Preparation of cellulose–starch composite gel and fibrous material from a mixture of the polysaccharides in ionic liquid

This paper reports the preparation of a cellulose–starch composite gel from an ionic liquid solution. The gel was obtained by keeping the homogeneous mixture of cellulose (10% w/w) and starch (5% w/w) in 1-butyl-3-methylimidazolium chloride (BMIMCl) for several days at room temperature and characterized by elemental analysis, X-ray diffraction, and thermal gravimetric analysis. Furthermore, the production of the fibrous material composed of cellulose and starch by reconstitution from the homogeneous mixture (10% w/w each) in BMIMCl is demonstrated.     

Enzymatic selective acylation of glycosides in ionic liquids: significantly enhanced reactivity and regioselectivity

The enzymatic selective acylations of carbohydrates in ionic liquids were explored in both organic solvents and ionic liquids to see any significant differences in terms of reactivity and regioselectivity between two different classes of reaction media. Monoprotected glycosides (methyl-6-O-trityl-glucosides and galactosides) were chosen as the substrates with Candida rugosa lipase as an acylation enzyme. Two organic solvents, THF and chloroform, and two ionic liquids, [BMIM]⁺PF₆⁻ ([BMIM]⁺ = 1-butyl-3-methylimidazolium) and [MOEMIM]⁺PF₆⁻ ([MOEMIM]⁺ = 1-methoxyethyl-3-methylimidazolium), were employed as reaction media. The enzymatic reactions were performed in the presence of vinyl acetate at room temperature. It was observed that the reactions in ionic liquids took place more rapidly and more selectively than those in conventional organic solvents.     

Natural wool/cellulose acetate blends regenerated from the ionic liquid 1-butyl-3-methylimidazolium chloride

Dissolution and blending one of the most commonly used natural polymers, i.e., wool using a green solvent ionic liquid is described. The cleaned natural wool from merino sheep was directly dissolved and regenerated from 1-butyl-3-methylimidazolium chloride (BMIMCl) without any modifications. BMIMCl was subsequently used to develop wool/cellulose acetate (CA) blends. Blending modification of wool in this IL green solvent led to significant increase in glass transition temperature (T_g) and thermal stability compared to the pure components. It was found that there exist strong intermolecular hydrogen bonding interactions between regenerated wool and CA. Moreover homogeneous surface morphology was observed in the blends with higher CA concentrations. At the final stage of the blending process, the IL solvent was recycled completely. This work presents a green processing route for development of novel natural wool blended materials.     

Pseudomonas cepacia lipase-catalysed resolution of racemic alcohols in ionic liquid using succinic anhydride: role of triethylamine in enhancement of catalytic activity

Racemic secondary alcohols were resolved via enantioselective acylation using succinic anhydride as acyl donor catalysed by lipase from Pseudomonas cepacia supported on celite (PS-C) in ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim]PF₆. Organic base, namely triethylamine as an additive in ionic liquid has been found to enhance the rate of the reaction.     

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.     

Succinoylation of sago starch in the N,N-dimethylacetamide/lithium chloride system

The modification reaction of sago starch with succinic anhydride (SA) using pyridine (PY) and/or 4-dimethyaminopyridine (DMAP) as catalyst and N,N-dimethylacetamide (DMA)/lithium chloride (LiCl) system as solvent was studied. A series of succinylated starch derivatives were prepared with a degree of substitution (DS) ranging from 0.14 to 1.54. The structure of the resulting polymers determined by means of ¹³C NMR spectroscopy indicated that substitution preferably occurs at the C₂ and C₆ hydroxyl groups. The thermal stability of the material was decreased by chemical modification. Effects of reactant molar ratio, reaction time, and the concentrations of DMAP and LiCl on the reaction efficiency are discussed.     

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.     

Optimization of (R,S)-1-phenylethanol kinetic resolution over Candida antarctica lipase B in ionic liquids

The kinetic resolution of racemates constitutes one major route to manufacture optically pure compounds. The enzymatic kinetic resolution of (R,S)-1-phenylethanol over Candida antarctica lipase B (CALB) by using vinyl acetate as the acyl donor in the acylation reaction was chosen as model reaction. A systematic screening and optimization of the reaction parameters, such as enzyme, ionic liquid and substrates concentrations with respect to the final product concentration, were performed. The enantioselectivity of immobilized CALB commercial preparation, Novozym 435, was assayed in several ionic liquids as reaction media. In particular, three different ionic liquids: (i) 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆], (ii) 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF₄] and (iii) 1-ethyl-3-methylimidazolium triflimide [emim][NTf₂] were tested. At 6.6% (w/w) of Novozym 435, dispersed in 9.520 M of [bmim][PF₆] at 313.15 K, using an equimolar ratio of vinyl acetate/(R,S)-1-phenylethanol after 3 h of bioconversion, the highest possible conversion (50%) was reached with enantiomeric excess for substrate higher than 99%.     

Direct enzymatic acylation of cellulose pretreated in BMIMCl ionic liquid

Cellulose esters are an important class of functional biopolymers with great interest in the chemical industry. In this work the enzymatic acylation of Avicel cellulose with vinyl propionate, vinyl laurate and vinyl stearate, has been performed successfully in a solvent free reaction system. At first cellulose was putted into the ionic liquid BMIMCl (1-n-butyl-3-methylimidazolium chloride) in order to facilitate the unwrap of the structure of the polysaccharide molecule and make it accessible to the enzyme. Thus, after this pretreatment the enzymatic esterification reaction was performed using various hydrolases. The enzymes capable of catalyzing the acylation of cellulose were found to be the immobilized esterase from hog liver and the immobilized cutinase from Fusarium solani, while the lipases used did not show any catalytic activity. Cellulose esters of propionate, laurate and stearate were synthesized with a degree of esterification of 1.9%, 1.3% and 1.0%, respectively. It is the first successful direct enzymatic acylation of cellulose with long chain fatty acids.     

Synthesis of amphiphilic amylose and starch derivatives

For non-food uses starch generally is modified in order to obtain products with properties suitable for various applications. In the present work, starch and amylose were hydrophobically modified through reactions with long-chain -alkyl epoxides (C₆ and C₁₂) in DMSO solution, in the presence of NaH as a catalyst. The molar substitution (MS) was calculated from NMR spectra. Derivatives with high as well as low MS values were obtained. In order to reach MS values above 1.5, the reaction had to be run for 150–300 h. Viscosity and GPC measurements indicated that the polysaccharides were degraded in DMSO under the influence of methyl sulfinyl anion, which presumably is the active catalyst.

The derivatives were also characterized by FTIR. The ratio between the peak areas for OH stretching and alkyl stretching vibrations, respectively, in the FTIR spectra, was found to be proportional to MS values determined from NMR spectra.

The solubility of the hydrophobically modified polysaccharide in various solvents was tested. Samples having C₁₂-alkyl side chains and MS>1 were soluble in toluene. The C₆ derivatives were water soluble up to a MS value of 0.3.     

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.     

Starch derivatives of high degree of functionalization. 1. Effective, homogeneous synthesis of p-toluenesulfonyl (tosyl) starch with a new functionalization pattern

Pure p-toluenesulfonyl (tosyl) starch with an insignificant formation of chlorodeoxy groups was prepared by reacting starch dissolved in the solvent system N,N-dimethyl acetamide in combination with LiCl. Interestingly, the viscosity of the starch dissolved in the solvent system increases with the increasing amount of LiCl. The tosyl starch samples obtained were characterized by means of elemental analysis, FITR and ¹³C NMR spectroscopy. The degree of substitution (DS_Tos) of the products can be controlled in range from 0.4 to 2.0 by adjusting the molar ratio of tosyl chloride per anhydroglucose unit up to 6.0 mol/mol. The tosyl starch samples are readily soluble in various organic solvents. As revealed by means of ¹³C NMR analysis as well as by analysis of the corresponding 6-iodo-6-deoxy derivatives, a faster tosylation at position 2 than at positions 6 and 3 takes place. The thermal stability of tosyl starch increases with increasing DS_Tos and degradation starts at 166°C for the sample of DS_Tos of 0.61. The remaining OH groups of tosyl starch are reactive and can be additionally modified by acetylation reactions.     

Properties of an ionic liquid-tolerant <Emphasis Type="Italic">Bacillus</Emphasis><Emphasis Type="Italic">amyloliquefaciens</Emphasis> CMW1 and its extracellular protease

An ionic liquid-tolerant bacterium, Bacillus amyloliquefaciens CMW1, was isolated from a Japanese fermented soybean paste. Strain CMW1 grew in the presence of 10 % (v/v) 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), a commonly used ionic liquid. Additionally, strain CMW1 grew adequately in the presence of the hydrophilic ionic liquids 10 % (v/v) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM]CF₃SO₃) or 2.5 % (v/v) 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]CF₃SO₃). Strain CMW1 produced an extracellular protease (BapIL) in the culture medium. BapIL was stable in the presence of 80 % (v/v) ionic liquids, [EMIM]CF₃SO₃, [BMIM]Cl, [BMIM]CF₃SO₃, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and functioned in 10 % (v/v) these ionic liquids. BapIL was stable at pH 4.0–12.6 or in 4004 mM NaCl solution, and exhibited activity in the presence of 50 % (v/v) hydrophilic or hydrophobic organic solvents. BapIL was completely inhibited by 1 mM PMSF and partially by 5 mM EDTA. BapIL belongs to the true subtilisins according to analysis of the deduced amino acid sequence. We showed that BapIL from the ionic liquid-tolerant B. amyloliquefaciens CMW1 exhibited tolerance to ionic liquid and halo, alkaline, and organic solvents.     

Cytochrome c dissolved in 1-allyl-3-methylimidazolium chloride type ionic liquid undergoes a quasi-reversible redox reaction up to 140°C

Solubility of cytochrome c, a typical heme protein, in a various ionic liquids has been analyzed. The solubility has been discussed with polarity parameters of the ionic liquids. Both hydrogen bond basicity and dipolarity/polarizability of the ionic liquids were confirmed to be influential factors to control the solubilization of cytochrome c. Polar ionic liquids such as 1-butyl-3-methylimidazolium chloride and 1-allyl-3-methylimidazolium chloride solubilized cytochrome c at 80°C, and the dissolved cytochrome c was found to keep its redox activity in these ionic liquids. The redox response of the dissolved cytochrome c was detected in 1-allyl-3-methylimidazolium chloride up to 140°C.     

Obtaining high transesterification activity for subtilisin in ionic liquids

It is known that subtilisin shows poor transesterification activity in ionic liquids (ILs). The present work, taking subtilisin as the system, explores approaches for biocatalyst preparations, which are capable of yielding higher/adequate transesterification activity in these solvents. Of all the approaches tried, enzyme precipitated and rinsed with n-propanol (EPRP) gave the best results (about 10,000 times increase in initial rates in 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF(6)]) over what is obtained with pH tuned lyophilized powders). In case of water soluble ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]), pH tuned lyophilized subtilisin did not show any transesterification activity. EPRP, however, gave an initial rate (for transesterification) of 2.78 mmol mg(-1) h(-1).     

Conversion of hexose into 5-hydroxymethylfurfural in imidazolium ionic liquids with and without a catalyst

Conversion of fructose and glucose into 5-hydroxymethylfurfural (HMF) was investigated in various imidazolium ionic liquids, including 1-butyl-3-methylimidazolium chloride (BmimCl), 1-hexyl-3-methylimidazolium chloride (HmimCl), 1-octyl-3-methylimidazolium chloride (OmimCl), 1-benzyl-3-methylimidazolium chloride (BemimCl), 1-Butyl-2,3-dimethylimidazolium chloride (BdmimCl), and 1-butyl-3-methylimidazolium p-toluenesulfonate (BmimPS). The acidic C-2 hydrogen of imidazolium cations was shown to play a major role in the dehydration of fructose in the absence of a catalyst, such as sulfuric acid or CrCl₃. Both the alkyl groups of imidazolium cations and the type of anions affected the reactivity of the carbohydrates. Although, except BmimCl and BemimCl, other four ionic liquids could only achieve not more than 25% HMF yields without an additional catalyst, 60–80% HMF yields were achieved in HmimCl, BdmimCl, and BmimPS in the presence of sulfuric acid or CrCl₃ in sufficient quantities.     

Use of ionic liquids as media for the biocatalytic preparation of flavonoid derivatives with antioxidant potency

Biocatalytic preparation of acylated derivatives of flavonoid glycosides was performed using various immobilized lipases in two different ionic liquids, namely 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF(4)) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF(6)). The influence of various reaction parameters on the performance and the regioselectivity of the biocatalytic process was pointed out, using as model reaction the acylation of naringin and rutin with vinyl butyrate, catalyzed by immobilized Candida antarctica lipase at 60 degrees C. The biocatalytic modification of flavonoids strongly depended on the ionic liquid used, the molar ratio of substrates, as well as the acyl donor chain length. The highest conversion yield (about 65% after 96 h of incubation) was obtained with short chain acyl donors (up to four carbon atoms), at a relatively high molar ratio (10-15) in both ionic liquids used. The amount of monoacylated flavonoid derivatives produced in a single-step biocatalytic process in [bmim]BF(4) was up to 5.5 g/L for monoacylated rutin and 30 g/L for monoacylated naringin. The regioselectivity of the process was higher in [bmim]BF(4) than in [bmim]PF(6) or organic solvents. Reaction rates observed in ionic liquids were up to four times higher than those reported for organic media. The acylation of sugar moiety of rutin with various acyl donors affected its antioxidant potential towards both isolated LDL and total serum model in vitro. A significant increase of antioxidant activity was observed for rutin-4'-O-oleate.     

Direct fabrication of all-cellulose nanocomposite from cellulose microfibers using ionic liquid-based nanowelding

All-cellulose nanocomposite was directly fabricated using nanowelding of cellulose microfibers as a starting material, in 1-butyl-3-methylimidazolium chloride (BMIMCl) as a solvent, for the first time. The average diameter of the reinforcing component (undissolved nanofibrils) in the nanocomposite made directly from cellulose microfibers (NC-microfiber) was 53 ± 16 nm. Owing to its high mechanical properties (tensile strength of 208 MPa and Young's modulus of 20 GPa), high transparency (76% at a wavelength of 800 nm), and complete barrier to air and biodegradability, the NC-microfiber is regarded as a high multiperformance material. The NC-microfiber made directly from cellulose microfibers showed similar macro-, micro-, and nanostructures and the same properties as those made from solvent-based welding of ground cellulose nanofibers (NC-nanofiber). Omitting the step of cellulose nanofiber production makes the direct production of all-cellulose nanocomposite from cellulose microfibers easier, shorter, and cheaper than using cellulose nanofibers as starting material. The direct nanowelding of macro/micrometer-sized materials is theorized to be a fundamental approach for making nanocomposites.     

Effect of ionic liquids alkyl chain length on horseradish peroxidase thermal inactivation kinetics and activity recovery after inactivation

The effects of different alkyl chain lengths of ionic liquids 1-ethyl-, 1-butyl- and 1-hexyl-3-methylimidazolium chloride, on the catalytic activity, thermal stability and deactivation kinetics of horseradish peroxidase were studied in the temperature range of 45–85 °C. The presence of 1-ethyl- and 1-butyl-ionic liquids up to 25 % (w/v) did not affect significantly the enzyme activity at 25 °C, whereas the addition of 1-hexyl-solvent resulted in lower activity of enzyme. Typical biphasic deactivation profiles were obtained and adequately fitted by a bi-exponential equation. When increasing ionic liquids concentration up to 25 % (w/v), the second phase of deactivation became more prominent, till leading to apparent first-order kinetics. Occurrence of activity regain, following thermal deactivation was found, reaching up 60–80 % of the initial activity, especially in 1-hexyl-3-methylimidazolium chloride. Activity regain was particularly noticeable in the first phase of deactivation. Temperature sensitivity of the Soret band maxima indicated that the enzyme prepared in buffer or 1-hexyl-3-methylimidazolium chloride had similar conformational changes in the haem region, but no correlations were found with activity decrease.     

Novozym 435-catalyzed regioselective benzoylation of 1-β-d-arabinofuranosylcytosine in a co-solvent mixture of C4MIm·PF6 and pyridine

Regioselective acylation of 1-β-d-arabinofuranosylcytosine (ara-C), using vinyl benzoate (VB) as acyl donor and Novozym 435 as catalyst, was carried out in various reaction media including pure organic solvents, organic solvent mixtures, and ionic liquid (IL)-containing systems. Although the reaction was highly regioselective in all the media assayed, remarkable enhancement of substrate conversion was achieved with a co-solvent mixture of 1-butyl-3-methylimidazolium hexafluorophosphate (C₄MIm·PF₆) and pyridine as the reaction medium, compared with other media tested. Additionally, the results demonstrated that the anions of ILs had a significant effect on the initial rate and substrate conversion. To better understand the reaction performed in IL-containing system, several variables were examined. The optimum molar ratio of VB to ara-C, initial water activity, temperature and shaking rate were 25:1, 0.11, 40°C and 250rpm, respectively. Under these optimum reaction conditions, the initial rate, substrate conversion, and regioselectivity were 0.49mMmin^?1, 99.4 and 99%, respectively. The product of the lipase-catalyzed reaction was characterized by ¹³C NMR and was shown to be 5′-O-benzoyl ara-C.