Simulations Reveal Conformational Changes of Methylhydroxyl Groups during Dissolution of Cellulose I尾 in Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate

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• 作者：Hanbin Liu ; Gang Cheng ; Michael Kent ; Vitalie Stavila ; Blake A Simmons ; Kenneth L Sale ; Seema Singh
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：July 19, 2012
• 年：2012
• 卷：116
• 期：28
• 页码：8131-8138
• 全文大小：462K
• 年卷期：v.116,no.28(July 19, 2012)
• ISSN：1520-5207

文摘

In this work, we use molecular dynamics (MD) simulations to study the dissolution of microcrystalline cellulose in the ionic liquid 1-ethyl-3-methylimidazolium acetate (abbreviated as [C2mim][OAc]) at 20 wt % loading. The interactions of [C₂mim][OAc] with the I_尾 cellulose structure at 120 掳C were studied. The results show that both the cation and the anion of [C₂mim][OAc] penetrate into the cellulose I_尾 crystal structure but that the anion in particular forms strong hydrogen bonds with cellulose. Our results also show that the methylhydroxyl groups of cellulose solvated in [C₂mim][OAc] are predominantly in the gauche鈥搕rans (gt) conformation, in contrast to the dominant trans鈥揼auche (tg) conformation of cellulose I_尾 in air or the gauche鈥揼auche (gg) conformation for cellulose chains in water or after pretreatment with ammonia. Because the gt conformation is found mainly in cellulose II, these simulations suggest that regenerated cellulose under similar pretreatment conditions is composed mainly of cellulose II, and this result was confirmed by X-ray diffraction of samples processed under similar pretreatment conditions. These simulations provide new insight into the efficacy of [C₂mim][OAc] pretreatment, suggesting that [C₂mim][OAc] interacts with and biases the methylhydroxyl groups of cellulose toward orientations that are consistent with the experimentally observed more easily hydrolyzed cellulose II.