Synthesis And Application Of Molecular Probes Based On Rhodamine Structure

A novel fluorescent“turn-on”type acidic pH probe based on rhodamine B derivatives,1-methylpiperazine rhodamine amide?MPRA?was designed and synthesized by simple method.Then its structure,photophysicalproperty as well as recognition properties for pH were also investigated.With a decrease of pH?pH?4.0?,almost nonfluorescent and colorless probe MPRA in The PBS/acetonitrile?1:1,v:v?buffer solution could emit strong fluorescence and exhibit simultaneously rose bengal color,suggesting ring-opening reaction of the probe MPRA induced by H⁺.The pH titration showed the fluorescence intensity of the probe MPRA for pH was linearly proportional in the range of 1.8-3.5 with the acidity constants K_a of 1.677 by using Henderson-Hasselbach equation.Moreover,the probe MPRA possessed quick response,no interference over other different metal cations,brilliant reversibility and stability between the pH of 1.8 and 7.0,implying its possible application for recognition and detection of pH in acidic environment.Finally,low cytotoxic MPRA had been successfully applied as fluorescence microscopic images of Escherichia coli.The results demonstrate that this probe has great potential in response H⁺in vivo and biological systems.Rhodamine 6G and hydrazine hydrate were used as raw materials to synthesize rhodamine 6G hydrazide.Then,a novel pH fluorescent molecular probe2,5-dimethoxybenzaldehyde rhodamine 6G Schiff base?RGSBD?was synthesized by rhodamine 6G hydrazide and 2,5-dimethoxybenzaldehyde under glacial acetic acid as catalyst.This compound was characterized by means of ¹H NMR,IR and fluorescence spectra.The colorless spirocyclic structure of probe RGSBD at high pH?pH?4?opened to the colored and highly fluorescent form at very low pH?pH<4.0?.When the pH of system was equal to 1.9,the fluorescence intensity of the probe RGSBD reached the maximum accompanying with obvious red-shifted of the maximum fluorescence peak.Further studies have shown that the probe has a good linear relationship between change of fluorescence intensity of probe and pH?1.9³.2?.Common metal ions had almost no interference with the fluorescent response of probe RGSBD to H⁺,indicating high selectivity of the probe.In addition,the probe exhibits satisfactory stability and reversibility.Above results suggest this probe can be promoted a new sensing material for studying pH in biological system.A novel molecular probe of N-?2-hydroxy-5-chlorophenyl?-based rhodamine B?HCPRH?was synthesized by simple two step reaction.Then its structure and fluorescence response were studied.Addition of Zn²⁺to N,N-dimethylformamide?DMF?solution of HCPRH resulted in increasement of fluorescence.At the same time,a fluorescent color change from colorless to yellow could be observed promptly by naked eyes under 365 nm ultraviolet lamp due to the blocked-C=N-isomerization process of probe,indicating that the probe HCPRH can be used for rapid,sensitive and naked eye recognition of Zn²⁺.Moreover,the fluorescence emission of this probe for Zn²⁺was hardly affected by other metal ions.The binding constant between HCPRH with Zn²⁺was calculated by Benesi-Hildebrand equation and the 1:1 binding mode was proposed based on the Job's method.In addition,according to the experimental results of fluorescence titration,the difference value of fluorescent intensity was proportional to Zn²⁺concentration in the range from 10²50?m with the detection limit of 3.6?m.This result suggests HCPRH can allow for detection micromolar Zn²⁺.Subsequent experimental studies have also shown that this molecular probe can be successfully applied for the continuous fluorescence response of Zn²⁺and S^2-.The fourth novel molecular probe of aminoacyl-?2-methylaminofuran?rhodamine amide derivative?RBFMA?was designed and synthesized and its structure was characterized.Adding Cu²⁺to the mixed solution of molecular probe in acetonitrile water,due to its chelation-inducing ring-opening effect on rhodamine spironolactone,the color of the solution solution rapidly changed from colorless to deep rose red within 2 s.It can be seen that the intensity of the absorption peak and the fluorescence intensity increase rapidly,indicating that the molecular probe can be used for rapid,sensitive and naked eye recognition of Cu²⁺,and the selectivity is better.According to the BH equation and the Job curve,it was confirmed that the aminoacyl-?2-methylaminofuran?rhodamine derivative and the Cu²⁺was stably bonded at a molar ratio of 1:1.In addition,according to the results of UV titration experiments,the UV-visible absorption peak intensity change and the Cu²⁺concentration of the molecular prob of aminoacylmethylaminofuran)rhodamineamide at 565 nm were found to be between 1 and 90?M.There is a good linear relationship between the detection limits of 0.32?M,which can be used for the micro-detection of Cu²⁺.Subsequent experimental studies have also shown that the molecular probe can be successfully used for continuous response to Cu²⁺and S^2-.Rhodamine 6G and hydrazine hydrate were used as raw materials to synthesize rhodamine 6G hydrazide,and then refluxed with 2-furoyl chloride in dichloromethane to obtain 2-methylfuran rhodamine 6G amide?RGFCA?.The fluorescent molecular probe is probed and characterized as necessary.Using this probe to study the fluorescence response of ClO^-in the system,the results show that the probe RGFCA can emit quickly bright yellow fluorescence after adding ClO^-in the system.Moreover,the fluorescence intensity of the probe RGFCA increases with the increase of ClO^-concentration.This is because ClO^-oxidizes the imino group of the probe RGFCA to-N=N-,and thereby causes ring-opening of the probe RGFCA,Hence the probe RGFCA exhibits bright yellow fluorescence.Further research shows that the fluorescence intensity of probe change value and ClO^-concentration between 5 and40?M had good linear relationship with detection limit of 1.81?M.The common anions and metal ions had almost no interference to the fluorescence signal of ClO^-,indicating good performance selection of the probe.Finally the probe RGFCA was successfully used to determine ClO^-concentration in the water samples.