Molar Solubility Research Articles

Measurement and correlation of solubility, Hansen solubility parameters and thermodynamic behavior of Clozapine in eleven mono-solvents

Mole-fraction solubility of Clozapine (CLZ) in eleven mono-solvents (methanol, ethanol, n-propanol, isopropanol, acetone, 1,2-dichloroethane, benzene, toluene, N,N-Dimethylformamide (DMF), n-Methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO)) at varied temperatures (from 283.15 K to 333.15 K at 5 K intervals) was experimentally determined by a classic gravimetric method under an atmosphere pressure of 0.101 MPa. The mole solubility of CLZ in the selected mono-solvents exhibited a positive relation with temperature. In addition, the solubility sequence of CLZ at 298.15 K is: DMF > DMSO > NMP > 1,2-dichloroethane > acetone > methanol > benzene > n-propanol > ethanol > toluene > isopropanol. The Hansen solubility parameters (HSPs) and solvents polarity were applied to explore this solubility behavior. The KAT-LSER model was calculated to investigate the solvent effect based on linear solvation energy relationships concept. Four thermodynamic models including the modified Apelblat model, Wilson model, NRTL model and UNIQUAC model were employed to correlate the experimental solubility, which indicated that both modified Apelblat model and NRTL model were more suitable in correlation with the measured solubility data. Furthermore, the solution thermodynamic properties (ΔdisGo, ΔdisHoand ΔdisSo) of CLZ in the selected eleven solvents were calculated by van't Hoff equation, and the positive values of ΔdisHo and ΔdisSo indicated that the dissolution process of CLZ in the measured mono-solvents was endothermic and entropy-driven.

Spectrophotometric investigation of surfactants mediated aqueous solubilization of Nile blue

In the current study, the solubilization of partially soluble Nile blue (NB) dye in an aqueous medium has been investigated. The solubilization was monitored using UV–Vis spectroscopic method by varying time intervals. The seven surfactants belong to different classes (cationic, anionic, non-ionic, and bio surfactant) were tested to examine their effects on the solubilization of Nile blue. The spectrum of NB in the presence of 10% methanol and varying concentrations of sodium dodecyl sulphate (SDS) showed the maximum absorbance among the tested solvents and surfactants. The spectra in anionic surfactant (SDS) closely resembled the spectra in methanol, a polar solvent. Whereas, in the cationic surfactants (CTAB and NDPC) it resembled with the spectra in chloroform, a non-polar solvent. The solubility of the NB was also examined by varying pH and introducing 0.2 to 1.0 M sodium chloride and potassium chloride salts in the NB solution at critical micelles concentration (cmc) of the selected surfactants. The solubility of NB was decreased with the increasing concentration of the salts irrespective of the surfactant nature due to the electronic shielding of ions, furnished by the salts. The solubilization was found to be maximum in the presence of sodium dodecyl sulphate (SDS) and about one half to the solubility in the methanol, while minimum with N-dodecyl pyridinium chloride (NDPC). The molar solubility of NB increased gradually from 2.3 ×10−6 to 8.6 × 10−6 (mol L−1) by raising the SDS concentration. The proposed natural surfactant, shikakai (SHI) was also facilitated the solubility of NB in the aqueous medium about threefold than water alone. The λmax of Nile blue shifted to longer wavelength and finally disappeared as the pH turned from acidic to alkaline. It has been concluded that the presence of SDS and SHI in the various biological applications can reduce the amount of NB and hence poses less hazardous effects to human health and the environment.

Dendrimer-based posaconazole nanoplatform for antifungal therapy

We examined formulating a new antifungal agent, posaconazole (POS) and its derivatives, with different molecular vehicles. Several combinations of drug and carrier molecules were synthesized, and their antifungal activities were evaluated against Aspergillus fumigatus. Posaconazole and four of its derivatives were conjugated to either generation 5 (G5) dendrimers or partially modified G5 dendrimers. The in vitro antifungal activities of these compounds suggest that conjugates with specific chemical linkages showed better fungistatic activity than direct conjugates to POS. In particular, a polyethylene glycol (PEG)-imidazole modified G5 dendrimer demonstrated improved antifungal efficacy relative to the parent G5 molecule. Further studies were then conducted with POS derived molecules coupled to PEG-imidazole modified G5 dendrimers to achieve a highly soluble and active conjugate of POS. This conjugated macromolecule averaged 23 POS molecules per G5 and had a high solubility with 50 mg/mL, which improved the molar solubility of POS from less than 0.03 mg/mL to as high as 16 mg/mL in water. The primary release profile of the drug in human plasma was extended to over 72 h, which is reflected in the in vitro inhibition of A. fumigatus growth of over 96 h. These POS–polymer conjugates appear to be novel and efficient antifungal agents.

Solubility determination and thermodynamic properties calculation of macitentan in mixtures of ethyl acetate and alcohols

Due to macitentan (form I) is hydrophobic and has poor solubility, in this work, the solubility of macitentan in (methanol + ethyl acetate), (ethanol + ethyl acetate) and (isopropanol + ethyl acetate) was studied and correlated. In three mixed solvents, the solubility increased with the increase of temperature. In pure solvents, the largest mole solubility data was in ethyl acetate (1.223 × 10−2 at 313.15 K), followed by methanol (6.02 × 10−4 at 313.15 K), ethanol (4.58 × 10−4 at 313.15 K) and isopropanol (2.46 × 10−4 at 313.15 K). The solubility increased monotonically with the increase of ethyl acetate mass fraction at all studied temperatures. In mixtures of (ethyl acetate + methanol), the values varied from 6.02 × 10−4 to 1.223 × 10−2 at 313.15 K, an increase of 20.32 folds, meanwhile, 26.70 folds for mixtures of (ethanol + ethyl acetate) and 49.72 folds for mixtures of (isopropanol + ethyl acetate). The values of relative average deviations (RAD) in three systems with Jouyban-Acree model are 6.20%, 5.95% and 4.95%, respectively. For CNIBS/R-K model, the data is less than 5.0% at the temperature range from 273.15 K to 293.15 K only in mixture of (ethyl acetate + methanol). However, the data of Residual Sum of Squares (RSS) for Jouyban-Acree model and CNIBS/R-K model are 5.72 and 2.26, respectively. According to the result of analysis, the CNIBS/R-K model could provide a suitable prediction in three mixed solvents. In the following, the analysis of apparent thermodynamic properties for the dissolution processes indicate the dissolution process is not only endothermic but also entropy-driving.

A true solubility versus the observed one for metal sodium in its molten chloride

Abstract A band gap of the molten sodium chloride is estimated more than 7 eV but its electrochemical window is less than 4 eV. These parameters limit a true mole solubility of metal sodium in its molten chloride by ~10−7% mol at 1173 K that is much less than 3% mol equal to the observed solubility of this metal as neutral atoms in the homogeneous molten sodium chloride at the same temperature. Such great difference between these magnitudes and transparency of the liquid with the observed sodium solubility indicate the existence of a micro-emulsion in the system, Na–NaCl when the high observed solubility of metal sodium in its molten chloride is a result of mixing two phases in the form of ultra thin dispersion of liquid metal and molten salt having the eutectic point Na0.06(NaCl)0.94.

Kojic acid in fourteen mono-solvents: Solubility data, Hansen solubility parameter and thermodynamic properties

In this research, solubility of kojic acid in fourteen mono-solvents was obtained by laser monitoring approach at various temperatures under 0.1 MPa. The mole solubility of kojic acid exhibited a positive relation with temperature. Moreover, the solubility sequence of kojic acid at 298.15 K is: dimethyl sulfoxide (DMSO) > N-methylpyrrolidone (NMP) > N, N-dimethylacetamide (DMAC) > N, N-dimethylformamide (DMF) > 2-methoxyethanol > 2-ethoxyethanol > acetic acid > methanol > 1,4-dioxane > ethanol > water > n-propanol > acetone > ethyl acetate. The Hansen solubility parameter (HSP) and solvents polarity were applied to explore this solubility behaviour. The experimental solubility data was correlated with five thermodynamic models including two-Suffix Margules, NRTL-SAC, NRTL, modified Apelblat equation and UNIQUAC model, and the calculated results indicated that all of models had great fitting effects with the measured solubility data. Furthermore, the solution thermodynamic properties (ΔdisGo, ΔdisHo, ΔdisSo) of kojic acid in investigated solvents were calculated by van’t Hoff equation. The positive values of ΔdisHo and ΔdisSo indicated that the dissolution process of kojic acid in all the measured solvents was endothermic and entropy-driven.

Solubility profiles of linagliptin in pure and mixed solvents: Interactions and thermodynamic parameters

During the linagliptin process development, several related probable raw materials related and process related impurities in the range of 0.05% to 0.15% were observed. The objective of this work is to study the solubility profiles of linagliptin in pure and mixed solvents and research the thermodynamic parameters. The function of temperature and solvent composition was evaluated by some thermodynamic models. Maximum mole solubility value at 313.15 K was obtained in methanol (3.02 × 10−3) in pure solvents, followed by ethanol (2.31 × 10−3), acetonitrile (1.72 × 10−3), n-propanol (1.25 × 10−3) and isopropanol (8.74 × 10−4). However, in mixtures of acetonitrile (w) + ethanol (1−w), the solubility profiles increased monotonically with the increasing temperature, and increased with the increasing mass fraction (w) of acetonitrile to a maximum data at w = 0.80 and then decreased at each temperature. In order to study the role played by different modes of interaction on solubility, a multiple linear regression analysis (MLRA) involving various solvent parameters was used. The results obtained indicate that polarity/polarizability of solvent has a greater influence on the solubility of linagliptin. The calculation of thermodynamic parameters in the dissolution process indicates that the dissolution was endothermic and entropy-driven. More importantly, the change of polarity of mixed solvent is helpful for the separation of several related probable raw materials related and process related impurities during the process development.

Preparation and in vitro characterization of rosuvastatin calcium incorporated methyl beta cyclodextrin and Captisol® inclusion complexes

Despite being the most effective hypolipidemic agent, poor physicochemical properties of Rosuvastatin calcium (RCa) remain challenging obstacles in the development of pharmaceutical dosage forms. Inclusion complexes (ICs) of RCa with cyclodextrin (CD) derivatives; methyl-beta-cyclodextrin (M-β-CD) and sulfobutylether-beta-cyclodextrin (SBE-β-CD; Captisol®) were formulated by kneading and freeze-drying (lyophilization) methods. Pysicochemical properties of ICs were evaluated by SEM, DSC, XRD, FT-IR, 1H-NMR analyses. Entrapment efficiency (EE), water solubility, in vitro release analyses were also performed. Safety and efficacy of the ICs were analyzed by cytotoxicity and permeation studies on Caco-2 cell lines. Both CDs indicated AL type phase solubility diagrams showing that [1:1] molar ratio. Apparent stability constants (K1:1) were found to be 60.93 M−1 for M-β-CD and 158.07 M−1 for Captisol®. High EE in the range of 93.50–105.40% was achieved. Molar solubility of RCa was increased 3.7- and 4.1-fold with M-β-CD and Captisol® ICs, respectively. In vitro release analyses have indicated the equivalence of dissolution profiles for M-β-CD and Captisol® based ICs to that of pure RCa (f2 > 50). Cytotoxicity studies on Caco-2 cell lines have revealed the safety of ICs for oral use. Permeability studies demonstrated that selected lyophilized F6 formulation has shown the best permeation rate with Papp value of 3.08 × 10−7 cm·s−1. Considering greater water solubility, lower toxicity, high efficiency of complexation as well as, RCa-like permeability and in vitro release behavior at pH 6.8; Captisol® based lyophilized F6 formulation was selected as the best IC to be used in oral dosage forms of RCa.

Solubility measurement, solubility behavior analysis and thermodynamic modelling of melatonin in twelve pure solvents from 278.15 K to 323.15 K

Solubility of melatonin in twelve mono-solvents including seven alcohols {methanol (MT), ethanol (ET), n-propanol (n-PrA), n-butanol (n-BT), i-butanol (i-BT), n-pentanol (n-PT) and n-hexanol (n-HeA)} and five esters {methyl acetate (MeAC), ethyl acetate (EtAC), n-propyl acetate (n-PrAC), n-butyl acetate (n-BtAC) and n-pentyl acetate (n-PtAC)} was determined by laser monitoring approach from 278.15 K to 323.15 K under 0.1 MPa. The experimental results indicate that the mole solubility of melatonin shows a positive relation with temperature variation. The solubility of melatonin in the twelve pure solvents at 298.15 K has order: MT (0.03570) > ET (0.02536) > n-PrA (0.01965) > n-BT (0.01524) > n-PT (0.01450) > i-BT (0.01267) > n-HeA (0.01136) > MeAC (0.008498) > EtAC (0.006587) > n-PrAC (0.004280) > n-BtAC (0.003410) > n-PtAC (0.02990). Moreover, the miscibility behavior of melatonin was further analyzed by the Hansen solubility parameter (HSP). The solvent effect of melatonin in tested pure solvents was investigated by using the KAT-LSER model. The four thermodynamic models including two-Suffix Margules, NRTL, NRTL-SAC and UNIQUAC models were applied to correlate the experimental solubility data of melatonin. Furthermore, the dissolution thermodynamic properties including the apparent standard dissolution enthalpy (ΔdisHo), the apparent standard dissolution entropy (ΔdisSo) and the apparent standard Gibbs energy change (ΔdisGo) of melatonin in investigated solvents were calculated by van't Hoff equation.

Solubility and ADMET profiles of short oligomers of lactic acid.

Polylactic acid (PLA) is a polymer with an increased potential to be used in different medical applications, including tissue engineering and drug-carries. The use of PLA in medical applications implies the evaluation of the human organism's response to the polymer inserting and to its degradation products. Consequently, within this study, we have investigated the solubility and ADMET profiles of the short oligomers (having the molecular weight lower than 3000 Da) resulting in degradation products of PLA. There is a linear decrease of the molar solubility of investigated oligomers with molecular weight. The results that are obtained also reveal that short oligomers of PLA have promising pharmacological profiles and limited toxicological effects on humans. These oligomers are predicted as potential inhibitors of the organic anion transporting peptides OATP1B1 and OATP1B3, they present minor probability to affect the androgen and glucocorticoid receptors, have a weak potential of hepatotoxicity, and may produce eye injuries. These outcomes may be used to guide or to supplement in vitro and/or in vivo toxicity tests such as to enhance the biodegradation properties of the biopolymer.

Solid-liquid equilibrium solubility, thermodynamic properties, solvent effect of Ipriflavone in twelve pure solvents at various temperatures

In this study, by using laser dynamic monitoring, the dissolution behavior of ipriflavone (IP) in pure solvents of methanol, ethanol, n-propanol, n-butyl alcohol, 1-pentanol, methyl acetate, DMF, DMAC, acetone, acetonitrile, methylbenzene at (278.15–323.15) K and dichloromethane at (278.15–308.15) K was investigated under 0.1 MPa. The results showed that the molar solubility of IP in pure solvents increases non-linearly with the increase of the experimental temperature. The order of the solubility of IP in the pure solvents studied is: dichloromethane > DMAC > DMF > methylbenzene > methyl acetate > acetone > acetonitrile > 1-pentanol > n-butyl alcohol > n-propanol > ethanol > methanol. Moreover, experimental solubility data were correlated well with five thermodynamic models (Apelblat, λH, NRTL, UNIQUAC, and Van't hoff model). The calculation results showed that the Apelblat model has the smallest average values of the relative deviation (ARD) and root mean square deviation (104RMSD), being 1.878% and 2.933, respectively. Furthermore, the influence of solvent–solute interactions on the solubility of IP in pure solvents was analyzed by using the KAT-LSER model. In addition, the apparent thermodynamic properties(△solG°, △solH°, △solS°) of IP in pure solvents were calculated by correlating experimental solubility data with the Van't hoff model. The results show that the dissolution process of IP in the experimental solvents was endothermic and entropy-driven.

Accuracy of Molar Solubility Prediction from Hansen Parameters. An Exemplified Treatment of the Bioantioxidant l-Ascorbic Acid

Estimating molar solubility from the Hildebrand-Scott relation employing Hansen solubility parameters (HSP) is widely presumed a valid semi-quantitative approach. To test this presumption and to determine quantitatively the inherent accuracy of such a solubility prognosis, l-ascorbic acid (LAA) was treated as an example of a commercially important solute. Analytical calculus and Monte Carlo (MC) simulation were performed for 20 common solvents with total HSP ranging from 14.5 to 33.0 (MPa)0.5 utilizing validated material data. It was found that, due to the uncertainty of the material data used in the calculations, the solubility prediction had a large scattering and, thus, a low precision. Prediction power is most adversely affected by the uncertainty of the HSP estimates (solvent and solute), followed by the solute heat of fusion. The solute melting temperature and molar volume have minor effects. Computed and experimental solubilities show the same qualitative behavior, while quantitative discrepancies reach one to three orders of magnitude. Solubility estimates were found to provide, at best, rough guiding information but, with the quality of material data on LAA available, they cannot be rated semi-quantitative. It is assumed that these results generally apply at least to solute-solvent systems with a material data quality and solubility similar to LAA.

Dual‐functionalized protic ionic liquids for efficient absorption of NH3 through synergistically physicochemical interaction

AbstractBACKGROUNDIonic liquids have become promising media for the treatment of tail gases containing ammonia (NH3), which causes serious environmental problems and threatens human health.RESULTSIn this work, four dual‐functionalized protic ionic liquids (DPILs) [CnOHim]X (n = 1, 2; X = [NTf2]−, [BF4]−, [SCN]−) with both weak acidity proton and hydroxyl group were designed and synthesized for enhanced NH3 separation. Among them, the maximum NH3 molar solubility of 3.11 mol NH3 mol–1 IL was achieved in [EtOHim][NTf2] at 40 °C and atmospheric pressure, and the highest mass solubility of NH3 could be 0.221 g NH3 g–1 IL in [EtOHim][SCN]; this is the highest value of any absorbent ever reported under the same conditions. Not only superior NH3 solubility, along with excellent selectivity of NH3/CO2 (65) and NH3/N2 (104), but also outstanding recyclability was exhibited in DPILs.CONCLUSIONSThe highly efficient performance of NH3 absorption by DPILs was ascribed to the synergistically physicochemical interaction between weak acidity proton, hydroxyl group and NH3, which was confirmed through both spectrum analysis and quantum chemical calculations. This work implied that DPILs have great potentials in NH3 separation and recovery of NH3‐containing tail gases. © 2020 Society of Chemical Industry

Determination of Thermodynamic Parameters from the Dissolution of Strontium Hydroxide in Water and Mixed Solvent Systems by pH-Metric Method

In this study, saturated solutions of Sr(OH)2 in pure water and in mixed solvent systems (methanol - water, ethanol - water, 1-propanol - water, and 2-propanol - water) at two temperatures were prepared and titrated with standard HCl solution by using pH metry. Using these titration data, the molar solubility (s), solubilty product (Ksp) and Gibbs free energy (Go), entropy change (ΔSand#176;) and enthalpy change (ΔHand#176;) for dissolution of strontium hydroxide was determined. At room temperature (20and#176;C), the s, Ksp, ∆Go were found to be 4.28 x 10-2 mol L-1, 3.13 x 10-4 mol3L-3 and 19.70 kJ mol-1 respectively. The ΔHand#176; and ΔSand#176; of the reaction is 2.90 kJ mol-1 and – 60.80 J. mol-1 K-1. With increasing percentage content of organic solvent in mixed solvents, the molar solubility and Ksp decreased and ∆Go, ΔHand#176; and ΔSand#176; values increased. The results were correlated with the dielectric constant value of the solvents used in the study.

Determination of Thermodynamic Parameters from the Dissolution of Strontium Hydroxide in Water and Mixed Solvent Systems by pH-Metric Method

In this study, saturated solutions of Sr(OH)2 in pure water and in mixed solvent systems (methanol - water, ethanol - water, 1-propanol - water, and 2-propanol - water) at two temperatures were prepared and titrated with standard HCl solution by using pH metry. Using these titration data, the molar solubility (s), solubilty product (Ksp) and Gibbs free energy (Go), entropy change (ΔSand#176;) and enthalpy change (ΔHand#176;) for dissolution of strontium hydroxide was determined. At room temperature (20and#176;C), the s, Ksp, ∆Go were found to be 4.28 x 10-2 mol L-1, 3.13 x 10-4 mol3L-3 and 19.70 kJ mol-1 respectively. The ΔHand#176; and ΔSand#176; of the reaction is 2.90 kJ mol-1 and – 60.80 J. mol-1 K-1. With increasing percentage content of organic solvent in mixed solvents, the molar solubility and Ksp decreased and ∆Go, ΔHand#176; and ΔSand#176; values increased. The results were correlated with the dielectric constant value of the solvents used in the study.

Abraham model correlations for describing dissolution of organic solutes and inorganic gases in dimethyl carbonate

ABSTRACT Experimental solubility data are reported for anthracene, biphenyl, benzil, benzoin, 1-chloroanthraquinone, phenothiazine, pyrene, salicylamide, thioxanthen-9-one, xanthene, benzoic acid, 4-tert-butylbenzoic acid, 4-chloro-3-nitrobenzoic acid, 3,4-dichlorobenzoic acid, 3,4-dimethoxybenzoic acid, 2-hydroxybenzoic acid, 4-methoxybenzoic acid, 2-methylbenzoic acid, 3-methylbenzoic acid, 3-methyl-4-nitrobenzoic acid, 4-nitrobenzoic acid and 3,4,5-trimethoxybenzoic acid dissolved in dimethyl carbonate at 298.15 K. Abraham model correlations are derived for solute transfer into dimethyl carbonate by combining our measured solubility data with published activity coefficient and solubility data retrieved from the published chemical and engineering literature. The derived Abraham model correlations back-calculate the 52 experimental molar solubilities and infinite dilution activity coefficients to within 0.13 log units.

Ferric-ferrous redox couple mediated low temperature symmetric flow fuel cell for direct conversion of biomass residues into electricity

As one of promising candidates for high-efficient energy conversion device, biomass flow fuel cells (BFFCs) can directly convert biomass into electricity at low temperature without noble metal catalyst. Most BFFCs utilize polyoxometalates which are high molecular weight inorganic clusters with low molar solubility in water and relative high cost. Here we report a new, cheap and environmentally benign symmetric biomass flow fuel cell (BFFC) mediated by simple Fe3+/Fe2+ redox couple on both sides, which can directly and efficiently convert various biomass residues into electricity at low temperature. Fe3+ in anode can efficiently oxidize biomass residues into high value chemicals, such as 5-hydroxymethylfurfural, furfural, etc., and simultaneously being reduced to Fe2+. The low electric potential Fe2+ in anode and the high electric potential Fe3+ in cathode are assembled into a fuel cell. The consumed Fe3+ in cathode can be regenerated immediately under the strong synergism of O2 and HNO3. The designed cell yields a power density 54.5 mW cm−2 and can discharge continuously more than 7 h at a constant current density 200 mA cm−2. The BFFC can successfully light 43 LED bubbles. This approach is highly desirable for the development of low cost, high-performance and environment-friendly biomass flow fuel cells.

Dissolution behavior and thermodynamic properties of apixaban in pure and mixed solvents

The solubility profile of apixaban in pure and mixed solvents within the temperature range from (288.15 to 328.15) K under atmosphere pressure (101.3 kPa) was studied and evaluated by some thermodynamics models. The solid state of apixaban in equilibrated form was characterized using powder X-ray diffraction (PXRD) technique. The maximum mole solubility in pure solvents was obtained in 1, 4-dioxane (3.648 × 10−3) at 328.15 K, and followed by methanol (1.967 × 10−3), acetone (7.885 × 10−4),ethanol (6.049 × 10−4), isopropanol (3.806 × 10−4), ethyl acetate (2.266 × 10−4), n-hexane (1.883 × 10−4), water (3.989 × 10−5). The solubility was quite small. Therefore, the solubility profile of apixaban in mixtures of (1, 4-dioxane + water) was further studied. Moreover, it increased at first and then decreased with the increasing mass fraction of 1, 4-dioxane. Moreover, the extended Hildebrand solubility approach (EHSA) was applied to evaluate the co-solvency phenomenon in mixed solvent at 298.15 K. In the following, the analysis of apparent thermodynamic properties indicates that the dissolution process in all selected solvents is an endothermic and entropy driven process.

Baryte cohesive layers formed on a (010) gypsum surface by a pseudomorphic replacement

The mineral replacement of gypsum (CaSO4·2H2O) by baryte (BaSO4) is relevant to technological and industrial applications, including its use as a plaster or stone consolidant in cultural heritage conservation. In the present study, we provide experimental evidence suggesting that, during the interaction of gypsum cleavage surfaces with barium-bearing solutions, a pseudomorphic replacement takes place and results in the formation of a crystallographically oriented baryte layer. This mineral replacement process is favoured by the porosity generated, due to the differences in molar volume and solubility between parent and product sulfate phases, allowing the progress of the reaction. The homogeneous micrometre-sized layer of baryte occurs most likely via a fluid-mediated interface-coupled dissolution–precipitation mechanism. A certain degree of crystallographic control on the polycrystalline BaSO4 product layer by the structure of the parent substrate (gypsum) is confirmed by electron microscopy observations and X-ray diffraction analyses. The structural control exerted by the cleavage gypsum surface on the baryte layer can be defined by the epitactic relationship: Gyp (010) || Bar (010). The formation of baryte increases with reaction time until passivation occurs at the replacement interface, probably due to a decreased porosity and loss of connectivity that thereby prevents further reaction. The investigation of these processes occurring on freshly cleaved single crystals of gypsum were complemented by studying the replacement of polycrystalline gypsum cubes, showing a homogeneous baryte surface layer on the sample. The results of this study thus offer interesting insights into the application of the replacement of gypsum by baryte as a conservation method for gypsum sculptures and plasterwork, increasing their resistance against water and humidity while preserving the surface features of the original mineral substrate.

Thermodynamic and Thermal Properties of Solvation for Nano Nickel Ferrite and Nano Zinc Ferrite Prepared by the Sol–Gel Method in Different CH3COOH Concentrations at Different Temperatures

The solubility of nickel ferrite and zinc ferrite in an aqueous solution of acetic acid was studied gravimmetrically by varying the concentration of acetic acid at different temperatures ranging from 25 to 45 °C. The molar solubility and thermodynamic parameters of nano nickel and nano zinc ferrites have been evaluated. In this work, we observed how the concentration of CH3COOH and temperature affected the solubility of nano nickel and nano zinc ferrites at temperatures of 298, 303, 308, 313, 318 K. The two ferrites were prepared by sol–gel method. Structure and particle size of the reaction products were determined by X-ray diffraction and TEM analysis. It was found that the two ferrites were pure powder of NiFe2O4 and ZnFe2O4 with a cubic structure with mean particle size 21 and 30 nm respectively. The solubility of the two ferrites in different solutions of CH3COOH was measured gravimmetrically by the evaporation process using I.R. Lamp. It was found that the solubility increased with an increasing mole fraction of different CH3COOH solutions and increased also with increasing of temperature due to more solvation process. All solvation parameters were discussed. We need to mix the two nano ferrites in a safe solvent for different cancer chemotherapy treatment. The aim of the work is to dissolve the very insoluble nano nickel and nano zinc ferrites in weak acid like acetic acid,which is used in hyperthermia and also kill cancer tumors. Also the uses of nano ferrites as magnetic fluid hyperthermia agents and good carriers for chemotherapeutic agent. The aim of this work is to dissolve the very insoluble nano nickel and nano zinc ferrites prepared by sol–gel in CH3COOH at different concentrations, then we can neutralize the excess acid. The target of this work is to increase the solubility of both nano nickel and nano zinc ferrites with increasing temperature. The aim also in this work is to give the helpful nickel nano ferrite data necessary for hyperthermia and killing cancer tumors, especially in the skin.