Synthesis of γ-Cyclodextrin Pyrene-Labeled at the Hetero Rim and Its Use in Fluorescent Molecular Sensing

Fluorogenic active host labeled at the upper and lower rims of -cyclodextrin, namely, mono-3^A-deoxy-3^A-pyrenebutylamido-6^X-O-mono-pyrenebutylate-mono-altro--cyclodetrin (mixture -1,X = A, B, C, D, E, F, G, or H), has been synthesized in order to investigate their host-guest complexation with steroidal compoundsusing fluorescence spectra. Monomer and excimer fluorescence was observed for mixture host. Inclusion of a guest molecule in the cyclodextrin cavity resultedin increased monomer fluorescence and decreased excimer fluorescence. The extent of monomerand excimer fluorescence variations ofmixture -1 with the guestwas used as an indication for the sensing ability. The guest inducedfluorescence changes were measured for 10^-7 M solutions of mixture -1.The values I/I ⁰ , where I ⁰ and I are fluorescence intensities in the absence and presence of a guest, respectively, and I is I ⁰ - I, were then used to describe the sensing ability.     

Fluorescent Molecular Recognition and Sensing System of Bis-Dansyl Modified γ-Cyclodextrins

Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified -cyclodextrins (-1, -2, -3, and -4, respectively) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I₀, where I and I₀ are fluorescence intensities in the presence and absence of a guest and I is I₀- I, was used as a parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host–guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host–guest complexes.     

A High Sensitivity Fluorescent Chemo-sensory System Based on β-Cyclodextrin Dimer Modified with Dansyl Moieties

-Cyclodextrin dimer linked with ethylenediamine at the upper rim of the cyclodextrin has been synthesized and then modified with two dansyl moieties inthe presence of N,N'-dicyclohexylcarbodiimide. The sensing ability and bindingproperty of the title compound were investigated for steroids and terpenoids. Thefluorescence intensity of this dimer was decreased when a host–guest complex was formed. The value I/I⁰, where I⁰ and I are fluorescence intensitiesin the absence and presence of a guest and I is I⁰- I, was used as a parameter of sensitivity. This host exhibited a much higher sensitivity and selective molecular recognition ability for bile acids such as ursodeoxycholic acid andchenodeoxycholic acid and terpenoids such as (-)-borneol than the dansyl-modifiedcyclodextrins reported previously including -cyclodextrin dimer. The behaviors of the appended moieties of the host during the formation of host–guest complexes were studied using induced circular dichroism (ICD) and fluorescence spectra. The ICD intensityof this dimer was decreased on accommodation of a guest and this spectral pattern of the title dimer was opposite to that of bis dansyl-modified -cyclodextrin monomer. Theguest-induced variations in the fluorescence and ICD intensities suggest that this dimer formed a 1 : 1 host–guest complex and the appended moieties act as a hydrophobic cap.     

Fluorescent Chemosensor Based on the Pyrene@2β-Cyclodextrin Complex: Response to Aromatic Amino Acids

The applicability of the pyrene@2β-cyclodextrin complex as a fluorescent chemosensor for aromatic amino acids has been studied by fluorescence spectroscopy. For the first time, it has been that the sensitivity of the complex to the implementation of D-enantiomers into its cavity is higher in comparison with the L-enantiomers of aromatic amino acids. Quantum-chemical calculations confirmed that the binding of the D-enantiomers of aromatic amino acids with P@2βCD is characterized by a greater energy of complexation in comparison with the L-enantiomers.     

Reversibly Switchable Fluorescent Molecular Systems Based on Metallacarborane–Perylenediimide Conjugates

Icosahedral metallacarboranes are θ-shaped anionic molecules in which two icosahedra share one vertex that is a metal center. The most remarkable of these compounds is the anionic cobalt-based metallacarborane [Co(C₂B₉H₁₁)₂]⁻, whose oxidation-reduction processes occur via an outer sphere electron process. This, along with its low density negative charge, makes [Co(C₂B₉H₁₁)₂]⁻ very appealing to participate in electron-transfer processes. In this work, [Co(C₂B₉H₁₁)₂]⁻ is tethered to a perylenediimide dye to produce the first examples of switchable luminescent molecules and materials based on metallacarboranes. In particular, the electronic communication of [Co(C₂B₉H₁₁)₂]⁻ with the appended chromophore unit in these compounds can be regulated upon application of redox stimuli, which allows the reversible modulation of the emitted fluorescence. As such, they behave as electrochemically-controlled fluorescent molecular switches in solution, which surpass the performance of previous systems based on conjugates of perylendiimides with ferrocene. Remarkably, they can form gels by treatment with appropriate mixtures of organic solvents, which result from the self-assembly of the cobaltabisdicarbollide-perylendiimide conjugates into 1D nanostructures. The interplay between dye π-stacking and metallacarborane electronic and steric interactions ultimately governs the supramolecular arrangement in these materials, which for one of the compounds prepared allows preserving the luminescent behavior in the gel state.     

Direct and Regioselective Di-α-fucosylation on the Secondary Rim of β-Cyclodextrin

A straightforward glycosylation method is described to regio- and stereoselectively introduce two α-l -fucose moieties directly to the secondary rim of β-cyclodextrin. Using NMR and MS fragmentation studies, the nonasaccharide structure was determined, which was also visualized using molecular dynamics simulations. The reported glycosylation method proved to be robust on gram-scale, and may be generally applied to directly glycosylate β-cyclodextrins to make well-defined multivalent glycoclusters.     

Host-guest Assembly Based on γ-Cyclodextrin-functionalized Multiwalled Carbon Nanotubes for Rutin Electrochemical Sensing

Here, we report multiwalled carbon nanotubes (MWCNTs) functionalized with γ-cyclodextrins (γCD) as a novel electrochemical strategy for Rutin determination, showing superior performance than β-cyclodextrins (βCD) modified MWCNTs, suggesting an adequate environment for host-guest interactions. Under optimized conditions, the sensor showed a linear range of 39–975 nmol L⁻¹ and a limit of detection of 7 nmol L⁻¹. When tested with quercetin, catechin, and caffeine, the platform presented high selectivity with an interference response <10 %. The method was employed to quantify Rutin in spiked pharmaceutical and herbal extracts, providing recovery of 93–98.4 %. Also, HPLC-PDA confirmed the method‘s accuracy.     

Study on Molecular Recognition of Pinocembrin with Methylated-β-Cyclodextrin

The inclusion behavior, inclusion capacity and inclusion mode of pinocembrin (PIN) with dimethyl-β-cyclodextrin (DM-β-CD) and trimethyl-β-cyclodextrin (TM-β-CD) were characterized by X-ray diffraction (XRD), thermal analysis, scanning electron microscopy (SEM), UV-visible spectral titration and molecular docking. The results showed that the packing ratio of PIN/DM-β-CD complex and PIN/TM-β-CD complex was 1:1. The water solubility of PIN increased by 817 times and 575 times in the inclusion complex with DM-β-CD and TM-β-CD, respectively. Molecular docking showed the PIN entered from the large end of the DM-β-CD molecule and penetrated through the cavity. The A and B rings of the PIN were respectively located at the big and small ends of the CD molecule. For the TM-β-CD, only A and C rings of the PIN entered the cavity of CD.     

Synthesis of Bis Dansyl-Modified β-Cyclodextrin Dimer Linked with Azobenzene and Its Fluorescent Molecular Recognition

Flexible dimeric host, 4,4'-azobenzenediamido-bis-{6-(2-dansyl-aminoethyl)6-deoxy--cyclodextrin}(beta; -1), has been synthesized in order to investigate itsfluorescent molecular sensory system transforming photoisomerization. Photoisomerizationof -1 was performed with photoirradiation by a 500W-Xelamp using a Corning 7-37 filter. Host beta; -1 showed puremonomer fluorescence, exhibiting a decrease in fluorescence intensity on accommodationof the guest, and the extent of fluorescence variation with a guest was employed to displaythe sensing ability of -1, in which the sensing parameter( I/I⁰)was used to describe the sensing ability. Host -1could detect chenodeoxycholic acid, ursodeoxycholic acid and hyodeoxycholic acid withhigh selectively. The behaviors of the appended moieties of -1during host-guest complexation were studied by induced circular dichroism (ICD) andfluorescence spectra and MM2 energy-minimized structure. The ICD and fluorescenceintensities of -1 decreased on the addition of a guest.The guest-induced variations in the ICD and fluorescence spectra, and MM2 energy-minimized structure suggested that the dansyl moieties of -1 worked as a hydrophobic cap when a host-guest complexation occurred.     

A Pseudorotaxane System Containing γ-Cyclodextrin Formed via Chiral Recognition with an AuI6AgI3CuII3 Molecular Cap

Solvent-mediated crystal-to-crystal transformations of [Au₆Ag₃Cu₃(H₂O)₃(d -pen)₆(tdme)₂]³⁺ (d -[ 1 (H₂O)₃]³⁺; pen²⁻= penicillaminate, tdme=1,1,1-tris(diphenylphosphinomethyl)ethane) to form unique supramolecular species are reported. Soaking crystals of d -[ 1 (H₂O)₃]³⁺ in aqueous Na₂bdc (bdc²⁻=1,4-benzenedicarboxylate) yielded crystals containing d -[ 1 (bdc)(H₂O)₂]⁺ due to the replacement of a terminal aqua ligand in d -[ 1 (H₂O)₃]³⁺ by a monodentate bdc²⁻ ligand. When γ-cyclodextrin (γ-CD) was added to aqueous Na₂bdc, d -[ 1 (H₂O)₃]³⁺ was transformed to d -[ 1 (bdc@γ-CD)(H₂O)₂]⁺, where a γ-CD ring was threaded by a bdc²⁻ molecule to construct a pseudorotaxane structure. While the use of dicarboxylates with an aliphatic carbon chain instead of bdc²⁻ afforded analogous pseudorotaxanes, such pseudorotaxane species were not formed when crystals of [Au₆Ag₃Cu₃(H₂O)₃(l -pen)₆(tdme)₂]³⁺ (l -[ 1 (H₂O)₃]³⁺) enantiomeric to d -[ 1 (H₂O)₃]³⁺ were soaked in aqueous Na₂bdc and γ-CD, affording only crystals containing l -[ 1 (bdc)(H₂O)₂]⁺.     

Studies on Molecular Recongnition of -Cyclodextrin with Diphenyl compounds

The cyclodextrins(CDs) are a class of cyclic oligosaccharides made up of six(α), seven(β) or more [α-(1,4)-linked] D-glucopyranose units, and shaped like truncated cones with primary and secondary hydroxyl groups crowning the narrower rim and wider rim respectively. As they have a hydrophobic cavity of appropriate dimension, they can bind with various guest moleculars, such as hydrocarbon, cyclohexane, aromatic compounds, to form inclusion complexes. The cyclodextins inclusion complexation…     

Performance Evaluation on a Modified β-Cyclodextrin Crosslinking Acid System

Russian Journal of Applied Chemistry - Maleic anhydride (MAH) and β-cyclodextrin (β-CD) were chosen to synthetize vinyl β-cyclodextrins monomer (MAH-β-CD) by alcoholysis...     

Hg2＋-Selective Fluorescent Chemosensor Based on Cation-π Interaction

Two sulphur-containing 4-aminonaphthalimide derivatives were investigated as Hg2＋ fluorescent chemosensors. In CH3CN, both sensors present a remarkable fluorescence enhancement to Cu2＋ and Fe3＋, but a selective fluorescence quenching to Hg2＋ among the other metal ions. A cation-π interaction between Hg〉 and the naphthalimide moiety was proposed and confirmed By the density tunetional theory（DFT）.     

New Approaches to Chemical Sensing‐Sensors Based on Polymer Swelling

Abstract

Although there is an extensive literature on polymer swelling, only in recent years has work been performed to exploit this phenomenon for chemical sensing. The lifetime of most sensors based on polymer swelling is limited by delamination of the polymer film. Swelling and shrinking introduce a shear force at the sensor/polymer interface that eventually severs the covalent bonds holding the polymer layer onto the substrate. This is a problem for any sensor configuration that involves immobilization of a swellable layer on a rigid substrate. Recently, sensor platforms have been developed to address this problem. Furthermore, coupling polymer swelling to optical, magneto, and electrochemical transduction technologies has greatly increased the scope of applications for sensors based on swellable polymers.     

А Potentiometric Sensor for Ketoprofen Based on a β-Cyclodextrin Derivative

Journal of Analytical Chemistry - The preparation of Ag/AgCl inner electrode in the polymer layer (coated wire electrode) and glassy carbon electrodes for ketoprofen...     

Effect of β-Cyclodextrin on the Micellization of Cetyltrimethylammonium in Aqueous Solution at High Temperature

Molar volume and conductivity measurements have been carried out at 338.2 K for cetyltrimethylammonium chloride (CTAC) + H₂O and CTAC + β-cyclodextrin (β-CD) + H₂O systems. The apparent critical micelle concentrations, the dissociation degree of the micelle, the transfer free energy for the hydrocarbon chain of CTAC, the standard partial molar volumes of CTAC in aqueous β-CD solution and the stoichoimetry for the inclusion complex of CTAC with β-CD have been determined. The influence of β-CD and its complex on the micellization processes of CTAC are analyzed under this temperature. It is shown that β-CD partly screened the hydrophobic hydrocarbon chain of CTAC molecules from contact with the surrounding medium, and retarded the formation of CTAC micelles in a certain extent. The thermodynamic activity of CTAC is decreased. The β-CD and its complexes do not participate the formation of micelles of CTAC, and the complex have no effect on the micelle properties once the micelles are formed. Based on a simple model, the number of CH₂ groups entered the cavity of β-CD was calculated. The result suggests that β-CD forms strong complex with CTAC, and the stoichoimetry is found to be 2:1. This supports our conductivity results.     

Molecular Exchanging Energy of Anionic／Cationic Surfactants System on the Surface of Solution

In order to study synergism of the mixed surfactants system with molecular exchanging energy ( ε ), the Lennard-Jones formula has been firstly introduced to evaluate the ε of the mixed system, CH3(CH2)nOSO 3^- /CH3(CH2)nN^ (CH3)3, directly from their molecular structure. The comparison of the calculated and the observed results showed that this method is practical.     

Synthesis of Ultra—high Molecular Weight Polystyrene with a Catalyst System Based on Calixarene—Yttrium Complex

Introduction　　Inordertoexploitnewapplicationsofrare earthcata lystsinpolymersynthesis,polymerizationofstyrenewithrareearthcatalysthasbeencarriedoutinourlabrecently .1 6 Inthispaperthenewcatalyticsystemofcalixarene yttriumforthepreparationofultra highmolecularweightpolystyrene(Mw>4× 10 5)isreported ,becauseofitsexcellentmechan icalandthermalcharacteristicscomparedwiththegeneralpurposepolystyrene.ExperimentalMaterials　　Styrene (chemicalreagentgrade)wasdriedovercalciumhydrideforseveraldays …     

Influence of the Water Content on the Thermal Behaviour of β-Cyclodextrin at Low and Very Low Temperature

Heat capacities of -CD·9.7H₂O weremeasured by adiabatic calorimetry in the temperature range10–300 K. Differential scanning calorimetry wasused to follow the evolution of the thermalbehaviour versus hydration ratio between 170 and300 K. At least three different behaviours wereobserved, according to the number, n, of watermolecules: 0 < n < 7, 7 < n < 10, and n > 10.These macroscopic results are discussed in terms oforganization differences between the most or theleast hydrated -CD. The structuring effectof the hydration water molecules is emphasised. Theexistence of two energetically distinct -CDhydrates (n < 10 and n > 10) seems to be confirmed. Thishypothesis is discussed in comparison with previousspectroscopic and structural studies.     

A PM3 Molecular Orbital Study on the Conformational Equilibrium of Cyclohexane upon α-Cyclodextrin Inclusion Complexation

The effect ofα-cyclodextrin (α-CD) inclusion complexation on the conformational equilibrium of cyclo- hexane wasstudied with thesemiempirical PM3 molecularorbital calculations. The calculation results indicated that the chair form of cyclohexane is 18.5 kJ·mol-1lower than that of boat one in energy, however, theα-cyclodextrin inclusion complex of boat cycl ohexane is 4.4 kJ·mol-1more stable than the complex of chair form. It demon-strated that the conformational equilibrium of cyclohexane was influenced by theα-CD inclusion complexation. Hence, caution should be given when extrapolating the conformational behaviors of the guest compounds in the supramolecular systems totheir free forms, since the interactionsbetween the host and guest significantly affect the conformation of the guest compounds.