| Zn(II) ion is the second most abundant transition metal ion in the human body after iron, and is an essential cofactor in many biological processes such as brain function and pathology, gene transcription, immune function, and mammalian reproduction. As the most prevalent contaminant in biological and environmental samples, Hg2+is widely distributed in air, water, and soil, which continues to be a major environmental and health concern. Therefore, the synthesis of chemosensors for recognition and sensing of these metal ions is of considerable significance, which is currently a hot topic in the supermolecular chemistry and relevant areas.In the first section of this thesis, we describe the synthesis of a novel AB type of clickable monomer,(S)-2-[(2-azido-1-phenylethyl-imino)methyl]-5-propargyloxy-phenol (AMPP) and the corresponding main-chain chiral poly(imine-triazole)s via the metal-free click reaction. With the thermally-induced polymerization, the polymers of Mn ranging from5.1×10to58.1×103can be easily prepared in a high yield by adjusting reaction parameters. For these polymers the fractions of1,4-substituted triazole are determined to be in the range of61.9-63.0%. The polytriazoles were characterized by FT-IR,1H NMR, and GPC, and their optical properties were studied by fluorescence and circular dichlorism (CD) spectroscopies. As a fluorescence chemosensor, these polymers exhibited selective remarkable "turn-on" fluorescence enhancement response toward Zn2+ion over other cations such as Na+, K+, Mg2+, Ca2+, Ag+, Pb2+, Cd2+, Hg2+, Mn2+, and Ni2+. Although the metal cations including Al3+, Cu2+, Cr3+and Fe3+would interfere the Zn2+-detection due to their fluorescence quenching, discrimination of Zn2+from these metal ions can be facilely achieved by the chiral polymer sensor because the CD spectral change induced by Zn2+is not only particularly noticeable but also different from those with other ions tested. Thus, the chiral polytriazoles (PAMPPs) can served as a fluorescent chiropical chemosensor for Zn2+detection.In the next section, we present the design, synthesis, and spectral properties of a new kind of polymer-based chemodosimeter that allows Hg2+to be highly recognised on the basis of distinct CD responses. The polymer was prepared from the ring-opening polymerization of a chiral2-oxazoline derivative,(S)-4-phenyl-2-(2-prop-2-ynyloxy)phenyl-2-oxazoline (PPOXa). The Sc(OTf)3-initiated ring-opening polymerization showed living reaction features, yielding poly(PPOXa)s with Mn of3100to7100and Mw/Mn<1.2. The sensing behavior of poly(PPOXa)s towards the addition of different metal species was studied using UV-Vis and CD spectroscopy. The results showed that the CD spectrum of free polymers (CH3CN/H2O4:1, pH7.0) exhibits a relatively weak band at～250nm, which may belong to the lateral benzamide residues. However, the addition of Hg2+(1equiv.) to the polymer solution led to the appearance of a new strong positive Cotton effect at284nm. Slight changes in CD were observed upon the addition of other metal ions including Na+, K+, Ag+, Ca2+, Mg2+, Ni2+, Mn2+, Pb2+, Cd2+, Cu2+, Al3+, Cr3+, Zn2+, and Fe3+. In addition, the water-soluable polymers from the copolymerization of2-ethyl-2-oxazoline (EtOx) and PPOXa was also demonstrated to show a similar CD change upon addition of Hg2+in aqueous media. The unique CD responsiveness of the polymeric chemodosimeters may be attributed to the changes in conformational states of the interacting chromophores as a result of the Hg(II)-assisted oxymercuration of alkynyl function and subsequent tautomerization. |
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