Lipase-catalyzed synthesis of fatty acid sugar ester using extremely supersaturated sugar solution in ionic liquids

Artificial nanotransport systems inspired by intracellular transport processes have been investigated for over a decade using the motor protein kinesin and microtubules. However, only unidirectional cargo transport has been achieved for the purpose of nanotransport in a microfluidic system. Here, we demonstrate bidirectional nanotransport by integrating kinesin and dynein motor proteins. Our molecular system allows microtubule orientation of either polarity in a microfluidic channel to construct a transport track. Each motor protein acts as a nanoactuators that transports microspheres in opposite directions determined by the polarity of the oriented microtubules: kinesin-coated microspheres move toward the plus end of microtubules, whereas dynein-coated microspheres move toward the minus end. We demonstrate both unidirectional and bidirectional transport using kinesin- and dynein-coated microspheres on microtubules oriented and glutaraldehyde-immobilized in a microfluidic channel. Tracking and statistical analysis of microsphere movement demonstrate that 87-98% of microspheres move in the designated direction at a mean velocity of 0.22-0.28 microm/s for kinesin-coated microspheres and 0.34-0.39 microm/s for dynein-coated microspheres. This bidirectional nanotransport goes beyond conventional unidirectional transport to achieve more complex artificial nanotransport in vitro.     

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.     

Optimization of lipase-catalyzed glucose fatty acid ester synthesis in a two-phase system containing ionic liquids and t-BuOH

Selective lipase-catalyzed synthesis of glucose fatty acid esters in two-phase systems consisting of an ionic liquid (1-butyl-3-methyl imidazolium tetrafluoroborate [BMIM][BF₄] or 1-butyl-3-methyl imidazolium hexafluorophosphate [BMIM][PF₆]) and t-butanol as organic solvent was investigated. The best enzyme was commercially available lipase B from Candida antarctica (CAL-B), but also lipase from Thermomyces lanuginosa (TLL) gave good conversion. After thorough optimization of several reaction conditions (chain-length and type of acyl donor, temperature, reaction time, percentage of co-solvent) conversions up to 60% could be achieved using fatty acid vinyl ester as acyl donors in [BMIM][PF₆] in the presence of 40% t-BuOH with CAL-B at 60 °C.     

Lipase-catalyzed glycerolysis in ionic liquids directed towards diglyceride synthesis

This work examined the lipase-catalyzed glycerolysis of triglycerides (TG) in a list of commercially available ionic liquids (ILs) with varied cations and anions for the purpose of developing an efficient reaction protocol for diglyceride (DG) production and to understand whether ILs could assist the reaction systems. The reaction performances (reaction rate, TG conversion and DG yield) were found to be greatly dependent on the structure and property of ILs. The reactions in [TOMA·Tf₂N] and Ammoeng 120 produced comparable yield of DG to those most efficient conventional systems but with less by-products. Temperature enhancement generally yields positive effect on the conversion of TG, which was much more significant for the ILs with high viscosity. Unusually, increasing substrate concentration in many types of ILs led to enhanced conversion and yield; whereas the increase of glycerol/TG ratio resulted in a dramatic improvement of the reactions in the ILs with strong acidic anions. This work also sorted out some promising IL candidates, namely the ILs with good DG formation selectivity and the ones being able to achieve high TG conversion, which offered possibility to design binary IL systems. Overall, this study presented the first attempt concerning evaluation and characterization of lipase-catalyzed glycerolysis of TG for DG production in IL-based systems.     

Feruloyl esterase-catalysed synthesis of glycerol sinapate using ionic liquids mixtures

The ability of a feruloyl esterase (AnFaeA), either in free or immobilised (cross-linked enzyme aggregates) form, to catalyse the esterification of glycerol, a major by-product of the biodiesel industry, with sinapic acid was studied in four hexafluorophosphate anion-containing ionic liquids: ([Bmim][PF(6)], [Omim][PF(6)], [C(2)OHmim][PF(6)] and [C(5)O(2)mim][PF(6)]). Such ionic liquids are considered 'green' reaction systems. The synthetic reaction was optimised in [C(2)OHmim][PF(6)] and the highest conversion yield was 72.5+/-2.1%, while, at the same reaction conditions in [C(5)O(2)mim] [PF(6)], a similar conversion yield was obtained (76.7+/-1.5%). AnFaeA was active in its free and immobilised form, with the latter retaining a part of its synthetic activity after 5 consecutive 24h-period reaction cycles. Sinapic acid was esterified to one of the primary hydroxyl groups of glycerol and retained, after esterification, 63.1+/-0.3% and 89.5+/-1.1% of its antioxidant activity against low-density lipoprotein oxidation, when added at concentrations of 10 and 60muM, respectively, in the assay mixture.     

Effect of ionic liquids on enzymatic synthesis of caffeic acid phenethyl ester

Although caffeic acid phenethyl ester (CAPE), an active flavonoid, plays an important role in the antioxidant activity of honeybee propolis, the isolation of CAPE from honeybee propolis is time-consuming due to wide variety of impurities present. Therefore, biochemical method to synthesize CAPE was investigated in this study. Since ionic liquids (ILs) possess some unique characteristics as appreciated alternatives to conventional solvents for certain biotransformation, the effect of ILs as reaction media for enzymatic synthesis of CAPE was assessed. Several factors including substrate molar ratio, and reaction temperature affecting the conversion yield of lipase-catalyzed CAPE synthesis were also investigated. Reaction yields were significantly higher in hydrophobic ILs than in hydrophilic ILs (almost zero). Among nine hydrophobic ILs tested, the highest conversion of synthetic reaction was obtained in 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([Emim][Tf(2)N]). A reaction temperature of 70 °C was found to give high conversion. In addition, optimal substrate molar ratio between phenethyl alcohol and caffeic acid (CA) was decreased significantly from 92:1 to 30:1 when ILs were used instead of isooctane.     

Optimization of lipase-catalyzed synthesis of caffeic acid phenethyl ester in ionic liquids by response surface methodology

Lipase-catalyzed caffeic acid phenethyl ester (CAPE) synthesis in ionic liquid, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([Emim][Tf₂N]), was investigated in this study. The effects of several reaction conditions, including reaction time, reaction temperature, substrate molar ratio of phenethyl alcohol to caffeic acid (CA), and weight ratio of enzyme to CA, on CAPE yield were examined. In a single parameter study, the highest CAPE yield in [Emim][Tf₂N] was obtained at 70 °C with a substrate molar ratio of 30:1 and weight ratio of enzyme to CA of 15:1. Based on these results, response surface methodology (RSM) with a 3-level-4-factor central composite rotatable design (CCRD) was adopted to evaluate enzymatic synthesis of CAPE in [Emim][Tf₂N]. The four major factors were reaction time (36–60 h), reaction temperature (65–75 °C), substrate molar ratio of phenethyl alcohol to CA (20:1–40:1), and weight ratio of enzyme to CA (10:1–20:1). A quadratic equation model was used to analyze the experimental data at a 95 % confidence level (p < 0.05). A maximum conversion yield of 99.8 % was obtained under the optimized reaction conditions [60 h, 73.7 °C, substrate molar ratio of phenethyl alcohol to CA (27.1:1), and weight ratio of enzyme to CA (17.8:1)] established by our statistical method, whereas the experimental conversion yield was 96.6 ± 2 %.     

Over-stabilization of Candida antarctica lipase B by ionic liquids in ester synthesis

Four different ionic liquids, based on dialkylimidazolium cations associated with perfluorinated and bis(trifluoromethyl)sulfonyl amide anions were used as reaction media for butyl butyrate synthesis catalyzed by free Candida antarctica lipase B at 2% (v/v) water content and 50 °C. Lipase had enhanced synthetic activity in all ionic liquids in comparison with two organic solvents (hexane, and 1-butanol), the enhanced activity being related to the increase in polarity of ionic liquids. The continuous operation of lipase with all the assayed ionic liquids showed over-stabilization of the enzyme. The reuse of free lipase in 1-butyl-3-methylimidazolium hexafluorophosphate in continuous operation cycles showed a half-life time 2300 times greater than that observed when the enzyme was incubated in the absence of substrate (3.2 h), and a selectivity higher than 90%.     

Oligonucleotide synthesis using ionic liquids as soluble supports

The continuing evolution of the methodology for the solution-phase synthesis of oligonucleotides using soluble ionic tags as handles for easy purification is described. This methodology may provide a more cost efficient route for the large scale synthesis of oligonucleotides.     

Kinetic study on the enzymatic resolution of homophenylalanine ester using ionic liquids

Two ionic liquids (ILs) were investigated as novel media for the enzymatic resolution of amino acid ester to obtain enantiomeric amino acid homophenylalanine. The effects of solvent nature, polarity, and concentration on the kinetic resolution were investigated. With change in solvent concentration, a systematic study shows that an improved enzyme activity can be obtained by adjusting these solvent parameters.     

pH-imprinted lipase catalyzed synthesis of dextran fatty acid ester

The application of enzymatic catalysis for the synthesis of polysaccharide-based surfactants was investigated. The polysaccharide dextran, a neutral bacterial polysaccharide consisting of -1,6 linked glucose units, was chemically modified by the attachment of hydrophobic groups through a transesterification reaction with a vinyl decanoate. A screening of commercially available lipases and protease for the synthesis of amphiphilic polysaccharides in DMSO suggested that lipase AY from Candida rugosa modified dextran T-40 with vinyl decanoate at the highest conversion. A pH-adjustment in a phosphate buffer at pH 7.5 prior to use is crucial to make this enzyme active in DMSO. The effect of enzyme concentration and mole ratio of fatty ester to dextran T-40 on the conversion and the rate of reaction were studied. Finally, investigation of the kinetics and regioselectivity of lipase AY-catalyzed modification offer a possibility to regulate the position and the extent of hydrophobic group attached to dextran. These two properties are fundamental for controlling the physico-chemical properties of the final polymeric surfactants.     

Lipase-catalyzed synthesis of 6-O-vinylacetyl glucose in acetonitrile

6-O-Vinylacetyl glucose was synthesized with an immobilized lipase using vinylacetic acid and glucose in water-miscible organic solvents, of which acetonitrile gave the highest conversion of 35% at 50 mM glucose and 600 mM vinylacetic acid. The addition of 3Å molecular sieves at 60 mg ml^–1 increased the conversion to 74%. The product, 6-O-vinylacetyl glucose, was polymerized to yield a water-soluble polymer with a molecular mass of about 5000.     

Lipase-catalyzed synthesis of hyperbranched poly-l-lactide in an ionic liquid

Hyperbranched poly-l-lactides have been synthesized by eROP in [C₄MIM][PF₆] media. The bis(hydroxymethyl)butyric acid molecule was used as the AB₂ core co-monomer and immobilized lipase B from Candida antarctica as biocatalyst. The degree of branching could be controlled by the reaction conditions, with the maximum achieved being 0.21. The successful achievement of the hyperbranched structure is attributed to the high solvent power of substrates and products in the ionic liquid besides sustained lipase activity.     

On the nature of ionic liquids and their effects on lipases that catalyze ester synthesis

Free and immobilized lipases from Candida antarctica (CALA and CALB), Thermomyces lanuginosus (TLL) and Rhizomucor miehei (RML) were used as catalysts in the synthesis of butyl propionate by transesterification in reaction media consisting in nine different ionic liquids. Enzyme activities were clearly dependent on the nature of the ions, the results being improving as the alkyl chain length of the imidazolium cation increased, and as a function of the type of anion ([PF₆], [BF₄] or [ethylsulphate]). The best synthetic activity (655.5 U/mg protein at 40 °C) was obtained when free CALB were assayed in the water-miscible IL cocosalkyl pentaethoxy methyl ammonium methosulfate ([CPMA][MS]), and was clearly related with the water content of the medium. The synthetic activity of free CALB in [CPMA][MS] was enhanced with the increase in temperature, while practically no effect was obtained for TLL. The ability of free CALB to synthesize aliphatic esters of different alkyl chain lengths, using different alkyl vinyl esters and 1-alkanols as substrates, was also studied in [CPMA][MS], the best results (4500 U/mg protein) being obtained for the synthesis of hexyl butyrate.     

Lipase-catalysed synthesis of glucose fatty acid esters in tert-butanol

Synthesis of 6-O-acylate--d-glycopyranose from underivatised substrates in anhydrous tert-butanol was achieved using immobilised lipases from Candida antarctica and Mucor miehei. Except for acetic acid, the initial reaction rates with the C. antarctica lipase were independent of acyl donor chain lengths and in a range of 3.9±0.4 mol glucose converted min–1 g enzyme preparation. The catalytic activity of the M. miehei lipase increased with increasing acyl donor chain length with a maximum for stearic acid of 0.45 mol min–1 g. Using maltose as substrate, the catalytic activity decreased by a factor of 48 and 20 with the lipase from C. antarctica and M. miehei, respectively, while with maltotriose no reaction was observed.     

Lipase-catalyzed synthesis of chlorogenate fatty esters in solvent-free medium

Chlorogenic acid (5-caffeoylquinic acid or 5-CQA) is an hydrophilic phenolic compound with antioxidant properties. Because of its high polarity, its antioxidant properties may be altered when formulated in oil based food or cosmetic preparations. Therefore, there is an interest in trying to enhance its hydrophobicity by grafting of an aliphatic chain. Such lipophilization reactions can be generally achieved through enzymatic catalysis. Our study consisted in synthesizing fatty cholorogenate esters in a two steps reaction. Firstly, 5-CQA was chemically esterified by methanol using an Amberlite IR120 H resin to obtain methyl chlorogenate that is more soluble in the fatty alcohols than 5-CQA. Secondly, this chlorogenate intermediate was transesterified with fatty alcohols of various chain lengths (C₄, C₈, C₁₂, or C₁₆) in the presence of Candida antarctica B lipase. Under optimal reaction conditions (a_w = 0.05; 5% (w/w) of biocatalyst), the transesterification rates were until two-fold higher than in the direct lipase-catalyzed esterification of chlorogenic acid by the same alcohols. The two-step reaction overall yield was between 61 and 93% depending on the alcohol chain length, whereas it was 40–60% for the direct esterification with the same alcohols.     

Lipase-catalyzed regioselective preparation of fatty acid esters of hydrocortisone

A series of fatty acid derivatives of hydrocortisone has been prepared by an enzymatic methodology. Nine 21-monoacyl products and one 3,11,17-triacetyl derivative, nine of them novel compounds, were obtained in a highly regioselective way through lipase-catalyzed esterification, transesterification and alcoholysis reactions. The influence of various reaction parameters such as acylating agent: substrate ratio, enzyme: substrate ratio, solvent, temperature and nature of acylating agent and alcohol was evaluated. Among the tested lipases, Candida antarctica lipase appeared to be the most appropriate and showed a high efficient behavior especially in a one-pot transesterification. The advantages presented by this methodology, such as mild reaction conditions and low environmental impact, make the biocatalysis a convenient way to prepare acyl derivatives of hydrocortisone. These lipophilic compounds are potential products in the pharmaceutical industry.     

Chiral ionic liquids: synthesis and applications

Over the last ten years, interest and publications involving ionic liquids have expanded exponentially. Thus far, they have predominantly been used in organic synthesis and separations. However, their use is rapidly expanding into other areas of science and technology. Research involving chiral ionic liquids has been much more limited and only recently has come to the forefront. In this work, we review the synthesis of chiral ionic liquids and their use. Today, this is an area of research that is poised for rapid development and expansion.     

Synthesis of biologically stable gold nanoparticles using imidazolium-based amino acid ionic liquids

A novel double-step reduction procedure for the synthesis of gold nanoparticles (AuNPs) using amino acid ionic liquids has been employed. 1-Dodecyl-3-methyl imidazolium tryptophan ([C(12)mim]Trp) and 1-ethyl-3-methyl imidazolium tryptophan ([C(2)mim]Trp) were used for this synthesis. The synthesized AuNPs were characterized by UV-vis spectroscopy, transmission electron microscopy and dynamic light scattering. The behavior of these AuNPs were also probed in a biological media. It was proven that AuNPs synthesized at [C(12)mim]Trp have more stability than AuNPs synthesized at [C(2)mim]Trp due to the longer alkyl chain of the imidazolium moiety. The solubility test shows that the resultant AuNPs have a hydrophilic nature. Finally, it was seen that due to the presence of a biomolecule, namely Trp, in the structure of AuNPs protecting shell, higher stability and biocompatibility was achieved in the biological media.     

Isoamyl acetate synthesis in imidazolium-based ionic liquids using packed bed enzyme microreactor

The acylation of isoamyl alcohol with acetic anhydride catalyzed by immobilized Candida antarctica lipase B was studied in ionic liquids (ILs) based on quaternary imidazolium cations with alkyl, alkenyl, alkynyl, benzyl, alkoxyl or N-aminopropyl side chains. Among the tested ILs, the highest enzyme activity together with the highest isoamyl acetate yield were obtained in [C₇mmim][Tf₂N]. No loss of lipase B activity was observed during one-month incubation in this hydrophobic IL without the presence of substrates. Isoamyl acetate synthesis using [C₇mmim][Tf₂N] as solvent was further studied in a continuously operated miniaturized enzymatic packed bed reactor at various flow rates and temperatures. Up to 92% isoamyl acetate yield could be obtained within 15 min by using 0.5 M acetic anhydride and 1.5 M isoamyl alcohol inlet concentrations at 55 °C, corresponding to the volumetric productivity of 61 mmol l^?1 min^?1, which to the best of our knowledge is the highest reported so far for this reaction. No decrease in productivity was experienced during the subsequent runs of continuous microbioreactor operation performed within 14 consecutive days. The benefits of reactor miniaturization along with the green solvent application were therefore successfully exploited for the development of a sustainable flavour ester production.