Cosolvent Concentration Research Articles

Isothermal Titration Calorimetry to Probe the Coil-to-Globule Transition of Thermoresponsive Polymers.

Isothermal titration calorimetry (ITC) is introduced as a new way to study the effect of cosolutes on the coil-to-globule transition of thermoresponsive polymers. From isothermal titrations, critical cosolute concentrations can be identified, at which a coil-to-globule transition occurs. The concept of a temperature-dependent critical cosolute concentration is proven employing different isomers of dihydroxybenzene (DHB) and one isomer of hydroxy benzaldehyde (mHBA) in solutions of two thermoreversible polymer, namely poly(N-isopropylacrylamide) (PNiPAM) and poly(N,N-diethylacrylamide) (PDEAM). It is shown that the temperature-dependent critical cosolute concentration, determined by ITC, and the cosolute concentration-dependent critical temperature, probed via differential scanning calorimetry (DSC), yield the same phase diagram. The advantage of employing ITC is the ability to probe even critical concentrations at very low temperatures, whereas the corresponding critical temperatures are not easily accessible in DSC. In addition, kinetic information about the coil-to-globule transition in different systems is obtained, and the effect of the DHB isomers on the transition temperature is found to scale as ortho > para > meta.

Impact of organic polar solvents (DMSO and DMF) on the micellization and related behavior of an anionic (AOT), cationic (CEM2AB) and cationic gemini surfactant (16-5-16)

The impact of cosolvents like aquo-organic media has a great focus of discursion in the field of chemical, industrial and pharmaceutical processes along with amphiphilic materials. Detailed study of dimethylsulfoxide and N,N-dimethyl formamide on the self-assembly and the energetic of three surfactants, anionic dioctyl sodium sulfosuccinate (AOT), cationic cetyl ethylhydroxy dimethylammonium bromide (CEM2AB) and cationic gemini N,N′-cetyl-N,N,N′,N′-tetramethyl-N-N′-pentanediyl diammonium dibromide (16-5-16) is clearly described by conductometric, tensiometric, spectro photometric, fluorimetric and calorimetric techniques. All of the surfactants used have equivalent tails, although type and size of their head groups are different. The solvent-composition-dependent properties are identified, and their quantifications are elaborated. The micellization process is assessed in terms of different solvent parameters and zeta potential values are also attempted through dynamic light scattering method (DLS). The values of both critical micelle concentration (cmc) and degree of dissociation increase with increasing concentration of cosolvent. The effect of solvent on free energy contribution to micellization, tail transfer Gibbs free energy, Gibbs adsorption energy etc. was studied. The enthalpy of micellization is estimated directly with the help of microcalorimeter for the lower range of DMSO solution. For AOT in aqueous medium, endothermic plot is observed whereas the other plots are exothermic in nature. Some micellar interfacial parameters were also our study of interest. The careful design of these conjugates exhibits properties which help to serve our focus. All of these results which are demonstrated is a new kind of endeavor.

Putting the Piezolyte Hypothesis under Pressure

A group of small molecules that stabilize proteins against high hydrostatic pressure has been classified as piezolytes, a subset of stabilizing cosolutes. This distinction would imply that piezolytes counteract the effects of high hydrostatic pressure through effects on the volumetric properties of the protein. The purpose of this study was to determine if cosolutes proposed to be piezolytes have an effect on the volumetric properties of proteins through direct experimental measurements of volume changes upon unfolding of model proteins lysozyme and ribonuclease A, in solutions containing varying cosolute concentrations. Solutions containing the proposed piezolytes glutamate, sarcosine, and betaine were used, as well as solutions containing the denaturants guanidinium hydrochloride and urea. Changes in thermostability were monitored using differential scanning calorimetry whereas changes in volume were monitored using pressure perturbation calorimetry. Our findings indicate that increasing stabilizing cosolute concentration increases the stability and transition temperature of the protein, but does not change the temperature dependence of volume changes upon unfolding. The results suggest that the pressure stability of a protein in solution is not directly affected by the presence of these proposed piezolytes, and so they cannot be granted this distinction.

Measurement of Microemulsion Viscosity and Its Implications for Chemical Enhanced Oil Recovery

Summary The rheological behavior of microemulsion systems was systematically investigated with mixtures of oil, brine, surfactant, cosolvent, and in some cases polymer to determine their effects. A microemulsion-rheology model was developed and used to interpret the experimental results. The optimal microemulsion/oil-viscosity ratio without cosolvent was roughly 5:6, but it can be reduced to a more favorable ratio of approximately 2 by adding cosolvent. Even though the amount of cosolvent needed is case dependent, a clear trend of microemulsion-viscosity reduction with increasing cosolvent concentration was observed. Limited evidence suggests that large hydrolyzed polyacrylamide (HPAM) molecules with a narrow molecular-weight (MW) distribution have negligible partitioning to Type II and Type III microemulsions.

Bioinspired flame retardant polymers of tyrosol

ABSTRACTThe enzyme catalyzed polymerization of flame retardant (FR) polymers from the renewable resource 2‐(4‐hydroxyphenyl) ethanol (HPE), commonly known as tyrosol, is presented. The synthesis is environmentally friendly and requires only monomer, peroxidase catalyst, dilute hydrogen peroxide, and deionized water. Phenolic polymers are produced in short, one pot, high yield reactions that require minimal purification. Fourier transform infrared spectroscopy and 1H‐NMR analysis suggest the polymers are coupled through the 1, 2, 4, and 5 positions of the phenol ring and through the phenoxy substituent. Thermogravimetric analysis and pyrolysis combustion flow calorimeter show HPE homopolymers exhibit very low heat release rate and total heat release, while copolymerization with phenol increases already high char yields. Gel permeation chromatography reveals the molecular weight of the polymer increases with ethanol cosolvent concentration. The alcohol cosolvent also increases the proportion of oxyphenylene linkages to the detriment of FR properties. Preliminary quantitative structure–activity relationship toxicity modeling predicts the polymers are negative for developmental toxicity and Ames mutagenicity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45394.

Protein Partial Molar Volumes in Multicomponent Solutions from the Perspective of Inverse Kirkwood-Buff Theory.

Inverse Kirkwood-Buff (KB) solution theory can be used to relate macroscopic quantities with molecular scale interactions and correlation functions, in the form of KB integrals. Protein partial specific volumes ([Formula: see text]) from high-precision density measurements can be used to quantify solvent-solute and solute-solute KB integrals. Currently, general expressions for [Formula: see text] as a function of cosolute concentration (c3) have been provided for only binary and ternary solutions. We derive a general multicomponent expression for [Formula: see text] in terms of the relevant KB integrals for the case of low (infinite dilution) protein concentration but arbitrary cosolute concentrations. To test the utility of treating a quaternary system with a pseudoternary approximation, α-Chymotrypsinogen (aCgn) solutions with a series of solutes (NaCl, sucrose, and trehalose) were compared as a function of solute concentration with and without buffer present. Comparison between those ternary and quaternary solutions shows equivalent results within experimental uncertainty and suggests the pseudoternary approximation may be reasonable. In the case of aCgn, doing so also revealed that the preferential interactions can depend on pH. Analysis of steric contributions also provides an example that illustrates how KB integrals allow one to interpret [Formula: see text] in terms of contributions from molecular volume, excluded volume, and hydration/solvation effects.

Production of salicylic acid in a three compartment bipolar membrane electrodialysis configuration

Abstract Salicylic acid is nowadays produced by the Kolbe-Schmitt reaction. Using this method, sodium salicylate is converted into salicylic acid by the addition of sulphuric acid. Electrodialysis is proposed for this production process and avoids the use of sulphuric acid and the production of an acidic sodium sulphate waste stream. The low solubility of salicylic acid in water can be overcome by using mixtures of water and a primary alcohol. However, preliminary results have indicated that bipolar membranes of large dimensions cannot be used in direct contact with these solvent mixtures. In this paper, a three compartment configuration is proposed, which resolves this problem by enclosing the solvent mixture with two cation-exchange membranes. An optimization of this configuration was performed by systematically varying different operating parameters. As the co-solvent, the use of methanol, ethanol and 1-propanol was tested. The results indicate that a high salicylate concentration, a low co-solvent concentration of 1-propanol and a low base concentration are the most optimal settings.

Investigation of Classical Organic and Ionic Liquid Cosolvents for Early-Stage Screening in Fragment-Based Inhibitor Design with Unrelated Bacterial and Human Dihydrofolate Reductases.

Drug design by methods such as fragment screening requires effective solubilization of millimolar concentrations of small organic compounds while maintaining the properties of the biological target. We investigate four organic solvents and three 1-butyl-3-methylimidazolium (BMIm)-based ionic liquids (ILs) as cosolvents to establish conditions for screening two structurally unrelated dihydrofolate reductases (DHFRs) that are prime drug targets. Moderate concentrations (10%-15%) of cosolvents had little effect on inhibition of the microbial type II R67 DHFR and of human DHFR (hDHFR), while higher concentrations of organic cosolvents generally decreased activity of both DHFRs. In contrast, a specific IL conserved the activity of one DHFR, while severely reducing the activity of the other, and vice versa, illustrating the differing effect of ILs on distinct protein folds. Most of the cosolvents investigated preserved the fold of R67 DHFR and had little effect on binding of the cofactor NADPH, but reduced the productive affinity for its substrate. In contrast, cosolvents resulted in modest structural destabilization of hDHFR with little effect on productive affinity. We conclude that the organic cosolvents, methanol, dimethylformamide, and dimethylsulfoxide, offer the most balanced conditions for early-stage compound screening as they maintain sufficient biological activity of both DHFRs while allowing for compound dissolution in the millimolar range. However, IL cosolvents showed poor capacity to solubilize organic compounds at millimolar concentrations, mitigating their utility in early-stage screening. Nonetheless, ILs could provide an alternative to classical organic cosolvents when low concentrations of inhibitors are used, as when characterizing higher affinity inhibitors.

Effect of co-solute concentration on the diffusion of linoleic acid from whey protein matrices

Structural relaxation of a delivery vehicle has been identified in the literature as a limiting parameter for the controlled diffusion of a bioactive compound. To further examine the kinetics of controlled release, this study designed a system of homogeneously dispersed linoleic acid in a high-solid whey protein matrix. Amorphous glucose-syrup liquid was added systematically up to about 48% (w/w), with the total solids level in the formulation being kept constant at 80% (w/w), and experimental observations were obtained over a broad timeframe and temperature range. Structural and physicochemical properties of the blend were monitored using dynamic oscillation in-shear, WAXD, FTIR and confocal laser scanning microscopy. A specific chromogenic reaction with UV–vis spectroscopy was employed to follow the release of linoleic acid under perfect sink conditions. Variation in the amount of glucose syrup, as the co-solute, within the high-solid whey protein network affected profoundly the values of the mechanical glass transition temperature. That was reflected in the kinetics of fatty acid diffusion from the glass transition region of our composite materials. Transport phenomena were quantified via the concept of effective diffusion coefficient, which increases with higher levels of glucose syrup leading to structural relaxation of the delivery vehicle.

Thermodynamic Properties and Solubility of Sodium and Potassium Chloride in Ethane-1,2-diol/Water Mixed Solvent Systems to High Temperatures

Solid sodium chloride solubility is measured at temperatures from 297 to 467 K at pressure of 6.45 MPa in ethane-1,2-diol/water mixed solvent systems and at a concentration of cosolvent up to 75% w/w. The corresponding solubility is also predicted from an extension of the unified theory of electrolytes to mixed solvents (J. Phys. Chem. B 2012, 116, 9033−9042) for sodium and potassium chloride up to 473.15 K and over the whole composition range of the cosolvent. A comparison of the predicted solubility with the corresponding experimental values from this study and the available literature data indicates good agreement in all cases to well within the uncertainties of the experimental data. Also, for the saturated solution of sodium and potassium chloride in ethane-1,2-diol/water mixed solvent systems, the stoichiometric activity coefficient values are estimated up to 473.15 K. These stoichiometric activity coefficients, over the complete range of mole fraction of the cosolvent, are then extended to all conc...

Formation of solvate structures by the ortho-, meta-, and para-isomers of hydroxybenzoic acid in supercritical fluid

The solvate structures formed by the ortho-, meta-, and para-isomers of hydroxybenzoic acid (o-HBA, m-HBA, and p-HBA) with a polar co-solvent (methanol at a concentration of 0.030 and 0.035 mole fractions) in supercritical carbon dioxide at a constant density of 0.7 g/cm3 and temperatures of 318 and 328 K have been studied by the classic molecular dynamics. It has been determined that a stable hydrogen-bonded complex with the co-solvent forms via the hydrogen of the carboxyl group for all isomers. The probability of this complex existence is high at all temperatures and concentrations. In the o-HBA molecule, the other functional groups are engaged in the intramolecular hydrogen bond, but not involved in interactions with methanol. It has been found that m-HBA and p-HBA can be involved in hydrogen bonds with methanol via hydroxyl hydrogen and oxygen atoms; they are characterized by the presence of one more co-solvent molecule (rarely, two molecules) in their solvation shell and intermittent formations/breakages of hydrogen bonds via other functional groups. These bonds are far less stable, and their formation is sensitive to change of temperature and co-solvent concentration. It has been concluded that the degree of selective solvation of m-HBA and p-HBA by co-solvent molecules is approximately the same, but the rate of structural rearrangements in the nearest environment of m-HBA is higher than that of p-HBA.

Two-Dimensional Infrared Spectroscopy Reveals Cosolvent-Composition-Dependent Crossover in Intermolecular Hydrogen-Bond Dynamics.

Cosolvents have versatile composition-dependent applications in chemistry and biology. The simultaneous presence of hydrophobic and hydrophilic groups in dimethyl sulfoxide (DMSO), an industrially important amphiphilic cosolvent, when combined with the unique properties of water, plays key roles in the diverse fields of pharmacology, cryoprotection, and cell biology. Moreover, molecules dissolved in aqueous DMSO exhibit an anomalous concentration-dependent nonmonotonic behavior in stability and activity near a critical DMSO mole fraction of 0.15. An experimental identification of the origin of this anomaly can lead to newer chemical and biological applications. We report a direct spectroscopic observation of the anomalous behavior using ultrafast two-dimensional infrared spectroscopy experiments. Our results demonstrate the cosolvent-concentration-dependent nonmonotonicity arises from nonidentical mechanisms in ultrafast hydrogen-bond-exchange dynamics of water above and below the critical cosolvent concentration. Comparison of experimental and theoretical results provides a molecular-level mechanistic understanding: a distinct difference in the stabilization of the solute through dynamic solute-solvent interactions is the key to the anomalous behavior.

Investigation of the effect of tetrahydrofuran and acetone as cosolvents in acrylonitrile–butadiene–styrene–based nanofiltration membranes

ABSTRACTIn this study, novel nanofiltration membranes were prepared with acrylonitrile–butadiene–styrene (ABS)–poly(ethylene glycol)–N,N‐dimethylacetamide–[tetrahydrofuran (THF)–acetone] as a cosolvent. All of the membranes were prepared by the phase‐inversion method and a casting solution technique. The effects of the cosolvent concentration in the casting solution and the evaporation time before the immersion/precipitation step on the membrane performance and properties were investigated. The prepared membranes were characterized through their permeation flux, salt rejection, and phase‐inversion time values. The salt rejection was increased from 53% for the bare ABS membrane to 73% for the membrane prepared with 40 wt % THF as a cosolvent. The water flux was decreased from 4345 to 1121 cc m−2 h−1 with the addition of THF to the casting solution. The addition of acetone to the casting solution improved the water flux from 4345 to 5607 cc m−2 h−1 and reduced the salt rejection from 53 to 36%. The evaporation time of THF and acetone led to similar effects on flux and rejection. However, with evaporation time, membranes prepared with acetone were denser than those prepared with THF; this was due to the lower boiling point and higher boiling rate of acetone at the same temperatures. This resulted in greater effects on the ABS performance and structure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44993.

Fractionation of biologically active components of grape seed (Vitis vinifera) by supercritical fluid extraction

Supercritical fluid extraction (SFE) was used for fractionation of grape seed to be applied in natural products of the food, cosmetic, or pharmaceutical industry. A two-step process was developed, consisting of conventional alcoholic extraction followed by SFE with carbon dioxide. The effects of pressure and concentration of co-solvent (ethanol) at constant temperature and solvent to feed-ratio were evaluated. The antioxidant activity of extracts and raffinates was measured with the DPPH* free radical scavenging assay. It was observed that supercritical carbon dioxide can be used in the described process for fractionation of an alcoholic grape seed extract to obtain a product with noticeably high antioxidant activity and a second one with no antioxidant activity or pro-oxidant activity.

Antioxidant capacity of Colombian seaweeds: 1. Extracts obtained from Gracilaria mammillaris by means of supercritical fluid extraction

Red seaweed Gracilaria mammillaris from the Colombian Caribbean coast were investigated as source of extracts with antioxidant activity (AA), by means of supercritical CO2 extraction with ethanol as co-solvent. A central composite design was used to investigate the effects of pressure (10, 20 and 30MPa), temperature (40, 50 and 60°C), and co-solvent concentration (2, 5 and 8%) on the extraction yield, AA, and total content of phenols and carotenes. The obtained extracts were compared with those produced using Soxhlet extraction at reduced pressure. The AA of samples was evaluated by determining their capacity for protecting an edible oil against oxidation, upon accelerated oxidation trials. The extracts obtained at 30MPa, 60°C and 8% co-solvent showed the highest AA, inhibiting in 42.1% the formation of TBARS after six days of accelerated oxidation. These results indicate that red seaweed G. mammillaris could be a promissory source of extracts with AA.

The study of peculiarities of parabens solvation in methanol- and acetone-modified supercritical carbon dioxide by computer simulation

Molecular dynamics simulation of solutions of methylparaben and propylparaben in supercritical carbon dioxide, modified by polar cosolvents (acetone and methanol) has been performed. The solvation features associated with the concentration of cosolvent in the fluid (0.03 and 0.06mol fraction), and with the choice of the thermodynamic state: at a temperature range of 318–348K at densities corresponding to experimental isobar 30MPa, and at change of density (0.507–0.851g/cm3) at constant temperature 328K have been researched. It is shown that the solvation of parabens in modified supercritical CO2 occurs due to the formation of hydrogen bonds with a cosolvent. Structural and dynamic parameters of these hydrogen bonds have been considered. Free energies of solvation of parabens in pure and modified supercritical CO2 at T=328K, P=21MPa and 30MPa, have been calculated. Evaluation of cosolvent induced solubility enhancement has been made on the basis of the free energy of solvation. It is found that the use of methanol as a cosolvent will result in many times greater increase in solubility of parabens in supercritical CO2, than the use of acetone. It is shown that the cosolvent induced solubility enhancement of parabens in acetone-modified supercritical CO2 is much less sensitive to such factors as change of fluid pressure and concentration of a cosolvent than that in methanol-modified supercritical CO2.

Humidity affects the morphology of particles emitted from beclomethasone dipropionate pressurized metered dose inhalers

The effects of propellant type, cosolvent content, and air humidity on the morphology and solid phase of the particles produced from solution pressurized metered dose inhalers containing the corticosteroid beclomethasone dipropionate were investigated. The active ingredient was dissolved in the HFA propellants 134a and 227ea with varying levels of the cosolvent ethanol and filled into pressurized metered dose inhalers. Inhalers were actuated into an evaporation chamber under controlled temperature and humidity conditions and sampled using a single nozzle, single stage inertial impactor. Particle morphology was assessed qualitatively using field emission scanning electron microscopy and focused ion beam-helium ion microscopy. Drug solid phase was assessed using Raman microscopy. The relative humidity of the air during inhaler actuation was found to have a strong effect on the particle morphology, with solid spheroidal particles produced in dry air and highly porous particles produced at higher humidity levels. Air humidification was found to have no effect on the solid phase of the drug particles, which was predominantly amorphous for all tested formulations. A critical level of air relative humidity was required to generate porous particles for each tested formulation. This critical relative humidity was found to depend on the amount of ethanol used in the inhaler, but not on the type of propellant utilized. The results indicate that under the right circumstances water vapor saturation followed by nucleated water condensation or ice deposition occurs during particle formation from evaporating propellant-cosolvent-BDP droplets. This finding reveals the importance of condensed water or ice as a templating agent for porosity when particle formation occurs at saturated conditions, with possible implications on the pharmacokinetics of solution pMDIs and potential applications in particle engineering for drug delivery.

Features of solvation of phenolic acids in supercritical carbon dioxide modified by methanol and acetone

The study of solvation of three phenolic acids, 3,4,5-trihydroxybenzoic acid (gallic acid), 3,4-dihydroxybenzoic acid (protocatechuic acid), and 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid), in pure, methanol-modified and acetone-modified (0.03 and 0.06mol fraction) supercritical (SC) carbon dioxide has been carried out by computational methods. Structural features of hydrogen-bonded complexes formation in modified SC media have been researched by using classical molecular dynamics at different densities corresponding to the experimental pressures 20 and 30MPa and temperatures from 313 to 333K. The results obtained have revealed that an increase of fluid density and cosolvent concentration provide increasing the average number of hydrogen bonds formed by the solute with cosolvent. Ab initio calculations of formation energy of hydrogen-bonded complexes solute – cosolvent have been performed. Solvation free energy of the phenolic acids in SC CO2 with and without cosolvents was evaluated by means of the Bennett’s acceptance ratio method. The solvation free energy has been found to be strongly dependent on the number of hydrogen bonds solute – cosolvent. Cosolvent-induced solubility enhancement values were also calculated. The results indicate that the increase in solubility of the phenolic acids is observed by passing from the pure SC CO2 through acetone-modified to methanol-modified solvent. Moreover the order of cosolvent-induced solubility enhancement magnitude depends on the number of hydrogen bonds solute – cosolvent and greatly on the concentration of the latter.

Particle size-controllable microwave-assisted solvothermal synthesis of the high-voltage cathode material LiCoPO4 using water/ethylene glycol solvent blends

Particle size-tuned platelets of the high-voltage cathode material LiCoPO4 for Li-ion batteries have been synthesized by a simple one-step microwave-assisted solvothermal process using an array of water/ethylene glycol (EG) solvent mixtures. Particle size control was achieved by altering the concentration of the EG co-solvent in the mixture between 0 and 100 vol%, with amounts of 0–80 vol% EG producing single phase, olivine-type LiCoPO4. The particle sizes of the olivine materials were significantly reduced from about 1.2 μm × 1.2 μm × 500 nm (0 vol% EG) to 200 nm × 100 nm × 50 nm (80 vol% EG) with increasing EG content, while specific surface areas increased from 2 to 13 m2 g-1. The particle size reduction could mainly be attributed to the modified viscosities of the solvent blends. Owing to the soft template effect of EG, the crystals exhibited the smallest dimensions along the [010] direction of the Li diffusion pathways in the olivine crystal structure, resulting in enhanced lithium diffusion properties. The relationship between the synthesis, crystal properties and electrochemical performance was further elucidated, indicating that the electrochemical performances of the as-prepared materials mainly depend on the solvent composition and the respective particle size range. LiCoPO4 products obtained from reaction media with low and high EG contents exhibited good electrochemical performances (initial discharge capacities of 87–124 mAh g−1 at 0.1 C), whereas materials made from medium EG concentrations (40–60 vol% EG) showed the highest capacities and gravimetric energy densities (up to 137 mAh g−1 and 658 Wh kg−1 at 0.1 C), excellent rate capabilities, and cycle life.

Time, Concentration, Ionic Strength and Solvents affects on Electronic Absorption Spectra of Association between Acid-Base Indicators

The association behavior between Acid-Base indicators in aqueous solution has been studied by UV–vis spectroscopy. The spectroscopic results show that association are formed evidenced by slightly red shift to lmax = 470nm and large hypo-chromic shift in absorbance signal upon addition of azo dye with creating new bands. Present of broad bands and isobestic point that indicate formation of simple dyes aggregate monomer- dimmer equilibria in neutral media. The degree of association depends on the concentration of methyl orange, Co-solvents, and ionic strength of the medium.