Simulation of a cellulose fiber in ionic liquid suggests a synergistic approach to dissolution
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Ionic liquids dissolve cellulose in a more efficient and environmentally acceptable way than conventional methods in aqueous solution. An understanding of how ionic liquids act on cellulose is essential for improving pretreatment conditions and thus detailed knowledge of the interactions between the cations, anions and cellulose is necessary. Here, to explore ionic liquid effects, we perform all-atom molecular dynamics simulations of a cellulose microfibril in 1-butyl-3-methylimidazolium chloride and analyze site–site interactions and cation orientations at the solute–solvent interface. The results indicate that Cl− anions predominantly interact with cellulose surface hydroxyl groups but with differences between chains of neighboring cellulose layers, referred to as center and origin chains; Cl− binds to C3-hydroxyls on the origin chains but to C2- and C6-hydroxyls on the center chains, thus resulting in a distinct pattern along glucan chains of the hydrophilic fiber surfaces. In particular, Cl− binding disrupts intrachain O3H–O5 hydrogen bonds on the origin chains but not those on the center chains. In contrast, Bmim+ cations stack preferentially on the hydrophobic cellulose surface, governed by non-polar interactions with cellulose. Complementary to the polar interactions between Cl− and cellulose, the stacking interaction between solvent cation rings and cellulose pyranose rings can compensate the interaction between stacked cellulose layers, thus stabilizing detached cellulose chains. Moreover, a frequently occurring intercalation of Bmim+ on the hydrophilic surface is observed, which by separating cellulose layers can also potentially facilitate the initiation of fiber disintegration. The results provide a molecular description why ionic liquids are ideal cellulose solvents, the concerted action of anions and cations on the hydrophobic and hydrophilic surfaces being key to the efficient dissolution of the amphiphilic carbohydrate.
KeywordsCellulose Ionic liquids Pretreatment MD simulation
This research was funded from the BioEnergy Science Center, a DOE Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science. It was also supported in part by the National Science Foundation through XSEDE resources provided by the National Institute of Computational Sciences under grant number TG-MCA08X032.
- BeMiller JN, Whistler L (1996) Carbohydrates. In: Fennema OR (ed) Food chemistry, 3rd edn. CRC, New York, pp 157–224Google Scholar
- Fukaya Y, Hayashi K, Kim SS, Ohna H (2010) Design of polar ionic liquids to solubilize cellulose without heating. In: Liebert T, Heinze T, Edgar K (eds) Cellulose solvents: for analysis, shaping and chemical modification, vol 1033. ACS, Washington, pp 55–66Google Scholar
- GAUSSIAN version 09 (2009) Wallingford, CT, Gaussian, Inc.Google Scholar
- Humphrey W, Dalke A, Schulten K (1996) VMD: visual molecular dynamics. J Mol Graph 14:33–38Google Scholar
- Liu C, Sun R, Zhang A, Li W (2010a) Dissolution of cellulose in ionic liquids and its application for cellulose processing and modification. In: Liebert T, Heinze T, Edgar K (eds) Cellulose solvents: for analysis, shaping and chemical modification, vol 1033. ACS, New York, pp 287–297Google Scholar
- MATLAB version 7.12.0 (2011) Natick, Massachusetts: The MathWorks Inc.Google Scholar
- Matthews J, Himmel M, Brady J (2010) Simulations of the structure of cellulose. In: Nimlos MR, Crowley MF (eds) Computational modeling in lignocellulosic biofuel production, vol 1052. ACS Symposium Series, pp 17–53Google Scholar
- Moulthrop J, Swatloski R, Moyna G, Rogers R (2005) High-resolution 13C NMR studies of cellulose and cellulose oligomers in ionic liquid solutions. Chem Commun 12:1557–1559Google Scholar
- Sellin M, Ondruschka B, Stark A (2010) Hydrogen bond acceptor properties of ionic liquids and their effect on cellulose solubility. In: Liebert T, Heinze T, Edgar K (eds) Cellulose solvents: for analysis, shaping and chemical modification, vol 1033. ACS, New York, pp 121–135Google Scholar