Preferential Interactions between Lithium Chloride and Glucan Chains in N,N-Dimethylacetamide Drive Cellulose Dissolution

Abstract

Naturally occurring cellulose is crystalline as a consequence of the strong interactions between the glucan chains that comprise it and therefore is insoluble in most solvents. One of the few solvent systems able to dissolve cellulose is lithium chloride (LiCl) dissolved in N,N-dimethylacetamide (DMA). By an integrated application of all-atom molecular dynamics (MD) simulations, reaction path optimization, free-energy calculations, and a force-matching analysis of coarse-grained atomistic simulations, we establish that DMA-mediated preferential interactions of Li(+) cations and Cl(-) anions with glucan chains enable cellulose dissolution in LiCl/DMA. The relatively weak solvation of Li(+), Cl(-), and glucan chains by DMA results in strong effective interactions of Li(+) and Cl(-) ions with the glucans, leading to cellulose dissolution. The small size of the Li(+) cations allows them to strongly couple to multiple interaction sites on the glucan chains of cellulose, including the spatially restricted regions around the ether linkages connecting neighboring glucose residues. Li(+) cations were thus identified as the main component responsible for driving cellulose dissolution. The mechanism for explaining the solubility of cellulose in the LiCl/DMA system deduced from the analysis of atomistic-scale simulations conducted in this work is also consistent with most of the empirical observations related to cellulose dissolution in salt/amide solvent systems.

LiCl-promoted-dehydration of fructose-based carbohydrates into 5-hydroxymethylfurfural in isopropanol

“…11 The Li + and Cl À played the key role for cellulose dissolution in LiCl containing solvent systems, and could keep strong interaction with the hydroxy groups (-OH) attached in cellulose chains. [12][13][14] Recently, Binder et al 15,16 found that the LiCl was an additive for promoting carbohydrates dehydration reactions in the presence of toxic CrCl 2 or CrCl 3 catalyst; and with the aid of LiCl, the yield of HMF elevated signicantly from fructose, glucose, and cellulose substrates in DMAc solvents; Chen et al 17 studied the promotion of LiCl on CrCl 2 , SnCl 4 or SnCl 2 catalyzed dehydration of glucose into HMF in the caprolactam solvent, achieving acceptable HMF yield of 55-67% with the suitable amount of LiCl additive. Moreover, LiCl could also act as a catalyst in catalytic ring-opening polymerization of lactide in the presence of hydroxyl-containing compounds, 18 catalytic Friedel-Cras reaction of electron-rich aromatic compounds with ethyl glyoxylate, 19 and catalytic coupling reactions of propylene oxide and CO 2 to produce propylene carbonate (PC) with the help of imidazolium halide.…”

Low‐energy collision‐induced dissociation (low‐energy CID), collision‐induced dissociation (CID), and higher energy collision dissociation (HCD) mass spectrometry for structural elucidation of saccharides and clarification of their dissolution mechanism in DMAc/LiCl

“…It should be noted that a combination of infrared spectroscopy in the gas phase and quantum chemical calculations has suggested that, in the presence of metal ions, sugars will adopt structures in which the coordination number of an attaching metal is as high as possible (4 in the case of Li + in that study), and the number of intramolecular hydrogen bonds inside the molecule is also maximized. This result, as well as all‐atom molecular dynamic simulations, show that during the dissolution process, depending upon the structure of the saccharide under study and the geometry of available oxygen atoms, there may be more than 1 solvent molecule in the coordination sphere of Li + which becomes displaced by hydroxyl oxygen or ring oxygen atoms of the sugar. Scheme A shows the proposed dissolution mechanism of Morgenstern et al as portrayed by Huang and coworkers .…”

Importance of Internal Porosity for Glucan Adsorption in Mesoporous Carbon Materials

“…43,44 Adding LiCl to DMA leads to significant changes in solvation and gives rise to a good solvent for dissolving cellulose because of the solvent-mediated preferential interactions of ions with the glucan. 45 The altered nature of solvation with LiCl in DMA also resulted in distinct behaviors of adsorption to carbon surfaces in MD simulations as compared to those in pure DMA. Persistent adsorption of glucan onto the graphene bilayer was observed in the DMA/LiCl system, in Figure 4.…”