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PubMed2001

Bridged bis(beta-cyclodextrin)s possessing coordinated metal center(s) and their inclusion complexation behavior with model substrates: enhanced molecular binding ability by multiple recognition.

To investigate quantitatively the cooperative binding ability of several beta-cyclodextrin oligomers bearing single or multiligated metal center(s), the inclusion complexation behavior of four bis(beta-cyclodextrin)s (2-5) linked by 2,2'-bipyridine-4,4'-dicarboxy tethers and their copper(II) complexes (6-9) with representative dye guests, i.e., methyl orange (MO), acridine red (AR), rhodamine B (RhB), ammonium 8-anilino-1-naphthalenesulfonic acid (ANS), and sodium 6-(p-toludino)-2-naphthalenesulfonate (TNS), have been examined in aqueous solution at 25 degrees C by means of UV-vis, circular dichroism, fluorescence, and 2D NMR spectroscopy. The results obtained indicate that bis(beta-cyclodextrin)s 2-5 can associate with one or three copper(II) ion(s) producing 2:1 or 2:3 bis(beta-cyclodextrin)-copper(II) complexes. These metal-ligated oligo(beta-cyclodextrin)s can bind two model substrates to form intramolecular 2:2 host-guest inclusion complexes and thus significantly enhance the original binding abilities of parent beta-cyclodextrin and bis(beta-cyclodextrin) toward model substrates through the cooperative binding of two guest molecules by four tethered cyclodextrin moieties, as well as the additional binding effect supplied by ligated metal center(s). Host 6 showed the highest enhancement of the stability constant, up to 38.3 times for ANS as compared with parent beta-cyclodextrin. The molecular binding mode and stability constant of substrates by bridged bis- and oligo(beta-cyclodextrin)s 2-9 are discussed from the viewpoint of the size/shape-fit interaction and molecular multiple recognition between host and guest.

Algorithms↗
PubMed2005

Inclusion complexes of PBN-type nitrone spin traps and their superoxide spin adducts with cyclodextrin derivatives: parallel determination of the association constants by NMR titrations and 2D-EPR simulations.

(1)H NMR and electron paramagnetic resonance (EPR) titrations were used to determine the association constants of the complexes of alpha-phenyl-N-tert-butylnitrone (PBN) analogues and their superoxide spin adducts, respectively, with methylated beta-cyclodextrins. A 1:1 stoichiometry for the nitrones with randomly methylated beta-cyclodextrin and 2,6-di-O-methyl-beta-cyclodextrin and 1:1 and 1:2 stoichiometries for the corresponding cyclodextrin-nitroxide complexes were observed. After the superoxide radical spin trapping reaction, EPR titrations afforded the association constants of the corresponding cyclodextrin-nitroxide complexes. Two-dimensional EPR simulations indicated a bimodal inclusion of the nitroxide free radical spin adducts into the cyclodextrins. For all the nitrone-cyclodextrin and nitroxide-cyclodextrin complexes, the association constants were always higher for the nitroxide complexes than for the nitrone complexes. A cooperative system concerning the complexation of the nitroxide spin adduct with a cyclodextrin was evidenced by EPR titrations. The efficiency of the cyclodextrin inclusion technique to trap superoxide and to resist bioreduction by sodium l-ascorbate was also investigated.

Cyclodextrins↗
PubMed1998

Co-administration of a water-soluble polymer increases the usefulness of cyclodextrins in solid oral dosage forms.

PURPOSE: The aim of this study was to investigate the effect of cyclodextrins (beta-CD, HP-beta-CD and (SBE)7m-beta-CD), and co-administration of a water-soluble polymer (HPMC) and cyclodextrins, on the oral bioavailability of glibenclamide in dogs. METHODS: Effects of cyclodextrins on the aqueous solubility of glibenclamide, with and without hydroxypropylmethylcellulose (HPMC), were determined by a phase-solubility method. Solid inclusion complexes were prepared by freeze-drying. Glibenclamide was administered orally and intravenously to beagle dogs. RESULTS: Aqueous solubility of glibenclamide increased as a function of cyclodextrin concentration, showing an AL-type diagram for beta-CD and an Ap-type diagrams for both of the beta-CD derivatives studied. HPMC enhanced the solubilising effect of cyclodextrins, but did not affect the type of phase-solubility diagram. Orally administered glibenclamide and its physical mixture with HP-beta-CD showed poor absolute bioavailability, while orally administered glibenclamide/cyclodextrin-complexes significantly enhanced the absolute bioavailability of glibenclamide. Orally administered glibenclamide/beta-CD/HPMC and glibenclamide/(SBE)7m-beta-CD/HPMC complexes showed similar absolute bioavailability compared to formulations not containing HPMC, even though 80% (in the case of (SBE)7m-beta-CD) or 40% (in the case of beta-CD) less cyclodextrin was used. CONCLUSIONS: The oral bioavailability of glibenclamide was significantly increased by cyclodextrin complexation. HPMC increased the solubilising effect of cyclodextrins and, therefore, the amount of cyclodextrin needed in the solid dosage form was significantly reduced by their co-administration. In conclusion, the pharmaceutical usefulness of cyclodextrins in oral administration may be substantially improved by co-administration of a water-soluble polymer.

Administration, Oral↗
PubMed2004

Intra- and intermolecular complexation in C6 monoazacoronand substituted cyclodextrins.

The preparation of 6(A)-deoxy-6(A)-(6-(2-(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)acetamido)hexylamino)-alpha-cyclodextrin, 3, 6(A)-deoxy-6(A)-(6-(2-(1,4,7,10,13-pentaoxa-16-azacyclooctadecan-16-yl)acetamido)hexylamino)-alpha-cyclodextrin, 4, and their beta-cyclodextrin analogues, 5 and 6, are described. (1)H (600 MHz) ROESY NMR spectra of the C(6) substituted beta-cyclodextrins, 5 and 6, are consistent with the intramolecular complexation of their azacyclopentadecanyl- and azacyclooctadecanyl(acetamido)hexylamino substituents in the beta-cyclodextrin annulus in D(2)O at pD = 8.5 whereas those of their alpha-cyclodextrin analogues, 3 and 4 are not complexed in the alpha-cyclodextrin annulus. This is attributed to the monoazacoronand components of the substituents being able to pass through the beta-cyclodextrin annulus whereas they are too large to pass through the alpha-cyclodextrin annulus. However, the substituents of 3 and 4 are intermolecularly complexed by beta-cyclodextrin to form pseudo [2]-rotaxanes. Metallocyclodextrins are formed by 5 through complexation by the monoazacoronand substituent component for which log (K/dm(3) mol(-1))= <2, 6.34 and 5.38 for Ca(2+), Zn(2+) and La(3+), respectively, in aqueous solution at 298.2 K and I= 0.10 mol dm(-3)(NEt(4)ClO(4)).

Azo Compounds↗
PubMed1995

Use of cyclodextrin and its derivatives as carriers for oligonucleotide delivery.

The use of antisense phosphorothioate oligodeoxynucleotides as tools for modulating gene expression represents a novel strategy for designing drugs to treat a variety of diseases. Several factors, including cellular uptake and internalization of the phosphorothioate oligodeoxynucleotide, are important parameters in determining the effectiveness of antisense agents as therapies. We have used cyclodextrin and its analogs as carriers to increase cellular uptake of phosphorothioate oligodeoxynucleotides. The studies were carried out using 35S-labeled and fluorescent-labeled phosphorothioate oligodeoxynucleotide in human T cell leukemia H9 cell line. Cellular uptake of phosphorothioate oligodeoxynucleotide in the presence of cyclodextrin was found to be concentration and time dependent. Using various cyclodextrin analogs, e.g., 2-hydroxypropyl beta-cyclodextrin (HPCD), hydroxyethyl beta-cyclodextrin (HECD), and a mixture of various hydroxypropyl beta-cyclodextrins (Encapsin), we observed increases in phosphorothioate oligodeoxynucleotide uptake, up to twofold to threefold in 48 hours. Confocal microscopy studies confirmed that oligonucleotide was present intracellularly. Cyclodextrin itself was not toxic at the concentration used. Cyclodextrins did not seem to affect the efflux of phosphorothioate oligodeoxynucleotide from cells. Stability of phosphorothioate oligodeoxynucleotide against endogenous cellular nucleases remained unchanged in the presence of cyclodextrins. These studies suggest that cyclodextrin and its analogs might be used successfully as carriers for oligonucleotide and analogs.

Amino Acid Sequence↗
PubMed1998

[A study on the binding of cyclodextrins with terbutaline enantiomers by chiral capilary zone electrophoresis].

The recognition mechanism of enantioselectivity in cyclodextrin-modified capillary zone electrophoresis (CD-CZE) on a racemic basic drug terbutaline was discussed. The equilibrium constants of host-guest complexation of terbutaline enantiomers with alpha-cyclodextrin, beta-cyclodextrin, 2,6-dimethyl-beta-cycoldextrin, 2,3,6-trimethyl-beta-cyclodextrin and 2-hydroxy-propyl-beta-cyclodextrin, and the thermodynamic parameters for chiral recognition procedure were determined respectively. It was found that the matching properties between cavity of cyclodextrins and enantiomers were interrelated with the equilibrium constants of binding complexes and selectivities(a) calculated from the ratio of binding constants of two enantiomers were in the same order of maximum electrophoretic mobility difference between two enantiomers responding with cyclodextrin additive. The experimental value of optimal concentration of cyclodextrin agreed with that calculated from the equation Copt = 1/(K1K2)1/2. From the thermodynamic parameter determination it was shown that the hydrogen-bonding interactions between terbutaline enantiomers and 2-hydroxy-propyl-beta-cyclodextrin and beta-cyclodextrin should be positive factors.

Cyclodextrins↗
PubMed1987

Cyclodextrins in drug carrier systems.

One of the important characteristics of cyclodextrins is the formation of an inclusion complex with a variety of drug molecules in solution and in the solid state. As a consequence of intensive basic research, exhaustive toxic studies, and realization of industrial production during the past decade, there seem to be no more barriers for the practical application of natural cyclodextrins in the biomedical field. Recently, a number of cyclodextrin derivatives and cyclodextrin polymers have been prepared to obtain better inclusion abilities than parent cyclodextrins. The natural cyclodextrins and their synthetic derivatives have been successfully utilized to improve various drug properties, such as solubility, dissolution and release rates, stability, or bioavailability. In addition, the enhancement of drug activity, selective transfer, or the reduction of side effects has been achieved by means of inclusion complexation. The drug-cyclodextrin complex is generally formed outside of the body and, after administration, it dissociates, releasing the drug into the organism in a fast and nearly uniform manner. In the biomedical application of cyclodextrins, therefore, particular attention should be directed to the magnitude of the stability constant of the inclusion complex. In the case of parenteral application, a rather limited amount of work has been done because the cyclodextrins in the drug carrier systems have to be more effectively designed to compete with various biological components in the circulatory system. However, the works published thus far apparently indicate that the inclusion phenomena of cyclodextrin analogs may allow the rational design of drug formulation and that the combination of molecular encapsulation with other carrier systems will become a very effective and valuable method for the development of a new drug delivery system in the near future.

Animals↗
PubMed1993

Evidence for beta-galactosidase catalyzed hydrolysis of paranitrophenyl-beta-D-galactopyranoside anchored in cyclodextrins.

The absorption maximum of p-nitrophenol upon mixing with molar equivalents of alpha-cyclodextrin (alpha-CD) or hydroxypropyl-beta-cyclodextrin (HPB) showed nearly 5 nm shift to the longer wavelength region, indicative of complex formation, while beta-cyclodextrin (beta-CD), gamma-cyclodextrin (gamma-CD) and hydroxyethyl-beta-cyclodextrin (HEB) produced only a marginal shift of about 1-2 nm, suggestive of a weaker interaction. It has been shown by circular dichroism spectral studies that the aglycon part of p-nitrophenyl-beta-D-glycoside (PNPG) is also encapsulated by alpha-cyclodextrin. The encapsulated form of PNPG could be hydrolyzed by beta-galactosidase, the temperature and pH-optima for hydrolysis of anchored substrates being essentially identical to that of free substrate. However, small but consistent increase in Km values were obtained for alpha-cyclodextrin-, HEB- and HPB-anchored substrates. The kcat values also registered an increase for the HEB- and HPB-anchored substrates. However, there was no increase in kinetic efficiency (kcat/Km) of enzyme. The inhibition noted at higher concentrations of HEB- and gamma-cyclodextrin-anchored PNPG but not with o-nitrophenyl-beta-D-galactoside (ONPG)-cyclodextrin mixture suggests that PNPG-cyclodextrin complexes were responsible for the inhibition. Taken together, these results suggest that the enzyme catalyses the hydrolysis of anchored substrates.

Cyclodextrins↗
PubMed1998

Cyclodextrin enhanced fluorimetric method for the determination of tryptamine.

The effect of native cyclodextrins (alpha-, beta- or gamma- with six, seven or eight glucose units, respectively), hydroxypropyl-beta-cyclodextrin, beta-cyclodextrin solubilized in urea, soluble starch and glucose in water solution on the fluorescence behaviour of tryptamine [3-(2-aminoethyl)indole] (T) was determined. In addition, the effect of methanol and propanol with and without beta-cyclodextrin or hydroxypropyl-beta-cyclodextrin was ascertained. From the fluorescence changes with pH and with beta-cyclodextrin or hydroxypropyl-beta-cyclodextrin, the values of the pKa of the ground and excited states and the association constants of T and TH [3-(2-ammoniumethyl)indole] with the two hosts were determined. The values are pKa = 9.5 +/- 0.2 and pKa* = 8.4 +/- 0.2; KAssocTH = (1.6 +/- 0.3) x 10(2) mol-1 dm3 and KAssocT = (2.8 +/- 0.3) x 10(2) mol-1 dm3 with beta-cyclodextrin, KAssocTH = (1.8 +/- 0.5) x 10(2) mol-1 dm3 and KAssocT = (4.9 +/- 0.9) x 10(2) mol-1 dm3 with hydroxypropyl-beta-cyclodextrin. The ratio of the fluorescence quantum yields for the bound and free substrate (phi b/phi f) were in the range 1.25-1.33. The detection limit for the better conditions where the host-guest interactions produce fluorescence enhancement was 0.454 +/- 0.002 ng ml-1 for the complex T-hydroxypropyl-beta-cyclodextrin in water. The method is simpler than others reported previously.

Spectrometry, Fluorescence↗
PubMed1997

Resolution of acylated dipeptide stereoisomers by capillary electrophoresis using sulfobutylether derivatized beta-cyclodextrin.

The separation of enantiomerically and diastereomerically related stereoisomers of acylated Asp-Phe dipeptides was explored using capillary electrophoresis (CE). This series of dipeptides included the alpha-L,L parent compound and the three other potential Asp containing stereoisomers (alpha-D,D, alpha-L,D, and alpha-D,L), as well the four possible isoAsp containing stereoisomers (beta-L,L, beta-D,D, beta-L,D and beta-D,L). The separation of these substances was explored using both neutral and charged cyclodextrins as the stereoisomer selector added to the running electrolyte. The major experimental parameters investigated included pH, the cyclodextrin type, and the cyclodextrin concentration. Due to differences in the pKa values of the carboxylic acid groups, adjustment of the separation buffer to between pH 3.0 and 4.0 provided for sufficient electrophoretic mobility differences to result in excellent separations of the diastereomerically related peptides in this pH region. The resolution of the enantiomerically related peptide stereoisomers was accomplished using low concentrations (1 mM) of the anionic cyclodextrin derivative, sulfobutylether-beta-cyclodextrin (SBE-beta-CD). This negatively charged cyclodextrin was found to be superior for the resolution of the enantiomerically related peptides as compared to native beta-cyclodextrin or the neutral derivatives, dimethyl beta-cyclodextrin and hydroxypropyl beta-cyclodextrin. An alternative approach using anionic or neutral surfactants in conjunction with the SBE-beta-CDs was also explored and found to be successful but problematic.

Acylation↗
PubMed2003

Enzymatic hydrolysis of diloxanide furoate in the presence of beta-cyclodextrin and its methylated derivatives.

In this study, we investigated the susceptibility to enzymatic and alkaline hydrolysis of diloxanide furoate (DF) and its cyclodextrin inclusion complexes, in aqueous solution. The cyclodextrins (CDs) utilized were beta-cyclodextrin (beta-CD), (2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD) and (2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD). All cyclodextrins studied provided a stabilizing effect to diloxanide furoate hydrolysis. In alkaline hydrolysis (pH 10.75), without the enzyme, beta-CD and TM-beta-CD provided similar effect on the stability of DF, with an inhibition factor in the order of 2.0. The DM-beta-CD, on the other hand, provided more pronounced stabilization effect than the other two CDs, with an inhibition factor around of 8. The maximum activity of the enzyme occured around pH 7.0. In the presence of enzyme, all cyclodextrins produced similar effect, with a DF hydrolysis inhibition factor in the order of 10. However, the plot of rate of hydrolysis versus [CD] fit with a equation based in a model that considers the association of the enzyme with the CDs. Therefore, it is concluded that the stabilization of DF is not only due to its cyclodextrin complex but also due to enzyme inhibition by cyclodextrin complexation.

Chemical Phenomena↗
PubMed1998

Double-blind multicenter study comparing alprostadil alpha-cyclodextrin with moxisylyte chlorhydrate in patients with chronic erectile dysfunction.

PURPOSE: We compared the efficacy and safety of alprostadil alpha-cyclodextrin and moxisylyte chlorhydrate to induce erections adequate for sexual intercourse in a prospective, randomized, parallel double-blind study in patients with erectile dysfunction. MATERIALS AND METHODS: A total of 156 men with erectile dysfunction due to organic, nonorganic and mixed origin was randomized into 2 parallel treatment groups receiving titrations of an individual optimum dose of alprostadil alpha-cyclodextrin or moxisylyte chlorhydrate. Erectile response was measured by the buckling test. A positive test was associated with axial erection rigidity that did not buckle/deform to 1.0 kg. load. The buckling test was repeated every 10 minutes for up to 60 minutes. RESULTS: A total of 56 patients (75%) in the alprostadil alpha-cyclodextrin group and 32 patients (40%) in the moxisylyte chlorhydrate group responded with at least 1 positive buckling test during the office period. Investigators assessed erections after alprostadil alpha-cyclodextrin to be adequate for sexual intercourse in 61 patients (81%) compared to 37 patients (46%) after moxisylyte chlorhydrate. All efficacy parameters in office reached statistical significance of p < 0.001 in favor of alprostadil alpha-cyclodextrin. During self-injection therapy at home 58 patients (85%) reported at least 1 rigid erection after alprostadil alpha-cyclodextrin compared to 37 patients (61%) after moxisylyte chlorhydrate. Patient and partner opinion of treatment achieved statistically significantly better scores in the alprostadil alpha-cyclodextrin group compared to the moxisylyte chlorhydrate group. CONCLUSIONS: Alprostadil alpha-cyclodextrin is significantly more effective than moxisylyte chlorhydrate in producing full penile rigidity in office and at home. Injection related side effects occur with the same frequency but moxisylyte results in more systemic side effects and alprostadil results in more painful and prolonged erections. Patients and partners are significantly more satisfied with alprostadil alpha-cyclodextrin.

Adrenergic alpha-Antagonists↗
PubMed2004

Two-site binding of beta-cyclodextrin to the Alzheimer Abeta(1-40) peptide measured with combined PFG-NMR diffusion and induced chemical shifts.

The interactions of Alzheimer's amyloid beta-peptide with cyclodextrins were studied by (1)H NMR: the translational diffusion coefficient of the peptide and chemical shift changes were studied by the presence of variable concentrations of cyclodextrins. For the full-length peptide, Abeta(1-40), the combined results of translational diffusion and chemical shift changes are consistent with a model where aromatic side chains interact with beta-cyclodextrin with dissociation constants in the millimolar range. The diffusion data were consistent with two beta-cyclodextrin molecules bound per peptide. The binding occurs at two sites, at F(19) and/or F(20) and at Y(10), with dissociation constants K(d)(F) = 4.7 mM and K(d)(Y) = 6.6 mM, respectively, in 10 mM sodium phosphate, pH 7.4 and 298 K. Shorter Alzheimer peptide fragments were studied to measure specific affinities for different binding sites. The N-terminal fragment Abeta(1-9) with a putative binding site at F(4) does not show measurable affinity for beta-cyclodextrin. The fragment Abeta(12-28) has similar apparent affinity (K(d) = 3.8 mM) to beta-cyclodextrin as the full-length peptide Abeta(1-40). Here, the diffusion data suggests a one-to-one stoichiometry, and the binding site is F(19) and/or F(20). Both diffusion results and chemical shift changes give the same affinity. A variant Abeta(12-28)G(19)G(20) without phenylalanines does not bind to beta-cyclodextrin. Other potential ligands, alpha-cyclodextrin, gamma-cyclodextrin, nicotine, and nornicotine do not bind to the Abeta(12-28) fragment. This study shows that combined (1)H NMR diffusion and chemical shift changes may be used to quantitatively determine affinities and stoichiometries of weak interactions, using unlabeled ligands and hosts of comparable sizes.

Alzheimer Disease↗
PubMed2006

Cyclodextrins sequester neuroactive steroids and differentiate mechanisms that rate limit steroid actions.

BACKGROUND AND PURPOSE: Neuroactive steroids are potent modulators of GABA(A) receptors and are thus of interest for their sedative, anxiolytic, anticonvulsant and anaesthetic properties. Cyclodextrins may be useful tools to manipulate neuroactive effects of steroids on GABA(A) receptors because cyclodextrins form inclusion complexes with at least some steroids that are active at the GABA(A) receptor, such as (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha5alphaP, allopregnanolone). EXPERIMENTAL APPROACH: To assess the versatility of cyclodextrins as steroid modulators, we investigated interactions between gamma-cyclodextrin and neuroactive steroids of different structural classes. KEY RESULTS: Both a bioassay based on electrophysiological assessment of GABA(A) receptor function and optical measurements of cellular accumulation of a fluorescent steroid analogue suggest that gamma-cyclodextrin sequesters steroids rather than directly influencing GABA(A) receptor function. Neither a 5beta-reduced A/B ring fusion nor a sulphate group at carbon 3 affected the presumed inclusion complex formation between steroid and gamma-cyclodextrin. Apparent dissociation constants for interactions between natural steroids and gamma-cyclodexrin ranged from 10-60 microM. Although gamma-cyclodextrin accommodates a range of natural and synthetic steroids, C(11) substitutions reduced inclusion complex formation. Using gamma-cyclodextrin to remove steroid not directly bound to GABA(A) receptors, we found that cellular retention of receptor-unbound steroid rate limits potentiation by 3alpha- hydroxysteroids but not inhibition by sulphated steroids. CONCLUSIONS AND IMPLICATIONS: We conclude that gamma-cyclodextrins can be useful, albeit non-specific, tools for terminating the actions of multiple classes of naturally occurring neuroactive steroids.

Animals↗
PubMed2001

Effect of water-soluble polymers on naproxen complexation with natural and chemically modified beta-cyclodextrins.

The combined effect of cyclodextrins (CDs) (beta-, methyl-beta-, hydroxypropyl-beta-cyclodextrins) and water-soluble polymers (sodium carboxymethylcellulose, hydroxypropylmethylcellulose, polyvinylpyrrolidone K30, polyethylene glycol 6000) on naproxen solubility improvement was studied. Phase solubility analysis at 25 degrees C was used to investigate the interaction of the drug with each cyclodextrin (or polymer, alone or in the presence of the different water-soluble polymers (or cyclodextrins). The combined use of polymer and cyclodextrin was always clearly more effective in enhancing the aqueous solubility of naproxen in comparison with the corresponding drug-polymer or drug-cyclodextrin binary systems, and the solubilization enhancement was not simply additive, but synergistic. Water-soluble polymers increased the complexation efficacy of cyclodextrins toward naproxen (as shown by the increased stability constants of the complexes), which resulted in enhanced drug solubility. No previous sonication or heating treatments of the drug-cyclodextrin-polymer suspensions was necessary to obtain this favorable effect. The best results were obtained in ternary systems with beta-cyclodextrin, which had a solubilizing effect toward naproxen in the presence of 0.25% w/v of the different hydrophilic polymers examined that was improved from 25% to about 80%, depending on the type of polymer.

Cyclodextrins↗
PubMed2006

Assessment of ternary iron-cyclodextrin-2-naphthol complexes using NMR and fluorescence spectroscopies.

Recent research has indicated that ternary complexes can be formed among carboxymethyl-beta-cyclodextrin, certain polycyclic aromatic hydrocarbons (PAHs) (e.g. anthracene and 2-naphthol), and Fe(2+) in aqueous solution. The formation of these ternary complexes has been suggested as the reason for improved reaction efficiency in iron catalyzed Fenton degradation (H(2)O(2)+Fe(2+)-->*OH+OH(-)+Fe(3+)) of PAHs and other pollutants. In the present work, several other cyclodextrins were examined to determine their ability to form similar ternary complexes with 2-naphthol and Fe(2+). Fluorescence and NMR techniques were employed in this study. Results showed that hydroxypropyl-beta-cyclodextrin, beta-cyclodextrin, and alpha-cyclodextrin were able to encapsulate 2-naphthol molecules, but their binding with Fe(2+) was weak. On the contrary, sulfated-beta-cyclodextrin has significant binding with Fe(2+), but it showed little inclusion of 2-naphthol molecules. Consequently, none of these four cyclodextrins formed significant amounts of ternary complexes in aqueous solution. The techniques used in this study provide useful methods for assessing the ability of cyclodextrins to form ternary complexes with guest compounds and metal ions.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed2002

The trapping of a spontaneously "flipped-out" base from double helical nucleic acids by host-guest complexation with beta-cyclodextrin: the intrinsic base-flipping rate constant for DNA and RNA.

Beta-cyclodextrin, which forms stable host-guest complexes with purine bases, induces the melting of RNA and DNA duplexes below their normal melting temperatures. Alpha-cyclodextrin, which does not form stable complexes, has no effect on either RNA or DNA. Gamma-cyclodextrin, which forms weaker complexes, has no effect on RNA and a smaller effect than beta-cyclodextrin on DNA. The rate of melting is kinetically first-order in duplex and, above about 20 mM beta-cyclodextrin, is independent of the beta-cyclodextrin concentration with a first-order rate constant, common to both RNA and DNA, of (3.5 +/- 0.5) x 10(-3) s(-1) at 61 degrees C (DNA) and at 50 degrees C (RNA). This is taken to be the rate constant for spontaneous "flipping out" of a base from within the duplex structure of the nucleic acids, the exposed base being rapidly trapped by beta-cyclodextrin. Like beta-cyclodextrin, nucleic acid methyltransferases bind the target base for methylation in a site that requires it to have flipped out of its normal position in the duplex. The spontaneous flip-out rate constant of around 10(-3) s(-1) is near the value of k(cat) for the methyltransferases (ca. 10(-3) to 10(-1) s(-1)). In principle, the enzymes, therefore, need effect little or no catalysis of the flipping-out reaction. Nevertheless, the flip-out rate in enzyme/DNA complexes is much faster. This observation suggests that the in vivo circumstances may differ from in vitro models or that factors other than a simple drive toward higher catalytic power have been influential in the evolution of these enzymes.

Chemical Phenomena↗
PubMed2006

Reversal of regioselectivity and enhancement of rates of nitrile oxide cycloadditions through transient attachment of dipolarophiles to cyclodextrins.

The reactions of nitrile oxides with monosubstituted dipolarophiles, such as propiolamide, typically afford proportionally 80 % or more of the 3,5-disubstituted cycloadducts. By contrast, the reactions of 6(A)-deoxy-6(A)-propynamido-beta-cyclodextrin with 4-tert-butylbenzonitrile oxide and 4-phenylbenzonitrile oxide afford >90 % and approximately 85 % of the corresponding 3,4-disubstituted isoxazoles, respectively. As well as reversing the regioselectivity, the cyclodextrin increases the rates of these cycloadditions. The extent of the acceleration is up to more than three orders of magnitude for the production of the cycloadduct preferred by the cyclodextrin, but even the rate of reaction to give the less favored regioisomer is increased. With 6(A)-deoxy-6(A)-propynamido-beta-cyclodextrin, the cycloadducts are not easily separated from the cyclodextrin, as the amide bond is not readily cleaved. In comparison, the regioselectivity of the cycloadditions of 4-tert-butylbenzonitrile oxide with acrylic acid, methacrylic acid, and crotonic acid is also altered by formation of the corresponding cyclodextrin esters, by factors of 500, >10, and >100, respectively. The rates of cycloaddition are also increased by up to 475 times, and in these cases the products of cycloaddition are readily released from the cyclodextrin through ester hydrolysis. Incorporating these processes into a reaction cycle, acylation of beta-cyclodextrin with p-nitrophenyl acrylate and subsequent treatment first with 4-tert-butylbenzonitrile oxide and then with base, the latter to catalyze ester hydrolysis and regenerate the beta-cyclodextrin, affords proportionally fivefold more of the 3,4-disubstituted isoxazoline than is produced directly from acrylic acid.

Acrylates↗