Inclusion complexes of ibuprofen and β-cyclodextrin: Supramolecular structure and stability

Easy and Effective Method for α-CD:N2O Host-Guest Complex Formation

α-CD:N2O "host-guest" type complexes were formed by a simple solid-gas reaction (N2O sorption into α-CD) under different gas pressures and temperatures. The new N2O inclusion method applied in the present study was compared with the already known technique based on the crystallization of clathrates from a water solution of α-CD saturated with N2O. A maximum storage capacity of 4.5 wt.% N2O was achieved when charging the cyclodextrin from a gas phase. The amount of included gas decreases to 1.3 wt.% when the complex is stored in air at 1 atm and room temperature, analogous to that achieved by the crystallization of α-CD:N2O. Furthermore, it was shown that the external coordination of N2O to either the upper or lower rim of α-CD without hydration water displacement is the preferred mode of binding, due to hydrogen bonds with neighboring -OH groups from the host macrocycle and three of the hydration water molecules nearby. The capacity of α-CD to store N2O and the thermal stability of the α-CD:N2O complex demonstrated promising applications of these types of complexes in food and beverages.

Enhanced Solubility of Ibuprofen by Complexation with β-Cyclodextrin and Citric Acid

The ability of β-CD to form inclusion complexes with ibuprofen (IBU) and at the same time to make a two-phase system with citric acid was explored in the present study for achieving improved solubility and dissolution rate of IBU. Mechanical milling as well as mechanical milling combined with thermal annealing of the powder mixtures were applied as synthetic methods. Solubility and dissolution kinetics of the complexes were studied in compliance with European Pharmacopoeia (ICH Q4B). β-CD and citric acid (CA) molecules were shown to interact by both ball milling (BM), thermal annealing, as well as BM with subsequent annealing. Complexes were also formed by milling the three compounds (β-CD, CA and IBU) simultaneously, as well as by a consecutive first including IBU into β-CD and then binding the formed β-CD/IBU inclusion complex with CA. As a result, ternary β-CD/IBU/CA complex formed by initial incorporation of ibuprofen into β-CD, followed by successive formation of a two-phase mixture with CA, exhibited notably improved dissolution kinetics compared to the pure ibuprofen and slightly better compared to the binary β-CD/IBU system. Although the addition of CA to β-CD/IBU does not significantly increase the solubility rate of IBU, it must be considered that the amount of β-CD is significantly less in the ternary complex compared to the binary β-CD/IBU.

β-Cyclodextrin functionalized agarose-based hydrogels for multiple controlled drug delivery of ibuprofen

Agarose hydrogels are three-dimensional hydrophilic polymeric frameworks characterised by high water content, viscoelastic properties, and excellent ability as cell and drug delivery systems. However, their hydrophilicity as gel systems makes loading of hydrophobic drugs difficult and often ineffective. The incorporation of amphiphilic molecules (e.g. cyclodextrins) into hydrogels as hosts able to form inclusion complexes with hydrophobic drugs could be a possible solution. However, if not properly confined, the host compounds can get out of the network resulting in uncontrolled release. Therefore, in this work, β-cyclodextrins-based host-guest supramolecular hydrogel systems were synthesised, with β-cyclodextrins (β-CD) covalently bound to the polymeric network, preventing leakage of the host molecules. Hydrogels were prepared at two different β-CD-functionalized polyvinyl alcohol (PVA)/agarose ratios, and characterised chemically and physically. Then ibuprofen, a drug often used as a gold standard in studies involving β-CD both in its hydrophilic and hydrophobic forms, was selected to investigate the release behavior of the synthesised hydrogels and the influence of β-CD on the release. The presence of β-CD linked to the polymeric 3D network ensured a higher and prolonged release profile for the hydrophobic drug and also seemed to have some influence on the hydrophilic one.

Complexes of Ibuprofen Thiazolidin-4-One Derivatives with β-Cyclodextrin: Characterization and In Vivo Release Profile and Biological Evaluation

Generally, NSAIDs are weakly soluble in water and contain both hydrophilic and hydrophobic groups. One of the most widely used NSAIDs is ibuprofen, which has a poor solubility and high permeability profile. By creating dynamic, non-covalent, water-soluble inclusion complexes, cyclodextrins (CDs) can increase the dissolution rate of low aqueous solubility drugs, operating as a drug delivery vehicle, additionally contributing significantly to the chemical stability of pharmaceuticals and to reducing drug-related irritability. In order to improve the pharmacological and pharmacokinetics profile of ibuprofen, new thiazolidin-4-one derivatives of ibuprofen (4b, 4g, 4k, 4m) were complexed with β-CD, using co-precipitation and freeze-drying. The new β-CD complexes (β-CD-4b, β-CD-4g, β-CD-4k, β-CD-4m) were characterized using scanning electronic microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction and a phase solubility test. Using the AutoDock-VINA algorithm included in YASARA-structure software, we investigated the binding conformation of ibuprofen derivatives to β-CD and measured the binding energies. We also performed an in vivo biological evaluation of the ibuprofen derivatives and corresponding β-CD complexes, using analgesic/anti-inflammatory assays, as well as a release profile. The results support the theory that β-CD complexes (β-CD-4b, β-CD-4g, β-CD-4k, β-CD-4m) have a similar effect to ibuprofen derivatives (4b, 4g, 4k, 4m). Moreover, the β-CD complexes demonstrated a delayed release profile, which provides valuable insights into the drug-delivery area, focused on ibuprofen derivatives.

How are N-methylcarbamates encapsulated by β-cyclodextrin: insight into the binding mechanism

Guest molecules containing chromophore groups encapsulated by β-cyclodextrin (β-CD) generate circular dichroism (CD) signals, which enables a preliminary prediction of their binding modes. However, the accurate determination of the representative binding conformation (RC) remains a challenging task due to the complex conformational space of these host-guest systems. Here, we combine a molecular dynamics/quantum mechanics/continuum solvent model (MD/QM/CSM) with induced circular dichroism (ICD) data (N. L. Pacioni, A. B. Pierini and A. V. Veglia, Spectrochim. Acta A Mol. Biomol. Spectrosc., 2013, 103, 319-324.) to explore the binding mechanism of β-CD with four N-methylcarbamate molecules: promecarb (PC), bendiocarb (BC), carbaryl (CY) and carbofuran (CF). In aqueous solution, their stability decreases as: PC > BC > CY > CF. Comparing the ECD spectra computed from TD-DFT with the ICD data can help eliminate many common binding configurations and identify the RC. The host-guest binding affinities (BAs) estimated using a ONIOM2(B971:PM6)/SMD model reproduce the measured binding trend, reveal the competition between the non-covalent interaction and solvent effect and explain the large difference in their binding modes. We also examine the fluctuations in the computed BA using similar structures.

Supersaturation maintenance of carvedilol and chlorthalidone by cyclodextrin derivatives: Pronounced crystallization inhibition ability of methylated cyclodextrin

Cyclodextrin (CD) is used to solubilize poorly water-soluble drugs by inclusion complex formation. In this study, we investigated the effect of CD derivatives on stabilizing the supersaturation by inhibiting the crystallization of two poorly water-soluble drugs, carvedilol (CVD) and chlorthalidone (CLT). The phase solubility test showed that β-CD and γ-CD derivatives enhanced the solubility of CVD to a greater extent, whereas the solubility of CLT was enhanced more by β-CD derivatives. The solubilization efficacy of CD derivatives was dependent on the size fitness between the drug molecule and the CD cavity. In the drug crystallization induction time measurement, the same initial drug supersaturation ratio (S) was employed in all the CD solutions, and the methylated CD derivatives greatly outperformed unmethylated CD derivatives in stabilizing the supersaturation of both CVD and CLT. The crystallization inhibition strength of CD derivatives was strongly affected by the CD derivative substituent. Moreover, the calculated logarithm of octanol/water partition coefficients (log P) of CD derivatives showed a good correlation with drug crystallization inhibition ability. Thus, the high hydrophobicity of methylated CD plays an essential role in inhibiting crystallization. These findings can provide a valuable guide for selecting appropriate stabilizing agents for drug-supersaturation formulations.

Current Status of Quantum Chemical Studies of Cyclodextrin Host-Guest Complexes

This article aims to review the application of various quantum chemical methods (semi-empirical, density functional theory (DFT), second order Møller-Plesset perturbation theory (MP2)) in the studies of cyclodextrin host-guest complexes. The details of applied approaches such as functionals, basis sets, dispersion corrections or solvent treatment methods are analyzed, pointing to the best possible options for such theoretical studies. Apart from reviewing the ways that the computations are usually performed, the reasons for such studies are presented and discussed. The successful applications of theoretical calculations are not limited to the determination of stable conformations but also include the prediction of thermodynamic properties as well as UV-Vis, IR, and NMR spectra. It has been shown that quantum chemical calculations, when applied to the studies of CD complexes, can provide results unobtainable by any other methods, both experimental and computational.

A review of controlled release from cyclodextrins: release methods, release systems and application

The controlled release of guest molecules from cyclodextrin (CD) inclusion complexes is very important for specific industrial applications in foods, medicine, cosmetics, textiles, agriculture, environmental protection, and chemical materials. The term "controlled release" encompasses several related methods, including those referred to as immediate release, sustained release and targeted release. Many different CD-based controlled release systems are currently used in practical applications. CD inclusion complexes, CD coupling, supramolecular hydrogels, and supramolecular micelles are among the most common. This review systematically introduces the principles and applications of CD-based controlled release systems, providing a theoretical basis for improving the bioavailability of effective substances and broadening their range of application.

Starch inclusion complex for the encapsulation and controlled release of bioactive guest compounds

The linear component of starch, especially amylose, is capable of forming inclusion complex (IC) with various small molecules. It could significantly modify the structure and properties of starch, and it could bring beneficial effects when bioactive compounds can be encapsulated. This review discusses the formation and characterization of the starch-guest IC and focuses on the recent developments in the use of starch ICs for the encapsulation and controlled release of bioactive guest compounds. A great number of guest compounds, such as lipids, aroma compounds, pharmaceuticals, and phytochemicals, were studied for their ability to be complexed with starch and/or amylose and some of the formed ICs were evaluated for the chemical stability improvement and the guest release regulation. Starch-guest ICs has a great potential to be a delivery system, as most existing studies demonstrated the enhancement on guest retention and the possibility of controlled release.

Comprehensive Characterisation of the Ketoprofen-β-Cyclodextrin Inclusion Complex Using X-ray Techniques and NMR Spectroscopy

Racemic ketoprofen (KP) and β-cyclodextrin (β-CD) powder samples from co-precipitation (1), evaporation (2), and heating-under-reflux (3) were analysed using X-ray techniques and nuclear magnetic resonance (NMR) spectroscopy. On the basis of NMR studies carried out in an aqueous solution, it was found that in the samples obtained by methods 1 and 2, there were large excesses of β-CD in relation to KP, 10 and 75 times, respectively, while the sample obtained by method 3 contained equimolar amounts of β-CD and KP. NMR results indicated that KP/β-CD inclusion complexes were formed and the estimated binding constants were approximately 2400 M^-1, showing that KP is quite strongly associated with β-CD. On the other hand, the X-ray single-crystal technique in the solid state revealed that the (S)-KP/β-CD inclusion complex with a stoichiometry of 2:2 was obtained as a result of heating-under-reflux, for which the crystal and molecular structure were examined. Among the methods used for the preparation of the KP/β-CD complex, only method 3 is suitable.

The study of chiral recognition on ibuprofen enantiomers by a fluorescent probe based on β-cyclodextrin modified ZnS:Mn quantum dots

In this paper, a fluorescence method for chiral detection of ibuprofen and its enantiomer was developed. The L-cystenine-capped ZnS:Mn quantum dots were synthesized and functionalized with β-cyclodextrin (β-CD-QDs). The β-CD-QDs exhibited different quenching effect to the S-(+)-ibuprofen and the R-(-)-ibuprofen based on the advantage of the inclusion complex of cyclodextrin. It was found that the quenching of β-CD-QDs by S-(+)-ibuprofen was due to the formation of inclusion complex through both static quenching and photoinduced electron transfer, but only slight quenching with the R-(-)-ibuprofen. The stability constants derived from Hildebrand-Benesi method and absorption titration experiments were applied to determine the stability constants of the formed complexes, the double reciprocal plots suggest that a conclusion complex with a ratio of 1:1 was formed between β-CD-QDs and S-(+)-ibuprofen, but did not with the R-(-)-ibuprofen. The fluorescence intensity of the β-CD-QDs was linearly dependent on the concentration of the S-(+)-IBP in the range of 0-0.5 nmol/L with an limit of detection of 0.29 nmol/L.