Investigation into polymorphism within ethenzamide-ethylmalonic acid cocrystal using Raman and terahertz vibrational spectroscopy

Two cocrystal polymorphs of ethenzamide (ETZ) and ethylmalonic acid (EMA) were synthesized by solvent evaporation. Crystal structure analysis revealed that the main amide - carboxyl heterosynthon in ETZ-EMA cocrystal Form I and Form II are the same, but the crystal structure of these two polymorphs are different. Terahertz (THz) and Raman vibrational spectroscopy were used to characterize ETZ, EMA, ETZ-EMA cocrystal polymorph Form I and Form II respectively. The experimental results showed that ETZ, EMA, ETZ-EMA cocrystal Form I and ETZ-EMA cocrystal Form II exhibited completely different characteristic peaks. Both THz and Raman vibrational spectroscopy can be used to distinguish ETZ-EMA cocrystal Form I from Form II. Furthermore, the investigation of phase transition induced by temperature and solid-state grinding was also performed. In the temperature phase transition experiments, when the powder sample was heated to a temperature range of 80-82 °C, the metastable ETZ-EMA cocrystal Form I transformed into the more stable ETZ-EMA cocrystal Form II. Solid-state grinding analysis revealed that the results of the ETZ-EMA cocrystal polymorph synthesis in grinding experiments depended on the polarity of the solvents used. Grinding without solvent or with high polarity solvents tended to result in the stable ETZ-EMA cocrystal Form II. Moreover, the metastable ETZ-EMA cocrystal Form I would transform into Form II after further grinding process. These results demonstrate that THz and Raman vibrational spectroscopy have high sensitivity and accuracy in the detection of both cocrystal synthesis and cocrystal polymorph phase transitions.

Vibrational spectroscopic detection and analysis of isoniazid-nicotinamide-succinic acid ternary cocrystal

In this paper, binary and ternary cocrystals in the ternary cocrystal system of isoniazid-nicotinamide-succinic acid were prepared by solvent evaporation and grinding methods. All of them were characterized by terahertz time-domain spectroscopy (THz-TDS), confirming that the cocrystals could be obtained by the above two methods. In addition, to investigate the formation of hydrogen bonds and their influence in cocrystal, several possible forms of hydrogen bond in cocrystal were simulated by density functional theory (DFT). The simulated result was in good agreement with the experimental result, indicating that the hydrogen bonds in cocrystal were the carboxyl groups on both side of succinic acid forming a pyridine N-carboxylic acid heterosynthon with pyridine N of isoniazid or nicotinamide respectively. Meanwhile, the vibrational modes of the cocrystal were analyzed to investigate the effect of hydrogen bond to the molecules. To further understand the formation process of ternary cocrystal in this system, Raman spectroscopy was used to analyze the cocrystal samples with different time of grinding. Process information of cocrystal formation were obtained by analyzing the changes of the characteristic peaks in the corresponding Raman spectra. These results provide a wealth of information and a unique approach to the analysis of both structures and intermolecular interactions shown within ternary cocrystal.

New Emerging Inorganic–Organic Systems for Drug-Delivery: Hydroxyapatite@Furosemide Hybrids

In the pharmaceutical market, the need to find effective systems for the efficient release of poorly bioavailable drugs is a forefront topic. The inorganic–organic hybrid materials have been recognized as one of the most promising systems. In this paper, we developed new Hydroxypapatite@Furosemide hybrids with improved dissolution rates in different media with respect to the drug alone. The hybrids formation was demonstrated by SEM/EDS measurements (showing homogeneous distribution of the elements) and FT-IR spectroscopy. The drug was adsorbed onto hydroxyapatite surfaces in amorphous form, as demonstrated by XRPD and its thermal stability was improved due to the absence, in the hybrids, of melting and decomposition peaks typical of the drug. The Sr substitution on Ca sites in hydroxyapatite allows increasing the surface area and pore volume, foreseeing a high capacity of drug loading. The dissolution tests of the hybrid compounds show dissolution rates much faster than the drug alone in different fluids, and also their solubility and wetting ability is improved in comparison to furosemide alone.

A toolbox for improving the workflow of NMR crystallography

NMR crystallography is a powerful tool with applications in structural characterization and crystal structure verification, to name two. However, applying this tool presents several challenges, especially for industrial users, in terms of consistency, workflow, time consumption, and the requirement for a high level of understanding of experimental solid-state NMR and GIPAW-DFT calculations. Here, we have developed a series of fully parameterized scripts for use in Materials Studio and TopSpin, based on the .magres file format, with a focus on organic molecules (e.g. pharmaceuticals), improving efficiency, robustness, and workflow. We separate these tools into three major categories: performing the DFT calculations, extracting & visualizing the results, and crystallographic modelling. These scripts will rapidly submit fully parameterized CASTEP jobs, extract data from the calculations, assist in visualizing the results, and expedite the process of structural modelling. Accompanied with these tools is a description on their functionality, documentation on how to get started and use the scripts, and links to video tutorials for guiding new users. Through the use of these tools, we hope to facilitate NMR crystallography and to harmonize the process across users.

Vibrational spectral and structural characterization of multicomponent ternary co-crystal formation within acetazolamide, nicotinamide and 2-pyridone

Ternary co-crystal, as a novel co-crystal design strategy developed on the basis of binary co-crystal, could be used to improve the physicochemical properties of active pharmaceutical ingredients (APIs) efficiently. However, it is difficult to obtain specific ternary co-crystals since such ternary one involves complex assembly of three different molecules. There are few reports on the micro-molecular structure respect of specific ternary co-crystal systems. In present work, 1:1:1 ternary co-crystal between acetazolamide (ACZ), nicotinamide (NAM) and 2-pyridone (2HP) has been synthesized successfully by mechanical grinding approach, and their structures are investigated by terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy combined with theoretical calculation at the molecular level. The experimental THz spectral results showed that ACZ-NAM-2HP ternary co-crystal and the starting parent materials exhibited a few distinct spectral features in frequency-domain absorption spectra. Likewise, the Raman spectral result also shows some difference between the co-crystal and starting raw materials. Through density functional theory (DFT) calculations, the theoretical THz/Raman spectra and vibrational modes of two kind of possible ternary co-crystal theoretical forms (form I and II) between ACZ, NAM and 2HP were obtained. By comparing experimental and theoretical spectral results, the most suitable structure and vibrational modes of ACZ-NAM-2HP ternary co-crystal were determined. These results provide a wealth of information and unique method for studying molecular assembly and also inter-molecular interactions in specific ternary co-crystals at the molecular level in the emerging pharmaceutical co-crystal fields.

Enhancing the solubility and permeability of the diuretic drug furosemide via multicomponent crystal forms

Furosemide (FSM) is a biopharmaceutical classification system (BCS) class IV drug, being a potent loop diuretic used in the treatment of congestive heart failure and edema. Due to its low solubility and permeability, FSM is known for exhibiting poor oral bioavailability. In order to overcome or even minimize these undesirable biopharmaceutical attributes, in this work we have focused on the development of more soluble and permeable multicomponent solid forms of FSM. Using solvent evaporation as crystallization method, a salt and a cocrystal of FSM with imidazole (IMI) and 5-fluorocytosine (5FC) coformers, named FSM-IMI and FSM-5FC, respectively, were successfully prepared. A detailed structural study of these new solid forms was conducted using single and powder X-ray diffraction (SCXRD, PXRD), Fourier Transform Infrared (FT-IR) and proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy and thermal analysis (thermogravimetry, differential scanning calorimetry and hot-stage microscopy). Both FSM-IMI and FSM-5FC showed substantial enhancements in the solubility (up 118-fold), intrinsic dissolution (from 1.3 to 2.6-fold) and permeability (from 2.1 to 2.8-fold), when compared to the pure FSM. These results demonstrate the potential of these new solid forms to increase the limited bioavailability of FSM.

Vibrational Spectroscopic Investigation into Novel Ternary Eutectic Formed between Pyrazinamide, Fumaric Acid, and Isoniazid

To improve the efficacy of anti-tuberculosis (anti-TB) therapy, drug-drug co-crystallization stands for an alternative approach to settle the tuberculosis problem. Directly co-crystallizing two typical parent anti-TB drugs (pyrazinamide, PZA and isoniazid, INH) into a single binary co-crystal could not be obtained successfully. Multicomponent eutectic are highly effective and useful for enhancing the dissolution rate, bioavailability, and physical stability of the poorly water-soluble active pharmaceutical ingredient (API) drugs, when the attempts of forming a binary co-crystal have failed. Therefore, the ternary eutectic composition conception was proposed in this study, in which fumaric acid (FA) was chosen as the molecule to connect two first-line anti-tubercular drugs. First of all, three starting materials (including PZA, INH, and FA) were grinded at a 1:1:1 molar ratio, the eutectic composition was investigated through vibrational spectroscopic techniques, including terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy. Additionally, the density functional theory (DFT) was utilized to simulate the optimized structures and vibrational modes of two possible theoretical eutectic composition forms. The THz absorption spectrum of the theoretical form I shows much more consistency with the experimental results than that of form II. Raman spectra also help to characterize the differences in vibrational modes between the eutectic composition and the starting parent compounds. The results provide us with both structural information and intermolecular hydrogen bonding interactions within specific multicomponent eutectic composition formulations based on Raman and terahertz vibrational spectroscopic techniques in combination with theoretical calculations.

Acid-ammonium heterodimer and N(ammonium)-H...N(pyridine) synthon preference in three salts of nicotinic acid with (1R,2R)-1,2-diphenylethylenediamine

Nicotinic acid (NA), known as vitamin B3, has been widely studied in pharmaceutical science. Herein, three salts derived from NA and (1R,2R)-1,2-diphenylethylenediamine (DPEN), including one solvent-free salt (DPEN)(NA)₂ and two solvated salts, (DPEN)(NA)₂(EA) and (DPEN)(NA)₂(ACN) (EA: ethyl acetate, ACN: acetonitrile), have been obtained and characterized by solid-state techniques. By the investigation of single-crystal structures, the synthons, acid-ammonium heterodimer and N_ammonium-H...N_pyridine between functional groups of 1,2-diphenylethylenediammonium and NA are revealed and further identified using Hirshfeld surface analysis. The utility of the synthons is further demonstrated by making salts with the NA isomer, isonicotinic acid. Here the synthon occurrences in cocrystals/salts of NA (including NA derivatives) and diamine coformers reported in the Cambridge Structure Database (CSD) are compared. The robustness of acid-ammonium heterodimer and N_ammonium-H...N_pyridine is investigated by a search of the CSD. The NA salts also show their improved solubility in pH 1.2, 4.5 and 6.8 buffer mediums compared with pure NA material.

Co-crystal synthesis: fact, fancy, and great expectations

Some strategies for driving co-crystal synthesis using a variety of competing non-covalent interactions are presented.

A new solvate of furosemide with dimethylacetamide

The loop diuretic furosemide is used widely in the treatment of congestive heart failure and edema, and is practically insoluble in water. The physicochemical and pharmacokinetic properties of drugs can be modified by preparing the drug in an appropriate solid-state form. A new solvate of furosemide with dimethylacetamide (DMA) {systematic name: 4-chloro-2-[(furan-2-yl)methylamino]-5-sulfamoylbenzoic acid N,N-dimethylacetamide disolvate}, C₁₂H₁₁ClN₂O₅S·2C₄H₉NO, (I), is reported. The channeled structure formed on slow crystallization contains DMA solvent molecules in its channels. This structure adds to the evidence of varied conformations observed across all known structures, so supporting the idea that this flexible molecule has conformational lability. The current structure also differs from those of other previously known furosemide solvates in the number of solvent molecules per furosemide molecule, viz. 2:1 instead of 1:1. Desolvation of (I) gives the most stable form of furosemide, i.e. Form I.

A furosemide–isonicotinamide cocrystal: an investigation of properties and extensive structural disorder

Multi-nuclear variable temperature solid state NMR, supported by DFT calculations, elucidates the nature of structural disorder in furosemide–isonicotinamide cocrystals.