Polymorphism and solvatomorphism 2005

Insightful vibrational imaging study on the hydration mechanism of carbamazepine

Anhydrous carbamazepine (CBZ) is an anti-convulsant drug commonly used to treat epilepsy and relieve trigeminal neuralgia. The presence of the dihydrate form in commercial CBZ tablets can change the dissolution rate of the active pharmaceutical ingredient (API), thus decreasing its activity. The hydration transformation can occur during wet granulation or storage, within a few weeks, depending on the ambient conditions. This work aims to investigate the effect of relative humidity (RH) in the transition of pure anhydrous CBZ (CBZ III) into the hydrate form by using confocal Raman microscopy with cluster analysis (CA). Firstly, several tablets of pure CBZ III containing different amounts of CBZ DH (50%, 10%, 1%, 0.5%) were prepared and analyzed by Raman imaging with CA. Our results show that CBZ DH crystals can be detected in the CBZ III tablets, at as low a concentration as 0.5%, giving distinct Raman features for the analysed polymorphs. The stability of pure anhydrous (CBZ III) tablets was then monitored by Raman imaging at room temperature (20-22 °C) and different RH (6%, 60% and 89%). The Raman imaging with CA showed that the anhydrous CBZ tablets start to convert into the hydrate form after 48 h, and it completely changes after 120 hours (5 days) at RH 89%. The tablets exposed to RH 6% and 60% did not demonstrate the presence of CBZ DH after 1 week of exposure. The exposure time was extended for 9 months in the former, and no CBZ DH was observed. A comparative study using IR imaging was also performed, demonstrating the viability of these vibrational imaging techniques as valuable tools to monitor the hydration process of active pharmaceutical ingredients.

Applications of Powder X-Ray Diffraction in Small Molecule Pharmaceuticals: Achievements and Aspirations

Since the discovery of X-ray diffraction and its potential to elucidate crystal symmetry, powder X-ray diffraction has found diverse applications in the field of pharmaceutical sciences. This review summarizes significant achievements of the technique during various stages of dosage form development. Improved understanding of the principle involved and development of automated hardware and reliable software have led to increased instrumental sensitivity and improved data analysis. These advances continue to expand the applications of powder X-ray diffraction to emerging research fields such as amorphous systems, mechanistic understanding of phase transformations, and "Quality by Design" in formulation development.

New Polymorph Form of Dexamethasone Acetate

A new monohydrated polymorph of dexamethasone acetate was crystallized and its crystal structure characterized. The different analytical techniques used for describing its structural and vibrational properties were: single crystal and polycrystal X-ray diffraction, solid state nuclear magnetic resonance, infrared spectroscopy. A Hirshfeld surface analysis was carried out through self-arrangement cemented by H-bonds observed in this new polymorph. This new polymorph form appeared because of self-arrangement via classical hydrogen bonds around the water molecule.

Stable Co-crystals of Glipizide with Enhanced Dissolution Profiles: Preparation and Characterization

Present study deciphers preparation of co-crystals of lipophilic glipizide by using four different acids, oxalic, malonic, stearic, and benzoic acids, in order to achieve enhanced solubility and dissolution along with stability. All co-crystals were prepared by dissolving drug and individual acids in the ratio of 1:0.5 in acetonitrile at 60-70°C for 15 min, followed by cooling at room temperature for 24 h. FT-IR spectroscopy revealed no molecular interaction between acids and drug as the internal structure and their geometric configurations remain unchanged. Differential scanning calorimetry revealed closer melting points of raw glipizide and its co-crystals, which speculates absence of difference in crystallinity as well as intermolecular bonding of the co-crystals and drug. PXRD further revealed that all the co-crystals were having similar crystallinity as that of raw glipizide except glipizide-malonic acid co-crystals. This minor difference in the relative intensities of some of the diffraction peaks could be attributed to the crystal habit or crystal size modification. SEM revealed difference in the crystal morphology for all the co-crystals. Micromeritic, solubility, dissolution, and stability data revealed that among all the prepared co-crystals, glipizide-stearic acid co-crystals were found superior. Hence, it was concluded that glipizide-stearic acid co-crystals could offer an improved drug design strategy to overcome dissolution and bioavailability related challenges associated with lipophilic glipizide.

Recent progress of structural study of polymorphic pharmaceutical drugs

This review considers advances in the understanding of active pharmaceutical ingredient polymorphism since around 2010 mainly from a structural view point, with a focus on twelve model drugs. New polymorphs of most of these drugs have been identified despite that the polymorphism of these old drugs has been extensively studied so far. In addition to the conventional modifications of preparative solvents, temperatures, and pressure, more strategic structure-based methods have successfully yielded new polymorphs. The development of analytical techniques, including X-ray analyses, spectroscopy, and microscopy has facilitated the identification of unknown crystal structures and also the discovery of new polymorphs. Computational simulations have played an important role in explaining and predicting the stability order of polymorphs. Furthermore, these make significant contributions to the design of new polymorphs by considering structure and energy. The new technologies and insights discussed in this review will contribute to the control of polymorphic forms, both during manufacture and in the drug formulation.

Conformations of benzene-based tripodal isatin-bearing compounds in the crystalline state

Studies of molecular conformations, examples of polymorphic forms, new solvates and analysis of supramolecular motifs giving interesting insights into molecular recognition phenomena are reported.

Pharmaceutical Cocrystals: Regulatory and Strategic Aspects, Design and Development

Cocrystal is a concept of the supramolecular chemistry which is gaining the extensive interest of researchers from pharmaceutical and chemical sciences and of drug regulatory agencies. The prominent reason of which is its ability to modify physicochemical properties of active pharmaceutical ingredients. During the development of the pharmaceutical product, formulators have to optimize the physicochemical properties of active pharmaceutical ingredients. Pharmaceutical cocrystals can be employed to improve vital physicochemical characteristics of a drug, including solubility, dissolution, bioavailability and stability of pharmaceutical compounds while maintaining its therapeutic activity. It is advantageous being a green synthesis approach for production of pharmaceutical compounds. The formation polymorphic forms, solvates, hydrates and salts of cocrystals during the synthesis reported in the literature which can be a potential issue in the development of pharmaceutical cocrystals. The approaches like hydrogen bonding rules, solubility parameters, screening through the CSD database or thermodynamic characteristics can be utilized for the rational design of cocrystals and selection of coformers for synthesis multi-component cocrystals. Considering the significance of pharmaceutical cocrystals pharmaceutical regulatory authorities in the United States and Europe issued guidance documents which may be helpful for pharmaceutical product registration in these regions. In this article, we deal with the design, synthesis, strategic aspects and characteristics of cocrystals along perspectives on its regulatory and intellectual property considerations.

An unusual density evolution between SrCdB2O5 polymorphs

Owing to the effect of atomic vibrations, a high-temperature phase usually features a relatively smaller density when compared with a low-temperature phase. In this work, a new SrCdB2O5 phase has been discovered. According to the crystallization temperature from low to high, the new SrCdB2O5 phase can be regarded as the high-temperature β-SrCdB2O5 phase. The density of β-SrCdB2O5 is obviously larger than that of α-SrCdB2O5, meanwhile β-SrCdB2O5 is energetically favored. This unusual density evolution phenomenon has been investigated. In addition, the Pb(2+)-doped compounds, PbxSr1-xCdB2O5 (x = 0.125, 0.25, 0.375, 0.5), have also been investigated by powder refinement.

Gelation or crystallization? Subtle balance of structural factors for assembly of DBA derivatives with methyl esters

The aggregation of a series of strained dehydrobenzoannulene derivatives with methyl ester groups is revealed.

Polymorphism and solid-to-solid phase transitions of a simple organic molecule, 3-chloroisonicotinic acid

Three polymorphs have been discovered for 3-chloroisonicotinic acid. Its thermal properties appear to be eventful, including sublimation, melting and recrystallization, and solid-to-solid phase transition. The polymorphism seemingly results from the disruption of molecular symmetry by chlorine substitution.

Multiple optical properties of a naphthoquinone pigment: 2-methyl-3-(hydroxyphenylthio)-1,4-naphthalenedione

Naphthoquinone pigments 2-methyl-3-(4- or 2-hydroxyphenylthio)-1,4-naphthalenedione show characteristic optical properties in solution and in the solid state. The position of the OH group in the pigment leads to varied optical properties, including a characteristic colour, in the solid state. The pigment with a 2-OH substituent displays solvatochromism in solution, and that with a 4-OH substituent displays optical chirality in the solid state.

Studies on solvatomorphism of betulinic acid

Five solvates of betulinic acid with dimethyl sulfoxide (I), methanol (II), ethanol (III), isopropyl alcohol (IV), and 2-butanol (V) have been described in this work. Methods of X-ray crystallography, thermal analysis, and Fourier transform infrared spectroscopy were introduced for solvatomorphic identifications and characterizations. The orientation of isopropenyl and carboxylic groups might differ because of single-bonding rotations. The incorporation of solvents resulted in changes of the crystal symmetry, intermolecular arrangements, stoichiometry, hydrogen bonding interactions, and so on. Adducted solvents contributed most to the stability of crystal lattices and led to the formation of crystalline forms. Solvates II-V with their single-crystal structures determined have been reported for the first time.

A new polymorph of Cd3B2O6: synthesis, crystal structure and phase transformation

A new high-temperature phase of Cd₃B₂O₆ (β-Cd₃B₂O₆) has been discovered and the phase transformation process between α- and β-Cd₃B₂O₆ was investigated.

Pharmaceutical cocrystals: the coming wave of new drug substances

Solid crystalline phases containing two cocrystallized components offer a new development pathway whereby one can potentially improve the physical characteristics (i.e., equilibrium solubility, dissolution rate, solid-state stability, etc.) of a drug substance that exhibits a profile that is less than desirable. In this commentary, the topic of pharmaceutical cocrystals will be briefly explored, and a short exposition of the solubility and dissolution rate advantages that have been realized in various systems will be provided. The Guidance for Industry document recently proposed by United States Food and Drug Administration will be outlined, and its requirements explained. Finally, the subset of pharmaceutical cocrystals that consist of a drug substance and a salt of that substance (termed a salt cocrystal) will be examined to illustrate this additional class of pharmaceutical cocrystals that may offer significant scientific and regulatory advantages.

Quantifying Solid-State Mixtures of Crystalline Indomethacin by Raman Spectroscopy Comparison with Thermal Analysis

This paper investigates Raman spectroscopy as a quick and reliable method to quantify the alpha (α) and gamma (γ) polymorphic forms of indomethacin compared to differential scanning calorimetry (DSC). Binary mixtures with different ratios of α and γ indomethacin were prepared and analyzed by Raman and DSC. The Raman method was found to be more reliable and superior compared to DSC. The partial conversion of the alpha to gamma polymorphic form during the DSC measurement was the major limitation for the use of full DSC as a quantitative method and resulted in difference between the calculated and measured enthalpy of both polymorphic forms.

Supramolecular stores of acetic acid--an alternative for metal-organic frameworks

A series of new complexes: [M(quin-2-c)(2)(H(2)O)(2)]x 4CH(3)COOH (M=Mn(2+), Co(2+) or Ni(2+), quin-2-c is quinoline-2-carboxylate ion) have been synthesized and characterized by X-ray single crystal study. The crystals of the complexes reveal very interesting 1D structures comprising acetic acid molecules. The processes of re- and desolvation of acetic acid by the manganese complex in mild conditions have been studied. The de- and resolvated materials were characterized by elemental analysis, IR spectroscopy and XRD study. The results show that binding of acetic acid is reversible and stoichiometric.

Characterization of solvatomorphs of methotrexate using thermoanalytical and other techniques

Identification and characterization of different forms of methotrexate were carried out by crystallization from different solvents. Five different forms of the drug were obtained. Appearance of a desolvation endotherm in the DSC accompanied by mass loss in TGA for forms I, II, IV and V showed these forms to be acetonitrile solvate hydrate (form I), trihydrate (forms II and IV) and dimethylformamide solvate (form V), respectively. However, the desolvation peak was absent in form III (obtained from methanol) indicating the absence of any solvent of crystallization. This form was found to be partially crystalline by its XRPD pattern. Solution calorimetry was further used to differentiate between the forms as they differ in lattice energy, resulting in different enthalpies of solution. The dissolution and solubility profiles were correlated with the enthalpy of solution and subsequently with crystallinity of all the forms; the least endothermic form (form III) had the highest dissolution rate.

Tracing coffee tabletop traces

Crystallization processes under different conditions are of fundamental interest in chemistry, pharmacy, and medicine. Therefore, we have studied the formation of micro- and nanosized crystals using water-caffeine (1,3,7-trimethyl-1 H-purine-2,6(3 H,7 H)-dione) solutions under ambient conditions as a relevant model system. When droplets of an aqueous caffeine solution evaporate and eventually dry on surfaces (glass, polystyrene, and polyester), stable "coffee tabletop" rings with a perimeter of typically 3 mm are formed after 20 to 50 min. Using a micro focus X-ray beam available at the BESSY muSpot-beamline, the fine structure of different caffeine needles can be distinguished. Unexpectedly, both crystal modifications (alpha- and beta-caffeine) are present, but locally separated in these rings. Furthermore, AFM studies reveal the presence of even smaller particles on a nanometer length scale. To eliminate influences of surface irregularities from the crystallization process, acoustic levitation of liquid samples was employed. Such levitated droplets are trapped in a stable position and only surrounded by air. The solvent in an ultrasonically levitated drop evaporates completely, and the resulting crystallization of caffeine was followed in situ by synchrotron X-ray diffraction. In this case, the diffraction pattern is in accordance with pure alpha-caffeine and does not indicate the formation of the room temperature polymorph beta-caffeine. Hence, our investigations open new vistas that may lead to a controlled formation of cocrystals and novel polymorphs of micro- and nanocrystalline materials, which are of relevance for fundamental studies as well as for pharmaceutical and medical applications.