Supramolecular Organization in Salts of Riluzole with Dihydroxybenzoic Acids-The Key Role of the Mutual Arrangement of OH Groups.

Intermolecular interactions, in particular hydrogen bonds, play a key role in crystal engineering. The ability to form hydrogen bonds of various types and strengths causes competition between supramolecular synthons in pharmaceutical multicomponent crystals. In this work, we investigate the influence of positional isomerism on the packing arrangements and the network of hydrogen bonds in multicomponent crystals of the drug riluzole with hydroxyl derivatives of salicylic acid.

Virtual Screening, Structural Analysis, and Formation Thermodynamics of Carbamazepine Cocrystals.

In this study, the existing set of carbamazepine (CBZ) cocrystals was extended through the successful combination of the drug with the positional isomers of acetamidobenzoic acid. The structural and energetic features of the CBZ cocrystals with 3- and 4-acetamidobenzoic acids were elucidated via single-crystal X-ray diffraction followed by QTAIMC analysis. The ability of three fundamentally different virtual screening methods to predict the correct cocrystallization outcome for CBZ was assessed based on the new experimental results obtained in this study and data available in the literature.

Influence of Co-amorphization on the Physical Stability and Dissolution Performance of an Anthelmintic Drug Flubendazole.

In this work, the co-amorphization approach was applied to flubendazole (FluBZ), resulting in the formation of two novel solid forms of FluBZ with l-phenylalanine (Phe) and l-tryptophan (Trp). A variety of physicochemical techniques have been used to describe new systems, including powder X-ray diffraction, thermal methods, infrared spectroscopy, and scanning electron microscopy. Co-amorphization has been shown to suppress crystallization tendency and considerably increase the shelf-life storage of amorphous flubendazole solid across a wide range of relative humidities.

Molecular Dynamics Simulation of Association Processes in Aqueous Solutions of Maleate Salts of Drug-like Compounds: The Role of Counterion.

The study of the formation of microstructures during the interaction of a protonated drug-like compound (API) with a maleic acid monoanion sheds light on the assembly processes in an aqueous solution at the molecular level. Molecular dynamics (MD) simulations coupled with density functional theory (DFT) calculations made it possible to find initial hydrogen bonding motifs during the assembly process, leading to the formation of heterodimers and trimers. The process of trimer formation [protonated API-maleic acid monoanion-protonated API] proceeds through the formation of three intermolecular H-bonds by the CO group of the maleic acid monoanion in both systems.

Comparison of Proton Acceptor and Proton Donor Properties of HO and HO in Organic Crystals of Drug-like Compounds: Peroxosolvates vs. Crystallohydrates.

Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (HO) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (HO) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by HO as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by HO.

A Combined Experimental and Theoretical Study of Nitrofuran Antibiotics: Crystal Structures, DFT Computations, Sublimation and Solution Thermodynamics.

Single crystal of furazolidone (FZL) has been successfully obtained, and its crystal structure has been determined. Common and distinctive features of furazolidone and nitrofurantoin (NFT) crystal packing have been discussed. Combined use of QTAIMC and Hirshfeld surface analysis allowed characterizing the non-covalent interactions in both crystals.

Polymorphic forms of antiandrogenic drug nilutamide: structural and thermodynamic aspects.

Attempts to obtain new cocrystals of nonsteroidal antiandrogenic drug nilutamide produced alternative polymorphic forms of the compound (Form II and Form III) and their crystal structures were elucidated by single-crystal X-ray diffraction. Apart from the cocrystallization technique, lyophilization was found to be an effective strategy for achieving polymorph control of nilutamide, which was difficult to obtain by other methods. The physicochemical properties and relative stability of the commercial Form I and newly obtained Form II were comprehensively investigated by a variety of analytical methods (thermal analysis, solution calorimetry, solubility, and sublimation), whereas for Form III, only a handful of experimental parameters were obtained due to the elusive nature of the polymorph.

Novel cocrystals of itraconazole: Insights from phase diagrams, formation thermodynamics and solubility.

In this work, the cocrystallization approach was applied to itraconazole (ITR), a very slightly soluble triazole antifungal drug, which led to the formation of two new solid forms of ITR with 4-aminobenzoic acid (4AmBA) and 4-hydroxybenzamide (4OHBZA). A thermodynamic analysis of the solid-liquid binary phase diagrams for the (ITR + 4AmBA) and (ITR + 4OHBZA) systems provided conclusive evidence of the cocrystal stoichiometry: 1:1 for the cocrystal with 4-aminobenzoic acid, and 1:2 for the cocrystal with 4-hydroxybenzamide. Powder X-Ray diffraction analysis confirmed the formation of two different polymorphic forms of the [ITR + 4OHBZA] (1:2) cocrystal obtained either through solution or melt crystallization.

Interplay of π-stacking and inter-stacking interactions in two-component crystals of neutral closed-shell aromatic compounds: periodic DFT study.

This paper bridges the gap between high-level computations of gas-phase models of 1 : 1 arene-arene complexes and calculations of the two-component (binary) organic crystals using atom-atom potentials. The studied crystals consist of electron-rich and electron-deficient compounds, which form infinite stacks (columns) of heterodimers. The sublimation enthalpy of crystals has been evaluated by DFT periodic calculations, while intermolecular interactions have been characterized by Bader analysis of the periodic electronic density.

Combined X-ray Crystallographic, IR/Raman Spectroscopic, and Periodic DFT Investigations of New Multicomponent Crystalline Forms of Anthelmintic Drugs: A Case Study of Carbendazim Maleate.

Synthesis of multicomponent solid forms is an important method of modifying and fine-tuning the most critical physicochemical properties of drug compounds. The design of new multicomponent pharmaceutical materials requires reliable information about the supramolecular arrangement of molecules and detailed description of the intermolecular interactions in the crystal structure. It implies the use of a combination of different experimental and theoretical investigation methods.

Solving the enigma of weak fluorine contacts in the solid state: a periodic DFT study of fluorinated organic crystals.

The nature and strength of weak interactions with organic fluorine in the solid state are revealed by periodic density functional theory (periodic DFT) calculations coupled with experimental data on the structure and sublimation thermodynamics of crystalline organofluorine compounds. To minimize other intermolecular interactions, several sets of crystals of perfluorinated and partially fluorinated organic molecules are considered. This allows us to establish the theoretical levels providing an adequate description of the metric and electron-density parameters of the C-F⋯F-C interactions and the sublimation enthalpy of crystalline perfluorinated compounds.

Pharmaceutical salts of emoxypine with dicarboxylic acids.

New salt forms of the antioxidant drug emoxypine (EMX, 2-ethyl-6-methylpyridin-3-ol) with pharmaceutically acceptable maleic (Mlt), malonic (Mln) and adipic (Adp) acids were obtained {emoxypinium maleate, CHNO·CHO, [EMX+Mlt], emoxypinium malonate, CHNO·CHO, [EMX+Mln], and emoxypinium adipate, CHNO·CHO, [EMX+Adp]} and their crystal structures determined. The molecular packing in the three EMX salts was studied by means of solid-state density functional theory (DFT), followed by QTAIMC (quantum theory of atoms in molecules and crystals) analysis. It was found that the major contribution to the packing energy comes from pyridine-carboxylate and hydroxy-carboxylate heterosynthons forming infinite one-dimensional ribbons, with [EMX+Adp] additionally stabilized by hydrogen-bonded C(9) chains of Adp ions.

Picosecond supercontinuum generation in large mode area photonic crystal fibers for coherent anti-Stokes Raman scattering microspectroscopy.

We perform a detailed theoretical and experimental investigation of supercontinuum generation in large-mode-area photonic crystal fibers pumped by a high-energy, high-repetition rate picosecond Nd:YVO laser, with the goal of using it as the Stokes beam in coherent anti-Stokes Raman scattering setup. We analyze the influence of fiber structure and length on the supercontinuum power, spectral shape, and group delay dispersion. We identify the experimental conditions for stable supercontinuum generation, with microjoule-level pulse energy and the spectrum extending beyond 1600 nm, which allows excitation of Raman frequencies up to 3000 cm and beyond.

Influence of Secondary Interactions on the Structure, Sublimation Thermodynamics, and Solubility of Salicylate:4-Hydroxybenzamide Cocrystals. Combined Experimental and Theoretical Study.

Cocrystal screening of 4-hydroxybenzamide with a number of salicylates (salicylic acid, SA; 4-aminosalicylic acid, PASA; acetylsalicylic acid, ASA; and salicylsalicylic acid, SSA) was conducted to confirm the formation of two cocrystals, [SA+4-OHBZA] (1:1) and [PASA+4-OHBZA] (1:1). Their structures were determined using single-crystal X-ray diffraction, and the hydrogen-bond network topology was studied. Thermodynamic characteristics of salicylic acid cocrystal sublimation were obtained experimentally.

Pharmaceutical salts of ciprofloxacin with dicarboxylic acids.

New salts of antibiotic drug ciprofloxacin (CIP) with pharmaceutically acceptable maleic (Mlt), fumaric (Fum) and adipic (Adp) acids were obtained and their crystal structures were determined. The crystal lattices of the fumarate and adipate salts were found to accommodate the water molecules, while the maleate salt was anhydrous. The dehydration and melting processes were analyzed by means of differential scanning calorimetry and thermogravimetric analysis.

Cocrystal screening of hydroxybenzamides with benzoic acid derivatives: a comparative study of thermal and solution-based methods.

The main problem occurring at the early stages of cocrystal search is the choice of an effective screening technique. Among the most popular techniques of obtaining cocrystals are crystallization from solution, crystallization from melt and solvent-drop grinding. This paper represents a comparative analysis of the following screening techniques: DSC cocrystal screening method, thermal microscopy and saturation temperature method.

Pharmaceutical cocrystals of diflunisal and diclofenac with theophylline.

Pharmaceutical cocrystals of nonsteroidal anti-inflammatory drugs diflunisal (DIF) and diclofenac (DIC) with theophylline (THP) were obtained, and their crystal structures were determined. In both of the crystal structures, molecules form a hydrogen bonded supramolecular unit consisting of a centrosymmetric dimer of THP and two molecules of active pharmaceutical ingredient (API). Crystal lattice energy calculations showed that the packing energy gain of the [DIC + THP] cocrystal is derived mainly from the dispersion energy, which dominates the structures of the cocrystals.

Salicylamide cocrystals: screening, crystal structure, sublimation thermodynamics, dissolution, and solid-state DFT calculations.

A new cocrystal of 2-hydroxybenzamide (A) with 4-acetamidobenzoic acid (B) has been obtained by the DSC screening method. Thermophysical analysis of the aggregate [A:B] has been conducted and a fusion diagram has been plotted. Cocrystal formation from melts was studied by using thermomicroscopy.

White light generation over three octaves by femtosecond filament at 3.9 µm in argon.

We report the first (to our knowledge) experimental results and numerical simulations on mid-IR femtosecond pulse filamentation in argon using 0.1 TW peak-power, 80 fs, 3.9 μm pulses.

Phase-stable sub-cycle mid-infrared conical emission from filamentation in gases.

Sub-single-cycle pulses in the mid-infrared (MIR) region were generated through a conical emission from a laser-induced filament. Fundamental and second-harmonic pulses of 25-fs Ti:sapphire amplifier output were focused into argon to produce phase-stable broadband MIR pulses in a well-focusable ring-shaped beam. The beam profile and spectrum of the MIR field are accurately reproduced with a simple calculation based on a four-wave mixing process.