Rhodamine-based Colorimetric/fluorimetric Probes For Effective Detection Of Metal Ions

Human factors and environmental changes cause a large number of heavy metal ions to enter the ecological environment.Then the metal ions enter human body through the food chain.A small amount of metal ions are beneficial to human body,but excessive metal ions will threaten human's health.Therefore,it is of great significance to detect the contents of heavy metal ions in the environments.In this dissertation,a series of rhodamine-based colorimetric/fluorimetric probes were synthesized.The spirolactam ring of rhodamine derivatives can be opened,which is induced by metal ions,and then coordinates with metal ions,companying with the changes of solution color and/or fluorescence,leading to the detection of various metal ions.In addition,the synthesized probe molecules were used for the cell imaging and the detection of metal ions in practical water samples.The main contents are as follows:1.The colorimetric/fluorimetric probe Rh6GCD was synthesized by coupling reaction of rhodamine 6G ethylenediamine and biphenyl anhydride,realizing the colorimetric/fluorimetric detection of Fe³⁺and Al³⁺ions.In the Tris-HCl buffer solution at pH 6.0,Rh6GCD was colorless and showed weak fluorescence.After adding Fe³⁺/Al³⁺,a strong absorption peak appeared at 530 nm and the color of the solution changed from colorless to pink.Simultaneously,the solution emitted strong fluorescence at 558 nm.In the colorimetric and fluorimetric titration experiments,Fe³⁺and Al³⁺showed good linear relationships in the range of 10-90?M and 10-70?M,respectively.The limits of detection?LoD?for colorimetric detection were 1.07?M and 2.73?M,respectively.The LoD for fluorimetric detection were 1.37?M and 2.76?M,respectively.Selectivity experiments demonstrated that Rh6GCD has good selectivity for Fe³⁺and Al³⁺,and cannot be interfered by other metal ions.Ethylenediamine tetraacetic acid disodium salt?EDTA-2Na?showed a stronger chelation with Fe³⁺and Al³⁺than that of Rh6GCD,which can remove Fe³⁺/Al³⁺coordinated with Rh6GCD to make the probe reusable.The results of Job's curve and high-resolution mass spectrometry demonstrated that Rh6GCD and Fe³⁺/Al³⁺was coordinated with the ratio of 1:1.H NMR confirmed that the spirolactam ring of Rh6GCD opened to form a delocalized xanthene group,and then coordinated with Fe³⁺/Al³⁺.The Rh6GCD probe was used in the fluorescence imaging study of HeLa cells.The results showed that strong green and red fluorescence emission occurred in the presence of Al³⁺and Fe³⁺,indicating that the probe can be used for the detection of Fe³⁺and Al³⁺in live HeLa cells.2.A new colorimetric/fluorimetric probe R6G-PA was synthesized based on rhodamine6G ethylenediamine and terephthalaldehyde,which realized the colorimetric/fluorimetric detection of Fe³⁺.Upon addition of Fe³⁺to Tris-HCl buffer solution?pH=6?containing R6G-PA,the solution changed from colorless to pink,and the fluorescence emission and absorption reached the maximum at room temperature in 20 min.This is because the spirolactam ring of R6G-PA opened based on the inducement of Fe³⁺,resulting in the coordination of Fe³⁺with carbonyl oxygen and imino nitrogen to form a complex.The R6G-PA solution had no obvious fluorescence emission upon addition of other metal ions,proving that the probe showed high selectivity to Fe³⁺and could not be interfered by other metal ions.There was a good linear relationship between the fluorescence intensity of R6G-PA and the concentration of Fe³⁺between 8-45?M.The LoD was 0.027?M,and the LoD of colorimetric detection was 0.1?M.The probe can realize the reversible detection by virtue of EDTA-2Na.The Job's curve showed that the stoichiometric ratio of R6G-PA and Fe³⁺was 1:2.In addition,the probe can also be used to detect Fe³⁺in real water samples.Therefore,the designed rhodamine derivative R6G-PA can highly selectively and sensitively detect aqueous Fe³⁺.3.The colorimetric/fluorimetric probe REHBA was synthesized from rhodamine hydrazide and polyhydroxy aromatic compound,which realized the simultaneous detection of multi-metal ions.REHBA can be used as a colorimetric probe for Cu²⁺and Co²⁺,and a fluorimetric probe for Pb²⁺.The colorless solution of REHBA turned into pink after addition of Cu²⁺/Co²⁺and a strong absorption peak at 560 nm appeared.The addition of Pb²⁺caused the solution to emit a strong fluorescence at 580 nm.In the presence of other metal ions,anions and amino acids,the detection of Cu²⁺/Co²⁺/Pb²⁺by REHBA could not be affected by these competitive compounds,indicating a strong anti-interference of REHBA.The colorimetric response of REHBA to Cu²⁺was reversible after adding EDTA,but it was not to Co²⁺.Thus,Cu²⁺and Co²⁺can be distinguished.The LoD of Cu²⁺,Co²⁺and Pb²⁺were 0.11?M,0.88?M and 0.73?M,respectively.The results demonstrated that REHBA had high selectivity,anti-interference and good detection sensitivity.The spirolactam ring in REHBA opened,and the metal ions were chelated with oxygen in carbonyl,nitrogen in imino,and oxygen in phenol to form REHBA-metal complexes with binding stoichiometric ratio of 1:1,resulting in the above-described UV-visible absorption and fluorescence behaviors.Furthermore,REHBA can also recognize Pb²⁺in living cells by fluorescence image and Cu²⁺,Co²⁺,and Pb²⁺in real water samples.The results indicate that the synthesized REHBA probe can effectively detect multi-metal ions simultaneously,and can also be used to detect metal ions in water and living cells.