Identification and quantification techniques of polymorphic forms - A review

In the pharmaceutical industry, the unexpected appearance of crystalline forms could impact the therapeutic efficacy of an Active Pharmaceutical Ingredient (API). For quality control, a thorough qualitative and quantitative monitoring of pharmaceutical solid forms is essential to ensure the detection and the quantification of crystalline forms, wither different or with the same chemical composition (polymorphs) at a low detection level. The purpose of this paper was to review and highlight the importance of choosing adequate solid-state techniques for detection and quantification APIs that present polymorphism - based on limits of detection (LOD) and quantification (LOQ), pharmacopeias specifications, international guidelines and studies reported in the literature. To this study, the powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), Infrared and Raman spectroscopies and solid-state nuclear magnetic resonance (NMR) were the solid-state techniques analyzed. Additionally, the Argentine, Brazilian, British, European, International, Japanese, Mexican and the United States of America pharmacopeias were reviewed. Based on the analysis performed, the advantages and disadvantages of these techniques, as well as the LOD and LOQ values of APIs were reported. In comparison to these solid-state techniques, reference material used for identification analyses should be previously identified with the corresponding polymorph. Without this previous procedure, the patterns, the spectra, and DSC curves of the reference material can only be used to confirm the mixture of solid forms, not being able to specify which polymorphs are contained in the sample. A major advantage of PXRD is the use of the calculated diffraction patterns obtained from the Crystallographic Information Frameworks (CIFs) files which could be used as a reference pattern without any other information, assistance technique, or physical standards. Regarding the quantification aspect, different pharmacopeias suggest various methods such as the PXRD combining with Rietveld method, which can be used to obtain lower LOD values for minority phases in the mixture of different substances without the need for a calibration curve. Raman spectroscopy can detect polymorphs in small particles and solid-state NMR spectroscopy is a powerful technique for quantification not only crystalline but also crystalline-amorphous mixtures. Finally, this review intends to be a useful tool to control, with efficiency and accuracy, the polymorphism of APIs in pharmaceutical compounds.

Unraveling Polymorphism Dependent Cytotoxicity, Cellular Uptake, and Live Cell Imaging Using Luminescent Polymorphs

Polymorphism-dependent cytotoxicity and cellular uptake of drug molecules have been studied for the past two decades. However, visualizing the polymorph-dependent cellular uptake and cytotoxicity using microscopy imaging technique has not been reported yet. The luminescent polymorph is an ideal candidate to validate the above hypothesis. Herein, we report the polymorph-dependent cellular uptake, cytotoxicity, and bio-imaging functions of polymorphs 1Y and 1R of a naphthalimide-phenothiazine dyad. These polymorphs show different luminescence colors in the solid state and exhibit aggregation-induced enhanced emission (AIEE) in the DMSO-Water mixture. Bioimaging, cytotoxicity assay, and fluorescence-activated cell sorting (FACS) studies revealed that these polymorphs show different levels of cytotoxicity, cellular uptake, localization, and imaging potential. Detailed photophysical, morphological, and biological studies revealed that the difference in molecular conformation in these polymorphs enables them to form aggregates of different sizes and morphology, which leads to the differential uptake of these into the cells and consequently shows different cytotoxicity and imaging potentials.

Pressure-Modulated Structural and Magnetic Phase Transitions in Two-Dimensional FeTe: Tetragonal and Hexagonal Polymorphs

Two-dimensional (2D) Fe chalcogenides with their rich structures and properties are highly desirable for revealing the torturous transition mechanism of Fe chalcogenides and exploring their potential applications in spintronics and nanoelectronics. Hydrostatic pressure can effectively stimulate phase transitions between various ordered states, allowing one to successfully plot a phase diagram for a given material. Herein, the structural evolution and transport characteristics of 2D FeTe were systematically investigated under extreme conditions by comparing two distinct symmetries, i.e., tetragonal (t) and hexagonal (h) FeTe. We found that t-FeTe presented a pressure-induced transition from an antiferromagnetic state to a ferromagnetic state at ∼3 GPa, corresponding to the tetragonal collapse of the layered structure. Contrarily, the ferromagnetic order of h-FeTe was retained up to 15 GPa, which was evidently confirmed by electrical transport and Raman measurements. Furthermore, T-P phase diagrams for t-FeTe and h-FeTe were mapped under delicate critical conditions. Our results can provide a unique platform to elaborate the extraordinary properties of Fe chalcogenides and further develop their applications.

Mitochondriotropic agents conjugated with NSAIDs through metal ions against breast cancer cells

Two copper(I) polymorphs of formula [Cu(SALH)(TPP)3] (1a and 1b) were prepared by the conjugation of the Non-Steroidal Anti-Inflammatory Drug (NSAID) salicylic acid (SALH2) with the mitochondriotropic agent triphenylphosphine (TPP) via metal ion. For comparison, the isomorph [Ag(SALH)(TPP)3] (2) was prepared. The conjugates 1a, 1b and 2 were characterized by melting point (m.p.), Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, Ultraviolet-Visible (UV-Vis) spectroscopy and nuclear magnetic resonance (1H NMR). The crystal structures of 1a, 1b and 2 were confirmed by X-ray diffraction crystallography (XRD). The ex vivo binding affinity of 1-2 towards CT (calf thymus)-DNA was studied by UV, fluorescence, viscosity and DNA Thermal Denaturation studies. Their inhibitory activity against lipoxygenase (LOX) (an enzyme which is mainly located in the mitochondrion) was determined. The in vitro activity of 1-2 was evaluated against human breast cancer cell lines MCF-7 (hormone depended (HD)) and MDA-MB 281 (hormone independent (HI)) cells. Compounds 1-2 inhibit stronger than cisplatin the cancerous cells. The molecular mechanism of action of 1-2 was suspected by the MCF-7 cells morphology and confirmed by DNA fragmentation, Acridine Orange/Ethidium Bromide (AO/EB) Staining and mitochondrial membrane permeabilization tests.

Amorphization of different furosemide polymorphic forms during ball milling: Tracking solid-to-solid phase transformations

Ball milling is used, not only to reduce the particle size of pharmaceutical powders, but also to induce changes in the physical properties of drugs. In this work we prepared three crystal forms of furosemide (forms Ⅰ, Ⅱ, and Ⅲ) and studied their solid phase transformations during ball milling. Powder X-ray diffraction and modulated differential scanning calorimetry were used to characterize the samples after each milling time on their path to amorphization. Our results show that forms Ⅰ and III directly converted into an amorphous phase, while form Ⅱ first undergoes a polymorphic transition to form Ⅰ, and then gradually loses its crystallinity, finally reaching full amorphousness. During ball milling of forms Ⅰ and Ⅱ, the glass transition temperature (Tg) of the amorphous fraction of the milled material remains almost unchanged at 75 °C and 74 °C, respectively (whilst the amorphous content increases). In contrast, the Tg values of the amorphous fraction of milled form III increase with increasing milling times, from 63 °C to 71 °C, indicating an unexpected phenomenon of amorphous-to-amorphous transformation. The amorphous fraction of milled forms I and II samples presented a longer structural relaxation (i.e., lower molecular mobility) than the amorphous fraction of milled form III samples. Moreover, the structural relaxation time remained the same for the increasing amorphous fraction during milling of forms I and II. In contrast, the structural relaxation times were always shorter for the amorphous fraction of form III, but increased with increasing amorphous content during milling, confirming amorphous-to-amorphous transformation.

Raman spectra and vibrational properties of FOX-7 under pressure and temperature: First-principles calculations

FOX-7 (1,1-diamino-2,2-dinitroethene) as one of the widely studied insensitive high explosives exists five polymorphs (α, β, γ, α', ε) whose crystal structures have been determined by XRD (X-rays Diffraction) and which are investigated by a density functional theory (DFT) approach in this work. The calculation results show that the GGA PBE-D2 method can reproduce the experimental crystal structure of FOX-7 polymorphs better. The calculated Raman spectra of FOX-7 polymorphs were compared in detail and fully with the experimental Raman spectra data and it was found that the calculated Raman spectra frequencies have an overall red-shift in middle band (800-1700 cm^-1), and that the maximum deviation does not exceed 4 % (The maximum point is the mode of CC in plane bending). The high-temperature phase transform path (α → β → γ) and the high-pressure phase transform path (α → α'→ε) can be well represented in the computational Raman spectra. In addition, crystal structure of ε-FOX-7 was performed up to 70 GPa to probe Raman spectra and vibrational properties. The results showed that the NH₂ Raman shift is jittering with pressure (not smooth compared to other vibrational modes) and NH₂ anti-symmetry-stretching appears red-shifted. The vibration of hydrogen mixes in all of other vibrational modes. This work shows that the dispersion-corrected GGA PBE method can reproduce the experimental structure, vibrational properties and Raman spectra very well.

Synthesis and Characterization of the Orthorhombic Sn3 O4 Polymorph

An unexplored tin oxide crystal phase (Sn₃ O₄ ) was experimentally synthesized via a facile hydrothermal method. After tuning the often-neglected parameters for the hydrothermal synthesis, namely the degree of filling of the precursor solution and the gas composition in the reactor head space, an unreported X-ray diffraction pattern was discovered. Through various characterization studies, such as Rietveld analysis, energy dispersive X-ray spectroscopy, and first-principles calculations, this novel material was characterized as orthorhombic mixed-valence tin oxide with the composition Sn^II ₂ Sn^IV O₄ . This orthorhombic tin oxide is a new polymorph of Sn₃ O₄ , which differs from the reported conventional monoclinic structure. Computational and experimental analyses showed that orthorhombic Sn₃ O₄ has a smaller band gap (2.0 eV), enabling greater absorption of visible light. This study is expected to improve the accuracy of hydrothermal synthesis and aid the discovery of new oxide materials.

Leveraging Crystalline and Amorphous States of a Metal-Organic Complex for Transformation of the Photosalient Effect and Positive-Negative Photochromism

Uncovering differences between crystalline and amorphous states in molecular solids would both promote the understanding of their structure-property relationships, as well as inform development of multi-functional materials based on the same compound. Herein, for the first time, we report an approach to leverage crystalline and amorphous states of a zero-dimensional metal-organic complex, which exhibited negative and positive photochromism, due to the competitive chemical routes between photocycloaddition and photogenerated radicals. Furthermore, different polymorphs lead to the on/off toggling of photo-burst movement (photosalient effect), indicating the controllable light-mechanical conversion. Three demos were further constructed to support their application in information encryption and anti-counterfeiting. This work provides the proof-of-concept of a state- and polymorph-dependent photochemical route, paving an effective way for the design of new dynamically responsive systems.

V and Cr substitution in dicalcium silicate under oxidizing and reducing conditions - Synthesis, reactivity, and leaching behavior studies

Dicalcium silicate (C₂S) is known to incorporate potentially hazardous metals (Cr and V) in a belite-rich cementitious system. The effect of the electrovalence nature of V and Cr on C₂S polymorphs' (α´, β, γ) stability under oxidizing and reducing conditions as well as their reactivity are systematically investigated via analyzing oxidation states, phase composition, bonding system, and microstructure as well as oxide composition quantitively. It is shown that C₂S can incorporate Cr (VI) and V(V) consequently leading to stabilization of α´, β-C₂S. Instead, Cr (II, III) and V < (V) tend not to substitute in C₂S. Despite reactive polymorphs (α´, β-C₂S) stability due to Cr (VI) and V(V) incorporation, the early age (48-72 h) C₂S reactivity is drastically reduced due to Cr (VI) and V (V) incorporation. Moreover, one batch leaching test revealed that the V (V) leaching is inversely proportional to aqueous Ca²⁺ ion at pH > 12 while Cr leaching is sensitive to its oxidation state, and dissolution of C₂S. Even though C₂S can incorporate Cr (VI) and V (V) ions, the final leaching is governed by the immobilization potential of C-S-H gel, pH as well as types of calcium chromate and vanadate complexes.

Baloxavir Marboxil Shows Anomalous Conversion of Crystal Forms from Stable to Metastable through Formation of Specific Solvate Form

Baloxavir marboxil is a novel cap-dependent endonuclease inhibitor of influenza. This study aimed to identify its polymorphs and their relationship with crystal engineering. Polymorph screening by evaporation gave forms I-III and solvate forms IV and V. Heating enabled the conversion of form III to form II, but did not enable that of forms I and II. The solvent-mediated transformation of the forms I-III by magnetic stirring in various solvents resulted in the formation of form I. These results indicate that form I is the stable form. However, all crystal forms transformed to form II after magnetic stirring in a 50% acetonitrile aqueous solution, which was not obtained from water or acetonitrile. The suspension in a 50% acetonitrile aqueous solution exhibited a novel X-ray diffraction pattern as shown in form VI. The measurement of the suspension by solid-state ¹³C-nuclear magnetic resonance revealed that the spectra of forms II and VI were similar. From these results, we conclude that the drug forms a solvate with both water and acetonitrile and spontaneously transforms to form II upon rapid desolvation under ambient conditions. This study elucidates the mechanism of unexpected convergence to a metastable form in a specific solvent and contributes to the crystal engineering of baloxavir marboxil.

Mannitol as an Excipient for Lyophilized Injectable Formulations

The review summarizes the current state of knowledge of mannitol as an excipient in lyophilized injectable small and large molecule formulations. When compared with glycine, the physicochemical properties of mannitol make it a desirable and preferred bulking agent. Though mannitol is a popular bulking agent in freeze-dried formulations, its use may pose certain challenges such as vial breakage or its existence as a metastable crystalline hemihydrate in the final cake, necessitating appropriate mitigation strategies. The understanding of the phase behavior of mannitol in aqueous systems, during the various stages of freeze-drying, can be critical for the optimization of freeze-drying cycle parameters in multi-component formulations. Finally, using a decision tree as a guiding tool, we demonstrate the use of orthogonal techniques for attaining a stable and cost-effective lyophilized drug product containing mannitol.

New salts of teriflunomide (TFM) - Single crystal X-ray and solid state NMR investigation

New salts of teriflunomide TFM (drug approved for Multiple Sclerosis treatment) with inorganic counterions: lithium (TFM_Li), sodium (TFM_Na), potassium (TFM_K), rubidium (TFM_Rb), caesium (TFM_Cs) and ammonium (TFM_NH₄) were prepared and investigated employing solid state NMR Spectroscopy, Powder X-ray Diffraction PXRD and Single Crystal X-ray Diffraction (SC XRD). Crystal and molecular structures of three salts: TFM_Na (CCDC: 2173257), TFM_Cs (CCDC: 2165288) and TFM_NH₄ (CCDC: 2165281) were determined and deposited. Compared to the native TFM, for all crystalline salt structures, a conformational change of the teriflunomide molecule involving about 180-degree rotation of the end group, forming an intramolecular hydrogen bond N-H⋯O is observed. By applying a complementary multi-technique approach, employing 1D and 2D solid state MAS NMR techniques, single and powder X-ray diffraction measurements, as well as the DFT-based GIPAW calculations of NMR chemical shifts for TFM_Na and TFM_Cs allowed to propose structural features of TFM_Li for which it was not possible to obtain adequate material for single crystal X-Ray measurement.

Topochemical Postulates: Are They Relevant for Topochemical Reactions Occurring at Elevated Temperatures?

A rigid inositol-derived monomer functionalized with azide and alkyne as the complementary reactive groups (CRGs) crystallized as three distinct polymorphs I-III. Despite the unsuitable orientation of CRGs in the crystals for complete polymerization, all the three polymorphs underwent regiospecific and quantitative topochemical azide-alkyne cycloaddition (TAAC) polymerization upon heating to yield three different polymorphs of 1,2,3-triazol-1,4-diyl-linked-poly-neo-inositol. The molecules in these polymorphs exploit the weak intermolecular interactions, free space in the crystal lattice, and heat energy for their large and cooperative molecular motion to attain a transient reactive orientation, ultimately leading to the regiospecific TAAC reaction yielding distinct crystalline polymers. This study cautions that the overreliance on topochemical postulates for the prediction of topochemical reactivity at high temperatures could be misleading.

Solubility and thermodynamic analysis of famotidine polymorphs in pure solvents

The present study investigates the solubility of famotidine polymorphs forms A and B between 298.15 K and 348.15 K in a range of pure solvents: water, methanol, ethanol, isopropanol and acetonitrile. Empirical and semi-empirical models have been fitted to solubility data determined experimentally by a gravimetric method. The solid phases have been characterized by FTIR and Raman spectroscopy, SEM and PXRD. In addition, heat capacities and melting data determined by DSC have been used to estimate the fusion thermodynamics and the activity of the solid phases as a function of temperature. The relationship between the famotidine polymorphs is monotropic, with form A being the stable polymorph. For both polymorphs, in terms of mass ratio, the solubility in the studied solvents decreases in the order methanol > water > ethanol > acetonitrile > isopropanol. The activity coefficient at saturation in all the solutions exceeds unity, showing a positive deviation with respect to ideality, which translates into solubilities significantly lower than the ideal values. Among the alcohols, a consistent correlation is observed between the polarity and the order of solubility.The Hildebrand solubility parameter is also well correlated with the order of solubilities in the studied solvents, with a higher solubility in more polar solvents, revealing the importance of the hydrogen bonding of the sulfamoyl group oxygens.

Discrimination of ranitidine hydrochloride crystals using X-ray micro-computed tomography for the evaluation of three-dimensional spatial distribution in solid dosage forms

A non-destructive discrimination method for crystals in solid dosage drug forms was first developed using a combination of Raman spectroscopy and X-ray micro-computed tomography (X-ray CT). Identification of the crystal form of an active pharmaceutical ingredient (API) at the appropriate pharmaceutical dosage is crucial, as the crystal form is a determinant of the quality and performance of the final formulation. To develop a non-destructive analytical methodology for the discrimination of solid API crystals in a solid dosage form, we utilized a combination of Raman spectroscopy and X-ray CT to differentiate between ranitidine crystal polymorphs (forms 1 and 2) in tablet formulations containing three excipients. The difference in electron density correlated with the true density between ranitidine polymorphs, thereby enabling the discrimination of crystal forms and visualization of their three-dimensional spatial localization inside the tablets through X-ray CT imaging. Furthermore, X-ray CT imaging revealed that the crystal particles were of varying densities, sizes, and shapes within the same batch. These findings suggest that X-ray CT is not only an imaging tool but also a unique method for quantitative physicochemical characterization to study crystal polymorphs and solid dosage forms.

Solid-State Overview of R-Baclofen: Relative Stability of Forms A, B and C and Characterization of a New Heterosolvate

A new polymorphic form (Form C) of enantiopure Baclofen was isolated and characterized. Crystal structures of R-Baclofen Form A and Form C were resolved from powder diffraction data, and cell parameters by profile matching for Form B. The relative stability of these three forms is proposed based on structural data, thermal analyses and solvent-mediated conversions. The experiments highlight the stability order A < C < B at 25 °C (A is the most stable form), whereas above 180 °C it would likely be: C < A < B (C being the stable modification). Moreover, a new heterosolvate of the molecule is observed in N,N-DMF/water mixture. This heterosolvate offers a new pathway to isolate pure R-Baclofen Form B provided the lactam impurity does not exceed 3%. Upon mechanical stress Form B tends to evolve to Form C.

Unveiling meloxicam monohydrate process of dehydration by an at-line vibrational multi-spectroscopy approach

Meloxicam (MLX) is a non-steroidal anti-inflammatory drug, extensively used for inflammatory diseases and pain treatments, which exhibits five known solids forms. Form IV of MLX, a zwitterionic monohydrate (MH), is an emblematic hydrate case with promissory dissolution properties in a poorly soluble drug. However, the lack of information about MH stability regarding the dehydration process and phase transition impedes the development of further stability studies. A multi-spectroscopic/chemometric approach was implemented coupling middle- (MIR), near-infrared (NIR) and Raman spectroscopies to monitor the heat-mediated dehydration process of MH. The application of multivariate curve resolution-alternating least squares (MCR-ALS) to multi-source spectra by data fusion allow a complete view of the phenomena, improving the selectivity and precision to establish the transition temperatures and to identify involved species. It was revealed a two-step mechanism, where MH changes to Form V at 90 °C obtaining its complete dehydration at 130 °C, Form V remains unchanged during the temperature range 130-190 °C and then the polymorphic conversion to Form I starts, which reaches 100 % at 230 °C before melting MLX (248 °C). The findings of this work allow set targets in the process control of products using MH. Additionally, MCR-ALS detected an event not evidenced by conventional thermal analysis, the transformation of Form V to Form I.

Novel green phosphorene as a superior chemical gas sensing material

Green phosphorus and its monolayer variant, green phosphorene (GreenP), are the recent members of two-dimensional (2D) phosphorus polymorphs. The new polymorph possesses the high stability, tunable direct bandgap, exceptional electronic transport, and directionally anisotropic properties. All these unique features could reinforce it the new contender in a variety of electronic, optical, and sensing devices. Herein, we present gas-sensing characteristics of pristine and defected GreenP towards major environmental gases (i. e., NH₃, NO, NO₂, CO, CO₂, and H₂O) using combination of the density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green's function approach (NEGF). The calculated adsorption energies, density of states (DOS), charge transfer, and Crystal Orbital Hamiltonian Population (COHP) reveal that NO, NO₂, CO, CO₂ are adsorbed on GreenP, stronger than both NH₃ and H₂O, which are weakly physisorbed via van der Waals interactions. Furthermore, substitutional doping by sulfur can selectively intensify the adsorption towards crucial NO₂ gas because of the enhanced charge transfer between p orbitals of the dopant and the analyte. The statistical estimation of macroscopic measurable adsorption densities manifests that the significant amount of NO₂ molecules can be practically adsorbed at ambient temperature even at the ultra-low concentration of part per billion (ppb). In addition, the current-voltage (I-V) characteristics of S-doped GreenP exhibit a variation upon NO₂ exposure, indicating the superior sensitivity in sensing devices. Our work sheds light on the promising application of the novel GreenP as promising chemical gas sensors.

Polymorphs and Amorphous State of Glipizide: Preparation and Solid-State Transformations

The solid-state diversity of active pharmaceutical ingredients can provide theoretical guidance for the production and storage of drugs. In this study, three solid forms of glipizide were obtained through various methods, and the solid-state transformations were extensively investigated. Form I could be prepared using evaporative crystallization, cooling crystallization, anti-solvent crystallization, and solvent-mediated slurry conversion experiments (SSCE). Form II was produced by milling. Form III was obtained by milling and SSCE. The results of solid-state transformations indicated that Form I transformed to II during neat milling at 25 °C. In contrast, solvent inhibited the solid-state transformations of Form I under liquid-assisted milling. Forms II and III remained invariable under neat milling at 25 °C, and solid-state transformation of Form III also did not occur in the liquid-assisted milling. In SSCE, the solvent's nature and its temperature significantly influenced the solid-state conversion of amorphous glipizide. Form II converted to either Form I or III in water above 50 °C, and only transformed into Form I at 25 °C. However, the solid-state transformation did not occur when pure Form I or III was stirred in water. Form II also converted to Form I in the organic solvents SSCE at different temperatures.

Polymorphs and pharmacokinetics of an antipsychotic drug candidate

A potent antipsychotic drug candidate, 7-(4-(4-(6-fluorobenzo[d]-isoxazol-3-yl)-piperidin-1-yl)butoxy)-4-methyl-8-chloro -2H-chromen-2-one mesylate(CY611), with good in vitro and in vivo antipsychotic effects was investigated for preformulation evaluation by crystallography methods. Three anhydrous polymorphs(Form I-III), a monohydrate(Form IV), and a NMP solvate(Form V) were discovered and characterized by powder X-ray diffraction, thermal analysis, attenuated total reflection-fourier transform infrared spectroscopy and scanning electron microscopy. Form I, monohydrate Form IV, and a NMP solvate Form V of the drug candidate were isolated, and their structures were determined by single crystal X-ray diffraction. IDR and relative stability experiment were performed. Although Form II has the fastest release rate in water, it easy transformed to monohydrate which has the lowest release rate. In vivo pharmacokinetic study showed that the Form III has the highest bioavailability at 35.4%. Considering the balance between the physicochemical properties, bioavailability and manufacturability of the available polymorphs, Form III may be the optimal form candidate for the eventual formulation.

Polymorphs of DP-VPA Solid Solutions and Their Physicochemical Properties

Different solid forms possess various physicochemical properties, which can significantly affect the stability, bioavailability, and manufacturability of the final product. DP-VPA, a complex of 1-stearoyl-2-valproyl-sn-glycero-3-phosphatidylcholine (DP-VPA-C₁₈) and 1-palmitoyl-2-valproyl-sn-glycero-3-phosphatidylcholine (DP-VPA-C₁₆), is currently under development as an antiepileptic drug. DP-VPA-C₁₆ and DP-VPA-C₁₈ crystallize together in solid solution forms. The solid forms of DP-VPA solid solution were studied herein. Powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), dynamic vapor sorption (DVS) and optical microscopy were used to characterize the different crystalline forms, known as polymorphs. The physicochemical properties, including hygroscopicity, thermodynamic behavior, and relative stability, of each form were investigated. DVS analysis showed that DP-VPA solid solution reduced the hygroscopicity of DP-VPA-C₁₆. The relative humidity stability study revealed that Forms A and B are relatively stable, while Forms A-1, B-1, C and D are highly unstable under natural humidity. Further analysis revealed that Form A transforms into Form B through milling. Given the physicochemical properties of the available physical forms, Form B may be the optimal form for the formulation and development of antiepileptic drugs.

Excited state intramolecular single proton transfer mechanism of pigment yellow 101 in solid state: Experiment and DFT calculation

To investigate fluorescence mechanism of Pigment Yellow 101 (P. Y. 101) in solid state, three aromatic aldehyde azines (1-3) including P. Y. 101 have been synthesized and compared with each other. Results indicated that P. Y. 101 prepared by solvothermal method is actually the mixture of two polymorphs, whose molecular packing mode can be transformed into each other by recrystallizing or external stimuli such as pressure and grinding. The ESIPT properties of 1-3 were investigated by DFT/TD-DFT calculations and time-correlated single photon counting (TCSPC) technique. Both experimental and theoretical results revealed that the dual fluorescence properties of P. Y. 101 in solid state are ascribed to the excited-state intramolecular single proton transfer fluorescence emissions of two structurally different polymorphs rather than the results of the sequential or concerted excited-state intramolecular double proton transfers, which provide a potential valuable tool for developing multistimuli-responsive luminescent materials.

Polymorphs, co-crystal structure and pharmacodynamics study of MBRI-001, a deuterium-substituted plinabulin derivative as a tubulin polymerization inhibitor

MBRI-001, a deuterium-substituted plinabulin derivative, has been reported to have better pharmacokinetic and similar antitumor effects in comparison with plinabulin. In this approach, we further carried out its polymorphs, co-crystal structure of MBRI-001-tubulin and tubulin inhibition study. Among the different polymorphs, Form F (MBRI-001/H₂O) was prepared and evaluated, which had better physical stability and suitable process for scale-up production. Co-crystal structure of MBRI-001-tubulin (PDB:5XI5) was prepared and analyzed. The result of tubulin polymerization assay demonstrated that MBRI-001 could inhibit tubulin polymerization which was similar as plinabulin. Subsequently, the anti-proliferative activities of plinabulin and MBRI-001 were evaluated against two different human lung cancer cell lines. In vivo study, MBRI-001 revealed similar antitumor inhibition in comparison with plinabulin in A549 xenograft tumor model. Therefore, we suggested that MBRI-001 could be developed as a promising anti-cancer agent in near future.

Effect of ultrasonic irradiation on morphology and polymorphic transformation of glycine

The polymorphic phase transformation of β-glycine to α-glycine was analyzed in the absence and presence of three different intensities of ultrasonic irradiation in a batch system at 25 °C. The experiments were performed to explore the effects of ultrasonic irradiation and its intensity on phase transformation time, morphology, storage stability, and filtration characteristics. The crystals obtained with and without ultrasound were characterized by X-ray diffraction (XRD). The XRD results showed that the ultrasound tended to reduce the transformation time. According to the scanning electron microscopy (SEM) images, the ultrasound had a significant effect on the crystal morphology. The highest ultrasound power applied yielded more rounded crystals compared to the crystals prepared in the absence of ultrasound. In addition to SEM analysis, detailed crystal shape analysis was performed and shape factors, namely the circularity, elongation, and convexity values, were determined quantitatively to get more information about the morphological changes related to the variations in the size and shape of the end products. From the morphological point of view, the circularity values of the crystals obtained under ultrasound were higher but the elongation values were smaller compared to the crystals obtained in the absence of ultrasound. It was also found that higher ultrasound decreased the length and width of the crystals, and the application of ultrasound increased the aspect ratio value from 0.483 to 0.657.

Physics, chemistry, and Hirshfeld surface analyses of gamma-irradiated thalidomide to evaluate behavior under sterilization doses

Thalidomide was indicated as a sedative and antiemetic and prescribed for pregnant women. Its tragic teratogenic effects culminated in withdrawal from the market. Since the discovery of its anti-angiogenic and anti-inflammatory actions, thalidomide has been used in the treatment of leprosy and multiple myeloma, which justify studies of its stability. We investigated the effects of irradiation of thalidomide up to 100 kGy (fourfold the usual sterilizing dose for pharmaceutics). The β polymorph of thalidomide was obtained in an isothermal experiment at 270 °C. All samples underwent gamma irradiation for specific times. At different doses, decomposition of the pharmaceutical was not observed up to 100 kGy. The observed effect was angle turning between the phthalimide and glutarimide rings modulated by repulsion towards the carbonyl group, leading to a stable energetic configuration, as measured by the equilibrium in the torsion angle after irradiation. The thalidomide molecule has a center of symmetry, so a full turn starting from 57.3° will lead to an identical molecule. Further irradiation will start the process again. Samples irradiated at 30 and 100 kGy have more compact unit cells and a lower volume, which leads to an increase in the intermolecular hydrogen interaction within the unit cell, resulting in higher thermal stability for polymorph α.

Correlative Raman spectroscopy and focused ion beam for targeted phase boundary analysis of titania polymorphs

Site-specific preparation of specimens using focused ion beam instruments for transmission electron microscopy is at the forefront of targeting regions of interest for nanoscale characterization. Typical methods of pinpointing desired features include electron backscatter diffraction for differentiating crystal structures and energy-dispersive X-Ray spectroscopy for probing compositional variations. Yet there are situations, notably in the titanium dioxide system, where these techniques can fail. Differentiating between the brookite and anatase polymorphs of titania is either excessively laborious or impossible with the aforementioned techniques. However, due to differences in bonding structure, Raman spectroscopy serves as an ideal candidate for polymorph differentiation. In this work, a correlative approach utilizing Raman spectroscopy for targeted focused ion beam specimen preparation was employed. Dark field imaging and diffraction in the transmission electron microscope confirmed the region of interest located via Raman spectroscopy and demonstrated the validity of this new method. Correlative Raman spectroscopy, scanning electron microscopy, and focused ion beam is shown to be a promising new technique for identifying site-specific preparation of nanoscale specimens in cases where conventional approaches do not suffice.

DRIFTS-based multivariate calibration and prediction of low-concentration polymorphic impurities in multiple lots of an active pharmaceutical ingredient, and outlier criteria

Mixtures of two polymorphic impurities with one lot of the desired form of an Active Pharmaceutical Ingredient (API), mostly binary mixtures, with up to 2% wt/wt of an impurity, were used for multivariate modeling via Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectra. The two obtained cross-validated models, significantly differing in accuracy, were used to predict the concentrations of these impurities in independent API lots. The predictions were found to be biased and with outliers, as revealed by the Q residuals criterion but not the other two outlier criteria. Updating the models with the spectra from the mixtures using multiple API lots produced very different calibration results: the model of the impurity with the strong IR response became noticeably worse, while the model of the impurity with less responsive IR signal changed only marginally. The updated models performed much better in the prediction as the bias for both polymorphs was reduced and the outlier-related issues mostly disappeared.

Polymorphic characterization and bioavailability of 20(R)-25-methoxyl-dammarane-3β,12β,20-triol, a novel dammarane triterpenoid saponin, as anticancer agents

This research, for the first time, obtained and reported three novel Form I, Form II, and Form III of 20(R)-25-methoxyl-dammarane-3β,12β,20-triol polymorphs, which were distinguished by PXRD, IR, DSC, and SEM. This study firstly exploited a rapid and feasible UHPLC-ESI-MS/MS method to determine plasma levels of 20(R)-25-OCH3-PPD within 4.5min. The composition of mobile phase was acetonitrile and 5mM ammonium acetate water (85:15, v/v) at a flow rate of 0.2mL/min on the BEH C18 Column (2.1mm×50mm, 1.7μm). The approach enhanced the efficiency of analysis compared to reported methods, making a 3-fold reduction in runtimes. The research exhibited that optimal crystal Form I displays higher bioavailability (P<0.05) compared to the other crystal forms. These findings hold great significance in the early research stages of 20(R)-25-OCH3-PPD polymorphs.

A comprehensive spectroscopic study of the polymorphs of diflunisal and their phase transformations

Understanding phase transitions in pharmaceutical materials is of vital importance for drug manufacturing, processing and storage. In this paper we have carried out comprehensive high-resolution spectroscopic studies on the polymorphs of the non-steroidal anti-inflammatory drug diflunisal that has four known polymorphs, forms I-IV (FI-FIV), three of which have known crystal structures. Phase transformations during milling, heating, melt-quenching and exposure to high relative humidity were investigated using Raman and terahertz spectroscopy in combination with differential scanning calorimetry and X-ray powder diffraction. The observed phase transformations indicate the stability order FIII>FI>FII, FIV. Furthermore, crystallization experiments from the gas phase and from solution by fast evaporation of different solvents were carried out. Fast evaporation of an ethanolic solution below 70°C was identified as a reliable and convenient method to obtain the somewhat elusive FII in bulk quantities.

Pharmaceutical properties of two ethenzamide-gentisic acid cocrystal polymorphs: Drug release profiles, spectroscopic studies and theoretical calculations

The aim of this study was to evaluate the stability and solubility of the polymorphic forms of the ethenzamide (ET) - gentisic acid (GA) cocrystals during standard technological processes leading to tablet formation, such as compression and excipient addition. In this work two polymorphic forms of pharmaceutical cocrystals (ETGA) were characterized by ¹³C and ¹⁵N solid-state nuclear magnetic resonance and Fourier transformed infrared spectroscopy. Spectroscopic studies were supported by gauge including projector augmented wave (GIPAW) calculations of chemical shielding constants.Polymorphs of cocrystals were easily identified and characterized on the basis of solid-state spectroscopic studies. ETGA cocrystals behaviour during direct compressionand tabletting with excipient addition were tested. In order to choose the best tablet composition with suitable properties for the pharmaceutical industry dissolution profile studies of tablets containing polymorphic forms of cocrystals with selected excipients were carried out.

Valsartan

Valsartan is an antihypertensive drug which selectively inhibits angiotensin receptor type II. Generally, valsartan is available as film-coated tablets. This review summarizes thermal analysis, spectroscopy characteristics (UV, IR, MS, and NMR), polymorphism forms, impurities, and related compounds of valsartan. The methods of analysis of valsartan in pharmaceutical dosage forms and in biological fluids using spectrophotometer, CE, TLC, and HPLC methods are discussed in details. Both official and nonofficial methods are described. It is recommended to use LC-MS method for analyzing valsartan in complex matrices such as biological fluids and herbal preparations; in this case, MRM is preferred than SIM method.

Effects of polymorphs on dissolution of cellulose in NaOH/urea aqueous solution

This study focused on the effect of cellulose crystal type on the dissolution of cellulose in aqueous NaOH/urea. Cellulose I, II, IIII, and IVI were prepared and characterized. Subsequently, the solubility of these cellulose samples in aqueous NaOH/urea was tested and the mechanism was determined by a combination of (1)H NMR spectroscopy and differential scanning calorimetry (DSC). The results indicated that, compared with the degree of polymerization (DP) and crystallinity index of cellulose, the cellulose crystal type had greater impact on cellulose dissolution. Specially, the solubility of the cellulose I, II, and III was progressively decreased, probably due to different hydrogen bond network and packing energy in it. The ability of cellulose I, II, III, and IV to form hydrogen bonds with sodium hydroxides was nearly the same, while gradually increased when cellulose preparations were associated with urea. Moreover, all the cellulose solutions showed good thermal stability.

Organic solvent desorption from two tegafur polymorphs

Desorption behavior of 8 different solvents from α and β tegafur (5-fluoro-1-(tetrahydro-2-furyl)uracil) has been studied in this work. Solvent desorption from samples stored at 95% and 50% relative solvent vapor pressure was studied in isothermal conditions at 30 °C. The results of this study demonstrated that: solvent desorption rate did not differ significantly for both phases; solvent desorption in all cases occurred faster from samples with the largest particle size; and solvent desorption in most cases occurred in two steps. Structure differences and their surface properties were not of great importance on the solvent desorption rates because the main factor affecting desorption rate was sample particle size and sample morphology. Inspection of the structure packing showed that solvent desorption rate and amount of solvent adsorbed were mainly affected by surface molecule arrangement and ability to form short contacts between solvent molecule electron donor groups and freely accessible tegafur tetrahydrofuran group hydrogens, as well as between solvents molecule proton donor groups and fluorouracil ring carbonyl and fluoro groups. Solvent desorption rates of acetone, acetonitrile, ethyl acetate and tetrahydrofuran multilayers from α and β tegafur were approximately 30 times higher than those of solvent monolayers. Scanning electron micrographs showed that sample storage in solvent vapor atmosphere promotes small tegafur particles recrystallization to larger particles.