Design And Synthesis Of Fluorescent Molecular Probes For The Detection Of Salicylic Acid

Agricultural crops are seriously damaged by various pathogens, causing severe production losses. To avoid or attenuate this damage, the plants themselves have evolved defense mechanisms. The chemical properties of salicylic acid?SA? are suitable to render it a player in a number of reactions and interactions with enzymes and molecular species playing important roles in the defense. The reception mechanism of SA is complex and further studies are required to comprehensively understand the molecular mechanism of SA signaling. Based on the high selectivity, low detection limits, real-time detection, and potential biological applications, fluorescent probes exerted promising applications for exploring the roles of SA. Especially, fluorescent probes possess potential function for the detection of endogenous SA.NPR1 protein has been circumstantially shown to bind SA through a coordination with the transition metal Cu²⁺. Inspired by this phenomenon, we expected to develop a Cu²⁺-based chemosensing ensemble for selective detection of SA. Firstly, the fluorescent ligand was designed for selectively recognizing and binding Cu²⁺ and forming a Cu-ensemble. And then the Cuensemble was treated as a fluorescent probe for selective detection of SA.A series of diacylhydrazine?diamide?-based and thiourea-based rhodamine B derivatives are synthesized with simple steps. Especially, probes 3 realized the tunable fluorescent detection for Cu²⁺, SA and S2- with completely different modes. Cu²⁺ acts not only as a selective recognizing guest but also a decomposition promoter. Only in the presence of Cu²⁺, probes 3 can be decomposed into rhodamine B and exhibit strongly fluorescent turn-on response in the mixed CH3OH-CH3 CN solution. Furthermore, probes 3 also can be tuned to form stable Cu-ensembles in methanol or acetonitrile for selective recognition of SA or S2-. The ensembles 3-Cu exhibited obvious fluorescent selectivity toward SA over other competitive molecules in methanol. Besides, 3-Cu also showed obvious fluorescent selectivity and reversible property for S2- in acetonitrile. On the base of probe 3, probe 4 showed higher sensitivity for selective detection of SA and S2- than probe 3. This work will provide an important reference for the application of fluorescence probe strategy in the selective detection of SA and understanding SA signaling mechanisms.