Selective Detection Of Acidic Amino Acids By A Surfactant-mediated Fluorescent Sensor In An Aqueous Phase

Amino acids are the basic units for the construction of biomolecules and are indispensable nutrients for living organisms.It has demonstrated that amino acids play an important role in the metabolism,physiological processes,organ function and nervous system regulation of organisms.The reducing or lacking certain amino acids will disturb the normal physiological processes and behaviors,and then lead to various diseases.Therefore,it is significant to sensitively and efficiently detect amino acids.So far,a variety of methods have been developed for the detection of amino acids.Compared with other detection methods,fluorescent sensors have drawn extensive attention due to a number of advantages including high sensitivity,good selectivity,simple operation and fast response.Amphiphilic surfactant molecules can not only spontaneously form supramolecular self-assemblies such as micelles,vesicles,liposomes,etc.but also provide a hydrophobic microenvironment for organic fluorophores to increase their solubility and stability in aqueous solution.Therefore,surfactant assemblies have been widely used in developing fluorescent sensors for detection of various analytes in aqueous solution,such as metal ions,explosives and proteins.Therefore,on the basis of the advantages of supramolecular fluorescent sensors and the significance of amino acid detection,this dissertation proposes to design and construct water-soluble supramolecular fluorescent sensors for less reported acidic amino acids by using surfactants to tune the emission of fluorescent probes.In particular,two projects have been performed and introduced as follows:In the first project of this dissertation,the binary ensemble based on the cationic dansyl derivative,1,and the anionic surfactant SDS,displays selective fluorescence quenching responses toward the acidic amino acids Asp and Glu.The detection limits for Asp and Glu were determined to be 0.6 ?M and 2.1 ?M,respectively.Time-resolved decay measurements reveal the quenching by Asp and Glu is static in nature and suggest that a complex is formed between the binary sensor and acidic amino acids.Fluorescence titration with H+ reveals similar fluorescence quenching,indicating the binding of H+ released from the acidic amino acids accounts for the selective quenching responses.Absorption studies reveal that both acidic amino acids and H+ can give rise to a new chromophore absorption band,coincident with the reduction in intensity of the two original peaks,implying that a complex is formed between 1/SDS and the H+ from Glu or Asp.Control studies with IPy and 1H NMR titration studies provide confirmatory evidence that the dansyl alkylamine group acts as the receptor for H+.Control experiments with 1 absent SDS show that the probe is not quenched significantly on exposure to Asp or Glu,underscoring the significant role played by SDS in the sensing process.The work reported here demonstrates that surfactant/chromophore assemblies are an effective approach to the sensitive and selective detection of the acidic amino acids,Asp and Glu.In the second project,the dansyl unit in the fluorescent molecule was replaced by signal-rich moiety,pyrene,resulting in a structurally similar fluorescent molecule,2.Similarly,the constructed binary ensemble based on the cationic pyrene derivative,2,and the anionic surfactant SDBS,displays selective turn-on responses toward the acidic amino acids Asp,Glu and GSH.The detection limits for Asp,Glu and GSH were determined to be 1.4 ?M for Asp,2.0 ?M for Glu and 1.2 ?M for GSH at 375 nm,and detection limit of Asp,Glu and GSH were 3.9,1.9 and 2.2 ?M at 490 nm,respectively.By comparing the responses of sensor system 2/SDBS to H+ and Asp,Glu and GSH,it was confirmed that the turn-on responses of Asp,Glu and GSH was caused by H+released from the acidic amino acids.The released H+ was combined by the electron-rich tertiary amines to hinder the PET effect,which induced the fluorescence enhancement of the sensing system,thus enabling highly sensitive and selective turn-on response and detection of Asp,Glu and GSH.