Monetite formed in mixed solvents of water and ethylene glycol and its transformation to hydroxyapatite

Agglomerated nanorods of hydroxyapatite have been synthesized using monetite as a precursor in a NaOH solution. Monetite consisting of nanosheets has been successfully synthesized by a one-step microwave-assisted method using CaCl(2).2.5H(2)O, NaH(2)PO(4), and sodium dodecyl sulfate (SDS) in water/ethylene glycol (EG) mixed solvents. The effects of the molar ratio of water to EG and the reaction time on the products were investigated. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectrometry (FTIR).     

水-乙二醇混合溶液中多组分电解质热力学

<正>电解质溶液热力学是物理化学研究的重要组成部分,在无机材料、化学工程、生物化工和湿法冶金以及海洋科学、地质科学和生命科学中具有重要的理论和实际意义。     

Density and viscosity of magnesium sulphate in formamide + ethylene glycol mixed solvents

Densities (ρ) and viscosities (η) of different strengths of magnesium sulphate (MgSO₄) in varying proportions of formamide (FA) + ethylene glycol as mixed solvents were measured at room temperature. The experimental values of ρ and η were used to calculate the values of the apparent molar volume, (φ_1,), partial molar volume, (φ₁,^ℴ) at infinite dilution,A- andB-coefficients of the Jones-Dole equation and free energies of activation of viscous flow, (Δμ ₁ ^0* ) and (Δμ ₂ ^0* ), per mole of solvent and solute respectively. The behaviour of these parameters suggests strong ion-solvent interactions in these systems and also that MgSO₄ acts as structure-maker in FA + ethylene glycol mixed solvents.     

3-甲基吡啶在有机物/水混合溶剂中的电氧化

在质子交换膜为隔膜的电解槽内,以丙酮、乙腈和2-丁酮与水分别构成混合溶剂体系,通过循环伏安和恒电位电解实验,探索了3-甲基吡啶在混合溶剂中在PbO2电极上的电氧化条件,并与纯水溶剂的情况相比,研究了氧化电流密度及生成烟酸的选择性和电流效率的变化.     

混合极性溶剂乙二醇／水中正负离子表面活性剂SDS／CTAB的界面性质研究

正负离子混合表面活性剂由于其特异的自组织行为及良好的稳定性,已成为研究生物膜和用于生物活性物质分离分析的理想模型[1-2],近年来,该体系在界面化学性质中得到了广泛的研究,但是由于正负电性中和,其水溶液很不稳定,一旦超过临界胶束浓度(CMC),极易发生沉淀,从而失去表面活性,使其应用受到限制.     

Reference value standards for pH measurements in 5, 15 and 30% (w/w) acetonitrile/water solvent mixtures at temperatures from 288.15 to 308.15 K

Reference value standards, pH (RVS), for 0.05 mol kg^?1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 5, 15 and 30% (w/w) acetonitrile/water mixed solvents at temperatures from 288.15 to 308.15 K are determined from reversible e.m.f. measurements of the cell Pt¦H₂¦KHPh + KCl¦AgCl|Ag|Pt. Values of the first ionisation constant of o-phthalic acid (H₂Ph; benzene-1,2-dicarboxylic acid) in these mixed solvents are also determined from analogous measurements. The consistency of the results is analysed by multilinear regression of the quantity p(a_HγCl) as a function of both solution composition and temperature. The standard pH (RVS) values determined are given by the equation pH (RVS) = 4.0080 + 6.330x + 16.177x² ? 115.3x³ + 0.3089u ? 201.0ux² + 909ux³ + 13.04v, where x is the mole fraction of acetonitrile in the mixed solvent, u = z/(1 + z), v = [ln(1 + z) ? u], z = (T ? θ)/θ, and θ = 298.15 K.     

Aggregation behaviour and thermodynamics of mixed micellization of 1-hexadecylpyridinium bromide and ionic liquid in ethylene glycol/water binary mixtures

Micellar behavior of binary combinations of ionic liquid, 1-tetradecyl-3-methylimidazolium bromide, with conventional cationic surfactant 1-hexadecylpyridinium bromide was investigated by means of conductometry to study the effect of cosolvent and water content and temperature. The critical micelle concentration and the degree of counterion association were calculated from the conductometry data. Thermodynamic parameters were obtained from the temperature dependence of the critical micelle concentration. The standard Gibbs energy of micellization increased with the increasing percentage of cosolvent as well as the mole fraction of C₁₄mimBr. The standard enthalpy and standard entropy of micelle formation were both decreased with the increasing temperature and the concentration of cosolvent. The entropy contribution was larger than the enthalpic one in pure water, whereas in the ethylene glycol/H₂O mixture the enthalpy contribution was predominant     

Solubility of daidzin in different organic solvents and (ethyl alcohol + water) mixed solvents

The solubility of daidzin in different organic solvents and (ethyl alcohol + water) mixed solvents was measured by high performance liquid chromatography (HPLC) analysis method from T = (283.2 to 323.2) K at atmosphere pressure. The results show that at higher temperature more daidzin dissolves, and moreover, the solubility increases with the ethyl alcohol mole fraction increase in the (ethyl alcohol + water) mixed solvents. The experimental solubility values were correlated by a simplified thermodynamic equation, λh equation and modified Apelblat equation. Based on the solubility of daidzin, the enthalpy and entropy of solution were also evaluated by van’t Hoff equation. The results illustrated that the dissolution process of daidzin is endothermic and entropy driven.     

Poly(ethylene glycol)-b-poly(epsilon-caprolactone) and PEG-phospholipid form stable mixed micelles in aqueous media

Novel mixed polymeric micelles formed from biocompatible polymers, poly(ethylene glycol)-b-poly(epsilon-caprolactone) (PEG(5000)-b-PCL(x)) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy poly(ethylene glycol) (PEG-DSPE), possess small size and high thermodynamic stability, raising their potential as long circulating carriers in the context of delivery of antineoplastic and antibiotic drugs. Formation of mixed polymeric micelles was confirmed using size exclusion chromatography and 1H NMR NOESY. Steady-state fluorescence measurements revealed depressed critical micellar concentrations indicative of a cooperative interaction between component hydrophobic blocks, which was quantified using the pseudophase model for micellization. Steady-state fluorescence measurements indicated that the mixed polymeric micelle cores possess intermediate micropolarity and high microviscosity. Pulsed field gradient spin-echo measurements were used to characterize micellar diffusion coefficients, which agree well with those obtained using dynamic light scattering. NOE spectra suggested that the hydrophobic polymer segments from individual components are in close proximity, giving evidence for the formation of a relatively homogeneous core. Contrary to one-component PEG(5000)-b-PCL(x) micelles, the mixed polymeric micelles could incorporate clinically relevant levels of the poorly water soluble antibiotic, amphotericin B (AmB). AmB encapsulation and release studies revealed an interesting composition-dependent interaction of the drug with the mixed polymeric micelle core.     

Secondary pH standards and their uncertainty in the context of the problem of two pH scales

Establishing a traceability route with all measurement and uncertainty relationships determined is an important aspect of traceability, and seems to be particularly striking in pH measurement. In this paper the issue of evaluation of secondary pH standards measured with reference to a primary standard in a differential cell with free diffusion type liquid junctions is considered. Relatively high uncertainty, U=0.015, has been assigned to such standards in the recent IUPAC Recommendations on pH (2001), because of a specific residual liquid-junction potential treated statistically as a contribution to the combined uncertainty. Close inspection of the problem leads to the conclusion that a correction for the residual liquid-junction potential should be applied to the measured value of a secondary pH standard. This can be considered as a correction for a known systematic effect on the traceability route. With available experimental data it is demonstrated that such a correction can reasonably be made for well-studied standard buffer systems. In this way the uncertainty associated with secondary pH standards is kept to a low level, and, what is more, the problem of two pH scales, a multi-standard scale and a single-standard scale, gains a proper solution. The need for different treatment of residual liquid-junction potentials at different levels in the measurement hierarchy is noted. Much attention is also given to rational categorization of pH standards in the hierarchy.     

Crystallization of nordstrandite in ethylene glycol / water solutions: electron microscopic studies

The present work shows the growth of nordstrandite microcrystals observed by transmission and scanning electron microscopy. Nordstrandite was synthesised from non-crystalline aluminium hydroxide reacted in 20% ethylene glycol/water solution, at room temperature. This material was characterized by TEM, SEM, SAED, XRD and EDS/TEM, during six month and revealed the formation and growth of nordstrandite. Fibrillar pseudoboehmite is the only aluminium hydroxide which could be identified during the first two weeks. The nuclei grow, from complete dissolution/recrystallization of pseudoboehmite fibrils, into platy rectangular microscrystals of nordstrandite. Some tabular microcrystals recrystallise, forming after six months only the multi-point nordstrandite stars. This electron-optical study suggest that the star shape results from the overlapping of rectangular plates, and pseudoboehmite fibrils act as the precursor of nordstrandite crystallisation in ethylene glycol/water solution.      

Enthalpy-entropy compensation in micellization of sodium dodecyl sulphate in water/methanol,water/ethylene glycol and water/glycerol binary mixtures

The enthalpy-entropy compensation in micellization of sodium dodecyl sulphate (SDS) in binary mixtures of water/methanol (MeOH), water/ethylene glycol (EG) and water/glycerol (GL) over a temperature range of 10–60°C was examined. When the cosolvent concentration was low, the critical micelle concentration (CMC) depended only on the total amount of the hydroxyl group added. When the cosolvent concentration was high, the increase in CMC followed the sequence: MeOH>EG>GL. Enthalpy and entropy changes were evaluated from which the compensation temperature was determined. Both enthalpy and entropy changes decreased on the addition of the cosolvents, indicating a lowering of solution hydrophobicity. The compensation temperature was found as a constant over the cosolvent concentration range, as a result, was not a good index for characterizing the solute/solvent interactions. The two reference temperatures at which the enthalpy-entropy change respectively became zero were strongly influenced by the cosolvent addition, therefore could serve as a proper index for solution hydrophobicity.     

Temperature dependent phase behavior of PNIPAM microgels in mixed water/methanol solvents

Temperature dependent phase behavior of poly(N-isopropylacylamide) (PNIPAM) microgels in water/methanol mixtures of different composition was studied with dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Using DLS, it is possible to measure the diffusion coefficient, and thus the size of particles exactly and directly; the variation of the phase transition temperature in the different solvents is also easy to detect by this method. With SANS measurements in D₂O/MeOD mixtures, some of the DLS results were confirmed. Moreover, SANS measurements give valuable information on the particle structure in different solvents. The experiments were compared with the theory of competitive hydration introduced by Tanaka et al. We found a good agreement of theory and experiment, and obtained the theoretical predictions: around the transition temperature, the composition of the bound methanol along the chains is higher than that of the outer solution, while the whole methanol composition inside the gel is lower. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1100–1111     

Reference value standards for pH measurements in 10, 30, 50, and 70% (w/w) 2-propanol/water solvent mixtures at temperatures from 288.15 to 318.15 K

Reference value standards, pH (RVS), for 0.05 mol kg^?1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 10, 30, 50 and 70% (w/w) 2-propanol/water solvent mixtures at temperatures from 288.15 to 318.15 K are determined from reversible e.m.f. measurements of the cell Pt¦H₂¦KHPh + KCl¦AgCl¦Ag¦Pt. The consistency of the present results is confirmed by multilinear regression analysis of the pH values obtained for each solution composition and temperature, allowing appropriate interpolation of pH (RVS) values within the range of the experiment. The ancillary values of the standard e.m.f. of the cell Pt¦H₂¦HCl¦AgCl¦Ag¦Pt are optimized through multilinear regression analysis of the available data in the literature, and the ancillary values of the first ionization constant of o-phthalic acid (H₂Ph; benzene-1,2-dicarboxylic acid) in these solvent mixtures are evaluated from reversible e.m.f. measurements of the cell Pt¦H₂¦H₂Ph + KHPh + KCl¦AgCl¦Ag¦Pt.     

Spectral characteristics of 2-aminodiphenylamine in different solvents and at various pH values.

The absorption and fluorescence spectra of 2-aminodiphenylamine (2ADA) have been studied as a function of solvent polarity and acid concentration. Analysis of solvatochromic and prototropic shifts of 2ADA reveals: (i) the presence of intramolecular hydrogen bonding between imino and amino groups in the ground state, (ii) dual fluorescence (360 and 430 nm) of the monocation (2ADA+) formed by the protonation of amino group; and (iii) proton-induced quenching of the monocation (2ADA+) fluorescence. In the dual fluorescence of 2ADA+, the longer wavelength emission at 430 nm is found to be from the twisted form of the monocation. The rate constants of the proton-induced quenching of 2ADA+ are determined.     

Electromotive-force studies of mixed electrolytes in mixed solvents. HCl+NH4Cl in methanol+water solvents at 25°C

Electromotive-force measurements of the cell Pt, H₂(g, 1 atm)|HCl(m₁), NH₄Cl(m₂), methanol(X%), Water(100–X)%|AgCl|Ag have been made at 25°C for m₁+m₂=1 mole-kg^–1 and X=0, 10, 20, 30, 40, and 50% methanol by weight. Hydrochloric acid obeys Harned's rule in aqueous solutions, but a quadratic term is required in the mixed solvents. The Harned coefficients for the acid vary with solvent composition, and this invalidates the applicability of Harned's method for estimating activity coefficients for single electrolytes in mixed solvents. This method is described and the reason for the inapplicability of the method is discussed in terms of ion-ion and ion-solvent interactions.     

Resolution of a chiral alcohol through lipase-catalyzed transesterification of its mixed carbonate by poly(ethylene glycol) in organic media

A simple approach to the resolution of chiral alcohols through a lipase-catalyzed transesterification of one enantiomer of the corresponding trifluoroethyl carbonate by a low molecular weight poly(ethylene glycol), PEG, is described. The method was demonstrated through resolution of (RS)-sec-phenethyl alcohol. The alcohol was converted to its 2,2,2-trifluoroethyl carbonate, 2, and the (R)-enantiomer was selectively transesterified with PEG in warm diisopropyl ether using porcine pancreas lipase, PPL, as the catalyst. The two carbonate enantiomers were easily separated by cooling and filtering off the solid PEG having the (R)-alcohol covalently attached. Hydrolysis of the unchanged (S)-carbonate was achieved in dilute aqueous base, and the enantiomeric excess of the (S)-alcohol was found to be 80% by NMR in the presence of the chiral shift reagent Eu(hfc)₃. Methanolysis of the modified (R)-PEG carbonate yielded (R)-sec-phenethyl alcohol having enantiomeric excess=96% by NMR with Eu(hfc)₃.     

Studies in isodielectric media. Part IV. Thermodynamics of protonation ofp-nitroaniline in ethylene glycol—Diethylene glycol mixtures at 25°C

The thermodynamic ionisation constant ofp-nitroanilinium ion was determined spectrophotometrically at 25°C in the near isodielectric mixtures of ethylene glycol (EG) and diethylene glycol (DEG) over the complete range of solvent compositions. thepK of the ion decreases continuously with the addition of diethylene glycol, passes through a minimum around 80 wt% of the same solvent and then increases. The variation of pK (pK _{mixed solvent}–pK _EG) with solvent composition was analyzed in terms of the changes inGibbs energies of transfer of the different species involved in the ionisation process in these mixtures.

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Untersuchungen in isodielektrischen Medien, 4. Mitt.: Thermodynamik der Protonierung von p-Nitroanilin in Ethylenglykol—Diethylenglykol-Mischungen bei 25°C

Zusammenfassung Die thermodynamischen Ionisierungskonstanten desp-Niroanilinium-Ions wurde spektrophotometrisch bei 25°C in den annähernd isodielektrischen Mischungen von Ethylenglykol—Diethylenglykol (EG—DEG) über den gesamten Bereich der Lösungsmittelzusammensetzungen gemessen. DerpK des Ions sinkt kontinuierlich mit der Zugabe von Diethylenglykol und geht bei etwa 80 Gew.%DEG durch ein Minimum. Die Änderung von pK (pK _{Lösungsm.-Gemisch}-pK _EG) mit der Lösungsmittelzusammensetzung wird als Wechsel in denGibbs-Energien des Transfers der verschiedenen in den Ionisierungsprozess verwickelten Spezies erklärt.

     

The solubility and solvation of salts in mixed nonaqueous solvents. 1. Potassium halides in mixed aprotic solvents

The solubilities of potassium fluoride, chloride, and bromide in acetonitrile, N,N-dimethylformamide, and dimethylsulfoxide and in binary mixtures of these solvents were determined at 25°C. The standard molar Gibbs free energies of solution, _solnG°, in the neat solvents were related to the polarizabilities and basicities of the anions and the dipole moments and acidities of the solvents. The values of _solnG° in the mixtures were fitted by expressions from the quasi-lattice quasi-chemical theory. The mean number of each kind of solvent in the nearest environment of the ions was obtained from these results.