Oscar Rodríguez

Ionic liquids as alternative co-solvents for laccase: Study of enzyme activity and stability

The activity and stability of commercial laccase (DeniLite base) in three different water soluble ionic liquids (ILs) (1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate, [emim][[MDEGSO4], 1-ethyl-3-methylimidazolium ethylsulfate, [emim][EtSO4], and 1-ethyl-3-methylimidazolium methanesulfonate, [emim][MeSO3]) have been studied and compared to that in two organic solvents (acetonitrile and dimethyl sulfoxide). Initial enzyme activities were similar among the ILs if the same conditions were used. A high reduction on initial enzyme activity was found with acidic pH (5.0). The effect of pH and solvent concentration on enzyme stability were investigated in more detail for 1 week. The enzyme maintained a high stability at pH 9.0 for all ILs tested. [emim][MDEGSO4] was the most promising IL for laccase with an activity loss of about 10% after 7 days of incubation. The kinetic studies in the presence of ABTS as substrate allowed to calculate the Michaelis- Menten parameters. Good agreement was found between experimental data and calculated values using the Michaelis-Menten mechanism, with a total average relative deviation of 2.1%.

Solubilities and diffusivities of water vapor in poly(methylmethacrylate), poly(2-hydroxyethylmethacrylate), poly(N-vinyl-2-pyrrolidone) and poly(acrylonitrile)

Abstract Sorption and diffusion data were obtained for water vapor in four different polymers: poly (methylmethacrylate) (PMMA), poly (2-hydroxyethylmethacrylate) (PHEMA), poly (N-vinyl-2-pyrrolidone) (PVP) and poly (acrylonitrile) (PAN) at 35 °C using a gravimetric sorption method. Highest sorption was for PVP, followed by PHEMA. PMMA and PAN sorbed very little water. All the polymers exhibit a BET type III sorption isotherm; the large upturn at high activity for PVP and PHEMA is probably due to plasticization of the polymers by water vapor. Sorption data were interpreted using Flory–Huggins theory and the Zimm and Lundberg cluster integral. Fickian diffusion is observed for PHEMA. For PVP, the fractional uptake Mt/M∞ is linear with the square root of the time up to Mt/M∞=0.6−0.8 for all water activities aw, but it shows a clear water sorption overshoot at aw=55.3% and aw=72.1%, probably due to macromolecular relaxation. PMMA sorption kinetics is also characterized by a maximum in the water uptake. The diffusion coefficient increases significantly with water concentration for PVP and PHEMA, weakly for PMMA, but it is independent of concentration for PAN.

Physical and equilibrium properties of diisopropyl ether+isopropyl alcohol+water system

Abstract Molar volume, isentropic compressibility, and molar refraction changes of mixing of the system diisopropyl ether (DIPE)+isopropyl alcohol (IPA)+water were determined at 298.15 K. These deviational properties were satisfactorily correlated with the composition data by means of Redlich–Kister polynomials. Tie line data have been determined at 298.15, 308.15, and 318.15 K for the ternary liquid–liquid equilibria, and were adequately correlated by means of the NRTL and UNIQUAC equation, and compared with results predicted by the UNIFAC method.

Solubility of Sugars and Sugar Alcohols in Ionic Liquids: Measurement and PC-SAFT Modeling

Biorefining processes using ionic liquids (ILs) require proper solubility data of biomass-based compounds in ILs, as well as an appropriate thermodynamic approach for the modeling of such data. Carbohydrates and their derivatives such as sugar alcohols represent a class of compounds that could play an important role in biorefining. Thus, in this work, the pure IL density and solubility of xylitol and sorbitol in five different ILs were measured between 288 and 339 K. The ILs under consideration were 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]), Aliquat dicyanamide, trihexyltetradecylphosphonium dicyanamide, and 1-ethyl-3-methylimidazolium trifluoroacetate. Comparison with the literature data was performed, showing good agreement. With the exception of [bmim][DCA], the solubility of these sugar alcohols in the other ILs is presented for the first time. The measured data as well as previously published solubility data of glucose and fructose in these ILs were modeled by means of PC-SAFT using a molecular-based associative approach for ILs. PC-SAFT was used in this work as it has shown to be applicable to model the solubility of xylitol and sorbitol in ILs (Paduszyński; et al. J. Phys. Chem. B 2013, 117, 7034-7046). For this purpose, three pure IL parameters were fitted to pure IL densities, activity coefficients of 1-propanol at infinite dilution in ILs, and/or xylitol solubility in ILs. This approach allows accurate modeling of the pure IL data and the mixture data with only one binary interaction parameter k(ij) between sugar and the IL or sugar alcohol and the IL. In cases where only the pure IL density and activity coefficients of 1-propanol at infinite dilution in ILs were used for the IL parameter estimation, the solubility of the sugars and sugar alcohols in the ILs could be predicted (k(ij) = 0 between sugar and the IL or sugar alcohol and the IL) with reasonable accuracy.

Studies of laccase from Trametes versicolor in aqueous solutions of several methylimidazolium ionic liquids

Stability and kinetic behavior of laccase from Trametes versicolor in the presence of several ionic liquids from the methylimidazolium family have been investigated. In general laccase stability diminished as the size of the alkylic substitute in the methylimidazolium ring increased. Higher concentrations of ionic liquids caused more destabilization than lower ones. Thus, low concentrations of [C(2)mim(+)][EtSO(4)(-)] allowed maintaining enzymatic stability. [C(4)mim(+)][Cl(-)] appeared to have a stabilizing effect on laccase, as little activity decay was observed within three weeks. Kinetic studies indicated that both [C(2)mim(+)][EtSO(4)(-)] and [C(4)mim(+)][Cl(-)] inhibited laccase activity, although 10-fold more [C(2)mim(+)][EtSO(4)(-)] than [C(4)mim(+)][Cl(-)] was required to cause the same degree of inhibition. A kinetic model was developed to represent the experimental data.

Characterization and interfacial properties of the surfactant ionic liquid 1-dodecyl-3-methyl imidazolium acetate for enhanced oil recovery

The use of surfactant ionic liquids has recently gained attention for surfactant-based enhanced oil recovery. The introduction of the surfactant character in ionic liquids combines interesting properties of both types of chemicals, which are relevant for this application. An imidazolium-based surfactant has been synthesized combined with an acetate counter-ion. The aggregation effects in water were evaluated by means of surface tension and electrical conductivity. The dynamic interfacial tensions between the aqueous solutions of the surfactant ionic liquid and crude oil (Saharan blend) were evaluated by the spinning drop method. The effect of different variables has been analyzed, namely the concentration of surfactant ionic liquid, electrolytes (NaCl) and alkalis (NaOH, Na2CO3), and temperature. Formulations of ionic liquids and alkalis were tested for the first time for enhanced oil recovery. The results obtained here improve significantly (at least one order of magnitude, most often two) previous results obtained up to now solely with ionic liquids.

New Generations of Ionic Liquids Applied to Enzymatic Biocatalysis

Ionic liquids are salts in a liquid state, combinations of cations and anions that are liquid at temperatures below 100 oC. Thus, they have been called Room-Temperature Ionic Liquids (RTILs, or just ILs) in order to differentiate them from traditional salts, which melt at much higher temperatures and receive the name of “molten salts”. In contrast to conventional or‐ ganic solvents, ILs usually have extremely low volatility. Indeed, vapor pressures for ILs are scarce in the literature exactly because they are extremely low (< 1 Pa) and have to be ob‐ tained at high temperatures (400-500 K) [1]. For this ”negligible” vapor pressure, ILs are of‐ ten said to be “green“ solvents when compared to traditional, environmentally harmful volatile organic compounds (VOCs). A big goal in the use of ILs in enzymatic reactions is the replacement of VOCs by ILs. In addition, ILs have other potential advantageous proper‐ ties such as reasonable thermal stability; ability to dissolve a wide range of organic, inorgan‐ ic and organometallic compounds; controlled miscibility with organic solvents (which is relevant for applications in biphasic systems) among others. All these properties make them very attractive non-aqueous solvents for biocatalysis. As they have been extensively descri‐ bed, ILs offer new possibilities for the application of solvent engineering to enzymatic reac‐ tions. Biocatalysis with ILs as reaction medium was first showed in the beginning of 2000 [2-4]. During the last decade, ILs have fast increased their attention as reaction media for en‐ zymes with some remarkable results [2-4]. The advantage of using ILs in enzymatic biocatal‐ ysis, as compared to VOCs, is the enhancement in the solubility of substrates or products without inactivation of the enzymes, high conversion rates and high activity and stability [5]. ILs are also being used as co-solvents in aqueous biocatalytic reactions, since ILs help to

Dissolution and fractionation of nut shells in ionic liquids.

The aim of this work was to study the dissolution of raw peanut and chestnut shells in ionic liquids. Dissolution of raw biomass up to 7wt% was achieved under optimized operatory conditions. Quantification of polysaccharides dissolved through quantitative 13Cq NMR revealed extractions of the cellulosic material to ionic liquids as high as 87%. Regeneration experiments using an antisolvent mixture allowed to recover the cellulosic material and the ionic liquid. The overall mass balance presented very low loss rates (<8%), recoveries of 75% and 95% of cellulosic material from peanut and chestnut shells, respectively, and the recovery of more than 95% of the ionic liquid in both cases. These results show the high potential of using nut shells and ionic liquids for biorefining purposes. Moreover, high recovery of ionic liquids favors the process from an economical point of view.

Stability and kinetic behavior of immobilized laccase from Myceliophthora thermophila in the presence of the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate.

The use of ionic liquids (ILs) as reaction media for enzymatic reactions has increased their potential because they can improve enzyme activity and stability. Kinetic and stability properties of immobilized commercial laccase from Myceliophthora thermophila in the water‐soluble IL 1‐ethyl‐3‐methylimidazolium ethylsulfate ([emim][EtSO4]) have been studied and compared with free laccase. Laccase immobilization was carried out by covalent binding on glyoxyl–agarose beads. The immobilization yield was 100%, and the activity was totally recovered. The Michaelis‐Menten model fitted well to the kinetic data of enzymatic oxidation of a model substrate in the presence of the IL [emim][EtSO4]. When concentration of the IL was augmented, the values of Vmax for free and immobilized laccases showed an increase and slight decrease, respectively. The laccase–glyoxyl–agarose derivative improved the laccase stability in comparison with the free laccase regarding the enzymatic inactivation in [emim][EtSO4]. The stability of both free and immobilized laccase was slightly affected by small amounts of IL (<50%). A high concentration of the IL (75%) produced a large inactivation of free laccase. However, immobilization prevented deactivation beyond 50%. Free and immobilized laccase showed a first‐order thermal inactivation profile between 55 and 70°C in the presence of the IL [emim][EtSO4]. Finally, thermal stability was scarcely affected by the presence of the IL.

Modeling of Ionic Liquid Systems: Phase Equilibria and Physical Properties

Ionic liquids (ILs) are a class of salts with a melting temperature below 100 °C, and the study of these compounds is considered priority by the U.S. Environmental Protection Agency. Due to their specific properties, which can be adjusted by changing either the cation or the anion, ILs have received great attention by the scientific community as potential replace‐ ments for volatile organic solvents (VOCs), and nowadays, ILs are starting to leave academ‐ ic labs and find their way into a wide variety of industrial applications [1]. For example, ILs are used for the dispersion of nano-materials at IOLITEC, Air Products uses ILs instead of pressurized cylinders as a transport medium for reactive gases, ION Engineering is com‐ mercializing technology using ILs and amines for CO2 capture and natural gas sweetening, and many others.