Exciton Coupling and Complexation Behaviour of β-Cyclodextrin Naphthoate

The host–guest complexation behaviour of-cyclodextrin 6-O-mono-2-naphthoate(1) and 6-[(N-2-naphthoyl-2-aminoethyl) amino]-6-deoxy--cyclodextrin (2) have been studied by the circular dichroism method. The exciton coupling band of 1 suggests that two naphthoyl moieties are partly included in one -CD cavity. Host 1 could form a dimer in a more polar solvent and the dimer could be dissociated in a less polar solvent or by adding a guest. Solvent-induced, concentrationinduced, and guest-induced circular dichroism variations were examined. No exciton coupling was observed for host 2.     

Supramolecular Linear Conglomerates Formed by β-Cyclodextrin Dimers and Sodium Deoxycholate

The formation of supramolecular structures by the complexation of two bile salts--sodium cholate (NaC) and sodium deoxycholate (NaDC)--with four new head-to-head g -cyclodextrin dimers was studied by NMR techniques. All dimers form 1:2 (dimer:bile salt) stoichiometry complexes with NaC. With NaDC, linear supramolecular conglomerates of an n : n stoichiometry were obtained for all dimers. ROESY spectra confirmed the presence of electrostatic interactions when a protonated amino group is present in the linking group. The dependence of the pseudo-equilibrium constants with the electrostatic interactions and steric hindrance is discussed.     

Preparation and Spectroscopic Study of Different Stoichiometric Solid Supramolecular Inclusion Complexes of β-Cyclodextrin with Short Chain Aliphatic Amines

The solid Supramolecular complexes of β-cyclodextrin (β-CD) with ethylenediamine 1, diethylenetriamine 2 and triethylamine 3 were obtained and characterized using elemental analysis, powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and 1H nuclear magnetic resonance spectroscopy. Based on the results of elemental analysis and 1H NMR, the guest-host stoichiometries of the three solid complexes were determined to be 5:2 for 1-β-CD, 1:1 for 2-β-CD, and 1:3 for 3-β-CD. The yields were relative to the molar volume ratio of guest toβ-CD cavity, and increased in the order: 1-β-CD<2-β-CD<3-β-CD. X-ray diffraction patterns of the inclusion complexes gave very good exhibitions not only in location of diffraction peaks but also in shape and diffraction intensity of the peaks due to the intermolecular complexations betweenβ-CD and the guests. The formation of host-guest inclusion complexes exhibited obviously enhanced phase change temperatures of the complexed guests such as 1 and 3. The H-5 protons located at the narrower rim inside the CD cavity experienced a higher shift upon inclusion while all other protons experienced lower shifts.     

Cucurbituril and β-Cyclodextrin as Hosts for the Complexation of Organic Dyes

The complexation of neutral organic molecules by cucurbituril and-cyclodextrin in formic acid was studied by means ofspectrophotometric titrations. In the case of -cyclodextrin thecomposition of the solvent has almost no influence upon the stability of thecomplexes formed. This situation is completely different for cucurbituril.Due to its interactions with protons the measured stability constants of thecomplexes formed with organic molecules increase with decreasing acidconcentration. At low acid concentrations cucurbituril forms more stablecomplexes with organic molecules than -cyclodextrin.     

Complexation of Aliphatic Alcohols by α- and β-Cyclodextrins and their Partial Methylated Derivatives in Aqueous Solution

The complexation of aliphatic alcohols by α- and β-cyclodextrins and their partially methylated derivatives has been studied by means of calorimetric titrations in aqueous solution. The methyl substituents have no pronounced influence upon the complex formation. α-Cyclodextrin and the partially methylated derivative form with only few exceptions more stable than β-cyclodextrin. With increasing chain length of the alcohols the values of the stability constants and reaction enthalpies increase in case of the complex formation with α-cyclodextrin and partially methylated α-cyclodextrin. In contrast the complex formation becomes disfavoured by the reaction entropy with an increasing number of methylene groups. The values of the reaction enthalpies with the β-cyclodextrins are close to zero. Thus the complexation is only favoured by entropic contributions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bi-directional Inclusion Complexation of Methylalkyl Viologens with β-Cyclodextrin and Naphthyl group-Tethered β-Cyclodextrins

Inclusion complexation of methylalkyl viologens(C₁C_nV²⁺; n = 7–10, 12) withmono-6-O-(2-sulfonato-6-naphthyl)-β-CD (1)and mono-6-O-(2-naphthyl)-β-CD (2) werestudied by steady-state and time-resolved fluorescencespectroscopies and compared with the binding of theviologens with native β-CD investigated by induced circulardichroism. The viologens form bimodal complexes with1 and 2, in which the bipyridinium group of theviologens is placed on the primary side (type I complex) andsecondary side (type II complex) of β-CD cavity, while thegroup is predominantly on the secondary side in complexeswith native β-CD. The microscopic binding constantsK_I and K _II were calculated from theanalysis of fluorescence data. The formation of the type Icomplexes with 1 and 2 appears to be largely dueto the charge–transfer interaction between the bipyridinium andnaphthyl groups in the complexes. This work shows thatthe location of the bipyridinium group in β-CDcomplexes and in the type II complexes of the viologens with1 and 2 depends little on the length of alkyl chainof the viologens.     

Inclusion Complexation of Carbaryl and β-Cyclodextrin in Solution and in the Solid State

This study was carried out with the aim ofinvestigating the interactions between-cyclodextrin and carbaryl, a carbamatepesticide, and their effect on some physico-chemicalproperties of carbaryl, such as aqueous solubility andlipophilicity. The interactions between carbaryl and-cyclodextrin were thoroughly investigated bothin solution and in the solid state. The effect of-cyclodextrin on the aqueous solubility ofcarbaryl was evaluated by the phase solubility method.The amount of carbaryl dissolved increased linearlywith the addition of -cyclodextrin according toan A_L type plot and without precipitation of thecomplex. The apparent stability constant of thecomplex was 289 ± 21 M^-1, assuming a 1 : 1stoichiometry; this value was confirmed by a methodbased on circular dichroism measurements.Equimolar carbaryl/-cyclodextrin solid systemswere prepared by physical-mixing and freeze-drying,and fully characterised by Differential ScanningCalorimetry, X-ray powder diffractometry and FourierTransform Infra-Red analysis. The results of the solidstate study demonstrated that the freeze-drying methodyields a system with a high degree of amorphisationand yields an inclusion complex.The dissolution profile of the pesticide was affectedby the physico-chemical properties of each solidsystem, the freeze-dried form dissolving more rapidly. However, the physical association of-cyclodextrin and carbaryl enhanced the aqueoussolubility of the insecticide as well.     

Selective Arylation of β-Cyclodextrin with an Ethylenediamino Group and Characteristics of Arylated β-Cyclodextrin Derivatives in Host–Guest Complexation

Mono-3-deoxy-(N-benzoyl-ethylenediamino)--CD, mono-3-deoxy-(N-benzylidene-ethylenediamino)--CD and mono-3-deoxy-(N-salicylidene-ethylenediamino)--CD, each having a flexible chain that bonds the aryl moiety on the secondary side of -CD, were prepared. The reaction processes might involve the formation of mono-(2,3-manno-epoxide)--CD as an intermediate under our reaction conditions. Further experiments showed that the aryl moiety which was bonded as a functional group on the primary side of -CD or on the secondary side of -CD with or without an ethylenediamino chain show remarkably different complexation properties in the complexation with small molecular guests such as alkanes, cycloketones etc.     

Manganese-Catalyzed β-Methylation of Alcohols by Methanol

We report an earth-abundant-metal-catalyzed double and single methylation of alcohols. A manganese catalyst, which operates at low catalyst loadings and short reaction times, mediates these reactions efficiently. A broad scope of primary and secondary alcohols, including purely aliphatic examples, and 1,2-aminoalcohols can be methylated. Furthermore, alcohol methylation for the synthesis of pharmaceuticals has been demonstrated. The catalyst system tolerates many functional groups among them hydrogenation-sensitive examples and upscaling is easily achieved. Mechanistic investigations are indicative of a borrowing hydrogen or hydrogen autotransfer mechanism involving a bimetallic K-Mn catalyst. The catalyst accepts hydrogen as a proton and a hydride from alcohols efficiently and reacts with a chalcone via hydride transfer.     

Interaction of β-Cyclodextrin with Unsaturated and Saturated Straight Chain Fatty Acid Anions Studied by Phenolphthalein Displacement

The interaction of -cyclodextrin (-CD) with palmitoleate, linolenate, caprinate and caprylate was studied by the displacement of phenolphthalein (PHP) from the -CD cavity. Absorbance values of -CD–PHP solutions at 550 nm in 0.020 mol L-1 Na2CO3 buffer, pH 10.5, at 21.0 ± 0.5 °C, increased as the fatty acid anion was added. The concentration range of fatty acid anion used was 0.390–32.1 × 10-4 mol L-1 in the study of palmitoleate and linolenate, 1.92–80.0 × 10-4 mol L-1 in the study of caprinate and 0.770–32.0 × 10-3mol L-1 in the study of caprylate. Concentrations of -CD and PHP were 1.00 × 10-3 mol L-1 and 1.00–3.00 × 10-4 mol L-1 respectively. Data were fitted by nonlinear regression to a two step complexation model. Complex formation constants thus determined for the 1 : 1 and 1 : 2, fatty acid anion : -CD complex were: (1.2 ± 0.2) × 104 and (2.9 ± 0.2) × 102 mol-1 L for palmitoleate, (9.3 ± 0.9) × 103 and (1.1 ± 0.1) × 102 mol-1 L for linolenate, (4.1 ± 0.2) × 103 and 81 ± 8 mol-1 L for caprinate, and (5.2 ± 0.7) × 102 and 27 ± 5 mol-1 L for caprylate respectively. The PHP–-CD complex was also evaluated as a spectrophotometric sensor for the determination of olive oil acidity.     

Experimental and Theoretical Studies on the Inclusion Complexation of β-Cyclodextrin with Phenothiazine Derivatives

Inclusion complexation of -cyclodextrin (-CD) with N-phenylphenothiazine ( 1), N-benzylphenothiazine ( 2) and N-phenethylphenothiazine ( 3) has been studied by means of UV-vis spectroscopy and molecular dynamics simulations. The association constants (K_a) were determined to be 126, 312 and 211 dm³/mol for inclusion of -CD with 1, 2 and 3, respectively. It shows that the K_a values are affected by the substituents of the guest compounds. The structures of the complexes and the conformation of the guest compounds bound by -CD in the complex have been discussed.     

Complexation of Volatile Organic Molecules from the Gas Phase with Cucurbituril and β-Cyclodextrin

Abstract

The first results about the complexing ability of the supramolecular ligand cucurbituril with different volatile organic molecules from the gas phase are presented. The behaviour of cucurbituril is similar to that of β-cyclodextrin. The capacity of both ligands was determined with toluene. Columns filled with β-cyclodextrin and cucurbituril have a capacity of 0.50 and 0.42 mol toluene per mol ligand, respectively. The extraction of volatile molecules is not limited to toluene, also several other organic molecules are complexed from the gas phase. The fluorescence spectra of the solid naphthaline and aniline complexes with cucurbituril and β-cyclodex-trin are presented. Comparing the differential scanning calorimetry (DSC) curves of cucurbituril, the cucurbituril toluene complex and silica gel with adsorbed toluene shows that a complexation and no adsorption takes place.     

Interaction of Fluorinated Alcohols with the β-Cyclodextrin/Acridine Complex

Abstract

The role of hydrogen bonding vs. hydrophobic interactions are evaluated with respect to the driving forces for alcohol complexation with β-cyclodextrin (β-CD). Simultaneous information is gathered regarding these considerations in the binding of acridine to the β-CD molecule.     

Solubility Study of Nimodipine Inclusion Complexation with α- and β-Cyclodextrin and some Substituted Cyclodextrins

The solubility of nimodipine was measured in aqueous solutions of the following cyclodextrins: -cyclodextrin (-CD), hydroxypropyl--CD (HP--CD), -cyclodextrin (-CD), random substituted methyl--CD (M--CD), three hydroxypropyl--CDs (HP--CD) with mutually different average degree of substitution, and hydroxypropyl--cyclodextrin (HP--CD). From the determined linear solubility diagrams the values of the binding constant K₁₁ of the inclusion complexes of nimodipine with the respective CDs were evaluated. The -CDs efficiently solubilized sparingly soluble nimodipine, the highest value of K₁₁ was found for M--CD (1680 M^-1), followed by -CD (550 M^-1) and HP--CDs, where the higher degree of substitution lowered K₁₁. Only slight solubilization of nimodipine was observed in the solutions of the -CDs and HP--CD.     

Affinity Capillary Electrophoresis Studies on the Influence of Alcohols on the Interaction of β-Cyclodextrin with Non-Steroidal Anti-Inflammatory Drugs

Summary The influences of methanol, ethanol, 1-propanol and 1-butanol on the binding constants of -cyclodextrin (-CD) with non-steroidal anti-inflammatory drugs such as acemetacin, indometacin, cinmetacin, sulindac and diclofenac sodium and the separation of these drugs were studied by affinity capillary electrophoresis. No obvious effect was observable upon addition of methanol up to 6% (v/v) in the running buffer, while the addition of other alcohols at the concentration of 2% resulted in obvious decrease in the binding constants of -CD with acemetacin, indometacin, cinmetacin and sulindac. With an increasing chain length of added alcohols, all of these changes increased. Upon additions of different alcohols in the running buffer the change of the binding constant of -CD with diclofenac sodium was inconspicuous. Based on these results, the separation conditions for these drugs were optimized. The presence of 6% methanol in the running buffer containing 3 mM -CD was helpful to the baseline separation of these drugs. The electrophorograms of these drugs in the presence of ethanol, 1-propanol and 1-butanol showed a worse separation due to the decrease in the binding constants. The methods for the separation of these drugs and the study on the binding constants possess the advantages of easy performance, high speed and low sample consumption. AcknowledgementThe authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (No.20275017), the Science Foundation of Jiangsu (No.BS2001063) and the Key Project of Cancer Institute of Jiangsu Province.     

Solvophobically Driven Complexation of Adamantyl Mannoside with β-Cyclodextrin in Water and Structured Organic Solvents

The effects of solvent and temperature on the complexation of adamantyl mannoside with β-cyclodextrin and 6-O-monotosyl-6-deoxy-β-cyclodextrin were explored experimentally and by means of molecular dynamics simulations. Efficient binding was observed only in hydrogen-bonded solvents, which indicated solvophobically driven complexation. The stability of the inclusion complex was considerably higher in aqueous media. A pronounced temperature dependence of Δ_rH^○ and Δ_rS^○, resulting in perfect enthalpy–entropy compensation, was observed in water. The complexation thermodynamics was in line with classical rationale for the hydrophobic effect at lower temperatures and the nonclassical explanation at higher temperatures. This finding linked cyclodextrin complexation thermodynamics with insights regarding the effect of temperature on the hydration water structure. The complexation enthalpies and entropies were weakly dependent on temperature in organic media. The signs of Δ_rH^○ and Δ_rS^○ were in accordance with the nonclassical hydrophobic (solvophobic) effect. The structures of the optimized product corresponded to those deduced spectroscopically, and the calculated and experimentally obtained values of Δ_rG^○ were in very good agreement. This investigation clearly demonstrated that solvophobically driven formation of cyclodextrin complexes could be anticipated in structured solvents in general. However, unlike in water, adamantane and the host cavity behaved solely as structure breakers in the organic media explored so far.     

Investigation of Haemolytic and Complexation Properties of γ-Cyclodextrin Carbonate Derivatives

New alkyl carbonates of -cyclodextrin have been obtained. These derivatives show lower haemolytic effect than the parent -cyclodextrin. The complexation behaviour was tested with three important drugs, namely: progesterone, diazepam and flurbiprofen. DSC analyses were consistent with the inclusion complex formation.     

Complexation of inorganic anions by β-cyclodextrin studied by polarography and 1H NMR

Abstract

Complexation of o-chloronitrobenzene with β-cyclodextrin has been studied in 0.1 M aqueous solutions containing PF₆ ^?, ClO₄ ^?, C₂O₄ ^2-, SCN^?, SO₄ ^2- and F^? anions by a polarographic method. Using an equation which takes account of the change in the cyclodextrin concentration due to the simultaneous complexation of the anion, both stability constants have been calculated. Interaction of the ClO₄ ^? anion with β-cyclodextrin has been confirmed by ¹H NMR techniques. It has been found that the ClO₄ ^? anion is trapped in the β-cyclodextrin cavity. The stability constant has been calculated. Results of polarographic and ¹H NMR studies have been compared.