Solid-state NMR in the analysis of drugs and naturally occurring materials

Multiple Natural Polymers in Drug and Gene Delivery Systems

Natural polymers are organic compounds produced by living organisms. In nature, they exist in three main forms, including proteins, polysaccharides, and nucleic acids. In recent years, with the continuous research on drug and gene delivery systems, scholars have found that natural polymers have promising applications in drug and gene delivery systems due to their excellent properties such as biocompatibility, biodegradability, low immunogenicity, and easy modification. However, since the structure, physicochemical properties, pharmacological properties and biological characteristics of biopolymer molecules have not yet been entirely understood, further studies are required before large-scale clinical application. This review focuses on recent advances in the representative natural polymers such as proteins (albumin, collagen, elastin), polysaccharides (chitosan, alginate, cellulose) and nucleic acids. We introduce the characteristics of various types of natural polymers, and further outline the characterization methods and delivery forms of these natural polymers. Finally, we discuss possible challenges for natural polymers in subsequent experimental studies and clinical applications. It provides an important strategy for the clinical application of natural polymers in drug and gene delivery systems.

Exploring the Conformational Equilibrium of Mefenamic Acid Released from Silica Aerogels via NMR Analysis

This study examines the influence of mefenamic acid on the physical and chemical properties of silica aerogels, as well as its effect on the sorption characteristics of the composite material. Solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and high-pressure ¹³C NMR kinetic studies were conducted to identify the presence of mefenamic acid and measure the kinetic rates of CO₂ sorption. Additionally, a high-pressure T₁-T₂ relaxation-relaxation correlation spectroscopy (RRCOSY) study was conducted to estimate the relative amount of mefenamic acid in the aerogel's pores, and a high-pressure nuclear Overhauser effect spectoscopy (NOESY) study was conducted to investigate the conformational preference of mefenamic acid released from the aerogel. The results indicate that mefenamic acid is affected by the chemical environment of the aerogel, altering the ratio of mefenamic acid conformers from 75% to 25% in its absence to 22% to 78% in the presence of aerogel.

Solid-state NMR methods for the characterization of bioconjugations and protein-material interactions

Protein solid-state NMR has evolved dramatically over the last two decades, with the development of new hardware and sample preparation methodologies. This technique is now ripe for complex applications, among which one can count bioconjugation, protein chemistry and functional biomaterials. In this review, we provide our account on this aspect of protein solid-state NMR.

Combining X-ray and NMR Crystallography to Explore the Crystallographic Disorder in Salbutamol Oxalate

Salbutamol is an active pharmaceutical ingredient commonly used to treat respiratory distress and is listed by the World Health Organization as an essential medicine. Here, we establish the crystal structure of its oxalate form, salbutamol oxalate, and explore the nature of its crystallographic disorder by combined X-ray crystallography and ¹³C cross-polarization (CP) magic-angle spinning (MAS) solid-state NMR. The *C-OH chiral center of salbutamol (note that the crystal structures are a racemic mixture of the two enantiomers of salbutamol) is disordered over two positions, and the tert-butyl group is rotating rapidly, as revealed by ¹³C solid-state NMR. The impact of crystallization conditions on the disorder was investigated, finding variations in the occupancy ratio of the *C-OH chiral center between single crystals and a consistency across samples in the bulk powder. Overall, this work highlights the contrast between investigating crystallographic disorder by X-ray diffraction and solid-state NMR experiment, and gauge-including projector-augmented-wave (GIPAW) density functional theory (DFT) calculations, with their combined use, yielding an improved understanding of the nature of the crystallographic disorder between the local (i.e., as viewed by NMR) and longer-range periodic (i.e., as viewed by diffraction) scale.

19F Solid-state NMR characterization of pharmaceutical solids

Solid-state NMR has been increasingly recognized as a high-resolution and versatile spectroscopic tool to characterize drug substances and products. However, the analysis of pharmaceutical materials is often carried out at natural isotopic abundance and a relatively low drug loading in multi-component systems and therefore suffers from challenges of low sensitivity. The fact that fluorinated therapeutics are well represented in pipeline drugs and commercial products offers an excellent opportunity to utilize fluorine as a molecular probe for pharmaceutical analysis. We aim to review recent advancements of ¹⁹F magic angle spinning NMR methods in modern drug research and development. Applications to polymorph screening at the micromolar level, structural elucidation, and investigation of molecular interactions at the Ångström to submicron resolution in drug delivery, stability, and quality will be discussed.

NMR technique and methodology in botanical health product analysis and quality control

Botanicals have played an important role in maintaining human health and well-being throughout history. During the past few decades in particular, the use of botanical health products has gained more popularity. Whereas, quality, safety and efficacy concerns have continuously been critical issues due to the intrinsic chemical complexity of botanicals. Chemical analytical technologies play an imperative role in addressing these issues. Nuclear magnetic resonance (NMR) spectroscopy has proven to be a powerful and useful tool for the investigation of botanical health products. In this review, NMR techniques and methodologies that have been successfully applied to the research and development of botanical health products in all stages, from plants to products, are discussed and summarized. Furthermore, applications of NMR together with other analytical techniques in a variety of domains of botanical health products investigation, such as plant species differentiation, adulteration detection, and bio-activity evaluation, are discussed and illustrated with typical examples. This article provides an overview of the potential uses of NMR techniques and methodologies in an attempt to further promote their recognition and utilization in the field of botanical health products analysis and quality control.

Research Progress of NMR in Natural Product Quantification

In the fields of medicine and health, traditional high-performance liquid chromatography or UV-visible spectrophotometry is generally used for substance quantification. However, over time, nuclear magnetic resonance spectroscopy (NMR) has gradually become more mature. Nuclear magnetic resonance spectroscopy has certain advantages in the quantitative analysis of substances, such as being nondestructive, having a high flux and short analysis time. Nuclear magnetic resonance spectroscopy has been included in the pharmacopoeiae of various countries. In this paper, the principle of nuclear magnetic resonance spectroscopy and the recent progress in the quantitative study of natural products by NMR are reviewed, and its application in the quantitative study of natural products is proposed. At the same time, the problems of using NMR alone to quantify natural products are summarized and corresponding suggestions are put forward.

Component Quantification in Solids with the Mixture Analysis Using References Method

Quantifying components in solid mixtures composed of the same chemical species exhibiting different physical forms represents a difficult challenge in many areas of chemistry. The development of small-molecule active pharmaceutical ingredients (APIs) is a classic example. APIs predominantly exhibit polymorphism and the propensity to form solvates and hydrates. The various API phases typically display different physical properties affecting chemical stability, processability, and bioperformance. Accordingly, API development critically relies on characterizing and quantifying the relevant API forms in complex mixtures in the presence of each other and in the presence of excipients. Presented here is a new solid-state-NMR-based quantification method for components in solid mixtures: mixture analysis using references (MAR). The method utilizes weighted pure component reference spectra in a linear combination fitting procedure to reproduce the corresponding mixture spectrum. The results yield the respective component contributions to the mixture composition. Using several model systems of varying complexity, the applicability and performance of the MAR analysis utilizing ¹³C and ¹⁹F cross-polarization magic-angle-spinning data are evaluated. Finally, the MAR method is compared to one of the most commonly applied traditional quantification methods. The results demonstrate that MAR performs with the same high accuracy as conventional methods. However, MAR exhibits clear efficiency advantages over conventional methods by requiring significantly less overall time (experimental and computational) and displaying remarkable robustness and general applicability. The MAR quantification protocol as presented here can easily be applied to nonpharmaceutical molecular systems in other branches of chemistry.

Physicochemical characterization and in vitro biological evaluation of solid compounds from furazolidone-based cyclodextrins for use as leishmanicidal agents

The discovery of new drugs and dosage forms for the treatment of neglected tropical diseases, such as human and animal leishmaniasis, is gaining interest in the chemical, biological, pharmaceutical, and medical fields. Many pharmaceutical companies are exploring the use of old drugs to establishing new drug dosage forms and drug delivery systems, in particular for use in neglected diseases. The formation of complexes with cyclodextrins is widely used to improve the stability, solubility, and bioavailability of pharmaceutical drugs, as well as reduce both the toxicity and side effects of many of these drugs. The aim of this study was to characterize solid compounds obtained from the association between furazolidone (FZD) and β-cyclodextrin (β-CD) or hydroxypropyl-β-cyclodextrin (HP-β-CD). The solid compounds were prepared in molar ratios of 1:1 and 1:2 (drug:CD) by kneading and lyophilization. Molecular docking was used to predict the preferred relative orientation of FZD when bound in both studied cyclodextrins. The resulting solid compounds were qualitatively characterized by scanning electron microscopy (SEM), thermal analysis (DSC and TG/DTG), X-ray diffraction (XRD), Raman spectroscopy with image mapping (Raman mapping), and ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) in the solid state. The cytotoxicity of the compounds against THP-1 macrophages and the 50% growth inhibition (IC₅₀) against Leishmania amazonensis promastigote forms were subsequently investigated using in vitro techniques. For all of the solid compounds obtained, the existence of an association between FZD and CD were confirmed by one or more characterization techniques (TG/DTG, DSC, SEM, XRD, RAMAN, and ¹³C NMR), particularly by a significant decrease in the crystallinity of these materials and a reduction in the melting enthalpy associated with furazolidone thermal events. The formation of more effective interactions occurred in the compounds prepared by lyophilization, in a 1:2 molar ratio of the two CDs studied. However, the formation of an inclusion complex was confirmed only for the solid compound obtained from HP-β-CD prepared by lyophilization (LHFZD1:2). The absence of cytotoxicity on the THP-1 macrophage lineages and the leishmanicidal activity were confirmed for all compounds. MHFZD1:2 and LHFZD1:2 were found to be very active against promastigote forms of L. amazonensis, while all others were considered only active. These results are in line with the literature, demonstrating the existence of biological activity for associations between drugs and CDs in the form of complexes and non-complexes. All solid compounds obtained were found to be promising for use as leishmanicidal agents against promastigote forms of L. amazonensis.

Molecular Mechanism of Crystalline-to-Amorphous Conversion of Pharmaceutical Solids from 19F Magic Angle Spinning NMR

Crystalline and amorphous materials usually possess distinct physicochemical properties due to major variations in long-range and local molecular packings. Enhanced fundamental knowledge of the molecular details of crystalline-to-amorphous interconversions is necessary to correlate the intermolecular structure to material properties and functions. While crystal structures can be readily obtained by X-ray crystallography, the microstructure of amorphous materials has rarely been explored due to a lack of high-resolution techniques capable of probing local molecular structures. Moreover, there is increasing interest in understanding the molecular nature of amorphous solids in pharmaceutical sciences due to the widespread utilization of amorphous active pharmaceutical ingredients (APIs) in pharmaceutical development for solubility and bioavailability enhancement. In this study, we explore multidimensional ¹³C and ¹⁹F magic angle spinning (MAS) NMR spectroscopy to study the molecular packing of amorphous posaconazole (POSA) in conjunction with the crystalline counterpart. Utilizing methods integrating homonuclear and heteronuclear ¹H, ¹³C, and ¹⁹F correlation spectroscopy and atomic ¹⁹F-to-¹³C distance measurements, we identified the major differences in molecular packing between crystalline and amorphous POSA. The intermolecular "head-to-head" interaction along the molecule's major axis, as well as the "head-to-tail" molecular packing perpendicular to the major axis in POSA crystals, was recapitulated by MAS NMR. Furthermore, critical intermolecular distances in the crystal lattice were determined. Most importantly, the head-to-tail contact of two neighboring molecules was found to be preserved in amorphous POSA, suggesting localized molecular order, whereas crucial interactions for head-to-head packing are absent in the amorphous form resulting in long-range disorder. Our study, likely one of the first documented examples, provides molecular-level structural details to understand the molecular mechanism of crystalline-to-amorphous conversion of fluorine-containing drug substances occurring in drug processing and development and establish a high-resolution experimental protocol for investigating amorphous materials.

Multinuclear solid-state NMR of complex nitrogen-rich polymeric microcapsules: Weight fractions, spectral editing, component mixing, and persistent radicals

The molecular structure of a crosslinked nitrogen-rich resin made from melamine, urea, and aldehydes, and of microcapsules made from the reactive resin with multiple polymeric components in aqueous dispersion, has been analyzed by ¹³C, ¹³C{¹H}, ¹H-¹³C, ¹H, ¹³C{¹⁴N}, and ¹⁵N solid-state NMR without isotopic enrichment. Quantitative ¹³C NMR spectra of the microcapsules and three precursor materials enable determination of the fractions of different components. Spectral editing of non-protonated carbons by recoupled dipolar dephasing, of CH by dipolar DEPT, and of C-N by ¹³C{¹⁴N} SPIDER resolves peak overlap and helps with peak assignment. It reveals that the N- and O-rich resin "imitates" the spectrum of polysaccharides such as chitin, cellulose, or Ambergum to an astonishing degree. ¹⁵N NMR can distinguish melamine from urea and guanazole, NC=O from COO, and primary from secondary amines. Such a comprehensive and quantitative analysis enables prediction of the elemental composition of the resin, to be compared with combustion analysis for validation. It also provides a reliable reference for iterative simulations of ¹³C NMR spectra from structural models. The conversion from quantitative NMR peak areas of structural components to the weight fractions of interest in industrial practice is derived and demonstrated. Upon microcapsule formation, ¹⁵N and ¹³C NMR consistently show loss of urea and aldehyde and an increase in primary amines while melamine is retained. NMR also made unexpected findings, such as imbedded crystallites in one of the resins, as well as persistent radicals in the microcapsules. The crystallites produce distinct sharp lines and are distinguished from liquid-like components by their strong dipolar couplings, resulting in fast dipolar dephasing. Fast ¹H spin-lattice relaxation on the 35-ms time scale and characteristically non-exponential ¹³C spin-lattice relaxation indicate persistent radicals, confirmed by EPR. Through ¹H spin diffusion, the mixing of components on the 5-nm scale was documented.

Ultrafast 1H MAS NMR Crystallography for Natural Abundance Pharmaceutical Compounds

Magic angle spinning (MAS) NMR is a powerful method for the study of pharmaceutical compounds, and probes with spinning frequencies above 100 kHz enable an atomic-resolution analysis of sub-micromole quantities of fully protonated solids. Here, we present an ultrafast NMR crystallography approach for structural characterization of organic solids at MAS frequencies of 100-111 kHz. We assess the efficiency of ¹H-detected experiments in the solid state and demonstrate the utility of 2D and 3D homo- and heteronuclear correlation spectra for resonance assignments. These experiments are demonstrated for an amino acid, U-¹³C,¹⁵N-histidine, and also for the significantly larger, natural product Posaconazole, an antifungal compound investigated at natural abundance. Our results illustrate the power for characterizing organic molecules, enabled by exploiting the increased ¹H resolution and sensitivity at MAS frequencies above 100 kHz.

Improving the Stability and the Pharmaceutical Properties of Norfloxacin Form C Through Binary Complexes with β-Cyclodextrin

Norfloxacin, an antibiotic that exists in different solid forms, has very unfavorable properties in terms of solubility and stability. Binary complexes of norfloxacin, in the solid form C, and β-cyclodextrin were procured by the kneading method and physical mixture. Their effect on the solubility, the dissolution rate, and the chemical and physical stability of norfloxacin was evaluated. To perform stability studies, the solid samples were stored under accelerated storage conditions, for a period of 6 months. Physical stability was monitored through powder X-ray diffraction, high-resolution ¹³C solid-state nuclear magnetic resonance, and scanning electron microscopy. The results showed evidence that the kneaded complex increased and modulated the dissolution rate of norfloxacin C. Furthermore, it was demonstrated that the photochemical stability was increased in the complex, without affecting its physical stability. The results point to the conclusion that the new kneading complex of norfloxacin constitutes an alternative tool to formulate a potential oral drug delivery system with improve oral bioavailability.

Chemometrics-assisted solid-state characterization of pharmaceutically relevant materials. Polymorphic substances

Current regulations command to properly characterize pharmaceutically relevant solid systems. Chemometrics comprise a range of valuable tools, suitable to process large amounts of data and extract valuable information hidden in their structure. This review aims to detail the results of the fruitful association between analytical techniques and chemometrics methods, focusing on those which help to gain insight into the characteristics of drug polymorphism as an important aspect of the solid state of bulk drugs and drug products. Hence, the combination of Raman, terahertz, mid- and near- infrared spectroscopies, as well as instrumental signals resulting from X-ray powder diffraction, ¹³C solid state nuclear magnetic resonance spectroscopy and thermal methods with quali-and quantitative chemometrics methodologies are examined. The main issues reviewed, concerning pharmaceutical drug polymorphism, include the use of chemometrics-based approaches to perform polymorph classification and assignment of polymorphic identity, as well as the determination of given polymorphs in simple mixtures and complex systems. Aspects such as the solvation/desolvation of solids, phase transformation, crystallinity and the recrystallization from the amorphous state are also discussed. A brief perspective of the field for the next future is provided, based on the developments of the last decade and the current state of the art of analytical instrumentation and chemometrics methodologies.

Co-grinding Effect on Crystalline Zaltoprofen with β-cyclodextrin/Cucurbit[7]uril in Tablet Formulation

This work aimed to investigate the co-grinding effects of β-cyclodextrin (β-CD) and cucurbit[7]uril (CB[7]) on crystalline zaltoprofen (ZPF) in tablet formulation. Crystalline ZPF was prepared through anti-solvent recrystallization and fully analyzed through single-crystal X-ray diffraction. Co-ground dispersions and mono-ground ZPF were prepared using a ball grinding process. Results revealed that mono-ground ZPF slightly affected the solid state, solubility, and dissolution of crystalline ZPF. Co-ground dispersions exhibited completely amorphous states and elicited a significant reinforcing effect on drug solubility. UV-vis spectroscopy, XRPD, FT-IR, DSC, ssNMR, and molecular docking demonstrated the interactions in the amorphous product. Hardness tests on blank tablets with different β-CD and CB[7] contents suggested the addition of β-CD or CB[7] could enhance the compressibility of the powder mixture. Disintegration tests showed that CB[7] could efficiently shorten the disintegrating time. Dissolution tests indicated that β-CD and CB[7] could accelerate the drug dissolution rate via different mechanisms. Specifically, CB[7] could accelerate the dissolution rate by improving disintegration and β-CD showed a distinct advantage in solubility enhancement. Based on the comparative study on β-CD and CB[7] for tablet formulation combined with co-grinding, we found that CB[7] could be considered a promising drug delivery, which acted as a disintegrant.

Understanding Surface and Interfacial Chemistry in Functional Nanomaterials via Solid-State NMR

Surface and interfacial chemistry is of fundamental importance in functional nanomaterials applied in catalysis, energy storage and conversion, medicine, and other nanotechnologies. It has been a perpetual challenge for the scientific community to get an accurate and comprehensive picture of the structures, dynamics, and interactions at interfaces. Here, some recent examples in the major disciplines of nanomaterials are selected (e.g., nanoporous materials, battery materials, nanocrystals and quantum dots, supramolecular assemblies, drug-delivery systems, ionomers, and graphite oxides) and it is shown how interfacial chemistry can be addressed through the perspective of solid-state NMR characterization techniques.

Stability of furosemide polymorphs and the effects of complex formation with β-cyclodextrin and maltodextrin

The effect of the formation of supramolecular binary complexes with β-cyclodextrin and maltodextrin on the chemical and physical stability of the polymorphs I and II of furosemide was evaluated in solid state. The solid samples were placed under accelerated storage conditions and exposed to daylight into a stability chamber for a 6-month. Chemical stability was monitored by high performance liquid chromatography, while the physical stability was studied by solid state nuclear magnetic resonance, powder X-ray diffraction and scanning electron microscopy. Changes in the physical appearance of the samples were evaluated. The studies showed a significant stabilizing effect of β-cyclodextrin on furosemide form II. Our results suggest that the complex formation is a useful tool for improving the stability of furosemide polymorphs. These new complexes are promising candidates that can be used in the pharmaceutical industry for the preparation of alternative matrices that improve physicochemical properties.

High-resolution magic angle spinning (1) H NMR measurement of ligand concentration in solvent-saturated chromatographic beads

A method based on (1) H high-resolution magic angle spinning NMR has been developed for measuring concentration accurately in heterogeneous materials like that of ligands in chromatography media. Ligand concentration is obtained by relating the peak integrals for a butyl ligand in the spectrum of a water-saturated chromatography medium to the integral of the added internal reference. The method is fast, with capacity of 10 min total sample preparation and analysis time per sample; precise, with a reproducibility expressed as 1.7% relative standard deviation; and accurate, as indicated by the excellent agreement of derived concentration with that obtained previously by (13) C single-pulse excitation MAS NMR. The effects of radiofrequency field inhomogeneity, spin rate, temperature increase due to spinning, and distribution and re-distribution of medium and reference solvent both inside the rotor during spinning and between bulk solvent and pore space are discussed in detail. © 2016 The Authors Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.

Consequences of New Approach to Chemical Stability Tests to Active Pharmaceutical Ingredients

There is a great need of broaden look on stability tests of active pharmaceutical ingredients (APIs) in comparison with current requirements contained in pharmacopeia. By usage of many modern analytical methods the conception of monitoring the changes of APIs during initial stage of their exposure to harmful factors has been developed. New knowledge must be acquired in terms of identification of each degradation products, especially volatile ones. Further research as toxicology prediction during in silico studies of determined and identified degradation products is necessary. In silico methods are known as computational toxicology or computer-assisted technologies which are used for predicting toxicology of pharmaceutical substances such as impurities or degradation products. This is a specialized software and databases intended to calculate probability of genotoxicity or mutagenicity of these substances through a chemical structure-based screening process and algorithm specific to a given software program. Applying of new analytical approach is proposed as the usage of PAT tools, XRD, HS-SPME GC-MS/MS, LC-MS/MS for stability testing. Described improvements should be taken into account in case of each drug existing already in the market as well as being implemented as new one.

35Cl solid-state NMR spectroscopy of HCl pharmaceuticals and their polymorphs in bulk and dosage forms

Herein, we demonstrate the use of 35Cl SSNMR for the structural fingerprinting of HCl salts of pharmaceuticals in both bulk and dosage forms.

Natural abundance 14N and 15N solid-state NMR of pharmaceuticals and their polymorphs

¹⁴N and ¹⁵N solid-state NMR at natural abundance are used in tandem for the investigation of pharmaceuticals and their polymorphs.

Solid-state NMR investigation of effect of fluorination and methylation on prednisolone conformation

Prednisolone (Prd) is a polymorphous synthetic corticosteroid that has three crystalline forms mediated by different solvents. In this study, we have demonstrated that solid-state {(1)H}(13)C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy is able to resolve the effects of methylation and fluorination on the conformation of the steroidal rings in Prd. Two compounds were chosen for the study, 6-α-methylprednisolone (Prd-6M) and 6-α-fluoroprednisolone (Prd-6F). The (13)C signals of Prd-6F showed primarily doublet patterns, with splittings of 40-380 Hz, indicating multiple ring conformations, whereas the (13)C signals of Prd and Prd-6M exhibited a singlet pattern, indicating a unique conformation. Using evidence from chemical shift deviation and anisotropy analysis, we have demonstrated by solid-state NMR that Prd-6F adopts two different steroidal ring conformations that are different from that of Prd-6M, and less similar to that of unsubstituted Prd.

Magic angle spinning NMR spectroscopy: a versatile technique for structural and dynamic analysis of solid-phase systems

Magic Angle Spinning (MAS) NMR spectroscopy is a powerful method for analysis of a broad range of systems, including inorganic materials, pharmaceuticals, and biomacromolecules. The recent developments in MAS NMR instrumentation and methodologies opened new vistas to atomic-level characterization of a plethora of chemical environments previously inaccessible to analysis, with unprecedented sensitivity and resolution.

Cation ion specifically induces a conformational change in trans-dehydroandrosterone - a solid-state NMR study

In this work, we demonstrated that calcium (Ca(+2)) is able to induce a conformational change in trans-dehydroandrosterone (DHEA). To this respect, solid-state NMR spectroscopy was applied to a series of DHEA molecules that were incubated with Ca(+2) under different concentrations. The high-resolution (13)C NMR spectra of the DHEA/Ca(+2) mixtures exhibited two distinct sets of signals; one was attributed to DHEA in the free form, and the second set was due to the DHEA/Ca(+2) complex. Based on chemical shift isotropy and anisotropy analyses, we postulated that Ca(+2) might have associated with the oxygen attached to C17 via a lone-pair of electrons, which induced a conformational change in DHEA. Apart from Ca(+2), we also incubated DHEA with magnesium (Mg(+2)) to determine whether Mg(+2) was able to interact with DHEA in a similar manner to Ca(+2). We found that Mg(+2) was able to induce a conformational change in DHEA deviated from that of Ca(+2). These solid-state NMR observations indicate that DHEA is able to interact with cations, such as Mg(+2) and Ca(+2), with specificity.

Improving furosemide polymorphs properties through supramolecular complexes of β-cyclodextrin

In this work, complexes of β-cyclodextrin and the two solid forms of furosemide were prepared and characterized for their potential pharmaceutical applications, with the interactions between the two compounds being studied in the solution and solid states. The solubility studies revealed different behaviors of the polymorphs. In particular, it was observed that the binary complex significantly increased the solubility of furosemide form I in the gastric simulated fluid, which resulted in a rise in the bioavailability of this formulation after oral administration. In addition, results using ssNMR, FT-IR, DSC, TGA, SEM and XRPD provided evidence of the formation of complexes after utilizing kneading and freeze-drying methods. A comparison with previous developed complexes that used maltodextrin as the ligand was performed. Our results suggest that these novel supramolecular complexes showed promise to be used in drug delivery systems with an application in pharmaceutical formulations.