Mixed Polar Solvents Research Articles

Effect of Confinement on the Properties of Sequestered Mixed Polar Solvents: Enzymatic Catalysis in Nonaqueous 1,4-Bis-2-ethylhexylsulfosuccinate Reverse Micelles.

The influence of different glycerol, N,N-dimethylformamide (DMF) and water mixtures encapsulated in 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/n-heptane reverse micelles (RMs) on the enzymatic hydrolysis of 2-naphthyl acetate by α-chymotrypsin is demonstrated. In the case of the mixtures with DMF and protic solvents it has been previously shown, using absorption, emission and dynamic light-scattering techniques, that solvents are segregated inside the polar core of the RMs. Protic solvents anchor to the AOT, whereas DMF locates to the polar core of the aggregate. Thus, DMF not only helps to solubilize the hydrophobic substrate, increasing its effective concentrations but surprisingly, it does not affect the enzyme activity. The importance of ensuring the presence of RMs, encapsulation of the polar solvents and the corrections by substrate partitioning in order to obtain reliable conclusions is highlighted. Moreover, the effect of a constrained environment on solvent-solvent interactions in homogenous media and its impact on the use of RMs as nanoreactors is stressed.

An Electrical Conductimetric Study of Association Phenomena of 4- Aminoantipyrine (4-AAp) Complexes in Mixtures of Methanol-Water at Different Temperatures

The aim of this work is to measure the electrical conductivity of Co (II) and Ni (II) complexes with 4-amino antipyrine in mixtures of different percentages of methanol and water at different temperatures. The data were analyzed using the Lee-Wheaton equation for unsymmetrical electrolytes, the conductivity parameters: ionic equivalent conductivity λM+2, association constant KA, and the distance parameter R are calculated. The ionic equivalent conductivity λM+2, increases with increasing temperature, which may attributed to the breaking of hydrogen bonds between solvated ion. Association constant KA increase with increasing temperature, which assumed the presences of simple coloumbic interactions between hard sphere ions in continuous medium. The distance parameter R are calculated at the bist fit values of standard deviation σΛ. Thermodynamic parameters from the relation between LnKA and 1T were calculated to examine the nature of interaction. Walden product were calculated which show the variation depending on electrochemical equilibrium between ions and the solvent molecules with the composition of the mixed polar solvents.

Molecular Organized Assemblies Formed by Tetradecyl Aryl Sulfonate

We investigated the micelles,reverse micelles,and microemulsions formed by three kinds of tetradecyl aryl sulfonates synthesized in our laboratory under different conditions using surface tension,iodine spectrometry,water solubilization,and phase diagram methods. The influences of molecular structure,solvents,inorganic saltss and short chain alcohols on these molecular organized assemblies were discussed. Results show that aqueous solutions or mixed polar solvents (EG-water) are unfavorable for micelle formation but that reverse micelle formation in non-polar solvents (n-heptane) is favorable when the branching coefficients of the lipophilic group in the tetradecyl aryl sulfonate molecules increase. A decrease in solvent polarity causes the surfactant solution to transform from a micellar solution to a monomer solution and then to a reverse micellar solution. Upon addition of inorganic salts or short chain alcohols,micelle formation is favored in aqueous solutions. Together with higher counter-ion valence states or alcohol alkyl carbon atoms,micelle formation increases even further. As the concentration of inorganic salt increases,the surfactant/ n-butanol/n-octane/NaCl/ water microemulsion systems transform from Winsor I to Winsor III and then to Winsor II at specific temperatures.

Membrane electrode sensitive to a cationic surfactant in aquo-organic media

An electrode originally sensitive to dodecyltrimethylammonium ions (DTA +) was proven to be sensitive to tetradecyltrimethylammonium ions (TTA +) and was used for determination of critical micelle concentration of tetradecyltrimethylammonium bromide (TTAB) in water. Moreover the response of the electrode was tested in presence of non-aqueous polar solvents i.e. dimethyl formamide (DMF) and dimethyl sulphoxide (DMSO) in water and was observed to be Nernstian within the concentration range studied (up to 40% v/v of DMF and DMSO). The validity of this electrode, for electrochemical measurements, was checked by comparing the critical micelle concentration values of TTAB obtained by using the electrode, with those obtained by conductivity measurements in mixed polar solvents. The effect of solvent on the micellization of TTAB has been discussed.

Small-Angle Neutron Scattering Characterization of Micelles Formed by Poly(dimethylsiloxane)-graft-polyether Copolymers in Mixed Polar Solvents

The self-assembled structure of an amphiphilic poly(dimethylsiloxane)-graft-polyether copolymer has been investigated in binary solvents consisting of water and one of the following polar organic solvents: 2-propanol, ethanol, formamide, or glycerol. Micelle structural parameters were obtained by fitting the core−corona form factor and hard-sphere interaction structure factor to small-angle neutron scattering (SANS) data obtained at contrast conditions where the solvents were fully deuterated and the copolymer was not. The siloxane copolymer forms in water at 20 °C micelles that consist of a “dry” core with a radius of about 6 nm and a solvated (about 40% polymer) corona with a thickness of 2 nm; the relatively thin corona may be due to the comb-type architecture of the siloxane copolymer. The micelle radii, micelle core radii, micelle association numbers, and polymer volume fractions in the micelle core and corona decreased with increasing cosolvent/water ratio in the mixed solvents containing 2-propanol, ethanol, or formamide. On the contrary, the addition of glycerol led to an increase of the micelle association number. The above findings are discussed in terms of the relative location of the polar organic solvents in the interior or exterior of the siloxane copolymer micelles. In particular, the micelle association numbers observed for different water−cosolvent mixtures can be correlated to the octanol−water partition coefficients of the respective cosolvents. A transition from spherical to ellipsoid micelles was observed upon an increase in the temperature: this is attributed to the desolvation of the polyether chains. This structural transition correlates with the solvent quality in the mixed solvents: ethanol and 2-propanol, which solvate the interior of the micelles, tending to keep the micelles spherical, while increased glycerol content in the mixed solvent leads to the formation of ellipsoids at a fixed temperature.

Vesicle formation of 1:1 cationic and anionic surfactant mixtures in N, N-dimethylformamide and tetrahydrofuran solutions

In the last two decades, many works on vesicle formation from natural amphiphiles (mainly phospholipids) and synthetic surfactants were reported [1,2]. However, up to 10 years ago amphiphiles used to form vesicles are mainly the double chained compounds including natural and synthesized amphiphiles. In 1989, Kaler et al. [3] revealed the vesicle formation from mixed cationic and anionic surfactants using cetyltrimethyl-ammonium tosylate and sodium dodecylbezene sulfonate. Similar work was done in our laboratory, using mixed surfactants of carboxylate and alkyltrimethylammonium compounds [4,5]. However, most works on vesicle formation have been involved in aqueous systems and those in non aqueous systems are less. Some works about vesicle formation in aprotic solvent systems were reported [6,7], which were concentrated on the systems of double-chained fluorocarbon surfactants [8–11]. On the other hand, the studies about vesicle formation in non aqueous polar solvent and mixed polar solvents’ systems are mainly on the liposome of phospholipids [12– 14]. Comparing with phospholipids and other double-chained amphiphiles, the cationic and anionic surfactants used as precursors for vesicle formation have the predominances of simple structure, excellent stability, and convenience in production. Therefore, investigation on vesicle formation by cationic and anionic surfactants is of great significance in both theoretics and applications. It is well known that many drugs are insoluble in water but soluble in organic solvents, and many useful reactions can be carried out in nonaqueous systems. However, the investigations about vesicle formation of mixed cationic and anionic surfactants in non-aqueous polar solvents are scanty. Obviously, it is important to study the vesicle formation in non aqueous or mixed solvents. In a previous paper [15], we reported the * Corresponding author.

Two luminescent intermediates of coelenterazine analog, peroxide and dioxetanone, prepared by direct photo-oxygenation at low temperature

A coelenterazine analog was photo-oxygenated at −78 C to give luminous intermediates. Irradiation in a mixed polar solvents as CF3CH2OH and MeOH with 13C- labeled analogs afforded the first evidence assignable to dioxetanone structure.

Correlation of unusual phase behaviour at elevated pressure

An unusual phase behaviour is in this context a phase behaviour which can not be correlated with a PVT model and the van der Waals approximation which is the most widely used mixture model in high pressure phase equilibrium thermodynamics. The van der Waals approximation is a successful model for correlation of phase equilibria in nonpolar fluid mixtures. All PVT models for reservoir fluids and in the petroleum industry are van der Waals approximations. In the chemical industry most phase equilibria are low pressure phase equilibria of systems containing polar compounds which can be correlated by means of an activity coefficient model. However, phase equilibria in systems containing mixed polar solvents and nonpolar solutes are difficult to correlate. In the last decade models have been developed which combine the complex composition dependence of activity coefficient models with equations of state. In the first part of the paper we review some rules of model developments set by the classical thermodynamics, although elementary, these rules are often overlooked, leading to inconsistent models. In the last part of the paper we review the state of the art of model developments and identify areas where further developments are warranted.

Solvent effects on chemiluminescence from the hydrogen peroxide-lucigenin reaction: Kinetics of light emission in mixed polar solvents

The effect of reaction media composition on reaction kinetics was studied for the reaction of lucigenin (10,10′-dimethyl-9,9′-biacridinium nitrate) with hydrogen peroxide and alkali. Chemiluminescent emission as well as lucigenin disappearance were recorded in mixtures of water with the co-solvents methanol, ethanol, 1-propanol, dimethylsulfoxide, and dimethylformamide. The kinetic results (base and peroxide concentration influence on the reaction rate and the relative chemiluminescence yield) are very similar in all the reaction media, suggesting that the fundamental step in the disappearance of lucigenin and in light emission decay is HO2− addition to lucigenin. Lucigenin can also disappear through dark reactions with OH− or H2O2. The co-solvent acts as a catalyst for the reaction with HO2− and increases both the initial chemiluminescence intensity and the decay rate constant.

Solvent effects in the reaction of lucigenin with basic hydrogen peroxide: Chemiluminescence spectra in mixed polar solvents

The chemiluminescent reaction of lucigenin with basic hydrogen peroxide has been studied in several mixtures of water with the cosolvents methanol, ethanol, 1-propanol, dimethylformamide, and dimethylsulfoxide. The chemiluminescence spectra depend on the cosolvent and its concentration in the reaction medium. With increasing cosolvent concentration, the chemiluminescence shifts to lower wavelengths. For similar cosolvents, the size of this shift increases with decreasing dielectric constant. In high-cosolvent-concentration mixtures, the chemiluminescence matches the fluorescent emission of N-methylacridone. Chemiluminescence from low-cosolvent-concentration mixtures is explained as the sum of the lucigenin and N-methylacridone fluorescent emissions, the lucigenin emission probably being a consequence of energy transfer from N-methyl-acridone. The cosolvent inhibits this energy transfer. These observations, taken together with our previous kinetic results, indicate that the reaction mechanism is the same in all the studied reaction media.

Spectroscopic properties of anisole in mixed polar solvents

Absorption and emission spectra, fluorescence quantum yields and lifetimes were studied for anisole in binary ethanol-water mixtures. The spectroscopic and photophysical properties show an exceptional behaviour in the aqueous solution. In water a strong nonradiative process, originating from the fluorescent state decreases the emission yield and lifetime. The results are discussed in terms of short range interactions between the solute and solvent.

Aspirin Degradation in Mixed Polar Solvents

Degradation studies were conducted on 0.2% w/v aspirin liquid formulation in a wide range of water-propylene glycol mixtures and water-triethylene glycol diacetate mixtures at four temperatures. The effect of a surfactant, polyoxyethylene (20) sorbitan monolaurate, on aspirin stability was also investigated. There was a linear relationship between water content and degradation rate constants. The surfactant increased aspirin degradation in all formulations. Formulations containing the higher concentration of the surfactant showed the greater aspirin decomposition.

Extended Hildebrand Solubility Approach: Methylxanthines in Mixed Solvents

The solubility profiles of theobromine, theophylline, and caffeine at 25° were examined in binary solvent systems including dioxane-formamide, water-polyethylene glycol 400, and glycerin-propylene glycol. Theobromine solubility was studied in dioxane-water mixtures, a solvent system that was investigated earlier for the solubility of theophylline and caffeine. Solubilities were calculated in these polar systems by a regression method, based on an extension of the Hilde-bland-Scatchard equation of regular solution theory. A linear relationship between the mixed solvent solubility parameter, δ1, and dielectric constant, ϵ, was introduced earlier and was confirmed in the present study. In addition, it was observed that a regression of log(activity coefficient) on ϵ in a second or higher degree polynomial provides reasonable solubility values for the methylxanthines in mixed solvents. A direct regression of molal or mole fraction (but not molar) solubility against δ1, ϵ, or against volume percent of one or the other solvent in a binary solvent mixture provided a suitable measure of solubility for these crystalline drugs in mixed polar solvents. The drug's solubility parameter as determined from peak solubility in mixed polar solvents varied somewhat, depending on the specific solvent system employed. It is suggested that a drug may exhibit one (or more) solubility parameters in nonpolar solutions and multiple solubility parameters in polar systems. The extended solubility approach serves for the back-calculation of solubilities in mixed solvent systems, even though the solubility parameter of the solute may vary from one solvent system to the next.

Electrostriction in Mixed Polar Solvents: Viscosity of Silver Nitrate in Methanol—Water Mixtures at 30°C

Article Electrostriction in Mixed Polar Solvents: Viscosity of Silver Nitrate in Methanol—Water Mixtures at 30°C was published on December 1, 1969 in the journal Zeitschrift für Physikalische Chemie (volume 68, issue 3_6).

Photo-Induced Trapped Electron in Rigid Media : Photobleaching Study in the Mixed Polar Solvents

An experimental study has been made on the optical absorption spectra on the photobleaching process of trapped electron ( e t - ) produced by photoionization of tryptophan in mixed polar solvents at 77°K. The population of e t - is decreased on the photobleaching process in these solvents according to the law which can be always expressed as the sum of two first-order decays. Two kinds of traps formed in the polar solvents have been shown to exist although the explicit mode of the trap is not clear. An assumption is presented that exchange of trapping of electron occurs between two traps on the photobleaching process of e t - .