Cosolvent Polarity Research Articles

The Polarity of Co-solvents Regulates the Charge Storage Mechanisms in Supercapacitors with Concentrated Electrolytes.

Developing better energy storage devices depends on comprehending the underlying mechanisms involved in charge storage. With the continuous conception of new electrolytes, this task becomes progressively more urgent and complex. An example is the utilization of co-solvated concentrated solutions. While these show promising electrochemical responses, their dynamic properties (especially under confinement) and their relationships with performance are not fully understood. Here, we combined modified step potential electrochemical spectroscopy and quasielastic neutron scattering to investigate systems composed of activated mesoporous carbon (AMC) and concentrated solutions of lithium bis(trifluoromethanesulfonyl)imide in acetonitrile co-solvated with either toluene or acetone. We report that acetone does not impair surface-controlled mechanisms, contrary to the case with toluene, which competes with charged species to populate the AMC's pores without contributing to charge storage. In turn, toluene promotes a greater overall capacitance owing to Faradaic processes, which may be related to changes in the solvation structures under confinement.

The role of quantum-chemical descriptors and sigma-profile overlapping of different co-solvents on tuning ethanolic extraction of soybean oil

Co-solvents can significantly improve ethanol efficiency in vegetable oil extraction, making their use a viable, cost-effective, and sustainable alternative to conventional solvents. The challenge, however, is to understand the complex interactions between the solvents and how this can affect the yield and quality of the extracted oil. In this study, the COnductor-like Screening Model with Segment Activity Coefficient and Hansen solubility parameters were combined and used to optimize soybean oil extraction using ethanol along with seven different co-solvents. In parallel, an experimental approach was carried out to verify the accuracy of the models. Both theoretical and empirical results indicated that the oil extraction yield decreased as the co-solvent polarity increased. The best performance in solubilizing non-polar lipids was observed for the mixture of 10 wt% of p-cymene, a non-polar solvent, with 90 wt% ethanol, reaching a yield of 24.35 g/100 g. According to the thermodynamic analysis, the effects of polarity weigh heavily on the standard entropy, which rules the driving force of mass transfer during the extraction. The interaction mechanisms were carefully investigated employing quantum mechanical calculations, revealing how the differences in chemical potential (μ), hardness (η), and electrophilicity (ω) underlie the macroscopic results and rule the efficiency obtained for different solvent ratios and combinations.

Heterogeneous dynamics in [BMIM][PF6] + Cosolvent binary Mixtures: Does It depend upon cosolvent Polarity?

It is known that dilution of ionic liquid with appropriate cosolvents modifies a number of physicochemical properties that include surface tension, viscosity, ion diffusivity and many others. The cosolvents, particularly when present in low concentrations, also undergo substantial changes in their inherent dynamics. The work reported here explores, via molecular dynamics simulations, the composition dependence of modifications on motional features of both the neutral cosolvent molecules and the charged molecular ions constituting the ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM] [PF6]). The cosolvents have been carefully chosen so that the polarities differ widely; they are acetonitrile (dipolar), 1,4-dioxane (quadrupolar) and n-hexane (non-polar). Mixture compositions studied are, FIL = 1.00, 0.90, 0.75, 0.50, 0.25, 0.10 and 0, FIL being the IL mole fraction. Signature of heterogeneous relaxations have been searched via examining several dynamical markers, such as, four-point density-time correlation functions, overlap functions, self-intermediate scattering functions, and other motional features arising from the deviations of displacements from Gaussian distributions. The presence of cosolvents affects the diffusivity of both the ions and the cosolvents, with dipolar acetonitrile causing the fastest ion diffusion in the mixture. Interestingly, all the dynamical heterogeneity features studied here have been found to respond significantly to both the cosolvent polarity and the mixture composition.

Cosolvent polarity dependence of solution structure in [BMIM] [PF6] + acetonitrile/1, 4-dioxane/hexane binary mixtures: Insights from composition dependent Voronoi polyhedra analyses, iso-surfaces and radial distribution functions

We investigate in this paper, via molecular dynamics simulations, the composition dependent solution structures in the binary mixtures composed of the ionic liquid (IL), 1-butyl-3methyl-imidazolium hexafluorophosphate, ([BMIM] [PF6]), and three different co-solvents of comparable sizes but with differing polarities. These cosolvents are acetonitrile (dipolar), 1,4-dioxane (quadrupolar) and hexane (non-polar). Five different IL mole fractions for the binary mixtures (FIL = 0.90, 0.75, 0.50, 0.25, 0.10) along with the neat solvents have been studied. The cosolvent polarity and concentration dependencies have been assessed through the examination of the composition dependent spatial and radial distribution functions, coordination numbers and the Voronoi polyhedra analyses. The solution structure is found to be dominated by the cosolvent clustering at high IL concentrations, and segregation of the IL into polar and non-polar domains in dilute IL solutions, their extent being strongly dependent upon cosolvent polarity. The aggregation behavior of the IL in the non-polar and dipolar binary mixtures is explained in terms of the Debye screening length (DSL). Such an explanation, however, fails to explain the comparable solubility of 1,4-dioxane in this IL. Isodensity surfaces constructed from the simulated spatial distribution functions show a dramatic cosolvent polarity dependence for the binary solution structure and reflects that microscopic phase segregation is the most pronounced for IL + hexane binary mixtures. The Voronoi polyhedra (VP) analyses indicate broader void and neck distributions upon dilution of the IL by cosolvents, suggesting increased heterogeneity in the solution structure of the binary mixtures. The severe phase segregation observed for [BMIM] [PF6] + hexane mixtures at the low IL concentrations did not allow similar VP analyses for this binary mixture for all the mixture compositions considered.

Co-solvent polarity tuned thermochromic nanotubes of cyclic dipeptide-polydiacetylene supramolecular system.

The cooperative non-covalent interactions arising from structurally integrated multiple molecules have emerged as a powerful tool for the creation of functional supramolecular structures. Herein, we constructed cyclic dipeptide (CDP)–polydiacetylene (PDA) conjugate (CDP–DA) by introducing cyclo(l-Phe-l-Lys) to the linear 10,12-pentacosadiynoic acid. Owing to extensive hydrogen bonding characteristics, together with structural chirality of cyclo(l-Phe-l-Lys) and strong π–π stacking diacetylenic template, CDP–DA generated supramolecular nanotubes. The structural visualization using scanning and transmission electron microscopy revealed chloroform/methanol co-solvent polarity tuned morphological transformation of intrinsic lamellar assemblies into nanotubes comprising single-wall and multi-wall structure. The mechanistic understanding by X-ray diffraction patterns confirms bilayer organization in lamellar structure, which forms nanotubes via a gradual lamellar curling-to-scrolling process. The supramolecular CDP–DA nanotubes are transformed into the rigid covalently cross-linked blue-phase polydiacetylene (CDP–PDA) by UV irradiation. Very interestingly, the blue-phase nanotubes display reversible thermochromic changing temperature up to 150 °C with excellent repeatability over a dozen thermal cycles. This work provides an efficient strategy for precise morphological control and aiding the perspective for development in nanostructures for functional devices.

Improving Product Specificity of Whole-Cell Alkane Oxidation in Nonconventional Media: A Multivariate Analysis Approach.

Two-liquid-phase reaction media have long been used in bioconversions to supply or remove hydrophobic organic reaction substrates and products to reduce inhibitory and toxic effects on biocatalysts. In case of the terminal oxyfunctionalization of linear alkanes by the AlkBGT monooxygenase the excess alkane substrate is often used as a second phase to extract the alcohol, aldehyde, and acid products. However, the selection of other carrier phases or surfactants is complex due to a large number of parameters that are involved, such as biocompatibility, substrate bioavailability, and product extraction selectivity. This study combines systematic high-throughput screening with chemometrics to correlate physicochemical parameters of a range of cosolvents to product specificity and yield using a multivariate regression model. Partial least-squares regression shows that the defining factor for product specificity is the solubility properties of the reaction substrate and product in the cosolvent, as measured by Hansen solubility parameters. Thus the polarity of cosolvents determines the accumulation of either alcohol or acid products. Whereas usually the acid product accumulates during the reaction, by choosing a more polar cosolvent the 1-alcohol product can be accumulated. Especially with Tergitol as a cosolvent, a 3.2-fold improvement in the 1-octanol yield to 18.3 mmol L-1 is achieved relative to the control reaction without cosolvents.

Residue-Specific Solvation-Directed Thermodynamic and Kinetic Control over Peptide Self-Assembly with 1D/2D Structure Selection.

Understanding the self-organization and structural transformations of molecular ensembles is important to explore the complexity of biological systems. Here, we illustrate the crucial role of cosolvents and solvation effects in thermodynamic and kinetic control over peptide association into ultrathin Janus nanosheets, elongated nanobelts, and amyloid-like fibrils. We gained further insight into the solvation-directed self-assembly (SDSA) by investigating residue-specific peptide solvation using molecular dynamics modeling. We proposed the preferential solvation of the aromatic and alkyl domains on the peptide backbone and protofibril surface, which results in volume exclusion effects and restricts the peptide association between hydrophobic walls. We explored the SDSA phenomenon in a library of cosolvents (protic and aprotic), where less polar cosolvents were found to exert a stronger influence on the energetic balance at play during peptide propagation. By tailoring cosolvent polarity, we were able to achieve precise control of the peptide nanostructures with 1D/2D shape selection. We also illustrated the complexity of the SDSA system with pathway-dependent peptide aggregation, where two self-assembly states (i.e., thermodynamic equilibrium state and kinetically trapped state) from different sample preparation methods were obtained.

Solubility of cinnamic acid in supercritical carbon dioxide and subcritical 1,1,1,2-tetrafluoroethane: Experimental data and modelling

To promote the extraction of natural cinnamic acid with supercritical and subcritical fluids, the solubility of cinnamic acid was measured respectively in supercritical carbon dioxide (SCCO2) by the dynamic method and in subcritical 1,1,1,2-tetrafluoroethane (sub-R134a) by the static method. The experiments were performed at temperatures from 308 K to 328 K and pressures of 9.0, 11.0, 13.0, 15.0, and 18.0 MPa. The solubility of cinnamic acid in SCCO2 and sub-R134a were compared by calculating the enhancement factor (δ), which indicated that the value of δ in sub-R134a is greater than that in SCCO2; meanwhile, the entrainment factor (ψ), which describes the influence of co-solvent (ethanol, ethyl acetate and n-pentane) on the cinnamic acid solubility in SCCO2, showed that the solubility of cinnamic acid in SCCO2 increased with the co-solvent polarity increasing. Six semi-empirical models (Chrastil, A-L, K-J, S-S, M-S-T, and Bartle) were used to correlate cinnamic acid solubility in binary system (cinnamic acid + SCCO2 or sub-R134a) and four models (Gonzalea, Sovova, Tang and Sauceau) were used to correlate cinnamic acid solubility in ternary system (cinnamic acid + SCCO2+co-solvent). The enthalpy values of cinnamic acid, including ΔHtotal, ΔHsub. and ΔHsol., were estimated through Chrastil and Bartle models; and the partial molar volume of cinnamic acid was calculated by K-J model. A new model was proposed on the basis of the molecular association theory and verified by 47 solid solutes solubility in SCCO2 or sub-R134a with satisfactory correlation results.

Co-solvent polarity controlled self-assembly of tetraphenylethylene-buried amphiphile for size-regulated tumor accumulation.

We report that the co-solvent polarity can precisely control the TPE-buried amphiphile 1 to self-assemble into nanoparticles (NPs) in water with size range from ∼21–32 nm to 55–68 nm to 95–106 nm. Excepted for size, these TPE-buried amphiphile fabricated NPs hold identical physical properties such as spherical shape, surface charge, and luminescent properties, and moreover, after covalent capture of the acrylate hydrophilic heads, the resulting cross-linked NPs (cNPs I–III) own excellent in vivo stability, which thus would be an ideal platform for investigating the size effects on tumor accumulation and penetration.

The structure of hydrated complexes of o-hydroxybenzoic acid in water-modified supercritical carbon dioxide: The Car-Parrinello molecular dynamics simulation

The study of the o-hydroxybenzoic acid (o-HBA)–water molecular structures formed in supercritical carbon dioxide (T=318K, ρ=0.7g/cm3) by Car-Parrinello molecular dynamics method has been performed. Atom–atom radial distribution functions, coordination numbers, average hydrogen bond (HB) numbers, and vibrational densities of states have been calculated from molecular trajectories saved during simulation procedure. It has been shown that, despite of the high co-solvent polarity, the hydroxyl group of the o-HBA preferably forms an intramolecular HB, whereas o-HBA–water hydrogen bonding involves only acid carboxyl group. The formed o-HBA–(H2O)2 complex and remaining water molecules compose a labile hydrogen-bonded cluster. The average HB number per water molecule is equal to 1.93, 26.4% out of the total amount of HBs formed by water molecules being water–o-HBA HBs, and the rest being water–water HBs. Evolution of hydrogen-bonded clusters has been analyzed, using instantaneous structures saved during the simulation. It was shown that water–water HBs are less stable than water–o-HBA ones.

Yttria stabilized zirconia synthesis in supercritical CO 2: Understanding of particle formation mechanisms in CO 2/co-solvent systems

The increasing interest of supercritical (SC) fluids for inorganic materials synthesis recently stimulated the development of innovative synthesis processes and strategies. The supercritical CO 2 aided sol–gel process, developed for preparing various ceramic oxide powders with attractive applications in cosmetics, chromatography, catalysis or solid oxide fuel cells, usually suffer from both reproducibility problems and poor knowledge of the key parameters defining the final powder characteristics. In the present work a specific effort has been put on the understanding of reaction mechanisms and process parameters like co-solvent polarity and ageing time of the starting solution, which appeared to play a crucial role for the control of powder characteristics. Two different reaction mechanisms have been proposed to explain the formation of tetragonal yttria-doped zirconia powders by a batch process in either CO 2/pentane or CO 2/isopropanol mixtures. The first mechanism corresponds to a CO 2 anti-solvent precipitation process while the other one is based on a condensation reaction as in the conventional sol–gel process. This improved understanding in particle formation allows better control of powder characteristics and reproducibility.

Control of pore size in mesoporous silica templated by a multiarm hyperbranched copolyether in water and cosolvent

Worm-like mesoporous silica with various pore sizes has been prepared successfully templated by a multiarm hyperbranched copolyether (PEHO- star-PPO). The pore size of the resultant mesoporous materials can be controlled easily through adjusting the ratio of water to cosolvent. As the molar ratio of water to ethanol changes from 0.02 to 0.73, the pore size of the calcined materials can be enlarged from 32 to 94 Å, attributing to the aggregation behavior of the multiarm hyperbranched polymer in different systems. Moreover, the pore size of the obtained mesoporous silica can be also adjusted by selecting different kinds of cosolvent. The polarity and solubility of cosolvents are believed to be two important factors in affecting the pore size. Thus, a facile and efficient method for controlling the pore size of mesoporous silica has been developed by using hyperbranched polymers as templates.

Selective Recovery of Tagatose from Mixtures with Galactose by Direct Extraction with Supercritical CO2 and Different Cosolvents

A selective fractionation method of carbohydrate mixtures of galactose/tagatose, using supercritical CO(2) and isopropanol as cosolvent, has been evaluated. Optimization was carried out using a central composite face design and considering as factors the extraction pressure (from 100 to 300 bar), the extraction temperature (from 60 to 100 degrees C), and the modifier flow rate (from 0.2 to 0.4 mL/min, which corresponded to a total cosolvent percentage ranging from 4 to 18% vol). The responses evaluated were the amount (milligrams) of tagatose and galactose extracted and their recoveries (percent). The statistical analysis of the results provided mathematical models for each response variable. The corresponding parameters were estimated by multiple linear regression, and high determination coefficients (>0.96) were obtained. The optimum conditions of the extraction process to get the maximum recovery of tagatose (37%) were 300 bar, 60 degrees C, and 0.4 mL/min of cosolvent. The predicted value was 24.37 mg of tagatose, whereas the experimental value was 26.34 mg, which is a 7% error from the predicted value. Cosolvent polarity effects on tagatose extraction from mixtures of galactose/tagatose were also studied using different alcohols and their mixtures with water. Although a remarkable increase of the amount of total carbohydrate extracted with polarity was found, selective extraction of tagatose decreased with increase of polarity of assayed cosolvents. To improve the recovery of extracted tagatose, additional experiments outside the experimental domain were carried out (300 bar, 80 degrees C, and 0.6 mL/min of isopropanol); recoveries >75% of tagatose with purity >90% were obtained.

New drug salt formation in biodegradable microspheres

Purpose. To investigate the effects of inorganic salts in the external phase of an oil-in-water (O/W) emulsion method during microsphere preparation. Methods. An O/W emulsion method was used to prepare poly( d, l-lactic acid) microspheres containing quinidine sulfate. Different inorganic salts were used in the external phase during microsphere preparation. Microsphere drug loading was determined by UV and the drug salt anions inside the microspheres were determined by ion chromatography. Results. New drug salts were formed during encapsulation in the microspheres when salts with non-common anions to the drug salt were used. Drug loading increased when NaClO 4 or NaSCN were used. The fraction of drug as the new salt in microspheres increased non-linearly with the salt concentration in the external phase, however, the fraction of drug as the new encapsulated salt was linearly related to drug loading. Drug loading decreased and new salt fraction increased with increasing organic solvent volume or with decreasing cosolvent polarity. Conclusions. Introducing salts containing non-common anions to the drug salt employed in the external phase of O/W emulsion microsphere method leads to new salt formation. The extent of new drug salt formation is affected by salt levels added, cosolvent type and polymer concentration.

The Influence of Cosolvent Polarity on the Flow Properties of Hydroalcoholic Gels. Empirical Models

The aim of this study was to investigate the influence of cosolvent polarity on the rheological flow properties of aqueous and hydroalcoholic gels obtained from the Carbopol Ultrez 10 base and used for topical applications. Specifically, we have examined the effect of pH (range 4.0--7.0) on the consistency and flow properties of dispersed systems in water and mixtures--15 : 85% v/v of methanol : water, ethanol : water, n-propanol : water and n-butanol : water--at a constant polymer concentration of 0.3% w/w. The gels, which had decreasing polarity values in the jellifying medium, showed qualitatively similar flow behavior, characteristic of pseudoplastic systems, and all of the flow curves were adjusted to the Ostwald model. Sigmoidal dose response functions were calculated to describe the flow and consistency indexes as a function of pH. As a result, the influence of alcohol polarity on the polymer network has been assessed meaningfully using the empirical parameters obtained: maximum consistency index value (k(max)), pH value required for 50% development of polymer network (pH(50)), and asymptotic flow index value (n(min)) for the fully structured gels.

Solubility study of polyacrylamide in polar solvents

AbstractContact angles and surface tension data were measured to obtain the surface tension components of polyacrylamide (PAM). According to Van Oss, Chaudhury, and Good (VCG) theory, the surface tension components were used to calculate the PAM solubility in five different polar solvents: water, ethylene glycol (EG), acetone, ethanol, and dimethyl formamide (DMF). It was found that PAM had a monopolar surface nature, which resulted in polymer dissolution in water. The solubility of PAM in water was greater than in EG, but PAM was solvophobic in the other three solvents. For PAM, water, and the second solvent (cosolvent) ternary system, the solubility of PAM could not be calculated directly. Surface tension was used as an index of polarity for cosolvent systems (the mixture of water and the second solvent). The cosolvent polarity decreased when the composition of the second solvent increased. PAM would be dissolved in the cosolvent when the system's polar contribution was greater than the apolar contribution. The apparent surface tension of PAM aqueous solutions was not sensitive enough to show polymer conformation changes when additive concentrations were changed. The solubility of PAM in binary polar solvent systems or ternary cosolvent systems was used to estimating the swelling properties of a PAM hydrogel under corresponding external conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1493–1499, 2004

Tetrakis[3-(diethylamino)propyl]- and Tetrakis[3-(diethylmethylammonio)propyl]phthalocyanines: The First Amphiphilic Phthalocyanines

Abstract The first amphiphilic cobalt (III) and copper phthalocyanines (V) have been prepared and are characterized by UV-absorption and magnetic circular dichroism (MCD) spectra in water and organic solvents and in their mixtures. These phthalocyanines exist as dimers in water and as monomers in some organic solvents. Monomer–dimer equilibrium was affected by solvent polarity (or hydrophobicity); with lower cosolvent polarity favoring formation of monomers. Cyclic voltammetry suggests that III adsorbed onto glassy carbon (GC) from an aqueous or acetonitrile (AN) solution in monomeric, irrespective of its state in solution. The CoII/I redox potential of III shifts anodically by adsorption onto GC, and this shift is larger when adsorbed from an AN solution than from an aqueous solution. Electroreduction of oxygen occurs at more positive potential at III-adsorbed GC in plain solution than at bare GC in III-dissolved solution.

Cosolvency and cosolvent polarity.

The solubilities of three poorly soluble drugs, phenytoin, benzocaine, and diazepam, in cosolvent-water mixtures have been previously shown to be approximated by the log-linear solubility equation; log (Sm/Sw) = sigma f, where Sm and Sw represent the solubilities of the drug in the solvent mixture and water, respectively, f is the volume fraction of cosolvent, and sigma is the slope of a plot of log (Sm/Sw) vs f. In this study, the slopes, sigma, of the solubility plots were related to indexes of cosolvent polarity including the dielectric constant, solubility parameter, surface tension, interfacial tension, and octanol-water partition coefficient. Those polarity indexes that reflect the cohesive properties of the solvents such as the solubility parameter and interfacial tension resulted in the highest correlations with the slope, sigma. The hydrogen bonding ability of the neat cosolvent, expressed as the density of proton donating groups (HBD) or acceptor groups (HBA), was also found to be highly correlated with sigma. Additional relationships derived from theories involving solubility parameters and interfacial tension provide improved correlations between the cosolvent polarity and sigma. These results and analysis provide the basis for the estimation from physicochemical parameters of the appropriate type and amount of cosolvent needed to solubilize nonpolar drugs.