Aqueous Solutions Of Α-cyclodextrin Research Articles

Pseudo-polymorphism of a camphor α-cyclodextrin complex

Crystalline products of vapor diffusion of an alcoholic solution of 1R,4R-camphor into an aqueous solution of α-cyclodextrin were prepared and subjected to X-ray structure analysis. Two different forms were obtained: a dimeric cavity formed by head-to-head association of cyclodextrin (phase A), and a complex set of monomeric cavities (phase B). Both contain camphor molecules orientationally disordered inside cavities. The structures are solvated by mixtures of water and ethanol. The structures significantly differ in chemical stabilities. Whilst phase A is relatively stable with respect to guest desorption, phase B rapidly reacts to change of its chemical environment manifested by cracking of crystals in solution. The phenomenon has been recorded and a short movie is included in the supplementary data.

Dipole-dipole interactions control the interfacial rheological response of cyclodextrin/surfactant solutions.

A recent surface rheological study has shown that aqueous solutions of α-cyclodextrin (αCD) with anionic surfactants (S) display a remarkable viscoelasticity at the liquid/air interface, which has not been observed in similar systems. The dilatational modulus is various orders of magnitude larger than those for the binary mixtures αCD + water and S + water. The rheological response has been qualitatively related to the bulk distribution of species, the 2 : 1 inclusion complexes (αCD2 : S) playing a fundamental role. In this work, we have developed a model that considers dipole-dipole interactions between 2 : 1 inclusion complexes ordered on the liquid/air interface. When the model is applied to the specific experimental conditions, the dependencies on concentration and temperature of the dilatational modulus and the surface tension were found to be in excellent agreement with the data, indicating clearly that dipole-dipole interactions determine and control the rheological behavior of the interface.

Dry Emulsions based on Alpha Cyclodextrin and Vegetable Oils for Buccal Delivery of Lipophilic Drugs

Background: Buccal delivery of drugs can be used as an alternative administration route to conventional oral route avoiding the liver first-pass effect and improving patient compliance. Objective: The goal of this work was to develop dry emulsions for buccal delivery of ketoprofen, used as a lipophilic model drug. The influence of two vegetable oils, olive oil or wheat germ oil, in the presence of α-cyclodextrin and different drying techniques on the dry emulsion properties was evaluated. Methods: Emulsions were prepared by adding olive oil or wheat germ oil to an aqueous solution of α-cyclodextrin and subsequently dried through an oven, freeze-dryer or spray-dryer. Dry emulsions were characterized in terms of yield, encapsulation efficiency, morphology and drug solid-state. In vitro drug release and permeation studies were carried out to evaluate dry emulsion ability to release the drug and to allow its permeation through the esophageal porcine epithelium. Results: The formation of stable and milky emulsion was assured by cyclodextrin ability to interact with oil components obtaining an inclusion complex with amphiphilic property able to act as a surfaceactive agent. The drying process influenced the yield and the encapsulation efficiency, while no significant differences were observed between olive oil and wheat germ oil. Freeze-dried emulsions, selected as the best formulations, resulted in fast release of drug thereby ensuring its permeation across the epithelium. Conclusion: Dry emulsions prepared with a simple and easy method, using natural ingredients and avoiding synthetic surfactants and organic solvents, could be used for buccal delivery of lipophilic drugs.

A visible and controllable porphyrin-poly(ethylene glycol)/α-cyclodextrin hydrogel nanocomposites system for photo response

The real-time controlling and tracking of the evolution and status of the hydrogel are important challenges for accurate and precise assessments. In this article, a visible and controllable hydrogel nanocomposites system for photo response was designed and developed based on a thermosensitive porphyrin-poly(ethylene glycol)/α-cyclodextrin hydrogel loaded with multi-walled carbon nanotubes (PPEG-MWNTs/α-CD). The PPEG-MWNTs/α-CD hydrogel was simply self-assembled with a carbon nanotubes dispersed porphyrin-poly(ethylene glycol) solution and an aqueous solution of α-cyclodextrin by homogeneous stirring. The structure and the optical and photothermal abilities of the hydrogel nanocomposites system were characterized in vitro. Moreover, the controlled disassembly of the hydrogel was monitored in real time by in vivo fluorescence imaging after subcutaneous injection using mice as models. The results demonstrated that the hydrogel disassembly can be efficiently accelerated under laser irradiation with the loading of carbon nanotubes by fluorescence imaging visualization. With the advantages of the photo response, fluorescence imaging tracking and photothermal remote controlling were combined into the hydrogel nanocomposites system.

Pickering emulsions with α-cyclodextrin inclusions: Structure and thermal stability

This paper explores structural, interfacial and thermal properties of two types of Pickering emulsions containing α-cyclodextrin inclusion complexes: on one hand, emulsions were obtained between aqueous solutions of α-cyclodextrin and different oils (fatty acids, olive oil, silicone oil) and on the other hand, emulsions were obtained between these oils, water and micro or nano-platelet suspensions with inclusion complexes of hydrophobically-modified polysaccharides. The emulsions exhibit versatile properties according to the molecular architecture of the oils. Experiments were performed by microcalorimetry, X-ray diffraction and confocal microscopy. The aptitude of oil molecules to be threaded in α-cyclodextrin cavity is a determining parameter in emulsification and thermal stability. The heat flow traces and images showed dissolution, cooperative melting and de-threading of inclusion complexes which take place progressively, ending at high temperatures, close or above 100°C. Another important feature observed in the emulsions with micro-platelets is the partial substitution of the guest molecules occurring at room temperature at the oil/water interfaces without dissolution, possibly by a diffusion mechanism of the oil. Accordingly, the dissolution and the cooperative melting temperatures of the inclusion crystals changed, showing marked differences upon the type of guest molecules. The enthalpies of dissolution of crystals were measured and compared with soluble inclusions.

Inclusional association as studied by the drying dissipative structure. Part 1. Drying patterns of α-, β- and γ-cyclodextrin

Macroscopic and microscopic drying patterns were observed on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous solutions of α-cyclodextrin (αCD), β-cyclodextrin (βCD), and γ-cyclodextrin (γCD), i.e., cone shape oligomers of polysaccharide. For all CD molecules, two kinds of macroscopic patterns, outside and inner broad rings and spoke lines formed. Multi-broad rings were formed for βCD in the inner region of the main broad ring at the outside edge especially at the high concentrations. Cooperative drying processes of the convection, sedimentation, and solidification were clarified. Microscopic drying patterns showing the formation of rod-like and/or sward-like crystals were observed mainly in the direction along the spoke lines. The microscopic patterns of βCD were similar to those of some of polysaccharides and polynucleotides the authors studied previously. α- and γ-cyclodextrins were slightly hygroscopic, and clear-cut drying patterns were not observed.

Molecular Fibers and Wires in Solid-State and Solution Self-Assemblies of Cyclodextrin [2]Rotaxanes

Cyclodextrin [2]rotaxanes have been prepared by coupling dimethylanilines with dicarboxylic acids using DMT-MM, in aqueous solutions of alpha-cyclodextrin, and the example illustrated shows unusual fluorescence emission and other spectroscopic behavior characteristic of the formation of molecular wires in solution, similar to the fibers observed in the solid state.

Effects of pH and Ionic Strength on the Stability of Nanobubbles in Aqueous Solutions of α-Cyclodextrin

Formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules is a spontaneous process. Using a combination of laser light scattering (LLS) and zeta-potential measurements, we investigated the effects of salt concentration and pH on their stability in alpha-cyclodextrin (alpha-CD) aqueous solutions. Our results reveal that the nanobubbles are unstable in solution with a higher ionic strength, just like colloidal particles in an aqueous dispersion, but become more stable in alkaline solutions. The zeta-potential measurement shows that the nanobubbles are negatively charged with an electric double layer, presumably due to adsorption of negative OH- ions at the gas/water interface. It is this double layer that plays a critical dual role in the formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules, namely, it not only provides a repulsive force to prevent interbubble aggregation and coalescence but also reduces the surface tension at the gas/water interface to decrease the internal pressure inside each bubble.

Ultrasonic investigations of inclusion complexation of α-cyclodextrin by iodide ions in pseudo-binary aqueous system

The paper reports study of the complexation processes in aqueous solutions of α-cyclodextrin and iodide ions. The speed and absorption of ultrasonic waves have been measured by the resonance method on a Resoscan™ System apparatus. Density and capacity of the system have been also measured. All measurements have been performed at the constant temperature T = 298.15 K. On the basis of these data, thermodynamical parameters — such as molar volume, molar adiabatic compressibility and their excess functions, have been calculated. To be able to express the concentration of the ternary solution in mole fraction, the initial solutions of the water/α-CD ratio of 550/1 (∼ 0.1 mol/l) and of the water/KI (or water/(KI + 0,77 I 2)) at the same ratio, have been prepared. The composition of molecular complexes formed in the solution has been determined on the basis of the correlation between the extremes of the excess functions and ultrasonic absorption for different compositions of the mixtures. The results obtained have suggested formation of inclusion complexes between α-cyclodextrin and iodide ions of the specific stoichiometric compositions: (α-CD) 2 I 3 −I 2, (α-CD) I 3 −I 2 and (α-CD) 2 I −.

“Pulling” Nanoparticles into Water: Phase Transfer of Oleic Acid Stabilized Monodisperse Nanoparticles into Aqueous Solutions of α-Cyclodextrin

This paper describes a general method to drastically improve the dispersity of oleic acid stabilized nanoparticles in aqueous solutions. We use oleic acid stabilized monodisperse nanoparticles of iron oxides and silver as model systems, and have modified the surface properties of these nanoparticles through the formation of an inclusion complex between surface-bound surfactant molecules and α-cyclodextrin (α-CD). After the modification, the nanoparticles of both iron oxide and Ag can transfer from hydrophobic solvents, such as hexane, to α-CD aqueous phase. The efficiency of the phase transfer to the aqueous solutions depends on the initial α-CD concentration. The α-CD/oleic acid complex stabilized nanoparticles can be stable for long periods of time in aqueous phase under ambient atmospheric conditions. Transmission electron microscopy (TEM), ultraviolet−visible (UV−vis) spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, and colorimetric methods have been used in the characterization of these...

Confinement effects on the photorelaxation of a proton-transfer phototautomer

We report on emission studies of excited phototautomers of 1 ′- hydroxy-2 ′-acetonaphthone in aqueous solutions of α-cyclodextrin (α-CD). Caging by α-CD provokes a ∼40 nm blue shift of the emission, and increases the emission lifetime from 90 ps to 1 ns. The rotational time of the caged phototautomers varies from 50 to 180 ps, while that of global rotational time of 1:2 complex (HAN:(α-CD) 2) is ∼950 ps. These results are explained on the basis of confinement effects on the twisting motion of the formed phototautomers within the cavities provided by one or two CD.

Fabrication and Characterization of Gold Nanoparticles by Femtosecond Laser Ablation in an Aqueous Solution of Cyclodextrins

Gold nanoparticles were produced by femtosecond laser ablation of a gold metal plate in an aqueous solution of α-cyclodextrin (CD), β-CD, or γ-CD. The gold nanoparticles exhibited the UV−vis absorption spectrum with a maximum absorption band at 520 nm, similar to that of gold nanoparticles chemically prepared in a solution. The size distribution of the nanoparticles measured by transmission electron microscopy (TEM) shifted to a drastically smaller size of ∼2−2.4 nm and narrower size distribution of less than 1−1.5 nm fwhm with an increase in the concentration of cyclodextrins. Both the particle size and size distribution were also dependent on the type of cyclodextrins used in aqueous solution. In particular, the gold colloids resulting from ablation in 10 mM β-CD were conspicuously stable under aerobic conditions without any protective agent present. CDs formed an inclusion complex with ablated atoms to reduce the total concentration of embryonic nanoparticles formed in the plume CDs, as evident by Raman spectroscopy. The consecutive particle growth due to the mutual coalescence between nanoclusters and their neighboring free gold atoms was severely limited in the presence of CDs.

Complexation between α-Cyclodextrin and Poly(ethylene oxide) Physically Adsorbed on the Surface of Colloidal Silica

Aqueous solutions of α-cyclodextrin (α-CD), a cyclic oligomer formed by six glucose units, complex spontaneously with poly(ethylene oxide), PEO, and several molecules of α-CD thread onto the host polymer chain. A new nanocomposite has been synthesized by the complexation of PEO physically adsorbed on the surface of colloidal silica with α-CD. The PEO monomers adsorbed on the silica surface were displaced by changing the degree of complexation and the MW of the polymer. As the inclusion of α-CD can only start from the extremity of the PEO chain, the fraction and length of the tails can be studied by changing the number of α-CD molecules threaded. Adsorbed PEO of 1000 molecular weight can be completely included in the cavities of α-CD molecules, resulting in a full displacement of the adsorbed polymer. However, for PEO 6k and 20k, the complexation of the chain is partial, that is, some nonincluded EO units remain adsorbed on the silica surface. In these cases, a gel containing silica was formed in the hydro...

α-Cyclodextrin/Polyethylene Glycol Polyrotaxane: A Study of the Threading Process

Aqueous solutions of α-cyclodextrin (α-CD) and polyethylene glycol (PEG) form interesting complexes, where several α-CD units are penetrated by the linear polymeric PEG chain and produce a so-called “polyrotaxane”. This supramolecular structure is stabilized by strong interactions between the α-CD hydrophobic internal cavity and the −CH2OCH2− moieties of PEG. When cyclodextrins have occupied the whole PEG chain, the polyrotaxanes aggregate and precipitate, forming a thick solid gel. Turbidity measurements at λ = 400 nm were used to study the threading phenomenon. The temperature of the solution and the composition of the solvent affect the formation of polyrotaxanes in a significant way. We propose a molecular model to explain the experimental findings in terms of a multistep threading process. The Gibbs free energy related to the formation of polyrotaxanes is calculated according to the transition state theory.

A new semi-preparative liquid chromatographic optical resolution of ferrocene derivatives by the use of aqueous solution of ?-cyclodextrin as a mobile phase and polyamide as a stationary phase

1-Ferrocenylethanol and its analogues were completely resolved into their enantiomers by liquid chromatography on a polyamide column using an aqueous solution of α-cyclodextrin as a mobile phase.

The Use of an α-Cyclodextrin Mobile Phase in the Thin-Layer Chromatographic Separation of Ortho, Meta, and Para Substituted Phenols

Abstract An aqueous solution of α-cyclodextrin (cyclohexaamylose) is demonstrated to be a very effective mobile phase in thin-layer chromatographic separations. The chromatographic behaviors of twenty-six substituted phenolic and naphtholic compounds using polyamide thin-layer stationary sheets are described. The Rf values were found to be dependent upon both the structural features of the phenolic compounds and the concentration of α-cyclodextrin in the mobile phase. A possible mechanism that accounts for the observed chromatographic behavior is presented. The advantages and disadvantages of the aqueous α-cyclodextrin mobile phase over the traditional pure or mixed organic solvent systems typically employed are discussed.