Polyelectrolyte microcapsules containing molecules of sulfated β-cyclodextrin in the structure of nanosized shell

Alternate adsorption of the molecules of poly(allylamine hydrochloride) (PAA) and sulfated β-cyclodextrin (sulfo-β-CD) is studied by piezoelectric microweighing upon the formation of coatings of nanosized thicknesses by the polyionic assembly procedure. The thickness of planar coatings on the surface of single-crystalline silicon is determined by ellipsometry. The layer-by-layer character of the formation of planar nanosized coating is revealed and assumptions about the structure of the PAA and sulfo-β-CD bilayers are stated. A comparison of the spherical microparticles of polystyrene, as well as manganese and calcium carbonates, demonstrated that it is feasible to use microparticles of calcium carbonate as a template for producing microcapsules. Microcapsules with shells containing five (PAA/sulfo-β-CD) layers are prepared and studied by confocal fluorescent microscopy.     

Inclusion of the Antidepressant Paroxetine in β-cyclodextrin

The X-ray structure and thermal stability of a -cyclodextrin inclusion complex of the antidepressant paroxetine [(3S-trans)-3-[(1,3-benzodioxol-5-yloxy)methyl]-4-(4-fluorophenyl)piperidine], with the formula ( -cyclodextrin)₂...paroxetine...28H₂O, are reported. On heating, the crystals dehydrate in two stages and begin to decompose from approximately 270 °C. An X-ray diffraction study at 173K showed that the complex crystallizes in the monoclinic system, space group P2₁ with a = 15.2262(3), b = 31.4771(1), c = 15.6739(1) Å, = 104.320(1)° and Z = 2 formula units. Refinement on F² converged at R1 = 0.066, wR₂ = 0.182 (21478 reflections). On encapsulation within a head-to-head -cyclodextrin dimer, the paroxetine molecule adopts an unusual `hairpin' conformation, stabilised by intramolecular ... interaction between the phenyl rings. The guest piperidine ring is located at the primary face of one host molecule of the dimer while the fluorophenyl and benzodioxole moieties respectively occupy the dimer interfacial region and the cavity of the second host molecule. Experimental and computed X-ray powder diffraction patterns for the complex are also reported. The mode of stacking of the dimeric complex units is shown to be one of at least three distinct variants which can be identified for -cyclodextrin complexes with similar unit cell dimensions and crystallizing in the same space group.     

The features of the synthesis and chemical behavior of some β-cyclodextrin silyl derivatives

Conditions are found for the regioselective silylation of the β-cyclodextrin primary hydroxy groups by diphenylmethylsilyl chloride and trimethylsilyl chloride. It is shown that the position of silyl substituents at the primary or secondary hydroxyl can be determined using ²⁹Si NMR spectroscopy. In the case of acetic and phosphorous acid chlorides, the subsequent functionalization of the secondary hydroxyls occurs with a significant removal of the protective silyl groups.     

Kinetics of peroxidase-catalyzed oxidation of quercetin in the presence of β-cyclodextrin

It is established that the rate of peroxidase-catalyzed oxidation of flavonoid quercetin is increased by 20% in the presence of macrocyclic complexing agent β-cyclodextrin. The comparison of the kinetic parameters of the indicated reaction in the presence and in the absence of β-cyclodextrin shows that its introduction does not significantly influence the specificity of the enzyme with respect to the reducing substrate (characterized as k _cat/K _M ratio), while the increase in the reaction rate does not depend on the duration of the incubation of quercetin with β-cyclodextrin. It is assumed that the increase of the reaction rate is associated with nonspecific interaction between β-cyclodextrin and quercetin oxidation product.     

Inclusion of the allicin mimic S-p-tolyl t-butylthiosulphinate in β-cyclodextrin

Allicin, the active thiosulphinate present in freshly crushed garlic, has potent antimicrobial activity but is chemically labile. As part of a study aimed at producing stable allicin analogues as potential antimicrobial agents, the allicin mimic S-p-tolyl t-butylthiosulphinate was synthesised and complexed with β-cyclodextrin (β-CD). The inclusion complex, β-CD·S-p-tolyl t-butylthiosulphinate·12.5H₂O, was characterised by thermal analysis techniques (HSM, TG, DSC), powder X-ray diffraction and single-crystal X-ray diffraction. The inclusion complex is dimeric (space group C222₁) with the guest disordered over three positions. Within each β-CD molecule of the dimer, each disordered guest component is located in the host cavity with the t-butyl group protruding slightly from the primary hydroxyl side, while the phenyl ring is situated near the secondary hydroxyl side and the thiosulphinate moiety is centrally located within the host cavity. Stereoselectivity of guest inclusion is implicit in the disordered model, which reflects a 2:1 ratio of S- and R-enantiomers in the β-CD cavity.     

Synthesis of SAPO-34 using metakaolin in the presence of β-cyclodextrin

SAPO-34 molecular sieves were synthesized by the addition of β-cyclodextrin(β-CD) as crystal growth inhibitor using metakaolin as silicon and aluminum sources. Properties of the obtained samples were characterized by XRD,SEM,N2adsorption–desorption,FTIR,XRF,EDX,NH293-TPD andSi MAS NMR. When β-CD was added,crystal size of the SAPO-34 crystals decreased. Variation of Si content from the crystal center to surface decreased while total Si content hardly changed.29 Si MAS NMR results showed that β-CD contributed to better Si dispersion and decreased the size of Si(4Si) patches. Moreover,the MTO(methanol-to-olefin) process was conducted to investigate the influence of β-CD on catalytic performance. The synthesized sample with molar ratio of β-CD/Al2O3 equaling 0.055 remained active for 610 min while the sample synthesized without β-CD for only 280 min,which indicates that the lifetime of catalyst synthesized with β-CD is greatly prolonged.     

Spectrofluorimetric study and determination of desipramine in the presence of β-cyclodextrin

The native fluorescence intensity of desipramine was enhanced in the presence of β-cyclodextrin in aqueous solution. The inclusion complex formation between these compounds was studied by spectrofluorimetry. A stable complex with a 2: 1 stoichiometry of β-cyclodextrin to desipramine was formed (logβ₂ = 9.29 ± 0.01). In the presence of an optimum concentration of β-cyclodextrin, the fluorescence intensity was linearly proportional to desipramine concentration in the range of 0.1–100 μg/mL (7.2 × 10^?7?1.0 × 10^?4 M) with a limit of detection of 7 × 10^?8 M. The method was successfully applied to the detection of desipramine in its tablets.     

Effects of inclusion of cetirizine hydrochloride in β-cyclodextrin

Following the preparation of inclusion complex of cetirizine (CTZ) and β-cyclodextrin (β-CD), the compound was investigated to assess the possibility of modifying the physicochemical properties (solubility, release, stability, permeability) of CTZ after complexation that are vital for subsequent formulation studies involving the said complex. Changes in FT-IR/Raman spectra, DSC thermograms and XRD diffractograms confirmed the formation of a CTZ–β-CD system. Hydrophilic interaction chromatography with a DAD detector was employed to determine alterations of the CTZ concentration during studies following complexation. An analysis of a phase-solubility diagram of c_CTZ?=?fc_β-CD indicated a linear rise in the solubility of CTZ as the concentration of β-CD increased. The inclusion of CTZ in a system with β-CD significantly reduced the instability of CTZ in the presence of oxidizing factors. It was also found that regardless of the pH of the acceptor fluids used in the release studies an increase was observed in the concentration of CTZ in CD system compared to its free form. The ability to permeate artificial biological membranes manifested by CTZ after complexation was enhanced as well. In summary, CD has significant potential to mask the bitter taste of CTZ and to counter the instability induced by oxidizing factors.     

Electrochemical determination of acetaminophen at a carbon electrode modified in the presence of β-cyclodextrin: role of the activated glassy carbon and the electropolymerised β-cyclodextrin

Acetaminophen is a well-known drug commonly used to provide pain relief, but it can also lead to acute liver failure at high concentrations. Therefore, there is considerable interest in monitoring its concentrations. Sensitive and selective acetaminophen electrochemical sensors were designed by cycling a glassy carbon electrode (GCE) to high potentials in the presence of β-CD in a phosphate electrolyte, or by simply activating the GCE electrode in the phosphate solution. Using cyclic voltammetry, adsorption-like voltammograms were recorded. The acetaminophen oxidation product, N-acetyl benzoquinone imine, was protected from hydrolysis, and this was attributed to the adsorption of acetaminophen at the modified GCE. The rate constants for the oxidation of acetaminophen were estimated as 4.3 × 10^–3 cm² s^–1 and 3.4 × 10^–3 cm² s^–1 for the β-CD-modified and -activated electrodes, respectively. Using differential pulse voltammetry, the limit of detection was calculated as 9.7 × 10^–8 M with a linear concentration range extending from 0.1 to 80 μM. Furthermore, good selectivity was achieved in the presence of caffeine, ascorbic acid and aspirin, enabling the determination of acetaminophen in a commercial tablet. Similar electrochemical data were obtained for both the β-CD-modified and activated GCE surfaces, suggesting that the enhanced detection of acetaminophen is connected mainly to the activation and oxidation of the GCE. Using SEM, EDX and FTIR, no evidence was obtained to indicate that the β-CD was electropolymerised at the GCE.

     

Novel and efficient supramolecular synthesis of pyrroles in the presence of β-cyclodextrin in water

A simple and efficient synthesis of highly substituted pyrroles was achieved in water medium via multi-component strategy, using amine,DMAD/DEAD as well as phenacyl bromide catalyzed by β-CD.Utilizing this protocol various pyrrole derivatives were synthesized in good to excellent yields.     

Peculiarities of phosphorescence of complexes between aromatic molecules and β-cyclodextrin at room temperature

Luminescence of complexes between -cyclodextrin and phenanthrene, fluorene, or naphthalene-d₈ in aqueous solutions was studied at room temperature. It is found that the addition of acetone, in the absence of heavy atoms, results in the phosphorescence of these complexes at 293 K due to triplet-triplet energy transfer. The conclusion is drawn that a heavy atom is necessary for population of a triplet level, because the intersystem crossing of an aromatic molecule in the cyclodextrin cavity is suppressed due to restriction of vibration-relaxation interactions with a medium. The phosphorescence multiply increases when lightscattering polycomplexes between an aromatic molecule and cyclodextrin in the presence of a heavy atom and a sensitizer are formed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1966–1969, October, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-O9961).     

Inclusion of Paracetamol into β-cyclodextrin nanocavities in solution and in the solid state

We report on steady-state UV-visible absorption and emission characteristics of Paracetamol, drug used as antipyretic agent, in water and within cyclodextrins (CDs): β-CD, 2-hydroxypropyl-β-CD (HP-β-CD) and 2,6-dimethyl-β-CD (Me-β-CD). The results reveal that Paracetamol forms a 1:1 inclusion complex with CD. Upon encapsulation, the emission intensity enhances, indicating a confinement effect of the nanocages on the photophysical behavior of the drug. Due to its methyl groups, the Me-β-CD shows the largest effect for the drug. The observed binding constant showing the following trend: Me-β-CD>HP-β-CD>β-CD. The less complexing effectiveness of HP-β-CD is due to the steric effect of the hydroxypropyl-substituents, which can hamper the inclusion of the guest molecules. The solid state inclusion complex was prepared by co-precipitation method and its characterization was investigated by Fourier transform infrared spectroscopy, 1H NMR and X-ray diffractometry. These approaches indicated that Paracetamol was able to form an inclusion complex with CDs, and the inclusion compounds exhibited different spectroscopic features and properties from Paracetamol.     

Selective monoallylation of β-cyclodextrin

Reaction of β-cyclodextrin with allyl bromide in dimethyl sulfoxide affords 2-О-allyl-β-cyclodextrin, while in dimethylformamide 6-О-allyl-β-cyclodextrin is formed. Optimal conditions of the reaction were found allowing to obtain the target products in quantitative yield.     

Unusual inversion phenomenon of β-cyclodextrin dimers in water

A conformational analysis of three triazole-containing bridged bis-β- cyclodextrins (CD) has been carried out to evaluate their recognition ability. NMR spectroscopy and ITC measurements clearly demonstrate that one of the CD glucopyranose units undergoes a 360° rotation in water so that the spacer linking the two CDs is deeply included into one of the CD cavities. The amplitude of this inversion phenomenon depends on the nature of the spacer and results in a limited accessibility to the CD cavities in line with previous catalytic results.     

Encapsulation of Satureja montana essential oil in β-cyclodextrin

Inclusion complexes between the Satureja montana essential oil and β-cyclodextrin were prepared by co-precipitation method with the four oil to β-cyclodextrin ratios of 5:95, 10:90, 15:85 and 20:80 (w/w) in order to determine the effect of the ratio on the inclusion efficiency of β-cyclodextrin for encapsulating oil volatiles. The characterization of the complex involved the analysis of the initial essential oil, the surface and the total extracted oils. The retention of essential oil volatiles reached a maximum of 93.15 % at the oil to β-cyclodextrin ratio of 15:85. Though, the maximum inclusion efficiency of β-cyclodextrin was achieved at the ratio of 20:80. The qualitative and quantitative composition of the volatiles in the total oil extracts was similar to the starting oil which is confirmed the high inhibition zone as antifungal and high antioxidant properties after encapsulation to β-cyclodextrin. This justifies the use of β-cyclodextrin as complexion agent for S. montana essential oil in the food and pharmaceutical industries.     

Ultrasonic study of the molecular encapsulation and the micellization processes of dodecylethyldimethylammonium bromide-water solutions in the presence of β-cyclodextrin or 2,6-di-o-methyl-β-cyclodextrin

Aqueous solutions of -cyclodextrin (-CD) or 2,6-di-o-methyl--cyclodextrin (DM--CD) and dodecylethyldimethylammonium bromide (D₁₂EDMAB) have been studied from speed of sound (u) data at 298.15 K, using a pulse-echo-overlap technique. The molecular encapsulation process of the surfactant monomer into the cyclodextrin cavity and its effect in the micellization process of the surfactant have been analyzed from theu measurements: I) as a function of [D₁₂EDMAB] in the presence of several initial cyclodextrin concentrations (-CD or.DM--CD); II) as a function of [cyclodextrin] (-CD or DM--CD), for an initial micellar solution of D₁₂EDMAB and; III) as a function of the [cyclodextrin]/[surfactant] stoichiometric concentrations. Both inclusion complexes formed (-CDD₁₂EDMAB) and (DM--CDD₁₂EDMAB) have stoichiometries of 11, and their association constantK have been determined using a model proposed in this work, based on the additivity of the different contributions of the involved species to the speed of sound. The apparent critical micellar concentration, cmc^*, of D₁₂EDMAB is found to increase linearly upon the addition of cyclodextrin (-CD or DM--CD). The free surfactant concentration in the micellar region, [D₁₂EDMAB]_f, decreases in the presence of -CD and slightly increases in the presence of DM--CD. The influence of the parcial methylation of the -cyclodextrin (-CDDM--CD) and of the polar head of the surfactant (D₁₂TAB D₁₂EDMAB) on the complextion and micellar parameters are also discussed.Supplementary material available: Tables of speed of sound (14 pages) are available from the authors.     

Characterization of the inclusion complex of β-cyclodextrin with sorbic acid in the solid state and in aqueous solution

Crystal structure of β-cyclodextrin (β-CD) complexes with sorbic acid, usually as food preservative, has been determined by single-crystal X-ray diffraction at 113 K. The space group of β-cyclodextrin-sorbic acid complex is P1 with unit cell dimensions of a = 15.284(3) Å, b = 15.402(3) Å, c = 17.981(4) Å, α = 99.67(3)°, β = 112.83(3)°, γ = 102.48(3)° and Z = 1. The result indicates that the β-CD molecules form head-to-head dimers which pack in the intermediate mode. Each dimer contains two guest molecules whose methyl groups are located at the dimer interface while the carboxyl groups protrude from the β-CD primary faces. Water molecules (25.5) are distributed outside the cyclodextrin cavity over 31 sites. Furthermore, nuclear magnetic resonance spectroscopy (¹H NMR) has been employed to investigate the inclusion behavior between the host β-CD and guest sorbic acid in aqueous solution. The results obtained enabled us to structurally characterize the β-CD inclusion complex with sorbic acid.     

Room temperature phosphorescence of α-bromonaphthalene induced by β-cyclodextrin in the presence of cyclohexane

β-Cyclodextrin (β-CD) can induce a-bromonaphthalene (BrN) to emit strong room temperature phosphorescence (RTP) in the presence of micro amounts of cyclohexane (c-hexane). Experiments of luminescence spectra, phosphorescence lifetime and fluorescence polarization prove the formation of c-hexane/β-CD/BrN ternary inclusion complex. The apparent formation constant of the ternary inclusion complex was determined and the effect mechanism of c-hexane on the RTP of BrN induced by β-CD is discussed.     

Effects of several inter-molecular interactions on the inclusion between methyl substituted β-cyclodextrin and some linear macromolecule in supercritical carbon dioxide medium

In this work, the inclusion between methyl substitute β-cyclodextrin and some linear macromolecule in supercritical carbon dioxide medium was investigated. The contributions from several factors were studied; such as the hydrogen bonding interaction between the host and guest, the hydrogen bonding interaction between the neighborhood cyclodextrin rims threaded on the polymer chain, and the matching between the host cavity and the size of the polymer axis.