Acetylation of wheat straw hemicelluloses in ionic liquid using iodine as a catalyst

Wheat straw hemicelluloses were acetylated with acetic anhydride using iodine as a novel catalyst in 1-butyl-3-methylimidzolium chloride ([C₄mim]Cl) ionic liquid (IL). Acetylated hemicelluloses with yield and degree of substitution (DS) from 70.5% to 90.8% and between 0.49 and 1.53, respectively, are accessible in a complete homogeneous procedure by changing the reaction temperature, reaction duration, the dosage of catalyst, and the dosage of acetic anhydride. The preferred reaction parameters that resulted in the highest DS were follows: 20:1 reactant molar ratio, 100 °C, 30 min, 15% iodine, in which about 83% hydroxyl groups in native hemicelluloses were esterified. The structural features of the acetylated hemicelluloses were characterized by ¹³C NMR and FT-IR spectroscopy. The thermal stability of the acetylated hemicelluloses increased upon chemical modification. It is the first time that we have demonstrated that ILs could be used as an environmentally friendly solvent for the chemical modification of hemicelluloses.     

Rheological properties of concentrated solutions of gellan in an ionic liquid

The rheological properties of solutions of gellan were examined at high concentrations where there is entanglement coupling between gellan chains. An ionic liquid 1-butyl-3-methylimidazolium chloride (BmimCl) was used as a solvent. Concentrated solutions of gellan in BmimCl were obtained by using a hot-molding technique. The concentration of gellan was varied from 1.9 × 10² to 4.8 × 10² kg m⁻³. The measurement temperature ranged from 50 to 100 °C. The master curve of the angular frequency dispersion of the storage modulus for the gellan solutions showed a rubbery plateau at high angular frequency. The molecular weight between entanglements (M_e) for gellan was obtained from the plateau modulus. From the concentration dependence curve of M_e, M_e for gellan in the molten state was determined to be 2.3 × 10³.     

The effects of high concentrations of ionic liquid on GB1 protein structure and dynamics probed by high-resolution magic-angle-spinning NMR spectroscopy

Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentrations of ionic liquids, has been challenging. In the present work the ¹³C, ¹⁵N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid–protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C₄-mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6–3.5 M, which corresponds to 10–60% v/v). Interactions between GB1 and [C₄-mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in ¹⁵N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C₄-mim]Br were assigned using 3D methods under HR-MAS conditions. Thus, HR-MAS NMR is a viable tool that could aid in elucidation of molecular mechanisms of ionic liquid–protein interactions.     

Amyloid formation using 1-butyl-3-methyl-imidazolium-based ionic liquids

Amyloid fibrils are highly organized protein filaments that can be used as novel biomaterials. In this study, we show that proteins could be selectively induced to form amyloid fibrils at room temperature by the introduction of imidazolium salts, which could trigger the self-assembly process with their hydrophobic and ionic properties.     

Homogeneous modification of sugarcane bagasse cellulose with succinic anhydride using a ionic liquid as reaction medium

The homogeneous chemical modification of sugarcane bagasse cellulose with succinic anhydride using 1-allyl-3-methylimidazolium chloride (AmimCl) ionic liquid as a reaction medium was studied. Parameters investigated included the molar ratio of succinic anhydride/anhydroglucose units in cellulose in a range from 2:1 to 14:1, reaction time (from 30 to 160min), and reaction temperature (between 60 and 110 degrees C). The succinylated cellulosic derivatives were prepared with a low degree of substitution (DS) ranging from 0.071 to 0.22. The results showed that the increase of reaction temperature, molar ratio of SA/AGU in cellulose, and reaction time led to an increase in DS of cellulose samples. The products were characterized by FT-IR and solid-state CP/MAS (13)C NMR spectroscopy, and thermal analysis. It was found that the crystallinity of the cellulose was completely disrupted in the ionic liquid system under the conditions given. The data also demonstrated that homogeneous modification of cellulose with succinic anhydride in AmimCl resulted in the production of cellulosic monoester. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Weak gel of chitin with ionic liquid, 1-allyl-3-methylimidazolium bromide

This paper reports the formation of weak gel of chitin with an ionic liquid, 1-allyl-3-methylimidazolium bromide (IL). When a mixture of 5% (w/w) chitin with IL was heated at 100 °C for 48 h, the clear liquid was obtained. The experimental process was observed by the CCD camera view and the SEM analysis. From a mixture of chitin with IL in the higher concentration (7%, w/w), a more viscous material, i.e., a gel-like material was obtained. The rheological evaluations showed that both 5% (w/w) and 7% (w/w) chitins with IL behaved as weak gels.     

Homogeneous phase synthesis of cellulose carbamate silica hybrid materials using 1-n-butyl-3-methylimidazolium chloride ionic liquid medium

Cellulose carbamate silica hybrid materials can be prepared in 78–84% yield using the homogeneous phase reaction of 3-(triethoxysilyl)propyl isocyanate with cellulose dissolved in 1-n-butyl-3-methylimidazolium chloride ionic liquid and then using NH₄OH catalyzed hydrolysis of triethoxysilyl groups and the sol–gel process. New cellulose carbamate silica hybrid materials produced were characterized by elemental analysis, FT-IR, and TG-DTA. The hydrophilic affinity of these materials is shown to decrease with the degree of substitution of the cellulose hydroxyl groups with carbamate groups.     

Cellulose extraction from wood chip in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl)

In the present study, 1-allyl-3-methylimidazolium chloride (AmimCl), an ionic liquid (IL), was used to extract cellulose from pine, poplar, Chinese parasol, and catalpa wood chips. Results show that pine is the most suitable wood species for cellulose extraction with ILs. Its cellulose extraction rate can reach as high as 62% under optimized conditions and its cellulose content is as high as 85% when DMSO/water is used as the precipitant. The dissolution process can be clearly observed by hot stage optical microscopy, and the reaction time can be significantly reduced by microwave irradiation. ¹³C CP/MAS NMR, FTIR, XRD, and SEM were used to analyze the cellulose-rich extracts of pine. Results show that IL dissolves pine wood by destroying inter and intramolecular hydrogen bonds between lignocelluloses. The major component of pine extract is cellulose with a homogeneous and dense structure. After extraction, AmimCl can be easily recycled and reused.     

Addition of ammonia and/or oxygen to an ionic liquid for delignification of miscanthus

Ammonia and/or oxygen were used to enhance the delignification of miscanthus dissolved in 1-ethyl-3-methylimidazolium acetate at 140 °C. After dissolution of the gas at 9 bar, water was added as antisolvent to regenerate the dissolved biomass. In a next step, an acetone/water mixture was used to remove carbohydrate-free lignin from the regenerated biomass. The lignin content in the final product was around 10%, much lower than the ca. 23% lignin content of the raw dry miscanthus. This lignin reduction is achieved without diminution of cellulose or of total carbohydrates recovered, relative to the recovery achieved with the ionic liquid pretreatment in contact with air or nitrogen.     

Dissolution of [RhCl(PPh3)3] in the ionic liquid, 1-ethyl-3-methyl imidazolium chloroaluminate(III), and its reaction with H2. The stabilization of Rh(I) species in an ionic liquid

The solution of [RhCl(PPh₃)₃] in acidic 1-ethyl-3-methylimidazolium chloroaluminate(III) ionic liquid (AlCl₃ molar fraction, x_AlCl3=0.67) was investigated by ¹H and ³¹P{¹H} NMR. One triphenyl phosphine is lost from the complex and is protonated in the acidic media, and cis-[Rh(PPh₃)₂ClX], (2), where X is probably [AlCl₄]⁻, is formed. On, standing, 2 is converted to trans-[Rh(H)(PPh₃)₂X], (3). The reaction of 2 and H₂ also produces trans-[Rh(H)(PPh₃)₂X], (3). ¹H and ³¹P{¹H} NMR support the suggestion that a weak ligand such as [AlCl₄]⁻, present in solution may interact with the metal centre. When [RhCl(PPh₃)₃] is dissolved in CH₂Cl₂/AlCl₃/HCl for comparison, two exchanging isomers of what is probably [RhH{(μ-Cl)₂AlCl₂}{(μ-Cl)AlCl₃}(PPh₃)₂], (6) and (7), are formed.     

A facile preparation of gel materials from a solution of cellulose in ionic liquid

This paper reports a facile preparation of a flexible gel material from a solution of cellulose (15% w/w) in an ionic liquid of 1-butyl-3-methylimidazolium chloride by keeping it at room temperature for 7 days. Elemental analysis data indicated that the obtained gel material was composed of cellulose, the ionic liquid, and water. Both XRD and TGA results suggested that crystalline structure of cellulose was largely disrupted in the material. However, the existence of non-crystalline aggregates was assumed by the XRD data of the material. The gel material was probably obtained by the formation of cellulose aggregates in the solution, attributed to the gradual absorption of water. When the material was heated at 120 degrees C, it became soft, and converted into a fluid at 150 degrees C. By keeping the soft material at room temperature for 2 days, a gel material was regenerated, which was more transparent compared with the original material.     

Preparation of cellulose graft poly(methyl methacrylate) copolymers by atom transfer radical polymerization in an ionic liquid

Cellulose graft poly(methyl methacrylate) copolymers were prepared by atom transfer radical polymerization (ATRP) in an ionic liquid. Cellulose chloroacetate, as a macroinitiator, was first synthesized by direct acylation of cellulose with chloroacetyl chloride without any catalysts under mild conditions in an ionic liquid, 1-allyl-3-methylimidazolium chloride (BMIMCl). Then, the macroinitiator was used for the ATRP of MMA mediated by the CuBr and 2,2′-bipyridine (bpy) catalysis system. The copolymerization was carried out in BMIMCl without homopolymer byproduct. The polymers were easily separated from the catalyst when the ionic liquid was used as reaction medium. The grafting copolymers were characterized by means of ¹H NMR, AFM and GPC. The results showed that the obtained copolymers had grafted polymer chains with well-controlled molecular weight and polydispersity, and the polymerization was a “living/controlled” system. Further, through AFM observation, it was found that the cellulose graft copolymer in solution could aggregate and self-assembly into sphere-like polymeric structure.     

Increased enantioselectivity in the enzymatic hydrolysis of amino acid esters in the ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate

The initial rate and enantioselectivity of enzymatic asymmetric hydrolysis of amino acid esters were examined in methylimidazolium-based ionic liquids with anions including tetrafluoroborate, chloride, bromide and bisulfate and in typical organic solvents. Papain displayed much higher enantioselectivity but lower activity in phosphate buffer solution of 1-butyl-3-methylimidazolium tetrafluoroborate BMIM·BF₄ than in other media tested (i.e. E=100, V ₀=0.21 mM min^-1 in BMIM·BF₄, E=2, V ₀=0.43 mM min^-1 in phosphate buffer, E=14-92, V ₀=0.22-0.25 mM min^-1 in organic solvents for D,L-phenylglycine methyl ester). The influence of BMIM·BF₄ on enzyme activity and enantioselectivity also varied with the substrate and the enzyme used. All of the enzymes assayed showed no activity or low enantioselectivity in the ILs with anions including chloride, bromide and bisulfate.     

Homogeneous butyrylation and lauroylation of poplar wood in the ionic liquid 1-butyl-3-methylimidazolium chloride

Wood meal was dissolved under identical conditions in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) and homogeneously esterified with butyryl chloride and lauroyl chloride in the presence of triethylamine as a neutralizer. The effect of the molar ratio of reagent to the hydroxyl groups in wood on the properties of the esterified wood and the possible mechanism of the homogeneous esterification of wood in this reaction medium were studied. Furthermore, the physicochemical properties of the esterified wood were characterized by FTIR, solid-state CP/MAS ¹³C NMR, TGA/DTG and SEM. The results confirmed that the homogeneous modifications were successfully processed and highly substituted wood esters could be obtained by reacting the dissolved wood in this homogeneous system.     

The study of factors affecting the enzymatic hydrolysis of cellulose after ionic liquid pretreatment

Cellulose resource has got much attention as a promising replacement of fossil fuel. The hydrolysis of cellulose is the key step to chemical product and liquid transportation fuel. In this paper a serials of chloride, acetate, and formate based ionic liquids were used as solvents to dissolve cellulose. The cellulose regenerated from ILs was characterized by FTIR and X-ray powder diffraction. From the characterization and analysis, it was found that the original close and compact structure has changed a lot. After enzymatic hydrolysis, different kinds of ionic liquids (ILs) have different yields of the reducing sugar (TRS). They are 100%, 90.72%, and 88.92% from 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), 1-butyl-3-methylimidazolium formate ([BMIM][HCOO]) respectively after enzymatic hydrolysis at 50 °C for 5 h. The results indicated that the yields and the hydrolysis rates were improved apparently after ILs pretreatment comparing with the untreated substrates.     

Acetone-soluble cellulose acetates prepared by one-step homogeneous acetylation of cornhusk cellulose in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl)

Cellulose samples extracted from cornhusk have been successfully acetylated in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). Without using any catalyst, cornhusk cellulose acetates (CCAs) with the degree of substitution (DS) in a range from 2.16 to 2.63 were prepared in one-step. Under the homogeneous state, the DS value of CCAs was easily controlled by the acetylation time. The obtained CCAs were characterized by means of FT-IR, ¹³C NMR, DSC, TGA, and a mechanical test. The NMR results showed that the distribution of the acetyl moiety among the three OH groups of the anhydroglucose unit shows a preference at the C₆ position. The CCAs exhibited good solubility in some organic solvents, such as acetone and DMSO. The cast CCA films from their acetone solutions had good mechanical properties. At the end of each acetylation of cornhusk cellulose, the ionic liquid AmimCl could be effectively recovered. Therefore, this study presents a promising approach and “green process” to make use of crop by-products.     

Cationic effect of imidazolium-based ionic liquid on the stability of myoglobin

The conformational change of myoglobin (Mb) during guanidine hydrochloride (GuHCl)-induced protein unfolding in the presence of various ionic liquids (ILs) in phosphate buffer was investigated using both the Soret band absorption and the fluorescence of tryptophan measurements. The GuHCl-induced denaturation midpoints of Mb derived from the absorption and fluorescence spectra were almost similar in the presence of 150 mM ILs with the same cation 1-butyl-3-methylimidazolium (Bmim⁺) but different anions (BF₄⁻, NO₃⁻, Cl⁻, and Br⁻) in phosphate buffer. In addition, the denaturation midpoints of Mb in the presence of ILs were little lower than those in the absence of ILs in phosphate buffer. For the sake of clarity and comparison, we also measured the GuHCl-induced denaturation midpoints of Mb in the presence of 150 mM sodium salts with different anions (BF₄⁻, NO₃⁻, Cl⁻, and Br⁻) in phosphate buffer and found that their corresponding denaturation midpoints of Mb were almost similar to those observed in the absence of sodium salts in phosphate buffer. These experimental data indicate that Bmim⁺ cation can promote the unfolding of Mb. Further experiments revealed that the denaturation ability of ILs increases with increasing alkyl chain length of imidazolium cation of ILs and that hydroxyl-substituted imidazolium cation could also promote the unfolding of Mb.     

Utility of ionic liquid for Geotrichum candidum-catalyzed synthesis of optically active alcohols

Ionic liquids have recognized as a solvent for Geotrichum candidum-catalyzed optical resolution and/or deracemization of racemic secondary alcohols, giving optically active alcohols. The immobilized Geotrichum candidum proceeded the enantioselective oxidation of alcohols, producing chiral alcohols in an ionic liquid. Further, deracemization of racemic alcohols was proceeded to give the corresponding chiral alcohols in high yield with excellent stereoselectivity by the Geotrichum candidum–NaBH₄ system in the mixture of MES buffer solution and ionic liquid.     

Reversible swelling of the cell wall of poplar biomass by ionic liquid at room temperature

Time-resolved autofluorescence, Raman microspectroscopy, and scanning microprobe X-ray diffraction were combined in order to characterize lignocellulosic biomass from poplar trees and how it changes during treatment with the ionic liquid 1-n-ethyl-3-methylimidazolium acetate (EMIMAC) at room temperature. The EMIMAC penetrates the cell wall from the lumen, swelling the cell wall by about a factor of two towards the empty lumen. However, the middle lamella remains unchanged, preventing the cell wall from swelling outwards. During this swelling, most of the cellulose microfibrils are solubilized but chain migration is restricted and a small percentage of microfibrils persist. When the EMIMAC is expelled, the cellulose recrystallizes as microfibrils of cellulose I. There is little change in the relative chemical composition of the cell wall after treatment. The action of EMIMAC on the poplar cell wall at room temperature would therefore appear to be a reversible swelling and a reversible decrystallization of the cell wall.     

Self-aggregation of trehalose in the mixed solvents of 1,3-dimethylimidazolium ionic liquid and water

Abstract

Conformational variations of solvated trehaloses in binary mixtures of 1,3-dialkylimidazolium ([dmim]Cl) ionic liquids and trehalose as well as ternary mixtures of trehalose, [dmim]Cl and water have been studied by molecular dynamics (MD) simulations with and without polarisable force fields. The interaction energy between anion Cl^? and water is stronger than that between water itself in the [dmim]Cl-water mixtures. Isolated water clusters were found in the binary [dmim]Cl-water mixtures with 60.0 and 75.0% mole fraction of water, but a continuous water network appears when the concentration of the mixture increases to 99.9%. In the case of binary mixtures of trehalose and [dmim]Cl, both non-polarisable and polarisable models demonstrated that the pyranose rings of trehalose displayed chair conformations. MD simulations with polarisation model could sample larger conformation space than that with non-polarisable model. A self-aggregation behaviour of trehalose was found in the ternary trehalose-[dmim]Cl-water mixtures, which can be rationalised by the stronger non-bonded interaction energy between trehalose molecules and anion Cl^? than that between trehalose molecules and water.