Study On Design, Synthesis And Properties Of Pyridinium-Base Anion Receptor

The design and synthesis of receptors capable of selective binding and sensing anion has received considerable attention in recent years, dued to the anions importance role in chemistry, biology, pharmacy and environmental sciences. Now, most receptors for anions mainly contained the binding-site groups:amino/amide, urea/thiourea, guanidine, pyrrole, porphyrin and phenolichydroxyle,et al. Recently, the receptors based on pyridinium has been received more and more attention, ascribed to the simple synthetic steps, the rich structures and flexible configuration. Our work group early reported the receptors based on amide-pyridinium, and found its property of formation intramolecular hydrogen bonding (IHB). When anions were added, IHB was disturbed by anions which controlled the initial configuration of the receptor,and the receptor configuration changed to achieved that the receptor selectively binds and senses the anions. Based on this idea, we have designed and synthesized some novel receptors for AcO-or H2PO4-, and the major contents are as follows:1. The dipodand flexible receptors L1～L3 were synthesized, and the interaction with anions were studied by UV-vis titration.The results shows that L1 can selectively 'naked-eyes' sense AcO-, following by the receptor solution color from colorless to yellow; the receptors L2 and L3 can response for AcO- and F-,the color changes as same as L1. The LTV-vis titration data indicated that a 1:1 stoichiometry complexs were formed between the receptors and target anions, and the binding properties of the receptors L1～L3 were diffrent from their spacers. The sensing and induce-fit process between L1 and AcO- were examined by 1H NMR spectroscopy and DFT calculations, and this selectivity was ascribed to hydrogen bonding, electrostatic interactions and conformational change.2. The tripodal flexible receptor HI and the dipodand receptor H2 based on carbonyl urea-pyridinium were synthesized, and the interaction with anions were studied by UV-vis titration.The results show that HI and H2 can selectively "naked-eyes" sense AcO- and F-following by the receptors solution color from colorless to yellow; The UV-vis titration data indicated that a 1:1 stoichiometry complexs were formed between the receptors and target anions, and the binding properties of the receptors L1, H1 and H2 were diffrent from their conformation and hydrogen bond dononrs. The sensing and induce-fit process between H1～H2 and anions were examined by 1H NMR spectroscopy and 2D-COSY NMR spectroscopy. 3. The receptors F1～F3 were synthesized, and the interaction with anions were studied by fluorescence titration.The results show that Fl can selectively sense H2PO4-, following by the fluorescence emission intensity of Fl increasing to 10 times and spectral bathochromic shift. The fluorescence titration data indicated that a 1:1 stoichiometry complex was formed between the receptors and H2PO4-. The receptor F2 has low selectivity for anions containing pull electricity groups which affects electron cloud density and receptor binding conformation. The receptor F3 has low selectivity for anions because of small conformation and unlikely intermolecular overlap upon addition of various anions. The process of H2PO4- inducing Fl self-assemble to form excimer was examined by fluorescence emission spectrum, UV-vis spectrum and 1H NMR spectroscopy,that it is significative in the sensing mechanism and the sensing result research.