Functionalization Of Methine Chain In Monocyanine Thiazole Orange And Its Application On Biothiols Detection

The introduction of heteroatom-containing substituents into the methine chain of the cyanine dyes can significantly change its structure and properties,and its applications in the fields of chemistry,biomedicine and photomedicine have been developed rapidly.However,there are still some problems,such as some heteroatom-containing substituents can only be introduced when a cyanine chromophore is being constructed,which requires multi-step reactions and complex operation.In addition,organic solvents are needed as cosolvents when dyes are applied in various fields,because of the low water solubility.In view of this,we explore the reaction of the thiazole orange monocyanine with heteroatom-containingelectrophilicreagentstodirectlyintroducedthe heteroatom-containing substituents to the methine chain via one-step for preparing monocyanine derivatives with no aggregating in water and high water solubility.The structure,photophysical properties,and biological applications of the synthesized heteroatom-containing monocyanines are investigated thereafter.This paper mainly includes the following contents:1.The synthesis,properties and applications progress of cyanine dyes containing heteroatom substitutes on the methine chain in recent years are reviewed.2.The reactions of TO with various heteroatom-containing electrophilic reagents are studied.Nine new containing heteroatom substituents monocyanine derivatives?meso-2TOs?are synthesized in one step.And the formation mechanism of meso-2TOs is investigated.The structures of all monocyanine derivatives are characterized by UV-vis,¹H NMR,¹³C{¹H}NMR,HRMS and elemental analysis,and some of the products are also characterized by X-ray single crystal diffraction.3.The spectral properties of all monocyanines in MeOH,PBS,DMSO and 90%glycerol-water are determined.The maximum absorption wavelength(?_max)of meso-2TOs1a-g is in the range of 437-549 nm,the emission wavelength(?_em)is in the range of530-602 nm;the?_max of meso-4TOs 2d-e is in the range of 550-556 nm and?_em is in the range of 600-603 nm.Compared with the parent TO,both the?_max and?_em of 1a-f and 2d-e are red-shifted,while 1g has a blue shift.The functionalization of the heteroatom-containing substituents on the methine chain renders the dye molecules twisted,reduces intermolecular?-?interaction,and prevents the aggregation,so that monocyanine derivatives exist in the form of monomer in solutions.4.The photostability of meso-TOs in aqueous PBS is investigated.After illumination for1 h,the absorbance of 1d-g only decrease by less than 7%,the absorbance of 2d almost unchanges,2e decreases by 19%,while the absorbance of parent 2TO and 4TO decrease by15%and 50%.The introduction of heteroatom-containing substituents such as alkyl,methylthio and formyl groups significantly improves the photostability of monocyanines.5.The solubility of meso-TOs in aqueous PBS is determined.The introduction of heteroatom-containing substituents into the methine chain can improve the water solubility.The 1a-c is nearly 40 times in comparison with parent 2TO,and a ca.3-5 times is found for 1d-f and 2d-e as that 2TO and 4TO,respectively.The solubility of 1g is about 1300times as that 2TO with the introduction of formyl group.6.The interaction between meso-2TOs 1a-g and biomolecules in aqueous PBS is studied.The results show that 1b can undergo redox reaction with biothiols,which can be used for trace,rapid and highly selective detection of biothiols.At the same time,the naked eye recognition of biothiols can also be realized according to the change of solution color.The interaction between 1b and cells is also investigated.The results show that 1b is low toxicity,good biocompatible,and it emits bright green fluorescence with 4T1 living cells,which realizes the visual fluorescence detection of endogenous biothiols.