(213c) Insights into Cellulose Dissolving in Ionic Liquids By Molecular Simulation

Insights
into Cellulose Dissolving in Ionic Liquids by Molecular Simulation

Xiaomin
Liu,^a Yao Li, ^a Yuling Zhao,^b Jianji Wang,^b
and Suojiang
Zhang^a,*

a State Key Laboratory of Multiphase Complex Systems, Institute of
Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China.

b Key Laboratory of Green Chemical Media and Reactions, Ministry of
Education, School of Chemistry and Environmental Science, Henan Normal
University, Xinxiang, Henan 453007, China.

Abstract

Ionic liquids (ILs) have been
used in an enormous number of chemical and biological processes. In recent
years, great progress has been made in the dissolution of cellulose with ILs.
However, the mechanism of cellulose dissolution has not been clearly
understood. ^[1,2]

Molecular simulations were
performed to investigate the effects of cation and anion structures on cellulose
dissolution in ILs. It was found that the
presence of electron-withdrawing group in alkyl chain of the cation enhanced
the interaction between the cation and cellulose by comparing the interaction
energy between [Amim]⁺ and [C₃mim]⁺ with cellulose.^[3]
Effects of anionic structure on the dissolution of cellulose in ILs revealed
that hydrogen bonds (HBs) were formed between anions of the ILs and hydroxyl
protons of cellulose. we also investigated the effects of electronegativity of
HB acceptor atoms, steric effect of alkyl chain length and electron-withdrawing
group of the anions on their HB acceptor ability. ^[4] Furthermore, molecular
simulations were performed to depict the cosolvent effect of cellulose dissolution
in imidazolium-based ILs. DMSO partially breaks down the ionic association of
[C₄mim][CH₃COO] by solvation of the cation and anion, but
no preferential solvation was observed. The dissociated anions would readily interact with cellulose to improve the
dissolution of cellulose. ^[5] Besides, the spontaneous dissolution
process was investigated through all-atom molecular dynamics simulations of
cellulose bunche in EmimAc and EmimCl within 0.5~2µs. Synergistic effect of
cations and anions was revealed by analysing the whole dissolving process in EmimAc.
Initially, cations bind to the side face of cellulose bunch and anions insert
into the cellulose strands to form HBs with hydroxyl groups. Then cations start
to intercalate into cellulose chains due to their strong electrostatic
interaction with the anions.

Figure 1. The
spontaneous dissolution snapshot of cellulose in EmimAc.

References

1. S. Zhang, J.
Sun, X. Zhang, et al, Chem. Soc. rev.,
2014, 43, 7838-7869.

2. K. Dong, Q.
Wang, S. Zhang, Sci. China Chem., 2015,
58,495-500.

3. Y. Zhao, X. Liu,
J. Wang, S. Zhang. ChemPhysChem,
2012, 13, 3126-3133.

4. Y. Zhao, X. Liu,
J. Wang, S. Zhang. Carbohydr. Polym.,
2013, 94: 723-730.

5. Y. Zhao, X. Liu,
J. Wang, S. Zhang. J. Phys. Chem. B,
2013, 117, 9042-9049.