The Design, Synthesis And Propertie Of Fluorescent Sensors Based On Boronic Acid And Thiourea Units

Molecular recognition, especially chiral recognition of saccharides and amino acids have attacted much interest during the past decade. Many researchers dedicated to the design, the synthesis and application of new sensors. Among these receptors, those bearing fluorescent properties are much attractive due to the merits of fluorescent assay such as short response time, excellent sensitivity, simplicity and low cost.Organic boronic acid compounds could be combined with carbohydrates, so the boronic acid group can be identified as saccharides sensing group. Sensing methods based on the boronic acid received extensive attentions in recent years;In addition,thiourea structure as the main structure of the anion recognition, has been extensively studied in the field of asymmetric catalysis, but in molecular recognition, especially chiral molecular recognition need to be further developed.This thesis mainly focuses on the design, synthesis and propertie of fluorescent sensors based on boronic acid and thiourea units.In the first chapter, we introduce the basis of the fluorescent molecular sensors and review the progresses by structures.In the second chapter, diboronic acid sensors R-1, S-1, R-2,S-2,3a-3b and4were prepared and their binding behaviour with saccharides was investigated. Chiral sensors1and2were found to be chemoselective fluorescent chemosensors for saccharides, such as D-glucose and D-galactose. R-1increased its fluorescence intensity upon the formation of intramolecular1:1complexes with D-glucose. The addition of D-glucose to R-1causes an increase in fluorescence, whilst the addition of D-glucose to S-1it produces smaller changes in fluorescence. Although, saccharides are available from nature as a single chiral form, we have shown that it is possible to use the chirality of a synthetic receptors to either enhance or reduce binding with a particular saccharide. Therefore, with this work we have demonstrated the importance of chiral units in the design of selective saccharide receptors and believe our results will encourage others to use chiral units in the design of other saccharide selective sensors with practical utility.In the third chapter, we designed and synthesized coumarin-based fluorescent sensor M1, M2, P1and P2. Sensor M2shows high selectivity toward Hg2+, but no significant responses toward other competitive cations.The fluorescence response mechanismof Hg2+-promoted reaction of thiosemicabazide is studied by1HNMR; P2is a ditopic fluorescent sensor for D-fructose and Hg2+. The system simultaneously recognises saccharidesand the Hg2+cation. We believe that our system will guide thedesign of new ditopic sensors with practical utility. We arecurrently working on developing saccharide selective receptors based on the principles outlined in this preliminary report.In the fourth chapter, we designed and synthesized fluorescent sensors la and lb based on chiral thiourea structure. Sensors la and lb show highly enantioselective of N-Boc-protected proline. Job plot analysis result indicates that sensor1can form a1:1stoichionmetric complex with Boc-Pro and it could be used as a fluorescence sensor for the determination of enantiomer composition of N-Boc-protected proline. We believe that our system will guide thedesign of new chiral sensors for amino acids with practical utility.