Studies On The Self-assemblies Of Cucurbit[n]Urils With Fluorescent Dyes And Their Applications

Cucurbit[n]urils, because of their different structures from the existed supramolecular microcyclar hosts such as crownether, cyclodextrin, and calixarene, were intensively studied by supramolecular chemists. The cucurbit[n]uril supramolecular systems were widely used in the fields of environmental chemistry, catalysis, material chemistry, life science and nanotechnology. Meanwhile, the complexes of fluorescent dyes and cucurbit[n]urils have been widely used in detection, imaging, laser and other aspects.About270-fold fluorescence enhancement was observed when the hemicyanine dye, trans-4-[4-(dimethylamino)styryl]-l-methylpyridinium iodide (DSMI), was included by cucurbit[6]uril (CB[6]). The1:1stoichiometry of DSMI-CB[6] complex was determined through optical spectra analysis and1H NMR measurement. The large fluorescence enhancement was achieved by prohibiting the twisted intramolecular charge transfer (TICT) process of DSMI inside the distorted cavity of CB[6], together with the ion-dipole interaction between DSMI and CB[6]. The distortion of the CB[6] cavity, being as the major reason for the huge fluorescence enhancement, was further confirmed by the calculation results. And then a resettable and reconfigurable logic gate was constructed with DSMI and CB[6] under different pH situations. This study lays a solid foundation for the design of molecular logic gates via supramolecular interaction mode.DSMI could bind with both CB[7] and DNA and DSMI could be included by CB[7] with1:2stoichiometry to form DSMI-CB[7] complex, which has a larger binding affinity than the DSMI-DNA complex. Therefore, CB[7] would inhibit the binding interaction between DSMI and DNA. Then we synthesised a novel hemicyanine derivation D2and investigated its supramolecular interaction between CB[7] and DNA. The branched structure of D2could induce the formation of DNA-D2-CB[7] ternary complex, which could decrease the inhibition of CB[7] to the binding affinity of dyes and DNA.A near-infrared fluorescent dye Hsd was designed and synthesized, which absorbed as hemicyane and emitted as Cy7and therefore produced a Stokes shift as large as224nm. Quantum chemistry calculations demonstrate that the large Stokes shift is produced by the combination of intramolecular charge transfer (ICT) and internal conversion. Significantly, Hsd showed selectively response to RNA in aqueous solution and fixed cells. Moreover, Hsd could be uptaken into the cells under the assistance of cucurbit[7]uril and selectively stain RNA in living cells. The introducing of CB[7] provides a novel platform to amplify the application of some cell-impermeant fluorescent stains through the supramolecular chemistry methods.Finally, a molecular beacon MB which could be assembled with CB[8] was designed and synthesized. The fluorescence and quencher groups on the molecular beacon possessed a naphthalene ether group and methylviologen group respectively, which could form a ternary complex with CB[8] and bring the fluorophore closer to the quencher. The formation of the ternary complex would increase the efficiency of FRET and is expected to improve the signal-to-noise ratio of molecular beacon. This idea provides a new method for improving the performance of molecular beacon.