 1168
• Main Authors: Tai, Hwan-Ching, Chang, Chih-Hui, Cai, Wenjie, Lin, Jer-Horng, Huang, Shing-Jong, Lin, Qian-Yan, Yuan, Eric Chung-Yueh, Li, Shu-Li, Lin, Ying-Chung Jimmy, Chan, Jerry Chun Chung, Tsao, Cheng-Si
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2023; Nature Publishing Group
• Subjects: 631/449/1659; 631/449/906; 82/6; Area; Aspect ratio; Biomedical and Life Sciences; Cellulose; Cellulose - chemistry; Core-shell structure; Decay; Diameters; Glucan; Iterative methods; Life Sciences; Magnetic Resonance Spectroscopy; Measurement methods; Microfibrils; Nanostructure; NMR; Nuclear magnetic resonance; Plant Sciences; Resonance scattering; Scattering cross sections; Seeds; Small angle X ray scattering; Solid state; Wood; X-ray diffraction; X-ray scattering
• ISSN: 2055-0278; 2055-0278
• DOI: 10.1038/s41477-023-01430-z

Wood cellulose microfibril (CMF) is the most abundant organic substance on Earth but its nanostructure remains poorly understood. There are controversies regarding the glucan chain number ( N ) of CMFs during initial synthesis and whether they become fused afterward. Here, we combined small-angle X-ray scattering, solid-state nuclear magnetic resonance and X-ray diffraction analyses to resolve CMF nanostructures in native wood. We developed small-angle X-ray scattering measurement methods for the cross-section aspect ratio and area of the crystalline-ordered CMF core, which has a higher scattering length density than the semidisordered shell zone. The 1:1 aspect ratio suggested that CMFs remain mostly segregated, not fused. The area measurement reflected the chain number in the core zone ( N core ). To measure the ratio of ordered cellulose over total cellulose ( R oc ) by solid-state nuclear magnetic resonance, we developed a method termed global iterative fitting of T 1 ρ -edited decay (GIFTED), in addition to the conventional proton spin relaxation editing method. Using the formula N  =  N core / R oc , most wood CMFs were found to contain 24 glucan chains, conserved between gymnosperm and angiosperm trees. The average CMF has a crystalline-ordered core of ~2.2 nm diameter and a semidisordered shell of ~0.5 nm thickness. In naturally and artificially aged wood, we observed only CMF aggregation (contact without crystalline continuity) but not fusion (forming a conjoined crystalline unit). This further argued against the existence of partially fused CMFs in new wood, overturning the recently proposed 18-chain fusion hypothesis. Our findings are important for advancing wood structural knowledge and more efficient use of wood resources in sustainable bio-economies. The number of glucan chains in the cellulose microfibril of wood has long been debated. X-ray and NMR techniques show that the number is 24. Each microfibril has a dense crystalline core surrounded by a semidisordered shell and remains segregated in new wood.