| Fluorescence imaging has been widely used in the field of biological applications because of its advantages of high sensitivity,high resolution,convenient operation conditions,nondestructive experiment and real-time monitoring.Using fluorescent dyes to detect biological microenvironment is an important part of imaging.The use of small molecule fluorescent probes has become a powerful tool in molecular imaging research.But in many fluorescent probes and biomarkers,only a limited number of traditional fluorescent dyes are used in the design of fluorescence imaging.Therefore,it is very important to design new fluorescent dyes to expand their application range.Aromatic nitrogen cation heterocyclic ring is an important component of aromatic nitrogen heterocyclic compounds.These compounds with nitrogen cation as the basic skeleton are widely found in nature.They form aromatic nitrogen cation alkaloids,such as berberine and other compounds.At the same time,aromatic nitrogen heterocyclic compounds have wide potential applications as fluorescent compounds,DNA binding dyes,ionic liquids and organic materials.Based on the biological activity of the nitrogen cation heterocyclic compounds and the planarity of the structure,it is a reasonable idea to design new functional dyestuffs based on these aromatic nitrogen cations.Hydrogen sulfide(H2S)plays a key role in the biological system.In recent years,studies have shown that it has been recognized as third basic endogenous signal molecules after nitric oxide and carbon monoxide.And the biological effects of endogenous hydrogen sulfide in the heart blood tube system,such as vasodilatation,inhibition of vascular smooth muscle cell proliferation,and display the negative inotropic action of the myocardium.In this paper,a series of aromatic nitrogen cation semi cyanine dyes were designed and synthesized with aromatic nitrogen cation heterocyclic ring as the basic structural unit.At the same time,a few fluorescent probes were designed and synthesized on the basis of this synthesis,and the optical and biological properties of them were deeply studied:1.A series of aromatic nitrogen cation skeleton dyes(1a-1f)are designed and synthesized based on heptamethine cyanine dyes and 2-amino pyridine derivatives.The reaction mechanism may be divided into four steps,which are nucleophilic substitution,Michael addition,proton transfer and elimination.These dyes have good photostability and thermal stability,and the dye la-d and 1f are in red and near infrared light regions,and their fluorescence intensity is basically stable at the value of pH 4.0-8.0,which means that they can be used as fluorescent dyes in biological and environmental conditions.Moreover,the dye lc has lysosomal targeting ability in Ges-1 normal cells and HeLacancer cells.2.The dye lc has excellent fluorescence properties because of its intramolecular hydrogen bonds and strong electrons in the structure,so it shows excellent fluorescence properties,and the dye lc has lysosome targeting ability in both Ges-1 normal cells and HeLa cancer cells.Based on this fact,two H2S fluorescent dyes were designed and synthesized.The maximum emission of the two dyes was in the red region,and they were all have good selectivity of H2S,the detection limit of H2S by probes 6a and 6b is 121 nM and 9.6 nM respectively,and the probe 6b has a faster response time for H2S(5 min).Cell experiments showed that all two molecules could be used as lysosome targeted probes to detect exogenous H2S in HeLa cancer cells.3.On the basis of the previous work,a near infrared fluorescent probe 8 with 7-nitrobenzofuran as the detection part of H2S was designed and synthesized,and the optical response to H2S was studied in detail.Probe 8 has good selectivity for H2S and has a lower detection limit of 178 nM.It also shows a stable fluorescence performance in the range of pH 7.0 to 9.0.Cell imaging experiments show that probe 8 has the mitochondrial targeted ability and it can be used for the exogenous H2S detection of HeLa cancer cells. |
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