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[Display omitted] • Two SA and FA cross-coupled dimers, SA-(β–O–4)-FA and α, β de-protonated SA-(β–5)-FA, were identified for the first time in vitro. • The yield of homo-coupled β–O–4 of SA was lower than 5%, which was overestimated in previous reports. • A tetrahydrofuran β–β coupled dehydrodimer of SA was discovered. During the lignification of grass cell walls, ferulate acts like a nucleation site that can cross couple with monolignols, i.e. coniferyl alcohol and sinapyl alcohol, to form dimeric products. Here we investigated in detail the ferulate-sinapyl alcohol cross-coupling products in an effort on better understanding the nature and scope of lignin-ferulate interactions. In a biomimetic oxidative system, sinapyl alcohol (SA) reacted with ethyl ferulate (FA), a simplified model for feruloyl polysaccharides in plants, to give a mixture of dozens of dimeric products. We delineated the structure of each product by GC-MS and NMR characterizations. It was found that sinapyl alcohol readily reacts with ethyl ferulate producing various cross-coupled dimers including SA-(β–5)-FA (compound 6), SA-(β–8)-FA (both ester and lactones, compounds 7 and 9), and SA-(β–O–4)-FA (compound 8) cross-coupled products in addition to homo-coupled products from ethyl ferulate or sinapyl alcohol. SA-(β–O–4)-FA 8 was identified for the first time in a vitro free radical biomimetic system and the homo-coupled SA-(β–O–4)-SA 3 from sinapyl alcohol was accurately quantified as less than 5%, while the half-open syringaresinol 5 was discovered when dimerization of SA was catalyzed by peroxidase in a biomimetic buffer system. Moreover, one new compound 18 formed by the cross-coupled linkage SA-(β–5)-FA (de-protonated) was identified by GC-MS and NMR, and one possible FA-(8–β)-SA dimer 19* was proposed. [ABSTRACT FROM AUTHOR]

• Luffa vine (LV) is a low-density natural plant fiber with a porous structure. • The secondary wall of LV fiber cell contains two layers with spiral thickening. • Sclerenchyma cell of LV exhibits excellent micromechanical properties. • The microscopic characteristics endow LV with good processability. • The pit pairs on cell walls provide good permeability to LV fibers. The exploration of luffa vine (LV) in the polymer composites field can contribute to the development of lightweight composites and expand their use in new wide scale applications. In this study, the physical and chemical properties and the microstructure of the LV fibers were investigated by various techniques. The results of LV density and microscopic characteristics indicated that this crop is a lightweight (with density mainly concentrated in 0.30–0.45 g cm−3) natural fiber with a porous structure (the ratio of wall to lumen: 0.2–0.3). Transmission electron microscopy and nanoindentation analyses showed that the secondary wall of the LV sclerenchyma cell is made up of two layers with spiral thickening and exhibiting a high nanoindentation modulus (7.8–10.4 GPa) and a high nanoindentation hardness (0.40–0.58 GPa). The chemical composition and X-ray diffraction analysis indicated that the LV has high lignin content (20–25%) and a relatively high relative crystallinity index of cellulose, which are conducive to increase the hardness of the LV fiber. Moreover, microscopic characteristics analysis also revealed that the LV fiber cells have a relatively high aspect ratio (30.3), there are pit pairs on the LV fiber cell walls, and the core fiber cells of the LV have relatively high flexibility coefficient (0.8), which are beneficial to increase the processability of composite materials with the LV fibers as reinforcement. [ABSTRACT FROM AUTHOR]