Dissolution and acetylation of ball-milled birch (Betula platyphylla) and bamboo (Phyllostachys nigra) in the ionic liquid [Bmim]Cl for HSQC NMR analysis

A method for nuclear magnetic resonance (NMR) characterization of whole cell wall components, including lignin, cellulose and hemicelluloses, was recently developed in our laboratory. The method described for fir (Abies sachalinensis) as a softwood consists of ball-milling of cell wall, dissolution in an ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), in situ acetylation, recovery of the material from the solution, and characterization of the product by 1H-13C correlation heteronuclear single quantum coherence (HSQC) NMR spectroscopy in dimethyl sulfoxide (DMSO)-d6. In the present paper, the performance of the method should be tested for a hardwood and a bamboo. Thus, Japanese white birch (Betula platyphylla) and hachiku bamboo (Phyllostachys nigra) have been investigated. Finely ball-milled birch and bamboo materials were completely dissolved in [Bmim]Cl at 100°C without severe chemical modification of the cell wall components. The dissolved cell walls were then subjected to in situ acetylation, and the ball-milled and fully acetylated cell walls were recovered from [Bmim]Cl. Longer ball-milling time was required for birch and bamboo cell walls, because of the lower solubility of acetylated birch and bamboo materials in DMSO-d6compared to the acetylated fir material. However, HSQC NMR experiments were successfully conducted, and the acetylated whole cell wall components in the birch and bamboo could be fully characterized. This method is applicable for the analysis of cell wall components of various plant biomasses without previous isolation. Further studies are necessary to improve the method.