Moderately and strongly supercooled liquids: A temperature-derivative study of the primary relaxation time scale

Stability Challenges of Amorphous Solid Dispersions of Drugs: A Critical Review on Mechanistic Aspects

The most common drawback of the existing and novel drug molecules is their low bioavailability because of their low solubility. One of the most important approaches to enhance the bioavailability in the enteral route for poorly hydrophilic molecules is amorphous solid dispersion (ASD). The solubility of compounds in amorphous form is comparatively high because of the availability of free energy produced during formulation. This free energy results in the change of crystalline nature of the prepared ASD to the stable crystalline form leading to the reduced solubility of the product. Due to the intrinsic chemical and physical uncertainty and the restricted knowledge about the interactions of active molecules with the carriers making, this ASD is a challenging task. This review focused on strategies to stabilize ASD by considering the various theories explaining the free-energy concept, physical interactions, and thermal properties. This review also highlighted molecular modeling and machine learning computational advancement to stabilize ASD.

Effervescence-induced amorphous solid dispersions with improved drug solubility and dissolution

The current study aimed to investigate drug carrier miscibility in pharmaceutical solid dispersions (SD) and include the effervescent system, i.e. Effervescence-induced amorphous solid dispersions (ESD), to enhance the solubility of a poorly water-soluble Glibenclamide (GLB). Kollidon VA 64, PEG-3350, and Gelucire-50/13 were selected as the water-soluble carriers. The miscibility of the drug-carrier was predicted by molecular dynamics simulation, Hansen solubility parameters, Flory-Huggins theory, and Gibb's free energy. Solid dispersions were prepared by microwave, solvent evaporation, lyophilization, and Hot Melt Extrusion (HME) methods. The prepared solid dispersions were subjected to solubility, in-vitro dissolution, and other characterization studies. The in-silico and theoretical approach suggested that the selected polymers exhibited better miscibility with GLB. Solid-state characterizations like FTIR and ¹H NMR proved the formation of intermolecular hydrogen bonding between the drug and carriers, which was comparatively higher in ESDs than SDs. DSC, PXRD, and microscopic examination of GLB and SDs confirmed the amorphization of GLB, which was higher in ESDs than SDs. Gibb's free energy concept suggested that the prepared solid dispersions will be stable at room temperature. Ex-vivo intestinal absorption study on optimized ESDs prepared with Kollidon VA64 using the HME technique exhibited a higher flux and permeability coefficient than the pure drug suggesting a better drug delivery. The drug-carrier miscibility was successfully studied in SDs of GLB. The addition of the effervescent agent further enhanced the solubility and dissolution of GLB. Additionally, this might exhibit a better bioavailability, confirmed by ex-vivo intestinal absorption study.

Derivative-based analysis for temperature and pressure evolution of dielectric relaxation times in vitrifying liquids

The derivative-based analysis for detecting regions of the validity of the Vogel-Fulcher-Tammann (VFT) dependence for superpressed and supercooled liquids is discussed. For the temperature (T) path the analysis introduced by Stickel [J. Chem. Phys. 104, 2043 (1996); J. Chem. Phys. 107, 1086 (1997)] is recalled. For the pressure (P) path the derivation based on the counterpart of the VFT dependence proposed in Paluch [J. Phys.: Condens. Mater 10, 4131 (1998)] is presented. The appearance of two ideal glass temperatures (T(0)) or pressures (P(0)), fragility strength coefficients (D(T), D(p)), and prefactors [formula--see text] for VFT equations in following dynamical domains, i.e., high-temperature (DeltaT(high)) and low-temperature (DeltaT(low)) or low-pressure (DeltaP(low)), and high-pressure (DeltaP(high)), is stressed. It is noteworthy that the values of T(0)(DeltaT(high)) > T(0)(DeltaT(low)), D(T)(DeltaT(high)) << D(T)(DeltaT(low)), and [formula--see text]. Analogous behavior was noted for isothermal DeltaP(L) and DeltaP(H) dynamic domains. A similar derivative-based approach is also applied to test the validity of the mode coupling theory (MCT) critical-like equation [formula--see text]. It yields the temperature T(X) and the MCT power ("critical") exponent [formula--see text] exclusively from the simple linear regression. The extension of such an analysis for the pressure path is also given. The hardly discussed question of the error of estimations of [formula--see text] and T(X) is emphasized. The relation between the derivative based behavior mentioned above and the apparent activation enthalpy (temperature path) or the apparent activation volume (pressure path) is indicated. The presented analysis was applied to discuss the dynamic crossovers in supercooled and superpressed diethyl phthalate, based on experimental data supplemented by those given in Pawlus [Phys. Rev. E 68, 021503 (2003)].