Presence Of Α-cyclodextrin Research Articles

Microbial 1,2-dehydrogenation of 6 Alpha-Methylhydrocortisone 11-trifluoroacetate

Transformation of 11-trifluoroacetate 6α-methylhydrocortisone (11-TFA MHC) by cells of actinobacteria Arthrobacter (Nocardioides) was carried out in the presence of α-cyclodextrin (α-CD). The composition and dynamics of the transformation products accumulation in the culture medium at various pH values and the ratio of α-CD/substrate were studied. It was shown that the addition of α-CD to the transformation medium at pH less than 7 promotes an increase in the rate of 1,2-dehydrogenation with the formation of 6 α-methylprednisolone 11-trifluoroacetate (11-TFA MPL). At pH over 7, the primary process is the hydrolysis of the 11β-trifluoroacetyloxy group. In this case, the participation of α-CD in these processes as an acceptor of the trifluoroacetyl ion is not excluded.

High Interfacial Viscoelasticity of Aqueous Mixed Dodecyltrimethylammonium Bromide-Sodium Dodecyl Sulfate Surfactants Forming Inclusion Complexes with α-Cyclodextrin.

Mixtures of anionic-cationic surfactants have shown high synergistic effects in the bulk solution and at the liquid/air interface. These studies have been limited to a reduced concentration range, where there is no formation of aggregates or precipitates. The addition of host molecules, such as cyclodextrins, to these systems reduces the effects of precipitation by forming inclusion complexes and also modifies the values of other surfactant properties, like the Krafft temperature and the critical aggregation concentration (CAC). We studied the interfacial synergistic effects promoted by electrostatic interactions, using the Rosen model to calculate an interaction parameter for mixtures of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in the presence of α-cyclodextrin (αCD), in aqueous solutions. We measured the CAC of SDS-DTAB-αCD mixtures using a pendant drop tensiometer, with the αCD concentration fixed at 10 mM and at 283.15 K. We performed rheological measurements on the mixtures where the surfactant total concentration is fixed below the measured CAC, varying the αCD concentration and temperature. We found that the dilatational modulus shows a clear correlation with the interaction parameter. It appears that the attractive interactions within the film are those due to the inclusion complexes formed by two αCD and one surfactant molecule, which according to the previous studies, is the dominant species in both the bulk and liquid/air interface. The synergistic effect observed here for SDS-DTAB surfactant mixtures with αCD can be applied to systems and processes (drop emission, drug delivery methods, stabilization of viral capsids and bacterial membranes, and emulsification) where interfacial processes require specific viscoelastic properties.

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.

Supramolecular Control over the Interparticle Distance in Gold Nanoparticle Arrays by Cyclodextrin Polyrotaxanes.

Amphiphilic nonionic ligands, synthesized with a fixed hydrophobic moiety formed by a thiolated alkyl chain and an aromatic ring, and with a hydrophilic tail composed of a variable number of oxyethylene units, were used to functionalize spherical gold nanoparticles (AuNPs) in water. Steady-state and time-resolved fluorescence measurements of the AuNPs in the presence of α-cyclodextrin (α-CD) revealed the formation of supramolecular complexes between the ligand and macrocycle at the surface of the nanocrystals. The addition of α-CD induced the formation of inclusion complexes with a high apparent binding constant that decreased with the increasing oxyethylene chain length. The formation of polyrotaxanes at the surface of AuNPs, in which many α-CDs are trapped as hosts on the long and linear ligands, was demonstrated by the formation of large and homogeneous arrays of self-assembled AuNPs with hexagonal close packing, where the interparticle distance increased with the length of the oxyethylene chain. The estimated number of α-CDs per polyrotaxane suggests a high rigidization of the ligand upon complexation, allowing for nearly perfect control of the interparticle distance in the arrays. This degree of supramolecular control was extended to arrays formed by AuNPs stabilized with polyethylene glycol and even to binary arrays. Electromagnetic simulations showed that the enhancement and distribution of the electric field can be finely controlled in these plasmonic arrays.

Development of Lignin Supramolecular Hydrogels with Mechanically Responsive and Self-Healing Properties

The development of functional polymers from renewable lignin is attractive due to the depletion of fossil fuel and increasing environmental usage. A series of poly(ethylene glycol) methyl ether methacrylate (PEGMA)-grafted lignin hyperbranched copolymers were prepared by atom transfer radical polymerization (ATRP). The chemical structures, molecular characteristic and thermal properties of these copolymers were evaluated and such copolymers were prepared in a range of molecular weights from 38.7 to 65.0 kDa by adjusting the PEGMA-to-lignin weight ratio. As a result from their hyperbranch architecture, their aqueous solutions were found to form supramolecular hydrogels with a very low critical gelation concentration of 1 wt % copolymers, in the presence of α-cyclodextrin (α-CD). The rheological properties of the supramolecular assemblies were investigated and these hydrogel systems showed tunable mechanical response and excellent self-healing capability. Combined with good biocompatibility, these new types...

Shape Memory Hydrogel based on a Hydrophobically-Modified Polyacrylamide (HMPAM)/α-CD Mixture via a Host-Guest Approach.

A novel thermally sensitive shape memory (SM) hydrogel is prepared by block copoly-merization of a cationic surfactant monomer, dimethylhexadecyl[2-(dimethylamino)ethylmethacrylate]ammoniumbromide (C(16)DMAEMA), and acrylamide (AM) in the presence of α-cyclodextrin (α-CD) using N,N'-methylenebisacrylamide (MBA) as a crosslinker. XRD, solid state (13)C NMR, and DSC measurements show that the crystalline domains, induced by the hydrogen bonds between α-CDs threaded on the hydrophobic units of the polymer chains through the host-guest approach, can reversibly melt and crystallize at different temperatures. Rheological measurements show that both the elastic modulus G' and viscous modulus G'' drastically change due to the formation and dissolution of the crystalline domains. These thermo-sensitive crystalline domains serve as reversible physical crosslinks, endowing the hydrogel with excellent SM properties. Cyclic experiments show that the hydrogel can recover to almost 100% of the deformation in each cycle and can be reused several times.

Complexation of alkyl glycosides with α-cyclodextrin can have drastically different effects on their conversion by glycoside hydrolases

Substrates present in aggregated forms, such as micelles, are often poorly converted by enzymes. Alkyl glycosides constitute typical examples and the critical micelle concentration (CMC) decreases with increasing length of the alkyl group. In this study, possibilities to hydrolyse alkyl glycosides by glycoside hydrolases were explored, and α-cyclodextrin was used as an agent to form inclusion complexes with the alkyl glycosides, thereby preventing micelle formation. The cyclodextrin complexes were accepted as substrates by the enzymes to variable extent. The β-glucosidases originating from Thermotoga neapolitana (Tn Bgl3B) and from almond were not at all able to hydrolyse alkyl β-glucosides in the presence of 100mM α-cyclodextrin. However, Aspergillus niger amyloglucosidase readily accepted the complexes as substrates. In reactions involving decyl and dodecyl maltosides, the presence of 100mM α-cyclodextrin caused an increase in reaction rate in most cases, especially at high substrate concentrations. Surprisingly, the amyloglucosidase-catalyzed hydrolysis of octyl-β-maltoside to glucose and β-octylglucoside was faster in the presence of α-cyclodextrin than without, even at substrate concentrations below CMC. A possible explanation of the observed rate enhancement is that binding sites on the carbohydrate binding domain of amyloglucosidase, known to bind cyclodextrins, help to guide the alkyl glycoside-cyclodextrin complex to the active site, and thereby promote its conversion.

Self-healing hybrid nanocomposite coatings with encapsulated organic corrosion inhibitors

To improve the protective properties of sol–gel-derived hybrid coatings against corrosion, encapsulated corrosion inhibitors (2-mercaptobenzothiazole (MBT) and 2-mercaptobenzimidazole (MBI)) were incorporated into hybrid coatings in the presence of α-cyclodextrin (α-CD). The encapsulation of corrosion inhibitors occurs through the formation of an inclusion complex between α-CD and corrosion inhibitors, which become active in corrosive electrolytes and can slowly diffuse out of the host material to ensure continuous delivery of the inhibitors to corrosion sites and long-term corrosion protection. Structural characterization of the hybrid coatings was performed using EIS, SEM coupled with EDX, and FTIR.

Lifting of the [formula omitted] surface reconstruction of Au(1 1 1) as a sensitive probe to monitor adsorption of cyclodextrin and its complexes in halide solutions

Stabilization of the (3×22) reconstruction of Au(111) in halide solutions by adsorbed, uncharged organic molecules was investigated using cyclic voltammetry. In aqueous solutions containing either iodide, bromide, or chloride, the presence of α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), or a ferrocene inclusion complex of the latter (Fc·β-CD) was found to shift the potential of the (3×22) to (1×1) transition positive by several tens of mV. This shift is explained by the inhibition of halide adsorption due to the need to displace adsorbed cyclodextrin species. The size of the shift follows the trend in the strength of interaction between the three halides and the Au surface. Changes to the CV shapes suggest an influence of the cyclodextrins on both the thermodynamics and kinetics of the reconstruction lifting event. Differences observed in CVs recorded with the three cyclodextrin adsorbates also demonstrate the utility of the potential dependent surface reconstruction processes of Au(111) as a probe of adsorbed species. Each halide/cyclodextrin combination was further examined by perturbing the electrode surface with potential cycling and subsequently recording CVs to monitor the recovery of the surface to an equilibrium state.

Geminal Imidazolium Salts: A New Class of Gelators

The gelling behavior of some geminal diimidazolium salts was investigated in solvents differing in polarity and hydrogen bond donor ability. The used salts, namely the 3,3'-di-n-decyl-1,1'(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(decim)(2)][Br](2) (1), the 3,3'-di-n-dodecyl-1,1'(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(dodecim)(2)][Br](2) (2), and the 3,3'-di-n-dodecyl-1,1'(1,4-phenylenedimethylene)diimidazolium ditetrafluoroborate [p-Xyl-(dodecim)(2)][BF(4)](2) (3), differ in the alkyl chain length and in the anion properties, such as size, shape, and coordination ability. In all cases in which gelation process was observed, the obtained gels were characterized by gel melting temperature determination, resonance light scattering, and UV-vis measurements. On the whole, the investigation allowed to get information about both the thermodynamic stability and the features of the aggregates characterizing the soft materials at the equilibrium. Data collected by us point out that the used organic salts are able to behave as both hydro- and organogelators. In particular, bromide salts formed hydrogels in the presence of α-cyclodextrin allowing to hypothesize that the gelation process is favored by the formation of supramolecular assemblies. To verify this hypothesis, 1D and 2D (1)H NMR measurements were carried out. Both the alkyl chain length and the anion ability to reticulate the three-dimensional network proved to be determinant factors in affecting the gelation process as well as the features of the gel phases. Finally, with the future aim to use the obtained gels as reaction media, the effect of a guest molecule such as the UV-vis active probe Nile Red was studied.

Cyclodextrin induced switch between heterolytic and homolytic dediazoniation mechanisms

We have investigated the kinetics and mechanism of dediazoniation of 4-nitrobenzenediazonium (4NBD) tetrafluoroborate in the presence of α-cyclodextrin, α-CD, and γ-cyclodextrin, γ-CD, under acidic (HCl, pH=2) conditions by employing a combination of spectrometric and chromatographic techniques. In the absence of CDs, dediazoniation follows first-order kinetics, with t1/2=22,000s at T=60°C, but addition of small amounts of either α-CD or γ-CD leads to more rapid but not first-order kinetics with t1/2∼400s when [α-CD]=20 [4NBD] or [γ-CD]=15 [4NBD]. Analyses of reaction mixtures by HPLC indicate that three main dediazoniation products are formed depending on the particular experimental conditions. These are 4-nitrophenol, ArOH, nitrobenzene, ArH, and 4-nitrochlorobenzene, ArCl. In the absence of CDs, the main dediazoniation product is the substitution product ArOH, but on increasing the concentration of CD, the reduction product ArH becomes predominant at the expense of ArOH, indicating that a switch between the heterolytic and homolytic reaction mechanisms take place under acidic conditions, where little significant ionization of the OH groups of the CDs takes place (pKa≈12). Addition of the surfactant sodium dodecylsulfate, SDS, blocks the CD cavity inhibiting 4NBD dediazoniation and decreasing the yields of ArH with a concomitant increase in that of ArOH, suggesting that 4NBD ions form an inclusion complex prior to reacting with the OH groups of the CDs. This O-coupling reaction leads to the formation of a highly unstable Z-diazo ether adduct that cannot isomerize to the much more stable E-isomer because of the geometric restrictions imposed by the CD cavity, splitting homolitically.

Spectrofluorimetry in organized media coupled to second-order multivariate calibration for the determination of galantamine in the presence of uncalibrated interferences

The present article describes the spectrofluorimetric determination of galantamine, a widely used acetylcholinesterase inhibitor, through excitation–emission fluorescence matrices and second-order calibration. With the purpose of enhancing the fluorescence intensity of this substance, the effect of different organized assemblies was evaluated. Although the interaction of galantamine with different cyclodextrins is weak, it was corroborated that the fluorescence intensity of this pharmaceutical in the presence of α-cyclodextrin is increased by a twofold factor. Among the studied micellar media, the anionic surfactant sodium dodecyl sulfate produced the largest signals for the compound of interest (sixfold enhancement), and was selected as auxiliary reagent for the subsequent determinations. The developed approach enabled the determination of galantamine at the ng mL −1 level without the necessity of applying separation steps, and in the presence of uncalibrated interferences. The applied second-order chemometric tools were parallel factor analysis (PARAFAC), unfolded partial least-squares coupled to residual bilinearization (U-PLS/RBL), and multidimensional partial least-squares coupled to residual bilinearization (N-PLS/RBL). The ability of U-PLS/RBL to successfully overcome spectral interference problems is demonstrated. The quality of the proposed method was established with the determination of galantamine in both artificial and natural water samples.

Colorimetric sensing of Cu 2+ using a cyclodextrin–dye rotaxane

A dye rotaxane having 8-hydroxyquinoline as coupling component was prepared in the presence of α-cyclodextrin and its structure identified using NMR. The dye rotaxane displayed high color strength regardless of the solvent used and responded to changes in pH based on tautomeric equilibrium, without any interference by the cyclodextrin macrocycle. Compared to the non-rotaxanated forms, the dye rotaxane displayed a characteristic spectral response to the presence of Cu 2+ which was attributed to the formation of a polymeric, metal–dye rotaxane complex which was of high solubility because of the presence of cyclodextrin. Thus, this approach can clearly be used as a facile and efficient sensor for copper ions.

Synthesis of micromulti-prisms polypyrrole boxes in the presence of α-cyclodextrin

Polypyrrole (PPy) boxes with micromulti-prisms have been synthesized in aqueous solution via a self-assembled method using α-cyclodextrin (α-CD) as a dopant and FeCl 3 as an oxidant. The morphology and the micro-structure of the as-synthesized PPy boxes were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier-transform infrared (FTIR) spectrum. The formation mechanism of the PPy boxes structure was also discussed. And the congregated structure of dissociative pyrrole monomers with the inclusion complexes (between α-CD and pyrrole monomer) was proposed to play a significant role in forming the multi-prisms sectional PPy-CD boxes.

Activity Coefficient Studies in Ternary Aqueous Solutions at 298.15 K: H2O + α-Cyclodextrin + Potassium Acetate and H2O + 18-Crown-6 + Hydroquinone Systems

Activity coefficients of the components in aqueous ternary solutions containing a fixed concentration of α-cyclodextrin and 18-crown-6 at various concentrations of the third solutes potassium acetate and hydroquinone, respectively (concentration range (0.0 to 0.20) mol·kg−1), at 298.15 K were derived from vapor pressure osmometry. Also, data for the osmotic coefficients and activity coefficients for aqueous binary solutions of potassium acetate are obtained and used along with the data for aqueous binary hydroquinone solutions reported earlier to analyze the data of the ternary mixtures. It is observed that there is a lowering of activity coefficients of potassium acetate as well as of hydroquinone in the presence of α-cyclodextrin and 18-crown-6, respectively, which is being attributed to incorporation of the acetate ion and hydroquinone into the α-cyclodextrin and 18-crown-6 cavities, respectively, to form 1:1 inclusion complexes in the solution phase. The salting-in and thermodynamic equilibrium consta...

Influence of Cyclodextrin in the Synthesis of Magnetite

ABSTRACTCyclodextrin (CD) has been studied intensively due to its ability to form inclusion complexes with a variety of guest molecules in the solid state. A few studies have paid attention to the use of CD to facilitate the synthesis of inorganic nanoparticles. In this work the synthesis of magnetite (M) is made in the presence of CD. The particle size of the inorganic material is controlled by the presence of CD, in which spherical particles of few nanometers are grown. The synthesis of Fe3O4 (M) in the presence of α-cyclodextrin (α-CD) and β-cyclodextrin (βCD) is described. The formation of an M-CD complex is studied in both cases by Fourier transform infrared spectroscopy (FT-IR) in order to elucidate the chemical bonding of the complex. The morphology and size of the particles are determined by Field Emission Scanning Electron Microscopy (FESEM) and software. X-ray diffraction (XRD) is used to confirm the formation of magnetite.

Activity Coefficient Studies in Ternary Aqueous Solutions at 298.15 K: H2O + α-Cyclodextrin + Potassium Acetate and H2O + 18-Crown-6 + Hydroquinone Systems

Activity coefficients of the components in aqueous ternary solutions containing a fixed concentration of α-cyclodextrin and 18-crown-6 at various concentrations of the third solutes potassium acetate and hydroquinone, respectively (concentration range (0.0 to 0.20) mol·kg−1), at 298.15 K were derived from vapor pressure osmometry. Also, data for the osmotic coefficients and activity coefficients for aqueous binary solutions of potassium acetate are obtained and used along with the data for aqueous binary hydroquinone solutions reported earlier to analyze the data of the ternary mixtures. It is observed that there is a lowering of activity coefficients of potassium acetate as well as of hydroquinone in the presence of α-cyclodextrin and 18-crown-6, respectively, which is being attributed to incorporation of the acetate ion and hydroquinone into the α-cyclodextrin and 18-crown-6 cavities, respectively, to form 1:1 inclusion complexes in the solution phase. The salting-in and thermodynamic equilibrium constant values have been determined using calculated transfer free energies and the method based on application of the McMillan−Mayer virial coefficient theory for solutions. It is noted that the complexation process is assisted by hydrophobic interaction between the complexed species. The apparent molar volume and calculation of virial coefficient for potassium acetate in binary aqueous solutions at 298.15 K are also reported and discussed.

Multiple Equilibria in the Complexation of Dibenzylimidazolium Bromide Salts by Cyclodextrins: Toward Controlled Self-Assembly

In aqueous solution, dibenzylimidazolium bromide salts form dimeric assemblies by T-stacking between an acidic proton of the imidazolium and the benzyl aromatic ring of another cation. This dimeric association can be disturbed by the addition of native cyclodextrins. The control of the majority species in solution can be made by the judicious choice of cyclodextrin concentration and its macrocycle size. The dimer is complexed directly by beta-cyclodextrin, whereas in the presence of alpha-cyclodextrin, the dimer is dissociated to form a 1:1 inclusion complex; at higher concentration, this 1:1 complex can dimerize.

Micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide, dodecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride in the presence of α-, β-, HP β- and γ-cyclodextrins

Conductivity, static fluorescence and 1H NMR measurements have been carried out to study the micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide (DDAB), dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TDAC) in absence and presence of α-cyclodextrin ( α-CD), β-cyclodextrin ( β-CD), hydroxypropyl- β-cyclodextrin (HP β-CD) and γ-cyclodextrin ( γ-CD). The conductivity measurements were carried out at 298.15 K. The influence of cyclodextrins on the micellar parameters, such as cmc ∗ (apparent critical micellar concentration), β (degree of ionization) have been analyzed. Thermodynamics of the systems was discussed in terms of the change in standard free energy of micellization, Δ G m 0 . Micellization was found to be less spontaneous in presence of cyclodextrins. The fluorescence intensity of the surfactant solutions is enhanced by the addition of cyclodextrins. The association constants obtained from conductivity and fluorescence data suggest the binding of γ-CD with the surfactants to be strongest among all the cyclodextrins used. 1H NMR chemical shift changes provide powerful means for probing the cyclodextrin–micellar interactions and inclusion of surfactant is shown by the change in the chemical shift of some of the guest and host protons in comparison with the chemical shifts of the same protons in the free compounds.

Enzyme-Responsive Snap-Top Covered Silica Nanocontainers

Mesoporous silica nanoparticles, capable of storing a payload of small molecules and releasing it following specific catalytic activation by an esterase, have been designed and fabricated. The storage and release of the payload is controlled by the presence of [2]rotaxanes, which consist of tri(ethylene glycol) chains threaded by α-cyclodextrin tori, located on the surfaces of the nanoparticles and terminated by a large stoppering group. These modified silica nanoparticles are capable of encapsulating guest molecules when the [2]rotaxanes are present. The bulky stoppers, which serve to hold the tori in place, are stable under physiological conditions but are cleaved by the catalytic action of an enzyme, causing dethreading of the tori and release of the guest molecules from the pores of the nanoparticles. These snap-top covered silica nanocontainers (SCSNs) are prepared by a modular synthetic method, in which the stoppering unit, incorporated in the final step of the synthesis, may be changed at will to target the response of the system to any of a number of hydrolytic enzymes. Here, the design, synthesis, and operation of model SCSNs that open in the presence of porcine liver esterase (PLE) are reported. The empty pores of the silica nanoparticles were loaded with luminescent dye molecules (rhodamine B), and stoppering units that incorporate adamantyl ester moieties were then attached in the presence of α-cyclodextrin using the copper-catalyzed azide−alkyne cycloaddition (CuAAC), closing the SCSNs. The release of rhodamine-B from the pores of the SCSN, following PLE-mediated hydrolysis of the stoppers, was monitored using fluorescence spectroscopy.