Do carboximide-carboxylic acid combinations form co-crystals? The role of hydroxyl substitution on the formation of co-crystals and eutectics

Multicomponent crystalline solid forms of aripiprazole produced via hot melt extrusion techniques: An exploratory study

Multicomponent crystalline solid forms (salts, cocrystals and eutectics) are a promising means of enhancing the dissolution behavior of poorly soluble drugs. The present study demonstrates the development of multicomponent solid forms of aripiprazole (ARP) prepared with succinic acid (SA) and nicotinamide (NA) as coformers using the hot melt extrusion (HME) technique. The HME-processed samples were characterized and analyzed using differential scanning calorimetry (DSC), hot stage microscopy (HSM), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). The DSC and HSM analyses revealed a characteristic single melting temperature in the solid forms, which differed from the melting points of the individual components. The discernible changes in the FTIR (amide C=O stretching) and PXRD results for ARP-SA confirm the formation of new crystalline solid forms. In the case of ARP-NA, these changes were less prominent, without the appearance or disappearance of peaks, suggesting no change in the crystal lattice. The SEM images demonstrated morphological differences between the HME-processed samples and the individual parent components. The in vitro dissolution and microenvironment pH measurement studies revealed that ARP-SA showed a higher dissolution rate, which could be due to the acidic microenvironment pH imparted by the coformer. The observations of the present study demonstrate the applicability of the HME technique for the development of ARP multicomponent solid forms.

The trimorphism of 3-hydroxybenzoic acid: an experimental and computational study

A computationally driven experimental search for polymorphs of 3-hydroxybenzoic acid confirmed the third form and the small energy differences between the polymorphs.

Influence of Halogen Substituent on the Self-Assembly and Crystal Packing of Multicomponent Crystals Formed from Ethacridine and Meta-Halobenzoic Acids

In order to determine the influence of halogen substituent on the self-assembly of the 6,9-diamino-2-ethoxyacridinium cations and 3-halobenzoate anions in the crystals formed from ethacridine and halobenzoic acids, the series of ethacridinium meta-halobenzoates dihydrates: ethacridinium 3-chlorobenzoate dihydrate (1), ethacridinium 3-bromobenzoate dihydrate (2), and ethacridinium 3-iodobenzoate dihydrate (3), were synthesized and structurally characterized. Single-crystal X-ray diffraction measurements showed that the title compounds crystallized in the monoclinic P21/c space group and are isostructural. In the crystals of title compounds, the ions and water molecules interact via N–H⋯O, O–H⋯O and C–H⋯O hydrogen bonds and π–π stacking interactions to produce blocks. The relationship between the distance X⋯O between the halogen atom (X=Cl, Br, I) of meta-halobenzoate anion and the O-atom from the ethoxy group of cation from neighbouring blocks and crystal packing is observed in the crystals of the title compounds.

Implication of Coformer Structural Diversity on Cocrystallization Outcomes of Telmisartan with Improved Biopharmaceutical Performance

Crystal engineering approach was utilized for the development of different multicomponent solid forms of telmisartan (TEL) to improve its oral bioavailability. In this context, two cocrystals, gentisic acid (GA) and maleic acid (MA), while two eutectic mixtures, para-aminobenzoic acid (PABA) and adipic acid (AA), were successfully prepared and characterized by different analytical tools. Both the cocrystals exhibited characteristic heterosynthons, viz. OH_acid⋯N_arom and OH_acid⋯O, to propagate new network. Structural features of coformers has been correlated with the outcomes of cocrystallization approach. Coformers having auxiliary functionality in addition to complementary functional groups have high propensity to generate cocrystals. However, multicomponent where auxiliary functionality is lacking, such combinations, is shown to form eutectic mixtures owing to strong homomeric interaction. Besides, the developed cocrystals and eutectic mixtures showed higher aqueous solubility (3-5.5-fold) and intrinsic dissolution rate (1-2.6-fold) over pure TEL. In vivo studies also revealed significant improvement in relative bioavailability (2-2.6-fold). The study also shed light on the implications of eutectic mixtures in mitigating the solubility issues of drugs which are often considered negative results of cocrystallization strategy.

Role of Structure, Microenvironmental pH, and Speciation To Understand the Formation and Properties of Febuxostat Eutectics

Cocrystallization studies were undertaken to improve the solubility of a highly water-insoluble drug, febuxostat (FXT), used in the treatment of gout and hyperuricemia. A liquid-assisted grinding (LAG) method was successfully employed, starting with the screening of various coformers for obtaining cocrystals. However, in this process, three eutectic systems with coformers (probenecid, adipic acid, and α-ketoglutaric acid) were formed. Affinities of the different functional groups to form a hydrogen bond and ΔpK_a differences, leading to the eutectic formation, were discussed. The eutectic systems thus formed were further characterized and analyzed using a differential scanning calorimeter (DSC) and powder X-ray diffraction (PXRD). Binary thermal phase diagrams were plotted using different ratios of the systems to confirm the formation of eutectics, and pH-dependent solubility studies exhibited a significant decrease in the solubility in comparison to that of the drug for all three eutectic systems. The solubility of FXT reduced from 46.53 μg/mL (pH 5.63) to 46.03 μg/mL, 28.53 μg/mL, and 18.88 μg/mL; 770.58 μg/mL (pH 8.21) to 307.574 μg/mL, 116.63 μg/mL, 113.40 μg/mL; and from 13165.97 μg/mL (pH 10.13) to 1409.737 μg/mL, 854.51 μg/mL, and 1218.99 μg/mL for FXT-probenecid, FXT-adipic acid, and FXT-α-ketoglutaric acid eutectic systems, respectively. Furthermore, the microenvironmental pH studies were carried out to understand the effect of the microenvironment on the solubility of these eutectic systems. The contribution to solubility from lattice and nonlattice forces considering the microenvironment was also discussed.

Functional materials based on molecules with hydrogen-bonding ability: applications to drug co-crystals and polymer complexes

The design, synthesis and property characterization of new functional materials has garnered interest in a variety of fields. Materials that are capable of recognizing and binding with small molecules have applications in sensing, sequestration, delivery and property modification. Specifically, recognition of pharmaceutical compounds is of interest in each of the aforementioned application areas. Numerous pharmaceutical compounds comprise functional groups that are capable of engaging in hydrogen-bonding interactions; thus, materials that are able to act as hydrogen-bond receptors are of significant interest for these applications. In this review, we highlight some crystalline and polymeric materials that recognize and engage in hydrogen-bonding interactions with pharmaceuticals or small biomolecules. Moreover, as pharmaceuticals often exhibit multiple hydrogen-bonding sites, many donor/acceptor molecules have been specifically designed to interact with the drug via such multiple-point hydrogen bonds. The formation of multiple hydrogen bonds not only increases the strength of the interaction but also affords unique hydrogen-bonded architectures.

Is Failure of Cocrystallization Actually a Failure? Eutectic Formation in Cocrystal Screening of Hesperetin

Cocrystal screening of hesperetin with certain countermolecules generated highly soluble noncovalent derivatives in the form of eutectics, instead of expected cocrystals. As adhesive forces established by complimentary functional groups on hesperetin and coformers were unable to overcome the stress due to size shape mismatch of component molecules, thus, eutectics were formed. Hesperetin, a polyphenolic antioxidant with potent anticancer and cardioprotective effects, has an underdeveloped role in modern therapeutics on account of its critically low aqueous solubility resulting in stunted bioavailability. The liquid-assisted cogrinding of hesperetin and coformers generated binary-phase eutectics in fixed stoichiometry with theophylline (1:1.5), adenine (2:1), gallic acid (1.5:1), and theobromine (2:1). Primarily characterized by lower melting endotherm in differential scanning calorimetry, the eutectics showed complete melting in hot-stage microscopy. Apart from characteristic V-shaped binary-phase diagram, no discernible changes in the FTIR and powder X-ray diffraction spectra further confirm eutectic formation. The morphological differences were analyzed by SEM measurements. A 2 to 4 times enhanced dissolution profile of the eutectics measured in pH 7.4 aqueous buffer was coupled with the in vitro (1,1-diphenyl-2-picryl hydroxyl free radical antioxidant assay and RBC antihemolytic assay) studies to present a complete preliminary data on the improved bioavailability of hesperetin eutectics.

A gallic acid–succinimide co-crystal landscape: polymorphism, pseudopolymorphism, variable stoichiometry co-crystals and concomitant growth of non-solvated and solvated co-crystals

A design aspect for selective formation of diverse solid forms such as solvates, hydrates and anhydrous forms has been successfully investigated in a gallic acid–succinimide co-crystal landscape.

A systematic structural study of halogen bonding versus hydrogen bonding within competitive supramolecular systems

As halogen bonds gain prevalence in supramolecular synthesis and materials chemistry, it has become necessary to examine more closely how such interactions compete with or complement hydrogen bonds whenever both are present within the same system. As hydrogen and halogen bonds have several fundamental features in common, it is often difficult to predict which will be the primary interaction in a supramolecular system, especially as they have comparable strength and geometric requirements. To address this challenge, a series of molecules containing both hydrogen- and halogen-bond donors were co-crystallized with various monotopic, ditopic symmetric and ditopic asymmetric acceptor molecules. The outcome of each reaction was examined using IR spectroscopy and, whenever possible, single-crystal X-ray diffraction. 24 crystal structures were obtained and subsequently analyzed, and the synthon preferences of the competing hydrogen- and halogen-bond donors were rationalized against a background of calculated molecular electrostatic potential values. It has been shown that readily accessible electrostatic potentials can offer useful practical guidelines for predicting the most likely primary synthons in these co-crystals as long as the potential differences are weighted appropriately.