Control over Polymorph Formation of Polydatin in Binary Solvent System and Structural Characterization

Thermal Characterization and Heat Capacities of Seven Polyphenols

Polyphenolic compounds are key elements in sectors such as pharmaceutics, cosmetics and food; thus, their physicochemical characterization is a vital task. In this work, the thermal behavior of seven polyphenols (trans-resveratrol, trans-polydatin, kaempferol, quercetin, myricetin, hesperidin, and (-)-epicatechin) was investigated with DSC (differential scanning calorimetry) and TGA (thermogravimetric analysis). Melting temperatures, enthalpies of fusion and decomposition temperatures were determined, and heat capacities were measured in the temperature range from 283.15 K to 363.15 K. Results were compared to the scarce experimental data available in the literature, showing a satisfactory agreement. All compounds were found to be thermally stable until melting, upon which they rapidly decomposed. Myricetin was the only polyphenol that presented polymorphic behavior, exhibiting two phase transitions prior to melting. Heat capacities increased minimally with temperature in the studied range. In addition, the group contribution method developed by Marrero and Gani was used to estimate the thermal properties of the polyphenols, achieving high accuracy for melting temperatures.

Polymorphism of Butyl Ester of Oleanolic Acid—The Dominance of Dispersive Interactions over Electrostatic

Oleanolic (OA) and glycyrrhetinic acids (GE), as well as their derivatives, show a variety of pharmacological properties. Their crystal structures provide valuable information related to the assembly modes of these biologically active compounds. In the known-to-date crystals of OA esters, their 11-oxo derivatives, and GE ester crystals, triterpenes associate, forming different types of ribbons and layers whose construction is based mainly on van der Waals forces and weak C-H···O interactions. New crystal structures of 11-oxo OA methyl ester and the polymorph of OA butyl ester reveal an alternative aggregation mode. Supramolecular architectures consist of helical chains which are stabilized by hydrogen bonds of O-H···O type. It was found that two polymorphic forms of butyl OA ester (layered and helical) are related monotropically. In a structure of metastable form, O-H···O hydrogen bonds occur, while the thermodynamically preferred phase is governed mainly by van der Waals interactions. The intermolecular interaction energies calculated using CrystalExplorer, PIXEL, and Psi4 programs showed that even in motifs formed through O-H···O hydrogen bonds, the dispersive forces have a significant impact.

Co-Crystals of Resveratrol and Polydatin with L-Proline: Crystal Structures, Dissolution Properties, and In Vitro Cytotoxicities

Resveratrol (RSV) and polydatin (PD) have been widely used to treat several chronic diseases, such as atherosclerosis, pulmonary fibrosis, and diabetes, among several others. However, their low solubility hinders their further applications. In this work, we show that the solubility of PD can be boosted via its co-crystallization with L-proline (L-Pro). Two different phases of co-crystals, namely the RSV-L-Pro (RSV:L-Pro = 1:2) and PD-L-Pro (PD:L-Pro = 1: 3), have been prepared and characterized. As compared to the pristine RSV and PD, the solubility and dissolution rates of PD-L-Pro in water (pH 7.0) exhibited a 15.8% increase, whereas those of RSV-L-Pro exhibited a 13.8% decrease. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay of pristine RSV, PD, RSV-L-Pro, and PD-L-Pro against lung cancer cell line A549 and human embryonic kidney cell line HEK-293 indicated that both compounds showed obvious cytotoxicity against A549, but significantly reduced cytotoxicity against HEK-293, with PD/PD-L-Pro further exhibiting better biological safety than that of RSV/RSV-L-Pro. This work demonstrated that the readily available and biocompatible L-Pro can be a promising adjuvant to optimize the physical and chemical properties of RSV and PD to improve their pharmacokinetics.

Selective Crystallization of d-Mannitol Polymorphs Using Surfactant Self-Assembly

Selective crystallization of polymorphs is highly sought after in industrial practice. Yet, state-of-the-art techniques either use laboriously engineered solid surfaces or strenuously prepared heteronucleants. We propose an approach where surfactants in solution self-assemble effortlessly into mesoscopic structures dictating the polymorphic outcome of the target solute. Sodium dodecyl sulfate (SDS) surfactant is used as a tailored additive to crystallize different polymorphic forms of a model active pharmaceutical ingredient, d-mannitol. Different mesoscopic phases of SDS template particular polymorphs: packed monolayers, micelles, and crystals favored the β, α, and δ forms of d-mannitol, respectively. A synergistic effect of topological templating and molecular interactions is proposed as the rationale behind the observed selective crystallization of polymorphs. This crystal engineering technique suggests that surfactant self-assemblies can be used as tailored templates for polymorphic control.