Study On The Cucurbit[7]uril/Palmatine Fluorescent Probe And Its Analytical Application

Supramolecular chemistry have a wide range of applicationsincluding chemical sensing, molecular switches, molecular machines,drug delivery, controlled drug release, their potential analyticalapplications were ignored. The interaction between thenon-fluorescent drugs and CB[n] has only just begun to be studiedusing fluorescent probes titration. Drugs are of great significance forhuman, and the establishment of a high-sensitivity determinationmethod is the urgent need of the drug analysis research. Theinteraction between CB[n] and drugs was confirmed via thefluorescent titration,1H NMR spectrum, and theoretical calculations.New spectrofluorimetric methods with high sensitivity and selectivitywere developed for the determination of drugs in aqueous solution.The proposed method had been successfully applied to thedetermination of non-fluorescent drugs in its samples with goodprecision and accuracy. The content of this paper are as follows: 1. Supramolecular chemists have observed that the structuraland chemical properties of CB can exert a profound effect on thephysical and chemical properties of a guest duringcomplexation.These effects open up a variety of uses for CB[7],including chemical sensing, molecular switches, molecularmachines, drug delivery, controlled drug release, competitionintetaction, and molecular catalysis within and between guests.The uses of CB[n] in these field are summarized.2. The Supramolecular interaction between palmatinehydrochloride （PAL） and cucurbit[7]uril （CB[7]） was studied byfluorescence spectrometry and1H NMR. CB[7] reacts with PAL toform a stable1:1host-guest complex. The fluorescence intensity ofthe complex enhanced gradually with the increase of CB[7]concentration. At the same time produced a strong fluorescenceemission, the association constant （K=1.18×10⁵L mol1） wascalculated by applying a deduced equation. From the temperaturedependence of the equilibrium constants, thermodynamicsparameters H and S values were obtained, indicating an enthalpicdriving force for complexation. Molecular modeling calculationswere optimized at the B3LYP/6-31G（d） level of density functionaltheory using the Gaussian03program. In the energy-minimizedstructure, the methoxy-isoquinoline moiety is embedded in CB[7], and the heterocyclic nitrogen is located in the vicinity of acarbonyl-laced portal. Two hydrogen bonds are formed between theheterocyclic nitrogen and carbonyl oxygen of CB[7]. The dihedralangle between the isoquinoline and the substituted benzene ringvaries from23.37°to8.09°. The main factors of palmatine producestrong fluorescence emission in the presence of CB[7] have beenidentified. In addition, the mechanism of host-guest interaction hasbeen derived by1H NMR and molecular modeling calculation, theformation steps of inclusion complexes has also been identified.3. Significant quenching of the fluorescence intensity of theCB[7]-PAL complex was observed with the addition of cartap. Basedon the significant quenching of the supramolecular complexfluorescence intensity, a new spectrofluorimetric method with highsensitivity and selectivity was developed for the determination ofCP in aqueous solution. The fluorescence quenching values （ΔF）showed good linear relationship with cartap concentrations from0.009μg mL^-1to2.4μg mL^-1with a detection limit0.0029μg mL^-1.The proposed method had been successfully applied to thedetermination of cartap residues in grain and vegetable withrecoveries of87.4–103%. In addition, the association constants ofthe complexes formed between the host and the guest weredetermined. The competing reaction and the supramolecular interaction mechanisms between the insectcide and PAL as theyfight for occupancy of the CB[7] cavity were studied usingspectrofluorimetry,¹H NMR, and molecular modeling calculations.4. The inclusion interaction of cucurbit[7]uril （CB[7]） withephedrine hydrochloric acid （EP） was studied by fluorescent probemethod. Significant quenching of the fluorescence intensity of theCB[7]-palmatine （PAL） fluorescent probe was observed with theaddition of EP, showing that EP was accommodated into thehydrophobic cavities of CB[7] and an endo-inclusion complex wasformed. The hydrophobic interaction between CB[7] and EP mainlycontributed to the formation of1:1type CB[7]-EP. Its complexconstant was determined to be K=（2.82±0.52）×10¹¹M^-1. Based onthe significant quenching of the supramolecular complexfluorescence intensity, a new spectrofluorimetric method with highsensitivity and selectivity was developed for the determination ofephedrine in aqueous solution. The fluorescence quenching values（ΔF） showed good linear relationship with ephedrine concentrationsfrom0.011μg mL^-1to2.8μg mL^-1with a detection limit0.0036μg mL^-1. The proposed method had been successfully applied to thedetermination of ephedrine in its pharmaceutical dosage forms withgood precision and accuracy. In addition, the interaction model ofthe supramolecular complexes formed between the host and the guest were established through theoretical calculations. Theinteraction mechanism between the CB[7] and EP was confirmedvia the1H NMR spectrum.