Exploring Cyclodextrin-Based Nanosponges as Drug Delivery Systems: Understanding the Physicochemical Factors Influencing Drug Loading and Release Kinetics.

Cyclodextrin-based nanosponges (CDNSs) are complex macromolecular structures composed of individual cyclodextrins (CDs) and nanochannels created between cross-linked CD units and cross-linkers. Due to their unique structural and physicochemical properties, CDNSs can possess even more beneficial pharmaceutical features than single CDs. In this comprehensive review, various aspects related to CDNSs are summarized. Particular attention was paid to overviewing structural properties, methods of synthesis, and physicochemical analysis of CDNSs using various analytical methods, such as DLS, PXRD, TGA, DSC, FT-IR, NMR, and phase solubility studies. Also, due to the significant role of CDNSs in pharmaceutical research and industry, aspects such as drug loading, drug release studies, and kinetics profile evaluation of drug-CDNS complexes were carefully reviewed. The aim of this paper is to find the relationships between the physicochemical features and to identify crucial characteristics that are influential for using CDNSs as convenient drug delivery systems.

Application of Molecular Dynamics Simulations in the Analysis of Cyclodextrin Complexes.

Cyclodextrins (CDs) are highly respected for their ability to form inclusion complexes via host-guest noncovalent interactions and, thus, ensofance other molecular properties. Various molecular modeling methods have found their applications in the analysis of those complexes. However, as showed in this review, molecular dynamics (MD) simulations could provide the information unobtainable by any other means. It is therefore not surprising that published works on MD simulations used in this field have rapidly increased since the early 2010s. This review provides an overview of the successful applications of MD simulations in the studies on CD complexes. Information that is crucial for MD simulations, such as application of force fields, the length of the simulation, or solvent treatment method, are thoroughly discussed. Therefore, this work can serve as a guide to properly set up such calculations and analyze their results.

Caffeine-Cyclodextrin Complexes as Solids: Synthesis, Biological and Physicochemical Characterization.

Mechanochemical and in-solution synthesis of caffeine complexes with α-, ß-, and γ-cyclodextrins was optimized. It was found that short-duration, low-energy cogrinding, and evaporation (instead of freeze-drying) are effective methods for the formation and isolation of these complexes. The products obtained, their pure components, and their mixtures were examined by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), FT-IR and Raman spectroscopy. Moreover, molecular modeling provided an improved understanding of the association process between the guest and host molecules in these complexes. The complexes were found to exhibit high toxicity in zebrafish (Danio rerio) embryos, in contrast to pure caffeine and cyclodextrins at the same molar concentrations. HPLC measurements of the caffeine levels in zebrafish embryos showed that the observed cytotoxicity is not caused by an increased caffeine concentration in the body of the organism, as the concentrations are similar regardless of the administered caffeine form. Therefore, the observed high toxicity could be the result of the synergistic effect of caffeine and cyclodextrins.

Application of combined solid-state NMR and DFT calculations for the study of piracetam polymorphism.

Piracetam, a popular nootropic drug, widely used in the treatment of age-associated mental decline and disorders of the nervous system such as Alzheimer's disease and dementia exists under normal pressure in three polymorphic forms (P1, P2 and P3) of different stability. In this work the relative stability of piracetam polymorphs depending on the temperature was studied using the ssNMR spectroscopy combined with ab initio DFT calculations. The ssNMR spectroscopy enabled the analysis of polymorphic phase transition in the case of pure active substance as well as polymorphic form identification in the analysis of the commercial solid dosage formulations. Quantum chemical calculations of phonon density of states were performed to obtain the temperature dependence of the enthalpy, entropy and free energy of the piracetam polymorphs in a quasi-harmonic approximation. GIPAW NMR calculations combined with molecular dynamics were performed to support the chemical shift assignment. The obtained results showed that DFT calculations can be used not only to obtain the NMR parameters but also to predict the influence of the temperature on the stability order of the polymorphic forms of molecular crystals.

Solid-state structure of N-o-, N-m-, and N-p-nitrophenyl-2,3,4-tri-O-acetyl-ß-D-xylopyranosylamines.

Comprehensive structural analyses were performed for N-o-, N-m-, and N-p-nitrophenyl-2,3,4-tri-O-acetyl-ß-D-xylopyranosylamines. Single-crystal X-ray diffraction data were collected and revealed that one compound under investigation undergoes temperature-dependent polymorph transitions (crystal structures of three polymorphs were obtained). The number of molecules in the independent part of the crystal unit cells was in agreement with the number of resonances in solid-state (13)C NMR spectra. Therefore, the compounds exist as single polymorphs at room temperature, as confirmed by powder X-ray diffraction measurements. Significant differences in (13)C chemical shifts between solution and solid-state NMR for selected carbon atoms confirmed the existence of intra- and/or intermolecular interactions.

The influence of cyclomaltooligosaccharides (cyclodextrins) on the enzymatic decomposition of l-phenylalanine catalyzed by phenylalanine ammonia-lyase.

Cyclomaltohexaose (α-cyclodextrin) and cyclomaltoheptaose (ß-cyclodextrin) as well as their four methyl ether derivatives, that is, hexakis(2,3-di-O-methyl)cyclomaltohexaose, hexakis(2,3,6-tri-O-methyl)cyclomaltohexaose, heptakis(2,3-di-O-methyl)cyclomaltoheptaose, and heptakis(2,3,6-tri-O-methyl)cyclomaltoheptaose were investigated as the additives in the course of enzymatic decomposition of l-phenylalanine catalyzed by phenylalanine ammonia-lyase. Only a few of those additives behaved like classical inhibitors of the enzymatic reaction under investigation because the values of the Michaelis constants that were obtained, as well as the maximum velocity values depended mostly atypically on the concentrations of those additives. In most cases cyclodextrins caused mixed inhibition, both competitive and noncompetitive, but they also acted as activators for selected concentrations. This atypical behaviour of cyclodextrins is caused by three different and independent effects. The inhibitory effect of cyclodextrins is connected with the decrease of substrate concentration and unfavourable influence on the flexibility of the enzyme molecules. On the other hand, the activating effect is connected with the decrease of product concentration (the product is an inhibitor of the enzymatic reaction under investigation). All these effects are caused by the ability of the cyclodextrins to form inclusion complexes.

Single-crystal and powder X-ray diffraction and solid-state 13C NMR of p-nitrophenyl glycopyranosides, the derivatives of D-galactose, D-glucose, and D-mannose.

The X-ray diffraction patterns, (13)C CP MAS NMR spectra, and powder X-ray diffraction analyses were obtained for selected p-nitrophenyl glycosides: alpha- and beta-D-galactopyranosides (1 and 2), alpha- and beta-D-glucopyranosides (3 and 4), and alpha- and beta-D-mannopyranosides (5 and 6). In X-ray diffraction analysis of 1 and 2, characteristic shortening and lengthening of selected bonds were observed in the molecules of 1 due to anomeric effect, and in the crystal lattice of 1 and 2, hydrogen bonds of complex network were detected. In the crystal asymmetric unit of 1 there were two independent molecules, whereas in 2 there was one molecule. For 1 and 3-6 the number of resonances in solid-state (13)C NMR spectra exceeded the number of the carbon atoms in the molecules, while for 2 there were distinct singlet resonances in its solid-state NMR spectrum. Furthermore, the powder X-ray diffraction (PXRD) performed for 1-3 and 5 revealed that 1, 3, and 5 existed as single polymorphs proving that the doublets observed in appropriate solid-state NMR spectra were connected with two non-equivalent molecules in the crystal asymmetric unit. On the other hand 2 existed as a mixture of two polymorphs, one of them was almost in agreement with the calculated pattern obtained from XRD (the difference in volumes of the unit cells), and the subsequent unknown polymorph existed in small amounts and therefore it was not observed in solid-state NMR measurements.

The influence of selected O-alkyl derivatives of cyclodextrins on the enzymatic decomposition of L-tryptophan by L-tryptophan indole-lyase.

A series of O-alkyl derivatives of cyclodextrin: heksakis[2,3,6-tri-O-(2'-methoxyethyl)]-alpha-cyclodextrin; heksakis(2,3-di-O-methyl)-alpha-cyclodextrin; heptakis(2,3-di-O-methyl)-beta-cyclodextrin; heksakis[2,3-di-O-methyl-6-O-(2'-methoxyethyl)]-alpha-cyclodextrin; heptakis[2,3-di-O-methyl-6-O-(2'-methoxyethyl)]-beta-cyclodextrin; heksakis[2,3-di-O-(2'-methoxyethyl)]-alpha-cyclodextrin and heptakis[2,3-di-O-(2'-methoxyethyl)]-beta-cyclodextrin have been synthesized. Purity and composition of the obtained substances were examined. The cyclodextrin derivatives listed above as well as (2-hydroxypropyl)-alpha-cyclodextrin and (2-hydroxypropyl)-beta-cyclodextrin, the two commercially available ones, have been investigated as the additives in the course of enzymatic decomposition of L-tryptophan by L-tryptophan indole-lyase. It has been found that each of cyclodextrin derivatives causes the inhibition of enzymatic process, both competitive and non-competitive. The competitive inhibition is connected with the formation of inclusion complexes between cyclodextrins and L-tryptophan, related to the geometry of these complexes. The mechanism of the non-competitive inhibition is not so evident; it could be related to the formation of the cyclodextrin complexes on the surface of the enzyme, leading to the change in the flexibility of the enzyme molecule.

(13)C CP MAS NMR and crystal structure of methyl glycopyranosides.

The X-ray diffraction analysis, (13)C CP MAS NMR spectra and powder X-ray diffraction patterns were obtained for selected methyl glycosides: alpha- and beta-d-lyxopyranosides (1, 2), alpha- and beta-l-arabinopyranosides (3, 4), alpha- and beta-d-xylopyranosides (5, 6) and beta-d-ribopyranoside (7) and the results were confirmed by GIAO DFT calculations of shielding constants. In X-ray diffraction analysis of 1 and 2, a characteristic shortening and lengthening of selected bonds was observed in molecules of 1 due to anomeric effect and, in crystal lattice of 1 and 2, hydrogen bonds of different patterns were present. Also, an additional intramolecular hydrogen bond with the participation of ring oxygen atom was observed in 1. The observed differences in chemical shifts between solid state and solution come from conformational effects and formation of various intermolecular hydrogen bonds. The changes in chemical shifts originating from intermolecular hydrogen bonds were smaller in magnitude than conformational effects. Furthermore, the powder X-ray diffraction (PXRD) performed for 4, 5 and 7 revealed that 7 existed as a mixture of two polymorphs, and one of them probably consisted of two non-equivalent molecules.

Crystal structure and solid-state 13C NMR analysis of N-o-, N-m- and N-p-nitrophenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylamines, and their N-acetyl derivatives.

The X-ray diffraction analysis of N-o-nitrophenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylamine (1), N-m-nitrophenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylamines, N-p-nitrophenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylamines, and their N-acetyl derivatives was performed. The sugar moieties always adopt (4)C1 conformations, however, due to crystal packing forces they are always slightly distorted. It was found that except N-acetyl, N-m-nitrophenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylamine (5), none of the glucopyranosylamines studied in this paper form strong hydrogen bonds in the crystal lattice. Additionally, (5) crystallizes with a molecule of water, which occupies a special crystallographic position (on the twofold axis) and links two sugar molecules by hydrogen bonds. The CP MAS NMR spectra confirmed the presence of the intermolecular hydrogen bond involving the molecule of water in (5). Moreover, it was proved that in (1) an intramolecular hydrogen bond is formed between the glycosidic linkage and the nitro group.

Crystal structure and solid-state 13C NMR analysis of N-p-nitrophenyl-alpha-D-ribopyranosylamine, N-p-nitrophenyl-alpha-D-xylopyranosylamine, and solid-state 13C NMR analysis of N-p-nitrophenyl-2,3,4-tri-O-acetyl-beta-D-lyxopyranosylamine and N-p-nitrophenyl-2,3,4-tri-O-acetyl-alpha-L-arabinopyranosylamine.

The X-ray diffraction analysis of N-p-nitrophenyl-alpha-D-ribopyranosylamine (1) and N-p-nitrophenyl-alpha-D-xylopyranosylamine (2) was performed. It was found that an independent part of the unit cell of compound 1 is formed by three molecules of sugar whereas the crystals of compound 2 have one molecule in the independent part of the crystal unit cell. Additionally, 1 crystallizes with one molecule of water. The solvent molecule forms an extensive hydrogen bond network with the hydroxyl groups of the sugar, and this efficiently stabilizes the crystal lattice. Contrary to 2, the sugar moieties of 1 adopt the 1C4 conformation. In the spectra of 2, N-p-nitrophenyl-2,3,4-tri-O-acetyl-beta-D-lyxopyranosylamine and N-p-nitrophenyl-2,3,4-tri-O-acetyl-alpha-L-arabinopyranosylamine the number of resonances does not exceed the number of carbon atoms in the molecules, thus indicating no polymorphism. In the spectrum of (1) the signals are split, confirming the presence of three independent molecules in the crystal unit cell.

Crystal structure and solid state 13C NMR analysis of nitrophenyl 2,3,4,6-tetra-O-acetyl-beta-D-gluco- and D-galactopyranosides.

The X-ray diffraction analysis of o-nitrophenyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside (1), m-nitrophenyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside, p-nitrophenyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside and o-nitrophenyl 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside was performed. It was found that except in the case of 1, all other crystals have one molecule in the independent part of the crystal unit cell. The results support the opinion that the nitro group does not conjugate effectively with the phenyl ring. In the 13C CP MAS spectrum of 1 the signals are split, confirming the presence of two independent molecules. Similarly, the 13C CP MAS NMR spectrum of p-nitrophenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside indicated the presence of two non-equivalent molecules in the crystal unit. One of these molecules has more conformational freedom enabling rotation of the phenyl ring.