1,721,040 research outputs found
A Solid-Gas Route to Polymorph Conversion in Crystalline [FeII( 5-C5H4COOH)2]. A Diffraction and Solid-State NMR Study.
No full textCryst. form I (monoclinic) and form II (triclinic) of ferrocene dicarboxylic acid [Fe(5-C5H4COOH)2] have been employed in solid-gas reactions at room temp. with the gaseous bases NH3, NH2(CH3), and NH(CH3)2. The two crystal forms behave in exactly the same way in the solid-gas reaction, generating the same products, identified as the anhyd. cryst. salts [NH4]2[Fe(5-C5H4COO)2] (1), [NH3CH3]2[Fe(5-C5H4COO)2] (2), and [NH2(CH3)2]2[Fe(5-C5H4COO)2] (3). Interestingly though, all these crystals revert via vapor release exclusively to the metastable cryst. form I. Starting materials and products have been investigated by single-crystal and powder diffraction and by 13C, 15N CPMAS and 1H MAS methods
Enantiospecific crystallisation behaviour of malic acid in mechanochemical reactions with vinpocetine
Full text link: We report an intriguing example of enantioselectivity in the formation of new multicomponent crystalline solid containing vinpocetine and malic acid. Several experimental data sets confirmed that the multicomponent system presents a clear enantiospecific crystallisation behaviour both in the solid-state and in solution: only the system consisting of vinpocetine and L-malic acid produces a free-flowing solid consisting of a new crystalline form, while the experiments with D-malic acid produced an amorphous and often deliquescent material. The new vinpocetine-L-malic system crystallizes in the monoclinic space group of P21 and in a 1:1 M ratio, where the two molecules are linked through intermolecular hydrogen bonds in the asymmetric unit. The vinpocetine-DL-malic system was partially crystalline (with also traces of unreacted vinpocetine) with diffraction peaks corresponding to those of vinpocetine-L-malic acid. Solid-state NMR experiments revealed strong ionic interactions in all the three systems. However, while vinpocetine-L-malic acid system was a pure and crystalline phase, in the other two systems the presence of unreacted vinpocetine was always detected. This resulted in a significant worsening of the dissolution profile with respect to vinpocetine-L-malic pure crystalline salt, whose dissolution kinetics appeared superior
Enabling Superprotonic Phase Transitions in Solid Acids via Supramolecular Complex Formation: The Case of Crown Ethers and Alkali Hydrogen Sulfates
Full text linkThis investigation, combining both structural and spectroscopic analyses, sheds light on the intricate relationship between conduction properties and the initiation of dynamic motions within the anhydrous crystalline materials of 18-crown-6·KHSO4 (1) and 18-crown-6·RbHSO4 (2) and proves how the formation of supramolecular complexes is pivotal for inducing solid–solid transitions, leading to superprotonic phases, i.e., crystalline solids exhibiting an enhanced ability to conduct protons, as elucidated through impedance spectroscopic measurements. This multifaceted approach deepens our understanding of the phenomenon and sets the stage for further exploration and application in solid-state protonic conductors
Investigation of Solid-State Forms between p-Aminosalicylic Acid and Adenine: Exploring Salts, Cocrystals and their Polymorphism
No full textThis study investigates the polymorphic behavior of multi-component adducts formed between p-aminosalicylic acid (PAS), a second-line anti-tuberculosis drug, and adenine (ADE), a hydrogen bond-rich coformer. Given a ΔpKa of 2.2 between PAS and ADE, within the salt–cocrystal uncertainty region, three distinct solid-state forms (an anhydrous and two hydrates) were synthesized via solvent-tuned liquid-assisted grinding and solution evaporation. Comprehensive characterization was performed using solid-state NMR, FT-IR and Raman spectroscopy, X-ray diffraction (SCXRD and PXRD), DSC, TGA, and in vitro dissolution tests. Results revealed significant differences in structure, hydrogen-bonding networks, and thermal properties among the forms, with PAS:ADE stoichiometries of 3:2 for the anhydrous form and 1:1 for the hydrated forms. These findings demonstrate the critical role of solvent and stoichiometry in directing adduct formation and polymorphism, offering insights for optimizing drug formulation and expanding intellectual property strategies in pharmaceutical development
Investigation of Dimethylammonium Solubility in MAPbBr3 Hybrid Perovskite: Synthesis, Crystal Structure, and Optical Properties
Full text linkThe possible existence of mixed methylammonium (MA)/dimethylammonium (DMA) lead bromide hybrid perovskites of general formula MA1-xDMAxPbBr3 (0 ≤ x ≤ 1) was investigated. A combined X-ray diffraction and solid-state nuclear magnetic resonance approach indicates that DMA can be incorporated up to about x = 0.30 while retaining the cubic lattice of MAPbBr3. By increasing the DMA content (x), the absorption shows a progressive blue shift and the band gap moves from about 2.17 eV (x = 0) to about 2.23 (x = 0.30) with a concomitant slightly faster recombination in the mixed cation powders
Halogen-Bond Effects on the Thermo- and Photochromic Behaviour of Anil-Based Molecular Co-crystals
Full text linkN-Salicilideneanilines are among the most studied thermo- and photochromic systems in the solid state. Although thermochromism is a general property of crystalline N-salicilideneanilines, photochromism is known in a limited number of cases. As a method for the construction of thermo- and photo-responsive molecular architectures, the co-crystallisation of 1,2,4,5-tetrafluoro-3,6-diiodobenzene (I2F4) with three selected imines of o-vanillin, named 1, 2 and 3, obtained through a condensation reaction with 3-aminopyridine, 4-bromoaniline and 4-iodoaniline, respectively, is reported herein. All crystals and co-crystals have been characterised by means of solid-state complementary techniques (X-ray diffraction, solid-state NMR spectroscopy, absorption and emission spectroscopy). The role of halogen bonding and crystal packing in the optical and chromic properties of all solid materials is discussed. All solids exhibit thermochromic behaviour, and three of them (2, 22 ⋅I2F4 and 32 ⋅I2F4) are also photochromic. Imine derivative 3 crystallises in two different polymorphic forms (3 A and 3 B) and a solvate (3Solv ). The bromo and iodo derivatives, 2 and 3 B, are isomorphous and form isomorphous co-crystals with I2F4, but behave differently when exposed to UV light because only crystalline 2 is photochromic. Interestingly, the replacement of bromine with iodine seems to turn off the photochromism because crystalline 3 A and 3Solv , and even the 20.7 30.3 solid solution, do not manifest photochromic behaviour.</p
Improving Biopharmaceutical Properties of Vinpocetine Through Cocrystallization
Full text linkVinpocetine is a poorly water soluble weakly basic drug (pKa 1⁄4 7.1) used for the treatment of several cerebrovascular and cognitive disorders. Because existing formulations exhibit poor bioavailability and scarce absorption, a dosage form with improved pharmacokinetic properties is highly desirable. Cocrystallization represents a promising approach to generate diverse novel crystal forms and to improve the aqueous solubility and in turn the oral bioavailability. In this article, a novel ionic cocrystal of vinpocetine is described, using boric acid as a coformer, and fully characterized (by means of differential scanning calorimetry, solid-state nuclear magnetic resonance, powder and singlecrystal X-ray diffraction, and powder dissolution test). Pharmacokinetic performance was also tested in a human pilot study. This pharmaceutical ionic cocrystal exhibits superior solubilization kinetics and modulates important pharmacokinetic values such as maximum concentration in plasma (Cmax), time to maximum concentration (tmax), and area under the plasma concentration-time curve (AUC) of the poorly soluble vinpocetine and it therefore offers an innovative approach to improve its bioavailability
Mechanochemical reactivity inhibited, prohibited and reversed by liquid additives: examples from crystal-form screens
Full text linkWe demonstrate that liquid additives can exert inhibitive or prohibitive effects on the mechanochemical formation of multi-component molecular crystals, and report that certain additives unexpectedly prompt the dismantling of such solids into physical mixtures of their constituents. Computational methods were employed in an attempt to identify possible reasons for these previously unrecognised effects of liquid additives on mechanochemical transformations
Engineering Codrug Solid Forms: Mechanochemical Synthesis of an Indomethacin-Caffeine System
Full text linkThis article reports on the preparation and solid-state characterization of an indomethacin−caffeine drug−drug cocrystal (or codrug) in a 1:1 stoichiometry. These two active ingredients are frequently coadministered as part of a therapy against strong migraines, in a commercially available fixed dose combination formulation. The X-ray crystal structure of the codrug is characterized by a hydrogen bond interaction between the carboxylic moiety of indomethacin and the purinic nitrogen atom of caffeine. The combination of multinuclear and multidimensional solid-state NMR measurements (1H MAS, 13C and 15N CPMAS, 1H DQ MAS, 13C−1H HETCOR, 14N−1H J- and D-HMQC), as well as IR data, provided spectroscopic evidence about the hydrogen atom position along the hydrogen bond axis, thereby confirming the neutral nature of the cocrystal. Furthermore, dissolution kinetic tests revealed superior bioavailability of indomethacin in the codrug compared to indomethacin alone and to an indomethacin−caffeine physical mixture. On the other hand, the melting point of indomethacin was slightly lower in the cocrystal rather than in the pure drug
Proton in a Confined Space: Structural Studies of H+âCrypt-111 Iodide and Some Halogen-Bonded Derivatives
Full text linkExperimental observations and modeling data are reported on the solid-state structural features of crypt- 111âHI (1) and the three-component co-crystals that 1 forms with α,Ï-diiodoperfluoroalkanes 2 aâd. X-ray analyses indicate that, in all five systems and at low temperature, the caged proton is covalently bonded to a single nitrogen atom and is involved in a network of intramolecular hydrogen bonds. In contrast, room-temperature, solid-state 15N NMR spectroscopy suggests magnetic equivalency of the two N atoms of crypt-111 in both 1 and co-crystals of 1 with diiodoperfluoroalkanes. Computational modelling confirms that the acidic hydrogen inside the cavity preferentially sits along the internitrogen axis and is covalently bonded to one nitrogen. The computed energy barriers suggest that the hopping of the encapsulated proton between the two N atoms of the cage can occur in the halogen-bonded co-crystals of 1â2, but it is hardly possible in the pure H+âcrypt-111 iodide 1. These different pictures of the proton position and dynamics obtained by using different techniques and conditions confirm the unique characteristics of the confined space within the cavity of crypr-111 and the distinctive features of processes occurring therein
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