Cooperative And Competitive Supramolecular Self-assembly Based On Cucurbit[n] Urils And Its Analytical Applications

As a type of novel synthetic acceptor, cucurbit[n]uril(Q[n]) possess highly polar carbonyl portals with a hydrophobic cavity. Q[n]s form remarkably stable complexes with a variety of guest molecules in aqueous solution through a combination of ion-dipole, hydrogen bonding, and hydrophobic interactions inside the cavity. The cooperative and competitive binding between Q[n]s and guest molecules will change the electronic absorption spectroscopy, fluorescence spectroscopy, and thermodynamic proterty which can be used for the determination of pesticides in real samplesIn this thesis, choosing the N-heterocyclic pesticide as model pesticides, some dye molecules as cooperative and competitive guests, supramolecular interaction of Q[n]s with these N-heterocyclic pesticide and dye molecules were studied in details with electronic absorption spectroscopy(UV-Vis), fluorescence spectroscopy, 1H NMR spectroscopy and isothermal titration calorimetry(ITC). The content of the study are as follows:(1) We studied the supramolecular interactions of the Q[8] with 3-indoleacetic acid(IAA) and viologen derivatives(PC1,2,4) in the water. The results showed that IAA and PC1,2,4 formed ternary host-guest complex with Q[8] in the water and the ratio was 1:1:1. We also studied the supramolecular interactions between Q[8] with paraquat(DQ) and 1-Adamantanamine(AD) in the water, and the results showed that both DQ and AD with Q[8] form ratio of 1:1 host-guest complex. AD has the priority to react with Q[8] and thus DQ was excluded out of the cavity of Q[8], which form the Q[8]/AD supramolecular complex.(2) Q[8]/ThT fluorescent probes based on host–guest binding has been developed.The supramolecular interaction between Q[8]/ThT fluorescent probes and N-heterocyclic pesticides, such as paraquat, diquat, difenzoquat, mepiquat chloride,Choline chloride, fuberidazole, carbendazol, thiabendazole, triticonazole, pencycuron,thidiazuron and tricyclazole was studied in details and formed Q[8]/ThT/pesticides cooperative supramolecular system. Furthermore, a new method based on fluorescence quenching of host–guest complexation was proposed for the determination of the two herbicides paraquat and diquat in river water and cabbages by cooperative binding of a fluorescent probe. Detection limits of 7.95×10-9 mol/L and 8.07×10-9 mol/L were obtained for paraquat and diquat, respectively. Recoveries obtained by the proposed method in water and cabbage extracts were 104–108%. The method is rapid, direct and simple.(3) The inclusion interaction between cucurbit[8]uril(Q[8]) with thiazole orange(TO) and two herbicides, paraquat and diquat, was investigated. The results showed that TO and herbicides both entered Q[8] cavity and also formed cooperative supramolcular system. Therefore, Q[8]/TO fluorescent probes based on cooperative binding has been proposed. Furthermore, a new method based on cooperative binding of a fluorescent probe was proposed for the determination of the paraquat and diquat in river water and cabbages. Detection limits were 7.95×10-9 mol/L for paraquat and8.07×10-9 mol/L for diquat, respectively. Recoveries obtained by the proposed method in water and cabbage extracts were 104–108%. The method can be used in the test of PQ and DQ in river water and cabbage.(4) The competitive reaction between paraquat(PQ) and neutral red(NR) for occupancy of the cucurbit[7]uril(Q[7]) cavity was studied spectrofluorimetry,ultraviolet-visible absorbance spectrometry, 1H nuclear magnetic resonance spectroscopy, and isothermal titration calorimetry. However, the addition of paraquat quenches the fluorescence intensity of Q[7]/NR fluorescent probe. Accordingly, a new fluorescence quenching methods for the determination of paraquat was established.The methods can be applied for quantifying paraquat. A linear relationship between the fluorescence quenching values and paraquat concentration exists in the range of0~8×10-6 mol/L, with a correlation coefficient of 0.9991. Detection limits were1.40×10-8 mol/L for paraquat. Recoveries obtained by the proposed method in water and cabbage extracts were 104–108%.