Spectrofluorimetric study of host-guest complexation of ibuprofen with beta-cyclodextrin and its analytical application

The characteristics of host-guest complexation between beta-cyclodextrin (beta-CD) and two forms of ibuprofen (protonated and deprotonated) were investigated by fluorescence spectrometry. 1:1 stoichiometries for both complexes were established and their association constants at different temperatures were calculated by applying a non-linear regression method to the change in the fluorescence of ibuprofen that brought about by the presence of beta-CD. The thermodynamic parameters (deltaH, deltaS and deltaG) associated with the inclusion process were also determined. Based on the obtained results, a sensitive spectrofluorimetric method for the determination of ibuprofen was developed with a linear range of 0.1-2 microg ml(-1) and a detection limit of 0.03 microg ml(-1). The method was applied satisfactorily to the determination of ibuprofen in pharmaceutical preparations.     

Complexation study of diclofenac with beta-cyclodextrin and spectrofluorimetric determination

The inclusional complexation between the anti-inflammatory pharmaceutical diclofenac and beta-cyclodextrin (beta-CD) was studied by potentiometry, spectrophotometry and spectrofluorimetry, in both acid and neutral pH. Guest-host 1:1 stoichiometries for the complexes in both media were determined, and their equilibrium constants were calculated. The values obtained from the different methods used are in very good agreement and are in the order of 10(3). From the analysis of the pKa value for diclofenac in both the absence and presence of beta-CD (4.84 and 4.90 respectively), it was inferred that in the inclusion complex the carboxylic group is located outside the cavity. Further structural characterization of the inclusate was carried out by means of 1H NMR spectra and AM1 semiempirical calculations. Based on the obtained results, a spectrofluorimetric method for the determination of diclofenac in the presence of beta-CD was developed in the range of 0-5 micrograms ml-1. Better limits of detection (0.03 microgram ml-1) and quantification (0.1 microgram ml-1) were obtained in this latter case with respect to those obtained in the absence of beta-CD. The method was satisfactorily applied to the quantification of diclofenac in pharmaceutical preparations.     

Investigation of the Belousov-Zhabotinsky reaction by thermal lensing

The supramolecular interaction of rubidate (chemically 2,3-naphthalenedicarboxylic acid, 1,4-dihydroxy-diethyl ester) and beta-cyclodextrin (beta-CD) has been studied by spectrofluorimetry. The influence of temperature on the supramolecular system has also been investigated and the thermodynamic parameters were calculated. The results show that beta-CD reacts with rubidate to form a 1:1 host-guest complex with an apparent association constant of 566+/-23 l mol(-1). It was also demonstrated that the thermodynamics of beta-CD-rubidate complex displayed a compensatory enthalpy-entropy relationship. Based on the significant enhancement of the fluorescence intensity of rubidate produced through complex formation, a spectrofluorimetric method for the determination of rubidate in bulk aqueous solution in the presence of beta-CD was developed. The linear relationship between the fluorescence intensity and rubidate concentration was obtained in the range from 2.7x10(-2) to 3.0 mug ml(-1), with a correlation coefficient of 0.9988. The detection limit was 8.2 ng ml(-1) and the relative standard deviation was 1.6%. There was no interference from the excipients normally used in tablet formulations. The application of the present method to the determination of rubidate in tablets gave satisfactory results and was compared with the reference method.     

Spectrofluorimetric determination of piroxicam in the presence and absence of beta-cyclodextrin

The complexation between beta-cyclodextrin (beta-CD) and piroxicam (PX) was investigated by both fluorescence and absorption spectrometry. A 1:2 guest:host stoichiometry for the complex was established, and its association constant was calculated by applying a non-linear regression method to the changes brought about by the presence of beta-CD in both the fluorescence and absorbance spectra of PX. During the study of the influence of the pH on the fluorescence emission of the complex, an efficient enhancement of the signals at acidic pH was observed. This suggests that the protonated form of PX is included more effectively than the ionized form in the beta-CD cavity. Based on the results obtained, spectrofluorimetric methods for the determination of PX were developed. The best limits of detection and quantification were obtained using beta-CD at an acidic pH. The dynamic range in this latter case was 0.02-1 microgram ml-1. The method was applied satisfactorily to the determination of piroxicam in a pharmaceutical preparation.     

Spectrofluorimetric determination of iron(III) with 2-pyridinecarbaldhyde-5-nitro-pyridylhydrazone in the presence of hexadecyltrimethylammonium bromide surfactant

2-pyridinecarbaldehyde-5-nitro-pyridylhydrazone (2PC-5NPH) was synthesized and its application in the spectrofluorimetric determination of Fe(III) ions in the presence of surfactants was examined. An emission peak of 2PC-5NPH, which increased remarkably by the addition of Fe(III), occurs at 420 nm upon excitation at 300 nm, and allows for the sensitive, selective determination of the ferric ion in the 0.20-1.45 mug ml(-1) range. The detection limit is 0.028 mug ml(-1) in the presence of hexadecyltrimethylammonium bromide (CTMAB).     

Spectrofluorimetric determination of diclofenac in the presence of alpha-cyclodextrin

This study focuses on the complex formed between alpha-cyclodextrin (CD) and the anti-inflammatory drug diclofenac in aqueous solution and also on its potential analytical applications. It was corroborated that the fluorescence emission band of diclofenac is significantly intensified in the presence of alpha-CD. From the changes in the fluorescence spectra, it was concluded that alpha-CD forms a 1:1 inclusional complex with diclofenac and its equilibrium constant was calculated to be 1.20(3)x10(3) M(-1). With the purpose of characterizing the inclusion complex, the acid-base behaviour of diclofenac in both the presence and absence of alpha-CD was spectrophotometrically investigated. From the results obtained, it was inferred that both the carboxyl and the secondary amino groups of the guest molecule remain outside the cyclodextrin cavity. Further details on the complex structure was obtained by (1)H NMR measurements and semiempirical calculations. In addition to the analysis of the alpha-CD-diclofenac interaction, a new approach for the quantification of diclofenac in the presence of alpha-CD is described in the range 0-5 mug ml(-1). An application of the method to the determination of the studied drug in pharmaceutical preparations is shown.     

Spectroscopic study of orange G-beta-cyclodextrin complex and its analytical application

The mechanism of the inclusion of orange G and beta-cyclodextrin (beta-CD) has been studied by using both spectrophotometry and infrared spectroscopy. Effects of the pH, concentrations of beta-CD, and ionic strength on the inclusion complex of beta-CD and orange G were examined. The result showed that orange G reacts with beta-CD to form a 1:1 host-guest complex with an apparent formation constant of 3.03 x 10(3)mol(-1)l. The thermodynamic parameters of inclusion complex, DeltaG(0), DeltaH(0), and DeltaS(0) were obtained. Based on the enhancement of the absorbance of orange G produced through complex formation, a ratiometric method spectrophotometrically for the determination of orange G in bulk aqueous solution in the presence of beta-CD was developed, which overcome the effect of condition change on the determination of orange G. The linear relationship between the absorbance and orange G concentration was obtained in the range of 1.0 x 10(-5) to 4.0 x 10(-5)mol l(-1), with a correlation coefficient of 0.9998. The detection limit was 3.6 x 10(-6)mol l(-1). The principal advantage of the proposed method is high accuracy because ratiometry was used in measurement.     

Spectrophotometric determination of trace copper with a Cu-diethyldithiocarbamate-beta-cyclodextrin colour system

A simple, selective and accurate spectrophotometric method for determination of trace copper with diethyldithiocarbamate(DDTC) in the presence of beta-cyclodextrin(beta-CD) in ammonia media has been developed. The apparent molar absorptivity of Cu(II)-DDTC-beta-CD inclusion complex is 1.3 x 10(4) 1 . mole(-1) . cm(-1) at 436 nm, and Beer's law is obeyed for copper in the range 0-150 mug/25 ml. The detection limit is 4.38 x 10(-7)M(S/N = 3). The proposed method has been successfully applied to the determination of copper in aluminium alloys, soils, millet, wheat flour, herbs, vegetables and some traditional Chinese herbal medicines with satisfactory results.     

Determination of trace europium based on new fluorimetric system of europium(III) with thenoyltrifluoroacetone and N,N'-dinaphthyl-N,N'-diphenyl-3,6-dioxaoctanediamide

In the present paper, N,N'-dinaphthyl-N,N'-diphenyl-3,6-dioxaoctanediamide acts as a specific reagent for enhancing the fluorescence intensity of Eu(III) complex with thenoyl trifluoroacetone (TTA), the spectrofluorimetric determination of trace amounts of Eu(III) based on the above system was carried out and its luminescence mechanism was studied. The excitation and emission wavelengths are 343.6 and 613.3 nm, respectively. The fluorescence intensities vary linearly with the concentration of europium(III) in the range 3.647x10(-3)-3.039 mug ml(-1) for the original fluorescence with a detection limit down to 2.279x10(-4) mug ml(-1) and the standard deviation is 0.063 mug ml(-1) for 10 times measurements, and in the range 7.598x10(-4)-0.0243 mug ml(-1) (SD=0.035 for 15 times measurements), 0.06078-0.6100 mug ml(-1) (SD=0.52 for 10 times measurements) for the first derivative fluorescence signal with a detection limit down to 8.566x10(-5) mug ml(-1). The interferences of other rare earths and some of inorganic ions are described. This method is a direct, rapid, selective and sensitive analytical method for the determination of trivalent europium in rare earth ore samples and high purity of rare earth oxides.     

Fluorimetric trace determination of cerium(III) with sodium triphosphate

Sodium triphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III). The purpose of this study was to investigate the spectrofluorimetric determination of trace amounts of Ce(III) in sodium triphosphate solution. The excitation and emission wavelengths are 303.5 nm and 353 nm respectively. Optimum sodium triphosphate concentration is found to be 0.074 g l(-1) at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range 0.001-45 mug ml(-1). The detection limit is 9.4 x 10(-4)mug ml(-1). The relative standard deviations for 30 mug ml(-1) and 0.05 mug ml(-1) Ce(III) in 0.074 g l(-1) sodium triphosphate solution are 1.1% and 0.72% respectively. Quenching effects of other lanthanides and some inorganic anions are described. This method is a direct and rapid analytical method for the determination of Ce(III) in rare earth mixtures and cerium concentrates.     

Nitrosation of 2-acetylcyclohexanone. 2. Reaction in water in the absence and presence of cyclodextrins

The kinetic study of the nitrosation of the enol of 2-acetylcyclohexanone (ACHE) has been performed in aqueous acid media in the absence and presence of alpha- and beta-cyclodextrin. The reaction is first-order with respect to both reactants concentration: [nitrite] and [ACHE]; but, unexpectly, the dependence of both [H(+)] or [X(-)] (X(-) = Cl(-), Br(-), or SCN(-)) is not simple first-order. The experimental findings have been explained on the basis of a reaction mechanism that considers the formation of a chelate-nitrosyl complex intermediate in steady-state. Addition of both alpha-cyclodextrin (alpha-CD) or beta-cyclodextrin (beta-CD) diminishs strongly the observed rate constant, k(o), measured either for enol-nitrosation or for enol-ketonization reactions. In the case of beta-CD, the inhibition effect is explained through the formation of nonproductive inclusion complexes between the enol (EH) and beta-CD of 1:1 stoichiometry. Nevertheless, the quantitative interpretation of k(o)-[alpha-CD] profiles requires the assumption that the inclusion complexes formation of both 1:1 (EH/alpha-CD) and 1:2 (EH/alpha-CD(2)) stoichiometries. In the case of enol-ketonization, the EH/alpha-CD complex is nearly as reactive as the uncomplexed enol.     

Assembly behavior of inclusion complexes of beta-cyclodextrin with 4-hydroxyazobenzene and 4-aminoazobenzene

To further reveal the factors governing the supramolecular assembly of beta-cyclodextrin (beta-CD) inclusion complexes, two aggregates (1 and 2) were prepared from the inclusion complexes of beta-CD with 4-hydroxyazobenzene and 4-aminoazobenzene, respectively, and their binding behavior were investigated by means of X-ray analysis, UV-vis, NMR, and circular dichroism spectra in both solution and the solid state. The obtained results indicated that the beta-CD/4-hydroxyazobenzene complex 1 could form head-to-head dimers (triclinic system, space group P1) in the solid state, which were further self-assembled to a linear supramolecular architecture by the intra- and interdimer hydrogen bond interactions as well as the intradimer pi-pi interactions. However, when the included guest 4-hydroxyazobenzene was switched to a 4-aminoazobenzene, the resultant beta-CD/4-aminoazobenzene complex 2 (monoclinic system, space group P2(1)) could be self-assembled to a wave-type supramolecular aggregate under similar conditions. Furthermore, the combination of crystallographic and spectral investigations jointly revealed the inclusion complexation geometry of beta-CD with 4-hydroxyazobenzene and 4-aminoazobenzene in both solution and the solid state, which demonstrated that the disparity of substituents in the azobenzenes played an important role in the inclusion complexation and molecular assembly, affecting not only the structural features of aggregates but also the binding abilities of azobenzenes with beta-CD.     

Synchronous-derivative phosphorimetric determination of 1- and 2-naphthol in irrigation water by employing beta-cyclodextrin

A room-temperature phosphorimetric (RTP) study of the inclusion process between 1- and 2-naphthol, beta-cyclodextrin (beta-CD) and 3-bromo-1-propanol as heavy atom pertuber has been performed. Experimental conditions were optimized for the formation of trimolecular complexes with lifetimes of 10.82 and 9.41 ms for 1- and 2-naphthol, respectively. A synchronous-derivative room-temperature phosphorimetric method has been proposed to the analysis of both naphthols in synthetic mixtures and irrigation water in the ratio 1:10 to 10:1; the limit of detection is 0.02 mug ml(-1) and the relative standard deviation (RSD) is about 6%.     

Simultaneous first-derivative spectrophotometric determination of iron(III) and molybdenum(VI) in cobalt-chromium and nickel-chromium alloys

A method is proposed for the simultaneous determination of iron(III) and molybdenum(VI) by first-derivative spectrophotometry based on the absorption spectra of their complexes with morin in the presence of a cationic surfactant. The zero-crossing measurement technique is found sutiable for the direct measurement of the first-derivative value at the specified wavelengths. Iron(III) (0.9-1.5 mug ml(-1)) and molybdenum(VI) (0.3-4.2 mug ml(-1)) in different ratios have been determined simultaneously. A critical evaluation of the proposed method is performed by statistical analysis of the experimental data. The method was applied to determine iron and molybdenum in different alloys.     

Simultaneous determination of manganese and zinc in mixtures using first- and second-derivative spectrophotometry

A new direct spectrophotometric determination of manganese with 5,8-dihydroxy-1,4-naphthoquinone (naphthazarin,NAZA) is reported. Absorption maximum, molar absorptivity and Sandell's sensitivity of 1:2 (M:L) complex are 695 nm, 1.88x10(4) l mol(-1) cm(-1) and 2.92 ng cm(-2), respectively. A linear calibration graph is obtained up to a concentration of 7.2 mug ml(-1) of manganese. The optimum range for determination (Ringbom) is between 0.20 and 6.8 mug ml(-1). A rapid method for simultaneous determination of manganese and zinc in their mixture using derivative spectra is described. The range 0.28-5.6 mug ml(-1) manganese could be determined in the presence of 0.33-6.8 mug ml(-1) zinc and vice versa. The developed method was applied to the simultaneous spectrophotometric determination of manganese and zinc in some synthetic mixtures and was found to give satisfactory results.     

Preconcentration and flame atomic absorption spectrometry determination of cadmium in mussels by an on-line continuous precipitation-dissolution flow system

A rapid, sensitive, accurate and precise flame atomic absorption method is described for the determination of cadmium in mussels. The method is based on the continuous precipitation of cadmium as an ion pair between tetraiodocadmate and quinine and dissolution of the precipitate with ethanol. The metal can be preconcentrated 32-fold using 15 ml of sample solution by using a time-based technique at a sampling flow rate of 3.0 ml min(-1). The proposed method allows the determination of cadmium in the range 0.25-5.5 mug g(-1). The precision (relative standard deviation) obtained for different amounts of cadmium is in the range 1.5-4.7% at the 0.25-5.0 mug g(-1) level. The method demonstrates high tolerance to interferences, and the data obtained are in agreement with the certified value of a selected reference material. This procedure was applied to the determination of cadmium in mussel samples from estuaries in Galicia (Spain).     

Katalytische bestimmung von silberspuren in wabetariger lösung und nach extraktion

The application of the catalysed oxidation of Bromopyrogallol Red by potassium per- sulphate for silver determination is discussed. In aqueous solution silver concentrations of 0.5- 1 mug/ml can be determined and 1- 13 ng/ml in the presence of 1, 10-phenanthroline as activator. In combination with solvent extraction, catalytic determination of the extracted silver is possible even in presence of 200 mug of iron(III), cobalt(II) and palladium(II). By means of an automatic variant of the simultaneous comparison method a more sensitive determination (0.2-20 ng/ml) was achieved.     

Novel behavior of O-methylated beta-cyclodextrins in inclusion of meso-tetraarylporphyrins

[structure: see text] The mechanism for formation of extremely stable 1:2 inclusion complexes of water-soluble meso-tetraarylporphyrins with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMe-beta-CD) in aqueous solutions has been studied by means of NMR spectroscopy and isothermal titration calorimetry. To simplify the system, 5,10,15-tris(3,5-dicarboxylatophenyl)-20-phenylporphyrin (1) was used as a guest porphyrin, because 1 forms only a 1:1 inclusion complex with cyclodextrin (CD). As host compounds, native beta-CD and the O-methylated-beta-CDs such as heptakis(2,3-di-O-methyl)- (2,3-DMe-beta-CD), heptakis(2,6-di-O-methyl)- (2,6-DMe-beta-CD), and TMe-beta-CDs were used. The thermodynamic parameters for complexation such as binding constants (K) and enthalpy (DeltaH degrees ) and entoropy changes (DeltaS degrees ) were determined by means of isothermal titration calorimetry. The K value for complexation of 1 with CD increases in the order beta-CD (K = (1.2 +/- 0.1) x 10(3) M(-)(1)) < 2,6-DMe-beta-CD ((1.2 +/- 0.1) x 10(4) M(-)(1)) < TMe-beta-CD ((6.9 +/- 0.4) x 10(6) M(-)(1)) < 2,3-DMe-beta-CD ((8.5 +/- 0.5) x 10(6) M(-)(1)), indicating participation of the secondary OCH(3) groups in extremely strong complexation of 1 with CD. Complex formation of 1 with beta-CD and 2,6-DMe-beta-CD is an enthalpically and entropically favorable process, while that with TMe-beta-CD and 2,3-DMe-beta-CD is an enthalpically much more favorable but an entropically less favorable process. The thermodynamic parameters suggest that inclusion of 1 into the cavities of TMe-beta-CD and 2,3-DMe-beta-CD is promoted by van der Waals interactions, which are stronger than those in the cases of beta-CD and 2,6-DMe-beta-CD. (13)C NMR spectra show that the conformations of both TMe-beta-CD and 2,3-DMe-beta-CD are altered upon inclusion of 1, while those of beta-CD and 2,6-DMe-beta-CD are mostly retained. On the basis of these results, it can be concluded that induced-fit type complexation of 1 with TMe-beta-CD and 2,3-DMe-beta-CD causes extremely strong binding of the host to the guest.     

Room-temperature phosphorescence of 6-bromo-2-naphthol included in beta-cyclodextrin in the presence of cyclohexane

The formation constant for a 1:1 binary complex between 6-bromo-2-naphthol (6B2N) and beta-cyclodextrin (CD) in aqueous solution was determined by both absorptimetric and fluorimetric methods. Room-temperature phosphorescence (RTP) was induced by adding small amounts of different apolar liquids as the third component, with cyclohexane producing the strongest enhancement effect. Microcrystals formed in the ternary system seem to be necessary for obtaining phosphorescence emission. The deoxygenation by flowing nitrogen does not improve the RTP signals, while the addition of sodium sulfite as chemical deoxygenant produces quenching of the signals. The calibration graph for 6-bromo-2-naphthol in the presence of beta-CD and cyclohexane was linear for the range of concentrations between 0.04 and 1 mug ml(-1), with a detection limit of 0.04 mug ml(-1).     

Simultaneous spectrofluorimetric determination of europium, dysprosium, gadolinium and terbium using chemometric methods

A spectrofluorimetric method for the simultaneous determination of dysprosium, europium, gadolinium and terbium in ternary and quaternary mixtures by the use of pyridine-2,6-dicarboxylic acid as a chelating agent was developed. The influence of chemical variables affecting the analytical reaction was evaluated. A partial least-squares procedure and PC Quant software were used to assess data obtained from a variable number of calibration solutions and wavelengths. The ensuing method was validated by applying it to the analysis of synthetic ternary (Eu-Dy-Tb) and quaternary mixtures (Eu-Dy-Gd-Tb) over the concentration ranges 60-550 mug Eu l(-1), 30-400 mug Dy l(-1) and 30-400 mug Tb l(-1) in the former, and 20-220 mug Eu l(-1), 20-235 mug Dy l(-1), 25-230 mug Gd l(-1) and 75-230 mug Tb l(-1) in the latter. The results obtained by using the two quantitation procedures are compared. The relative errors in the determinations were less than 8% in most cases.