Study on the supramolecular systems of 5-(2-hydroxy phenyl)-10,15,20-tris (4-methoxy phenyl) porphyrin with cyclodextrins

In neutral phosphate buffer solutions of pH 7.4, the inclusive complexation of 5-(2-hydroxy phenyl)-10,15,20-tris(4-methoxy phenyl) porphyrin (o-HTPP) with alpha-cyclodextrin (alpha-CD), beta-CD, heptakis (2,3,6-tri-O-methyl)-beta-CD (TM-beta-CD), SBE-beta-CD, HP-beta-CD and gamma-CD has been examined by means of UV-vis and fluorescence spectroscopy. The formation of inclusion complexes has been confirmed on the base of changes of spectroscopy properties. The o-HTPP forms 1:2 inclusion complexes with TM-beta-CD and 1:1 inclusion complexes with the other five cyclodextrins. The formation constants (K) of o-HTPP for the formation of the inclusion complexes have been estimated from the absorbance and fluorescence intensity changes in neutral phosphate buffer solutions. The K value (2.89x10(7)), which is the formation constant for the formation of the 1:2 inclusion supramolecular, is nearly 10(4) times than those of the 1:1 inclusion complexes. Compared to the other five cyclodextrins, the strongest inclusion ability of TM-beta-CD can be explained that the hydrogen bond plays significant role in the inclusion process. UV-vis experiments also showed that the cavity of TM-beta-CD causes the transform of the state of o-HTPP. In addition (1)H NMR data and 2D-ROSEY NMR spectra support the inclusion conformation of the o-HTPP-CD supramolecular system, indicating the interaction mechanism of inclusion processes.     

Complexation behavior of alpha-, beta-, and gamma-cyclodextrin in modulating and constructing polymer networks

A systematic study of the host-guest complexation by alpha-, beta-, and gamma-cyclodextrin (CD) in either the free state or as substituents of poly(acrylic acid) (PAA) with the hydrophobic n-octadecyl groups, C18, substituted onto PAA (HMPAA) and its effect on polymer aggregation and network formation is reported. Free alpha-CD, beta-CD, and gamma-CD mask hydrophobic associations between the C18 substituent of HMPAA in aqueous solution and form host-guest complexes with a 1:1 or CD:C18 substituent stoichiometry at 0.5 wt % polymer concentration. For alpha-CD this host-guest stoichiometry changes to 2:1 or 2alpha-CD:C18 at > or =1 wt % polymer concentrations but not for beta-CD and gamma-CD. Shear-thickening occurs when gamma-CD complexes C18 HMPAA substituents. Upon addition of sodium dodecyl sulfate, SDS (SDS:CD = 1:1), the hydrophobic associations between C18 diminished by alpha-CD masking were fully restored, were only partly restored in the case of beta-CD, and not restored for gamma-CD. When alpha- and beta-CD substituted PAA (alpha-CDPAA and beta-CDPAA) were mixed with HMPAA polymer, networks formed. As for free beta-CD, the beta-CD substituents of beta-CDPAA also formed 1:1 or beta-CD:C18 stoichiometry host-guest complexes with the C18 substituents of HMPAA. The alpha-CD substituents of alpha-CDPAA also formed 1:1 or alpha-CD:C18 stoichiometry host-guest complexes with some indication of the formation of 2:1 or 2alpha-CD:C18 stoichiometry host-guest complexes at polymer concentrations > or =1 wt %. The polymer networks formed by beta-CDPAA with HMPAA are less viscous than those formed by alpha-CDPAA, for which shear-thickening occurs at polymer concentrations > or =2 wt %. It is evident that the difference in CD annular size and its match with the C18 of HMPAA control the diversity of the interactions of alpha-CD, beta-CD, gamma-CD, alpha-CDPAA, and beta-CDPAA with HMPAA.     

Study of the complexation of fisetin with cyclodextrins

In this work, the interaction between fisetin (3,3',4',7-tetrahydroxyflavone) (Fis) and cyclodextrins (CDs) (alpha and beta) was studied through UV-vis absorption, steady-state fluorescence, induced circular dichroism, and (1)H NMR experiments with dependence on temperature and pH. Some experimental data were compared with quantum-mechanics studies based on the SAM1 (AMPAC) semiempirical model, as well as with the B3LYP and MPW1PW91 functional models from density functional theory using the 6-311G and 3-21G basis sets. The spectroscopic measurements show that Fis does not form stable complexes with alpha-CD. On the other hand, at pH 4.0 and 6.5, the complex Fis-beta-CD is formed in a Fis:beta-CD 1:1 stoichiometry and an equilibrium constant (K) of 900 +/- 100 M(-1). In basic medium (pH 11.5), K decreases to 240 +/- 90 M(-1) because Fis deprotonation leads to its better solubilization in water. Molecular modeling points out that Fis is not totally inserted into the inner cavity of beta-CD. The formation of the inclusion complex renders an environment that enhances intramolecular excited state proton transfer. The inclusion complex is formed preferentially via entry of the Fis phenyl group into beta-CD.     

A spectroscopic study of the inclusion of azulene by beta- and gamma-cyclodextrins

The inclusion of azulene (AZ) inside the cavities of beta-cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD) was studied using absorption, fluorescence and induced-circular dichroism spectroscopy. The inclusion of AZ into the cavity of beta-CD has a stoichiometry of 1:1, whereas that of AZ/gamma-CD complex is 1:2. The equilibrium constants for the formation of the two complexes were calculated to be 780+/-150 M(-1) for AZ:beta-CD and (4.5+/-0.86)x10(5) M(-2) for AZ:(gamma-CD)(2). The latter is due to a stepwise equilibrium mechanism in which a 1:1 complex is formed with a binding constant of 775 M(-1), followed by the formation of a 1:2 complex with a binding constant of 580 M(-1). The difference between the two binding constant values is slight, indicating an almost equal contribution from each of the gamma-CD molecules to the overall binding in AZ:(gamma-CD)(2). From the induced-circular dichroism spectra, the inclusion of AZ was found to be axial in AZ:beta-CD and nearly axial in AZ:(gamma-CD)(2).     

Interaction of 4-hydroxybiphenyl with cyclodextrins: effect of complex structure on spectroscopic and photophysical properties

The structures, spectroscopic and photophysical properties of the inclusion complexes between 4-OH-biphenyl and cyclodextrins (CD) in water were studied theoretically and experimentally. The complex structures were predicted using a dynamic Monte Carlo procedure including solvation effects and analyzed via computed and experimentally determined circular dichroism. The interpretation of the induced circular dichroism spectra indicated the formation of stable 2:2 complexes between the probe and alpha-CD, while 1:1 structures account for the circular dichroism induced by beta- and gamma-CD. Fluorescence emission quantum yields and lifetimes, measured as a function of the CD concentration, confirmed the formation of this higher order complex with alpha-CD. Prototropic equilibration in the singlet excited state was found to be depressed in 2:2 complexes due to the hydrophobic environment of the OH groups, while it remained unperturbed in 1:1 complexes, where the substituent is exposed to the aqueous environment. Triplet-triplet absorption and triplet quenching data supported this interpretation. The photophysical properties of both the 1:1 and the 2:2 complexes are characterized by a significant reduction of the nonradiative decay rates.     

Demicellization of a mixture of cationic-anionic hydrogenated/fluorinated surfactants through selective inclusion by alpha- and beta-cyclodextrin

The interactions between alpha- and beta-cyclodextrin (alpha-/beta-CD) and an equimolar mixture of octyltriethylammonium bromide (OTEAB) and sodium perfluorooctanoate (SPFO) were studied by 1H and 19F NMR, surface tension, conductivity, and dynamic light scattering. It was shown that beta-CD could destroy the mixed micelles of OTEAB-SPFO by selective inclusion of SPFO. As beta-CD was added, the system was observed to undergo a process like this: beta-CD preferentially included SPFO to form 1:1 beta-CD/SPFO complexes. As the inclusion of SPFO was almost saturated, the mixed micelles broke and all OTEAB was released and exposed to aqueous surroundings. Then 1:1 beta-CD/OTEAB and 2:1 beta-CD/SPFO complexes significantly formed simultaneously. Contrary to beta-CD, alpha-CD exhibited selective inclusion to OTEAB and only weak association with SPFO. alpha-CD could also destroy the mixed micelles of OTEAB-SPFO; however, the demicellization ability of alpha-CD is much smaller than that of beta-CD. These conclusions were also well supported by the calculations of binding constants and DeltaG degrees . Different from the complexes of CD/conventional surfactants, the complexes of beta-CD/SPFO or alpha-CD/OTEAB formed by selective inclusion of CD in the mixed cationic-anionic surfactants may have contributed to the surface activity of the aqueous mixtures. The complexes of alpha-CD/OTEAB showed much more significant contribution to the surface activity than that of the complexes of beta-CD/SPFO.     

Study on the interaction of 5-pyridine-10,15,20-tris-(p-chlorophenyl)porphyrin with cyclodextrins and DNA by spectroscopy

The interaction of 5-pyridine-10,15,20-tris-(p-chlorophenyl)porphyrin (PyTPP) with beta-CD and TM-beta-CD were examined by UV-vis absorption, fluorescence and (1)H NMR spectroscopy. PyTPP prefers to form the 1:1 inclusion complex with TM-beta-CD but hardly form inclusion complex with beta-CD. An inclusion constant (K) for the formation of PyTPP-TM-beta-CD inclusion complex has been evaluated to be 4.4x10(3)L/mol from the absorbance changes. This K value is nearly the same as that 4.5x10(3)L/mol obtained from the fluorescence intensity changes. Compared to beta-CD, the inclusion ability of TM-beta-CD with PyTPP is stronger. It indicates that the hydrophobic effect plays an important role in the inclusion procedure. The mechanism of inclusion interaction was carried out by 1H NMR technique. Furthermore, the interaction of PyTPP with DNA is shown here. It can bind DNA by out-side stacking along the DNA helix but not by intercalation because of the high electron density in the porphyrin core. The binding constant and binding number of PyTPP to DNA are 4.3x10(3) and 1.3, respectively. The interaction of PyTPP with DNA was further carried out in the presence of TM-beta-CD. The significant decrease of the binding constant and binding number were observed and the interaction of porphyrin-bound DNA has been inhibited, which was due to the fact that PyTPP inter into the cavity of TM-beta-CD and influence binding affinity of PyTPP to DNA.     

Mechanistic study of opposite migration order of dimethindene enantiomers in capillary electrophoresis in the presence of native beta-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin

The possible mechanisms of the opposite affinity pattern of the enantiomers of dimethindene [(R,S)-N,N-dimethyl-3[1(2-pyridyl)ethyl]indene-2-ethylamine] (DIM) towards native beta-cyclodextrin (beta-CD) and heptakis(2,3,6-tri-O-methyl-)-beta-CD (TM-beta-CD) were studied using capillary electrophoresis (CE), NMR spectrometry, electrospray ionization mass spectrometry (ESI-MS) and X-ray crystallography. NMR spectrometry allowed to estimate the stoichiometry of the complex and to determine the binding constants. As found using ESI-MS, together with more abundant 1:1 complex, a complex with 1:2 stoichiometry may also be present in a rather small amount in a solution of DIM and beta-CD. One-dimensional ROESY experiments indicated that the geometry of the complexes of DIM with native beta-CD depends on the ratio of the components in the solution. In the 1:1 solution of DIM and beta-CD the complex may be formed by inclusion of the indene moiety of DIM into the cavity of beta-CD on the primary side and into the cavity of TM-beta-CD into the secondary side. The most likely structural reason for lower affinity of the enantiomers of DIM towards the cavity of TM-beta-CD compared to native beta-CD could be elucidated. The indene moiety does not enter the cavity of TM-beta-CD as deeply as the cavity of beta-CD. This may be the most likely explanation of significantly higher affinity constants of DIM enantiomers towards the latter CD compared to the former one. The marked difference between the structure of the complexes may also be responsible for the opposite affinity pattern of the DIM enantiomers towards beta-CD and TM-beta-CD.     

Evidence for complexes of different stoichiometries between organic solvents and cyclodextrins

The influence of the organic solvent on the acid and basic hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) in the presence of alpha- and beta-cyclodextrins has been studied. The observed rate constant was found to decrease through the formation of an unreactive complex between MNTS and the cyclodextrins. In the presence of dioxane, acetonitrile or DMSO, the inhibitory effect of beta-CD decreased on increasing the proportion of organic cosolvent as a result of a competitive reaction involving the formation of an inclusion complex between beta-CD and the cosolvent. The disparate size of the organic solvent molecules resulted in stoichiometric differences between the complexes; the beta-CD-dioxane and beta-CD-DMSO complexes were 1 : 1 whereas the beta-CD-acetonitrile complex was 1 : 2. The basic and acid hydrolysis of MNTS in the presence of alpha-CD showed a different behavior; thus, the reaction gave both 1 : 1 and 2 : 1 alpha-CD-MNTS complexes, of which only the former was reactive. This result was due to the smaller cavity size of alpha-CD and the consequent decreased penetration of MNTS into the cavity in comparison to beta-CD. The acid hydrolysis of MNTS in the presence of alpha-CD also revealed decreased penetration of MNTS into the cyclodextrin cavity, as evidenced by the bound substrate undergoing acid hydrolysis. In addition, the acid hydrolysis of MNTS in the presence of acetonitrile containing alpha-CD gave 1 : 1 alpha-CD-acetonitrile inclusion complexes, which is consistent with a both a reduced cavity size and previously reported data.     

Separation of monomethyl-benz[a]anthracene isomers using cyclodextrin-modified electrokinetic chromatography

Cyclodextrin-modified electrokinetic chromatography (CD-EKC) was investigated for the separation of 12 monomethylbenz[a]anthracene (MBA) isomers. Combined use of a polymeric surfactant, poly(sodium 10-undecenyl sulfate) (poly-SUS), with various types of neutral cyclodextrins (CDs) [beta-CD, gamma-CD, dimethyl-beta-CD (DM-beta-CD), trimethyl-beta-CD (TM-beta-CD) and hydroxypropyl-beta-CD (HP-beta-CD)] were successful in CD-EKC separation of the MBA isomers. Baseline resolution of 10 of the 12 isomers, except for 9-MBA and 2-MBA, was achieved with gamma-CD at pH 9.75. The beta-CD, gamma-CD, and beta-CD derivatives (DM-beta-CD, TM-beta-CD, HP-beta-CD) were found to have different resolution and selectivity. Additionally, the tR/t0 values of isomers were found to be dependent on the type and concentration of the CD additives. In general, tR/t0 values of MBA isomers decrease with an increase in the concentration of beta-CD derivatives, whereas the reversed was true when the concentrations of native beta-CD and gamma-CD were varied. The combination of 5 mM gamma-CD, 0.5% (w/v) poly-SUS, 35% (v/v) acetonitrile at a pH of 9.75 provided the best selectivity and resolution of the MBA isomers with a separation time of 110 min. However, the use of 30 mM DM-beta-CD under similar EKC conditions resulted in much faster separation (ca. 16 min) of 10 MBA isomers.     

Molecular electrostatic potentials and hydrogen bonding in alpha-, beta-, and gamma-cyclodextrins

Cyclodextrins (CDs) are cyclic oligomers of glucose having the toroid of sugars elaborating a central cavity of varying size depending on the number of glucoses. The central hydrophobic cavity of CD shows a binding affinity toward different guest molecules, which include small substituted benzenes to long chain surfactant molecules leading to a variety of inclusion complexes when the size and shape complementarity of host and guest are compatible. Further, interaction of guest molecules with the outer surface of alpha-CD has also been observed. Primarily it is the electrostatic interactions that essentially constitute a driving force for the formation of inclusion complexes. To gain insights for these interactions, the electronic structure and the molecular electrostatic potentials in alpha-, beta-, and gamma-CDs are derived using the hybrid density functional theory employing the three-parameter exchange correlation functional due to Becke, Lee, Yang, and Parr (B3LYP). The present work demonstrates how the topography of the molecular electrostatic potential (MESP) provides a measure of the cavity dimensions and understanding of the hydrogen-bonded interactions involving primary and secondary hydroxyl groups. In alpha-CD, hydrogen-bonded interactions between primary -OH groups engender a "cone-like" structure, while in beta- or gamma-CD the interactions from the primary -OH with ether oxygen in glucose ring facilitates a "barrel-like" structure. Further, the strength of hydrogen-bonded interactions of primary -OH groups follows the rank order alpha-CD > beta-CD > gamma-CD, while the secondary hydrogen-bonded interactions exhibit a reverse trend. Thus weak hydrogen-bonded interactions prevalent in gamma-CD manifest in shallow MESP minima near hydroxyl oxygens compared to those in alpha- or beta-CD. Furthermore, electrostatic potential topography reveals that the guest molecule tends to penetrate inside the cavity forming the inclusion complex in beta- or gamma-CD.     

Study on the aggregation and electrochemical properties of Rose Bengal in aqueous solution of cyclodextrins

The interactions of Rose Bengal (RB) with alpha-cyclodextrin (alpha-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD), hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD), heptakis(2,3,6-tri-O-methyll)-beta-cyclodextrin (TM-beta-CD) were studied in aqueous solutions of 0.1 M KClO(4) and 0.1 M LiClO(4) by vis absorption, fluorescence spectroscopy as well as electrochemical measurements at 298 K. The spectrophometric results indicate that RB is included in all beta- and gamma-CDs forming complexes with a stoichiometry 1:1 whose stability is slightly higher in KClO(4) than in LiClO(4) solutions. The complex stability constants determined for salt-containing CD solutions are lower than those for water solutions. The complexation of RB with beta- and gamma-CD and the differences between the complexes obtained in the presence of the two salts were confirmed by an electrochemical study.     

Molecular recognition thermodynamics and structural elucidation of interactions between steroids and bridged bis(beta-cyclodextrin)s

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.     

Effect of cyclodextrins on saccharide sensing function of a fluorescent phenylboronic acid in water.

An inclusion complex consisting of a fluorescent phenylboronic acid (C1-APB) and beta-cyclodextrin (beta-CD) acts as a supramolecular saccharide sensor whose response mechanism is based on photoinduced electron transfer (PET). This study evaluated four kinds of cyclodextrins (alpha-CD, beta-CD, gamma-CD, and NH(2)-beta-CD) by comparing their pH profiles, and confirmed that beta-CD was the best host for C1-APB because the C1-APB/beta-CD complex exhibited high affinity for saccharides as well as high fluorescent recovery upon saccharide binding. An investigation of the beta-CD concentration effect revealed the formation of a 1:1 inclusion complex of C1-APB with beta-CD. The observed saccharide selectivity of the C1-APB/beta-CD complex is in the following order: D-fructose (4039 +/- 69 M(-1)) > D-ribose (1083 +/- 26 M(-1)) > L-arabinose (474 +/- 11 M(-1)) > D-galactose (318 +/- 3 M(-1)) > maltotoriose (135 +/- 5 M(-1)) > D-glucose (114 +/- 2 M(-1)) > maltose (81 +/- 2 M(-1)). In addition to monomer emission, dimer emission from pyrene dimers was observed in the spectra for the C1-APB/gamma-CD complex, which allowed a ratiometric analysis. This study shows that the combination of a simple fluorescent probe, C1-APB, with various CDs diversifies the response systems for saccharide recognition.     

Effect of cyclodextrins on the stability of adriamycin, adriamycinol, adriamycinone and daunomycin

The stability of adriamycin (ADR), adriamycinol, adriamycinone (ADR-ONE) and daunomycin in the presence of alpha-, beta- and gamma-cyclodextrins (CDs) was studied using high-performance liquid chromatography. It was found that alpha-CD did not affect the degradation of tested compounds, beta-CD caused a little effect and gamma-CD resulted in pronounced stabilizing effect. The formation of complexes between ADR and ADR-ONE with CDs was monitored by fluorescence spectroscopy. The fluorescence spectrum of ADR-gamma-CD complex had an activation maximum at 460 nm, emission maximum at 555 nm and a shoulder at 585 nm. A similar finding was observed in case of alpha-CD. In case of beta-CD, the fluorescence intensity at 580 nm peak enhanced less than in case of gamma-CD. With ADR-ONE, alpha-CD did not cause any significant change compared with the spectrum of free molecule. On the other hand, it was noticed that, the fluorescence spectra of ADR-ONE with both beta- and gamma-CD were the same but showed a significant difference to the spectrum of free molecule, especially the molar fluorescence of the 585 nm emission peak.     

Homodimerization and heteroassociation of 6-O-(2-sulfonato-6-naphthyl)-gamma-cyclodextrin and 6-deoxy-(pyrene-1-carboxamido)-beta-cyclodextrin

6-O-(2-sulfonato-6-naphthyl)-gamma-cyclodextrin (1) and 6-deoxy-(pyrene-1-carboxamido)-beta-cyclodextrin (2) were prepared. Homodimerizations of 1 and 2 and heteroassociation between 1 and 2 were investigated by (1)H NMR, circular dichroism, and fluorescence spectroscopic methods. The compounds 1 and 2 form head-to-head dimers with dimerization constants of 140 +/- 50 and 270 +/- 70 M(-)(1), respectively. We also determined the association constants of 1 with beta-CD as 270 +/- 20 M(-)(1) and 2 with gamma-CD as 100 +/- 30 M(-)(1) from fluorescence and circular dichroism titration data, respectively. The heteroassociation between 1 and 2 was manifested in increased circular dichroism ellipticities of 2, downfield shift of the H-2 proton of the pyrene group of 2, and upfield shift of the H-5 proton of the naphthyl group of 1 upon mixing 1 and 2. The analysis of circular dichroism titration data of 2 with 1 gave the association constant as 9300 +/- 1600 M(-)(1). The NMR and circular dichroism spectra suggested that the naphthyl group of 1 is deeply included into the beta-CD cavity of 2, while the pyrene group of 2 is partially inserted in the gamma-CD cavity of 1 in the complex. The energy-minimized structure from molecular modeling of the complex supports this. We believe that the facile heteroassociation of two cyclodextrin derivatives having different sizes of cavity and pendant group could be utilized as a useful strategy for assembling functionalized CDs for various applications.     

Thermodynamic study on the effects of beta-cyclodextrin inclusion with berberine.

The fluorescence enhancement of berberine (Berb) as a result of complex with beta-cyclodextrin (beta-CD) is investigated. The association constants of alpha-CD and beta-CD with Berb are 60 and 137 M(-1) at 20 degrees C in pH 7.20 aqueous solution. Effects of temperature on the forming inclusion complexes of beta-CD with Berb have been examined through using fluorescence titration. Enthalpy and entropy values calculated from fluorescence data are -33.7 kJ mol(-1) and 74.3 J x mol(-1) K(-1) respectively. It was found that the dielectric constant of beta-CD cavity is about 24 in a rough analogy with absolute alcohol. These results suggest that the extrusion of 'high energy water' molecules from the cavity of beta-CD and hydrophobic interaction upon the inclusion complex formation are the main forces of the inclusion reaction. Effect of pH on the association of beta-CD with Berb was also studied. Mechanism of the inclusion of beta-CD with Berb is further studied by absorption and NMR measurements. Results show that beta-CD forms a 1:1 inclusion complex with Berb.     

Cyclodextrin effect on solvolysis of substituted benzoyl chlorides

A kinetic study was carried out on the solvolysis of substituted benzoyl chlorides in the presence of alpha-, beta- and gamma-CD. Combination of the substituent dependent mechanism for solvolysis of benzoyl chlorides and the complexation ability of the cyclodextrin yields the following experimental behavior: (i) catalysis by beta- and gamma-CD for solvolysis of electron-attracting substituted benzoyl chlorides due to the reaction with its hydroxyl group C(6); (ii) absence of alpha-CD influence on solvolysis of benzoyl chlorides with electron withdrawing substituents; (iii) inhibition of solvolysis of benzoyl chlorides with electron-donating groups. This behavior is observed for solvolysis of meta/para substituted substrates in the presence of beta-CD, solvolysis of meta-substituted benzoyl chlorides in the presence of alpha-CD and solvolysis of para-substituted benzoyl chlorides in the presence of gamma-CD. This decrease in the rate constant is a consequence of the complexation of the substrate in the cyclodextrin cavity and its low solvation ability, causing the rate of solvolysis in its interior to be negligible. (iv) The solvolysis of meta-substituted benzoyl chlorides in the presence of gamma-CD yields a new behavior where the reaction of the complexed substrate is not negligible in the interior of the cyclodextrin cavity, which has been interpreted as a consequence of incomplete expulsion of hydration water from its cavity when the complexation takes place. (v) The experimental results obtained in the presence of alpha-CD show that meta-substituted benzoyl chlorides give rise to host : guest complexes with 1 : 1 stoichiometries, whereas those which are para-substituted cause a 2 : 1 stoichiometry to be formed. This difference in behavior has been interpreted taking into account the size of the different benzoyl chlorides and their accommodation in the alpha-CD cavity.     

Study on the supramolecular system of 5-(p-hydroxyphenyl)-10,15,20-tris-(4-chlorophenyl)porphyrin with cyclodextrins and its analytical characteristics

The supramolecular systems of 5-(p-hydroxyphenyl)-10,15,20-tris-(4-chlorophenyl)porphyrin (p-HTClPP) with beta-cyclodextrin (beta-CD), heptakis(2,3,6-tri-O-methyl)-beta-CD (TM-beta-CD), carboxymethyl-beta-cyclodextrin (CM-beta-CD) and sulfurbutylether-beta-CD (SBE-beta-CD) have been investigated by means of absorption, fluorescence and (1)H NMR spectroscopy. The formation of inclusion complexes has been confirmed on the base of changes of spectroscopy properties. "The double reciprocal method" has been used to determine the stoichiometry and the inclusion constants of p-HTClPP with the four cyclodextrins (CDs). The results show that p-HTClPP can form 1:1 inclusion complexes with the four CDs. Compared with parent native beta-CD, the inclusion abilities of modified beta-CDs with p-HTClPP are stronger. It indicates that the hydrophobic effect plays an important role in the inclusion procedure. The mechanism of inclusion interaction was examined by (1)H NMR technique. During the study of p-HTClPP-TM-beta-CD supramolecular complex, an efficient enhancement of fluorescence intensity was observed. Based on this phenomenon, fluorometric method for the determination of p-HTClPP was developed. The relationship between fluorescence intensity and the concentration of p-HTClPP is linear from 1.0 x 10(-9) to 7.0 x 10(-6)mol L(-1). The limit of detection is 8.3 x 10(-10)mol L(-1) and the relative standard deviation (R.S.D.) is 1.3% (n=8). This research will provide useful information for further application of p-HTClPP.     

Interactions of tetrakis(4-N-methylpyridyl)porphyrin with cyclodextrins and disodium phthalate in aqueous solution

In pH 7.3 buffers, the interactions of a cationic porphyrin, tetrakis(4-N-methylpyridyl)porphyrin (TMPyP), with cyclodextrins (CDs) and disodium phthalate (DSP) have been examined by means of absorption, fluorescence, and induced circular dichroism spectroscopy. α-CD, β-CD, and γ-CD form a 1:1 inclusion complex with a TMPyP monomer, which dimerizes in solution without CD. TMPyP also forms a 1:1 organic cation–organic anion complex with DSP. The 1:1 TMPyP–DSP complex forms a ternary CD–TMPyP–DSP inclusion complex with α-, β-, and γ-CD, in which a DSP molecule is not incorporated into the CD cavity. From the fluorescence intensity change, the␣equilibrium constants have been evaluated for the formation of the inclusion complexes and the organic cation–anion complexes.