Solid-state 15N Nuclear Magnetic Resonance Research Articles

Diamine-appended metal-organic framework for carbon capture from wet flue gas: Characteristics and mechanism

Due to the superior CO2 adsorption capacity and selectivity, amine-functional solid adsorbents have received increasing attention. Nevertheless, amine-functionalized polyporous materials have a large performance deviation when considering carbon removal capacity under wet flue gas. Therefore, a variety of metal–organic frameworks (MOFs) with amine functionality are synthesized in this work by appending diamine with a propylene linker to Mg2(dobpdc) (dobpdc4- = 4,4′-dioxido-3,3′-biphenyldicarboxylate) and screened under the simulated flue gas environment with a high water content (7 v%). The results indicate that ndmpn-grafted Mg2(dobpdc) (ndmpn = N,N-dimethyl-1,3-propanediamine) has a high CO2 adsorption capacity of 1.72 mmol/g at 60 °C with an extremely low regeneration heat (2.26 GJ/ton CO2 at the desorption temperature of 145 °C). Adsorption property of ndmpn-Mg2(dobpdc) at high humidity is even more excellent than that of another well-reported diaminopropene-appended MOF, dmpn-Mg2(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine). Herein, van der Waals (vdW)-corrected density functional theory (DFT) calculations are used to quantitatively analyze binding strengths and water effects on it between diamine-appended Mg2(dobpdc) and CO2. It is revealed that the addition of water makes ammonium carbamate chains produced in ndmpn-Mg2(dobpdc) more stable. These chemisorption structures under humid conditions have also been disclosed by using 15N solid-state nuclear magnetic resonance (NMR) spectroscopy experiments and DFT calculation. To conclude, we unveil the binary adsorption characteristics and mechanism of ndmpn-Mg2(dobpdc). It enables a thorough understanding of this compound and highlights its potential as a promising adsorbent under humid conditions for post-combustion applications.

15N CP/MAS NMR as a Tool for the Mechanistic Study of Mechanical Stimuli-Responsive Materials: Evidence for the Conformational Change of an Emissive Dimethylacridane Derivative.

Mechanochromic luminescent molecules are currently attracting considerable attention because of their promising technological applications, but understanding their mechanism of action is challenging and is thus hindering our deeper understanding of these materials. The conformational change of 9,9'-dimethyl-9,10-dihydroacridane derivative 1 was examined using solid-state 15N nuclear magnetic resonance (NMR) spectroscopic techniques without using a specifically 15N-labeled compound. A difference between the two conformers was clearly observed in the measurements and was assigned to the ⟨pl⟩ and ⟨bf⟩ spatial structures. The results were supported by quantum chemical calculations on 15N NMR chemical shifts of each isomer. The technique presented here can clearly identify the structural changes caused by crushing a powder sample. Such structural changes are difficult to determine using X-ray diffraction (XRD) measurements.

Relating algal-derived extracellular and intracellular dissolved organic nitrogen with nitrogenous disinfection by-product formation

The dissolved organic nitrogen (DON) pool from algal-derived extracellular and intracellular organic matter (EOM and IOM) comprises proteins, peptides, free amino acids and carbohydrates, of which, proteins can contribute up to 100% of the DON. Previous reports of algal-derived DON character have focused on bulk properties including concentration, molecular weight and hydrophobicity. However, these can be similar between algal species and between the EOM and IOM even when the inherent molecular structures vary. A focus on bulk character presents challenges to the research on algal-derived nitrogenous-disinfection by-product (N-DBP) formation as N-DBP formation is sensitive to the changes in molecular structure. Hence, the main aim of this study was to characterize algal EOM and IOM-derived DON, specifically proteinaceous-DON, using a combination of bulk and molecular characterization techniques to enable a more detailed exploration of the relationship between the character of algal-derived proteins and the N-DBP formation potential. DON from the EOM and IOM of four commonly found algae and cyanobacteria in natural waters were evaluated, namely Chlorella vulgaris, Microcystis aeruginosa, Dolichospermum circinale, and Cylindrospermopsis raciborskii. It was observed that 77-96% of total DON in all EOM and IOM samples was of proteinaceous origin. In the proteins, DON concentrations were highest in the high molecular weight fraction of IOM-derived bulk proteins (0.13–0.75 mg N L−1) and low to medium molecular weight fraction of EOM-derived bulk proteins (0.15–0.63 mg N L−1) in all species. Similar observations were also made via sodium dodecyl sulphate polyacrylamide gel electrophoresis and liquid chromatography-high resolution mass spectrometry. Solid-state 15N nuclear magnetic resonance (NMR) spectroscopy of the EOM and IOM revealed the existence of common aliphatic and heterocyclic N-groups in all samples, including a dominant 2° amide peak. Species dependent variability was also observed in the spectra, particularly in the EOM; e.g. nitro signals were found only in the Cylindrospermopsis raciborskii EOM. Dichloroacetonitrile (DCAN) and N-nitrosamine concentrations from the EOM of the species evaluated in this study were lower than the guideline limits set by regulatory agencies. It is proposed that the dominant 2° amide in all samples decreased N-DBP formation upon chlorination. For chloramination, the presence of nitro groups and aliphatic and heterocyclic N-DBP precursors could cause variable N-nitrosamine formation. Compared to non-algal impacted waters, algae-laden waters are characterised by low organic carbon: organic nitrogen ratios of ∼7–14 and elevated DON and protein concentrations. Hence, relying only on bulk characterization increases the perceived risk of N-DBP formation from algae-laden waters.

Carbon Dioxide Capture Chemistry of Amino Acid Functionalized Metal-Organic Frameworks in Humid Flue Gas.

Metal-organic framework-808 has been functionalized with 11 amino acids (AA) to produce a series of MOF-808-AA structures. The adsorption of CO2 under flue gas conditions revealed that glycine- and dl-lysine-functionalized MOF-808 (MOF-808-Gly and -dl-Lys) have the highest uptake capacities. Enhanced CO2 capture performance in the presence of water was observed and studied by using single-component sorption isotherms, CO2/H2O binary isotherm, and dynamic breakthrough measurements. The key to the favorable performance was uncovered by deciphering the mechanism of CO2 capture in the pores and attributed to the formation of bicarbonate as evidenced by 13C and 15N solid-state nuclear magnetic resonance spectroscopy studies. On the basis of these results, we examined the performance of MOF-808-Gly in simulated coal flue gas conditions and found that it is possible to capture and release CO2 by vacuum swing adsorption. MOF-808-Gly was cycled at least 80 times with full retention of performance. This study significantly advances our understanding of CO2 chemistry in MOFs by revealing how strongly bound amine moieties to the MOF backbone create the chemistry and environment within the pores, leading to the binding and release of CO2 under mild conditions without application of heat.

Characterizing Nitrogen Sites in Nitrogen-Doped Reduced Graphene Oxide: A Combined Solid-State 15N NMR, XPS, and DFT Approach

Despite the potential applications in energy storage and conversion systems such as Li–oxygen batteries and fuel cells, the nature and distribution of doped nitrogen sites in reduced graphene oxides are still not well understood. In this work, we report a combined approach of 15N solid-state nuclear magnetic resonance (NMR) spectroscopy alongside the predominantly used X-ray photoelectron spectroscopy (XPS) to characterize the nitrogen environments in reduced graphene oxides. Application of 1H–15N low-power double-quantum cross polarization under fast magic angle spinning with the Carr–Purcell–Meiboom–Gill scheme shows selective detection of protonated sites with low-power radio-frequency irradiation. NMR shift calculations of a series of N-containing molecules and a graphene nanoflake model were performed to help interpreting the experimental data. This work demonstrates a powerful approach to identify and quantify the different nitrogen environments in doped graphene materials and can also be widely applied to similar graphitic carbon-based materials with other dopants.

Toward Bridging a Gap Between Model and Natural Membranes for Biophysical Studies

To study their lipid interactions or obtain valuable structural information, membrane peptides or proteins need to be maintained in a lipid system as close as possible to their natural environment. Model membranes are employed in a variety of biophysical techniques such as nuclear magnetic resonance (NMR). However, developing a method that could allow peptide extraction and reconstitution in a native or near-native membrane would be an asset. In this work, we propose an approach inspired by bicelles, which can orient in the magnetic field. We prepared magnetically-orientable phosphatidylcholine (PC) liposomes using the membrane softening detergent Tween80 (polyoxyethylene sorbitan monooleate) which is also used to extract soluble and membrane-bound proteins. Our 31P and 2H solid-state NMR results show that TWeen80 mixed to DMPC and DPPC bilayers leads to elongated oriented structures which align over a wide range of lipid-to-detergent molar ratios (2<q<13) and temperatures (25-80oC). This can be ascribed to the miscibility of Tween80 and PC molecules, as shown by the thermotropic behavior of these mixture in infrared spectroscopy. We show that the orientation with respect to the magnetic field direction can be flipped from parallel to perpendicular by addition of lanthanides ions. Using a 15N-labeled model KALP transmembrane peptide, 15N solid-state NMR spectra showed that Tween80-based PC membranes can reveal a peptide orientation, thus providing valuable data for structural determination. Altogether, our work shows that Tween80 could be exploited for membrane protein extraction, reconstitution and structural studies without requiring to a detergent removal step. This approach has the potentiel to be used with more complex membrane bilayers including native bological membranes.

Stereochemical Effects on the Self-Assembly of Pyrenylalanine-Phenylalanine Dipeptide

Abstract The design and control of self-assembling biomaterials have significantly attracted attention over the last decades because of their broad ranges of applications. Here, we introduce the self-assembled fibers of the pyrene connected dipeptides, l-pyrenylalanine-l-phenylalanine (l-Pyr-l-Phe) and d-pyrenylalanine-l-phenylalanine (d-Pyr-l-Phe), and their structural analysis using experimental and computational techniques. While l-Pyr-l-Phe self-assembled into solid fibers, d-Pyr-l-Phe self-assembled into hydrogels with different morphologies. Fluorescence spectroscopy revealed monomer and red-shifted excimer emissions of the self-assembled l-Pyr-l-Phe and d-Pyr-l-Phe dipeptide nanostructures, respectively. This result was related to different 13C and 15N solid-state nuclear magnetic resonance (NMR) data on the backbone and side-chains of the self-assembled dipeptides. Molecular dynamics simulations demonstrated detailed information about the chirality effects of the dipeptides on their self-assembled structures.

Co-crystals, Salts or Mixtures of Both? The Case of Tenofovir Alafenamide Fumarates.

Tenofovir alafenamide fumarate (TAF) is the newest prodrug of tenofovir that constitutes several drug products used for the treatment of HIV/AIDS. Although the solid-state properties of its predecessor tenofovir disoproxil fumarate have been investigated and described in the literature, there are no data in the scientific literature on the solid state properties of TAF. In our report, we describe the preparation of two novel polymorphs II and III of tenofovir alafenamide monofumarate (TA MF2 and TA MF3). The solid-state structure of these compounds was investigated in parallel to the previously known tenofovir alafenamide monofumarate form I (TA MF1) and tenofovir alafenamide hemifumarate (TA HF). Interestingly, the single-crystal X-ray diffraction of TA HF revealed that this derivative exists as a co-crystal form. In addition, we prepared a crystalline tenofovir alafenamide free base (TA) and its hydrochloride salt (TA HCl), which enabled us to determine the structure of TA MF derivatives using 15N-ssNMR (15N-solid state nuclear magnetic resonance). Surprisingly, we observed that TA MF1 exists as a mixed ionization state complex or pure salt, while TA MF2 and TA MF3 can be obtained as pure co-crystal forms.

Tautomerism of azo dyes in the solid state studied by 15N, 14N, 13C and 1H NMR spectroscopy, X-ray diffraction and quantum-chemical calculations

The azo–hydrazo tautomerism of four model azo dyes in the solid state is investigated by multinuclear solid-state nuclear magnetic resonance (SS-NMR) spectroscopy, X-ray diffraction and quantum-chemical calculations. The measurement of 15N SS-NMR spectra is the most straightforward way to determine the tautomeric state of solid azo compounds. Unfortunately, the sensitivity of these nuclei for SS-NMR is very low and the acquisition of 15N spectra in a reasonable time may be challenging. It is demonstrated that a natural abundance of almost 100% of another nitrogen isotope, 14N, can be exploited for the investigation of the tautomerism. Indirect detection of 14N nuclei via protons is an elegant approach for the rapid and unequivocal determination of the tautomeric form. Furthermore, a comparison of experimental carbon SS-NMR chemical shifts with those obtained in solution or by quantum-chemical computations can be used for the same purpose.

Solid-state vibrational circular dichroism studies of L- and D-serine

d-Serine is considered a key endogenous substance involved in several enzymatic reactions in the human body. In this study, solid-state vibrational circular dichroism (VCD) measurements of enantiomeric serine were performed for spectroscopic distinction between d- and l-serine. The mirror-image VCD signals of the isomers in the KBr pellets were observed in the mid-infrared range of 1800–1250 cm−1. The calculated infrared (IR) and VCD spectra for the optimized serine structures were in good agreement with the corresponding observed spectra. In addition, the chemical shift values estimated from the shielding constants of the optimized structure of serine corresponded with the observed values in 13C and 15N solid-state nuclear magnetic resonance spectra, supporting the VCD assignments. Our results suggest the need for further study of VCD to develop a sensitive and high-resolution spectroscopic technique for the detection of d-amino acids.

Structural Characterization and Pharmaceutical Properties of Three Novel Cocrystals of Ethenzamide With Aliphatic Dicarboxylic Acids

Ethenzamide (ET) was screened in cocrystallization experiments with pharmaceutically acceptable coformer molecules to discover materials of improved physicochemical properties, that is, higher solubility and better stability. Three novel cocrystals of ET with glutaric, malonic, and maleic acids were obtained by neat grinding and slow evaporation from solution. The purpose of the study was to notice the changes in the geometry and interactions of ET molecule in crystalline phase introduced by different acid and relate them to physicochemical properties of pure ET. Therefore, the crystal structure of the cocrystals was determined by single crystal X-ray diffraction analysis. The powder samples were characterized by differential scanning calorimetry, Fourier-transform infrared spectroscopy, and 13C and 15N solid-state nuclear magnetic resonance spectroscopy. Spectroscopic studies were supported by gauge including projector augmented wave calculations of chemical shielding constants. The high stability of cocrystals during direct compression was proved. The solubility in simulated gastric fluids for studied cocrystals appeared to be approximately 1.6 times-fold higher than ET. The dissolution rates of all ET cocrystals were not faster than the pure drug, but after 240 min, more drugs were released.

Solid-State NMR Characterization of the Structure of Self-Assembled Ile–Phe–OH

Solid-state nuclear magnetic resonance (NMR) spectroscopy provides significant structural information regarding the conformation and dynamics of a variety of solid samples. In this study, we recorded the 13C and 15N solid-state NMR spectra of a self-assembled isoleucine-phenylalanine (Ile&ndash;Phe&ndash;OH) dipeptide. Immediately after the addition of hexane to a solution of concentrated peptide in ethyl acetate, the peptide visually aggregated into a nanofiber. Then, we obtained well-resolved 13C and 15N NMR signals of the natural, isotopic-abundant Ile&ndash;Phe&ndash;OH peptide in the nanofiber. Furthermore, we calculated the chemical shift values of the reported crystal structure of the Ile&ndash;Phe dipeptide via the density functional theory (DFT) calculation and compared these results with the experimental values. Notably, the two sets of values were in good agreement with each other, which indicated that the self-assembled structure closely reflected the crystal structure. Therefore, herein, we demonstrated that solid-state NMR characterization combined with DFT calculations is a powerful method for the investigation of molecular structures in self-assembled short peptides.

Evolution of nitrogen species in landfill leachates under various stabilization states

In this study, nitrogen species in landfill leachates under various stabilization states were investigated with emphasis on organic nitrogen. Ammonium nitrogen was found to be approximately 1300mg/L in leachates from younger landfill units (less than 10years old), and approximately 500mg/L in leachates from older landfill units (up to 30years old). The concentration and aerobic biodegradability of organic nitrogen decreased with landfill age. A size distribution study showed that most organic nitrogen in landfill leachates is <1kDa. The Lowry protein concentration (mg/L-N) was analyzed and showed a strong correlation with the total organic nitrogen (TON, mg/L-N, R2=0.88 and 0.98 for untreated and treated samples, respectively). The slopes of the regression curves of untreated (protein=0.45TON) and treated (protein=0.31TON) leachates indicated that the protein is more biodegradable than the other organic nitrogen species in landfill leachates. XAD-8 resin was employed to isolate the hydrophilic fraction of leachate samples, and it was found that the hydrophilic fraction proportion in terms of organic nitrogen decreased with landfill age. Solid-state 15N nuclear magnetic resonance (NMR) was utilized to identify the nitrogen species. Proteinaceous materials were found to be readily biodegradable, while heterocyclic nitrogen species were found to be resistant to biodegradation.

Solution and Solid-State Nuclear Magnetic Resonance Structural Investigations of the Antimicrobial Designer Peptide GL13K in Membranes.

The antimicrobial peptide GL13K encompasses 13 amino acid residues and has been designed and optimized from the salivary protein BPIFA2 to exhibit potent bacteriocidal and anti-biofilm activity against Gram-negative and Gram-positive bacteria as well as anti-lipopolysaccharide activity in vitro and in vivo. Here, the peptide was analyzed in a variety of membrane environments by circular dichroism spectroscopy and by high-resolution multidimensional solution nuclear magnetic resonance (NMR) spectroscopy. Whereas in the absence of membranes a random coil conformation predominates, the peptide adopts a helical structure from residue 5 to 11 in the presence of dodecylphosphocholine micelles. In contrast, a predominantly β-sheet structure was observed in the presence of lipid bilayers carrying negatively charged phospholipids. Whereas 15N solid-state NMR spectra are indicative of a partial alignment of the peptide 15N-1H vector along the membrane surface, 2H and 31P solid-state NMR spectra indicate that in this configuration the peptide exhibits pronounced disordering activities on the phospholipid membrane, which is possibly related to antimicrobial action. GL13K, thus, undergoes a number of conformational transitions, including a random coil state in solution, a helical structure upon dilution at the surface of zwitterionic membranes, and β-sheet conformations at high peptide:lipid ratios.

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.

Enhanced NMR Discrimination of Pharmaceutically Relevant Molecular Crystal Forms through Fragment-Based Ab Initio Chemical Shift Predictions.

Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction. Fragment methods allow hybrid density functionals to be employed routinely in chemical shift prediction, and we have recently demonstrated appreciable improvements in the accuracy of the predicted shifts when using the hybrid PBE0 functional instead of generalized gradient approximation (GGA) functionals like PBE. Here, we investigate the solid-state 13C and 15N NMR spectra for multiple crystal forms of acetaminophen, phenobarbital, and testosterone. We demonstrate that the use of the hybrid density functional instead of a GGA provides both higher accuracy in the chemical shifts and increased discrimination among the different crystallographic environments. Finally, these results also provide compelling evidence for the transferability of the linear regression parameters mapping predicted chemical shieldings to chemical shifts that were derived in an earlier study.

Probing the Carbonyl Functionality of a Petroleum Resin and Asphaltene through Oximation and Schiff Base Formation in Conjunction with N-15 NMR.

Despite recent advances in spectroscopic techniques, there is uncertainty regarding the nature of the carbonyl groups in the asphaltene and resin fractions of crude oil, information necessary for an understanding of the physical properties and environmental fate of these materials. Carbonyl and hydroxyl group functionalities are not observed in natural abundance 13C nuclear magnetic resonance (NMR) spectra of asphaltenes and resins and therefore require spin labeling techniques for detection. In this study, the carbonyl functionalities of the resin and asphaltene fractions from a light aliphatic crude oil that is the source of groundwater contamination at the long term USGS study site near Bemidji, Minnesota, have been examined through reaction with 15N-labeled hydroxylamine and aniline in conjunction with analysis by solid and liquid state 15N NMR. Ketone groups were revealed through 15N NMR detection of their oxime and Schiff base derivatives, and esters through their hydroxamic acid derivatives. Anilinohydroquinone adducts provided evidence for quinones. Some possible configurations of the ketone groups in the resin and asphaltene fractions can be inferred from a consideration of the likely reactions that lead to heterocyclic condensation products with aniline and to the Beckmann reaction products from the initially formed oximes. These include aromatic ketones and ketones adjacent to quaternary carbon centers, β-hydroxyketones, β-diketones, and β-ketoesters. In a solid state cross polarization/magic angle spinning (CP/MAS) 15N NMR spectrum recorded on the underivatized asphaltene as a control, carbazole and pyrrole-like nitrogens were the major naturally abundant nitrogens detected.

15N solid-state nuclear magnetic resonance study of pyrolyzed metal-polyaniline cathode catalysts for oxygen reduction in fuel cells

The oxygen reduction reaction (ORR) activity of pyrolyzed metal-free and metal (Mn, Fe, Co, Ni and Cu)-containing polyaniline (PANI) in polymer electrolyte fuel cell (PEFC) was studied. The metal-free PANI800 shows quite poor ORR catalytic activity, whilst the metal-containing PANIMe800 display a better ORR activity. The 15N CP/MAS NMR spectra of PANINi800 and PANICu800 show one weak peak at 118 ppm and there is no peak observed in PANIFe800, against that of PANI800, PANIMn800, PANICo800 and PANINi800 show two peaks at 273 and 118 ppm assigned to the pyridinic and pyridinium nitrogens. It is because of the paramagnetic effect of metal ions. The 15N spin-echo NMR spectra of PANIMe800 with fast recycle delay show the peaks at 140 and 270 ppm assigned to the graphitic and pyridinic nitrogens, against that of PANI800 shows no peak. The spectra of PANIMn800, PANICo800, PANINi800 and PANICu600 also contain a very broaden peak at 430 ppm assigned to the nitrogen with Fermi-contact effect from metal ions. The spectra of PANIFe800 show some spinning side bands and the average Fe3+–15N distance can be calculated. The some amount of iron ion are relieved and average Fe3+–15N distance increase after acid washing and the ORR activity decreases.

Catalytic roles of βLys87 in tryptophan synthase: 15N solid state NMR studies

The proposed mechanism for tryptophan synthase shows βLys87 playing multiple catalytic roles: it bonds to the PLP cofactor, activates C4′ for nucleophilic attack via a protonated Schiff base nitrogen, and abstracts and returns protons to PLP-bound substrates (i.e. acid–base catalysis). ε-15N-lysine TS was prepared to access the protonation state of βLys87 using 15N solid-state nuclear magnetic resonance (SSNMR) spectroscopy for three quasi-stable intermediates along the reaction pathway. These experiments establish that the protonation state of the ε-amino group switches between protonated and neutral states as the β-site undergoes conversion from one intermediate to the next during catalysis, corresponding to mechanistic steps where this lysine residue has been anticipated to play alternating acid and base catalytic roles that help steer reaction specificity in tryptophan synthase catalysis. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications. Guest Editors: Andrea Mozzarelli and Loredano Pollegioni.

13C and 15N solid-state NMR studies on albendazole and cyclodextrin albendazole complexes

13C and 15N solid-state nuclear magnetic resonance (NMR) spectra were recorded from albendazole (ABZ) and from ABZ:β-cyclodextrin, ABZ:methyl-β-cyclodextrin, ABZ:hydroxypropyl-β-cyclodextrin and ABZ:citrate-β-cyclodextrin, which were prepared by the spray-drying technique. ABZ signals were typical of a crystalline solid for the pure drug and of an amorphous compound obtained from ABZ:cyclodextrin samples. Relevant spectral differences were correlated with chemical interaction between ABZ and cyclodextrins. The number and type of complexes revealed a strong dependence on the cyclodextrin group substituent. Solid-state NMR data were consistent with the presence of stable inclusion complexes.