Partial-solubility parameters of naproxen and sodium diclofenac

Rank-based ant system method for non-linear QSPR analysis: QSPR studies of the solubility parameter

The solubility parameter (δ) plays a unique role in the development of stable pharmaceutical formulations for assessing phase segregation during product synthesis. Understanding this parameter helps to determine how a drug substance will behave when processed or when dosed in vivo. The aim of this work was to develop a novel comprehensive yet rapid and accurate Quantitative Structure-Property Relationship (QSPR) method based on the rank-based ant system feature selection. The method was coupled with the multiple linear regression and support vector regression and applied to the assessment of solubility parameters for a diverse dataset of 1804 chemical compounds. The models were validated by solubility prediction of 360 test set compounds which were not used in building models. The developed models have high prediction power characterized by r (2) values 0.75 and 0.82, and RMSE values 1.96 and 1.65 (J/(cm(3)))(0.5) for the external test set. Various validation techniques and comparison results with the novel optimized support vector regression indicate that the developed models can be used to determine the solubility parameters for a diverse set of chemicals with an acceptable accuracy. The developed models can be beneficial for designing new chemical materials with desired solubility parameter values.

Determination and evaluation of solubility parameter of satranidazole using dioxane-water system

Satranidazole, a potent broad spectrum antiprotozoal, is a poorly water-soluble drug and has low bioavailability on oral administration. One of the important methods to improve the solubility and bioavailability of a less water-soluble drug is by the use of cosolvents. The solubility enhancement produced by binary blends with a cosolvent (dioxane) was studied against the solubility parameter of solvent blends (δ(1)) to evaluate the solubility parameter of drug (δ(2)). Solubility parameter of drug (δ(2)) was evaluated in blends of dioxane-water system. The results obtained were compared with the δ(2) values obtained using Molar Volume Method and Fedor's Group Substitution Method. The binary blend water-dioxane (10:90) gave maximum solubility with an experimental δ(2) value of 11.34 (Cal/cm(3))(0.5) that was comparable to the theoretical values of 11.34 (Cal/cm(3))(0.5) determined by Molar Volume Method and 11.3928 (Cal/cm(3))(0.5) when determined by Fedor's Group Substitution Method, which is in good agreement with solubility measurement method.

Use of solubility parameter to design dry suspension of cefaclor as a dual pack system

One of the important methods to improve the solubility of a less water-soluble drug is by the use of co solvents. The solubility enhancement produced by two binary blends with a common co solvent (water-propylene glycol and propylene glycol-ethyl acetate) was studied against the solubility parameter of solvent blends (δ₁) to evaluate the solubility parameter of drug (δ₂). The binary blend water:propylene glycol (20:80) gave maximum solubility with an experimental δ₂ value of 16.52 (Cal/cm³)^0.5 that was comparable to the theoretical value of 16.52 (Cal/cm³)^0.5 determined by molar volume method and 16.35 (Cal/cm³)^0.5 when determined by method proposed by Lin and Nash. The solvent blend water:propylene glycol (20:80) in which the drug exhibited maximum solubility was used as the reconstituting medium for formulation of dry suspension of cefaclor. The percentage cumulative drug release of cefaclor from the formulation F7 was compared to the marketed formulation by calculating the f1 (dissimilarity factor) and f2 (similarity factor) factors. A higher f1 value and f2 value below 50 indicates difference between the two dissolution profiles.

Ex Vivo Study of Transdermal Permeation of Four Diclofenac Salts from Different Vehicles

The ex vivo permeation of diclofenac was studied using four different salts (sodium, potassium, diethylamine, and epolamine) dissolved in four different solvents (water, propylene glycol (PG), Transcutol, and oleic acid (OA)) as donor phases through a human skin membrane. The four salts show different solubility values and different behavior in the four solvents, which are also permeation enhancers and this fact further is connected to the permeation results. The same order of magnitude of fluxes through the membrane as those previously reported for acidic diclofenac released from buffer solutions of pH >7 were found, taking into account differences originated by different membranes and other parameters tested in the experiments. Saturation concentration for the four salts in different solvents, necessary to calculate permeation coefficients, was critically evaluated; a short discussion made it possible to explain that corrections in the solubility values must be considered, related to the complex behavior in solution of these salts. Statistical processing of the experimental data suggests that differences between the four salts in promoting absorption of the drug is unproven; while differences are evident between the solvents, water is the most effective enhancing vehicle. Aqueous formulations containing diclofenac salt with an organic base appear to be the best combination to promote permeation in topical applications.

Prediction of solubility parameters using partial least square regression

The total solubility parameter (delta) values were effectively predicted by using computed molecular descriptors and multivariate partial least squares (PLS) statistics. The molecular descriptors in the derived models included heat of formation, dipole moment, molar refractivity, solvent-accessible surface area (SA), surface-bounded molecular volume (SV), unsaturated index (Ui), and hydrophilic index (Hy). The values of these descriptors were computed by the use of HyperChem 7.5, QSPR Properties module in HyperChem 7.5, and Dragon Web version. The other two descriptors, hydrogen bonding donor (HD), and hydrogen bond-forming ability (HB) were also included in the models. The final reduced model of the whole data set had R(2) of 0.853, Q(2) of 0.813, root mean squared error from the cross-validation of the training set (RMSEcv(tr)) of 2.096 and RMSE of calibration (RMSE(tr)) of 1.857. No outlier was observed from this data set of 51 diverse compounds. Additionally, the predictive power of the developed model was comparable to the well recognized systems of Hansen, van Krevelen and Hoftyzer, and Hoy.

Diclofenac Salts. III. Alkaline and Earth Alkaline Salts

Diclofenac salts containing the alkaline and two earth alkaline cations have been prepared and characterized by scanning electron microscopy (SEM) and EDAX spectroscopy; and by thermal and thermogravimetric analysis (TGA): all of them crystallize as hydrate when precipitated from water. The salts dehydrate at room temperature and more easily on heating, but recovery the hydration, when placed in a humid environment. X-ray diffraction spectra suggest that on dehydration new peaks appear on diffractograms and the lattice of the salts partially looses crystallinity. This phenomenon is readily visible in the case of the calcium and magnesium salts, whose thermograms display a crystallization exotherm, before melting or decomposing at temperatures near or above 200 degrees C; these last salts appear to form solvates, when prepared from methanol. The thermogram of each salt shows a complex endotherm of dehydration about 100 degrees C; the calcium salt displays two endotherms, well separated at about 120 and 160 degrees C, which disappear after prolonged heating. Decomposition exotherms, before or soon after the melting, appear below 300 degrees C. The ammonium salt is thermally unstable and, when heated to start dehydration, dissociates and leaves acidic diclofenac.

Relationship between swelling of hydroxypropylmethylcellulose and the Hansen and Karger partial solubility parameters

A model that relates the equilibrium swelling of hydroxypropylmethylcellulose to the partial solubility parameters of both the polymer and the solvents is proposed to interpret and correlate the experimental data. The non-specific interactions are expressed as the dispersion delta(d) and polar delta(p) solubility parameters of Hansen, or as a combination of both. Hydrogen bonding is represented by the acidic delta(a) and the basic delta(b) Karger solubility parameters. The results are compared with models including the same parameters for non-specific interactions (delta(d) and delta(p)) and the Hansen hydrogen bonding parameter delta(h). Equilibrium swelling of this hydrophilic polymer that is widely used in drug formulation is measured in pure solvents covering a wide polarity range. In a qualitative way, swelling increases in solvents with higher Hildebrand solubility parameters and stronger hydrogen bonding capability, and it decreases in non-polar solvents. Single polarity indexes, such as the Hildebrand solubility parameter or the partition coefficient (PC), do not fit well the overall experimental data. The best correlations were obtained with the proposed model, providing at the same time an interpretation consistent with the physical meaning of the terms included in the equation. Swelling increases as the non-specific interactions of the polymer and the solvents become alike, and as the Lewis acid-base interactions of the polymer (1) and the solvent (2) represented by the products delta(1a)delta(2b) and delta(1b)delta(2a) become greater. Conversely, hydrogen bonding self association of the solvents (the product delta(1a)delta(1b)) lowers swelling. The results show that the Karger hydrogen bonding parameters provide a better approach than the Hansen hydrogen bonding parameter to correlate the swelling behavior of a hydrophilic polymer.

Hydrophilic solutes in modified carbon dioxide extraction-prediction of the extractability using molecular dynamic simulation

Super- and subcritical carbon dioxide (CO2) extractions of crude drugs were simulated by molecular modelling to predict the extractability of different hydrophilic plant constituents under various extraction conditions. The CO2 extraction fluids were simulated either with pure CO2 or with solvent modified CO2 at different pressures and temperatures. Molecular modelling resulted in three different solubility parameters: the total solubility parameter delta and the partial solubility parameters delta(d) for the van der Waals and delta(EL) for the polar forces. Thus, delta(EL) enabled the estimation of the polarity of the extraction fluids and the solute molecules. If the value of delta(EL) of the extraction fluid reached the value of the solute molecule in the crude drug, i.e. minimum extraction value, the compound was soluble at the distinct extraction conditions. For a further increase in yield of the hydrophilic solutes, the polarity of the extraction fluid had to be increased, too. That means delta(EL) of the fluid exceeded the minimum extraction value. All simulations were verified by CO2 extractions of the secondary roots of Harpagophytum procumbens (harpagoside, stachyose) and the seeds of Aesculus hippocastanum (aescin). CO2 extractions of the flowers of Matricaria recutita ((-)-alpha-bisabolol) were obtained from literature data. These four constituents with different properties, like molecular size and the allocation of polar functional groups were extracted, analysed, simulated and the extract content was correlated with the extraction fluid used, respectively.

A new method to determine the partial solubility parameters of polymers from intrinsic viscosity

A modification of the extended Hansen method, formerly used to determine the partial solubility parameters of drugs and non-polymeric excipients is tested with a polymer for the first time. The proposed method relates the logarithm of the intrinsic viscosities of the polymer in a series of solvents and solvent mixtures with the Hansen (three parameter model) and Karger (four parameter model) partial solubility parameters. The viscosity of diluted solutions of hydroxypropyl methylcellulose (HPMC) was determined in pure solvents and binary mixtures of varying polarity. The intrinsic viscosity was obtained from the common intercept of the Huggins and Kraemer relationships. The intrinsic viscosity tends to increase with increasing the solubility parameter of the medium. The results show that hydrogen bonding and polarity of the polymer largely determine polymer-solvent interactions. The models proposed provided reasonable partial and total solubility parameters for the polymer and enable one to quantitatively characterize, for the first time, the Lewis acid-base ability of a polymer thus, providing a more realistic picture of hydrogen bonding for solvent selection/compatibility and to predict drug-polymer interactions. Combination of the dispersion and polar parameters into a single non-specific solubility parameter was also tested. The results extend earlier findings and suggest that the models are quite versatile and may be applied to drugs, non-polymeric and polymeric excipients.

Thermodynamics of solutions III: comparison of the solvation of (+)-naproxen with other NSAIDs

Naproxen was studied by classical thermoanalytical methods, namely sublimation calorimetry, solution calorimetry and the solubility method. Temperature dependence of a saturated vapor pressure was obtained and the sublimation enthalpy, deltaHsub(0) and entropy, deltaSsub(0) and their relative fraction of the total process were calculated. These parameters yielded for naproxen were compared to the respective data of other naphthalene derivatives. The crystal lattice energy of naproxen was calculated by two force fields (Gavezzotti et al. and Mayo et al.) and compared to the experimental data. Contributions of different motifs of the naproxen molecule to the total packing energy were analyzed. The Gibbs energy of solvation as well as enthalpic and entropic terms thereof in aliphatic alcohols have been studied for naproxen, and compared to model substances and other non-steroid anti-inflammatory drugs (benzoic acid, diflunisal and flurbiprofen). The major driving force of the solvation process is the enthalpy. The respective contributions of the specific and the non-specific solvation interactions in terms of absolute and relative values have been investigated.

Solubility predictions for crystalline nonelectrolyte solutes dissolved in organic solvents based upon the Abraham general solvation model

The Abraham general solvation model is used to predict the saturation solubility of crystalline nonelectrolyte solutes in organic solvents. The derived equations take the form of log (CS/CW) = c + rR2 + sπ2H + aΣα2H + bΣβ2H + vVx and log (CS/CG) = c + rR2 + sπ2H + aΣα2H + bΣβ2H + l log L(16) where CS and CW refer to the solute solubility in the organic solvent and water, respectively, CG is a gas-phase concentration, R2 is the solute's excess molar refraction, Vx is McGowan volume of the solute, Σα2H and Σβ2H are measures of the solute's hydrogen-bond acidity and hydrogen-bond basicity, π2H denotes the solute's dipolarity and (or) polarizability descriptor, and log L(16) is the solute's gas-phase dimensionless Ostwald partition coefficient into hexadecane at 298 K. The remaining symbols in the above expressions are known equation coefficients, which have been determined previously for a large number of gas–solvent and water–solvent systems. Computations show that the Abraham general solvation model predicts the observed solubility behavior of anthracene, phenanthrene, and hexachlorobenzene to within an average absolute deviation of about ±35%.Key words: solubility predictions, organic solvents, nonelectrolyte solutes, partition coefficients.

Proposition of group molar constants for sodium to calculate the partial solubility parameters of sodium salts using the van Krevelen group contribution method

The aim of this study is to propose, for the first time, a set of group molar constants for sodium to calculate the partial solubility parameters of sodium salts. The values were estimated using the few experimental partial solubility parameters of acid/sodium salt series available either from the literature (benzoic acid/Na, ibuprofen acid/Na, diclofenac Na) or determined in this work (salicylic acid/Na, p-aminobenzoic acid/Na, diclofenac), the group contribution method of van Krevelen to calculate the partial parameters of the acids, and three reasonable hypothesis. The experimental method used is a modification of the extended Hansen approach based on a regression analysis of the solubility mole fraction of the drug lnX(2) against models including three- or four-partial solubility parameters of a series of pure solvents ranging from non-polar (heptane) to highly polar (water). The modified method combined with the four-parameter model provided the best results for both acids and sodium derivatives. The replacement of the acidic proton by sodium increased the dipolar and basic partial solubility parameters, whereas the dispersion parameter remained unaltered, thus increasing the overall total solubility parameter of the salt. The proposed group molar constants of sodium are consistent with the experimental results as sodium has a relatively low London dispersion molar constant (identical to that of -OH), a very high Keesom dipolar molar constant (identical to that of -NO(2), two times larger than that of -OH), and a very high hydrogen bonding molar constant (identical to that of -OH). The proposed values are: F((Na)d)=270 (J cm(3))(1/2) mol(-1); F((Na)p)=1030 (J cm(3))(1/2) mol(-1); U((Na)h)=17000 J mol(-1). Like the constants for the other groups, the group molar constants proposed for sodium are certainly not the exact values. However, they are believed to be a fair approximation of the impact of sodium on the partial solubility parameters and, therefore, can be used as such in the group contribution method of van Krevelen.

The modified extended Hansen method to determine partial solubility parameters of drugs containing a single hydrogen bonding group and their sodium derivatives: benzoic acid/Na and ibuprofen/Na

Sodium salts are often used in drug formulation but their partial solubility parameters are not available. Sodium alters the physical properties of the drug and the knowledge of these parameters would help to predict adhesion properties that cannot be estimated using the solubility parameters of the parent acid. This work tests the applicability of the modified extended Hansen method to determine partial solubility parameters of sodium salts of acidic drugs containing a single hydrogen bonding group (ibuprofen, sodium ibuprofen, benzoic acid and sodium benzoate). The method uses a regression analysis of the logarithm of the experimental mole fraction solubility of the drug against the partial solubility parameters of the solvents, using models with three and four parameters. The solubility of the drugs was determined in a set of solvents representative of several chemical classes, ranging from low to high solubility parameter values. The best results were obtained with the four parameter model for the acidic drugs and with the three parameter model for the sodium derivatives. The four parameter model includes both a Lewis-acid and a Lewis-base term. Since the Lewis acid properties of the sodium derivatives are blocked by sodium, the three parameter model is recommended for these kind of compounds. Comparison of the parameters obtained shows that sodium greatly changes the polar parameters whereas the dispersion parameter is not much affected. Consequently the total solubility parameters of the salts are larger than for the parent acids in good agreement with the larger hydrophilicity expected from the introduction of sodium. The results indicate that the modified extended Hansen method can be applied to determine the partial solubility parameters of acidic drugs and their sodium salts.