Stability of natamycin and its cyclodextrin inclusion complexes in aqueous solution

Aqueous solutions of natamycin and its beta-cyclodextrin (beta-CD), hydroxypropyl beta-cyclodextrin, and gamma-cyclodextrin (gamma-CD) inclusion complexes were completely degraded after 24 h of exposure to 1000 lx fluorescent lighting at 4 degrees C. After 14 days of storage in darkness at 4 degrees C, 92.2% of natamycin remained in active form. The natamycin:beta-CD complex and natamycin:gamma-CD complex were significantly more stable (p < 0.05) than natamycin in its free state in aqueous solutions stored in darkness at 4 degrees C. Clear poly(ethylene terephthalate) packaging with a UV light absorber allowed 85.0% of natamycin to remain after 14 days of storage under 1000 lx fluorescent lighting at 4 degrees C. Natamycin:cyclodextrin complexes can be dissociated for analysis in methanol/water/acetic acid, 60:40:5, v/v/v. Natamycin and its complexes in dissociated form were quantified by reverse phase HPLC with detection by photodiode array at 304 nm.     

Preparation and characterization of inclusion complex of iprodione and beta-cyclodextrin to improve fungicidal activity

The effect of beta-cyclodextrin (beta-CD) on the improvement of the fungicidal activity of iprodione has been investigated. The inclusion complexation of beta-CD with iprodione has been prepared and characterized by integrating some analytical techniques (such as electrospray ionization-mass spectrometry, differential scanning calorimetry, thermogravimetry, x-ray diffraction, and scanning electron microscopy) and molecular simulation methods. The beta-CD/iprodione inclusion complex has exhibited different spectroscopic features and properties from iprodione. The stoichiometric ratio and stability constant describing the extent of formation of inclusion complexes have been determined by phase solubility studies. The calculated apparent stability constant of the iprodione/beta-CD complex was 407.5 M-1. The obtained inclusion complexes were found to significantly improve the water solubility of iprodione, and there is a 4.7-fold increase in the presence of 13 mM beta-CD as compared with the solubility of iprodione in deionized water in the absence of beta-CD. The bioassay demonstrated that the complex displayed over two-fold increase of the fungicidal activity. In addition, the possible structure of the beta-CD/iprodione complex was proposed according to the results of the molecular dynamic simulation. The present study provided useful information for a more rational application of iprodione, diminishing the use of organic solvents and increasing its efficacy.     

Inclusion complex of conjugated linoleic acid (CLA) with cyclodextrins

Conjugated linoleic acid (CLA) inclusion complexes with alpha-cyclodextrin (alpha-CD), beta-cyclodextrin (beta-CD), and gamma-cyclodextrin (gamma-CD) (designated CLA/CDs inclusion complexes) were prepared to determine the mole ratio of CLA complexed with CDs and the oxidative stability of CLA in the CLA/CDs inclusion complexes. When measured by GC, (1)H NMR, and T(1) value analyses, 1 mole of CLA was complexed with 5 mol of alpha-CD, 4 mol of beta-CD, and 2 mol of gamma-CD. The oxidation of CLA induced at 35 degrees C for 80 h was completely prevented by the formation of CLA/CDs inclusion complexes.     

Preparation and characterization of inclusion complex of norflurazon and beta-cyclodextrin to improve herbicide formulations

The formulation of inclusion complexes of the herbicide norflurazon as guest and beta-cyclodextrin (beta-CD) as host has been studied as a first step in the use of cyclodextrins to obtain improved formulations of this herbicide. The interaction of norflurazon with beta-CD produced the formation of an inclusion complex in solution and in solid state. The inclusion of norflurazon in beta-CD in solution was studied by phase solubility, and an apparent stability constant of 360 M(-)(1), a 1:1 stoichiometric ratio for the complex, and up to 5-fold increase in norflurazon solubility were determined. Three processing methods (kneading, spray drying and vacuum evaporation) were used to prepare norflurazon-beta-CD solid inclusion complexes. X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy techniques were used to study the solid complexes. From the different solid systems, an increase of norflurazon aqueous dissolution rate was obtained in comparison to the uncomplexed herbicide. This finding is a first step to obtain controlled release and/or protective formulations of norflurazon, which allow a more rational application of norflurazon, diminishing the use of organic solvents and increasing its efficacy.     

Encapsulation of olive leaf extract in beta-cyclodextrin

Olive leaf extract, rich in oleuropein, formed an inclusion complex with beta-cyclodextrin (beta-CD) upon mixing of the components in aqueous media and subsequent freeze-drying. Inclusion complex formation was confirmed by differential scanning calorimetry (DSC). DSC thermograms indicated that the endothermic peaks of both the olive leaf extract and the physical mixture of olive leaf extract with beta-CD, attributed to the melting of crystals of the extract, were absent in DSC thermogram of inclusion complex. Moreover, DSC studies under oxidative conditions indicated that the complex of olive leaf extract with beta-CD was protected against oxidation, since it remained intact at temperatures where the free olive leaf extract was oxidized. Phase solubility studies afforded A L type diagrams, 1:1 complex stoichiometry, a moderate binding constant ( approximately 300 M (-1)), and an increase of the aqueous solubility by approximately 50%. The formation of the inclusion complex was also confirmed by nuclear magnetic resonance (NMR) studies of beta-CD solutions in the presence of both pure oleuropein and olive leaf extract. The NMR data have established the formation of a 1:1 complex with beta-CD that involves deep insertion of the dihydroxyphenethyl moiety inside the cavity from its secondary side.     

Improvement of oxidative stability of conjugated linoleic acid (CLA) by microencapsulation in cyclodextrins

Oxidative stability of conjugated linoleic acid (CLA) encapsulated in alpha-, beta-, and gamma-cyclodextrins (designated CLA/CDs microencapsules) was studied by measuring the headspace-oxygen depletion in airtight serum bottles and by measuring the peroxide values (POV). The rate of oxygen depletion was reduced from 41.0 (control) to 21.5, 2.1, 1.2, and 1.1 micromol/L.h(-)(1) by CLA/alpha-CD microencapsules at 1:1, 1:2, 1:4, and 1:6 mole ratios, respectively, indicating that CLA oxidation was completely protected by a 1:4 mole ratio of CLA/alpha-CD. Such a protective effect by CLA/beta-CD or CLA/gamma-CD microencapsules was achieved at a 1:6 mole ratio, but the effect by CLA/beta-CD was slightly greater than that by CLA/gamma-CD. The protective effect of alpha-, beta-, and gamma-CDs for CLA oxidation was confirmed by their POV-reducing abilities in CLA/CDs. These results suggest that alpha-CD was the most effective for the protection of CLA oxidation by microencapsulation, followed by beta-CD and gamma-CD.     

Characterization of inclusion complexation between fenoxaprop-p-ethyl and cyclodextrin

Cyclodextrins (CDs) derived from natural starches are capable of forming inclusion complexes with a variety of organic compounds. This work evaluated the complexation role of CDs toward fenoxaprop-p-ethyl (FE) in an attempt to assess their potential as new formulation additives for more efficient FE delivery and better environmental approaches. beta-CD and its two derivatives, randomly methylated beta-CD (RAMEB) and 2-hydroxypropyl beta-CD (HP-beta-CD), were tested. The solubility of FE was enhanced in the presence of the CDs due to the formation of inclusion complexes, with RAMEB being >6 times more effective than the other two. The complexation was confirmed by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), where the FE melting peaks in DSC, the FTIR bands, and the XRD peaks were generally weakened. Within the tested time up to 60 min, the dissolution of the FE-CD complexes resulted in higher FE concentrations than did that of FE by itself. The dissolution of the FE-RAMEB complex was much faster than other complexes and FE alone. These results indicate that RAMEB was a better inclusion complexation agent for FE in terms of both solubility enhancement and dissolution rate. RAMEB may thus be used to improve FE delivery and to mobilize FE in soil for bioremediation.     

Preparation, stabilization, and bioefficacy of beta-cyclodextrin inclusion compounds of chloramidophos

Cyclodextrins are common compounds capable of forming inclusion complexes with a variety of pesticides to improve their solubility, bioavailability, and stability. In this study, chloramidophos (CP) was inclusion-complexed with beta-cyclodextrin (beta-CD) by a kneading method in an attempt to gain a more stable but equally effecacious formulation compared with CP alone. A 1:1 CP-beta-CD complex with an inclusion constant of 203.0 M(-1) was determined to exist by UV spectrophotometry. The structural identification, thermal stability, and biological assays of the CP-beta-CD complex were then carried out with a product with the maximum guest loading efficiency. The data measured by differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), and X-ray diffraction (XRD), where the endothermic peaks of beta-CD, the FT-IR bands, and the XRD peaks were generally changed, deduced the formation of complex. Results of the thermal stability assay showed that the degradation rate of CP in 14-day incubation was slowed by a factor of 3.6 when it was complexed with beta-CD. Then, activity and toxicity of CP influenced by the encapsulated process of beta-CD were evaluated by an in vitro acetylcholinesterase (AChE) inhibition assay and an acute aquatic toxicity assay, respectively. No significant differences were found in both the two biological assays by a t-test. This indicated that the encapsulation process greatly improved the thermal stability of the pesticide with no adverse effects on bioefficacy compared to that of CP. There is a promising outlook for CP-beta-CD to be produced as the active ingredient of various formulation additives of CP for its continued application.     

Improvement of antifungal activity of 10-undecyn-1-ol by inclusion complexation with cyclodextrin derivatives

The inclusion complexation behavior between 10-undecyn-1-ol and cyclodextrin (CD) derivatives, namely, randomly methylated beta-CD (RM-beta-CD) and hydroxypropyl-beta-CD (HP-beta-CD), was studied in terms of solubility improvement, apparent stability constant, and the inclusion ratios of the resultant inclusion complexes. The aqueous solubility of 10-undecyn-1-ol was greatly improved through complexation with the CD derivatives. RM-beta-CD is comparatively more efficient in solubilizing 10-undecyn-1-ol with an apparent stability constant outstripping that of HP-beta-CD by about an order of magnitude. Comparative in vitro evaluations of the growth inhibition effects of inclusion complex solutions toward Rosellinia necatrix, a phytopathogenic fungus, were performed. In comparison with the positive control, appreciable improvements of the antifungal activity of 10-undecyn-1-ol through the addition of CD derivatives were observed visually. The improvement was evaluated in terms of area covered by the mycelia of Rosellinia necatrix and their growth rate. RM-beta-CD was proven to be more effective compared to HP-beta-CD with regard to the reduction of both fungal mycelium-covered area and growth rate constant, presumably owing to greater solubility enhancement by RM-beta-CD and thus the bioavailability of 10-undecyn-1-ol. Inclusion complexation of 10-undecyn-1-ol with CD derivatives suggests a potential means for production of an environmentally friendly 10-undecyn-1-ol-based fungicide to counteract R. necatrix.     

Improvement of the desorption of the herbicide norflurazon from soils via complexation with beta-cyclodextrin

The effect of beta-cyclodextrin (beta-CD) on the removal of the herbicide norflurazon (NFL) from soils has been investigated. The interaction of NFL with beta-CD in solution yielded the formation of a water-soluble inclusion complex at 1:1 stoichiometric ratio, which gave an increase in NFL solubility. Desorption studies of NFL previously adsorbed on six soils of different characteristics have been performed in the presence of 0.01 M beta-CD or 0.01 M Ca(NO(3))(2) as extractant solutions. Positive hysteresis was observed in all soils when 0.01 M Ca(NO(3))(2) solution was used, indicating that desorption of NFL from these soils was not completely reversible. On the contrary, the application of beta-CD solutions to soils where NFL had been previously adsorbed increased very much its desorption, and a negative hysteresis was obtained for all soils studied; that is, more NFL was desorbed with respect to NFL adsorption isotherm. A clear relationship was observed between the physicochemical characteristics of the soils and the beta-CD concentration necessary to remove the herbicide, the percentages of desorption observed for each soil being inversely related to the values obtained for the Freundlich sorption capacity parameter of the herbicide, K(f). In general, high desorption yields can be obtained with very low beta-CD concentrations, which is an important advantage from an economic point of view, although in those soils that present an extremely high NFL adsorption, higher amounts of beta-CD should be used. The results obtained indicate the high extracting power of beta-CD toward the herbicide previously adsorbed on the soils and the potential use of beta-CD for in situ remediation of pesticide-contaminated soils.     

Complexation of several fungicides with beta-cyclodextrin: determination of the association constants and isolation of the solid complexes

The formation of inclusion complexes with beta-cyclodextrin was studied for several popular fungicides of different types: prochloraz, 2-phenylphenol, thiophanate methyl, 8-hydroxyquinoline, and benalaxyl. Phase solubility diagrams showed that in all cases complexation takes place, leading to an important increase of water solubility in prochloraz and benalaxyl. Equilibrium association constants could be determined from the phase solubility data and from NMR titrations in the case of 2-phenylphenol. Because of the low solubility of the complex formed between 8-hydroxyquinoline and beta-cyclodextrin, the corresponding association constant could not be determined. The solid complexes of fungicide-cyclodextrin were prepared and isolated by different methods. The isolation of real complexes and not physical mixtures was confirmed in the cases of prochloraz, 2-phenylphenol, and benalaxyl by differential scanning calorimetry.     

Water solubility of flavor compounds influences formation of flavor inclusion complexes from dispersed high-amylose maize starch

High-amylose maize starch, with and without native lipid, was used to make inclusion complexes with flavor compounds to investigate the effect of water solubility of flavor compounds on inclusion complex formation. Two pairs of terpenes, having high and low water solubility, were used. Aqueous starches were dispersed by heat before adding the flavor compound. The amounts of starch, native lipid, and flavor compound in precipitates were determined, and inferences about the physical state were made using data from X-ray diffraction and differential scanning calorimetry. The water solubility of the flavor compound was related to the extent of inclusion complexation. For the higher water solubility flavor compounds, starch yield and flavor entrapment were higher, producing precipitates with the V 7 pattern. Complex formation with the low-solubility flavor compounds was most effective in the presence of native lipid, producing precipitates with the V 6 pattern. The lipid in native high-amylose maize starch may enhance complexation with low-solubility compounds by forming ternary coinclusion complexes of starch-lipid-flavor.     

Thermal stability of anthocyanin extract of Hibiscus sabdariffa L. in the presence of beta-cyclodextrin

The thermal stability of anthocyanin extract isolated from the dry calyces of Hibiscus sabdariffa L. was studied over the temperature range 60-90 degrees C in aqueous solutions in the presence or absence of beta-cyclodextrin (beta-CD). The results indicated that the thermal degradation of anthocyanins followed first-order reaction kinetics. The temperature-dependent degradation was adequately modeled by the Arrhenius equation, and the activation energy for the degradation of H. sabdariffa L. anthocyanins during heating was found to be approximately 54 kJ/mol. In the presence of beta-CD, anthocyanins degraded at a decreased rate, evidently due to their complexation with beta-CD, having the same activation energy. The formation of complexes in solution was confirmed by nuclear magnetic resonance studies of beta-CD solutions in the presence of the extract. Moreover, differential scanning calorimetry revealed that the inclusion complex of H. sabdariffa L. extract with beta-CD in the solid state was more stable against oxidation as compared to the free extract, as the complex remained intact at temperatures 100-250 degrees C where the free extract was oxidized. The results obtained clearly indicated that the presence of beta-CD improved the thermal stability of nutraceutical antioxidants present in H. sabdariffa L. extract, both in solution and in solid state.     

Complexation of several benzimidazole-type fungicides with alpha- and beta-cyclodextrins

The potential increase in water solubility of three benzimidazole-type fungicides (thiabendazole, carbendazim, and fuberidazole) due to complexation with alpha- and beta-cyclodextrins was investigated. Fluorescence emission spectra of the fungicides in the presence of different concentrations of the cyclodextrins were measured. Analysis of these spectra by the method of principal components global analysis (PCGA) yielded precise values for the association constants and the emission spectra of the fungicide-cyclodextrin inclusion complexes. Phase-solubility diagrams confirmed the formation of inclusion complexes between each of the fungicides and beta-cyclodextrin and showed significant increases of their solubilities due to complexation.     

Study on the supramolecular interaction of curcumin and beta-cyclodextrin by spectrophotometry and its analytical application

The supramolecular interaction of curcumin and beta-cyclodextrin (beta-CD) has been studied by spectrophotometry. The mechanism of the inclusion was studied and discussed based on the variations of pK(a), absorption intensity, and infrared spectrograms. The results show that beta-CD reacts with curcumin to form a 2:1 host-guest complex with an apparent formation constant of 5.53 x 10(5) mol(-2) x L2. Based on the enhancement of the absorbance of curcumin produced through complex formation, a spectrophotometric method for the determination of curcumin in bulk aqueous solution in the presence of beta-CD was developed. The linear relationship between the absorbance and curcumin concentration was obtained in the range of 0-15 microg/mL, with a correlation coefficient (r) of 0.9991. The detection limit was 0.076 microg/mL. The proposed method was used to determine the curcumin in curry and mustard with satisfactory results.     

Study on the supramolecular interaction of thiabendazole and beta-cyclodextrin by spectrophotometry and its analytical application

The beta-cyclodextrin-thiabendazole (beta-CD-TBZ) inclusion complex was synthesized and its structure characterized by (1)H NMR and IR. The mechanism of the supramolecular interaction of TBZ and beta-CD has been studied and discussed by spectrophotometry. The results showed that the phenyl ring of TBZ was included in the beta-CD cavity to form a 1:1 host-guest complex with an apparent formation constant of 1.60 x 10(3) mol(-1).L. On the basis of the enhancement of the absorbance of TBZ produced through complex formation, a spectrophotometric method for the determination of TBZ in bulk aqueous solution in the presence of beta-CD was developed. The linear relationship between the absorbance and TBZ concentration was obtained in the range of 8.86 x 10(-7)-1.45 x 10(-5) mol/L. The detection limit was 2.71 x 10(-7)mol/L, and the relative standard deviation was 0.86%. The interference of 48 coexisting substances was slight. The proposed method has been successfully applied to the determination of TBZ in fruits with recoveries of 96-103%.     

Preparation and characterization of the inclusion complex of chlorpyrifos in cyclodextrins to improve insecticide formulations

The chemical control of crops by organophosphate insecticide treatment is usually limited because the insecticides do not maintain their efficiency for long periods for several reasons, including environmental conditions or rapid degradation of the active ingredient. Chlorpyrifos is an organophosphate insecticide used worldwide to control a variety of soil insects and arthropods in a wide range of crops. It is easily soluble in organic solvents but shows poor water solubility. The inclusion of chrorpyrifos in cyclodextrins (CDs) improves its water solubility, bioavailability, and insecticidal activity and helps prevent overdosing, leading to more cost-effective and more environmentally friendly agricultural practices. Solubility studies of chlorpyrifos in the presence of different types of CDs show G2-beta-CDs to be the most effective CDs in the complexation process, giving 1:2 complexes, with complexation constant (Kc) values of 12.34 +/- 3.1 M(-1) for K1 and 3895 +/- 183 M(-1) for K2. These complexation constant values were corroborated by applying a fluorimetric method.     

Enhancing effect of hydroxypropyl-β-cyclodextrin on the intestinal absorption process of genipin

The purpose of this work is to investigate the effect of the genipin/hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex on the intestinal absorption of genipin and identify its mechanism of action. The phase solubility profile was classified as A(L) type, indicating the formulation of a 1:1 stoichiometry inclusion complex. Fourier transform infrared spectroscopy, Differential scanning calorimetry, X-ray powder diffractometry, and (1)H nuclear magnetic resonance (NMR) and two-dimensional (2D) (1)H rotating-frame Overhauser enhancement (ROESY) NMR spectroscopies further confirmed the formulation of the inclusion complex with superior dissolution properties than the drug alone. The results of single-pass intestinal perfusion showed that the intestinal absorption of genipin was affected by P-glycoprotein (Pgp). The absorption rate and permeability value of the inclusion complex were significantly higher than the free drug, suggesting that its enhancing effect was involved in its solubilizing effect and Pgp inhibitory effect. The mechanisms of HP-β-CD on Pgp inhibition were demonstrated by restraining the Pgp ATPase activity rather than changing the fluidity of the cell membrane.     

Interaction of cyclodextrins with aliphatic acetate esters and aroma components of La France pear

The interaction between aliphatic acetate esters, which are the major flavor components of La France pear (Pyrus communis L.), and cyclodextrins (CDs) was studied to obtain fundamental data for preparing powdered pear flavor materials. The complexing abilities of alpha-, beta-, or gamma-CD with six kinds of aliphatic acetate esters were compared. alpha-CD formed the highest numbers of complexes with all of the esters. All of the CDs produced complexes more readily with the more hydrophobic esters. Among our samples of freeze-dried pear juice containing dissolved alpha-, beta-, or gamma-CD, the juice with alpha-CD retained the greatest amount of esters. These data demonstrate that alpha-CD is an effective material with which to prepare powdered pear flavor materials. The nuclear Overhauser effect, measured by (1)H NMR spectra, of an alpha-CD-butyl acetate or alpha-CD-hexyl acetate complex showed that these esters were included in the alpha-CD cavity.     

Glycosylation of genistin into soluble inclusion complex form of cyclic glucans by enzymatic modification

The enzymatic modification of genistin to enhance its water solubility was studied using two glycosyltransferases, cyclodextrin glucanotransferase from alkalophilic Bacillus sp. I-5 and 4-alpha-glucanotransferase from Thermus scotoductus. Two different catalytic reactions, the transglycosylation and cyclization activities, were observed when the reaction was performed with soluble starch as a donor and genistin as an acceptor. The reaction products were isolated and identified as [Glc(alpha1-4)](1-22)-Glc(beta1-7)-genisteins and cycloamylose with DP 8-12 by HPLC and MALDI-TOF MS. A beta-amylase treatment revealed inclusion complexes composed of Glc(alpha1-4)-Glc(beta1-7)-genistein/Glc(alpha1-4)-Glc(alpha1-4)-Glc(beta1-7)-genistein and cycloamylose with DP 8-12. The results indicated that the cycloamylose formed by the cyclization reaction of the enzyme included Glc(alpha1-4)-Glc(beta1-7)-genistein/Glc(alpha1-4)-Glc(alpha1-4)-Glc(beta1-7)-genistein. The presence of cycloamylopectin, in which the Glc(alpha1-4)-Glc(beta1-7)-genistein/Glc(alpha1-4)-Glc(alpha1-4)-Glc(beta1-7)-genistein was enclosed, was also observed with HPLC, HPSEC-MALLS, and MALDI-TOF MS analyses. The solubility of genistin was highly improved, and the solution containing glycosylated genistin and the inclusion complex demonstrated excellent properties of transparency and stability during storage at 4 degrees C.