Cocrystallization-driven self-assembly with vanillic acid offers a new opportunity for surmounting fast and excessive absorption issues of antifungal drug 5-fluorocytosine: a combined theoretical and experimental research

The cocrystal of 5-fluorocytosine (FCY) with vanillic acid (VAA) was assembled via a cocrystallization technique, giving a novel understanding for conquering the dose-limited hepatotoxicity caused by the rapid and almost complete absorption of FCY.

Salts of purine alkaloids caffeine and theobromine with 2,6-dihydroxybenzoic acid as coformer: structural, theoretical, thermal and spectroscopic studies

The study of various forms of pharmaceutical substances with specific physicochemical properties suitable for putting them on the market is one of the elements of research in the pharmaceutical industry. A large proportion of active pharmaceutical ingredients (APIs) occur in the salt form. The use of an acidic coformer with a given structure and a suitable pK_a value towards purine alkaloids containing a basic imidazole N atom can lead to salt formation. In this work, 2,6-dihydroxybenzoic acid (26DHBA) was used for cocrystallization of theobromine (TBR) and caffeine (CAF). Two novel salts, namely, theobrominium 2,6-dihydroxybenzoate, C₇H₉N₄O₂⁺·C₇H₅O₄^- (I), and caffeinium 2,6-dihydroxybenzoate, C₈H₁₁N₄O₂⁺·C₇H₅O₄^- (II), were synthesized. Both salts were obtained independently by slow evaporation from solution, by neat grinding and also by microwave-assisted slurry cocrystallization. Powder X-ray diffraction measurements proved the formation of the new substances. Single-crystal X-ray diffraction studies confirmed proton transfer between the given alkaloid and 26DHBA, and the formation of N-H...O hydrogen bonds in both I and II. Unlike the caffeine cations in II, the theobromine cations in I are paired by noncovalent N-H...O=C interactions and a cyclic array is observed. As expected, the two hydroxy groups in the 26DHBA anion in both salts are involved in two intramolecular O-H...O hydrogen bonds. C-H...O and π-π interactions further stabilize the crystal structures of both compounds. Steady-state UV-Vis spectroscopy showed changes in the water solubility of xanthines after ionizable complex formation. The obtained salts I and II were also characterized by theoretical calculations, Fourier-transform IR spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and elemental analysis.

On the molecular basis of H2O/DMSO eutectic mixtures by using phenol compounds as molecular sensors: a combined NMR and DFT study

NMR and DFT studies of phenol compounds as molecular sensors were carried out to investigate H₂O/DMSO eutectic mixtures at a molecular level. The experimental ¹H NMR chemical shifts of the OH groups, δ_exp(OH), of phenol, paracoumaric acid, and vanillic acid show maximum deshielding and, thus, hydrogen bond interactions in the range of mole fractions 0.20 < χ(DMSO) < 0.33. In the mole fractions χ(DMSO) < 0.2, a progressive decrease in δ_exp(OH) was observed which demonstrates a decrease in hydrogen bond interactions at infinite dilution in H₂O, despite the increase in the number of available hydrogen bond acceptor and donor sites. DFT calculated δ_calc(OH) of minimum energy solvation clusters were shown to be in reasonable agreement with the pattern in experimental δ_exp(OH) data. The chemical shift deshielding and, thus, increased hydrogen bond interactions in the natural product + DMSO + nH₂O (n = 2, 3) solvation clusters, relative to complexes in DMSO or H₂O solutions, cannot be attributed to a single structural parameter of the cooperative interactions between H₂O and DMSO molecules with the phenol OH groups of the natural products. The minimum energy conformers of phenol compounds + 2H₂O + DMSO complexes are in excellent agreement with a recent low temperature neutron diffraction experiment of 3D₂O + DMSO and demonstrate a general structural motif of solvation complexes. The combined use of ¹H NMR and DFT studies with emphasis on δ(OH) of phenol compounds, as molecular sensors, can provide an effective method for the study of solute-solvent interactions at the atomic level.

Challenges and opportunities of pharmaceutical cocrystals: a focused review on non-steroidal anti-inflammatory drugs

The focus of the review is to discuss the relevant and essential aspects of pharmaceutical cocrystals in both academia and industry with an emphasis on non-steroidal anti-inflammatory drugs (NSAIDs). Although cocrystals have been prepared for a plethora of drugs, NSAID cocrystals are focused due to their humongous application in different fields of medication such as antipyretic, anti-inflammatory, analgesic, antiplatelet, antitumor, and anti-carcinogenic drugs. The highlights of the review are (a) background of cocrystals and other solid forms of an active pharmaceutical ingredient (API) based on the principles of crystal engineering, (b) why cocrystals are an excellent opportunity in the pharma industry, (c) common methods of preparation of cocrystals from the lab scale to bulk quantity, (d) some latest case studies of NSAIDs which have shown better physicochemical properties for example; mechanical properties (tabletability), hydration, solubility, bioavailability, and permeability, and (e) latest guidelines of the US FDA and EMA opening new opportunities and challenges.

Synthon hierarchy in theobromine cocrystals with hydroxybenzoic acids as coformers

Cocrystals, solids composed of molecular and/or ionic compounds connected by noncovalent interactions, are objects of interest in crystal engineering. Theobromine, as an active pharmaceutical ingredient, was used in cocrystallization with dihydroxybenzoic acids.

Temperature-induced phase transition of isonicotinamide-malonic acid (2/1) and supramolecular construct analysis of isonicotinamide structures

The isonicotinamide-malonic acid (2/1) co-crystal salt (2IN·C3) exhibits a first-order displacive structural phase transition from low-temperature triclinic P1̅ crystal structure to high-temperature monoclinic C2/c crystal structure and vice versa at the transition temperatures of 298 (1) and 295 (1) K, respectively, as determined by variable-temperature SCXRD analysis and DSC measurements. The asymmetric unit of 2IN·C3 comprises three malonic acid molecules and six isonicotinamide molecules at the low-temperature phase, and this is reduced to a half-molecule of malonic acid and an isonicotinamide molecule in the high-temperature phase. The carboxyl and pyridinium H atoms are disordered at both phases. The observed phase transition near room temperature is triggered by the molecular displacement of the isonicotinamide molecule and the syn-anti conformational transformation of the malonic acid molecule with deviation angles of 10.4 and 11.7°, respectively, which induced an energy change of 19.1 kJ mol−1 in the molecular cluster comprising a central isonicotinamide molecule and eight neighboring molecules. However, the total interaction energy of the molecular cluster of a central malonic acid molecule and eight neighboring molecules does not change significantly upon the phase transition. The molecules of isonicotinamide structures except IN·IN+·triazole ‒ form zero-dimensional finite arrays or one-dimensional chains as the primary supramolecular construct by carboxyl···pyridyl (−35.9 to −56.7 kJ mol−1) and carboxamide···carboxamide (−53.6 to −68.7 kJ mol−1) or carboxyl···carboxamide (−52.6 to −67.1 kJ mol−1) synthons.

Co-crystals and salts of vanillic acid and vanillin with amines

Co-crystals and salts of vanillin and its oxidized form vanillic acid with amine-type molecules.

Pharmaceutical solvates, hydrates and amorphous forms: A special emphasis on cocrystals

Active pharmaceutical ingredients (APIs) may exist in various solid forms, which can lead to differences in the intermolecular interactions, affecting the internal energy and enthalpy, and the degree of disorder, affecting the entropy. Differences in solid forms often lead to differences in thermodynamic parameters and physicochemical properties for example solubility, dissolution rate, stability and mechanical properties of APIs and excipients. Hence, solid forms of APIs play a vital role in drug discovery and development in the context of optimization of bioavailability, filing intellectual property rights and developing suitable manufacturing methods. In this review, the fundamental characteristics and trends observed for pharmaceutical hydrates, solvates and amorphous forms are presented, with special emphasis, due to their relative abundance, on pharmaceutical hydrates with single and two-component (i.e. cocrystal) host molecules.