Α-cyclodextrin In Aqueous Solution Research Articles

Supramolecular Gold Stripping from Activated Carbon Using α-Cyclodextrin.

We report the molecular recognition of the Au(CN)2- anion, a crucial intermediate in today's gold mining industry, by α-cyclodextrin. Three X-ray single-crystal superstructures-KAu(CN)2⊂α-cyclodextrin, KAu(CN)2⊂(α-cyclodextrin)2, and KAg(CN)2⊂(α-cyclodextrin)2-demonstrate that the binding cavity of α-cyclodextrin is a good fit for metal-coordination complexes, such as Au(CN)2- and Ag(CN)2- with linear geometries, while the K+ ions fulfill the role of linking α-cyclodextrin tori together as a result of [K+···O] ion-dipole interactions. A 1:1 binding stoichiometry between Au(CN)2- and α-cyclodextrin in aqueous solution, revealed by 1H NMR titrations, has produced binding constants in the order of 104 M-1. Isothermal calorimetry titrations indicate that this molecular recognition is driven by a favorable enthalpy change overcoming a small entropic penalty. The adduct formation of KAu(CN)2⊂α-cyclodextrin in aqueous solution is sustained by multiple [C-H···π] and [C-H···anion] interactions in addition to hydrophobic effects. The molecular recognition has also been investigated by DFT calculations, which suggest that the 2:1 binding stoichiometry between α-cyclodextrin and Au(CN)2- is favored in the presence of ethanol. We have demonstrated that this molecular recognition process between α-cyclodextrin and KAu(CN)2 can be applied to the stripping of gold from the surface of activated carbon at room temperature. Moreover, this stripping process is selective for Au(CN)2- in the presence of Ag(CN)2-, which has a lower binding affinity toward α-cyclodextrin. This molecular recognition process could, in principle, be integrated into commercial gold-mining protocols and lead to significantly reduced costs, energy consumption, and environmental impact.

A volumetric approach: Interactions of some local anesthetical drugs with α-cyclodextrin in aqueous solutions at 298.15 K

The density measurements have been carried out for ternary aqueous solutions containing a fixed concentration (∼0.1mol·kg−1) of α-cyclodextrin (α-CD) and varying concentrations (∼0.003 to ∼0.21mol·kg−1) of some local anesthetical drugs, namely procaine hydrochloride (PC·HCl), lidocaine hydrochloride monohydrate (LC·HCl) and tetracaine hydrochloride (TC·HCl) at 298.15K. The density data are used to determine apparent molar volumes of the drug molecules in ternary solutions at finite concentrations (ϕV) as well at infinitely dilute solutions (ϕV0). Following the methods developed by Høiland et al. as well by Jolicoeur et al. and using the infinite dilution volume values for the drugs in ternary and binary solutions and incorporating the equilibrium constant values for the complexation between α-CD and drugs, volume changes due to encapsulation or complexation have been estimated. It is observed that all the studied hydrochlorides exhibit high positive volume change due to complexation. The results are discussed in terms of host-guest interaction and structural specificity of guest molecules.

Calculation of binding affinities for linear alcohols to α-cyclodextrin by twin-system enveloping distribution sampling simulations

Comparison of three variants of the GROMOS force field for carbohydrates, 53A6GLYC, 56A6CARBO_R and a small modification of the latter, referred to as 56A6CARBO_R+, has been conducted by examining the standard binding free enthalpy of linear alcohols from 1-butanol to 1-dodecanol to α-cyclodextrin in aqueous solution. The double decoupling approach was employed to calculate the standard binding free enthalpy of 1-hexanol, while for all other compounds relative binding free enthalpies for pairs of alcohols differing by two carbon atoms were calculated from twin-system enveloping distribution sampling simulations. While all three force fields slightly overestimate the magnitude of the standard binding free enthalpy of 1-hexanol the 53A6GLYC and 56A6CARBO_R+ parameter sets are a little closer to the experimental data than 56A6CARBO_R. For relative binding free enthalpies no significant difference between the force fields was observed. All three force fields support those experimental measurements that found a distinct increase in the binding affinity with increasing number of carbon atoms even for longer chain lengths up to 1-dodecanol.

The Role of Normal Versus Twisted Intramolecular Charge Transfer Fluorescence in Predicting the Forms of Inclusion Complexes of Ethyl-4-dialkylaminobenzoate with α-Cyclodextrin in Aqueous Solution

An evidence is introduced through the b- and the twisted intramolecular charge transfer (TICT) fluorescence of ethyl-4-(N,N-dimethylamino)benzoate (EDMAB) and ethyl-4-(N,N-diethylamino)benzoate (EDEAB), confirming the role of donor size on the formation and emission of various inclusion complexes formed between these probes and α-CD in aqueous solution. A large variation in the b-fluorescence band of EDEAB as compared to that of EDMAB and a large variation in the TICT-fluorescence band of EDMAB as compared to that EDEAB, as the concentration of α-CD is increased in their aqueous solutions are observed. These variations are supported by time resolved fluorescence (TRF) spectra, fluorescence decay lifetimes and red edge effect (REE) results.

Bioactive Supramolecular Hydrogel with Controlled Dual Drug Release Characteristics

Heparin, a powerful anticoagulant used for the prophylaxis of both surgical and medical thrombosis, was covalently incorporated into a supramolecular hydrogel network. For this attempt, heparin was first conjugated with amino-terminated poly(ethylene glycol) methyl ether by carbodiimide chemistry and then used to interact with α-cyclodextrin in aqueous solution. The rheological measurements and X-ray diffraction analyses were used to characterize the hydrogel formation. It was found that the gelation kinetics and hydrogel properties could be modulated by changing the amount of conjugated heparin or α-cyclodextrin. By circular dichroism analyses and in vitro release experiments, resultant hydrogel material was found to have a great potential as an injectable matrix for the encapsulation and sustained release of model protein drug (bovine serum albumin). By in vitro release, blood clotting, and hemolysis experiments, such a supramolecular hydrogel was also confirmed to have a controlled release profile for conjugated heparin and shows good anticoagulant and blood-compatible properties.

Inclusion Complex of n-Octyl β-d-Glucopyranoside and α-Cyclodextrin in Aqueous Solutions: Thermodynamic and Structural Characterization

Inclusion Complex of n-Octyl β-<scp>d</scp>-Glucopyranoside and α-Cyclodextrin in Aqueous Solutions: Thermodynamic and Structural Characterization

PdII and PtII Complexes with Amphiphilic Ligands: Formation of Micelles and [5]Rotaxanes with α‐Cyclodextrin in Aqueous Solution

[3]Pseudorotaxanes [1(alpha-CD)(2)][X] (X=Cl, NO(3)), prepared from reaction of an N-alkylbipyridinium [4,4'-bpy-N-(CH(2))(10)OC(6)H(3)-3,5-(OMe)(2)][X] ([1][X]) and alpha-CD, react with M(NO(3))(2)(en) (M=Pd, Pt; en=1,2-ethylenediamine) in a 2:1 molar ratio to afford [5]rotaxanes [M{(4,4'-bpy-N-(CH(2))(10)OC(6)H(3)-3,5-(OMe)(2))(alpha-CD)(2)}(2) (en)][NO(3)](4) ([2(alpha-CD)(4)][NO(3)](4), M=Pd; [3(alpha-CD)(4)][NO(3)](4), M=Pt). A similar reaction of [1][Cl] with [M(NO(3))(2)(en)] (M=Pd, Pt) produces amphiphilic Pd and Pt complexes, [2][NO(3)](4) and [3][NO(3)](4). Complexes [2][NO(3)](4) and [3][NO(3)](4) form micelles in the presence of small amounts of dyes (Nile red and pyrene) in water. The critical micelle concentration (CMC) was determined by the absorption peak of the dye, which is encapsulated in the micelles in solution. Micelle formation is confirmed by dynamic light scattering measurement of the solution and TEM (transmission electron microscopy) images of the micelles deposited from the solution. Addition of alpha-CD to the aqueous solution containing these amphiphilic complexes results in degradation of the micelle structure and the formation of [5]rotaxanes, [2(alpha-CD)(4)][NO(3)](4) and [3(alpha-CD)(4)][NO(3)](4).

Supramolecular Hydrogels Induced Rapidly by Inclusion Complexation of Poly(ε-caprolactone)−Poly(Ethylene Glycol)−Poly(ε-caprolactone) Block Copolymers with α-Cyclodextrin in Aqueous Solutions

On the basis of the synthesis of water-soluble poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL) block copolymers, the supramolecular hydrogels were fabricated rapidly in aqueous solutions by their inclusion complexation with alpha-cyclodextrin. X-ray diffraction (XRD) analyses confirmed the supramolecular self-assemblies of alpha-cyclodextrin threaded onto amphiphilic PCL-PEG-PCL block copolymers. The resulting hydrogels display a high degree of elasticity, with the storage modulus (G') greater than the loss modulus (G'') over the entire range of frequency. Moreover, their viscosity greatly diminished as they were sheared. By controlling the molecular weight of the PEG component in the block copolymers and the content of the block copolymer, their rheological properties could be modulated. Such hydrogel materials have the potential to be used as tissue engineered scaffolds, biosensors in the human body, and carriers for controlled drug delivery.

Thermodynamic Data for the Complex Formation of Alkylamines and Their Hydrochlorides with α-Cyclodextrin in Aqueous Solution

The formation of complexes between α-cyclodextrin and n-alkylamines and their hydrochlorides has been studied in aqueous solution using calorimetric titrations. All alkylamines form stronger complexes than the corresponding hydrochlorides. The values of the reaction enthalpies are smaller for the alkylamine hydrochlorides compared with the alkylamines. By increasing the number of methylene groups, these differences become smaller. In addition, the reaction enthalpies for protonation of the alkylamines and their complexes with α-cyclodextrin have been measured. The heat of protonation of these complexes is always smaller compared with the alkylamines. Due to the protonation and the formation of a strong solvation shell around the ammonium group the interactions with α-cyclodextrins are weakened. From a thermodynamic cycle using all measured reactions, it can be concluded that the aggregation of the alkylamines with long alkyl chains (heptyl-, octyl-, and nonylamine) has an influence on the values of the reaction enthalpies and entropies for the protonated form only.

Binding of Substituted Acetic Acids to α-Cyclodextrin in Aqueous Solution

Complex binding constants of 23 aliphatic acids with α-cyclodextrin in aqueous solution were measured by potentiometry, solubility, or competitive spectrophotometry at 25°C. All systems formed 1:1 acid:cyclodextrin complexes, and some of them also formed 1:2 complexes. The conjugate acids formed stronger complexes than did the conjugate bases (except for glycine). Empirical correlations of complex stabilities are shown with partition coefficients, surface areas, molar refraction, and other descriptors. Complex stability appears to result from the hydrophobic effect, the dispersion interaction, and interaction of the carboxylic acid group with the cyclodextrin.

Room-temperature phosphorescence of 6-bromo-2-naphthol included by α-cyclodextrin in aqueous solution

In aerated aqueous solutions, room-temperature phosphorescence of 6-bromo-2-naphthol is observed with an inclusion complex composed of one 6-bromo-2-naphthol (BN) and two α-cyclodextrin (α-CD) molecules, whereas a 1 : 1 α-CD–BN inclusion complex does not phosphoresce at room temperature.

Chiral molecular recognition: a19F nuclear magnetic resonance study of the diastereoisomer inclusion complexes formed between fluorinated amino acid derivatives and α-cyclodextrin in aqueous solution

A 19F NMR spectroscopic study (282.35 MHz) of the formation of diastereoisomeric inclusion complexes by fluorinated amino acid derivatives and α-cyclodextrin (αCD) in 10% aqueous D2O solution yields the apparent stability constants KR and KS/dm3 mol–1= 7.7 ± 0.3 and 8.2 ± 0.3 for protonated α-(p-fluorophenyl)glycine (1 + H), 21.5 ± 0.4 and 22.5 ± 0.4 for deprotonated α–(p-fluorophenyl)glycine (1 – H), 14.4 ± 0.1 and 14.6 ± 0.1 for N-acetyl-α-(p-fluorophenyl)glycine (2), 13.1 ± 0.5 and 14.1 ± 0.5 for deprotonated N-acetyl-α-(p-fluorophenyl)-glycine (2– H), and 12.4 ± 0.3 and 10.6 ± 0.4 for deprotonated N-(p-fluorobenzoyl)valine (3– H), where the first and second of each pair of values refers to the diastereoisomer formed between αCD and the R and S enantiomer, respectively. The chemical shifts of the R-amino acid derivative ·αCD inclusion complexes are upfield from those of their S analogues for deprotonated N-(p-fluorobenzoyl)valine (3– H), deprotonated α-(p-fluorophenyl)glycine (1– H), and deprotonated N-acetyl-α-(p-fluorophenyl)glycine (2– H), but this relationship is reversed for protonated α-(p-fluorophenyl)glycine (1+ H) and N-acetyl-α-(p-fluorophenyl)glycine (2+ H). In the case of the N-(p-fluorobenzoyl)valine ·αCD inclusion complex (3·αCD) the chemical shift difference between the diastereo-isomers formed with the R and S enantiomers is too small for quantitative analysis and accordingly a composite KR,S/dm3 mol–1= 8.3 ± 0.3 was determined. The factors causing the variations in apparent stability constants and chemical shifts are discussed.

Calorimetric and diffusional behaviour of the system α-cyclodextrin-L-phenylalanine in aqueous solution

The interaction of L-phenylalanine with α-cyclodextrin in aqueous solution has been studied by calorimetry at 25°C. The results indicate that inclusion occurs: the value of the association constant is in very good agreement with that obtained from diffusion measurements.

Ultrasonic and electrochemical studies of the interactions of the drug chlorocyclizine hydrochloride with α-cyclodextrin and surfactant micelles

Using a drug-selective membrane electrode it has been shown that the cationic drug chlorocyclizine hydrochloride forms a 1 : 1 inclusion compound with α-cyclodextrin in aqueous solution. The drug also forms mixed micelles with cetyltrimethylammonium bromide, and the partition coefficient of the drug between aqueous and micellar phase was estimated using sound velocities. The kinetics of both processes have been measured using ultrasonic relaxation and it is found that the rate constant for the formation of the 1 : 1 inclusion compound is a factor of ca. 40 times lower than the corresponding rate constant for drug association with the mixed micelle. In both cases one would expect both the bimolecular processes to be diffusion controlled. The reasons for the difference in rate constants are discussed.

Conformational differences between α-cyclodextrin in aqueous solution and in crystalline form: A molecular dynamics study

The computer simulation technique of molecular dynamics is a powerful tool to delineate the conformational differences between a molecule in different environments. As an illustration, the difference between an α-cyclodextrin molecule in aqueous solution and in crystalline form is determined. Two molecular dynamics simulations are compared. In one simulation, one α-cyclodextrin form in a “truncated octahedron box” containing 611 water molecules is simulated over 90 picoseconds to mimic the solution structure. In the other simulation, the crystalline form is modelled by a molecular dynamics simulation of four unit cells in space group P2 12 12 1 containing 16 α-cyclodextrin molecules and 96 water molecules over a period of 15 picoseconds. The solution structure of α-cyclodextrin deviates by about 0·1 nm from that in the crystal and shows twice as much mobility of the atoms. The experimentally observed twist of glucose unit 5 out of alignment with the other five glucose units in the α-cyclodextrin torus that is present in the crystal simulation, disappears in the simulation in solution, but the glucosidic torsion angles around the ring remain asymmetric. The hydrogen-bonding patterns in crystal and in solution are rather different. This means that in a crystal structure, the molecule and its (hydration) hydrogen-bonding scheme represent only one static minimum energy picture, whereas the molecular dynamics simulations yield a description of all the many hydrogen-bonding configurations that can occur in solution.

Kinetic and equilibrium studies associated with the formation of inclusion compounds involving n-butanol and n-pentanol in aqueous cyclodextrin solutions

The equilibrium constants associated with the inclusion compounds of n-butanol and n-pentanol with α-cyclodextrin in aqueous solutions have been measured using the head-space analysis technique involving gas chromatography. These data confirm that a 1:1 inclusion complex is formed. The kinetics associated with the formation of these inclusion compounds have been studied using the ultrasonic relaxation method. From a detailed analysis of relaxation data it is clear that the kinetics of the process do not conform to the simple behaviour suggested by the equilibrium experiments. In addition there are also discrepancies between values of the volume change of the reaction determined independently from relaxation and density data. The significance of these results is discussed in terms of a two-step mechanism for the formation of the complex.

Inclusion Compounds. XIX.1a The Formation of Inclusion Compounds of α-Cyclodextrin in Aqueous Solutions. Thermodynamics and Kinetics

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInclusion Compounds. XIX.1a The Formation of Inclusion Compounds of α-Cyclodextrin in Aqueous Solutions. Thermodynamics and KineticsF. Cramer, W. Saenger, and H.-Ch. SpatzCite this: J. Am. Chem. Soc. 1967, 89, 1, 14–20Publication Date (Print):January 1, 1967Publication History Published online1 May 2002Published inissue 1 January 1967https://doi.org/10.1021/ja00977a003RIGHTS & PERMISSIONSArticle Views2041Altmetric-Citations586LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts