Molecular Dynamics Simulation on the Structure of Cellulose Inclusion Complexes and Interactions Between Cellulose Chains and Solvent Molecules in Alkali/urea Aqueous Solution†

doi:10.7503/cjcu20170683

Abstract

Abstract:

The detail structure of cellulose inclusion complexes(ICs) in alkali/urea aqueous solution was investigated using molecular dynamics simulation. The spatial structure of cellulose ICs, the hydrogen-bonding network, the interactions between cellulose chains and solvent molecules and the effect of alkali metal ions on the formation of ICs were studied. The simulation results showed that the sodium ions and hydroxide ions mostly located and formed stable absorption conformation around hydroxyl and hydroxymethyl groups of cellulose. Urea molecules preferred to occupy the faces of the hydrophobic pyranose rings and form hydrogen bonds with hydroxyl groups and the pyranose ring oxygen. The interactions between cellulose chains and solvent molecules were also simulated. Nearby the hydroxyl groups, the non-bonding interactions between solvent molecules and hydroxylic oxygen atoms of cellulose were in the order of Na⁺>NH₂CONH₂>OH^->H₂O. On the faces of the pyranose rings of cellulose, urea molecules exhibited the strongest interaction with hydroxylic oxygen atoms. The effects of alkali metal ions in KOH/urea and NaOH/urea aqueous solutions on the stability of ICs were also discussed. Compared with K⁺, Na⁺ could form a more stable configuration of cellulose ICs.

Key words: Molecular dynamics simulation, Cellulose inclusion complex, Alkali/urea aqueous solution

CLC Number:

TrendMD:

LIU Gang, ZHANG Heng, SUN Heng, ZHU Hongxia, ZHANG Yuhan, ZHU Qingzeng, YUAN Shiling. Molecular Dynamics Simulation on the Structure of Cellulose Inclusion Complexes and Interactions Between Cellulose Chains and Solvent Molecules in Alkali/urea Aqueous Solution^†[J]. Chem. J. Chinese Universities, 2018, 39(4): 714.

Figures/Tables 10

Fig.1 Repeating unit of cellulose molecules

Table 1 Partial atomic charges of cellulose

Atom	Charge/e	Atom	Charge/e
C1	0.340	O2, O3, O6	-0.650
C2, C3, C4	0.140	O1	-0.650
C5	0.110	O5	-0.400
C6	0.050	HO2, HO3, HO6	0.420
H1, H2, H3, H4, H5, H6	0.090

Fig.2 Time profiles of the total energy (the last 10 ns)

Fig.3 Side view of cellulose inclusion complexesThe cellulose and urea molecules are displayed in stick mode. Water molecules are displayed in ball and stick mode. Sodium ions and hydroxide ions are displayed in CPK mode.

Fig.4 Front view of cellulose inclusion complexes

Fig.5 Radial distribution functions g(r) of Na+(A), O of OH- (B) and C of urea(C) around the oxygen atoms of cellulose molecules

Fig.6 Hydrogen-bonding network of cellulose inclusion complexes(A, B), and the typical hydrogen-bonding structure(C-E)(A) Top view; (B) side view. The hydroxide ions and sodium ions are displayed in CPK mode. The cellulose molecule is displayed in stick mode. Water molecules are displayed in line mode.

Fig.7 Interaction energy between hydroxy groups(A), acetalic oxygen atoms(B) and solvent molecules, respectively

Fig.8 Spatial distribution functions of sodium ions(yellow), oxygen atoms of hydroxide ions(cyan) and carbon atoms of urea(magenta)

Fig.9 PMFs(A) and the binding energy(B) of hydroxyl groups and metal ions

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