Search Results
Abstract
Indomethacin is known to exhibit polymorphism and solvates, the different forms obtained do not exhibit the same solubility and their bioavailabilities are different. It is of a prime importance to identify the various polymorphic and solvated forms. This study was carried out by: DSC (different scanning calorimetry), TG (thermogravimetric analysis), X-ray diffraction and thermomicroscopy. Seven solvates, with acetone, benzene, dichloromethane, tetrahydrofurane, propanol, chloroform and diethylether, were isolated and studied. Their formulae have been determined by thermogravimetric analysis and their X-ray patterns on powder are presented, by DSC their behaviour after desolvation is recorded, the temperature and the enthalpy of fusion are measured and by this way the form obtained is deduced.
Polymorph formation from solvate desolvation
Spironolactone forms I and II from the spironolactone-ethanol solvate
Abstract
Spironolactone (C24H32O4S) usually crystallizes into an orthorhombic phase, named Form II. Another orthorhombic phase, named Form I, is also known but seems difficult to obtain. Studies of the kinetics of desolvation of the ethanol solvate at room temperature showed that these two forms can be obtained through different mechanisms of desolvation.
Abstract
Lipophilic calix[4]resorcinarene derived from lauryl aldehyde forms stable crystalline solvates with a range of organic solvents: acetone, 1,4-dioxane, methylethylvketone, dimethylformamide, dimethylacetamide, N-methylpyrrolidinone, butyronitrile, methanol, 1,2-dimethoxybenzene and acetonitrile. The composition and thermal stability of these solvates was followed by thermogravimetric method, indicating a stoichiometry ranging from 1 to 3 (calixresorcinarene/solvent). The activation energy was evaluated for the selected solvates. Molecular modelling, using Hyperchem 5.0 software, was applied to the selected solvates.
Abstract
Compositions of the solid solvates of C60 with 1,2-dichlorobenzene and 1,3,5-trimethylbenzene were determined with the help of experimental procedures developed. Possible correlations between compositions and thermodynamic properties were discussed.
Abstract
A combined analysis of structural data and experimental results (DSC, temperature-resolved XRPD and hot stage optical microscopy) revealed that the dehydration mechanism of cortisone acetate monohydrate (CTA·H2O) involves a collective and anisotropic departure of water molecules followed by a cooperative structural reorganization toward the anhydrous polymorph CTA (form 2). In spite of the lack of crystal structure data, it can be postulated from experimental data that thermal decomposition of the dihydrated form (CTA·2H2O) and of the tetrahydrofuran solvate (CTA·THF) toward another polymorph (CTA (form 3)) also proceeds according to a cooperative mechanism, thus giving rise to probable structural filiations between these crystalline forms of CTA. The crystal structure determination of two original solvates (CTA·DMF and CTA·DMSO) indicates that these phases are isomorphous to the previously reported acetone solvate. However, their desolvation behaviour does not involve a cooperative mechanism, as could be expected from structural data only. Instead, the decomposition mechanism of CTA·DMF and CTA·DMSO starts with the formation of a solvent-proof superficial layer, followed by the partial dissolution of the enclosed inner part of crystals. Hot stage optical microscopy observations and DSC measurements showed that dissolved materials (resulting from a peritectic decomposition) is suddenly evacuated through macroscopic cracks about 30°C above the ebullition point of each solvent. From this unusual behaviour, the necessity to investigate rigorously the various aspects (thermodynamics, kinetics, crystal structures and physical factors) of solvate decompositions is highlighted, including factors related to the particular preparation route of each sample.
Abstract
Isostructural solvates of the 1:1 molecular complex between the antibacterial drugs tetroxoprim (TXP) and sulfametrole (SMTR) with formulae TXPSMTRCH3OH (I), TXPSMTRC2H5OH (II) and TXPSMTRH2O (III), were investigated to establish their propensity for guest exchange. Separate exposure of powdered (I), (II) and (III) to a saturated atmosphere of each solvent of the complementary solvate pair at ambient temperature resulted in reversible solvent exchange in all cases. DSC and TG were the methods of choice for monitoring the exchange processes since (I)-(III) have distinct onset temperatures of desolvation and characteristic mass losses. Interpretation of the results in terms of the known locations of the solvent molecules in crystals of (I)-(III) led to the conclusion that solvent exchange probably proceeds by a co-operative mechanism involving material transport through channels while the common host framework is maintained.
Abstract
The crystalline solvates containing fullerenes and (di)methylnaphthalenes were investigated by thermal analyses and X-ray diffraction methods. It was found that C60 with (di)methylnaphthalenes forms two types of stable solvates: either at the molar ratio 1:2 decomposing at temperatures close to 100C or at 1:1 molar ratio decomposing in the temperature range 120–214C. Crystalline lattice and thermal stability of the solvates depends on the structure of the solvent molecules. The strong solute-solvent interaction is also manifested by the modification of the C60 absorption spectra in solution. The results are discussed using semiempirical quantum chemistry methods.
Abstract
Single crystals of the N,N-dimethylformamide (DMF) solvate (1:1) of flurbiprofen (FBP) were grown for the first time and characterised by X-ray diffraction, IR spectrophotometry, DSC and solution calorimetric methods. The structure may be characterised as a layer-structure, where DMF double-sheets are arranged between FBP double-sheets. The FBP and DMF molecules are linked to each other by a hydrogen bond, which is formed between the hydroxyl group of FBP and the carbonyl group of DMF. The conformation of FBP molecules in the DMF solvate differs from analogous enantiomers in the unsolvated form. The differences are discussed from the point of view of the influence of the nature of the solvent on selective crystallisation of the enantiomers. A peculiarity of the solvate is its low melting point, 37.30.2C, with respect to the unsolvated phase, 113.50.2C. Based on solution enthalpies of the solvated and unsolvated phases dissolved in DMF, the difference in crystal lattice energies, 9.8 kJ mol-1, was calculated and the difference in entropies, 33 J mol-1 K-1 estimated. A possible mechanism explaining the low melting point of the solvate is discussed.
Abstract
In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C60, C70 and the piperazine monoadduct of [60] fullerene C60 N2C4H8 with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.
Abstract
Pharmaceutical solids can often form solvated species which can affect the material’s physical and chemical stability. Carbamazepine (CBZ) has been proven to form a 1:1 solvate with acetone. This report investigates the solvation behavior of CBZ over a wide temperature and acetone concentration range using Dynamic gravimetric Vapor Sorption (DVS). The solvation transition point increased from 62.5% P/P 0 at 10°C to 97.8% P/P 0 at 30°C, resulting in a 15.9 kJ mol−1 heat of solvation. The desolvation kinetics were studied between 15 and 30°C, indicating CBZ desolvation is a first-order reaction with autocatalysis by the desolvated product and an activation energy of 81.9 kJ mol−1.
