Reactive oxygen species (ROS) and reactive nitrogen species (RNS), saccharide (i.e. monosaccharide, disaccharide and polysaccharide), are continuously generated, transformed and consumed in the living systems. As a consequence of their significant value towards human health in aerobic life, it is very important and has drawn much attention in the chemical and biological sensing of the species. It is our long-standing interest in the recognition of monosaccharide (e.g. glucose) through exploration of various boronate-based fluorescence probes, thus, based on the previous work, we started on the design, synthesis and evaluation of novel fluorescent chemosensors for breakthrough discoveries in the detection of saccharide and ROS selectively and specifically, which are made up of different receptors and diverse singaling fluorophores, e.g. anthracene, coumarin, fluorescein, naphthalimine. Firstly, “integrated” and “insulated” boronate-based fluorescent probes (2-naphthylboronic acid and N-Methyl-o-(aminomethyl)phenylboronic acid) have been evaluated for the detection of hydrogen peroxide in the presence of saccharides (i.e. D-fructose). In the presence of D-fructose the initial fluorescence intensity of the “insulated” system is much higher and produces a blue visible fluorescence. Based on the experimental observation above in the boronate-based systems (i.e. B-N bond protection), a new water-soluble boronate-based fluorescent probe was designed and evaluated for the detection of peroxynitrite (much stronger oxidant) in the presence of D-fructose. The enhanced fluorescence of probe when bound with D-fructose was switched off in the presence of peroxynitrite. While, other reactive oxygen/nitrogen species led to only slight fluorescence decreases due to protection by the internal N-B interaction. The interaction of probe with D-fructose not only strengthens the fluorescence signal, but also protects the boronic acid to oxidation by other ROS/RNS. Therefore, under conditions generating various ROS/RNS, the boronate-based sugar complex preferentially reacts with peroxynitrite (ONOO−). The sensor displays good “on-off” response towards peroxynitrite both in RAW 264.7 cells and HeLa cells. A new ICT (internal charge transfer) sensing system was developed for the detection of hydrogen peroxide and peroxynitrite. The probe displayed an enhanced fluorescence change when bound with D-fructose due to the prolonged N-B distance. The fluorescence intensity of the probe dropped down both in the detection of H2O2 and ONOO− which was attributed to the oxidation of arylboronic acid even though in the presence of D-fructose. Using the self-assembly of aromatic boronic acids with Alizarin Red S (ARS), we developed a new chemo/biosensor for the selective detection of peroxynitrite. Phenylboronic acid, benzoboroxole and 2-(N, N-dimethylaminomethyl) phenylboronic acid were employed to bind with ARS to form the complex probes. In particular the ARS-NBA system with a high binding affinity can preferably react with peroxynitrite over hydrogen peroxide and hypochlorite due to the protection of the boron via the solvent-insertion B-N interaction. Our simple system produces a visible naked-eye colorimetric change and on-off fluorescence response towards peroxynitrite. By coupling a chemical reaction that leads to an indicator displacement, we have developed a new sensing strategy, referred to herein as RIA (Reaction-based Indicator displacement Assay). Next, we developed a novel class of simple materials for sensing monosaccharides by the functionalization of graphene oxide (GO) with boronate-based fluorescence probes. The composite materials were characterized by atomic force microscopy, Raman spectroscopy, and UV-vis/fluorescence spectroscopy. The strong fluorescence of the fluorescence probes is quenched in the presence of GO through fluorescence resonance energy transfer (FRET). The BA@GO composite sensors formed provide a useful platform for fluorogenic detection of monosaccharides based on the strong affinity between the boronic acid receptor and monosaccharides. The BA@GO composite sensor displayed a “turn-on” fluorescence response with a good linear relationship towards fructose over a range of other saccharides.Next, new water-soluble copper (II) complex fluorescence probes were developed and evaluated for the detection of nitric oxide and nitroxyl in a physiological condition. A significant fluorescence “off-on” response displayed by using the copper (II) complex for the detection of NO and HNO (Na2N2O3 as a donor). Under pathological conditions generating various ROS/RNS, the copper (II) complex fluorescent probe preferentially reacts with NO/HNO over other reactive oxygen species. The dual-analyte recognitions of the simple, sensitive probe were further applied in living cell for the exogenous NO/HNO. In the following work, we synthesised a phosphorous-based compound for the detectionof HNO which derived from Angeli’s salt in a biological condition. Significantly, it displayed a high sensitivity and selectivity toward HNO over other various ROS species, especially NO since they have a similar chemical property. The underlying mechanism was attributed to the cleavage of C-O bond induced by Staudinger Ligation.
|Date of Award
|27 Jan 2015
|Tony James (Supervisor) & Steven Bull (Supervisor)
- Boronic acid, ROS, Fluorescence probe