Dioxane-water Mixtures Research Articles

Simultaneous lower and upper critical solution temperature‐type co‐nonsolvency behaviour exhibited in water–dioxane mixtures by linear copolymers and hydrogels containing N‐isopropylacrylamide and N,N‐dimethylacrylamide

AbstractThe co‐nonsolvency behaviour in water–dioxane mixtures of linear copolymers and hydrogels consisting of N‐isopropylacrylamide (NIPAM) and N,N‐dimethylacrylamide (DMAM) was studied as a function of solvent composition and temperature. The composition of the copolymers, P(NIPAM‐co‐DMAMx), in DMAM units, x, varies from x = 0 up to x = 100%. It is shown that the copolymers combine the lower critical solution temperature (LCST)‐type co‐nonsolvency behaviour of poly‐NIPAM with the upper critical solution temperature (UCST)‐type co‐nonsolvency behaviour of poly‐DMAM. Depending on x, both the LCST‐ and UCST‐type co‐nonsolvency behaviour may be simultaneously observed in water‐rich and dioxane‐rich solvent mixtures, respectively. Due to this complex phase separation behaviour, the variation of the reduced viscosity of the linear copolymers, as well as the swelling–deswelling behaviour of the respective hydrogels, are shown to be temperature‐ and solvent‐sensitive. Copyright © 2006 Society of Chemical Industry

Stability of copper(II) complexes with cellulose complexite in water-dioxane mixtures

The complexing properties of cellulose complexite with respect to copper(II) ions in water-1,4-dioxane (DO) mixtures are determined. The stoichiometry and stability constants of copper(II) complexes with the hydroxamic groups of the polymer are determined. The equilibrium speciation diagrams for the complexes at pH 2.0–6.0 are plotted; stereochemical configurations are suggested. The effect of the solvation parameters of the complexite on complex formation is analyzed.

Complexation studies of N,N′-ethylene-bis(salicylideneimine)-cation complexation behavior in dioxane-water mixtures by conductometric studies

The tetradentate-ligand Schiff base derived from salicylaldehyde and 1,2-diaminoethane has been synthesized. The stability constants and thermodynamic values for the complexation between ZnCl2, Cu(NO3)2, and AgNO3 salts and the ligand in 80% dioxane-water were determined by conductance measurements. The order of the formation constant for complexes of the ligand with Cu(II), Zn(II), and Ag(I) ions was found to be: Ag(I) < Cu(II) < Zn(II). The magnitudes of these ion association constants are related to the nature of the solvation of the cation and the complexed cation.

Micellar effects on the molecular aggregation and fluorescence properties of benzazole-derived push–pull butadienes

The absorption and fluorescence spectral behaviour of 1-(2-benzoxazolyl)-4-( p-dimethylaminophenyl)buta-1,3-diene and its benzothiazolyl analogue (abbreviated as BODB and BTDB, respectively) have been investigated in dioxane–water mixtures and micellar environments using steady-state techniques. In water, water-rich mixtures or premicellar solutions, BODB and BTDB tend to form molecular aggregates labelled as H-aggregates. These aggregates dissociate on adding surfactants forming micellized monomers. In all micellar media the fluorescence quantum yield is greatly enhanced along with a large hypsochromic shift. Also, in TX-100, CTAB and SDS both dienes show dual emission from the locally excited (LE) and intramolecular charge transfer (ICT) states. For BTDB in TX-100 and DODB in all solutions, the LE fluorescence predominates, while for BTDB in CTAB and SDS, the ICT fluorescence is the predominant. The fluorescence shifts suggest that the fluorescing molecules penetrate the core of the micellar unit in TX-100, whereas in CTAB and SDS they occupy the interfacial region. The binding constants and the micelle properties (such as polarity and CMC) have been determined using both dienes as probes.

Proton-ligand stability constants of cefadroxil and stability constants of its metal complexes in aqueous-organic mixtures

Proton-ligand stability constants of cefadroxil and its metal-ligand stability constants with Cu 2+ , Cd 2+ and Co 2+ ions were determined pH-metrically at 30 °C and ionic strength of 0.15 M KCl in aqueous, water-alcohol (75: 25% v/v) and water-dioxane (75: 25% v/v) mixtures. Cefadroxil formed 1: 1 (ML) complexes with Cd 2+ and Co 2+ whereas 1: 2 (ML 2 ) with Cu 2+ in aqueous, water-alcohol (75: 25% v/v) and water-dioxane (75: 25% v/v) mixtures.

Synthesis, characterisation and polar effect of the substituent on the reaction mechanism of 3-aminophenyl phosphate esters

The kinetics and mechanism of the acid hydrolysis of 3-aminophenyl phosphate esters have been studied in 0.1 to 6.0 mol dm -3 HCl at 90 ± 0.5 °C. The effects of temperature, solvent and substrate concentration on the rate of hydrolysis have been studied and the results suggest that the hydrolysis of monoester occurs by the cleavage of P-O bond fission. The rate coefficients estimated are fairly in good agreement with the experimentally observed ones. Bond fission, molecularity and order of reaction have been supported by Arrhenius parameters, Zucker-Hammett hypothesis, concentration, solvent effect etc. A study of the reaction in dioxane water mixture suggested the nature of transition state in which charges are developed due to the bimolecular attack of water molecule. Comparative isokinetic rate data of similarly substituted phenyl phosphate monoesters, whose mechanism is known, supported P-O bond fission.

Thermodynamics of electrolytes in mixed solvent media — Application of the Pitzer ion interaction approach

Although for a long time considerable attention has been paid to the application of the Pitzer ion interaction approach to describe the thermodynamic properties of a variety of aqueous electrolyte solutions, such studies in mixed solvent media are still scarce. The present paper discusses the application of the Pitzer ion interaction approach in the case of electrolyte solutions in mixed solvent media. In particular, a comprehensive equation for the thermodynamic properties of hydrochloric acid in dioxane–water mixtures within the temperature range 273.15 to 323.15 K has been generated in the ion interaction (Pitzer) equation form on the basis of electrochemical cell measurements of the hydrochloric acid available in the literature. It was necessary to set varying values of the exponential coefficients α1 and α2 of the standard Pitzer model in different mixed solvent media to achieve a satisfactory fit. The present model quantitatively reproduces the experimental cell electromotive forces over the entire concentration and temperature range used for the experiments. The Pitzer ion interaction approach is, thus, proved to be a very valuable method for the correlation and prediction of thermodynamic properties of electrolytes in mixed solvent media. The implications of the Pitzer ion interaction parameters (β(0), β(1) β(2), and Cϕ) have also been discussed in terms of interionic forces. The present study also stresses the need for additional emf measurements to help interpolation through the dioxane composition. Key words: Pitzer's equations, Pitzer ion interaction parameter, activity coefficients, emf, hydrochloric acid.

Control of the lower critical solution temperature—type cononsolvency properties of poly( N-isopropylacrylamide) in water—dioxane mixtures through copolymerisation with acrylamide

The behaviour of the homopolymers poly( N-isopropylacrylamide) (PNIPAM), polyacrylamide (PAM) and random copolymers of N-isopropylacrylamide (NIPAM) with acrylamide (AM) was studied by turbidimetry and viscometry in mixtures of water with dioxane. It was found that the well-known lower critical solution temperature-type cononsolvency properties of PNIPAM in water–dioxane mixtures, observed in the water-rich region, can be effectively controlled by copolymerisation of NIPAM with AM. Thus, the cononsolvency properties of the copolymers in water–dioxane mixtures are shifted to higher temperatures and restricted within a narrower solvent composition region as the acrylamide content of the copolymers increases. A significant decrease of the reduced viscosity of the systems exhibiting phase separation properties was observed upon heating, indicative of the collapse of the (co)polymer chains as temperature approaches the corresponding cloud point temperature. Furthermore, when temperature is fixed close to the cloud point temperature, the reduced viscosity decreases with increasing the volume fraction of dioxane, φ, as far as the solvent mixtures are rich in water. On the contrary, the reduced viscosity of PNIPAM in dioxane-rich mixtures is found significantly higher, indicative of an expansion of the polymer chain, as compared to the reduced viscosity of this polymer in the two pure solvents.

Self-association of free base porphyrins with aminoacid substituents in AOT reverse micelles

The aggregation properties of aminosulfonyl porphyrins with aminoacid substituents: methionine with the acid function methylated, PMe t C H 3 ; phenylalanine, PPhe; attached to the para positions of the meso phenyls of the porphyrin, was followed in organic solvents, water–dioxane mixtures and in reverse micelles of aerosol OT (AOT RM), using absorption, steady-state and time-resolved fluorescence. In AOT RM in the absence of water, both porphyrins are mainly present as monomers with the Soret band around 420 nm and with emission maxima around 649 and 717 nm. In the presence of water accounted for by parameter ω 0, ω 0 = [H 2O]/[AOT], the solubility of both porphyrins is enhanced and followed by important spectral changes similar to those observed in the solvent mixtures: new maxima in absorption around 405 nm and in emission around 670 nm. A concomitant increase of the aggregates’ contribution is found for PMe t C H 3 , whereas for PPhe the effect is much more pronounced until ω 0 = 10, above which a de-aggregation process occurs, due to competition between intra- and inter-molecular interactions. The small resonant light scattering signals observed points to the existence of aggregates of small dimensions whose nature is discussed in terms of exciton theory.

About the singular behavior of the ionic condensation of sodium chondroitin sulfate: Conductivity study in water and water–dioxane mixture

In this work, we generalized the (Bjerrum–Debye–Fuoss–MSA) double layer model to an ellipsoidal polyion (chondroitin sulfate) of (∣ Z s∣ e) structural charge, L s structural length, R minor axe and ( R 2 + L 2/4) 1/2 major axe. With L ⩽ L s. Na + counter ions are distributed on the contact (or condensed) layer and on the Debye layer (ionic atmosphere). Both layers are ellipsoidal equipotentials of, respectively, R and d minor axes and are concentric to the polyion. With d = ( R + 1/2 Γ), Γ is the Debye–MSA screen parameter. The equilibrium distribution of Na + ions is derived from a “two states” statistical approach, leading to a general implicit expression for the rate of condensation (1 − α). The generality of this formula results from the fact that it takes into account the finite size of the polyion ( L ≠ ∞ and R ≠ 0) and allows to calculate α for different conformations of the polyion: (ellipsoidal L ≠ 0, cylindrical: L = L s, spherical: L → 0, and Manning’s model: RL −1 → 0). The main conclusion of this model is that, α obeys to the Ostwald’s principle of dilution ( α → 1 when C Na+ → 0). This result is contrary to Manning’s theory, for which α is a constant α M independent on the concentration C i : α M = b S/(∣ Z i ∣ L b), with b S = L s/∣ Z s∣ and L b = e 2/( εkT) is the Bjerrum length. However, our analysis shows that the rate of variation: (∂ α/∂ C i ) in a given range of concentration, depends on the structural parameter b S. Indeed, the critical Manning condition ( α −1 α M = 1, ⇒(∂ α/∂ C i ) ≈ 0), is compatible with the general following “rod-like model” approximation: ( 1 - α ) ≈ | Z i | ( π b S ) [ 4 π Z i 2 L b ] [ - b S ″ α ] [ α C i R 2 ] [ 1 - b S ″ α ] ; with b S ″ = α M - 1 only for some peculiar values of b S and L b (i.e., dielectric constant: ε). In water at 25 °C ( ε = 78.3), this singular behavior occurs for a range of a relative low or moderate concentration for some polyelectrolytes of b S structural parameter of about 5.8 Å. This is the case of sodium chondroitin sulfate in water ( b S = 5.72 Å). The addition of dioxane increases L b, consequently, α is shifted from its Manning’s value. In order to verify this dioxane effect, we have compared experimental equivalent conductibilities Λ exp of sodium chondroitin sulfate in water ( no shift) and water–dioxane (60 wt%) mixture ( positive shift), to their theoretical values Λ M, Λ c th and Λ s th corresponding, respectively, to the Manning, cylindrical and spherical models. This comparison allows also, to explain the conformation “chosen” by the polyion, in order to minimizing the friction effects (due to: viscosity; ionic and dielectric relaxations) and therefore, to optimize its mobility by the shift of its rate of ionic condensation α.

On the Role of the Solvent and Substituent on the Protonation Equilibria of Di-Substituted Anilines in Dioxane–Water Mixed Solvents

Protonation constants of a number of di-substituted anilines were determined potentiometrically in 0, 20, 30, 40, 50, and 60% (v/v) dioxane–water mixtures at (25.00 ± 0.02) ∘C with an ionic strength of 0.10 mol-dm−3 sodium perchlorate. The data are discussed in terms of the electronic character of the substituents. Two different methods were used to study the effects of the solvents on the protonation constants; one involved a single polarity parameter, the Dimroth–Reichardt parameter ET(30); the other involved the Kamlet–Taft multi-parametric method. The protonation constants of di-substituted anilines correlate with the molecular parameters for the dipolarity/polarizability of the solvent, π∗, and its hydrogen-bond acceptor ability, β.

2-(2-Selenocyanic acid ethyl ester)-1 H-benz[de] isoquinoline-1,3-(2 H)-dione, synthesis photophysics and interaction with bovine serum albumin: A spectroscopic approach

The compound 2-(2-selenocyanic acid ethyl ester)-1 H-benz[de] isoquinoline-1,3-(2 H)-dione (SEBID), a ubiquitous, bioactive naphthalimide derivative is expected to possess an anticancer, anti-tumor and other important therapeutic activities of significant potency with low systematic toxicity. In this paper, the synthesis of the compound, photophysics of the newly prepared naphthalimide derivative and its interaction with model transport protein Bovine serum albumin (BSA) have been reported using the absorption and steady state fluorescence spectroscopic techniques exploiting the intrinsic fluorescence emission properties of BSA as a probe. Interaction of this organoselenium compound in different dioxane–water mixtures with increase in the polarity of the medium has been studied spectroscopically. Interaction of SEBID with BSA leads to a dramatic decrease in the fluorescence intensity of BSA, which suggests the binding of SEBID with the tryptophan residue of BSA. Furthermore, different thermodynamic parameters for SEBID–BSA interaction have been calculated. Rationalization of the data has been attempted, particularly in relation to prospective applications in the biomedical research.

Interaction of pyrene-end-capped poly(ethylene oxide) with bovine serum albumin and human serum albumin in aqueous buffer medium: A fluorometric study

The photophysical behavior of a hydrophobically tailored water-soluble polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), has been studied in aqueous buffered bovine serum albumin (BSA) and human serum albumin (HSA) media. In buffered aqueous solution the polymer shows dual emission corresponding to the monomer and the excimer of pyrene moiety. The relative intensity of the monomer to the excimer emission shows interesting variation with the addition of BSA and HSA and is indicative of significant interaction of these albumin proteins with the polymer. The binding interaction has been shown to have a prominent role on the steady state fluorescence anisotropy of the two emission bands. Attempt has been made to determine the micropolarities of the protein microenvironments from a comparison of the variation of the monomer to excimer relative fluorescence intensities of the probe in water–dioxane mixtures with varying composition.

Slow solvation dynamics of 4-AP and DCM in binary mixtures

In a binary mixture of benzene and dimethylformamide (DMF), solvation dynamics of 4-aminophthalimide (4-AP) and 4-(dicyanomethylene)-2-methyl-6-( p-dimethylaminostyryl)-4H-pyran (DCM) displays a slow component. As mole fraction of DMF increases from 0.028 to 0.28 the average solvation time (〈 τ s〉) for 4-AP decreases from 830 to 450 ps while for DCM it decreases from 450 to 100 ps. In dioxane–water mixtures 〈 τ s〉 for DCM is 250 ps which remains unaffected as mole fraction of water increases from 0.22 to 0.50.

The benzil–benzilic acid rearrangement in high-temperature water

The rearrangement of benzil is base (and not acid) catalyzed under conventional conditions (water–dioxane mixture around 100 °C). We examined this reaction in high-temperature water (HTW) between 300–380 °C with the intent of studying a reaction that proceeds solely by base catalysis in this more environmentally benign medium. The rearrangement proceeds in neutral HTW without addition of base, but the yield of rearrangement products is nearly insensitive to pH at near-neutral conditions. Adding larger amounts of base, however, leads to much higher yields and 100% selectivity to rearrangement products. Likewise, adding larger amounts of acid leads to comparable yields, but less than 100% selectivity. The selectivity to rearrangement products generally increased with pH at near-neutral and basic conditions whereas the selectivity to benzil decomposition products (a competing thermal pathway) exhibited a maximum at near-neutral conditions. We conclude that the benzil rearrangement is catalyzed by acid, base, and water in HTW. The dominant mechanism shifts as the pH changes. This system shows that mechanisms that are unimportant at conventional reaction conditions can become dominant in HTW. It also demonstrates the ability to use pH to direct the selectivity of a reaction in HTW.

Solvent and Substituent Effects on the Protonation of Anilines in Dioxane–Water Mixtures

Protonation constants of a number of mono-substituted anilines were determined potentiometrically in 0, 20, 30, 40, 50, and 60% (v/v) dioxane–water mixtures at (25.00 ± 0.0.02)°C at an ionic strength of 0.1 mol-dm−3 in sodium perchlorate. The data from the potentiometric titrations were evaluated using the BEST computer program. The trends in the values of the protonation constants of anilines were explained in terms of the nature of substituent and the solute–solvent and solvent–solvent interactions. Furthermore, the effects of the substituents on the basicity of aniline, the additivies of these effects, and the applicability of the Hammett equation to the behavior of these substituents are discussed.

Solubility and phase separation of benzocaine and salicylic acid in 1,4-dioxane–water mixtures at several temperatures

The solubilities of benzocaine and salicylic acid were determined in water–dioxane mixtures at several temperatures (5–40 °C for benzocaine and 10–40 °C for salicylic acid). The solubility curves as a function of dioxane ratio showed a maximum at 90% dioxane at all temperatures. Above 25 °C, the homogeneous mixture splits into two liquid immiscible phases. For benzocaine, the initial dioxane concentration range at which phase separation takes place increased with temperature (50–60% at 25 °C, 50–70% at 30–35 °C and 40–70% at 40 °C). For salicylic acid, the dioxane concentration required for phase separation (40–60% dioxane) did not change with temperature. Phase separation was not related to solid phase changes (polymorphism or solvates). The phase composition and drug extraction at the drug-rich phase were determined. The apparent enthalpies of the solution process were a nonlinear function of the dioxane ratio for both drugs. The apparent enthalpy of solution of benzocaine was larger than that expected at the upper limit of phase separation (70% dioxane), whereas for salicylic acid the apparent enthalpy of solution decreased abruptly at the region corresponding to phase separation (40–70% dioxane). Both drugs showed a nonlinear pattern of enthalpy–entropy compensation.

Synthesis, Characterization and Stability Constants of Polynuclear Metal Complexes

Unsymmetric tridentate ligands, 4-methyl-2,6-di(4-methyliminomethyl)phenol (HL1), 4-(t-butyl)-2,6-di(4-methylphenyliminomethyl)phenol (HL2), 2,6-di(4-bromophenyliminomethyl)-4-methylphenol (HL3), 2,6-di(4-bromophenyliminomethyl)-4-(t-butyl)phenol (HL4), 2,6-di(4-hydroxyphenyliminomethyl)-4-methylphenol (HL5) and 4-(t-butyl)-2,6-di(4-hydroxyphenyliminomethyl)phenol (HL6), and their binuclear CuII, CoII and NiII complexes were synthesized and characterized by elemental analysis, FT-IR, u.v.-vis spectrometry magnetic moments, 1H(13C)-n.m.r. and mass spectral data. Also, the electrical conductivities of the complexes have been measured using 10-3 M solutions in MeCN. The complexes are weak electrolytes. In the electronic spectra of the complexes of the HL1-HL6 ligands, the 480-410 nm band has been determined as the charge-transfer band. While the HL5 and HL6 ligands have five potential donor atoms, other ligands have only three. Protonation constants of the ligands have been studied in dioxan-water mixtures. In addition, the antimicrobial properties of the ligands and their metal complexes have been studied:Bacillus megaterium, Micrococcus luteus, Corynebavterium xenosis, Enterococcus faecalis, bacteria and Saccoramyces cerevisia, yeast. The keto-enol tautomeric equilibria of the ligands have been investigated in polar and non-polar solvents.

Fluorometric investigation of interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3- a] quinolizine with bovine serum albumin

Interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3- a] quinolizine (AODIQ) with a model transport protein, bovine serum albumin (BSA), has been studied using steady state fluorescence and fluorescence anisotropy experiments. Upon binding with BSA, the charge transfer (CT) fluorescence exhibits appreciable hypsochromic shift along with an enhancement in the fluorescence intensity. Gradual addition of BSA leads to the marked increase in the fluorescence anisotropy ( r). From the high value of fluorescence anisotropy ( r=0.30) it is argued that the probe molecule is located in motionally restricted environment of the protein. Addition of urea to the protein bound AODIQ leads to the decrease in fluorescence intensity as well as fluorescence anisotropy ( r) indicating the release of AODIQ molecule to the aqueous buffer medium, thus supporting the idea that the protein, in its native form, binds with the probe. The binding constant and free energy change (Δ G 0) for the interaction of AODIQ with BSA have been evaluated from relevant fluorescence data. Polarity of the microenvironment has been determined from a comparison of the variation of fluorescence property of the probe in dioxane–water mixture with varying composition.

Photophysics of pyrene-end-capped poly(ethyleneoxide) in aqueous micellar environments

The photophysical behavior of pyrene-end-capped poly(ethyleneoxide) (PYPY) has been studied in different aqueous micellar environments like cetyltrimethylammonium bromide (CTAB, cationic), triton X-100 (TX-100, non-ionic) and sodium dodecyl sulfate (SDS, anionic). In pure aqueous medium, the polymer solution shows dual emission corresponding to the monomer and the excimer. The relative intensity of the monomer and the excimer emissions shows interesting variation with the addition of the surfactants leading to the determination of the critical micellar concentrations (CMCs) of the micelles. The determined CMCs for CTAB and TX-100 micelles are in good agreement with the existing literature values. In SDS, however, variation of different fluorometric parameters against surfactant concentration results in the CMC values noticeably different from the reported CMC values for SDS micelles. This has been attributed to the interaction between SDS and the poly(ethyleneoxide) (PEO) chain of the polymer leading to the formation of mixed micelles. The micropolarity around the fluorophore has been determined in the micellar environments from a comparison of the variation of the relative fluorescence intensities of the monomer to the excimer band in water–dioxane mixtures with varying composition.