Water Cosolvent Research Articles

Co-Solvent Selection for Supercritical Fluid Extraction (SFE) of Phenolic Compounds from Labisia pumila.

A preliminary study was conducted to study the effects of different types and concentrations of co-solvents based on yield, composition and antioxidants capacity of extract prior to optimization studies of supercritical fluid extraction (SFE) of Labisia pumila (locally referred to as ‘kacip fatimah’). The following co-solvents were studied prior to the optimization of supercritical carbon dioxide (SC–CO2) technique: ethanol, water, methanol, as well as aqueous solutions of ethanol–water and methanol–water (50% and 70% v/v). By using the selected co-solvents, identification of phenolic acids (gallic acid, methyl gallate and caffeic acid) was determined by using High-Performance Liquid Chromatography (HPLC). Then, the antioxidant capacity was evaluated by using three different assays: total phenolic content (TPC), ferric reducing/antioxidant power (FRAP) and free radical-scavenging capacity of 2,2-diphenyl-1-picrylhydrazyl (DPPH). SC–CO2 with 70% ethanol–water co-solvent was superior in terms of a higher combination of phenolic compounds extracted and antioxidants capacity. Overall, SC–CO2 with co-solvent 70% ethanol–water technique was efficient in extracting phenolic compounds from L. pumila, and thus the usage of this solvent system should be considered for further optimization studies.

Practical two‐step chain extension method to prepare sulfonated waterborne polyurethanes based on aliphatic diamine sulphonate

AbstractWe reported a novel synthesis route to fabricate sulfonated aliphatic waterborne polyurethane dispersions (SWPU) only based on 2‐[(2‐aminoethyl) amino] ethane sulphonate sodium (AAS‐Na) by two‐step chain extension method with the assistance of acetone and water cosolvent. When AAS‐Na was added, only less than 50% of AAS‐Na was incorporated into polyurethane chain in the first‐step chain extension and the residual AAS‐Na formed molecular aggregates which were insoluble in acetone due to the high polarity of AAS‐Na. Subsequently, the mixture of acetone and water was added, the residual AAS‐Na aggregates dissolved, undertaking the further second‐step chain extension reaction, and the ultimate reaction conversion of AAS‐Na rose to more than 90%. The mechanism for acetone and water cosolvent to affect the preparation of SWPU dispersions was studied, as well as the water resistance, mechanical properties and hydrolysis resistance of as‐prepared SWPU dispersions. With the decrease of AAS‐Na content from 2.0% to 1.2%, the peak area of the melting peaks for SWPU films increased, as well as the water resistance. And the as‐prepared polyester SWPU exhibited good hydrolytic stability.

Improved pervaporation efficiency of thin-film composite polyamide membranes fabricated through acetone-assisted interfacial polymerization

•Promoting the separation efficiency of pervaporation membranes is a must to meet the growing demands of society. In this study, acetone-assisted interfacial polymerization was employed to produce thin-film composite (TFC) pervaporation membranes with improved performance. Two monomers were considered—diethylenetriamine (DETA) and trimesoyl chloride (TMC); they reacted with each other to form a thin polyamide layer, which was deposited on a hydrolyzed polyacrylonitrile (HPAN) substrate. Aqueous solutions containing different concentrations of acetone were used to dissolve DETA. Introducing acetone as a cosolvent of water enhanced the sorption of DETA in the HPAN support. It also altered and improved the physicochemical properties of the TFC membranes. An optimum concentration of 50 wt% aqueous acetone solution was established. Through acetone-assisted interfacial polymerization, a TFC membrane was then fabricated, and it exhibited a high separation efficiency: permeation flux = 1641 ± 134 g∙m−2 h−1 and water concentration in the permeate = 98%–99% (feed =70 wt% aqueous isopropanol solution). Moreover, the modified TFC membrane displayed a high separation performance at a wide range of operating conditions.

Effect of thermochemically fractionation before hydrothermal liquefaction of herbaceous biomass on biocrude characteristics

Abstract Hydrothermal liquefaction (HTL) of fractionated two types herbaceous biomass (kenaf and miscanthus) by dilute acid, organosolv, alkaline, or demineralization process was carried out under ethanol water co-solvent at 350 °C for 30 min to examine the biocrude yield and characteristics. The biocrude properties were comprehensively characterized by HPLC, elemental, GC-MS, and TGA analysis. Fractionation technologies before HTL effectively increased biocrude yield up to 38% compared to that of untreated herbaceous biomass (31%), except for organosolv fractionation of miscanthus, especially, HTL after alkaline fractionation showed high yield and energy recovery ratio up to 70%. Elemental analysis showed that HHV of biocrude was negatively affected by hydrolysis reaction of high lignin content after dilute acid fractionation. The GC-MS analysis revealed that carbohydrates-derived compound significantly increased in the biocrude obtained after organosolv and alkaline fractionation due to holocellulose increases through fractionation process. Additionally, TGA results indicated that the ratio of high-boiling-point compounds in biocrude obtained after demineralization was expanded compared with untreated due to ash removal, which could act as a catalyst.

The modified supercritical media for one-pot biodiesel production from Chlorella vulgaris using photochemically-synthetized SrTiO3 nanocatalyst

Abstract In this research, a one-pot production of biodiesel, hydrocarbons, oxygenates, and aromatics form Chlorella vulgaris was performed in supercritical methanol without catalyst and in the presence of TiO2 and SrTiO3 nanocatalysts. The reaction in the presence of SrTiO3 showed the highest production yield of fatty acid methyl esters (FAMEs). The co-solvents water, chloroform, diethyl ether, and n-hexane were used for modifying the supercritical medium to affect the product yields in SrTiO3-catalyzed process. The SrTiO3 nanocatalyst was photochemically prepared and the leaching of catalysts into the products was evaluated. Results showed that for all products except oxygenates, the addition of diethyl ether and chloroform to methanol had a slightly positive effect on the production yields. For all products, n-hexane co-solvent showed the best performance with production yields of 16.65, 2.42, 2.12, and 0.57 mg.g−1biomass for FAMEs, oxygenates, hydrocarbons, and aromatics, respectively. Furthermore, the water showed no significant effect on production yields except in the case of oxygenates. The results may be due to the high ability of n-hexane for dissolving the biomass in the reaction condition. Also, the ICP-OES detected no trace amounts of catalyst in the final product and it confirms that the photochemical method for catalyst preparation can prevent the catalyst leaching.

Modeling of supercritical fluid extraction by enhancement factor of cosolvent mixtures

ABSTRACT In this study, Sovová mass transfer-based mathematical model for supercritical fluid extraction was modified by incorporating a cosolvent enhancement factor. Modeling of supercritical carbon dioxide with different cosolvent mixtures was successfully performed in the extraction of model plants (Phyllanthus niruri and Polygonum minus) with an average absolute relative deviation (AARD) of less than 7.90%. The existence of non-typical extraction curves in SCO2 with alcohol–water cosolvent was also well fitted and predicted by the modified model. In the extraction of both plants, internal mass transfer was found to be the rate-limiting factor in the first phase of extraction, namely pre-extraction. Abbreviations: A: surface area; ɛ: porosity; dp : particle size or size distribution; D: vessel diameter; EC : enhancement factor; EC,V : enhancement factor in vapor phase; EC,L: enhancement factor in liquid phase; f: total solvent flow rate; H: height; kXa: mass transfer coefficient in solid phase; kYa : mass transfer coefficient in fluid phase; mt : mass of extract; MCER : global extraction yield at constant extraction rate; N: mass of the inert solid; : moles of solvent without cosolvent; : moles of solvent with cosolvent; : total solvent moles without cosolvent; : total solvent moles with cosolvent; P: pressure; Qf : solvent mass flow rate; Sij : selectivity; t: extraction time; T: temperature; tCER : the end of the first extraction period; tFER : the end of the second extraction period; U: solvent superficial velocity; W: model parameter related to the diffusion in solid phase; xi, xj : solvent mole fraction in liquid phase; Xk : mass of hardly accessible solute; Xo : initial mass of extractable material; Xp : ratio of extractable material at particle surface in solid phase; yi, yj : solvent mole fraction in vapor phase; : mole fraction of pure governing solvent; : mole fraction of the solvent in the cosolvent mixtures; Y*: solute solubility in the solvent; YCER : solubility at constant extraction rate; Z: model parameter related to convection in the fluid phase; zw : parameter of the second extraction period; ρf : solvent density; ρs : sample density; μ: viscosity.

Solution-Processable PEDOT:PSS:α-In2Se3 with Enhanced Conductivity as a Hole Transport Layer for High-Performance Polymer Solar Cells

Two-dimensional (2D) nanosheets have attracted significant attention in photovoltaic devices in recent years owing to their outstanding photoelectric properties. Herein, 2D α-In2Se3 nanosheets with high conductivity and suitable work function are synthesized by liquid-phase exfoliation method. To ameliorate the low conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (2.21 × 10-3 S cm-1), α-In2Se3 nanosheets are directly added into PEDOT:PSS to obtain the PEDOT:PSS:α-In2Se3 composite film. The composite film exhibits excellent optical transmittance, suitable work function, and enhanced conductivity (1.54 × 10-2 S cm-1). To profoundly investigate the mechanism of conductivity improvement, X-ray photoelectron spectroscopy, Raman spectroscopy, electron paramagnetic resonance, and atomic force microscopy are conducted. The results show that the synergistic effect of 2D α-In2Se3 nanosheets and isopropyl alcohol/deionized water cosolvent screens the Coulombic attraction among PEDOT and PSS. The screening effect results in the partial removal of PSS and the benzoid-quinoid transition of PEDOT. In addition, α-In2Se3 nanosheets may serve as physical linkers for PEDOT chains. Both these effects are beneficial to increase the interfacial contact area between PEDOT chains and form a larger conductive network of PEDOT, leading to an enhanced conductivity. The composite film is first employed as a hole transport layer (HTL) in polymer solar cells (PSCs). The power conversion efficiency (PCE) of the poly[2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione)] (PBDB-T):3,9-bis(2-methylene(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)dithieno-[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC)-based device with composite HTL is 10% higher than that of the unmodified PBDB-T:ITIC-based device, and the maximum PCE of 15.89% is achieved in the (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene))-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c']dithiophene-4,8-dione))] (PM6):(2,2'-((2Z,2Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2,″3″:4',50]thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) (Y6) system. More interestingly, the stability of devices with composite HTL is improved owing to the partial removal of PSS. Thus, the PEDOT:PSS:α-In2Se3 composite can be a potential HTL material in PSCs.

The Dynamics of Lignin in Melt

Lignocellulosic biomass shows great potential as renewable sources of biofuels, materials and chemicals. However, to fully harvest this potential, we must first understand the fundamental molecular processes that drive the deconstruction of biomass to various fuels and chemicals. A major obstacle in sustainability of a biorefinery is valorization of lignin, a major plant biopolymer thattakes up approximately 20-30% of plants by mass. Lignin is ideally suited as a precursor of value-added biomaterials because its high content of carbon and is major waste product from the pulp and paper industry. However, the rigidity of lignin, makes it the most recalcitrant component of plant biomass, and it is therefore necessary to use pre-treatments to enhance the efficiency of the biomass breakdown. The main role of pre-treatment, typically involving the use of solvents, is to soften the material, which facilitates deconstruction and conversion of biomass. At the atomic level this means softening the lignin by increasing its atomic fluctuations.Therefor understanding how the dynamics of lignin is modified by the solvent pretreatment could lead to a better understanding how to soften the material.To this end we have investigated the nanoscale dynamics of lignin in a melt with tetrahydrofuran (THF) as a water cosolvent using both molecular dynamics (MD) neutron spectroscopy. MD probes similar length- and timescales as quasi-elastic neutron scattering (QENS) so the neutron scattering profile can be calculated from the atomic positions in the simulation trajectories, thus results from MD and NS can be directly compared.

Efficient polysulfide trapping enabled by a polymer adsorbent in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been viewed as promising candidates for next-generation high-energy rechargeable batteries due to their high theoretical energy density. However, their practical application is severely impeded by the notorious shuttle effect of soluble polysulfides. Herein, a nature polymer of konjac glucomannan (KGM) was adopted as polysulfide-adsorbing agent by coating on carbon nanofiber (CNF) mats for polysulfide-trapping interlayers in Li-S batteries. A uniform coating method was developed by improving the wettability of CNFs to aqueous solutions using ethanol as a co-solvent of water. It is revealed that not only the KGM polymer itself but also the coating quality is critical to prevent polysulfide diffusion. With the improved coating quality and the strong chemisorption of KGM, the shuttle effect was effectively suppressed and excellent electrochemical performance was demonstrated with a high reversible capacity of 1286 mAh g−1 at 0.2C, good cycling stability with a capacity retention of 84% after 400 cycles at 1C and high rate capability. Our findings provide a facile way to address the shuttle behavior of Li-S batteries using low-cost and environmental friendly materials, which are very promising for large-scale energy storage applications.

Fast predictions of liquid-phase acid-catalyzed reaction rates using molecular dynamics simulations and convolutional neural networks.

The rates of liquid-phase, acid-catalyzed reactions relevant to the upgrading of biomass into high-value chemicals are highly sensitive to solvent composition and identifying suitable solvent mixtures is theoretically and experimentally challenging. We show that the complex atomistic configurations of reactant–solvent environments generated by classical molecular dynamics simulations can be exploited by 3D convolutional neural networks to enable accurate predictions of Brønsted acid-catalyzed reaction rates for model biomass compounds. We develop a 3D convolutional neural network, which we call SolventNet, and train it to predict acid-catalyzed reaction rates using experimental reaction data and corresponding molecular dynamics simulation data for seven biomass-derived oxygenates in water–cosolvent mixtures. We show that SolventNet can predict reaction rates for additional reactants and solvent systems an order of magnitude faster than prior simulation methods. This combination of machine learning with molecular dynamics enables the rapid, high-throughput screening of solvent systems and identification of improved biomass conversion conditions.

Thermodynamic analysis and preferential solvation of sulfamethazine in acetonitrile + water cosolvent mixtures

This paper presents the solubility of sulfamethazine (SMT) in the acetonitrile (MeCN) + water (W) cosolvent system at nine temperatures. From the solubility experimental data, the thermodynamic functions of solution, mixing, and transfers are calculated and analyzed using the Perlovich graphical method. On the other hand, an enthalpy−entropy compensation analysis is performed and the preferential solvation parameters are calculated using the Kirkwood-Buff (IKBI) inverse integral method. The result of the performed calculations indicates that the SMT solution process is endothermic with entropic favor, where the addition of MeCN has a positive cosolvent effect between pure water and the mixture with w1 = 0.90. As for the preferential solvation, the SMT molecule is preferentially surrounded by water in water- and MeCN-rich mixtures, and in intermediate mixtures, the SMT molecule tends to be surrounded by MeCN.

Water as DES-cosolvent on the morphology tuning and photochromic enhancement of tungsten oxide-molybdenum oxide nanocomposite

In this study, we report the utilization of different water contents (0–40vol.%) as cosolvent to ethaline, ChCl:EG (deep eutectic solvent) at the mole ratio of 1:2 to prepare binary oxide of tungsten oxide-molybdenum oxide nanocomposite in an ambient environment, followed by characterization using XRD, FTIR, SEM, TEM, TGA, XPS and UV–vis spectroscopy. The as-prepared composite composed of aggregated particles at low temperature of 60°C, in the crystallite sizes ranging from ˜48.40 to 71.97nm, with water cosolvent acting as bad solvent. Further characterizations revealed that the atomic percentage ratios of tungsten and molybdenum components increase with decrease in carbon content as the water content increases, while the morphology changes from cubic to prismatic polyhedral-like structures at low temperature, in addition to retaining ˜73% of its original weight above 700°C. The UV–vis analysis revealed broad absorption at 239–374nm with a threshold value of 527nm and can attain maximum photochromic response in less 60s on exposure to UV–vis light irradiation.

A Multifunctional Cosolvent Pair Reveals Molecular Principles of Biomass Deconstruction.

The complex structure of plant cell walls resists chemical or biological degradation, challenging the breakdown of lignocellulosic biomass into renewable chemical precursors that could form the basis of future production of green chemicals and transportation fuels. Here, experimental and computational results reveal that the effect of the tetrahydrofuran (THF)-water cosolvents on the structure of lignin and on its interactions with cellulose in the cell wall drives multiple synergistic mechanisms leading to the efficient breakdown and fractionation of biomass into valuable chemical precursors. Molecular simulations show that THF-water is an excellent "theta" solvent, such that lignin dissociates from itself and from cellulose and expands to form a random coil. The expansion of the lignin molecules exposes interunit linkages, rendering them more susceptible to depolymerization by acid-catalyzed cleavage of aryl-ether bonds. Nanoscale infrared sensors confirm cosolvent-mediated molecular rearrangement of lignin in the cell wall of micrometer-thick hardwood slices and track the disappearance of lignin. At bulk scale, adding dilute acid to the cosolvent mixture liberates the majority of the hemicellulose and lignin from biomass, allowing unfettered access of cellulolytic enzymes to the remaining cellulose-rich material, allowing them to sustain high rates of hydrolysis to glucose without enzyme deactivation. Through this multiscale analysis, synergistic mechanisms for biomass deconstruction are identified, portending a paradigm shift toward first-principles design and evaluation of other cosolvent methods to realize low cost fuels and bioproducts.

Recovery of Polyphenols from Grape Pomace Using Polyethylene Glycol (PEG)-Grafted Silica Particles and PEG-Assisted Cosolvent Elution.

Adsorption on a functionalized surface can be an effective way of purifying polyphenols from complex plant extracts. Polymeric resins that rely on hydrophobic interactions suffer from low selectivity, weak affinity towards polyphenols, and lack tunability therefore making the purification of polyphenols less efficient. In this study, a purification process for the recovery of polyphenols from grape pomace extract was successfully developed using hydrogen bonding affinity ligands grafted on silica particles and PEG-assisted elution solvents. Bare silica (SiO2) and polyethylene glycol (mPEG)-grafted silica microparticles with molecular weights of 2000 and 5000 were tested to determine their polyphenol binding and release characteristics. Functionalizing the surface of bare silica with mPEG ligands increased the adsorption capacity by 7.1- and 11.4-fold for mPEG-2000 and mPEG-5000 compared to bare silica particles, respectively. This was likely due to the introduction of more polyphenol binding sites with mPEG functionalization. Altering the molecular weight (MW) of mPEG grafted on silica surfaces provided tunability in the adsorption capacity. A complete recovery of polyphenols (~99.9%) from mPEG-grafted silica particles was achieved by utilizing PEG–ethanol or PEG–water cosolvent systems. Recovered polyphenols showed up to ~12-fold antioxidant activity compared to grape pomace extract. This study demonstrates that mPEG-grafted silica particles and elution of polyphenols with PEG cosolvents can potentially be used for large-scale purification of polyphenols from complex plant extracts and simplify the use of polyphenols, as PEG facilitates remarkable solvation and is an ideal medium for the final formulation of polyphenols.

Formation of Methylene Linkage for N-Heterocycles: Sequential C-H and C-O Bond Functionalization of Methanol with Cosolvent Water.

An iron-catalyzed methylene forming strategy is disclosed through sequential C-H and C-O bond functionalization of methanol with cosolvent water. This protocol provides an easy and novel access to methylene-tethered imidazo[1,2- a]pyridine and 2-aminopyridine analogues in a sustainable manner and represents a complementary approach to traditional methylene forming strategies.

Solubility enhancement (Solid Dispersions) novel boon to increase bioavailability

The solubility of a solute is the maximum quantity of solute that can dissolve in a certain quantity of solvent or quantity of solution at a specified temperature. Solubility is one of the important parameter to achieve desired concentration of drug in systemic circulation for pharmacological response to be shown. Solubility is essential for the therapeutic effectiveness of the drug, independent of the route of administration. Low aqueous solubility is the major problem encountered with formulation development of new chemical entities as well as for the generic development. Poorly soluble drugs are often a challenging task for formulators in the industry Conventional approaches for enhancement of solubility have limited applicability, especially when the drugs are poorly soluble simultaneously in aqueous and in non-aqueous media. Drug with poor water solubility cause slow dissolution rates, generally show erratic and incomplete absorption leading to low bioavailability when administered orally. Solubilization may be affected by cosolvent water interaction, micellar solubilization, reduction in particle size, inclusion complexes, solid dispersion, and change in polymorph. Some new technologies are also available to increase the solubility like micro emulsion, self-emulsifying drug delivery system and supercritical fluid technology. This present review details about the different approaches used for the enhancement of the solubility of poorly water-soluble drugs include particle size reduction, nanonization, pH adjustment, solid dispersion, complexation, co‐solvency, hydrotropy etc. The purpose of this article is to describe the techniques of solubilization for the attainment of effective absorption and improved bioavailability.
 Keywords: Solubility, Solubility Enhancement, bioavailability, solid dispersion, Solid Dispersion, Solubilization.

A combined calorimetric, spectroscopic and molecular dynamic simulation study on the inclusion complexation of (E)-piceatannol with hydroxypropyl-β-cyclodextrin in various alcohol + water cosolvents

(E)-Piceatannol, a naturally occurring polyphenol, has gained increasing interests in pharmaceutical and food industries due to the health-promoting effects. However, the application of (E)-piceatannol is severely limited by its low solubility and poor bioavailability. Cosolvation and complexation are two effective methods to increase the solubility of insoluble active compounds. The effect of alcohol + water cosolvents on the inclusion complexation of (E)-piceatannol with hydroxypropyl-β-cyclodextrin (HP-β-CD) was investigated using isothermal titration calorimetry, fluorescence spectroscopy and molecular dynamics simulation. The stoichiometry and thermodynamic parameters for the complexation process were obtained. The results showed a 1:1 stoichiometry between (E)-piceatannol and HP-β-CD. The complexation constants decreased with the increase of the alcohol concentration and the alkyl chain length, but increased with the increasing number of hydroxyl groups of the alcohols. The main driving forces for the inclusion process were obtained from the enthalpy and entropy changes. The effect of temperature on the inclusion complexation was discussed in terms of the heat capacity change calculated from the temperature dependence of enthalpy change. The differences in thermodynamic parameters in different cosolvents were explained in detail based on the assumption that the alcohol acts both as a solvent and as a competitor to (E)-piceatannol. Both binding enthalpy and binding entropy exhibited a noticeable temperature dependence with almost complete enthalpy–entropy compensation. Fluorescence intensity of (E)-piceatannol increased with the increasing concentration of HP-β-CD and showed a slight hypsochromic shift. The microscopic structure of the inclusion complex in different alcoholic cosolvents was obtained from the molecular dynamics simulation. These results illustrated the importance of optimizing the solvent systems when utilizing cyclodextrins as food or drug carriers.

Influence of glycerol on the cooling effect of pair hydrophobicity in water: relevance to proteins' stabilization at low temperature.

Glycerol, as a cosolvent of water, stabilizes proteins under extreme conditions (both at high and low temperatures). However, the mechanism of stabilization of proteins by glycerol at low temperature is still elusive. Because the decrease of hydrophobic interactions at a lower temperature is one of the crucial factors for the cold denaturation, we ask here whether glycerol protects the hydrophobic interactions upon cooling and thereby acts against cold denaturation. Here, we have performed potential of mean force (PMF) calculations, using the umbrella sampling technique, between a pair of methane hydrophobic solute molecules either in pure water or in binary mixtures of water and glycerol for two different compositions and each of them at four different temperatures. We have found that glycerol increases the pair hydrophobic interaction at all the temperatures studied and that the enhancement is more prominent at the lower temperatures studied here. Decomposition of the PMF into the enthalpic and the entropic components and detailed molecular structural analyses give insight into the above observation. We have found that the enhancement of the hydrophobic interaction with increasing glycerol concentration occurs primarily due to the strengthening of the glycerol-water interaction near the associated methane solute molecule pair and the tetrahedral ordering of the H-bonding network being made uniform around the solute by the added glycerol molecules. These results indirectly justify the efficacy of glycerol for the preservation of proteins against cold denaturation at low temperature.

Prediction of Acid Red 138 solubility in supercritical CO2 with water co-solvent.

Acid Red 138, as a weak acid azo dye with a long alkyl chain, is widely used for protein fiber dyeing while it cannot dissolve in supercritical carbon dioxide. The objective of this study is to investigate the solubility of Acid Red 138 with water at the temperatures of 353.15, 363.15, 373.15, 393.15 and 413.15 K and over a pressure range of 20 to 26 MPa. The test results revealed that the phase equilibrium of water and Acid Red 138 was affected by the competition between pressure and density of supercritical carbon dioxide. Furthermore, the experimental solubilities were correlated by three types of density-based model. Good agreement with less than 3.36% of average absolute relative deviation between the calculated and the experimental data of water was achieved. In addition, the Chrastil model, Mendez-Santiago–Teja model and Sung–Shim model exhibited excellent correlation results for Acid Red 138 solubilities with the AARD values of 8.58%, 6.06% and 5.19%. Better understanding of the solubility behavior of Acid Red 138 in supercritical carbon dioxide displays potential for developing a microemulsion system for the eco-friendly dyeing of natural fibers.

The Dependence of Temperature and Composition on the Equilibrium Solubility and Thermodynamic Studies of Bioactive N-(9-Fluorenylmethoxycarbonyloxy)succinimide in Various Water–Cosolvent Mixtures

The equilibrium solubility of N-(9-fluorenylmethoxycarbonyloxy)succinimide in {dimethyl sulfoxide (DMSO), ethanol, ethylene glycol (EG), N,N-dimethylformamide (DMF)} plus water were determined by means of the isothermal equilibrium method at (283.15–328.15) K under atmosphere pressure. The measured values of N-(9-fluorenylmethoxycarbonyloxy)succinimide are positively increased with the increase of temperature in a certain cosolvent composition; however, that decreased when the content of water was gradually increasing and the largest solubility data was observed in pure DMF (0.04989 in mole fraction, 328.15 K). The mole fraction solubility in monosolvents ranked as DMF (9.693 × 10–3, 298.15 K) > DMSO (6.406 × 10–3, 298.15 K) > ethanol (8.237 × 10–4, 298.15 K) > EG (3.136 × 10–4, 298.15 K) > water (7.378 × 10–6). Under conditions of the same temperature and cosolvent composition, the solubility maximum of N-(9-fluorenylmethoxycarbonyloxy)succinimide was found in (DMF + water, 9.693 × 10–3 in mole fraction ...