Search results for "Cyclodextrin"
showing 10 items of 266 documents
Optical planar Bragg grating sensor for real-time detection of benzene, toluene and xylene in solvent vapour
2012
Abstract We report on an optical planar Bragg grating sensor functionalized by a comparatively simple method to detect substances such as benzene, toluene and xylene (BTX). The functionalization is performed by allyl substituted γ -cyclodextrin derivatives which are immobilized on the sensor surface by dip coating. Our results prove the capability of this functionalized sensor system to detect lowest concentrations of BTX in solvent vapour in real-time with a sensitivity of 3±0.4 pm/100 ppm for benzene, 8±1 pm/100 ppm for toluene and 32±1 pm/100 ppm for m-xylene. Taking into account the spectral resolution and repeatability of the interrogation system this corresponds to a minimum concentra…
Spectrophotometric determination of binding constants between some aminocyclodextrins and nitrobenzene derivatives at various pH values
2002
Abstract The inclusion capacity of three modified cyclodextrins—namely mono-(6- N , N -dimethylamino-6-deoxy)- ( 3 ), mono-6-(2-aminoethyl)-amino-6-deoxy- ( 4 ) and mono-6-(2- N , N -dimethylaminoethyl)-amino-6-deoxy- ( 5 ) β-cyclodextrin, with six para -substituted nitrobenzenes ( A – F ) has been investigated at three different pH values. Molecular interactions in inclusion complexes have also been investigated by means of molecular mechanics (MM2/QD) models. The desolvation of the cyclodextrin is the most important factor in determining the binding ability of the various hosts. However, for a given host, electrostatic and van der Waals interactions and the formation of a hydrogen bond be…
Thermodynamics of cyclodextrin-star copolymer threading-dethreading process
2015
We investigated the interactions of a star-like copolymer with cyclodextrins (CD) with different cavity size. Direct measurements of thermodynamic properties were done, and the application of proper molecular models was useful for the interpretation of the involved phenomena. The CD–copolymer inclusion complexes were characterized by isothermal titration calorimetry. The copolymer aggregation induced by temperature was investigated by differential scanning calorimetry, volume and compressibility measurements. The behavior of the ternary T1107/CD/water mixture was interpreted considering competing equilibria. The investigated systems showed an interesting temperature responsive behavior so t…
Binding equilibria between beta-cyclodextrin and p-nitro-aniline derivatives: the first systematic study in mixed water-methanol solvent systems.
2009
Abstract Complexation equilibria, in mixed water–methanol solvent media, between native β-cyclodextrin and a set of suitably selected p -nitro-aniline derivatives were studied by means of polarimetry. The effects exerted by the organic co-solvent on the conditional inclusion free energies Δ G cond 0 and the differential molar optical rotations Δ Θ were thoroughly analyzed under the perspective of the enthalpy–entropy compensation effect. Experimental data suggest an intimate participation (‘dynamic co-inclusion’) of solvent molecules in the formation and in the conformational dynamics of the host–guest inclusion complex.
Two-Component Hydrogels Formed by Cyclodextrins and Dicationic Imidazolium Salts
2013
In the framework of our recent interest in studying the gelling behaviour of imidazolium salts, we took into account the possibility of obtaining two-component hydrogels by combining cyclodextrins and dicationic imidazolium salts. In particular, we used diimidazolium salts differing in the alkyl chain length and in the size, shape, and coordination ability of the anion, namely the 3,3′-di-n-decyl- and 3,3′-di-n-dodecyl-1,1′-(1,4-phenylenedimethylene)diimidazolium dibromide, and 3,3′-di-n-dodecyl-1,1′-(1,4-phenylenedimethylene)diimidazolium ditetrafluoroborate and dihexafluorophosphate. As far as cyclodextrins are concerned, to gain information on the effects of different sized cyclic oligos…
Calorimetric investigation of the complex formation between surfactants and α-, β- and γ-cyclodextrins
1992
Abstract A calorimetric technique has been used to study complex formation between α-, β- and γ-cyclodextrins (αCD, βCD and γCD) and some surfactants (sodium dodecylsulphate (SDS), hexadecyl trimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl) phenoxypoly(oxyethyleneglycol) (Triton X-100)). The experimental data indicate that some complexes (SDS-αCD, SDS-βCD and CTAB-αCD) are very stable and allow direct determination of their stoichiometry and molar enthalpy of complex formation. Those for other complexes closely fit a model based on an equilibrium reaction between surfactant, cyclodextrin and a single complex. According to the model, data analysis allows determination of the …
Capping α-Cyclodextrin with Cyclotriveratrylene by Triple Disulfide-Bridge Formation
2013
Disulfide-bond formation is an expeditious coupling reaction to make macropolycyclic symmetrical receptors. It is used here for the preparation of unsymmetrical cavitands based on α-cyclodextrin (α-CDX) and cyclotriveratrylene (CTV) analogues. Accordingly, diastereomeric hemicryptophanes 2a and 2b were obtained in 11 % isolated yield by the iodine oxidation of a 1:1 mixture of racemic cyclotrithiophenolene (3) and the C3-symmetric trithiol derivative of permethylated α-cyclodextrin (PM α-CDX) 4. Remarkably, the target hemicryptophanes were obtained in a 5:3 diastereomeric ratio. The reaction produced mainly (34 %) a singly disulfide-bridged PM α-CDX dimer 7, however no traces of triply disu…
Chiral recognition of protected amino acids by means of fluorescent binary complex pyrene/heptakis-(6-amino)-(6-deoxy)-β-cyclodextrin
2006
The ability of the binary complex pyrene (Py)/heptakis-(6-amino)-(6-deoxy)-β-cyclodextrin (am-β-CD) to act as a chiral selector was tested at two pH values (8.0 and 9.0). Phenylalanine (Phe), methionine (Met) and histidine (His) were used as chiral model molecules. The stability of ternary complexes Py/am-β-CD/amino acid was determined by means of spectrofluorimetric measurements. The data collected showed an increase in stability going from the binary to ternary complex and above all the possibility to use the binary complex as a chiral selector. Finally, data collected at two pH values showed that the binary complex is a better chiral selector when charged rather than in its neutral form.
Binding properties of mono-(6-deoxy-6-amino)-β-cyclodextrin towards p-nitroaniline derivatives: a polarimetric study
2009
Abstract Polarimetry was used in order to investigate the formation of supramolecular complexes between mono-6-amino-β-cyclodextrin and various p-nitroaniline derivatives at two different pH values. Comparison with the behaviour of native β-cyclodextrin gave us the opportunity to consider the effect exerted by the presence of charged groups, having different solvation requirements, on the binding equilibrium. Data offer some support to the hypothesis of ‘dynamic co-inclusion’ of solvent molecules within the host–guest complex.
The binary pyrene/heptakis-(6-amino-6-deoxy)-β-cyclodextrin complex: A suitable chiral discriminator. Spectrofluorimetric study of the effect of some…
2002
The effect of some α-amino acids and their esters on the stability of the binary pyrene/heptakis-(6-amino-6-deoxy)-β-cyclodextrin (py/am-β-CD) complex has been studied by means of fluorescence spectroscopy at two pH values (8.0 and 9.0). The binary complex was generally stabilized by adding the ternary agent at pH 8.0. A more varied substrate effect is observed at pH 9.0 where am-β-CD is present in the uncharged form. The conditional constant (β2) values determined by L/D α-amino acids show that the binary complex is a suitable receptor for chiral recognition. The enantiomer selectivity values obtained, ranging from 1.2 up to 7.4, are generally higher than those reported for α-amino acids a…