Fluorescence Enhancement Of Cyclodextrins & Cucurbit[n] Uril On Guest Molecules And Their Analytical Application

Supramolecular chemistry is the domain of chemistry beyond that of molecules that focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components.The forces responsible for the spatial organization may vary from weak(intermolecular forces,electrostatic or hydrogen bonding)to strong(covalent bonding),provided that the degree of electronic coupling between the molecular component remains small with respect to relevant energy parameters of the component.While traditional chemistry focuses on the covalent bond,supramolecular chemistry examines the weaker and reversible noncovalent interactions between molecules.These forces include hydrogen bonding,metal coordination,hydrophobic forces,van der Waals forces,pi-pi interactions and electrostatic effects.Important concepts that have been demonstrated by supramolecular chemistry include molecular self-assembly,folding,molecular recognition,host-guest chemistry,mechanicallyinterlocked molecular architectures,and dynamic covalent chemistry.The study of non-covalent interactions is crucial to understanding many biological processes from cell structure to vision that rely on these forces for structure and function.Biological systems are often the inspiration for supramolecular research.With the development of analytical science,due to the diversity and complexity of the analytical components,the selective and sensitive analytical methods must be adopted for the study of trace elements.Supramolecular host compound molecules with high molecular recognition ability of an object,for analytical chemistry,forms the foundation of separation,detection and quantitative determination,for the development of specificity,high specificity,selective analysis method provides a broad prospect.This thesis choose two of the most important subject in supramolecular chemistry——cyclodextrin and cucurbituril,the mechanism of complexation were studied,respectively.And the difference of the two kinds of the supramolecular subject about selective inclusion object were investigated.Based on the fluorescence enhancement of the host on the guest,three new fluorescence analysis test method about capsaicin,carbendazim and thiabendazole were established.The dissertation includes following four chapters:Chapter 1: Introduction.A brief review of investigation progress of CDs&CB[n]s inlusion complex on analytical chemistry was summarized.Chapter 2: Fluorescence enhancement of hydroxypropyl-?-cyclodextrin on capsaicin and its analytical application.The host–guest inclusion system of hydroxypropyl-?-cyclodextrin(HP?CD)with capsaicin was investigated by fluorescence spectra,Job's plot and phase solubility studies.The results showed that the capsaicin was encapsulated in the HP?CD's cavity to form a 1:2 stoichiometry host–guest inclusion complex and the inclusion constant(Kc = 743.95 L/mol)was confirmed by the phase solubility diagram.Furthermore,several experimental conditions were optimized in order to obtain the maximum fluorescence signal.On the basis of the enhancement of the fluorescence of capsaicin produced through complex formation,a spectrofluorimetric method for the determination of capsaicin in bulk aqueous solution in the presence of HP?CD was developed.The linear relationship between the fluorescence intensity and capsaicin concentration was obtained in the range of 0.05-20 ?g/m L.The detection limit was 0.04 ?g/m L,and the relative standard deviation was 1.25%.The proposed method has been successfully applied to the determination of capsaicin in chili powder with recoveries of 99.5-105.6%.Chapter 3: Fluorescence enhancement of cucurbituril on carbendazim and its analytical application.The increase in fluorescence intensity with respect to carbendazim that occurs as a result of supramolecular-complex formation between carbendazim and cucurbit[7]uril has been studied.This host–guest interaction has been employed to develop a sensitive and selective method for carbendazim determination in Lanzhou lily samples.The association constant and stoichiometry of the complex form a 1:2 stoichiometry host–guest inclusion complex,thus showing that the proposed method is sensitive enough to meet legal requirements.The linear relationship between the fluorescence intensity and carbendazim concentration was obtained in the range of 1.00×10-8—1.00×10-5 mol/L.The detection limit was 4.05× 10-9 mol/L,The proposed method has been successfully applied to the determination of carbendazim in Lanzhou lily with recoveries of 96.0-102.0%.Chapter 4: Fluorescence enhancement of cucurbituril on thiabendazole and its analytical application.The mechanism of the supramolecular interaction of thiabendazole and cucurbit[7] uril has been studied and discussed by spectrophotometry.The results showed that thiabendazole was included in the cucurbit[7] uril cavity to form a 1:1 host-guest complex.On the basis of the enhancement of the fluorescence intensity of thiabendazole produced through complex formation,a fluorescence spectrophotometric method for the determination of thiabendazole in agaricus bisporus in the presence of cucurbit[7] was developed.The linear relationship between the fluorescence intensity and thiabendazole concentration was obtained in the range of 5×10-8 –1×10-5mol/L,and the relative standard deviation was 1.55%,the determination of thiabendazole in agaricus bisporus with recoveries of 96.0-100.0%.