Construction And Properties Of New Two-component Systems For Monosaccharides

It is well known that monosaccharides not only play important roles in biological systems but also lead to some diseases, such as renal glycosuria, cystic fibrosis, diabetes and some cancers which are correlated with the breakdown of glucose transport in human body. Therefore, how to design a specific sensing system for monosaccharides and to study the important process of life as a probe is very meaningful. However, due to monosaccharide with only one kind of functional group (hydroxyl) and many variable configurations in aqueous solution, it is rather difficult to obtain highly sensitive and selective receptors for sensing monosaccharides. Hence, exploring facile bonding ways and developing new systems for sensing monosaccharides are necessary for chemists, biologists and medical scientists. The successful reuslt not only can give the reliable means for medical diagnosis but also may provide molecular biology basis for exploring the complex life processes.The action mechanism of these ensembles for sensing monosaccharides in the thesis is listed as follows:It is a two-component ensemble. The sensing original system is composed of fluorescent quantum dots or dyes that serve as the fluorescent reporter unit and boronic acid-substituted cationic bipyridiniums that act dully as a flurescence quencher and a saccharide receptor. The fluorescence sensing mechanism relies on the formation of a ground state charge-transfer complex, which results to the sensing system fluorescence quenched, between the fluorescent groups and bipyridinium by electrostatic interaction. Upon saccharide binding, changes in the electronic and/or steric states of the ground state charge-transfer complex cause charges in the fluorescence emission of the sensing original system. This thesis mainly includes the following five aspects:The first chapter:a brief overview of the structures of the carbohydrate, carbohydrate analysis methods and the research progress of fluorescent sensors is given in this paper. Next, the main topic of paper is also proposed. The second chapter:Three effective detection systems for D-glucose were constructed by fluorescent quantum dot (FQD) and boronic acid functional benzyl viologens (BBVs). The sensing mechanism based on fluorescence "on-off-on" processes was proposed. In the ensemble, fluorescent quantum dot (FQD) with amino and carboxyl was used as fluorecsent reported section and its fluorescence was modified by boronic acid functional benzyl viologens (BBVs). The BBVs acted as both quenchers and receptors roles in these systems. There sensing systems of FQD/BBVs all displayed higher detection efficiency for D-glucose in pH=7.4buffer solutions. The research results can provide a feasible method for the application of fluorescent quantum dots in the field of molecular recognition.The third chapter:A highly selective ensemble for D-fructose was formed by fluorescent quantum dot (FQD) and tetraboronic acid functionalized benzyl viologen (ToBV). The two-component system showed a high selectivity and sensitivity only for D-fructose in familiar D-monosaccharides. The high selectivity of the sensing system for D-fructose was depended on stable pyranose ester form of D-fructose and suitable boronic acid position of ToBV. The sensing processes of the ensemble to D-fructose were observed under365nm UV-Vis light by naked eyes. The results are helpful for designing and synthesizing high selective chemosensors in the futher.The fourth chapter:A highly selective switch for D-fructose was formed by water soluble fluorescent dye HPTS and boronic acid functionalized pyridine salt m-P3BQ. The sensing ensemble shows a high selectivity and sensitivity only for D-fructose in aqueous solution. The sensing ensemble is facile and simple. The high selectivity of the sensing ensemble for D-fructose may be depended on suitable spacer width of boronic acids and stable pyranose ester form of D-fructose with m-P3BQ. The research results can offer a new strategy to design and synthesize highly selective monosaccharides probes.The fifth chapter:Summary and prospects.