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1.
Proton nuclear magnetic resonance spectroscopy ((1)H NMR), which has become an important tool for the study "in situ" of beta-cyclodextrin (beta-CD) complexes, was used to study and structurally characterize the inclusion complexes formed between beta-CD and isoproturon, fenuron, monuron and diuron. The high variation of the chemical shifts from the proton located inside the cavity (H-3, H-5 and H-6) coupled with the non variation of the one located outer sphere of the beta-CD (H-1, H-2 and H-4) provided clear evidence of the inclusion phenomena. Two-dimensional rotating frame Overhauser effect spectroscopy (ROESY) experiments were carried out to further support the proposed inclusion mode.  相似文献   

2.
The inclusion complex of beta-cyclodextrin with gossypol was synthesized by using a convenient method of microwave irradiation. The structure of the complex was determined by 1H NMR, IR spectroscopy, and as well as the elemental analysis; the thermal stability was studied by means of differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The association constant between gossypol and beta-cyclodextrin measured via UV spectroscopy was 4462M(-1) at room temperature, following stoichiometry 1:2.  相似文献   

3.
To investigate quantitatively the cooperative binding ability of several beta-cyclodextrin oligomers bearing single or multiligated metal center(s), the inclusion complexation behavior of four bis(beta-cyclodextrin)s (2-5) linked by 2,2'-bipyridine-4,4'-dicarboxy tethers and their copper(II) complexes (6-9) with representative dye guests, i.e., methyl orange (MO), acridine red (AR), rhodamine B (RhB), ammonium 8-anilino-1-naphthalenesulfonic acid (ANS), and sodium 6-(p-toludino)-2-naphthalenesulfonate (TNS), have been examined in aqueous solution at 25 degrees C by means of UV-vis, circular dichroism, fluorescence, and 2D NMR spectroscopy. The results obtained indicate that bis(beta-cyclodextrin)s 2-5 can associate with one or three copper(II) ion(s) producing 2:1 or 2:3 bis(beta-cyclodextrin)-copper(II) complexes. These metal-ligated oligo(beta-cyclodextrin)s can bind two model substrates to form intramolecular 2:2 host-guest inclusion complexes and thus significantly enhance the original binding abilities of parent beta-cyclodextrin and bis(beta-cyclodextrin) toward model substrates through the cooperative binding of two guest molecules by four tethered cyclodextrin moieties, as well as the additional binding effect supplied by ligated metal center(s). Host 6 showed the highest enhancement of the stability constant, up to 38.3 times for ANS as compared with parent beta-cyclodextrin. The molecular binding mode and stability constant of substrates by bridged bis- and oligo(beta-cyclodextrin)s 2-9 are discussed from the viewpoint of the size/shape-fit interaction and molecular multiple recognition between host and guest.  相似文献   

4.
To investigate quantitatively the cooperative binding ability of beta-cyclodextrin dimers, a series of bridged bis(beta-cyclodextrin)s with 2,2'-diselenobis(benzoyl) spacer connected by different lengths of oligo(ethylenediamine)s (2-5) and their platinum(IV) complexes (6-9) have been synthesized and their inclusion complexation behavior with selected substrates, such as Acridine Red, Neutral Red, Brilliant Green, Rhodamine B, ammonium 8-anilino-1-naphthalenesulfonate, and 6-p-toluidino-2-naphthalenesulfonic acid, were investigated by means of ultraviolet, fluorescence, fluorescence lifetime, circular dichroism, and 2D-NMR spectroscopy. The spectral titrations have been performed in aqueous phosphate buffer solution (pH 7.20) at 25 degrees C to give the complex stability constants (K(S)) and Gibbs free energy changes (-DeltaG degrees ) for the inclusion complexation of hosts 2-9 with organic dyes and other thermodynamic parameters (DeltaH degrees and TDeltaS degrees ) for the inclusion complexation of 2-5with fluorescent dyes ANS and TNS. The results obtained indicate that beta-cyclodextrin dimers 2-5 can coordinate with one or two platinum(IV) ions to form 1:1 or 1:2 stoichiometry metallobridged bis(beta-cyclodextrin)s. As compared with parent beta-cyclodextrin (1) and bis(beta-cyclodextrin)s 2-5, metallobridged bis(beta-cyclodextrin)s 6-9 can further switch the original molecular binding ability through the coordinating metal to orientate two beta-cyclodextrin cavities and an additional binding site upon the inclusion complexation with model substrates, giving the enhanced binding constants K(S) for both ANS and TNS. The tether length between two cyclodextrin units plays a crucial role in the molecular recognition with guest dyes. The binding constants for TNS decrease linearly with an increase in the tether length of dimeric beta-cyclodextrins. The Gibbs free energy change (-DeltaG degrees ) for the unit increment per ethylene is 0.32 kJ.mol(-)(1) for TNS. Thermodynamically, the higher complex stabilities of both ANS and TNS upon the inclusion complexation with 2-5 are mainly contributed to the favorable enthalpic gain (-DeltaH degrees ) by the cooperative binding of one guest molecule in the closely located two beta-cyclodextrin cavities as compared with parent beta-cyclodextrin. The molecular binding ability and selectivity of organic dyes by hosts 1-9 are discussed from the viewpoints of the multiple recognition mechanism and the size/shape-fitting relationship between host and guest.  相似文献   

5.
Díaz AN  Feria LS  Sánchez FG 《Talanta》1994,41(4):509-514
The inclusion of dulcin in alpha- and beta-cyclodextrin has been studied by fluorescence spectroscopy. To quantitatively describe complex formation between the beta-cyclodextrin and dulcin, an association constant of 290 M(-1) at 21 degrees was obtained. The thermodynamics associated with the complex formation between dulcin and beta-cyclodextrin in aqueous solution has been studied. The obtained value of DeltaG(0) = -13.7 kJ/mole at 21 degrees , together with DeltaH(0) = -33.6 +/- 2.3 kJ/mole and DeltaS(0) = -67.2 +/-8.3 Jmole(-1) K(-1) indicate that dulcin has a very marked tendency to associate with beta-cyclodextrin in water. The inclusion complex of dulcin in beta-cyclodextrin has been used to determine dulein in the range 0.13-5 mug/ml the method has been applied to determine dulcin in soft drinks.  相似文献   

6.
A structural study of the inclusion compound of tolbutamide (TBM) with beta-cyclodextrin (beta-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was attempted by means of 1H-nuclear magnetic resonance (1H-NMR) experiments and computer molecular modelling. To establish the stoichiometry and stability constant of the beta-CD:TBM complex, the continuous variation method was used. The presence of true inclusion complexes between TBM and beta-CD or HP-beta-CD in solution was clearly evidenced by the 1H-NMR technique. Changes in chemical shifts of H-3 and H-5 protons, located inside the CD cavity, associated with variations in the chemical shifts of TBM aromatic protons provided clear evidence of inclusion complexation, suggesting that the phenyl moiety of the drug molecule was included in the hydrophobic cavity of CDs. This view was further supported by the observation of intermolecular NOEs between TBM and beta-CD and by the aid of a molecular modelling program, which established the most probable structure of the complex. The molecular graphic computation confirmed that the minimum energy, positioning TBM relative to beta-CD, occurs when the aromatic ring of TBM is included within the beta-CD cavity by its wider side, leaving the aliphatic chain externally, which is in good agreement with the results of 1H-NMR studies.  相似文献   

7.
Inclusion complexes of atenolol with beta-cyclodextrin (beta-CD) in aqueous solution have been investigated with (1)H NMR and UV-vis spectroscopy. The stoichiometry of this inclusion complex was established to be equimolar (1:1) and its stability constant was determined by UV-vis spectroscopy. The crystal structure of the beta-CD-atenolol (1:1) inclusion compound has been solved from synchrotron powder diffraction data using direct-space search techniques. The crystal structure model and (1)H NMR data are in good agreement and, with support of Hyperchem MM+ molecular dynamics results, suggest which protons are likely to be involved in the inclusion process that leads to the supramolecular architecture of this guest-host complex.  相似文献   

8.
The ability of beta-cyclodextrin (beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD), and carboxymethyl-beta-cyclodextrin (CM-beta-CD) to break the aggregate of the methylene blue (MB) and to form 1:1 inclusion complexes has been studied by absorption and fluorescence spectroscopy. Experimental conditions including concentrations of various cyclodextrins (beta-CD, HP-beta-CD and CM-beta-CD) and media acidity were investigated for the inclusion formation in detail. The formation constants are calculated by using steady-state fluorimetry, from which the inclusion capacity of different cyclodextrins (CDs) is compared. The results suggest that the charged beta-cyclodextrin (CM-beta-CD) is more suitable for inclusion of the cationic dye MB than the neutral beta-cyclodextrins (beta-CD, HP-beta-CD) at pH>5. A mechanism is proposed which is consistent with the stronger binding of MB with CM-beta-CD compared with the other CDs at pH>5.  相似文献   

9.
Al-catechin/beta-cyclodextrin and Al-quercetin/beta-cyclodextrin (beta-CD) inclusion compounds were synthesized and characterized by IR, UV-vis, 1H and 13C NMR and TG and DTA analyses. Because quercetin is sparingly soluble in water, the stability constants of the Al-quercetin/beta-CD and Al-catechin/beta-CD compounds were determined by phase solubility studies. The AL-type diagrams indicated the formation of 1:1 inclusion compounds and allowed calculation of the stability constants. The thermodynamic parameters were obtained from the dependence of the stability constants on temperature and results indicated that the formation of the inclusion compounds is an enthalpically driven process. The thermal decomposition of the solid Al-quercetin/beta-CD and Al-catechin/beta-CD inclusion compounds took place at different stages, compared with the respective precursors, proving that an inclusion complexation process really occurred.  相似文献   

10.
The molecular recognition behaviors of some representative bile salts by three 3,6'-bridged beta-cyclodextrin dimers with oligo(ethylenediamino) linkers in different lengths, i.e. 3,6'-(ethylenediamino-bridged) beta-cyclodextrin dimer (1), 3,6'-(diethylenetriamino-bridged) beta-cyclodextrin dimer (2), and 3,6'-(triethylenetetraamino-bridged) beta-cyclodextrin dimer (3), were investigated in aqueous phosphate buffer solution (pH 7.20) at 25 degrees C by means of 2D NMR spectroscopy and isothermal titration microcalorimetry. Owing to the cooperative host-linker-guest binding mode between host and guest, these 3,6'-bridged beta-cyclodextrin dimers showed significantly enhanced binding abilities and molecular selectivities as compared with native beta-cyclodextrin through the simultaneous contributions of hydrophobic, hydrogen bond, and electrostatic interactions. Thermodynamically, the inclusion complexations of these beta-cyclodextrin dimers with bile salts were mainly driven by large enthalpic gain, accompanied by slight to moderate entropic loss. An enthalpy-entropy compensation analysis demonstrated that these beta-cyclodextrin dimers experienced large conformational changes and extensive desolvation effect upon inclusion complexation with guest molecules.  相似文献   

11.
A series of bridged bis(beta-cyclodextrin(CD))s (2-7) were synthesized, i.e., bridged bis(beta-CD)s 2 and 3 bearing binaphthyl or biquinoline tethers and bridged bis(beta-CD)s 4-7 possessing dithiobis(benzoyl) tether, and their complex stability constants (KS), enthalpy (DeltaH degrees), and entropy changes (DeltaS degrees) for the 1:2 inclusion complexation with representative steroids, deoxycholate, cholate, glycocholate, and taurocholate, have been determined in an aqueous phosphate buffer solution of pH 7.20 at 298.15 K by means of titration microcalorimetry. The original conformations of bridged bis(beta-cyclodextrin)s were investigated by circular dichroism and 1H ROESY spectroscopy. Structures of the inclusion complexes between steroids and bridged bis(beta-CD)s in solution were elucidated by 2D NMR experiments, indicating that anionic groups of two steroid molecules penetrate, respectively, into the two hydrophobic CD cavities in one 6,6'-bridged bis(beta-CD) molecule from the secondary rim to give a 1:2 binding mode upon inclusion complexation. The results obtained from titration microcalorimetry and 2D NMR experiments jointly demonstrate that bridged bis(beta-CD)s 2, 3 and 5-7 tethered by protonated amino group possessing different substituted groups can enhance not only the molecular binding ability toward steroids by electrostatic interaction but also molecular selectivity. Thermodynamically, the resulting 1:2 bis(beta-CD)-steroid complexes are formed by an enthalpy-driven process, accompanied by smaller entropy loss. The increased complex stability mainly results from enthalpy gain, accompanied by large conformational change and extensive desolvation effects for the 1:2 inclusion complexation between bis(beta-CD)s and steroids.  相似文献   

12.
In this study, cyclodextrin inclusion complexes with rutin were prepared via co-precipitation method. Stability constant and solubility energy of beta-cyclodextrin complex were calculated as 262 M?1 and 1,737 kJ mol?1, respectively. Aqueous solubility of rutin was increased with inclusion complex of beta-cyclodextrin. The effect of temperature on both aqueous solubility of free rutin, and its inclusion complex was also studied. Characterization of cyclodextrin complexes were conducted with UV–Vis spectrophotometry, Fourier transform infrared spectroscopy, X-ray diffractometry, differential scanning calorimetry, thermal gravimetric analysis, nuclear magnetic resonance spectroscopy and scanning electron microscopy techniques. Characterization results supported formation of inclusion complexes. Dissolution profiles of rutin, physical mixture and inclusion complex of rutin were observed at 37 °C. Dissolution results proved the effect of cyclodextrin addition on solubility rate of rutin. After loading rutin and its complexes into silk fibroin based films, release tests were performed at 37 °C in neutral pH conditions for 24 h. Most of the rutin were released from silk fibroin films within the first 5 h and the rest of it was released slowly (sustained release). Electron microscope analyses showed that films had homogenous and dense morphologies. These results revealed that silk fibroin is useful for preparing bioactive films loaded with natural compounds and for modifying their release behaviour at physiological conditions.  相似文献   

13.
Crystalline 1:1 inclusion complexes with beta-cyclodextrin (beta-CD) and the sodium salt of nimesulide (4-nitro-2-phenoxymethanesulfonanilide), and the sodium salt of the derivative 2-phenoxymethanesulfonanilide, have been prepared by co-precipitation from aqueous solution. The presence of true inclusion complexes was supported by elemental analysis, thermogravimetry and powder X-ray diffraction. FTIR and 13C CP MAS NMR spectroscopy confirmed that no chemical modification of the guests occurred upon formation of inclusion complexes. The reaction of the precursors 2-phenoxynitrobenzene and 2-phenoxyaniline with beta-CD was also studied and crystalline inclusion complexes with a 2:1 (host-to-guest) stoichiometry were isolated. The interaction of the different guest species with beta-CD host molecules was studied theoretically by carrying out ab initio calculations. Favourable inclusion geometries were obtained for the four guests mentioned above. On the other hand, it was found that the inclusion of the neutral guests nimesulide and 2-phenoxymethanesulfonanilide was considerably less favourable. This is in agreement with the experimentally observed difficulty in isolating true inclusion complexes containing these guests and beta-CD. The calculated lower stability is attributed to the different steric hindrance arising from the different conformational preferences of neutral and anionic forms.  相似文献   

14.
A series of novel 6,6'-bis(beta-cyclodextrin)s linked by 2,2'-bipyridine-4,4'-dicarboxy tethers; that is, 2,2'-bipyridine-4,4'-dicarboxy-bridged bis(6-O-beta-cyclodextrin) (2) and N,N'-bis(2-aminoethyl )-2,2'-bipyridine-4,4'-dicarboxamide-bridged (3), N,N'-bis(5-amino-3-azapentyl)-2,2'-bipyridine-4,4'-dicarboxamide-bridged (4) and N,N'-bis(8-amino-3,6-diazaoctyl)-2,2'-bipyridine-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-cyclodextrin) (5), has been synthesized as cooperative multipoint-recognition receptor models. The inclusion complexation behavior of 2-5 with organic dyes; that is, ammonium 8-anilino-1-naphthalenesulfonate, Brilliant Green, Methyl Orange, Acridine Red, and Rhodamine B, has been investigated in aqueous phosphate buffer solutions (pH 7.20) at 25 degrees C by means of ultraviolet, fluorescence, and circular dichroism spectrometry as well as by fluorescence lifetime measurements. The spectral titrations gave the complex stability constants (Ks) and Gibbs' free energy changes (deltaG degrees) for the inclusion complexation of 2-5 with the organic dyes and other thermodynamic parameters (deltaH degrees and deltaS degrees) for the inclusion complexation of 2-4 with the fluorescent dyes Acridine Red and Rhodamine B. Bis(beta-cyclodextrin)s 2-5 displayed higher binding abilities toward most of the examined dye molecules than native beta-cyclodextrin 1; this is discussed from the viewpoints of the size/shape-fit concept, the induced-fit interaction, and cooperative, multipoint recognition by the bridging chain and the dual hydrophobic cavities. Thermodynamically, the inclusion complexation of 2-4 with Acridine Red is totally enthalpy driven with a negative or minor positive entropic contribution, but the inclusion complexation with Rhodamine B is mainly entropy-driven with a mostly positive, but occasionally negative, enthalpic contribution; in some cases this determines the complex stability.  相似文献   

15.
The slightly water-soluble flavonoid quercetin (QUE) and its inclusion with either beta-cyclodextrin (betaCD), hydroxypropyl-beta-cyclodextrin (HP-betaCD) or sulfobutyl ether-beta-cyclodextrin (SBE-betaCD) were investigated. The stoichiometric ratios and stability constants describing the extent of formation of the complexes have been determined by phase-solubility measurements; in all cases type-A(L) diagrams have been obtained (soluble 1:1 complexes). The results showed that the inclusion ability of betaCD and its derivatives was the order: SBE-betaCD>HP-betaCD>betaCD. Kinetic studies of DPPH with QUE and CDs complexes were done. The results obtained indicated that the QUE-SBE-betaCD complex was the most reactive form. The scavenging capability of QUE and CDs complexes with DPPH and galvinoxyl was studied using ESR spectroscopy. All complexes showed a higher scavenging capability with both radicals, compare quercetin in water. Beside, these results indicated that the complexes formed maintained the quercetin antioxidant activity.  相似文献   

16.
A series of novel bis(beta-cyclodextrin)s tethered with organoselenium linkers, i.e., 6,6'-(o-phenylene-diseleno)-bridged bis(beta-cyclodextrin) (2), 6,6'-[2,2'-diselenobis(benzoyloxy)]-bridged bis(beta-cyclodextrin) (3), and 6,6'-[2,2'-diselenobis[2-(benzoylamino)ethylamino]]-bridged bis(beta-cyclodextrin) (4), were synthesized from beta-cyclodextrin (1). The inclusion complexation behavior of 1-4 with some dyes, such as 8-anilinonaphthalenesulfonate (ANS), Brilliant Green, Crystal Violet, Tropaeolin OO, Auramine O, and Methyl Orange, was investigated in aqueous phosphate buffer solution (pH 7.20) at 25 degrees C by UV-vis, fluorescence, and circular dichroism spectrometry, as well as fluorescence lifetime measurements. The complex stability constants (Ks) and Gibbs free energy changes (delta Go) for the stoichiometric 1:1 inclusion complexation of 1-4 with the dyes were obtained by the spectrophotometric or spectropolarimetric titrations. The bis(beta-cyclodextrin)s 2-4 showed much higher affinities toward these guest dyes than native beta-cyclodextrin 1 with fairly good molecular selectivities. The cooperative binding abilities of these bis(beta-cyclodextrin)s are discussed from the viewpoints of size/shape-fit interaction, induced-fit concept, and multiple recognition mechanism.  相似文献   

17.
The complex of a derivative of beta-cyclodextrin, that is mono[6-deoxy-6-(2-butenedinitrile-2,3-dimercapto sodium salt)]-beta-cyclodextrin (6-mnt-beta-CD), with titanocene (titanocene di[mono[6-deoxy-6-(2-butenedinitrile-2,3-dimercapto)]-beta-cyclodextrin], Cp2Ti[6-mnt-beta-CD]2) has been synthesized and characterized by IR spectroscopy, UV spectroscopy, elemental analysis, thermogravimetry, 1H- and 13C-NMR spectroscopy. The stoichiometry of the target molecule was determined by 1H-NMR spectroscopy and elemental analysis.  相似文献   

18.
The interaction of 15 steroidal drugs with a water-soluble beta-cyclodextrin polymer was studied by reversed-phase thin-layer chromatography in the absence and in the presence of 0.1 M sodium chloride. The relative strength of interaction was calculated and the relationship between the hydrophobicity parameters of the drugs and the strength of the drug-beta-cyclodextrin polymer was elucidated by principal component analysis. Drugs readily formed inclusion complexes with the cyclodextrin derivatives; the strength of the interaction was higher in the presence of sodium chloride. It was assumed that the formation of inclusion complexes may influence the behaviour of the drugs resulting in modified biological efficacy.  相似文献   

19.
Complex stability constants (KS), standard molar enthalpic changes (DeltaH degrees ), and entropic changes (TDeltaS degrees ) for the inclusion complexations of native beta-cyclodextrin (1) and two oppositely charged beta-cyclodextrins, i.e., mono(6-amino-6-deoxy)- beta-cyclodextrin (2) and mono[6-O-6-(4-carboxylphenyl)]- beta-cyclodextrin (3), with two (ferrocenylmethyl)dimethylaminium derivatives, i.e., FC4+Br(-) and FC8+Br(-), were determined at 25 degrees C in aqueous phosphate buffer solution (pH 7.20) by means of isothermal titration microcalorimetry (ITC). Cyclic voltammetry studies showed that the ferrocene groups of the guests were included in the beta-cyclodextrin cavity to form host-guest complexes. As compared with neutral beta-cyclodextrin, the positively charged host 2 showed decreased binding toward (ferrocenylmethyl)dimethylaminium guests. This was attributed to electrostatic repulsion, while the negatively charged host 3 displayed increased binding due to electrostatic attractions. Thermodynamically, the ionization of host CDs affects both enthalpic and entropic changes of host-guest complexations presumably by changing the hydrophobicity and the desolvation effect of hosts upon inclusion complexation. Moreover, the solvent effect was also discussed from the viewpoint of thermodynamics.  相似文献   

20.
The interaction of cloxacillin sodium with beta-cyclodextrin (beta-CD) has been studied by several analytical techniques, including (1)H NMR, fluorescence spectroscopy, infrared spectroscopy. In this paper, solid inclusion complex of cloxacillin sodium with beta-CD was synthesized by the coprecipitation method. In addition, the characterization of the inclusion complex has been proved by fluorimetry, infrared spectroscopy and 1D, 2D NMR. The experimental results confirmed the existence of 1:1 inclusion complex of cloxacillin sodium with beta-CD. The formation constant of complex was determined by fluorescence method and (1)H NMR. Spacial configuration of complex has been proposed on 2D NMR technique.  相似文献   

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