An ionic liquid as reaction media for radiation-induced grafting of thermosensitive poly (N-isopropylacrylamide) onto microcrystalline cellulose

This paper reports a homogeneous modification of microcrystalline cellulose (MCC) in ionic liquids via radiation-induced grafting. Thermosensitive poly (N-isopropylacrylamide) (PNIPAAm) was successfully grafted onto MCC in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) ionic liquid using γ-ray irradiation technique at room temperature. The grafting yield (GY) increased with dose up to 40 kGy, while decreased slightly with dose rate from 22 to 102 Gy/min. The results of TGA indicated that cellulose grafted PNIPAAm (cellulose-g-PNIPAAm) had higher thermal stability than that of ungrafted regenerated cellulose (reg-cellulose). The crystalline structure of original MCC was largely destroyed during the dissolution process according to the XRD profiles, and grafting PNIPAAm onto cellulose further decreased the intensity of crystallinity. SEM showed that reg-cellulose and cellulose-g-PNIPAAm films displayed dense and homogeneous morphology. Moreover, the resulting cellulose-g-PNIPAAm exhibited obvious thermal sensitivity with a lower critical solution temperature around 35 °C, which was observed from the swelling behavior in water at different temperatures.     

Lipase-catalyzed synthesis of glucose fatty acid ester using ionic liquids mixtures

Novozym 435-catalyzed synthesis of 6-O-lauroyl-d-glucose in ionic liquids (ILs) was investigated. The highest lipase activity was obtained in water-miscible [Bmim][TfO] which can dissolve high concentration of glucose, while the highest stability of lipase was shown in hydrophobic [Bmim][Tf(2)N]. The optimal activity and stability of lipase could be obtained in [Bmim][TfO] and [Bmim][Tf(2)N] mixture (1:1, v/v). Specifically, the activity of lipase was increased from 1.1 to 2.9 micromolmin(-1)g(-1) by using supersaturated glucose solution in this mixture, compared with reaction using saturated solution. After 5 times reuse of lipase, 86% of initial activity was remained in this mixture, while the residual activity in pure [Bmim][TfO] was 36%. Therefore, the productivity obtained by using ILs mixtures was higher than those in pure ILs.     

Elucidating Interactions and Conductivity of Newly Synthesised Low Bandgap Polymer with Protic and Aprotic Ionic Liquids

In this paper, we have examined the conductivity and interaction studies of ammonium and imidazolium based ionic liquids (ILs) with the newly synthesised low bandgap polymer (Poly(2-heptadecyl-4-vinylthieno[3,4-d]thiazole) (PHVTT)). Use of low bandgap polymers is the most suitable way to harvest a broader spectrum of solar radiations for solar cells. But, still there is lack of most efficient low bandgap polymer. In order to solve this problem, we have synthesised a new low bandgap polymer and investigated its interaction with the ILs to enhance its conductivity. ILs may undergo almost unlimited structural variations; these structural variations have attracted extensive attention in polymer studies. The aim of present work is to illustrate the state of art progress of implementing the interaction of ILs (protic and aprotic ILs) with newly synthesised low bandgap polymer. In addition to this, our UV-Vis spectroscopy, confocal Raman spectroscopy and FT-IR spectroscopy results have revealed that all studied ILs (tributylmethylammonium methyl sulfate ([N₁₄₄₄][MeSO₄] from ammonium family) and 1-methylimidazolium chloride ([Mim]Cl, and 1-butyl-3-methylimidazolium chloride ([Bmim]Cl from imidazolium family) have potential to interact with polymer. Our semi empirical calculation with help of Hyperchem 7 shows that protic IL ([Mim]Cl) interacts strongly with the low bandgap polymer through the H-bonding. Further, protic ILs shows enhanced conductivity than aprotic ILs in association with low bandgap polymer. This study provides the combined effect of low bandgap polymer and ILs that may generate many theoretical and experimental opportunities.     

The role of different anions in ionic liquids on Pseudomonas cepacia lipase catalyzed transesterification and hydrolysis

Lipase Pseudomonas cepacia (PS) catalyzed transesterification of ethyl 3-phenylpropanoate with eleven alcohols was investigated in three ionic liquids [ILs], [Bmim]BF₄, [Bmim]PF₆, and [Bmim]Tf₂N, consisting of an identical cation and different anions. The yields were higher in hydrophobic ILs [Bmim]Tf₂N (55–96%) and [Bmim]PF₆ (22–95%), than in hydrophilic [Bmim]BF₄ (0–19%). The incubation of lipase PS in hydrophobic ILs for a period of 20–300 days at room temperature resulted in an increased yield of 62–98% in [Bmim]Tf₂N and 45–98% in [Bmim]PF₆, respectively. The lipase PS-hydrophobic IL mixture was recycled five times without any decrease in the yield of the products. In another set of experiments, the hydrolytic activity of the enzyme was determined after incubation in each of the three ILs and in hexane for 20 days at room temperature. It was found to be 1.8- and 1.6-fold higher in [Bmim]Tf₂N and [Bmim]PF₆, respectively, remained unchanged in [Bmim]BF₄ and was 1.6 times lower in hexane as compared to the non-incubated enzyme.     

Sugarcane bagasse pretreatment using three imidazolium-based ionic liquids; mass balances and enzyme kinetics

ABSTRACT: BACKGROUND: Effective pretreatment is key to achieving high enzymatic saccharification efficiency in processing lignocellulosic biomass to fermentable sugars, biofuels and value-added products. Ionic liquids (ILs), still relatively new class of solvents, are attractive for biomass pretreatment because some demonstrate the rare ability to dissolve all components of lignocellulosic biomass including highly ordered (crystalline) cellulose. In the present study, three ILs, 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl), 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) are used to dissolve/pretreat and fractionate sugarcane bagasse. In these IL-based pretreatments the biomass is completely or partially dissolved in ILs at temperatures greater than 130[DEGREE SIGN]C and then precipitated by the addition of an antisolvent to the IL biomass mixture. For the first time mass balances of IL-based pretreatments are reported. Such mass balances, along with kinetics data, can be used in process modelling and design. RESULTS: Lignin removals of 10% mass of lignin in bagasse with [C4mim]Cl, 50% mass with [C2mim]Cl and 60% mass with [C2mim]OAc, are achieved by limiting the amount of water added as antisolvent to 0.5 water:IL mass ratio thus minimising lignin precipitation. Enzyme saccharification (24 h, 15FPU) yields (% cellulose mass in starting bagasse) from the recovered solids rank as: [C2mim]OAc(83%)>[C2mim]Cl(53%) = [C4mim]Cl(53%). Composition of [C2mim]OAc-treated solids such as low lignin, low acetyl group content and preservation of arabinosyl groups are characteristic of aqueous alkali pretreatments while those of chloride IL-treated solids resemble aqueous acid pretreatments. All ILs are fully recovered after use (100% mass as determined by ion chromatography). CONCLUSIONS: In all three ILs regulated addition of water as an antisolvent effected a polysaccharide enriched precipitate since some of the lignin remained dissolved in the aqueous IL solution. Of the three IL studied [C2mim]OAc gave the best saccharification yield, material recovery and delignification. The effects of [C2mim]OAc pretreatment resemble those of aqueous alkali pretreatments while those of [C2mim]Cl and [C4mim]Cl resemble aqueous acid pretreatments. The use of imidazolium IL solvents with shorter alkyl chains results in accelerated dissolution, pretreatment and degradation.     

Hydrolysis of insoluble cellulose to glucose catalyzed by cellulase‐containing liposomes in an aqueous solution of 1‐butyl‐3‐methylimidazolium chloride

The liposome containing cellulase from Trichoderma viride was prepared under the condition that an appreciable amount of cellulase was incorporated in lipid membranes. The liposomal cellulase and free enzyme were examined in their hydrolytic activities to insoluble cellulose powder CC31 in the acetate buffer solution (pH 4.8) of 15 w/w% [Bmim][Cl] (1‐butyl‐3‐methylimidazolium chloride). The mean diameter and size distribution of cellulase‐containing liposome were practically unchanged under the above condition. The free cellulase was deactivated more rapidly than the liposomal cellulase in catalyzing the hydrolysis of 2.0 g/l CC31 at 45°C in the presence of [Bmim][Cl] for 48 h. The activities of liposomal and free cellulase to cellobiose as soluble substrate were less susceptible to [Bmim][Cl] than their cellulolytic activities to CC31, meaning that β‐glucosidase is relatively stable among the three enzyme components of cellulase. The rate of glucose production could be appreciably improved by the pretreatment of CC31 with [Bmim][Cl] alone at 120°C for 30 min followed by the liposomal cellulase‐catalyzed hydrolysis of the substrate at 45°C at the [Bmim][Cl] concentration of 15 w/w%. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1190–1196, 2013     

Enhanced activity and stability of ionic liquid-pretreated lipase

The activity and stability of Mucor javanicus lipase pretreated with various ionic liquids (ILs) were investigated. The results show that the activity and stability of lipase pretreated with ILs were higher than those of untreated lipase for the hydrolysis reaction in an aqueous medium. The activities of lipase pretreated with ILs such as [Bmim][PF₆], [Emim][Tf₂N], [Bmim][BF₄] and [Emim][BF₄] were 1.81, 1.66, 1.56 and 1.60 times higher than that of untreated lipase, respectively. Furthermore, activities of lipase in ILs were well maintained even after 7 days of incubation in ILs at 60 °C, while untreated lipase in phosphate buffer was fully inactivated only after 12 h of incubation at the same temperature. These results suggest that pretreatment of lipase with ILs might form IL-coated lipase which causes the structural change of lipase, and thus, enhances the activity and stability of lipase in aqueous solution.     

Mechanistic insights into the effect of imidazolium ionic liquid on lipid production by <Emphasis Type="Italic">Geotrichum fermentans</Emphasis>

Background

Ionic liquid (IL) pretreatment has emerged as a promising technique that enables complete utilization of lignocellulosic biomass for biofuel production. However, imidazolium IL has recently been shown to exhibit inhibitory effect on cell growth and product formation of industrial microbes, such as oleaginous microorganisms. To date, the mechanism of this inhibition remains largely unknown.

Results

In this study, the feasibility of [Bmim][OAc]-pretreated rice straw hydrolysate as a substrate for microbial lipid production by Geotrichum fermentans, also known as Trichosporon fermentans, was evaluated. The residual [Bmim][OAc] present in the hydrolysate caused a reduction in biomass and lipid content (43.6 and 28.1%, respectively) of G. fermentans, compared with those of the control (7.8 g/L and 52.6%, respectively). Seven imidazolium ILs, [Emim][DEP], [Emim]Cl, [Amim]Cl, [Bmim]Cl, [Bzmim]Cl, [Emim][OAc], and [Bmim][OAc], capable of efficient pretreatment of lignocellulosic biomass were tested for their effects on the cell growth and lipid accumulation of G. fermentans to better understand the impact of imidazolium IL on the lipid production. All the ILs tested inhibited the cell growth and lipid accumulation. In addition, both the cation and the anion of IL contributed to IL toxicity. The side chain of IL cations showed a clear impact on toxicity. On examining IL anions, [OAc]^? was found to be more toxic than those of [DEP]^? and Cl^?. IL exhibited its toxicity by inhibiting sugar consumption and key enzyme (malic enzyme and ATP-citrate lyase) activities of G. fermentans. Cell membrane permeability was also altered to different extents in the presence of various ILs. Scanning electron microscopy revealed that IL induces fibrous structure on the surface of G. fermentans cell, which might represent an adaptive mechanism of the yeast to IL.

Conclusions

This work gives some mechanistic insights into the impact of imidazolium IL on the cell growth and lipid accumulation of oleaginous yeast, which is important for IL integration in lignocellulosic biofuel production, especially for microbial lipid production.

     

Regenerating cellulose from ionic liquids for an accelerated enzymatic hydrolysis

The efficient conversion of lignocellulosic materials into fuel ethanol has become a research priority in producing affordable and renewable energy. The pretreatment of lignocelluloses is known to be key to the fast enzymatic hydrolysis of cellulose. Recently, certain ionic liquids (ILs) were found capable of dissolving more than 10wt% cellulose. Preliminary investigations [Dadi, A.P., Varanasi, S., Schall, C.A., 2006. Enhancement of cellulose saccharification kinetics using an ionic liquid pretreatment step. Biotechnol. Bioeng. 95, 904-910; Liu, L., Chen, H., 2006. Enzymatic hydrolysis of cellulose materials treated with ionic liquid [BMIM]Cl. Chin. Sci. Bull. 51, 2432-2436; Dadi, A.P., Schall, C.A., Varanasi, S., 2007. Mitigation of cellulose recalcitrance to enzymatic hydrolysis by ionic liquid pretreatment. Appl. Biochem. Biotechnol. 137-140, 407-421] suggest that celluloses regenerated from IL solutions are subject to faster saccharification than untreated substrates. These encouraging results offer the possibility of using ILs as alternative and non-volatile solvents for cellulose pretreatment. However, these studies are limited to two chloride-based ILs: (a) 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), which is a corrosive, toxic and extremely hygroscopic solid (m.p. approximately 70 degrees C), and (b) 1-allyl-3-methylimidazolium chloride ([AMIM]Cl), which is viscous and has a reactive side-chain. Therefore, more in-depth research involving other ILs is much needed to explore this promising pretreatment route. For this reason, we studied a number of chloride- and acetate-based ILs for cellulose regeneration, including several ILs newly developed in our laboratory. This will enable us to select inexpensive, efficient and environmentally benign solvents for processing cellulosic biomass. Our data confirm that all regenerated celluloses are less crystalline (58-75% lower) and more accessible to cellulase (>2 times) than untreated substrates. As a result, regenerated Avicel((R)) cellulose, filter paper and cotton were hydrolyzed 2-10 times faster than the respective untreated celluloses. A complete hydrolysis of Avicel((R)) cellulose could be achieved in 6h given the Trichoderma reesei cellulase/substrate ratio (w/w) of 3:20 at 50 degrees C. In addition, we observed that cellulase is more thermally stable (up to 60 degrees C) in the presence of regenerated cellulose. Furthermore, our systematic studies suggest that the presence of various ILs during the hydrolysis induced different degrees of cellulase inactivation. Therefore, a thorough removal of IL residues after cellulose regeneration is highly recommended, and a systematic investigation on this subject is much needed.     

Optimization of lipase-catalyzed glucose ester synthesis in ionic liquids

Lipase-catalyzed esterification of glucose with fatty acids in ionic liquids (ILs) mixture was investigated by using supersaturated glucose solution. The effect of ILs mixture ratio, substrate ratio, lipase content, and temperature on the activity and stability of lipase was also studied. The highest yield of sugar ester was obtained in a mixture of 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim][TfO]) and 1-methyl-3-octylimidazolium bis[(trifluoromethyl)-sulfonyl]amide ([Omim][Tf₂N]) with a volume ratio of 9:1, while Novozym 435 (Candida antarctica type B lipase immobilized on acrylic resin) showed the optimal stability and activity in a mixture of [Bmim][TfO] and [Omim][Tf₂N] with a 1:1 volume ratio. Reuse of lipase and ILs was successfully carried out at the optimized reaction conditions. After 5 times reuse of Novozym 435 and ILs, 78% of initial activity was remained.     

Ionic liquids as selectors for controlling the crystallization nucleation of hen egg white lysozyme

Ionic liquids (ILs) have biomaterial applications and are used for protein crystallization. The effect of two imidazolium-based ILs, 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) and 1,3-dimethylimidazolium iodide ([dmim]I), on the nucleation kinetics of lysozyme was investigated by determining the nucleation induction time, and nucleation parameters were evaluated. The values of interfacial tension calculated for solutions with added 30 g/L ILs [C₄mim]Cl and [dmim]I, and without added ILs were 99.03, 109.7, and 107.3 mJ/m², respectively. Compared with solutions without IL addition, the critical free energy change, size, and molecular number of critical nuclei decreased and the nucleation rate increased after the addition of [C₄mim]Cl. In contrast, the critical free energy change, size, and molecular number of critical nuclei increased and the nucleation rate decreased after the addition of [dmim]I. These new findings provide insights into controlling lysozyme crystallization separation, and present ILs as potentially useful additives for controlling the crystallization of macromolecules.     

Hydrolysis of cellulose in SO₃H-functionalized ionic liquids

Influence of acidity and structure of ionic liquids on microcrystalline cellulose (MCC) hydrolysis was investigated. MnCl₂-containing ionic liquids (ILs) were efficient catalysts and achieved MCC conversion rates of 91.2% and selectivities for 5-hydroxymethyl furfural (HMF), furfural and levulinic acid (LA) of 45.7%, 26.2% and 10.5%, respectively. X-ray diffractometry indicated that catalytic hydrolysis of MCC in ionic liquids resulted in the changes to MCC crystallinity and transformation of cellulose I into cellulose II. SO₃H-functionalized ionic liquids showed higher activities than non-functionalized ILs. The simplicity of the chemical transformation of cellulose provides a new approach for the use this polymer as raw material for renewable energy and chemical industries.     

Structural comparison and enhanced enzymatic hydrolysis of eucalyptus cellulose via pretreatment with different ionic liquids and catalysts

Eucalyptus was fractionated with mild alkaline process, and the obtained cellulose fraction was pretreated with various ionic liquids (ILs) to enhance the enzymatic saccharification. The results showed that the ILs used was efficient for the hydrolysis of cellulose, with the maximum total reducing sugars (TRS) yield over 80% at 50 °C. The regenerated cellulose substrate exhibited a significant improvement about 4.4–6.4 folds enhancement on saccharification rate during the first 4 h reaction. The crystallinity index (CrI) of cellulose via 1-ally-3-methylimidazolium ([AMIM]Cl) pretreatment was significantly decreased from 70.2% to 31.2%, resulting in structural change from cellulose I to cellulose II, which enabled the cellulase enzymes easier access to hydrolyze cellulose. However, 1-butyl-3methylimidazolium acesulfamate ([BMIM]Ace) pretreatment had no large effect on the CrI although a high conversion yield in glucose was obtained. The surface morphologies of the regenerated substrate which was pretreated via 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) showed more porous and incompact network of cellulose when compared with the untreated substrate. This result indicated a better accessibility by cellulases to the cellulose surface. Besides, a certain amount of catalysts such as MgCl₂ and H₂SO₄ could improve the rate of enzymatic saccharification.     

Effects of aurothiomalate and gold(III) complexes on spontaneous motility of isolated human oviduct

Organic gold complexes have different biological activity, depending on their potential for interactions with key functional molecules.The aim of this study was to investigate potential of several newly synthesized organic gold complexes to influence spontaneous motility of the Fallopian tubes.The effects of [Au(bipy)Cl(2)](+) (dichloride(2,2'-bipyridyl)aurate(III)-ion), aurothiomalate, [Au(DMSO)(2)Cl(2)]Cl and DMSO on spontaneous motility of Fallopian tubes were tested on the isolated tube segments in vitro. Aurothiomalate (from 2.9?×?10(-9) to 4.9?×?10(-4)?M/l), [Au(bipy)Cl(2)]Cl (from 3.3?×?10(-9) to 4.2?×?10(-5)?M/l) and DMSO (from 1.9?×?10(-8) to 1.0?×?10(-5)?M/l) did not affect spontaneous contractions of the isolated Fallopian tube ampulla, while [Au(DMSO)(2)Cl(2)]Cl (from 2.9?×?10(-9) to 4.2?×?10(-5)?M/l) showed concentration-dependent increase (stimulation) of spontaneous contractions of the isolated Fallopian tube isthmus, and remained without effect on the isolated ampulla.The drugs designed as organic gold complexes with weaker bonds between the gold itself and organic part of a molecule could adversely affect motility of the Fallopian tubes, and theoretically fertility of women taking such drugs in their reproductive age.     

Pseudo-enzymatic hydrolysis of 4-nitrophenyl myristate by human serum albumin

Most of the esterase properties of human serum albumin (HSA) are the result of multiple irreversible chemical modifications rather than turnover. The HSA-catalyzed hydrolysis of 4-nitrophenyl myristate (NphOMy) is consistent with the minimum three-step mechanism involving the acyl-enzyme intermediate HSA-OMy: Under all the experimental conditions, values of K(s) (= k(-1)/k(+1)), k(+2), and k(+2)/K(s) determined under conditions where [HSA] ≥ 5 × [NphOMy] and [NphOMy] ≥ 5 × [HSA] match very well each other. The deacylation process is rate limiting in catalysis (i.e., k(+3) < k(+2)) and k(-2)~k(-3)~0 s(-1). The pH dependence of k(+2)/K(s), k(+2), and K(s) reflects the acidic pK(a)-shift of one ionizing group from 8.9 ± 0.2 in NphOMy-free HSA to 6.8 ± 0.3 in the HSA:NphOMy adduct. The HSA-catalyzed hydrolysis of NphOMy is inhibited competitively by diazepam, indicating that Tyr411 is the active-site nucleophile.     

Catalytic conversion of cellulose to 5-hydroxymethyl furfural using acidic ionic liquids and co-catalyst

Efficient catalytic conversion of microcrystalline cellulose (MCC) to 5-hydroxymethyl furfural (HMF), is achieved using acidic ionic liquids (ILs) as the catalysts and metal salts as co-catalysts in the solvent of 1-ethyl-3-methylimidazo-lium acetate ([emim][Ac]). A series of acidic ILs has been synthesized and tested in conversion of MCC to HMF. The effect of reaction conditions, such as reaction time, temperature, catalyst dosage, metal salts, water dosage, Cu(2+) concentration and various acidic ILs are investigated in detail. The results show that CuCl(2) in 1-(4-sulfonic acid) butyl-3-methylimidazolium methyl sulfate ([C(4)SO(3)Hmim][CH(3)SO(3)]), is found to be an efficient catalyst for catalytic conversion of MCC to HMF, and 69.7% yield of HMF is obtained. A mechanism to explain the high activity of CuCl(2) in [C(4)SO(3)Hmim][CH(3)SO(3)] is proposed. To the best of our knowledge, this report first proposes that the Cu(2+) and [C(4)SO(3)Hmim][CH(3)SO(3)] show better catalytic performance in catalytic conversion of MCC to HMF.     

Synthetic procedures to monomethyl-platinum(II) complexes containing nitrogen ligands of biological relevance

The complex trans-bis(dimethylsulfoxide)chloromethylplatinum(II) (1) is fairly soluble in water, where it undergoes multiple equilibria involving the formation of geometrically distinct [Pt(H(2)O)(DMSO)Cl(CH(3))] aqua-species. On reacting an aqueous solution of 1 with monodentate nitrogen donor ligands L, such as pyridines or amines, two well distinct patterns of behavior can be recognized: (i) a single stage fast substitution of one DMSO by the entering ligand, yielding a complex of the type trans(C,N)-[Pt(DMSO)(L)Cl(CH(3))] which contains four different groups coordinated to the metal and which undergoes a slow conversion into its cis-isomer, (ii) a double substitution affording cationic complex ions of the type cis-[Pt(L)(2)(DMSO)(CH(3))](+). When this latter reaction is carried out using sterically hindered ligands, slow rotation of the bulk ligand around the Pt[bond]N bond allows for the identification of head-to-head and head-to-tail rotamers in solution, through (1)H NMR spectrometry. The addition of chloride anion to 1 leads to the anionic species cis-[Pt(DMSO)Cl(2)(CH(3))](-), where a molecule of DMSO still remains coordinated to the metal center, despite its quite fast rate of ligand exchange (k(exch) with free DMSO=12+/-1 s(-1)). The reaction of complex 1 with bidentate ligands, such as ethylenediamine (en) or simple amino acids, leads to the cationic species [Pt(en)(DMSO)(CH(3))](+) or to the neutral [Pt(DMSO)(N[bond]O)(CH(3))], (where N[bond]-O[double bond]GlyO(-), AlaO(-)).     

Intermolecular charge transfer involving tryptophan, tyrosine and three electron-bonded intermediates derived from methionine

Oxidation processes of radiation-generated three-electron-bonded intermediates derived from methionine Met2[S+...S] and Met[S...X] (X=Cl,Br) were investigated through reaction with tryptophan and tyrosine, using the optical pulse radiolysis method. Bimolecular rate constants have been measured for the reactions Met2[S+...S] with TrpH(k=3.8 x 10(8) dm3 mol-1 s-1 and k = 4.9 X 10(8) dm3 mol-1 s-1 at at ph 1 and 4.3, respectively) and Met2[S+...S] with tyrosine, k=3.8 x 10(7) dm3 mol-1 s-1. Rate constants for intermolecular transformation of Met[S...Br] and Met[S...Cl] into TrpH+. or Trp. were also estimated. They varied from 4.7 X 10(8) dm3 mol-1 s-1 (bromide species) to 1.0 X 10(9)dm3 mol-1 s-1 (chloride species). It has also been established azide radicals N-6, N.3 in contrast to dihalide radicals (X-2) do not form transients of Met[S...X] (X = N3)-type. However, oxidation of N-3 by Met2[S+...S] occurs with a bimolecular rate constant of 2.8 X 10(8) dm3 mol-1 s-1. These results are discussed in the light of some equilibria which have been proposed earlier for methionine-halide systems.     

Enhanced production of fructose palmitate by lipase-catalyzed esterification in ionic liquids

For the enhancement of enzyme activity, application of ultrasound irradiation on lipase-catalyzed esterification of fructose with palmitic acid in ionic liquids (ILs) mixture containing supersaturated fructose solution was investigated. In the mixture of [Bmim][TfO] and [Omim][Tf₂N] (1:1, v/v), 1.44 times higher enzyme activity (29.2 μmoL/min/g) was achieved under ultrasound irradiation. Besides, ultrasound irradiation enhanced enzyme stability in viscous ILs mixture. After 5 times reuse of Novozym 435 and ILs mixture, 84.4% of initial enzyme activity was remained under ultrasound irradiation, while the residual activity using magnetic stirring only method was 76.2%. These results show that enzymatic reaction in viscous ILs mixture under ultrasound irradiation is an effective method for enzyme activity, as well as, enzyme stability resulting in economic competitiveness of green process.     

Swelling and dissolution of cellulose. Part IV: Free floating cotton and wood fibres in ionic liquids

The objective of this paper is to investigate if the swelling and dissolution mechanisms found for aqueous solvents are valid for non-aqueous ones. Three different ionic liquids were used and the swelling and dissolution mechanisms were investigated by optical methods. Native and enzymatically treated cellulose fibres (cotton and wood fibres) are dipped into three ionic liquids (1-N-butyl-3-methylimidazolium chloride ([C4mim]+Cl−)/DMSO, allylmethylimidazolium bromide ([Amim]+Br−) and butenylmethylimidazolium bromide ([Bmim]+Br−). ([C4mim]+Cl−)/DMSO shows a swelling of cellulose by ballooning and then dissolution. ([Amim]+Br−) and ([Bmim]+Br−) show a homogeneous swelling but no dissolution. The swelling and dissolution mechanisms of cellulose in ionic liquids are similar to those observed in aqueous solvents. It indicates that the swelling and dissolution mechanisms are entirely due to the way cellulose fibres are structured, not depending on the type of solvent. The quality of the solvent is giving the type of mechanism.