Dioxane-water Mixtures Research Articles

Hofmann degradation of acrylamide copolymer: Synthesis of amine functionalized thermoplastic hydrogel

The amine functionalization of an acrylamide copolymer was achieved via Hofmann degradation. The starting material, poly(acrylamide-co-methyl methacrylate), was synthesized by radical precipitation polymerization. Using this copolymer, Hofmann degradation at 0°C in a water-dioxane mixture was done using sodium hypochlorite and NaOH. The resulting hydrogel could be dissolved in water-tetrahydrofuran mixtures, and the cast film had a water content of 73%. It was found that the conversion to primary amine was lower, and the extent of a side reaction was higher, compared to those of an acrylamide homopolymer. This was presumed to be due to the lack of the neighboring group effect among acrylamide units since it was a random copolymer. Further modification of this polymer by reacting the amine group is considered to obtain the desired properties for biomedical applications. © 1996 John Wiley & Sons, Inc.

Thermodynamics of the tautomeric, hydration and hemiacetalization of 5-deoxypyridoxal and pyridoxal in water-dioxane mixtures

The resolution of electronic spectra using log-normal curves has permitted a quantitative description of the equilibria of pyridoxal, one of the vitamin B6 molecules, and of the related 5-deoxypyridoxal in solution. Tautomeric, hydration and hemiacetalization equilibrium constants for water-dioxane mixtures of these compounds are reported (0–70% weight fraction in dioxane) at temperatures ranging from 10°C to 50°C. These results provide the standard thermodynamic function changes for the indicated processes in the different mixtures studied. The aldehyde content in the two compounds increases concomitantly with the dioxane content of the solution and also when it changes from the cationic to the anionic species. 5-deoxypyridoxal becomes significantly more hydrated in its more protonated form, K h (+a)/K h (±a)≈7–8, as do other aldehydes. Hemiacetalization in pyridoxal follow a similar pattern, K he (±a)/K he (−a)≈20–30, due principally to differences in the enthalpy contribution. Hemiacetalization is favored over hydration by ∼20.6 kJ-mol−1 in water solution.

Environmental effects on radiative and nonradiative transitions of some merocyanine dyes in homogeneous and microheterogeneous systems

Singlet excitation energies of some merocyanine dyes have been determined from absorption and fluorescence spectra in 1,4-dioxane-water mixtures and in anionic (SLS), cationic (CTAB) and nonionic (TX-100) micellar solutions. Fluorescence quantum yields have been measured and fluorescence lifetimes have been obtained by integration methods. Plots of the photophysical properties against the solvent polarity parameter, E T (30), showed double linear correlations in the dioxane-water mixture. Solubilization in micelles produces effects similar to those observed in mixtures with a high water content. The observed behavior was interpreted in terms of solvent clustering and solute compartmentalization.

Ab-initio studies on electroosmotic separation: separation of 1,4-dioxane in water solution

A novel technique in membrane separation based on the phenomenon of electroosmosis, recently developed by us [Jain et al., J. Membrane Sci., 78 (1993) 53] has been used to demonstrate the practicability of the phenomenon for the separation of 1,4-dioxane from a dioxane-water mixture. The method shows favourable prospects as a membrane separation process, at least for the separation of close boiling mixtures, provided that the components of the mixture possess a large difference in their dielectric constant values. The analysis of the data indicates that the separation of dioxane increases as the dioxane concentration in the feed solution increases. It is also found that the separation of dioxane increases as the applied electrical potential difference across the membrane increases.

Fluorometric assay for horseradish peroxidase in organic media

A fluorometric method for assaying the activity of horseradish peroxidase (HRP) in organic media has been developed. This method is designed on the basis of the disparity in the spectral properties of substrates and corresponding resultant polymers. It monitors the fluorescence quenching of substrate during enzymatic catalysis, and works efficiently in a number of organic media (such as dioxanewater mixture, acetone-water mixture, and alcohol-water mixture, and so forth) toward many substrates. This assay is simpler, more rapid, and more convenient compared with the commonly used HPLC method. It is qualitatively reproducible and can also be used for quantitative calculation of the substrate conversion.

The Behavior of Paracetamol in Mixtures of Amphiprotic and Amphiprotic-Aprotic Solvents. Relationship of Solubility Curves to Specific and Nonspecific Interactions.

The solubility of paracetamol was studied at 25°C in mixtures of amphiprotic and aprotic solvents of varying polarity (ethyl acetate-ethanol, ethanol-water, dioxane-water). A plot of the solubility mole fraction of the drug versus the solubility parameter of the solvent mixtures reached a peak in dioxane-water, and two solubility maxima within the polarity range provided by the ethanol-water and ethanol-ethyl acetate mixtures. This chameleonic can be quantitatively described in terms of cavity formation, nonspecific and specific interactions, represented by the Hildebrand solubility parameter and the acidic and basic solubility parameters of the solvent mixtures. The model predicts two solubility maxima, as found experimentally. The behavior of paracetamol in dioxane-water mixtures is similar to that of other drugs, showing a single maximum, although a small peak and a valley are also observed near the solubility parameter region where the maximum in ethanol-water appears. An increase in the temperature of fusion of the solid phase by about eight degrees was observed after equilibration of the powder with ethanol, ethyl acetate and dioxane. No changes in the solid phase were observed in water and aqueous mixtures below 50% water. The same change in the solid phase was also found in ethanol-ethyl acetate mixtures; it was independent of the nature and cosolvent ratio and had little effect on the relative variation of solubility with solvent composition. The solid phase contributes as a constant to the total solubility.

Thermodynamics of the solution equilibria of 3-hydroxypyridine and pyridoxine in water-dioxane mixtures

The thermodynamics of tautomeric and microscopic ionization equilibrium constants of 3-hydroxypyridine and pyridoxine have been determined in waterdioxane mixtures (0–70% weight fraction in dioxane) ranging from 10°C to 50°C. Generally, for both types of processes, the entropic contributions to the Gibbs energy predominate and this tendency increase concomitantly with the dioxane content in the media. The thermodynamic parameters are consistent with the corresponding values obtained from macroscopic ionization processes. An equation for the equilibrium constant K as a function of temperature and a solvent characteristic parameter is proposed to predict the K values throughout the whole range of the temperature and solvent compositions studied.

Protonation constants of some substituted 2-hydroxy-1-naphthalideneanilines in dioxan-water mixtures

The protonation constants of ten Schiff's bases synthesized by the condensation of 2-hydroxy-1-naphthaldehyde with aniline and o-, m-, and p-substituted methylanilines, ethylanilines and methoxyanilines in various dioxan-water mixtures have been determined potentiometrically using an electrode system calibrated in concentration units of the hydrogen ion. The influence of substituents in the molecular structure on the protonation constants is discussed. The log K 2 values relating to the protonation of imine nitrogen atoms are in accordance with the Hammett relationship for all solvent compositions. A reverse relationship is observed between log K 2 for all Schiff's bases and the mole fraction of dioxan. However, the log K 1 values corresponding to the protonation of naphtholate O-ions have been found to increase with the increase in concentration of dioxan. Both electrostatic and non-electrostatic contributions influencing these constants are briefly discussed.

Thermodynamic Functions of Ionisation of Benzoic and Substituted Benzoic Acids in Dioxan-Water Mixtures

Thermodynamic Functions of Ionisation of Benzoic and Substituted Benzoic Acids in Dioxan-Water Mixtures

Thermodynamic parameters of lanthanoid(III) complexation with 3-(α,δ-dicarboxy- n-propylidenehydrazino)-5,6-diphenyl-1,2,4-triazine(DCPT). part 2

The complex formation equilibria between lanthanoid(III) and DCPT ions have been studied by potentiometry in 75% (v/v) dioxane-water mixture and 0.10M KNO 3 as constant ionic medium, at 10, 20, 30 and 40°C. A series of mononuclear protic [Ln(HL)] 2+, [Ln(HL) 2] +, [Ln(HL) 3], [LnL(HL) 2] −, [LnL 2(HL)] 2− and non-protic [LnL 3] 3− complex species were found in solutions and their formation constants, ethalpies and entropies were determined. It was established that the stepwise Gibbs energies of the protonated complexes varied in the sequence − ΔG Ln(HL) > − ΔG Ln(HL) 2 > − ΔG Ln(HL) 3 , and the stepwise enthalpies the order was − ΔH Ln(HL) > − ΔH Ln(HL) 2 > − ΔH Ln(HL) 3 , and the entropy markedly increased in the order ΔS Ln(HL) > ΔS Ln(HL) 2 > ΔS Ln(HL) 3 . The results are discussed in relation to changes in the metal-water and metal-ligand bond strength. The variation of the thermodynamic parameters as a function of ionic potential of lanthanide elements is discussed in terms of the different hydration numbers of lighter and heavier lanthanide(III) ions.

Fluorescence monitoring of the hydrophobic surface of dextrin using p-toluidinonaphthalenesulfonate

The effect of the linear oligosaccharides dextrin (α-1a,4e-D-glucopyranose) and dextran (α-1,6-D-glucopyranose) on the emission properties of 2-(p-toluidino)-6-naphthalenesulfonate (TNS) has been studied in aqueous solution. TNS exhibits a 30-fold fluorescence enhancement on binding to dextrin, while with dextran there is only a marginal increase in the emission intensity. The polarity values of the binding sites are estimated by comparing the nonradiative rates of TNS with those in aqueous dioxane-water mixtures. The results indicate that the binding surface of dextrin is markedly less polar than that of dextran. This difference is attributed to the differing stereochemical constraints imposed on the two chains. The binding constants of TNS with the two polysaccharides in pure water have been determined in the presence and absence of several salting-in denaturants and salting-out reagents. Salting-in agents cause a decrease in the number of TNS molecules bound to the dextrin surface and an increase in the local polarity, while the salting-out agent LiCl increases the number of TNS molecules bound to dextrin. The interaction of TNS with dextran, however, is found to be very weak even in the presence of LiCl. Energy minimization studies reveal a hydrophobic surface for dextrin while no such amphiphilicity is observed in dextran.

Aggregation Behaviour of Some Reactive Dyes

The absorption spectra of aqueous solutions of monochlorotriazine reactive dyes, C.I. Reactive Red 9 and Reactive Orange 13 were measured in the presence of 5, 10, 25 and 50% (v/v) of ethanol, pyridine and dioxane-water mixtures and in varied concentrations of KCl, NaCl and LiCl. The varying position, intensity and shape of absorption bands are interpreted in terms of aggregation and disaggregation of dyes in solutions. The aggregation behaviour of the reactive dyes in solutions and in the presence of additives is related to their apparent deviations from Beer's law and aggregation numbers (N). The aggregation constant (K.) of the monomer/dimer equilibrium is calculated. Dyes in ethanol-water mixtures record a larger aggregation number and aggregation constant than in the presence of pyridine. Dioxane is classified as anon-polar solvent and hence has a more disaggregating influence. The value of the aggregation number and constant are increased with increasing salt conentration and the order of degree of aggregation is KCl > NaCl > LiCl related to the order of ionic radii of K+, Na+ and Li+ ions.

Pressure effect on proton jumps in dioxane-water mixtures at 25�C

The limiting molar conductances Λo of hydrochloric acid and potassium chloride in 2.5, 5, 10, and 15 mol% 1,4-dioxane-water mixtures were determined at 25°C as a function of pressure up to 196.1 MPa from the conductances measured in the dilute concentration range. The value of Λo(HCl) was two to three times larger than that of Λo(KCl) in each solvent mixture as well as in pure water. The excess proton conductance, as estimated by the equation [λ E o =Λo(HCl)−Λo(KCl)], increased with pressure in each solvent mixture, although the value of λ E o itself decreased rapidly with an increase in the dioxane content. The rate of increase in λ E o with pressure was not so large in dioxane-water mixtures as in pure water, and became smaller with an increase in the dioxane content in contrast to the cases of ethanol-water and t-butyl alcohol (TBA)-water mixtures. These results are discussed in terms of the difference between a dioxane and an ethanol or a TBA molecule in ability to stabilize the hydrogen-bonded networks of water in the water-rich region.

Thermodynamics of transfer processes, 1. Solubility of hydrophilic solutes in dioxane-water mixtures

The solubility profiles of oxalic and malonic acid in various dioxane-water mixtures are reported. These values are analyzed in terms of dipole moment and solubility parameter using theHildebrand treatment for regular solutions. The effect of temperature upon the solubility values was investigated and thus the thermodynamic parameters of the solutions were derived. The thermodynamic transfer functions of oxalic and malonic acid from water to aquo-dioxane mixtures were also calculated and analyzed in terms of solute-solvent interactions.

Isotherm of water sorption by human serum albumin in dioxane: Comparison with calorimetric data

AbstractThe dependence of the amount of water bound to human serum albumin (HSA) suspended in water–dioxane mixtures vs the equilibrium water concentration in the liquid phase was determined by the Fisher method at 298 K. The Langmuir model was used in order to describe the isotherm of the sorption of water by HSA at low water concentrations in the solvent. The calculated equilibrium constant of water adsorption (3.8 ± 0.6 l mol−1) is in good agreement with the adsorption constant obtained earlier from calorimetric data. The comparison of the determined isotherm of water sorption by HSA with the reported enthalpies of suspension formation showed that at low water concentrations in the solvent, water sorption is the only process contributing to the heat effects of the formation of the ‘protein + liquid’ heterogeneous system. From this comparison, the enthalpy of water adsorption by HSA was evaluated as −11.9 ± 1.7 kJ mol−1. At higher water concentrations in the solvent the amount of water adsorbed by HSA increased considerably. This increase in the amount of water on HSA at water activities above 0.5 is assumed to be due to the enlargement of the protein surface area.

New phase diagram for N-arylacrylamide/acrylamide/sodium acrylate copolymer gel

Examination was made of changes in the volume of N-arylacrylamide(NAA)/acrylamide/sodium acrylate copolymer gel immersed in acetone–water and dioxane–water mixtures. The gel underwent reversible volume change from a swollen to collapsed state via discontinuous volume change with increase in solvent composition. Volume change at the transition point decreased with increase in NAA content, and the transition point shifted first toward lower solvent content with increase in NAA content and then toward higher solvent content. This is a volume phase transition characterized by two conventional patterns. Plots of transition solvent composition as a function of gel polymer composition indicated a nobel phase diagram for the polymer gel, which is essentially equivalent to miscibility diagram usually observed for polymer solutions.

Kinetics of the silver ion-promoted hydrolysis of 2-methyl-2-(substituted phenyl)-1,3-dithianes in 10% dioxane–water mixtures. Implications for cyclic acetal hydrolysis catalysed by hydrogen ions

The hydrolysis of 1,3-dithianes derived from para-substituted acetophenones is promoted by silver ions. Kinetic study using a 10%(v/v) dioxane–water solvent shows that, when [Ag+]≲ 0.2 mol dm–3, the p-NO2, -Cl, -H and -Me derivatives hydrolyse via rapidly-formed 1 Ag+ : 1 dithiane-complexes, but that the p-MeO derivative forms an unreactive 1 : 1-complex and hydrolyses via a 2 Ag+ : 1 dithiane-complex. Comparison of the kinetic parameters with those available for analogous open-chain S,S-acetals reveals that cyclisation leads to a substantial (> 104-fold) overall loss of reactivity and that this loss arises both from a lowering of acetal basicity towards Ag+ and from a slower rate of hydrolysis of the 1 : 1-complex. The implications for hydrogen ion-catalysed hydrolyses of cyclic acetals are discussed, as are the reasons for the lower reactivity of the cyclic acetals.

Solubility Parameter-Based Methods for Predicting the Solubility of Sulfapyridine in Solvent Mixtures

AbstractSulfapyridine is used to test the extended Hildebrand approach for predicting solubility in dioxane-water mixtures. The method provided good agreement with the experimental data. A modification of this method, that directly relates the logarithm of the mole fraction solubility with the solubility parameter of the solvent mixture (δ1) gave results comparable to that of the extended Hildebrand approach. This suggests that the volume fraction of the solvent can be disregarded in the solubility equation. The modified method does not require the knowledge of the ideal solubility of the drug. A single equation based on the solubilities of several sulfonamides is able to accurately calculate the solubility profile of sulfapyridine from 0 to 70% water in dioxane. Beyond 70% water, the extended Hildebrand method or its simplified form provide less errors, but these methods require 12-14 experimental solubilities, whereas the single equation only needs two experimental solubilities.

Raman study of dioxane–D2O mixtures by analysis of the O–D band structure

AbstractChanges in the isotropic and anisotropic component profiles of the O—D stretching bands of D2O were studied in the range 0–0.5 mole fraction (m.f.) of 1,4—dioxane. The contribution of the CH Raman band of dioxane was subtracted using Raman spectra of dioxane—water mixtures in the same concentration range. A Fourier deconvolution technique was employed to resolve the overlapped components in the spectra. The information on the positions of the components in the isotropic spectra was used to fit them with symmetric components of mixed Gaussian—Lorentzian type. The wavenumbers of the resolved components in the isotropic and anisotropic spectra and the ratio of the intensities of the symmetric Fermi resonance components in the isotropic spectra were used to determine the concentration dependence of intermolecular, intramolecular and Fermi resonance parameters. The intermolecular and intramolecular interaction constants do not change significantly up to about 0.07–0.10 m.f. of dioxane and then gradually decrease. The Fermi resonance constant W does not change noticeably over the concentration range studied. The wavenumbers of the unperturbed O–D oscillator exhibits two different rates of increase with concentration of dioxane. The observed variations in the analysed parameters are interpreted in terms of hydrophobic hydration, hydrophobic interaction and hydrogen bonding in dioxane–water mixtures.

Molecular Properties of PPO Excimer Luminescence in a Binary Solvent

Abstract Time resolved emission spectra and the luminescence decay of 2,5-diphenyloxasole in dioxane-water mixtures disclose an important influence of water on the observed luminescence. We suppose that this is caused by structural changes of the solution connected with its water content.