Ion Recognition In Aqueous Solution Synergistically Regulated By Multiple Supramolecular Interactions

Ion recognition is an essential mechanism and process that maintains cellular homeostasis,regulates biochemical signal transduction,modulates gene transcription,and controls cell proliferation in various life processes.Typically,receptors recognize specific ions by various supramolecular interactions specifically and selectively,which may be accompanied by changes in electromagnetic and photophysical properties.Compared with a single supramolecular interaction,multiple supramolecular interactions can enhance recognition capabilities synergistically.Cooperation of multiple supramolecular interactions is achieved by adjusting multiple binding sites to favorable spatial positions and orientations for ion recognition,which makes the involved"weak"interactions become"stronger".In fact,water plays a critical role in the maintenance and regulation of living organisms.Developing ion recognition systems in aqueous phase is crucial for monitoring ion levels within living systems and environmental contexts.Previous reports of synergistic multiple supramolecular interactions are conducted in organic solvents or mixed solvent systems of organic solvents and water.To best of our knowledge,few ion recognition systems based on cooperation of multiple supramolecular interactions have been conducted in pure aqueous environments.Researches of ion recognition in aqueous solution are still limited by two main challenges:the poor water solubility of rigid receptors and strong hydration of ions that tend to weaken ion recognition.This dissertation aims to improve the water solubility of receptors by modifying them with water-soluble moieties and enhance ion recognition capabilities by employing the synergy of multiple interactions.Three ion recognition systems were established based on synergy of multiple interactions for recognition and detection of ions in aqueous solution.This paper mainly achieves the following outcomes:（1）An anion-binding system was constructed through cooperation of macrocycle effects interactions and hydrogen bonding.The system used macrocyclic molecules to stabilize the conformation of diphenylurea derivatives and improve binding strength by increasing the number of hydrogen bonding sites,thus bound anions in aqueous solution successfully.Water-soluble DPUPy was obtained by modifying diphenylurea derivatives with pyridinium groups.An extended dimer DPUPy₂·CB[8]₂ was formed through macrocycle effects between DPUPy and cucurbit[8]uril（CB[8]）in aqueous solution.CB[8]not only stabilized the effective recognition conformation of DPUPy but also doubled the hydrogen bonding recognition sites.Experimental results revealed that the stoichiometry between DPUPy₂·CB[8]₂ and Cl^–was 1:1 with a binding constant of 2.32×10² M^–1,and the detection limit of Cl^–was 97 n M in aqueous solution.As a control,no Cl^–recognition occurred in the folded complex DPTPy·CB[8]forming by diphenylthiourea derivative DPTPy because none effective recognition conformation was exposed.Besides,no respond of binding anions for both DPUPy and DPTPy was detected due to lack sufficient hydrogen bonding sites.The aforementioned results substantiated anion recognition was achieved successfully by DPUPy₂·CB[8]₂through synergy of multiple interactions in aqueous solution.（2）An anion-binding system was constructed through cooperation of electrostatic interactions and hydrophobic effects.The recognition of anions in aqueous solution was accomplished through electrostatic interactions,followed by the aggregation of the receptor molecules under hydrophobic effects after anion binding,thus brought about the ion recognition signal by emission enhancing.DPUPy-Bz was obtained by introducing flexible hydrophobic benzyl groups to both ends of DPUPy which used in the previous work.The pyridinium salt groups in DPUPy-Bz bound with PF₆^–through electrostatic interactions,leading to the formation of random aggregates accompanying by green fluorescence emission.DPUPy-Bz recognized PF₆^–selectively based on changes in fluorescence intensity.The detection limit of PF₆^–was 137 n M in aqueous solution.Furthermore,this dissertation provided two pathways for enhancing emission using the same molecule in aqueous solution.One involved anion-induced random aggregation,while the other involved precise dimerization induced by macrocycle hosts.It was observed that the emission of random aggregates exhibited dynamically reversible responsiveness to temperature.The luminescence properties could also be regulated by changing the concentration of anions.Additionally,the luminescent properties of the precise dimers remained consistent under varying conditions of anion concentration,temperature changes,and the presence or absence of solvents.（3）A cation-binding system was constructed through cooperation of hydrogen bonding and metal coordination interactions.We introduced intramolecular hydrogen bonds to enhance the planarity of the receptor and optimized the spatial arrangement of metal coordination sites to realize Pb²⁺recognition and detection in aqueous solution.The introduction of amide and carboxyl groups onto the 2,5-diphenyloxadiazole-based molecules was designed to promote the planarity of the receptor molecules.Simultaneously,the carboxyl groups served as metal coordination sites,enhancing the water solubility of the receptor molecules.Upon the addition of Pb²⁺to HEPES aqueous solutions of three receptor molecules,namely OBCA1,OBCA2,and OBCA3,new emission peaks emerged in their fluorescence spectra,indicating the binding of receptors and Pb²⁺.Notably,OBCA1 exhibited the optimal sensitivity and selectivity to Pb²⁺.Experimental results revealed that the stoichiometry between OBCA1 and Pb²⁺was 1:1,with a binding constant（K_a）of 4.51×10³ M^–1in HEPES aqueous solutions.Additionally,the intensity ratio(I₄₃₂/I₃₈₃)could be served as an accurate indicator for Pb²⁺detection in complex environments,with a detection limit of 431 n M.Moreover,the presence of various other metal ions did not significantly interfere with the detection of Pb²⁺by using OBCA1.