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Study on Supramolecular Effect between β-cyclodextrin and Organic Dyes

Author: WeiJingJuan
Tutor: LiuQi
School: Henan Normal
Course: Analytical Chemistry
Keywords: Supermolecular chemistry β-cyclodextrin Neutral red Methylene blue Fluorescenceyellow Alizarin violet Molecular modeling
CLC: O621.1
Type: Master's thesis
Year: 2012
Downloads: 125
Quote: 0
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Abstract


If molecular is a room, we can think supermolecular is a building or a neighborhood. A molecule ismade up of atoms by covalent bond，supermolecular is made up of moleculars by intermolecularinteractions. When supermolecular consists of dozens of atoms or thousands of moleculars byintermolecular interactions, it will show some different chemical or physical properties. Cyclodextrins（CDs） as the most important host in supermolecular chemistry which have been widely used in manyfields.The present paper studies the interaction of β-Cyclodextrin (β-CD) and organic pigments on the basisof the theory of supermolecular chemistry. The mechanism of the inclusion of the supermolecular systemshas been studied by using UV–vis, fluorescence, infrared spectroscopy and thermodynamic parameters. Atthe same time, the forms of inclusion complex are proved by the Molecular Dynamics Simulations.The major conclusions can be summarized as follows：1、In acidic medium, neutral red can directly reacts with nitrite to form a new compound with nofluorescence intensity. But the protonated form (NRH+) of the dye does not form an Inclusion complex withβ-cyclodextrin, only the neutral form (NR) can. After adding right amount of NaOH and β-cyclodextrin, thefluorescence intensity of neutral form (NR) is largely enhanced because of inclusion complexation. A newfluorescent spectrophotometry based on this principle has been developed to determine trace nitrite. Itsmaximum excitation wavelength is451nm, and the maximum emission wavelength is576nm. The linearrange, detection limit and relative standard deviation were4～160μg/L,1.58μg/L and1.2%, respectively.The common coexisting ions do not interfere in the determination. This method was used to determinenitrite in water and vegetables samples with satisfactory results.2、In acidic medium, Methylene blue (MB) can directly reacts with Ascorbic acid (AA) to form ionassociation complex with no fluorescence intensity. At pH=4, after adding right amount of β-cyclodextrin,the fluorescence intensity of MB is largely enhanced because of inclusion complexation. A new fluorescentspectrophotometry based on this principle has been developed to determine AA. Its maximum excitationwavelength is660nm, and the maximum emission wavelength is678nm. The linear range, detection limit and relative standard deviation were0.05～24mg/L,0.09688mg/L and3.9%, respectively. The commoncoexisting ions do not interfere in the determination. This method was used to determine AA in sampleswith satisfactory results.3、At pH=4，the lactonic structure of fluorescence yellow (FY) and β-cyclodextrin (β-CD) formed1:1inclusion complex which fluorescence and UV-Vis absorption intensity both decreased by the addition ofβ-CD. Effect of the pH, solvents and ionic strength on the inclusion of FY and β-CD were examined.Meanwhile, the thermodynamic parameters of inclusion reaction at pH4, ΔG, ΔH and ΔS were obtained.Additionaly, molecular modeling and infrared spectrum have been carried out which provide detailedinsights regarding the encapsulation process.4、The formation mechanism of two type of inclusion of alizarin violet (AV) and β-cyclodextrin (β-CD)has been studied by spectrophotometry, and the stoichiometric ratio of the complexations was to be1:1atpH10/12. Effect of the pH, concentrations of β-CD, solvents and ionic strength on the inclusions of AV andβ-CD were examined. Meanwhile, the thermodynamic parameters of inclusion reaction at pH10/12, ΔG, ΔHand ΔS were obtained. Molecular modeling and semiempirical calculation have been carried out whichprovide detailed insights regarding the encapsulation process.

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