Novel Colorimetric And Fluorescent Schiff-base Probes For The Detection Of Ions

Chapter 1:The concept and principles of Schiff-base fluorescent probe design are introduced.And the latest research progress in recent years on the development of Schiff-base fluorescent probes for ion recognition is reviewed.Chapter 2:A simple assay for the detection of Fe³⁺ in water by fluorescence spectroscopy was developed.The assay is based on a commercially available reagent,Azomethine-H?A-H?,and allows sensing of traces levels of Fe³⁺with high selectivity over other cations.A significant fluorescence quenching of A-H at 424 nm was found after binding with Fe³⁺ in 100%aqueous solution at pH 7.0,while other physiologically relevant metal ions posed little interferences.The fluorescence responses can be well described by the modified Stern-Volmer equation.A good linear relationship?R2=0.9904?was observed up to 1.6×10-5mol/L Fe³⁺ ions.The detection limit,calculated following the 3?IUPAC criteria,was 1.95x 10-7mol/L.Moreover,the colorimetric and fluorescent response of A-H to Fe³⁺ can be conveniently detected by the naked eye,which provides a facile method for visual detection of Fe³⁺.The proposed method was used to determine Fe³⁺ in water samples.Moreover,inverted fluorescence microscopy imaging using Human Umbilical Vein Endothelial cells showed that A-H could be used as an effective fluorescent probe for detecting Fe³⁺ in living cells.Chapter 3:A new simple Schiff-base ligand 2-Hydroxy-l-naphthaldehyde-?2-pyridyl?hydrazone?HL?was synthesized and characterized as a fluorescent probe.In aqueous solution containing 10%ethanol?Hexamethylenetetramine-HCl buffer,pH5.3?,HL selectively binds Al³⁺ to form a 1:1 ligand/metal complex,resulting in a color change from colorless to yellow-green and a significant fluorescence enhancement at 454 nm.The addition of EDTA quenches fluorescence of the HL A1³⁺ complex,indicating that HL serves as a reversible chemosensor for Al³⁺.Under the optimum conditions,the dynamic range of the system was found to be linear up to 4.0×10-6 M Al³⁺ ion with a limit of detection of 36.6 nM.The probe is very effective for detection of intracellular Al³⁺ through fluorescence microscopic imaging.Chapter 4:A very simple molecule derived from 2-Hydroxy-1-naphthaldehyde and 2-aminopyridine?L?functions as dual-mode sensors for Al³⁺ and HSO4-in mixed aqueous medium.Based on the inhibition of C=N isomerization and chelation-enhanced fluorescence?CHEF?,L functions as a fluorescence "turn on" sensor for Al³⁺ in buffered aqueous medium.The sensing process is reversible and the sensitivity of the fluorescent based assay?80.5nM?for Al³⁺is far below the limit recommended in the World Health Organization?WHO?guidelines for drinking water?7.41?M?.In addition,L shows a highly selective colorimetric response to HSO4-ions by changing its color from yellow to colorless immediately.The sensing is suggested to proceed via a hydrolysis process.Both of the HSO4-and Al³⁺recognition processes are proven to be hardly influenced by other coexisting ions.L is very effective for detecting intracellular Al³⁺ in live cells through fluorescence microscopic imaging.Moreover,the probe could be used as a practical,visible colorimetric test kit for HSO4-.The binding mode of the probe with Al³⁺ was further addressed by DFT and TDDFT computational studies.