Preparation and characterization of inclusion complexes of beta-cyclodextrin with ionic liquid

The solubilities of beta-cyclodextrin (beta-CD), ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), and their mixture in water were determined, and the conductivity of these aqueous solutions was measured. It was demonstrated that beta-CD and bmimPF6 could enhance the solubility of each other, and the solubility curves of each were linear with gradients of about 1. The conductivity decreased remarkably with increasing beta-CD concentration, and a discernible break in the conductivity curve could be observed when beta-CD and bmimPF6 were equimolar in the solution. The solubility and conductivity results indicated that inclusion complexes (ICs) of 1:1 stoichiometry were formed. The inclusion compounds were further characterized by using powder X-ray diffraction (XRD) analysis, 13C CP/MAS (cross-polarization magic-angle spinning) NMR and 1H NMR spectroscopy, and thermogravimetric analysis (TGA). The results showed that the ICs were a fine crystalline powder. The host-guest system exhibited a channel-type structure and each glucose unit of beta-CD was in a similar environment. The decomposition temperature of the ICs was lower than that of bmimPF6 and beta-CD individually.     

Stabilization of dyes against hydrolytic decomposition by the formation of inclusion compounds

The decomposition reactions of the dyes phenol blue and murexide were measured spectroscopically in acidic solution at different temperatures. From these reaction rates and their temperature dependence in the absence and presence of various hosts, the stability constants and the reaction enthalpies of the dye complexes with noncyclic dextrins, cyclodextrins and cucurbituril were calculated.-Cyclodextrin enhances the stability of phenol blue in acidic solution. This effect is even more pronounced with cucurbituril. Due to the molecular structure of murexide this dye cannot form inclusion complexes with hosts containing hydrophobic cavities.     

Circular dichroism spectra of the inclusion complexes of phlorizin in cyclodextrins

Two aromatic rings of a phlorizin molecule form inclusion complexes with -CD and -CD. Induced circular dichroism spectra of these complexes have been measured to estimate the orientation of the two aromatic rings in the hydrophobic space of CDs. Apparent complex formation constants have been also estimated for each complex. It is concluded that phlorizin forms a stronger inclusion complex with -CD than with -CD.     

Relationships between the stability,circular dichroism spectrum and type of substitution in inclusion complexes formed between phenophthalein and different cyclodextrins

The perturbation of the three-site interaction of phenolphthalein on complexation with different cyclodextrins (CDs) has been investigated as a function of the type and degree of substitution of the CD. The UV visible spectra are practically identical, while the circular dichroism spectra change dramatically both in intensities and signs. Parallel to this, the stability constants are influenced not only by the size of the cavity but also by the substitution of its rims, particularly by that of the primary hydroxyls. The two phenomena can be related to allow conclusions concerning the mode of inclusion.     

The effects of increasing NaCl concentration on the stability of inclusion complexes in aqueous solution

Equilibrium constants and standard molar enthalpies of reaction were determined by titration calorimetry for the reaction of 1-butanol with 2-hydroxypropyl-b-cyclodextrin (HP-b-CD) in aqueous solution at different concentrations of NaCl (0-1.9 M). The standard molar free energy and entropy changes associated to the complexation were calculated from the corresponding equilibrium constants, K, and standard enthalpies determined experimentally. In NaCl solutions the inclusion complexes ButOH/HP-b-CD are more stable than in water and their stability increases at increasing NaCl concentration; otherwise, the standard molar enthalpy associated to the formation of the complexes does not change with the increasing of salt concentration. The dependence of K on NaCl concentration were used to evaluate the number of water molecules displaced from the hydration shells of HP-b-CD and ButOH in forming complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Structural Characterisation of Two Novel Diastereoisomeric Naproxen Appended β-Cyclodextrin Derivatives

The condensation reaction of 6-deoxy-6-amino(2-aminoethyl)-cyclomaltoheptaose (β-CyDen) and racemic [(R, S)-2-(6-methoxy-2-naphthyl) propanoic acid] (R,S-naproxen) affords two new diastereoisomeric naproxen-appended β-cyclodextrin derivatives. The structural analysis of these two β-CyD derivatives, undertaken by combined use of circular dichroism (CD) and 1D or 2D NMR techniques, shows that the naphthalene ring of the naproxen is included in the CyD cavity in both derivatives. The CD spectra are consistent with an axial complexation model, moreover, the self-inclusion mode is further corroborated by ¹H NMR ROESY spectra which also suggest the orientation of the naphthyl moiety in the cavity of both the diastereoisomers.     

Helix formation of poly(phenylacetylene) derivatives bearing amino groups at the meta position induced by optically active carboxylic acids

Two novel phenylacetylene derivatives bearing diethylaminomethyl groups at the meta position on phenyl groups [3‐(N,N‐diethylaminomethyl)phenyl]acetylene ( 1 ) and [3,5‐bis(N,N‐diethylaminomethyl)phenyl]acetylene ( 2 ) were synthesized and polymerized with [Rh(nbd)Cl]₂ (nbd: norbornadiene). Both monomers gave highly cis–transoidal stereoregular polymers that exhibited an induced circular dichroism (ICD) in the UV–visible region, probably because of a prevailing one‐handed helical conformation upon complexation with optically active carboxylic acids such as mandelic acid and lactic acid. The sign of the Cotton effects reflected the absolute configuration of the chiral acids. Therefore, these polymers can be used as a novel probe for determining the configuration of chiral acids. The polymers were stable in the presence of chiral acids in solution. The poly‐ 1 complexed with chiral acids exhibited a split‐type ICD, whereas the poly‐ 2 complexed with chiral acids showed a different, non‐split‐type ICD. The ICD pattern of the poly‐ 1 /chiral acids complexes dramatically changed with an increase in the concentration of the chiral acids, thus showing a non‐split‐type ICD similar to those of the poly‐ 2 /chiral acid complexes. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3180–3189, 2001     

Formation of poly(ethylene glycol) inclusion complexes in aqueous solutions of mixed cyclodextrins

Even though the addition of modified cyclodextrins (modified CDs) accelerates the precipitation in aqueous solutions of poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) the final amount of formed solid complex remains unchanged, with no significant presence of modified CDs detected by MALDI-TOF mass spectrometry. Thus unsuitability of kinetic turbidity measurements for determination of binding parameters was confirmed. On the other hand, theoretical calculations based on a model of a chain of freely accessible binding sites demonstrated that the results do not necessarily contradict the finding that individual modified CD molecules can thread onto PEG chains with the efficiency comparable to that of natural (unmodified) α-CD.     

Crystalline inclusion complexes of diterpenoid isosteviol with aromatic compounds

Crystalline inclusion complexes of diterpenoid isosteviol (ent-16-ketobeyeran-19-oic acid) with individual benzene, o-, m-, p-xylenes, ethylbenzene, isopropylbenzene, o-and m-nitoranilins, benzaldehyde, styrene and naphthalene are obtained and characterized by single crystal X-ray diffraction. As determined by GC and ¹H NMR spectroscopy, isosteviol selectively includes toluene from the equimolar benzene-toluene mixture, o-xylene from a commercial mixture of xylenes, o-and m-nitroanilins from their mixture with p-nitroanilin, and also styrene from styrene-ethylbenzene and styrene-isopropylbenzene mixtures thus yielding crystalline inclusion complexes.     

Chiral complexation and aggregation of bilirubin with serum albumin at a liquid/liquid interface

The chiral complexation of bilirubin (BR) with bovine and human serum albumin (BSA and HSA), and the aggregation of the complexes at the heptane+chloroform(5:1)/water interface were studied via UV/Vis absorption and circular dichroism (CD) measurements in combination with the centrifugal liquid membrane (CLM) method. The interfacial adsorptivities of BR, BSA and their complexes were also studied by performing interfacial tension measurements at the interface. The changes in the absorbances and the induced CD amplitudes of the interfacial BR-BSA complex provided insights into the mechanism of the conformational enantioselective complexation at the interface, and indicated that the chiral conversion induced by the complexation with BSA was from the P(+) form to the M(-) form of BR. The broadening of the 450 nm band and the appearance of a new shoulder at 474 nm further supported the formation of aggregates of the complexes at the interface. The dependence of the CD amplitude on the molar ratio of BSA to BR revealed that the composition of the complex was 1:1 BSA:BR. The probable interfacial reaction scheme was proposed, and the affinity constant of BR-BSA at the interface was found to be 4.67 x 10(8) M(-2). The interfacial complexation and aggregation of BR and HSA were weaker than those of the BR-BSA complex due to the different BR binding positions adopted for BSA and HSA and the binding effect of chloroform.     

Polymer/surfactant interactions at the air/water interface

The development of neutron reflectometry has transformed the study and understanding of polymer/surfactant mixtures at the air/water interface. A critical assessment of the results from this technique is made by comparing them with the information available from other techniques used to investigate adsorption at this interface. In the last few years, detailed information about the structure and composition of adsorbed layers has been obtained for a wide range of polymer/surfactant mixtures, including neutral polymers and synthetic and naturally occurring polyelectrolytes, with single surfactants or mixtures of surfactants. The use of neutron reflectometry together with surface tensiometry, has allowed the surface behaviour of these mixtures to be related directly to the bulk phase behaviour. We review the broad range of systems that have been studied, from neutral polymers with ionic surfactants to oppositely charged polyelectrolyte/ionic surfactant mixtures. A particular emphasis is placed upon the rich pattern of adsorption behaviour that is seen in oppositely charged polyelectrolyte/surfactant mixtures, much of which had not been reported previously. The strong surface interactions resulting from the electrostatic attractions in these systems have a very pronounced effect on both the surface tension behaviour and on adsorbed layers consisting of polymer/surfactant complexes, often giving rise to significant surface ordering.     

Structure-retention studies on the inclusion complex formation of some polycyclic aromatic hydrocarbons with β-cyclodextrin

Summary The retention behaviour of a group of polycyclic aromatic hydrocarbons having nearly equal ionization potentials but different molecular polarizability values was investigated using reversed-phase HPLC. Methanol-water binary systems containing -cyclodextrin were applied as the mobile phase. The relationships between the capacity factors, molecular polarizabilities and the shape parameter of solute molecules are discussed.     

Thermodynamic evaluation of antibacterial activity for inclusion complexes of amoxicillin with cyclodextrins

The antibacterial action of amoxicillin (AMPC) and the inclusion complexes of AMPC with α-, β- and γ-cyclodextrins (α-CD, β-CD and γ-CD, respectively) to Escherichia coli B (E. coli) was evaluated by isothermal titration microcalorimetry and by petri-dish bioassay method. The effects of the compounds on produced heat during the exponential phase of the E. coli growing were measured and the growing rate constants of the cells was calculated from the power-time (p-t) curve before and after the treatment with AMPC. Results from the both methods showed that the antibacterial activity became stronger in the following order: AMPC-βCD > AMPC-γCD ≈ AMPC-αCD > AMPC only.     

Effect of the secondary structure of poly-L-lysine on the adsorption at the water/dodecane interface

The adsorption of poly-L-lysine of different conformation (-helix, -sheet and random coil) at the water/dodecane interface has been studied by interfacial tension measurements using the drop volume method. The experimental adsorption isotherms provide information about a critical aggregation concentration, the maximum interfacial tension depression_max and the minimum area A occupied by adsorbed molecules at the interface. Differences in_max exist between -helix and -sheet and, moreover, in the area values between random-coil on the one side and -helix and -sheet on the other hand.     

Complex of lysozyme and Myramistin: formation and adsorption at the water–xylene interface

1. Download : Download high-res image (127KB)
2. Download : Download full-size image

     

Spectroscopic characterisation of the inclusion complexes between the antifungal drugs naftifine and terbinafine and cyclodextrins

The complexation of naftifine (NF) and terbinafine (TB) with cyclodextrins (CDs) has been investigated by UV/visible and ¹H NMR spectroscopy, ROESY techniques and also ESI-MS. Both drugs form 1:1 inclusion complexes with all the CDs tested except with α-CD, as deduced from the Benesi–Hildebrand plots and confirmed by ESI-MS and NMR spectroscopy (Job plot method). The K ₁₁ values for NF decrease in the order β-CD > methylated β-CD > 2-hydroxypropyl-β-CD >γ-CD. The determination of the enthalpy and entropy provides information about the main driving forces in the process. The stability constants of the complexes NF–β-CD, TB–β-CD and TB–γ-CD determined by ¹H NMR spectroscopy are in agreement with the values obtained by UV. For TB–β-CD, the value is higher, due to the fact that the length of the TB aliphatic chain allows a deeper inclusion of the naphthalene group inside the corresponding β-CD molecule, according to the 2D ROESY experiments.     

A kinetic study of the formation of beta-cyclodextrin complexes with monomolecular films of fatty acids and glycerides spread at the air/water interface

The kinetics of formation of inclusion complexes between beta-cyclodextrin and monolayers of one-, two- and three-chained lipid molecules, namely, oleic acid (OA), monoolein (MO), diolein (DO) and triolein (TO), was investigated at various pH using three independent dynamic methods. The formation and solubilization of soluble inclusion beta-CD/OA and beta-CD/MO complexes was detected by measuring the decrease of the surface area and surface pressure of the OA and MO monolayers in the presence of beta-CD within a wide range of concentrations. A third approach, describing the dilatational properties of the monolayers, influenced by the formation and solubilization of the complexes, was developed. Using the three above-mentioned independent methods, the rate constants of formation (k1) and dissociation (k2) of beta-CD/OA and beta-CD/MO, were determined. We observed that solubilization flux i s for OA monolayer increases with pH and at pH 11 reached a value, which is closed to the diffusion flux iD and the process thus becomes diffusion controlled. For MO monolayer no significant effects of pH was observed above pH 6. The surface pressure (Deltapi)--area per molecule (A) and surface potential (DeltaV)--area per molecule (A) isotherms and rheological properties of DO and TO monolayers were measured in the presence or absence of beta-CD. DO and TO form water-insoluble complexes with beta-CD, as visualized by AFM images.     

Interfacial behavior of sulforhodamine 101 at the polarized water/1,2-dichloroethane interface studied by spectroelectrochemical techniques

The transfer mechanism of an amphoteric rhodamine, sulforhodamine 101 (SR101), across the polarized water/1,2-dichloroethane (DCE) interface was investigated using cyclic voltammetry, differential voltfluorometry and potential-modulated fluorescence (PMF) spectroscopy. The voltammetric response for the ion transfer of SR101 monoanion from water to DCE was observed as the diffusion-controlled transfer process. An unusual voltammetric response was found at 0.15 V more negative than the formal transfer potential of SR101⁻ in the cyclic voltammogram and voltfluorogram. The frequency dependence of the PMF responses confirmed the presence of the adsorption processes at negative potentials. In addition, a further transient adsorption step was uncovered at The interfacial mechanism of SR101 is discussed by comparing the results obtained from each technique.     

Investigation of the oxidation of hydroquinone at the liquid/liquid interface

<正>The oxidation of hydroquinone(QH_2) was investigated for the first time at liquid/liquid(L/L) interface by scanning electrochemical microscopy(SECM).In this study,electron transfer(ET) from QH_2 in aqueous to ferrocene(Fc) in nitrobenzene (NB) was probed.The apparent heterogeneous rate constants for ET reactions were obtained by fitting the experimental approach curves to the theoretical values.The results showed that the rate constants for oxidation reaction of QH_2 were sensitive to the changes of the driving force,which increased as the driving force increased.In addition,factors that would affect ET of QH_2 were studied.Experimental results indicated ion situation around QH_2 molecule could change the magnitude of the rate constants because the capability of oxidation of QH_2 would be affected by them.     

Inclusion complexes of the natural product gossypol. Clathrate type inclusion complexes of gossypol with carbonyl group containing guests

The crystal structures of 2:1 inclusion complexes of gossypol with methyl propionate (GPMEP) and ethyl acetoacetate (GPEAA) have been determined by X-ray structure analysis. The crystals of GPMEP, C₃₀H₃₀O₈l/2 C₄H₈O₂, are monoclinic, space groupC2/c,a=11.079(3),b = 30.724(7), c = 16.515(5) Å, = 90.46(2)°,V = 5621(3) Å,Z = 8,D _x = 1.33 g cm^–3. The structure has been refined to the finalR value of 0.059 for 1899 observed reflections. The crystals of GPEAA, C₃₀H₃₀O₈l/2 C₆H₁₀O₃, are monoclinic, space groupC2/c,a=11.095(2),b=30.604(9),c = 16.955(5) Å, = 88.27(2)°,V = 5754(3) Å,Z = 8,D _x = 1.35 g cm^–3. The structure has been refined to the finalR value of 0.056 for 2502 observed reflections.In contrast to previously investigated inclusion complexes of gossypol the host molecules do not form centrosymmetric dimersvia hydrogen bonds. In the crystal structures the racemic gossypol is separated into enantiomers forming alternating bimolecular layers. Nearly perpendicular to these chiral bilayers run elongated cavities enclosed on each side by layers of opposite chirality. The surface of these layers is hydrophobic, the polar groups are hidden inside the layer. Guest molecules which are hydrogen bonded to the host are included in cylindrically shaped cavities. Possible hydrogen bonds between host and guest are analysed for this isostructural class of complexes.