One-pot synthesis of 1,2,3-triazoles from boronic acids in water using Cu(II)-β-cyclodextrin complex as a nanocatalyst

We report here the one-pot synthesis of 1,2,3-triazoles of arylboronic acids in water. An efficient method has been developed for the synthesis of 1,2,3-triazoles via a one-pot reaction of an arylboronic acid with sodium azide in the presence of Cu(2)-β-CD (CD = Cyclodextrin) as a nanocatalyst in water followed by a click cyclization reaction with an alkyne at room temperature in air without any additives. This method is simple, rapid, and high yielding.     

Fluorescent detection of cholesterol using β-cyclodextrin functionalized graphene

A fluorescence based cholesterol detection method has been developed using competitive host-guest interaction between graphene bound β-cyclodextrin (β-CD) with rhodamine 6G (R6G) and cholesterol. Fluorescence of β-CD incorporated R6G is quenched by graphene but is 'turned on' by cholesterol as it replaces R6G from the β-CD host.     

Thermodynamic study on inclusion complex formation of riboflavin with hydroxypropyl-β-cyclodextrin in water

The inclusion complex formation of riboflavin (RF) with hydroxypropyl-β-cyclodextrin (HP-β-CD) in water was investigated by ¹H NMR, UV-vis spectroscopy, and solubility methods. A 1:1 stoichiometry and thermodynamic parameters of complex formation (K, Δ_c G ⁰, Δ_c H ⁰, and Δ_c S ⁰) were determined. Complexation was characterized by negative enthalpy and entropy changes due to prevalence of van der Waals interactions and hydrogen bonding between polar groups of the solutes. A partial insertion of RF into macrocyclic cavity was revealed on the basis of ¹H NMR data and molecular mechanics calculation. Location of benzene ring of RF molecule inside the hydrophobic cavity of HP-β-CD results in an increase of aqueous solubility of the former.     

Electrochemical chiral recognition of tryptophan using a glassy carbon electrode modified with β-cyclodextrin and graphene

We report on a method for electrochemical enantioselective recognition of tryptophan (Trp) enantiomers. It is based on competitive host-guest interaction between a deoxy-(2-aminoethylamino)-β-cyclodextrin (CD) bound to graphene nanosheets and the Cu(II) complexes of the Trp enantiomers via a ligand exchange mechanism. Chiral recognition was investigated via cyclic voltammetry and electrochemical impedance spectroscopy. The results reveal that the CD bound to graphene displays a stronger interaction with the Cu(II) complex of L-Trp than to that of D-Trp. The method was applied to the determination of the ratio of Trp enantiomers in mixtures.

Molecular recognition of a self-assembled monolayer of a polydithiocarbamate derivative of β-cyclodextrin on silver

The synthesis and molecular recognition properties of a new sulfur containing β-cyclodextrin (β-CD) derivative chemisorbed on a silver surface are described. Hepta-6-amino-6-deoxy-β-CD was allowed to react with CS₂ in the presence of ammonia to give a mixture of partially substituted dithiocarbamate derivatives with an average degree of substitution of 4.5. A modified silver electrode with this derivative is capable of discriminating between the three positional isomers of nitrobenzoate ion and nitrophenol, as determined by cyclic voltammetry. Only the meta- and para-isomers give a signal corresponding to the reduction of the nitro group. This is attributed to the different orientations of the nitro group with respect to the silver surface after inclusion in the CD cavity. Experiments in the presence of cyclohexanol showed a decrease in signal intensity of the meta- and para-isomers which is associated with the competitive complexation of this guest, suggesting that the electroactive probe is complexed to the cavity.     

Voltammetric chiral discrimination of tryptophan using a multilayer nanocomposite with implemented amino-modified β-cyclodextrin as recognition element

An electrochemical chiral multilayer nanocomposite was prepared by modifying a glassy carbon electrode (GCE) via opposite-charge adsorption of amino-modified β-cyclodextrin (NH₂-β-CD), gold-platinum core-shell microspheres (Au@Pts), polyethyleneimine (PEI), and multi-walled carbon nanotubes (MWCNTs). The modified GCE was applied to the enantioselective voltammetric determination of tryprophan (Trp). The Au@Pts enable an effective immobilization of the chiral selector (NH₂-β-CD) and enhance the electrochemical performance. Scanning electron microscopy, transmission electron microscopy, UV-vis spectroscopy, FTIR and electrochemical methods were used to characterize the nanocomposite. Trp enantiomers were then determined by differential pulse voltammetry (DPV) (with a peak potential of +0.7 V vs. Ag/AgCl). The recognition efficiency was expressed by an increase in peak height by about 32% for DPV determinations of L-Trp compared to D-Trp in case of a 5 mM Trp solution of pH 7.0. Response was linear in the 10 μM to 5.0 mM concentration range, and the limits of detection were 4.3 μM and 5.6 μM with electrochemical sensitivity of 43.5 μA·μM^?1·cm^?2 and 34.6 μA·μM^?1·cm^?2 for L-Trp and D-Trp, respectively (at S/N =?3).

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Graphical Abstract Schematic of an electrochemical chiral multilayer nanocomposite composed of multi-walled carbon nanotubes (MWCNTs), polyethyleneimine (PEI), gold-platinum core-shell microspheres (Au@Pt) and amino-modified β-cyclodextrin (NH₂-β-CD). It was prepared by modifying a glassy carbon electrode (GCE) for enantioselective voltammetric determination of tryptophan (Trp) enantiomers.

     

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.     

The development of a cholesterol biosensor using a liquid crystal/aqueous interface in a SDS-included β-cyclodextrin aqueous solution

Sodium dodecyl sulphate (SDS) including β-cyclodextrin (β-CD) (β-CD_SDS) was used to detect cholesterol at the 4-cyano-4′-pentylbiphenyl (5CB)/aqueous interface in transmission electron microscopy (TEM) grid cells. The β-CD acts as a host for SDS (guest). The guest SDS enclosed within the β-CD cavity was replaced with cholesterol by injecting cholesterol solution into the TEM cell at concentrations greater than 3 μM. The replacement of SDS with cholesterol was confirmed by pH measurement and high performance liquid chromatography (HPLC). The SDS excluded from the β-CD altered the planar orientation of the 5CB confined within the TEM grid cell to a homeotropic orientation. This planar-to-homeotropic transition was observed using a polarized optical microscope under crossed polarizers. This convenient TEM grid cell provides a new method for the selective detection of cholesterol without immobilization of the detecting receptors (enzyme, antibody, or aptamer) or the use of sophisticated instruments.     

Enhanced stereoselectivity of a Cu(II) complex chiral auxiliary in the synthesis of Fmoc-L-γ-carboxyglutamic acid

L-γ-Carboxyglutamic acid (Gla) is an uncommon amino acid that binds avidly to mineral surfaces and metal ions. Herein, we report the synthesis of N-α-Fmoc-L-γ-carboxyglutamic acid γ,γ'-tert-butyl ester (Fmoc-Gla(O(t)Bu)(2)-OH), a suitably protected analogue for Fmoc-based solid-phase peptide synthesis. The residue was synthesized using a novel chiral Cu(II) complex, whose structure-based design was inspired by the blue copper protein rusticyanin. The five-coordinate complex is formed by Shiff base formation between glycine and the novel ligand (S)-2-(N-(2-methylthio)benzylprolyl)aminobenzophenone in the presence of copper. Michael addition of di-tert-butyl methylenemalonate to the α-carbon of the glycine portion of the complex occurs in a diastereoselective fashion. The resulting (S,S)-complex diastereomer can be easily purified by chromatography. Metal complex decomposition followed by Fmoc protection affords the enantiomerically pure amino acid. With the use of this novel chiral complex, the asymmetric synthesis of Fmoc-Gla(O(t)Bu)(2)-OH was completed in nine steps from thiosalicylic acid in 14.5% overall yield.     

Thermodynamic studies of inclusion complex between cetyltrimethylammonium bromide (CTAB) and β -cyclodextrin ( β -CD) in water/n-butanol mixture,using potentiometric technique

The behaviour of the inclusion complex consisting of cetyltrimethylammonium bromide (CTAB) and β-cyclodextrin (β-CD) in water/n-butanol mixture was studied using ion selective electrodes sensitive to surfactant ions. The experiments were carried out at different temperatures and different composition of water/alcohol. The data obtained indicate that the inclusion complexes S(CD) and S(CD)₂ had formed between CTAB and β-CD in water/alcohol mixture environment. In addition to the 1 : 1 complex, CTAB formed 1 : 2 complexes with β-CD. Further investigation showed that K ₁ for S(CD) was greater than K ₂ for S(CD)₂, and the values of K_i were reduced with increasing butanol concentration. Finally, thermodynamic parameters of the complexation, i.e. ΔH°, ΔG° and ΔS° were also calculated. The obtained thermodynamic data showed that the hydrophobic interaction is the main factor for inclusion complex formation and tendency of complex formation has been reduced with increasing of medium hydrophobicity.     

Enantioselective phosphorescence behavior of naproxen in β-cyclodextrin supramolecular complex

In the presence of small amount of 1-iodo butane (IBu) (0.1 % (v/v)), Naproxen (Nap) displays strong room temperature phosphorescence (RTP) in β-cyclodextrin (β-CD) solution without deoxygenation because of the formation of ternary complex of β-CD, Nap, and IBu. The results indicate that β-CD shows good enantiodiscrimination for (R)-Nap and (S)-Nap. The RTP intensity of (R)-Nap is larger than that of (S)-Nap, the difference being 29.2 %. Both (R)-Nap and (S)-Nap exhibit single exponential phosphorescence decay with different lifetimes of 2.535 ± 0.056 and 1.798 ± 0.076 ms for (R)-Nap and for (S)-Nap, respectively. The corresponding association constants evaluated for (R)-Nap/β-CD/IBu and (S)-Nap/β-CD/IBu ternary complexes are (8.02 ± 0.15) × 10³ and (2.50 ± 0.06) × 10³ L mol^?1, respectively. Thus, the observation of RTP differences between (R)-Nap and (S)-Nap can be attributed to their different ability to form complexes with chiral β-CD.     

Host–guest inclusion complex of β-cyclodextrin and benzoic acid in water–ethanol solvents: spectroscopic and thermodynamic characterization of complex formation

Journal of Thermal Analysis and Calorimetry - In this study, an inclusion complex of benzoic acid with β-cyclodextrin (BA-βCD) was obtained from water–ethanol solvents. The yield of...     

The first synthesis of a water-soluble α-cyclodextrin/C60 supramolecular complex using anionic C60 as a building block

A novel supramolecular inclusion complex of α-CD/C₆₀ was synthesized using anionic C₆₀. The reaction progress was monitored in situ by visible and near-IR spectroscopy. The obtained complex was characterized by UV-vis, ¹³C NMR, MALDI-TOF, and cyclic voltammetry. The induction and dispersion forces are considered to be the major driving forces for the formation of a resulting α-CD/ inclusion complex.     

Thermodynamics of inclusion complex formation of β-cyclodextrin with a variety of surfactants differing in the nature of headgroup

The inclusion complexation of β-cyclodextrin with various surfactants, possessing the same alkyl chain length but differing in the hydrophilic headgroup, was investigated by isothermal titration microcalorimetry. Sodium dodecyl sulfate, sodium dodecyl sulfonate, dodecyltrimethylammonium bromide and dodecyl(dimethyl)amine oxide were investigated. The major aim of this study was to elucidate the effects of temperature and the nature of the headgroup on the complex formation. Thermometric titrations were effected between the temperatures (288 and 348) K. The results provided the stoichiometry, the equilibrium constant and the reaction enthalpy of complexation. Changes in Gibbs energy, entropy and van’t Hoff enthalpy were additionally calculated.     

Photoinitiated polymerization of β-cyclodextrin/methyl methacrylate host/guest complex in the presence of water soluble photoinitiator, thioxanthone-catechol-O,O′-diacetic acid

β-Cyclodextrin (β-CD) was used to complex the monomer, methyl methacrylate (MMA), yielding a water-soluble host/guest complex. Photoinitiated polymerization of β-CD/MMA complex was achieved in the presence of thioxanthone-catechol-O,O′-diacetic acid (TX-Ct), a one component water soluble photoinitiator. Photodecarboxylation of TX-Ct in water seems to be an important reaction mechanism. Therefore, resulting alkyl radicals are able to initiate the polymerization of β-CD/MMA host/guest complex in water.     

Electrochemical signal modulation in homogeneous solutions using the formation of an inclusion complex between ferrocene and β-cyclodextrin on a DNA scaffold

Two DNA conjugates modified with ferrocene and β-cyclodextrin were prepared as a pair of probes that work cooperatively for DNA sensing, in which the electrochemical signal of ferrocene on one probe was significantly "quenched" by the formation of an inclusion complex with β-cyclodextrin of the other probe on the DNA templates.     

Spectral characteristics of desipramine in β-cyclodextrin cavity through inclusion complex

The inclusion complexation behavior and its characterization of Desipramine (DP) with β-Cyclodextrin (β-CD) in solution phase are analyzed by UV and fluorescence spectroscopy. The solid inclusion complex is characterized by FT-IR, SEM, Powder XRD and TG/DTA. The stoichiometric ratio of the complexation is found to be 1:1. The orientation and structure of the complex are proposed based on the analysis of Patch-Dock server. The formation of inclusion complex has been confirmed on the base of the changes of spectroscopic properties will be encapsulated in partly either by any aromatic ring or by the aliphatic side chain. But our results showed that the aliphatic group of DP is in the cavity of β-CD.β-CD encapsulation and enhances the in-vitro cytotoxicityeffect of DP compound by forming inclusion complex in the solid state.