Fluorescent Probe For Aluminium And Iron Based On Schiff Base Derivatives:Design,Synthesis And Performance Studies

Aluminum and iron are two kinds of most abundant metal elements in the earth’s crust,and also closely related with human lives.Aluminum is not necessary for human body;and excessive exposure to aluminum may cause many diseases and disorders in nervous system.Iron is an important essential element which has been found in the heme of hemoglobin and other various biological macromolecules.Iron deficiency may lead to anemia,low immunity and other pathological reactions of the body,and excess iron accumulation is also hazardous to people’s health.Usually,metal elements exist in living cells and tissues in the form of ion.Therefore,the implementation of fast,real-time and efficient detection of these metal ions plays a vital role for understanding their mechanism of promoting or inhibiting the physiological and biochemical reactions in living organisms,as well as the pathological causes of some relevant diseases.Molecular fluorescent probe,with high selectivity,sensitivity,relatively simple handling and low cost,has drawn widespread and considerable attention in recent years.A few fluorescent probes have been reported in detecting aluminum ions.Most aluminum ion fluorescent probes remain the disadvantages in poor solubility,complex synthetic methodology etc.Iron ion commonly performs as fluorescence quenching agent,hindering the application of many fluorophores in iron ion probe development.Therefore,how to design the fluorescent probe for detecting aluminium or iron ions with high selectivity and efficiency is a challenge to scientists.Object:Design and synthesis of aluminium and iron ions fluorescent probe compounds based on Schiff base derivatives.Evaluation of the fluorescence properties of the probe molecules in terms of luminescence mechanism and structure-activity relationship.Investigation of the selectivity and sensitivity of the probes in detection of metal ions in aqueous solution.Screening of the fluorescent probe in detecting aluminium and iron ions in the cells.Method:Infrared spectrum,nuclear magnetic resonance spectrum were employed for structural analysis and characterization.Selectivity,sensitivity and other properties of probe molecules were evaluated by UV-Vis absorption spectroscopy,fluorescence emission spectroscopy.Metal ion detection in cells was performed by using the method of automatic inverted fluorescence microscopy.Results:A novel fluorescent probe H₃L for Al³⁺has been designed and synthesized based on 2-hydroxy-naphthalene formaldehyde Schiff base derivatives.H₃L recognized aluminium ion and emitted a strong fluorescence in methanol solutions（Φ=0.27）.The detectability of the probe for Al³⁺was up to 4.2×10^-7 M as determined by fluorescent titration.The usual metal ions existed in cells could not interfere the fluorescence from H₃L-Al³⁺complex,only Cu²⁺and Fe³⁺had somewhat quenching action.The result of Job’s plot curve fitting showed that the coordinating ratio of H₃L and Al³⁺was 1:1 in H₃L-Al³⁺solution.The data of NMR titration revealed that Al³⁺interacted with the napthol-OH,imine-N,and–NH–group of H₃L.The distribution of Al³⁺in cells could be observed under microscopy.At the same time,four intermediates RhN1-4 and three final products RhN4SB1-3 for iron ion detection were synthesized based on Rhodamine B lactam derivatives.RhN4SB3 was selected as iron ion fluorescent probe based on fluorescence resonance energy transfer mechanism（FRET）,showing a very low detection limit(10^-10 M).A specific fluorescence(λ_em=576 nm,Φ=0.21)was emitted when the probe RhN4SB3 and Fe³⁺formed complex.Selectivity and anti-interference ability were examined with some other metal ions usually present in organisms.Conclusion:We have synthesized and characterized Schiff base derived aluminum ion fluorescent probe H₃L with high selectivity,sensitivity,anti-interference performance,and acceptable solubility in water.We also synthesized and screen the structure of the rhodamine B lactam Schiff base derived iron ion fluorescent probe RhN4SB3,of iron ions with high selectivity and high sensitivity and excellent anti-interference performance.UV-Vis spectroscopy,fluorescence spectroscopy,and the experimental results of fluorescence lifetime gave provident for photophysic mechanism of fluorescence resonance energy transfer（FRET）in the iron ion binding progress.Two kinds of metal ion fluorescence probe for detection of Al³⁺and Fe³⁺we designed,provides an important experimental information in continuing development and structure modification in our follow-up studies of aluminum ion,iron ion fluorescent probes.