Study And Application Of Inclusion Complex Formation Between β-cyclodextrin And Azo Dyes

Cyclodextrin chemistry, as a new subject, has been the hot topic of manyresearchers recently, and the β-cyclodextrin most. It is well known that cyclodextrins(CDs) can form inclusion complexes and change the physical properties. CDs areused extensively in many fields, such as rug carrier, food and flavours, textiles,separation process, environment protection and catalysis. The formation of thehost-guest complexes is mainly controlled by the non-convalent interactions betweenthem such as van der Waals interactions, hydrophobic interactions, static interaction,pole-pole interactions and hydrogen bonds. On the other hand, the inclusioncomplexes are also formed in terms of guest molecule chemical structure, polarity andmolecule dimensions. Recently, the molecular recognition behavior of cyclodextrinhas been studied comprehensively. The inclusion of the host-guest was confirmedsystematic by means of elemental analysis, X-ray diffraction, conductometrictechnique, NMR spectroscopy, fluorescence technique, spectrophotometric andelectrochemical measurement.Dyes are known as the color additive in food and cosmetic and basicallysynthetically produced, and azo dyes most. The quantity of the dyes affects people'shealth and safety directly. Therefore, it is important to establish method in the azodyes measurement and separation. Furthermore, because of the hydrophobic benzenering, azo dyes could be investigated as typical guest molecule, which can form stableinclusion complex with cyclodextrins. In recent years, cyclodextrins are developing inthe study of recognition and azo dyes detection, due to the specific affinity and goodselectivity.The first chapter of this paper reviews the study and application of the inclusioncomplex between β-cyclodextrin and azo dyes in recent years.In this paper, the mechanism of the inclusion of Tropaeolin OO, Orange G, 1-(2,4-dimethylphenylazo)-2-naphthol, 1-[4-(phenylazo) phenyl] azo-2-naphthalene andβ-CD has been studied by spectrophotometry, respectively. The inclusion depth of theguest molecule in the host molecule was demonstrated by infrared spectrometry.Effects of the pH, concentrations of β-CD, solvents and ionic strength on the inclusioncomplexes were examined. The stoichiometric ratio, an apparent formation constantand the thermodynamic parameters of inclusion reaction, ?G0, ?H0 and ?S0 wereobtained. We note that absorbance signal measurements were restricted in singlewavelength. In addition, in most practical applications, absorbance changes can alsobe caused by many other poorly quantified or variable factor, such as incident lightintensity, dye concentration, and environment around dye (pH, polarity, temperature,and so on). Thus, it is necessary to produce more feasible techniques to compensatefor these effects. A ratiometric method, which allows the measurement of changes inthe ratio of the absorbance of two wavelengths, has been one answer to the problemsposed by single wavelength measurement.The ratiometric method spectrophotometrically for the determination of orange Gin aqueous solution in the presence of β-CD was developed. The changes in the ratioof the absorbance of 479nm and 322nm were determined. The analyticalcharacteristics of orange G in the presence of β-CD are significantly improved.Obvious decrease in the detection limit is achieved with respect to the solutionswithout β-CD and the widened linear range both can be concluded that an improvedsensitivity for the spectrophotometric determination of orange G in the aqueoussolution can be achieved in the presence of β-CD. The fluorimetric method also beused to study the inclusion complex between orange G and β-CD.The spectrophotometric ratiometry having improved sensitivity for determinationof 1-(2, 4-dimethylphenylazo)-2-naphthol (Sudan Ⅱ) in the bulk solution wasdeveloped. The Sudan II in chilli paste was separated by thin layer chromatographyand determined the changes in the ratio of the absorbance of 556nm and 514nmaccording to the proposed method. Decrease in the detection limit and the obviouslydecrease in the relative standard deviation both can be concluded that an improvedsensitivity for the determination of Sudan Ⅱ in the aqueous solution by ratiometricmethod spectrophotometrically can be achieved in the presence of β-CD.