Dioxane-water Mixtures Research Articles

STRUCTURE AND THERMAL PROPERTIES OF MALEATED LIGNIN-RECYCLED POLYSTYRENE COMPOSITES

In this work, the changes caused by a chemical modification of the properties and chemical structures of lignin are studied. Lignin from a mixture of Eucalyptus globulus and Eucalyptus nitens obtained through the kraft pulping process was used. The lignin was isolated by acid precipitation and modified by a reaction with maleic anhydride. Maleated lignin (ML) was incorporated to recycled polystyrene (rPS) at 2, 5, and 10 wt-% by a melt-blending process. Fourier transformed infrared spectroscopy (FT-IR) was used to determine the ML structure, and the morphology of rPS/ ML composites was studied by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the glass-transition temperature (T g ) and the thermal stability of rPS and rPS/ ML composites and were compared with virgin PS. The T g values of rPS and their composites were higher than those of the virgin PS. TGA revealed that the thermal stability of rPS with 2 and 5% of ML was slightly greater than that of the virgin PS. These results suggest that postconsumer PS can be used to obtain composite materials with good thermal properties. 4 . Alkaline lignin isolated from sugar cane bagasse blended with polar poly- mers as polyvinyl alcohol ( PVA), showed an increase of thermal stability due at least some miscibility of the lignin / PVA blend. The mechanical properties of the blends were not reported 5 . Lignin as powder product of the prehydrolysis of beech wood was used as filler on low density polyethylene (LDPE) and polypropylene (PP). In small concentration lignin acts as a stabilizer for PP, but over 10% acts as an initiator of degradation. On LDPE, lignin acts as a stabilizer at concentrations greater than 10%. For both polymers (PP and LDPE), the mechanical properties decrease with increasing lignin content 6 . Alkali lignin from bamboo was used to prepare poly(4-vinylpyridine) (PVP) / lignin blend film by the casting method. The glass transition temperature (T g ) of these blends increased with the increase of lignin content, which indicated that these blends were able to form a miscible phase due to the formation of intermolecular hydrogen bond between the hydroxyl of lignin and the pyridine ring of poly( 4-vinyl pyridine). The thermostability of these blends decreased with the increase of lignin content. Initially, an appreciable increase in the measured tensile strength was achieved with a lignin content of 15 %, at which the maximum value of tensile strength was reached but, the strain behaviour of these blend films was deteriorated 7 .In other study, commercial lignin (Protobind 100SA-140) was used as filler with and without silica , on polysiloxane as polymeric matrix. The results of the thermomechanical, physical, and thermal investigations have evidenced the fact that lignin inserted in a silicon matrix does not alter its properties, and in some cases (e.g. mechanical properties), it even induces a slight improvement of these, leading to the conclusion that lignin can be used as an extender for silicones, with positives effects mainly on the material's cost 8 . The miscibility of hardwood Kraft lignin with several synthetic polymers, polyethylene oxide (PEO), polyethylene terephthalate (PET), PP and PVA, has been analysed using thermal analysis and FT-IR spectroscopy. Miscible blends were observed in lignin / PEO and lignin / PET blends, while immiscible blend behavior in the blends of lignin / PP and lignin / PVA were reported 9 . Lignin from beech wood pre-hydrolysis with dioxane water mixture was used to study the oxidative stability of PP and recycled PP. Lignin was used in the concentration range from 0.5 to 10 wt-% with a commercial antioxidant (Irganox 1010). The antioxidant effect is increased with lignin concentration up to 5 wt-% 10

Dehydration of dioxane by pervaporation using filled blend membranes of polyvinyl alcohol and sodium alginate

Pervaporation membranes were made by solution blending of polyvinyl alcohol (PVA) and sodium alginate (SA). Accordingly, five different blends with PVA:SA weight ratio of 75:25, 50:50, 25:75, 20:80 and 10:90 designated as PS1, PS2, PS3, PS4 and PS5, respectively, were prepared. Each of these blends was crosslinked with 2, 4 and 6wt% glutaraldehyde and the resulting fifteen (5×3) membranes were used for pervaporative separation of 90wt% dioxane in water. The membranes made from PS4 and PS5 were not stable during pervaporation experiments. Among the stable membranes PS3 membrane crosslinked with 2wt% glutaraldehyde showed the best results for flux and selectivity. Thus, it was filled with nano size sodium montmorillonite filler and used for separation of dioxane–water mixtures over the entire concentration range of 80–99.5wt% dioxane in water. The membranes were also characterized by mechanical properties, FTIR, SEM, DTA–TGA and XRD.

Stability of binary complexes of L-aspartic acid in dioxan–water mixtures

Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in (0–60% v/v) 1,4-dioxan (Dox)-water mixtures was studied pH metrically at 303±0.1 K and at an ionic strength of 0.16 M. The models contained ML, ML2, ML2H2, ML2H3 and ML2H4 species. The trend in the variation of stability constants with Dox content was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of Dox-water media was also presented. KEY WORDS: Binary complexes, Stability constants, Aspartic acid, Speciation, Dioxan Bull. Chem. Soc. Ethiop. 2013, 27(3), 367-376.DOI: http://dx.doi.org/10.4314/bcse.v27i3.5

Ionic Strength Dependence of Four Stepwise Protonation Constants for Folic Acid in Different Aqueous Solutions of Dioxane

The protonation equilibria of vitamin B9 (folic acid) was studied at 298.15 K in a different water–dioxane mixtures [100 wdioxane = 20 %, 40 %, 60 %, and 80 %] with an ionic strength of 0.15 mol·dm–3 NaNO3. The influence of dioxane content on the protonation processes was explained. Also, four protonation constants have been determined in 60 % dioxane with an ionic strengths of (0.15, 0.20, 0.25, and 0.30) mol·dm–3 NaNO3 using the pH-potentiometric technique. HYPERQUAD 2008, a program based on nonlinear least-squares curve fitting was used to determine these four stepwise protonation constants of folic acid from the analysis of pH-potentiometric data. From the determined protonation constants, the representative folate species distribution diagrams were provided by HYSS 2009 program and discussed.

Potentiometric determination of stability constants and thermodynamic data for dimethyltin(IV) dichloride complexes with iminobis(methylphosphonic acid) in water and dioxane–water mixtures

The interaction of dimethyltin(IV) (DMT) with iminobis(methylphosphonic acid) (IDP) was investigated at 25 °C and ionic strength 0.1 mol dm−3 NaCl using the potentiometric technique. The formation constants of the complexes formed in solution were calculated using the non-linear least-squares program MINIQUAD-75. The stoichiometry and stability constants for the complexes formed are reported. The results showed the formation of 110, 111, 112, 11-1, and 11-2 for DMT–IDP complexes. The concentration distribution of the various complex species was evaluated. The effect of dioxane as a solvent on the hydrolysis of DMT and both the protonation and the formation constants of DMT complexes with IDP was discussed. The thermodynamic parameters ΔH° and ΔS° were calculated from the temperature dependence of the equilibrium constants. The effect of ionic strength on the hydrolysis of DMT, the protonation of IDP, and the formation constants of DMT–IDP complexes was also discussed.

Nabumetone Solubility Prediction in Dioxane-Water Mixtures Using Extended Hildebrand Solubility Approach

The extended Hildebrand solubility parameter approach is used to estimate the solubility of nabumetone in binary solvent systems. The solubility of nabumetone in various dioxane-water mixtures was analyzed in terms of solute-solvent interactions using a modified version of Hildebrand-Scatchard treatment for regular solutions. The solubility of nabumetone in the binary solvent, dioxane-water shows a bell-shaped profile with a solubility maximum well below the ideal solubility of the drug. This is attributed to solvation of the drug with the dioxane-water mixture, and indicates that the solutesolvent interaction energy is larger than the geometric mean (δ1δ2) of regular solution theory. The new approach provides an accurate prediction of solubility once the interaction energy (W) is obtained. In this case, the energy term is regressed against a polynomial in δ1 of the binary mixture. Quadratic, cubic, and quartic expressions of ‘W’ in terms of solvent solubility parameter were utilized for predicting the solubility of nabumetone in various dioxanewater mixtures. But from these three polynomial expressions, a quartic expression of ‘W’ in terms of solvent solubility parameter was found suitable for predicting the solubility and yields an error in mole fraction solubility of ~7.346%, a value approximating that of the experimentally determined solubility. Thus the method has potential usefulness in preformulation and formulation studies during which solubility prediction is important for drug design.

Study of hydrogen bonding and thermodynamic behavior in water–1,4-dioxane mixture using time domain reflectometry

A picosecond time domain reflectometry (TDR) technique was used to measure complex permittivity of water–dioxane mixtures in frequency range of 10–30GHz covering entire concentrations range and in temperature range of 0–25°C. The Luzar theoretical model is used to compute the binding energies and average number of hydrogen bond for water–water and water–dioxane molecules. The number of hydrogen bond density is found to be maximum for the mixture with water concentration Xw=0.7. The negative values of the excess parameters suggest significant heteromolecular hydrogen bonding interactions between water and dioxane molecules. The relationships between hydrogen bond density as obtained by the Luzar model and excess dielectric parameters is also discussed.

Solving the trade-off phenomenon in separation of water–dioxan mixtures by pervaporation through crosslinked sodium–alginate membranes with polystyrene sulfonic acid-co-maleic acid

Polymeric membranes composed of sodium alginate and polystyrene sulfonic acid-co-maleic acid were prepared using a solution technique. The resulting membranes were characterized by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Membranes were tested for their ability to separate water–dioxan mixtures in the temperature range of 30–50°C. The experimental results demonstrated that both flux and separation factor were increased simultaneously with increasing the PSSA-MA content in the membrane. The permeation flux of pure Na-Alg membrane was increased dramatically from 7.1 to 10.6×10−2kg/m2h with increasing the mass% of PSSA-MA, and correspondingly its separation factor was increased from 6400 to 22,500 at 30°C for 10 mass% of water in the feed. The total flux and flux of water were found to be overlapping each other particularly for crosslinked membranes, suggesting that these membranes could be used effectively to break the azeotropic point of water–dioxan mixture. From the temperature dependent permeation values, the Arrhenius activation parameters were estimated.

On the Influence of Molecular Structure on the Conductivity of Electrolyte Solutions – Sodium Chloride in Dioxane–Water Mixtures

AbstractTheoretical calculations of the conductivity of sodium chloride in water+1,4-dioxane mixtures are presented and compared with experimental measurements. The method of direct correlation force in the framework of the interionic theory is used for the calculation of transport properties in connection with the associative mean spherical approximation (AMSA). The effective interactions between ions in solutions are derived with the help of Monte Carlo calculations on the Born–Oppenheimer level. This work is based on earlier studies on structure of dioxane+water mixtures and the solvation of ions in it.

Effect of nanocavities on the torsional dynamics of thioflavin T in various non-aqueous reverse micelles

The photophysics of thioflavin T (ThT) were observed in different non-aqueous reverse micelles by using steady state absorption and emission spectroscopy and time resolved fluorescence spectroscopy. We have used glycerol, ethylene glycol, dimethyl formamide, methanol and acetonitrile as polar solvents to form reverse micelles. In all reverse micelles with increase in w (w = [polar solvent]/[AOT]) the fluorescence quantum yield decreased in a regular way. The time resolved fluorescence study of ThT in different reverse micelles shows the similar trend as like above. We had plotted a calibration curve using the fluorescence quantum yield of ThT in glycerol-methanol mixtures vs. viscosity and from that curve we found that ThT faced a greater microviscosity in glycerol pool of AOT/isooctane/glycerol reverse micelles than in the pure glycerol, even at the highest w value. In all reverse micelles the emission quantum yield of ThT was retarded several times compared to neat solvents. We have found that the fluorescence quantum yield of ThT decreased with gradual increase in polarity by studying the emission properties of ThT in dioxane-water mixtures of different polarity.

N-Alkyl ammonium 2-acrylamido-2-methylpropanesulfonates: Synthesis, properties, and polymerization

Polymerizable surfactant organic salts based on n-alkylamines and 2-acrylamido-2-methylpropanesulfonic acid—n-dodecyl ammonium 2-acrylamido-2-methylpropane sulfonate and n-cetyl ammonium 2-acrylamido-2-methylpropane sulfonate—are synthesized, characterized, and studied for the first time. Their critical micelle concentrations in water are estimated by the methods of conductometry and viscometry. The appearance of micelles in water is confirmed by atomic-force microscopy. As evidenced by some features, cetyl ammonium 2-acrylamido-2-methylpropanesulfonate forms reverse micelles in xylene. The polymerization of n-alkyl ammonium 2-acrylamido-2-methylpropane sulfonates that gives rise to stoichiometric polyelectrolyte-colloid complexes is performed in systems based on solvents of various polarities: from low-polarity xylene and dioxane to water. In low- and high-polarity systems, the features of polymerization are typical for micellar polymerization. (It is completed within several minutes.) In dioxane-water mixtures having intermediate polarities, the rate of polymerization is much lower. The polymerization of the monomers in xylene affords stable organic gels. The resulting polymers are water-insoluble, but are soluble in several alcohols and chloroform. Films cast from chloroform solutions demonstrate a well-defined layer structure.

Speciation Studies of Diorganotin(IV) Complexes with 3,3-Bis(1-methylimidazol-2-yl)propionate—Displacement Reaction by DNA Constituents

The interaction of 3,3-bis(1-methylimidazol-2-yl)propionate (BIMP) with dimethyltin(IV) dichloride (DMT), dibutyltin(IV) dichloride (DBT), and diphenyltin(IV) dichloride (DPT) is investigated at 25°C and 0.1 M ionic strength in water for dimethyltin(IV), and in a 50% dioxane-water mixture for dibutyltin(IV) and diphenyltin(IV). The stepwise formation constants of the 1 : 1 and 1 : 2 complexes formed in solution are calculated from potentiometric measurements using the nonlinear least-square program MINIQUAD-75. The concentration distribution of the various complex species is evaluated as a function of pH. Displacement reactions of the coordinated 3,3-bis(1-methylimidazol-2-yl)propionate by inosine and inosine-5′-monophosphate are investigated from calculations based upon equilibrium properties.

Structural, spectral, DFT, pH-metric and biological studies on Cr(III), Mn(II) and Fe(III) complexes of dithione heterocyclic thiosemicarbazide ligand

Cr(III), Mn(II) and Fe(III) complexes derived from the quadruple potential dithione heterocyclic thiosemicarbazide ligand (H2PET) have been prepared and characterized by conventional techniques. The isolated complexes were assigned the formulae, [Cr(HPET)(H2O)2Cl2]·3H2O, [Mn(HPET)(H2O)Cl]2 and [Fe(HPET)(H2O)2Cl2]·H2O, respectively. IR data revealed that the ligand behaves as monobasic bidentate through (CN)py and (CS) groups in both Cr(III) and Fe(III) complexes. In the binuclear Mn(II) complex, H2PET acts as NSNS monobasic tetradente via (CN)py, (CS), (CS) and the new azomethine, (NC)* groups. An octahedral geometry for all complexes was proposed. The bond lengths, bond angles, HOMO, LUMO and dipole moment have been calculated by DFT using materials studio program to confirm the geometry of H2PET and its metal complexes. The ligand association constant and the stability constants of its complexes in addition to the thermodynamic parameters were calculated from pH metrically at 298, 308 and 318°K in 50% dioxane–water mixture, respectively. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats–Redfern and Horowitz–Metzger methods. Moreover, the anti-oxidant (using ABTS and DPPH methods), anti-hemolytic, and cytotoxic activities of the compounds have been tested.

Photophysical Properties of 7‐(diethylamino)Coumarin‐3‐carboxylic Acid in the Nanocage of Cyclodextrins and in Different Solvents and Solvent Mixtures

The photophysical properties of 7-(diethylamino) coumarin-3-carboxylic acid (7-DCCA) were studied in cyclodextrins (α, β, γ,-CDs), different neat solvents and solvent mixtures by using steady state absorption, emission and time-resolved fluorescence spectroscopy. We have observed that with gradual increase in concentration of β-CD the fluorescence quantum yield and lifetime decreased in a regular pattern whereas with gradual increase in concentration of γ-CD the fluorescence quantum yield and lifetime gradually increased. With addition of urea, the fluorescence quantum yield and lifetime of 7-DCCA in CDs increased. Binding constant calculation shows that 7-DDCA forms 1:1 complex with β-CD and with γ-CD it forms 1:1 and 1:2 (guest:host) inclusion complex. We proposed that the dye molecule formed capping complex with β-CD by means of hydrogen bonding and after addition of urea the hydrogen bonding network broke down and part of dye molecule entered inside the cavity of β-CD. The photophysics of 7-DCCA was studied in dioxane-water mixture and ethylene glycol-acetonitrile mixture to know the effect of polarity and viscosity of the media. The photophysics of 7-DCCA was also studied in different neat solvents. It was found that the photophysics of 7-DCCA depended on the structural feature of the solvents and solvent mixtures.

Synthesis, characterization and protein separation efficiency of N-isopropylacrylamide-co-N-tertiary butylacrylamide-co-acrylamide-based hydrogels

In the present study, hydrogels were prepared by free radical polymerization in water–dioxane mixture with fixed molar ratio (25 mol%) of N-isopropylacrylamide (NIPAM) and varying remaining molar concentrations of N-tert-butylacrylamide (NTBA) and acrylamide (AAm). The structure of the resultant hydrogels was studied by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The thermal properties of the hydrogels were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) methods. DSC thermograms were used for the quantitative determination of free, interfacial and bound water contents. The result showed that the free and interfacial water contents increased with increase in the hydrophilic AAm content, and the bound water content increased with hydrophobic NTBA content in the hydrogels. Swelling behavior of the hydrogels was evaluated at different temperatures. The percentage swelling and diffusion kinetic parameters (network structure constant, type of diffusion and diffusion constant) were calculated for all samples. The diffusion was found to be Fickian type for copolymer having equimolar concentrations of NTBA and AAm and non-Fickian type for others. Diffusion coefficients of the hydrogels were found to be increased with increasing temperature. In addition, poly(NIPAM-co-NTBA-co-AAm) hydrogels were used in concentration separation process for BSA solution. The result showed that the copolymer with equimolar NTBA and AAm contents has high separation efficiency with good thermoresponsive behavior among all copolymers.

Study of Ternary Complex Stability Constants of Some Toxic Metal Ions with l-Histidine and l-Glutamic Acid in Dioxan–Water Mixtures

The stability constants of ternary complexes of Pb(II), Cd(II) and Hg(II) ions with l-histidine and l-glutamic acid were determined pH metrically in the concentration range of 0–60 % v/v dioxan–water mixtures maintaining an ionic strength of 0.16 mol l−1 at 303.0 K. Alkalimetric titrations were carried out in different relative concentrations [M:L:X = 1.0:2.5:2.5, 1.0:2.5:5.0, 1.0:5.0:2.5 for Pb(II) and Cd(II) and 1.0:5.0:5.0, 1.0:5.0:10.0, 1.0:10.0:5.0 for Hg(II)] of metal (M) to histidine (L) to glutamic acid (X). Stability constants of ternary complexes were calculated and various models were refined with MINIQUAD75. The best fit chemical models were selected based on statistical parameters and residual analysis. The species detected are MLXH3, MLXH2, MLXH and ML2X for Pb(II), MLX2H2 and ML2X for Cd(II) and MLXH3 and MLXH2 for Hg(II). The relative stabilities of the mixed ligand complexes were compared with those of the binary complexes. The enhanced stability associated with the ternary complex is attributed to chelate effect, stacking interactions and hydrogen bonding.

Binuclear copper(II), cobalt(II) and Nickel(II) complexes of N1-ethyl-N2-(pyridin-2-yl) hydrazine-1,2-bis(carbothioamide): Structural, spectral, pH-metric and biological studies

Binuclear Cu(II), Co(II) and Ni(II) complexes derived from N1-ethyl-N2-(pyridin-2-yl) hydrazine-1,2-bis(carbothioamide) (H2PET) have been prepared and characterized by elemental analysis, spectral (IR, UV–vis, EI mass, ESR and 1HNMR) and magnetic measurements. The isolated complexes assigned the general formula, [M(HPET)(H2O)nCl]2·xH2O where M=Cu(II), Co(II) and Ni(II), n=2, 1, 0 and x=0, 0.5 and 0, respectively. IR data revealed that the ligand behaves as monobasic tridentate through (CN)py, (C-S) and new azomethine, (NC)∗ groups in the Co(II) complex but in Cu(II) complex, the ligand coordinate via both (CS) groups, one of them in thiol form as well as the new azomethine group. In Ni(II) complex, H2PET acts as NSNS monobasic tetradente via (CN)py, (C–S), (CS) and the new azomethine, (NC)∗ groups. An octahedral geometry is proposed for all complexes. pH- metric titration was carried out in 50% dioxane–water mixture at 298, 308 and 318 °K, respectively and the dissociation constant of the ligand as well as the stability constants of its complexes were evaluated. Also the kinetic and thermodynamic parameters for the different thermal decomposition steps of the complexes were determined by Coats–Redfern and Horowitz–Metzger methods. Moreover, the anti-oxidant, anti-hemolytic, and cytotoxic activities of the compounds have been tested.

Speciation Studies of Pb(II), Cd(II) and Hg(II) Complexes of 1,10-Phenanthroline in 1,4 Dioxan–Water Mixtures

Speciation of Pb(II), Cd(II) and Hg(II) complexes of 1,10-phenanthroline has been studied pH metrically in 1,4 dioxan–water mixtures (0.0–60.0 %, v/v) at 303 K and an ionic strength of 0.16 mol dm−3. The predominant species detected are ML and ML2 for Pb(II), ML, ML2 and ML3 for Cd(II) and ML2 and ML3 for Hg(II). The trend in the variation of stability constants of these species with decreasing dielectric constant of the medium is attributed to the electrostatic and non-electrostatic forces and the complexing ability of the co-solvent. The species distribution and the feasible equilibria for the formation of the species are also presented.

Solvent Effect on Protonation Equilibria of l-Aspartic Acid and Ethylenediamine in Dioxan–Water Mixtures

A pH-metric study of protonation equilibria of l-aspartic acid and ethylenediamine in dioxan-water media of varying composition (0–60 % v/v) has been made at different concentrations of the ligands maintaining an ionic strength of 0.16 mol l−1 at 303.0 K. The best fit chemical models are arrived at using MINIQUAD75 based on statistical parameters like crystallographic R factor, χ2, skewness and kurtosis. The variation in the protonation constants with the dielectric constant of the medium is attributed to the electrostatic and non electrostatic forces.

Potentiometric Determination of the Stability Constants of Trimethyltin(IV) Chloride Complexes with Imino-bis(Methylphosphonic Acid) in Water and Dioxane–Water Mixtures

The interaction of trimethyltin(IV) (TMT) with imino-bis(methylphosphonic acid) (IDP), abbreviated as H4L, was investigated at 25 °C and at ionic strength 0.1 mol⋅dm−3 (NaNO3) using a potentiometric technique. The formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants are reported for the complexes formed. The results show the formation of 110, 111, 112 and 11-1 complexes for the TMT–IDP system. The concentration distribution of the various complex species was evaluated. The effect of dioxane as a solvent, on both the protonation constants and the formation constants of trimethyltin(IV) complexes with IDP, is discussed. The thermodynamic parameters ΔH∘ and ΔS∘ calculated from the temperature dependence of the equilibrium constants were evaluated. The effect of ionic strength on the protonation constants of IDP is also discussed.