Cosolvent Concentration Research Articles

Controlled transition of microcapsules from coil conformation to globule during the expansion of the pulse jet of nanoparticle suspension of TiO2 in supercritical (CO2) polyethylene glycol solution

The process of microencapsulation of titanium dioxide nanoparticles during the expansion of a supersonic jet of TiO2 suspension in a solution of polyethylene glycol (PEG 8000) in supercritical CO2 into a vacuum and background gas (helium) has been studied experimentally. The dependence of the position of the microcapsule transition point on the jet axis from the coil to a globular conformation on the temperature in the reactor and on the pressure of the background gas at different co-solvent concentrations has been established. A re-entrant (globule-coil) transition has been recorded at a greater distance from the nozzle exit than the point of collapse.

Experimental determination of second virial coefficients by small-angle X-ray scattering: a problem revisited

This investigation examines the validity of employing single-solute theory to interpret SAXS measurements on buffered protein solutions-the current practice despite the necessity to regard the buffer components as additional non-scattering solutes rather than as part of the solvent. The present study of bovine serum albumin in phosphate-buffered saline supplemented with 20-100g/L sucrose as small cosolute has certainly verified the prediction that the experimentally obtained second virial coefficient should contain protein-cosolute contributions. Nevertheless, the second virial coefficient determined for protein solutions supplemented with high cosolute concentrations on the basis of single-solute theory remains a valid means for identifying conditions conducive to protein crystallization, because the return of a slightly negative second virial coefficient based on single-solute theory [Formula: see text] still establishes the existence of slightly associative interactions between protein molecules, irrespective of the molecular source-protein self-interactions and/or protein-cosolute contributions.

Effect of Temperature on the Cononsolvency of Poly(N-isopropylacrylamide) (PNIPAM) in Aqueous 1-Propanol

The wide range of applications of poly(N-isopropylacrylamide) (PNIPAM) is based on the temperature dependence of its coil-to-globule transition, which strongly relies on the solvent. Here, we focus on the cononsolvency effect of PNIPAM oligomers in aqueous 1-propanol mixtures that is studied by molecular dynamics simulations of single chains and membrane-like arrangements. The complete phase diagram is sketched from the radius of gyration of the simulated oligomers, and it is compared to that obtained from the hydrodynamic radius of PNIPAM microgels, finding a good agreement. At the water-rich region, the decrease of the lower critical solution temperature (LCST) with increasing cosolvent concentration is independent of the polymer length and concentration. In this region, the radius of gyration of our simulated oligomer is strongly temperature dependent and a coil–globule transition temperature is easily captured. Conversely, at the alcohol-rich region, simulations show a monotonically increasing radius of gyration of the oligomer with alcohol concentration, a radius that is practically independent of temperature. This finding is in line with a polymer phase separation, showing an upper critical solution temperature (UCST) for a small cosolvent concentration window, which depends on the polymer length and concentration. Hence, in this case, polymer–polymer effective interactions are key to phase separation instead of its single chain conformation, contrasting with the coil–globule transition. Indeed, we find a soft-coil like structure for the simulated oligomer around a propanol molar fraction of 0.24, which is close to the mixture composition where the UCST phase transition is detected. Finally, in line with an UCST scenario, our simulated membrane turns unstable at high temperature and alcohol concentration.

Supercritical fluid extraction in isolation of cyclitols and sugars from chamomile flowers.

The aim of the present study was to develop an optimization procedure for supercritical fluid extraction parameters, in order to obtain the highest possible yield of sugars and cyclitols from plant material. Response surface methodology based on Box-Behnken design was applied to evaluate the effect of: temperature (40, 60, 80°C), pressure (100, 200, 300bar), and co-solvent (methanol) percentage (20, 25, 30%). As a result of the optimization process, we found that the highest amount of sugars (15.02 mg/gof dried material) and cyclitols (0.86 mg/g of dried material) was obtained when the following parameters were applied: 80°C, 228 bar, and 30% of methanol. Moreover, co-solvent concentration and temperature had a higher influence onto the obtained amounts compared with the pressure.

Non-linearity in dipolar solvation dynamics in water-ethanol mixture: Composition dependence of free energy landscape.

Liquid mixtures of water and amphiphilic solutes exhibit a string of yet unexplained anomalies in the low cosolvent (or solute) concentration regime. Among such solutions, mixtures of water and ethanol stand out for their distinctive role in biology. We study, in this binary mixture, the composition dependent difference between the nonequilibrium and the equilibrium solvent responses to a dipolar probe indole in the low-to-intermediate concentration regime. The usually employed linear response formalism seems to break down at low ethanol concentration. The nonequilibrium solvent response is particularly different from that of the equilibrium solvent response in the concentration (xEtOH) between 0.07 and 0.12. We introduce an order parameter in terms of the changing local composition at the nearest neighbor separation. This order parameter captures the anomalies faithfully. The anomalies are seen to arise from a competition between hydrophilic and hydrophobic interactions and are most prominent at the small-to-intermediate length scale. We attempt to rationalize the results in terms of a composition dependent free energy length scale.

Effect of H-bonding effect on reverse micelle extraction of bovine serum albumin

The extraction of bovine serum albumin (BSA) was carried out by using reverse micelles formed by cationic surfactant dodecyltrimethylammonium bromide (DTAB), N-dodecyl-N-2-hydroxyethyl-N,N-dimethyl-ammonium bromide (HDAB) and N-dodecyl-N,N-2-dihydroxyethyl-N-methyl ammonium bromide (DHAB). The factors like pH, surfactant concentration, salt concentration, and co-solvent concentration were investigated. The good maintenance of the secondary structure of BSA after extraction was confirmed by UV spectra. A wider aqueous phase pH range was achieved and less amount of surfactant was needed on efficient forward extraction when hydroxyethyl group was presented in the surfactants’ head group, suggesting an important role of H-bonding effect. At lower pH or high salt concentration, reasonable backward extraction efficiencies were observed in all systems. The little difference of the head group of these surfactants resulted in quite different performance in the extraction process, which provided deeper insight on the effect of fine adjustment of surfactant structure on protein extraction.

Green preparation process using methyl lactate for cellulose-acetate-based nanofiltration membranes

Cellulose acetate (CA) membranes were prepared via phase inversion using methyl lactate as a green solvent and 2-methyltetrahydrofuran as a green co-solvent with or without evaporation period prior to immersion of the cast polymer solution in the coagulation bath. The membrane morphologies were characterized using scanning electron microscopy and the membrane performance was screened using aqueous rose bengal (RB) or MgSO4 feed solutions. With CA-concentration in the casting solution increasing from 8 to 20 wt%, RB-rejection increased from 31.1% to 99.5%, while permeance decreased from 32.0 to 2.4 L/m2·h·bar. CA-membranes cast from a 10 wt% polymer solution had a RB-rejection higher than 92.0% with good permeance around 3.5 L/m2·h·bar at low co-solvent concentration (10 wt%). However, with increased co-solvent concentration (i.e. 30–50 wt%), both rejection and permeance surprisingly decreased, regardless evaporation time. For membranes cast from a 20 wt% polymer solution, RB-rejection remained around 99% and permeance decreased with increasing co-solvent concentration in the casting solution. MgSO4 rejection was around 93.0% for membranes cast from a 20 wt% polymer solution with 10 wt% co-solvent without evaporation (at a flux of 1.0 L/m2·h·bar) and 96.5% with evaporation at a flux of 1.3 L/m2·h·bar.

The Effect of Additives on the Viscosity and Dissolution of Cellulose in Tetrabutylphosphonium Hydroxide.

An electrolyte solution of tetrabutylphosphonium hydroxide (TBPH) in water can dissolve over 20 wt % of cellulose in minutes and therefore constitutes a promising alternative green solvent system compared to known imidazolium- or dimethylacetamide-based systems. Overcoming the disadvantage of the extremely high viscosity of TBPH/cellulose solutions can facilitate their use for various applications. In this study, the application of cosolvents for the reduction, and thus adjustability, of the viscosity is addressed. Even well-known antisolvents can be easily deployed, resulting in a dramatic drop in viscosity. High concentrations of cosolvents (excluding ethanol) are tolerated without precipitation of the dissolved cellulose. Furthermore, the effect of the cosolvents on the additional dissolution of cellulose is discussed. The amount of dissolved cellulose is quantified by 13 C NMR spectroscopy.

Supercritical extraction with carbon dioxide and co-solvent from Leptocarpha rivularis

The aim of this work was to investigate the effect of temperature (40–60 °C), pressure (10–20 MPa) and co-solvent concentration (0–2 wt.%) on extraction yield from L. rivularis leaves using ethanol-modified supercritical carbon dioxide. Extraction assays were carried out in a Process Development Unit using a Box-Behnken design. Extraction yield ranged from 14.7 to 53.1 g/kg dry substrate, with the highest value being achieved at 60 °C, 20 MPa and 2 wt.%. The pressure and the co-solvent concentration had a significant effect on extract recovery. To complement the analysis, recognized bioactive compounds, such as the flavonoids quercetin, kaempferol and resveratrol and the terpenes α-thujone, β-caryophyllene and caryophyllene oxide were quantified in the selected extract. Antioxidant activity and the inhibition of key enzymes linked to diabetes mellitus (α-amylase and α-glucosidase) were exhibited by the extract. These results demonstrate the potential benefit of L. rivularis extract for human health.

Conformational transitions of poly(ethylene oxide) in supersonic jets of supercritical CO2

The supersonic gas jets are proposed as a tool for researching conformational transitions of polymer chain molecules in untraditional (supercritical) fluids. The working fluid of the jet and the solvent for polymers in this case are supercritical fluids. This method is used for the microencapsulation of TiO2 nanoparticles in poly(ethylene oxide) (Mv = 8,000,000). The suspension of TiO2 nanoparticles in the polymer solution in supercritical carbon dioxide is expanded into vacuum or background gas. The substrate of the jet resulting from rapid expansion was investigated by SEM. Along the axis of the jet, zones of coil-globule-coil transitions were found. The position and extent of these zones can be controlled by varying the conditions in the reactor (pressure, temperature, co-solvent concentration) and background gas pressure in the nozzle chamber.

Solubility of 4-amino-2,6-dimethoxypyrimidine in aqueous co-solvent mixtures revisited: Solvent effect, transfer property and preferential solvation analysis

The preferential solvation parameters of 4-amino-2,6-dimethoxypyrimidine in four aqueous co-solvent mixtures of methanol (1) + water (2), ethanol (1) + water (2), isopropanol (1) + water (2) and DMF (1) + water (2) were derived from their available solubility data by using the inverse Kirkwood–Buff integrals method. In water-rich compositions for the four aqueous co-solvent mixtures, the value of δx1,3 was negative, which showed that the 4-amino-2,6-dimethoxypyrimidine was preferentially solvated by water. In intermediate composition and co-solvent-rich composition, 4-amino-2,6-dimethoxypyrimidine was preferentially solvated by the co-solvent (methanol, ethanol, isopropanol or DMF). The preferential solvation magnitude of 4-amino-2,6-dimethoxypyrimidine was highest in isopropanol mixtures than in the other three solvent mixtures. The higher solvation by co-solvents could be explained in terms of the higher basic behavior of the solvents interacting with the Lewis acidic groups of the 4-amino-2,6-dimethoxypyrimidine. The contributions from solute-solvent and solvent-solvent interactions to the solvent effect were studied by using the linear solvation energy relationships. Furthermore, transfer Gibbs free energy (ΔtrGo), enthalpy (ΔtrHo), and entropy (ΔtrSo) were derived, demonstrating that the solubilization capacity was more favorable in the intermediate concentration of co-solvents.

Effects of cosolvent on dissolution behaviors of PVAc in supercritical CO2: A molecular dynamics study

The dissolution behavior of polymers in CO2 has become increasingly important to the applications of CO2 in industry. Experimental results showed that PVAc could be dissolved in CO2 at a high pressure. When cosolvents such as ethanol, acetic acid, and ethyl acetate were present in the system, the transition points could be decreased with the increase in cosolvent concentration. In this work, the influence mechanisms of cosolvents on dissolution behaviors of PVAc in supercritical CO2 were investigated by molecular dynamics simulation methods. First, the cohesive energy and solubility parameters of PVAc, cosolvents and CO2 were analyzed. Compared with CO2, the mixtures of CO2 and cosolvents have closer solubility parameters with PVAc to enhance the dissolubility of PVAc within them. Moreover, the mechanism of PVAc dissolution in CO2 and the effects of cosolvents on decreasing the transition points were investigated. The Lewis acid–Lewis base (LA-LB) interactions between O atoms in PVAc and C atoms in CO2 are the main influencing factors of PVAc dissolution in CO2. The presence of cosolvent can generate new interactions, such as hydrogen bonding and LA-LB interactions, which have different influences on the LA-LB interactions between PVAc and CO2. Ethanol and ethyl acetate have no great influence on these LA-LB interactions, while acetic acid exerts considerable influence.

Non-covalent interactions in bmimCl/co-solvent mixtures: A FTIR spectroscopy and computational study

Ionic liquids such as 1-butyl-3-methylimidazolium chloride (bmimCl) are efficient solvents for cellulose, but high viscosity of the resulting solutions hampers further cellulose shaping and derivatization. To solve this problem, mixtures of ILs with various organic co-solvents are often employed in place of neat ILs. So far, the intermolecular interactions in such mixtures are poorly understood, which hinders further development of this class of cellulose solvents. In this work, we utilized infrared spectroscopy (IR) and quantum chemical model calculations to study the intermolecular interactions in differently concentrated mixtures of bmimCl with two typical co-solvents, dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMAc). First, we refined the assignment of the relevant characteristic bands in the IR spectra of the individual mixture components. This then helped us to reveal that bmim+-DMSO and bmim+-DMAc associates, stabilized by hydrogen bonds between the imidazolium ring CH groups and oxygens of DMSO or DMAc, are formed in the studied mixtures. Importantly, only a relatively small fraction of co-solvent molecules (up to ca. 20 mol% for DMSO and ca. 45 mol% for DMAc) are involved in the associate formation, leaving a large proportion of bmimCl molecules non-solvated. While the maximum co-solvent concentration at which direct cellulose dissolution can be achieved is considerably different for DMSO and DMAc, the corresponding molar ratio of bmimCl to interacting co-solvent molecules was the same for both the studied systems (about 2.5:1). We propose that this ratio might be related to the critical size of bmimCl clusters necessary for achieving cellulose dissolution. Furthermore, increasing the temperature from 25 to 80 °C resulted in a significantly decreased fraction of interacting solvent molecules for bmimCl/DMSO but not for bmimCl/DMAc. This indicates that the comparatively lower tendency of DMSO to form associates with bmimCl is due to the lower strength of the underlying hydrogen bond. The results of this study illustrate how intermolecular interactions influence the macroscopic performance of different IL-based solvent systems.

Free-energy analysis of the hydration and cosolvent effects on the β-sheet aggregation through all-atom molecular dynamics simulation.

Energetics was analyzed for the aggregation of an 11-residue peptide. An all-atom molecular dynamics simulation was conducted with explicit solvent, and the energy-representation theory of solution was employed to compute the solvation free energies of the peptide and its aggregates. The aggregation in the pure-water solvent was observed to be inhibited by the solvation. The driving force of aggregate formation is the interactions among the peptide molecules, and the sum of the intra-aggregate and solvation terms per monomer is more favorable for larger aggregates. The effect of the cosolvent was then examined by focusing on the mixtures of water with urea and dimethyl sulfoxide (DMSO). It was actually shown that the derivative of the excess chemical potential of a flexible solute species with respect to the cosolvent concentration is determined exactly by the corresponding derivative of the free energy of solvation. The cosolvent effect on the equilibrium of aggregate formation can thus be addressed by comparing the solvation free energies with and without the cosolvent, and both the urea and DMSO cosolvents were found to inhibit the aggregation. The cosolvent-induced change in the solvation free energy was further decomposed into the contributions from the cosolvent and water. Their dependencies on the degree of aggregation were seen to be weak for large aggregates, and the roles of the electrostatic, van der Waals, and excluded-volume components in the solvation energetics were discussed.

Facile preparation of polyacrylonitrile-co-methylacrylate based integrally skinned asymmetric nanofiltration membranes for sustainable molecular separation: An one-step method

While polyacrylonitrile (PAN) has been widely used to prepare membranes, it is still not handy to prepare PAN integrally skinned asymmetric (ISA) nanofiltration (NF) membrane via direct immersion precipitation phase inversion method. Herein, a low-cost and commercial polyacrylonitrile-co-methylacrylate, P(AN-co-MA), was demonstrated to prepare ISA NF membranes via a one-step immersion precipitation phase inversion process. It was found that increasing P(AN-co-MA) concentration in NMP can shift the membranes from ultrafiltration (UF) to NF range. The addition of a co-solvent in dope could further improve dye rejection. Effects of solvent (NMP or DMF)/co-solvent (THF and 1,4-dioxane) type and mass ratio in dope solution on membrane separation performance were further investigated. The membrane prepared from a 20% polymer concentration and a NMP/1,4-dioxane ratio of 3:1 showed 87.4% methyl orange (MO) rejection and 98.3% rose bengal (RB) rejection, and simultaneously a relatively high water permeance of 55.22 L m−2 h−1 bar−1. Increase in the content of co-solvent in solvent/co-solvent mixture would depress the formation of macrovoids, lead to a dense top layer and contribute to high dye rejections. The low-cost and one-step process to prepare P(AN-co-MA) ISA NF membranes disclosed in this study paved a new way for sustainable molecular separation.

Fast enantioseparation of indole phytoalexins in additive free supercritical fluid chromatography

A series of chiral indole phytoalexins with potential anticancer and antimicrobial activity were enantioseparated in supercritical fluid chromatography. Two polysaccharide-based chiral stationary phases composed of tris-(3,5-dimethylphenylcarbamate) derivatives of amylose or cellulose coated on 2.5 μm silica particles were successfully used. The influences of the polysaccharide backbone, co-solvent type and co-solvent content in the mobile phase on retention, enantioselectivity and enantioresolution of indole phytoalexins were investigated. Fast baseline separations were achieved for 26 from 27 tested compounds. Amylose‐based chiral stationary phase provided higher number of baseline resolutions of the indole phytoalexins than the cellulose-based one. However, certain complementary enantioresolution results towards the studied compounds were observed between the investigated columns. The relationship between structure of the indole phytoalexins and their chromatographic behavior in supercritical fluid chromatography was discussed.

Equilibrium solubility determination, modelling and thermodynamic aspects of 6-chloroguanine in aqueous co-solvent mixtures of N,N-dimethylformamide, isopropanol, 1,4-dioxane and dimethyl sulfoxide

The equilibrium solubility of 6-chloroguanine in four co-solvent mixtures of dimethyl sulfoxide (DMSO) (1) + water (2), N,N-dimethylformamide (DMF) + water (2), isopropanol (1) + water (2) and 1,4-dioxane (1) + water (2) over the temperature range from (278.15 to 333.15) K were reported. At the same temperature and composition of DMSO, DMF, isopropanol or 1,4-dioxane, the mole fraction solubility of 6-chloroguanine was highest in DMSO (1) + water (2) mixtures, and lowest in 1,4-dioxane (1) + water (2) mixtures. By using the Jouyban-Acree, van’t Hoff-Jouyban-Acree and Apelblat-Jouyban-Acree models, 6-chloroguanine solubility was well correlated obtaining RAD lower than 5.83% and RMSD lower than 4.82 × 10−4. Quantitative values for the local mole fraction of DMSO (DMF, isopropanol or 1,4-dioxane) and water around the 6-chloroguanine were computed by using the Inverse Kirkwood–Buff integrals method applied to the determined solubility data. For the DMF (1) + water (2) mixture with composition 0.20 < x1 < 0.69, DMSO (1) + water (2) mixture with composition 0.20 < x1 < 1 and 1,4-dioxane (1) + water (2) mixture with composition 0.18 < x1 < 0.35, 6-chloroguanine is preferentially solvated by the co-solvent. For the isopropanol (1) + water (2) mixture with composition 0.25 < x1 < 0.70, 6-chloroguanine is preferentially solvated neither by isopropanol nor by water. However, in the other regions for the four co-solvent mixtures, 6-chloroguanine is preferentially solvated by water. The dissolution process of 6-chloroguanine in solvent solutions was endothermic. Furthermore, transfer Gibbs energy (ΔtrG°), enthalpy (ΔtrH°), and entropy (ΔtrS°) were calculated, demonstrating that the solubilization capacity was more favorable with the increase in the co-solvent concentration.

Physiologically-Relevant Crowding Effects on the SH3-Son of Sevenless Interaction

Nearly all biological processes, including tightly regulated protein-protein interactions implicated in cell signaling, occur inside living cells where the concentration of macromolecules can exceed 300 g/L. One such interaction that occurs along the cellular membrane, is between a globular 7-kDa SH3 domain and a 25-kDa intrinsically disordered region of Son of Sevenless (SOS). Despite its importance as a mediator in the mitogen-activated protein kinase signaling pathway present in all eukaryotic cells, most biophysical characterizations of this complex are performed in dilute buffered solutions where cosolute concentrations rarely exceed 10 g/L. We are investigating the effects of crowding, or high concentrations of physiologically-relevant cosolutes, on the equilibrium thermodynamics and kinetics of binding between SH3 and SOS. The SH3 domain is labeled with a fluorine atom on its sole tryptophan, allowing the interaction to be monitored with 19F NMR. Subsequent NMR lineshape analysis allows quantification of both rate constants, and hence the equilibrium constant. Two systems are used. The first system, a control, comprises the SH3 domain and a SOS-derived peptide. Experiments using a range of biologically-relevant molecules reveal that the kinetics are affected more than the stability of the complex. The origins of these effects are likely increased viscosity and electrostatic interactions with crowder molecules. The second system is that between SH3 and the full-length disordered region of SOS. Crowding effects are expected to be larger in magnitude than those observed for the peptide studies based on hypotheses from traditional crowding theory. These experiments are the first to analyze the effects of crowding on a protein-intrinsically disordered protein complex and have immediate implications for understanding the effects of the cellular environment on protein-protein interactions.

Extraction, isolation and purification of tetrahydrocannabinol from the Cannabis sativa L. plant using supercritical fluid extraction and solid phase extraction

The tetrahydrocannabinol (THC) was obtained from Cannabis sativa L. plant material using supercritical fluid extraction (SFE) and solid phase extraction (SPE). SFE was utilized at different pressures (15–33 MPa), temperatures (40–80 °C) and ethanol (EtOH) as co-solvent (0–5%). The effect of extraction parameters on response variables (yield and THC content in raw extract) was evaluated. Keeping both temperature and co-solvent concentration constant at 60 °C and 2% respectively, the highest THC content in raw extracts reaches 37.85% at 33 MPa and 36.18% at 15 MPa. One extract with high THC content was selected and submitted for purification-isolation by SPE. One final fraction with a 90.1% of THC was obtained using a single SPE step. This fraction was analyzed by GC, RP-HPLC and NMR to verify the THC purity. A sequential SFE-SPE process allows to obtain high purity THC from the cannabis plant, which is suitable as quality control material or analytical standard.

Thermodynamics of the Acid–Base Equilibria of Glycyl–Glycyl–Glycine and the Formation of Its Complex with a Copper(II) Ion in Aqueous–Organic Solvents

A summary is presented of original data on the thermodynamics of the formation of copper(II) ion complex with glycyl–glycyl–glycine, the acid–base equilibria of glycyl–glycyl–glycine in aqueous–organic solvents, and published sources that reflect the effect the concentration of the organic cosolvent has on the stability of the coordination compounds of amino acids and peptides with d metal ions and the enthalpies of their formation. Analysis of the solvation characteristics of the reagents shows that upon moving from water to water–ethanol and water–dimethylsulfoxide solvents, the copper(II) complexes with a glycyl–glycyl–glycine zwitterion and a glycinate ion are mainly strengthened through the resolvation of ligands, which is characteristic of the formation of ionic complexes of d metals in aqueous–organic solvents.