Bridged ¦Â-cyclodextrin Host Molecules For Research And Analytical Applications Of Bioactive Molecules

Cyclodextrins (CDs) are a class of cyclic oligosaccharides with six to eight d-glucose units linked byα-1, 4-glucose bonds. They possess a hydrophilic exterior and a hydrophobic cavity capable of including a variety of inorganic/organic hydrophobic compounds which possess suitable polarity and dimension via host-guest complexation. CDs are extensively studied as not only excellent receptors for molecular recognition but also functional building blocks to construct molecular devices. Among various functional CDs, bridged bisCDs, which comprises two CDs cavities linked by a functional bridge, is a greatly promising candidate. In comparison with native CDs and mono-modified CDs, bridged bisCDs exhibit significant high binding ability and molecular recognition through the cooperative binding of two adjacent CDs units. Moreover, the linker can supply a well-organized pseudo-cavity that in turns provides additional binding interactions with accommodated guest molecules.Based on the intramolecular cooperative binding and multiple recognition of bridged bis (β-CDs) with functional linkers in solution, as well as their unique properties and wide applications, we have carried out two aspects of investigation: First, a novel metallobridged bis (β-CDs) was synthesized and characterized by means of 1H NMR, IR, element analysis and redox iodometric titration. The fluorescence of metallobridged bis (β-CDs) was weak compared with bis (β-CDs) which had not formed complex with copper (II) because of the paramagnetism of copper (II) ions. Glutathione could form complexes with copper (II) derived from the metallobridged bis (β-CDs). This competitive complexation with copper (II) can lead to a significant fluorescence recovery of the bis (β-CDs). Therefore, a rapid and simple spectrofluorimetric method was developed for the determination of glutathione. The analytical application for glutathione was investigated in PBS buffer solution of pH 6.00 at room temperature. The linear range of the method was 0.30 ~ 20.0μmol L-1 with the detection limit of 63.8 nmol L-1. There was no interference from the plasma constituents. The proposed method had been successfully applied to the determination of glutathione in human plasma.Second, avidin modified gold nanoparticles (AGNPs)– bis (β-CDs) - fluorescein has been designed as a selective fluorescent probe for detecting biotin content utilizing FRET. Inclusion of fluorescein into bis (β-CDs) makes FRET occur through donor and quencher nearby. FRET switches off by the addition of the competitive biotin which affords high binding ability with avidin. This competitive binding restores the fluorescence of the quenched fluorescein. This phenomenon suggests that the AGNPs- bis (β-CDs)-FL is effective as a fluorescent probe for biotin recognition. The analytical application for biotin was investigated in Tris-HCl buffer solution of pH 7.6 at room temperature. The linear range of the method was 0.80 ~ 20.0μg/mL with the detection limit of 57.0 ng/mL.