Thermodynamics of the Enantiotropic Pharmaceutical Compound Benzocaine and Solubility in Pure Organic Solvents

Assessment of Binary Agarose-Carbopol Buccal Gels for Mucoadhesive Drug Delivery: Ex Vivo and In Vivo Characterization

Agarose (AG) is a naturally occurring biocompatible marine seaweed extract that is converted to hydrocolloid gel in hot water with notable gel strength. Currently, its mucoadhesion properties have not been fully explored. Therefore, the main aim of this study was to evaluate the mucoadhesive potential of AG binary dispersions in combination with Carbopol 934P (CP) as mucoadhesive gel preparations. The gels fabricated via homogenization were evaluated for ex vivo mucoadhesion, swelling index (SI), dissolution and stability studies. The mucoadhesive properties of AG were concentration dependent and it was improved by the addition of CP. Maximum mucoadhesive strength (MS) (27.03 g), mucoadhesive flow time (FT) (192.2 min), mucoadhesive time in volunteers (MT) (203.2 min) and SI (23.6% at 4 h) were observed with formulation F9. The mucoadhesive time investigated in volunteers (MT) was influenced by AG concentration and was greater than corresponding FT values. Formulations containing 0.3%, w/v AG (F3 and F9) were able to sustain the release (~99%) for both drugs till 3 h. The optimized formulation (F9) did not evoke any inflammation, irritation or pain in the buccal cavity of healthy volunteers and was also stable up to 6 months. Therefore, AG could be considered a natural and potential polymer with profound mucoadhesive properties to deliver drugs through the mucosal route.

Cyclic Ether-Water Hybrid Electrolyte-Guided Dendrite-Free Lamellar Zinc Deposition by Tuning the Solvation Structure for High-Performance Aqueous Zinc-Ion Batteries

The serious zinc dendrites and poor cyclability at high cathode loading owing to the strong solvation effect of traditional aqueous electrolytes are the main bottlenecks to the development of aqueous rechargeable zinc-ion batteries (ARZIBs). Here, we design an ether-water hybrid zinc-ion electrolyte with bifunctional roles of not only unplugging the dendrites bottleneck at the Zn anode but also extending the cycle life at high cathode loading. A cyclic ether (1,4-dioxane (DX)) is incorporated into traditional ZnSO₄-based electrolytes to finely tune the solvation sheath of Zn²⁺. DX is found to guide the deposition orientation of zinc along the (002) plane, leading to not a dendritic structure but distinctively dense lamellar deposition due to the stronger affinity of the cyclic DX molecules toward Zn(002) than that of water, which is proven by density functional theory calculations. The cycling lifespan of the Zn anode extends up to over 600 h at 5.0 mA cm^-2 and maintains extremely high Coulombic efficiency of 99.8%, thereby further enabling the Zn-MnO₂ full cells to stably cycle at an ultrahigh mass loading of 9.4 mg cm^-2, paving the way to their practical applications. This work also provides a novel electrolyte regulating solution for other aqueous multivalent metal-ion batteries.

Thermodynamics and Intermolecular Interactions of Nicotinamide in Neat and Binary Solutions: Experimental Measurements and COSMO-RS Concentration Dependent Reactions Investigations

In this study, the temperature-dependent solubility of nicotinamide (niacin) was measured in six neat solvents and five aqueous-organic binary mixtures (methanol, 1,4-dioxane, acetonitrile, DMSO and DMF). It was discovered that the selected set of organic solvents offer all sorts of solvent effects, including co-solvent, synergistic, and anti-solvent features, enabling flexible tuning of niacin solubility. In addition, differential scanning calorimetry was used to characterize the fusion thermodynamics of nicotinamide. In particular, the heat capacity change upon melting was measured. The experimental data were interpreted by means of COSMO-RS-DARE (conductor-like screening model for realistic solvation-dimerization, aggregation, and reaction extension) for concentration dependent reactions. The solute-solute and solute-solvent intermolecular interactions were found to be significant in all of the studied systems, which was proven by the computed mutual affinity of the components at the saturated conditions. The values of the Gibbs free energies of pair formation were derived at an advanced level of theory (MP2), including corrections for electron correlation and zero point vibrational energy (ZPE). In all of the studied systems the self-association of nicotinamide was found to be a predominant intermolecular complex, irrespective of the temperature and composition of the binary system. The application of the COSMO-RS-DARE approach led to a perfect match between the computed and measured solubility data, by optimizing the parameter of intermolecular interactions.

Thermodynamic Characteristics of Phenacetin in Solid State and Saturated Solutions in Several Neat and Binary Solvents

The thermodynamic properties of phenacetin in solid state and in saturated conditions in neat and binary solvents were characterized based on differential scanning calorimetry and spectroscopic solubility measurements. The temperature-related heat capacity values measured for both the solid and melt states were provided and used for precise determination of the values for ideal solubility, fusion thermodynamic functions, and activity coefficients in the studied solutions. Factors affecting the accuracy of these values were discussed in terms of various models of specific heat capacity difference for phenacetin in crystal and super-cooled liquid states. It was concluded that different properties have varying sensitivity in relation to the accuracy of heat capacity values. The values of temperature-related excess solubility in aqueous binary mixtures were interpreted using the Jouyban–Acree solubility equation for aqueous binary mixtures of methanol, DMSO, DMF, 1,4-dioxane, and acetonitrile. All binary solvent systems studied exhibited strong positive non-ideal deviations from an algebraic rule of mixing. Additionally, an interesting co-solvency phenomenon was observed with phenacetin solubility in aqueous mixtures with acetonitrile or 1,4-dioxane. The remaining three solvents acted as strong co-solvents.

Phase solubility diagrams and energy surface calculations support the solubility enhancement with low hygroscopicity of Bergenin: 4-Aminobenzamide (1: 1) cocrystal

Herein, we reported a new bergenin: 4-aminobenzamide (BGN-4AM) cocrystal with significantly enhanced solubility and low hygroscopicity probed from two aspects such as phase solubility diagrams and theoretical calculations. Compared with anhydrous BGN, BGN-4AM solubilities in water and different buffer solutions (pH = 1.2, 4.5, 6.8) increase significantly. It is noted that BGN-4AM solubility in pH = 6.8 buffer solution presents 32.7 times higher than anhydrous BGN. Interestingly, BGN-4AM (0.31 ± 0.07%) showcases lower hygroscopicity than anhydrous BGN (9.31 ± 0.16%). The predicted and experimental solubilities agree with each other when considering solubility product (K_sp) and solution binding constant (K₁₁) in phase solubility diagrams, indicating the solution complexes formation occurs. Further crystal surface-water interactions and Bravais, Friedel, Donnay-Harker (BFDH) analyses based on Density Functional Theory with dispersion correction (DFT-d) methods support the enhanced solubility. The water probe demonstrates an average interaction energy of -6.48 kcal/mol on the 002 plane of BGN-4AM, and only -5.47 kcal/mol on the 011 plane of BGN monohydrate. The lower lattice energy of BGN-4AM guarantees its lower hygroscopicity than BGN monohydrate. BGN-4AM with enhanced solubility and low hygroscopicity can be a potential candidate for further formulation development.

Influence of solvent on crystal nucleation of benzocaine

The influence of the solvent in nucleation of benzocaine FII was explored by measuring nucleation induction times, probing solvent–solute interactions with spectroscopy and modelling the strength of solvent–solute intermolecular interactions using DFT.