Designing And Recognition Studies Of Copper Ion Chemosensors Based-on Pyridine Aldehyde Derivatives

Copper is commonly used as a kind of heavy metal element for the production and essential life that involved about two dozen of the role of the enzyme in the organic body, such as superoxide dismutase, tyrosinase, dopamine hydroxylase lysylacid oxidase, cytochrome oxidase, and ceruloplasmin protein. However, when the concentration of the copper ion is above the normal level, the cells will be damaged or even be deleteriousness and then lead to organ dysfunction injury. Thus, designing a new kind of chemical sensor that can achieve fast and effective detection of copper ion, has great significance. It is well known that, the extranuclear of copper ion is3d9, so the copper ion is a kind of paramagnetic ion, and having a strong quenching of fluorescence. Much effort has been devoted to the development of Cu2+selective fluorescent chemosensors because of biological and environmental importance of Cu2+. So far, various Cu2+sensors have been proposed, however, most of them show a turn-off fluorescence quenching response, because Cu2+usually acts as a quencher via an energy or electron-transfer process. Thus, the development of fluorescent and colorimetric sensors for Cu2+has received considerable attention in recent years as this metal ion is an essential trace element in biological systems and also a significant environmental pollutant.Rhodamine or fluorescein was extensively used as a fluorescent labeling reagent and a dye laser source because of their excellent spectroscopic properties, properties such as high fluorescence quantum yields, large molar extinction coefficients, and long absorption and emission wavelengths extending to the visible region. On the basis of the spirolactam (non fluorescent) to ring-open amide (fluorescent) equilibrium of rhodamine or fluorescein, most of rhodamine or fluorescein fluorescent probes based on rhodamine hydrazide derivatives or fluorescein hydrazidederivatives for various cations via chromogenical and fluorogenical signals have been successfully fabricated as the fluorescence enhancement type. The metal ion-responding mechanism of these sensors is based on the structural changes of rhodamine or fluorescein. These rhodamine and fluorescein derivatives are colorless (weak absorption) and non-fluorescent in the spiro ring system, but when the ring-opening of these derivatives induced by the analyte takes place, fluorophores such as fluorescein and rhodamine will be relased, they will exhibit a pink or red color (strong absorption) and strong fluorescence emission at a relatively long wavelength. So, rhodamine-based and fluorescein-based derivative probes that were applied in detecting the concention of heavy metal have become a hot research.This thesis is based on original work in our laboratory, rhodamine and fluorescein fluorescence signal act as the report groups, combined with good characteristics of the subject to object. By using UV-visible and fluorescence spectra, we explored recognition ability of probe for heavy metal ions Cu2+, and further explored the mechanism of molecular recognition. In this paper, we designed and synthesised four fluorescent molecular probes for ion detection. The specific contents are as follows:the synthesis of a series of pyridine aldehyde derivatives fluorescent probes (2-pyridylaldehyde fluorescein hydrazone (FHP), ortho-pyridylaldehyde rhodamine hydrazone (RHP1), mets-pyridylaldehyde rhodamine hydrazone (RHP2), and para-pyridylaldehyde rhodamine hydrazone (RHP3) in Chapter2and Chapter3. Their structures were characterized using1HNMR,13C NMR, elemental analysis and mass spectrometry. We also study their recognition ability through observing the UV-visible spectroscopy and fluorescence spectroscopy. The experimental results are as follows:(1) In the solution of10mM of pH=7.0of HEPES/CH3OH (V/V=1:1),2-pyridylaldehyde fluorescein hydrazone (FHP) can recognize Cu2+with very high selectivity, both UV-Vis spectrophotometrically and visually, via a simple coordination action between FHP and Cu2+. PPi/XO can coordinate with Cu2+and remove it from the FHP-Cu2+complex, which makes the probe response reversible and it can be reused. However, after FHP-Cu2+was stored for a few hours, the Cu2+caused FHP to hydrolyze and the release of the fluorophore (ring-opened fluorescein hydrazine). This made the probe an irreversible chemosensor. The reaction time can be controlled, so the probe is reversible and multifunctional. Moreover, confocal fluorescence microscopy confirmed that FHP can be used to monitor Cu2+in living cells using general fluorescence methods. These results are significant and interesting, because this is a new type of chemosensor that may be applied in living cells.(2) No absorption peak at559nm is detected from RHP1when it is in its free form with a closed ring in the solution of pH=7.0HEPES/CH3OH (V/V=1:1). As the concentration of Cu2+increased, so did the absorbance at559nm. In the presence of several metal ions, we investigated the ability of RHP1to detect Cu2+in the presence of other metal ions. The other ions did not interfere with the detection of Cu2+after adding various metal ions. These results show that probe has high selectivity for Cu2+, and can be used for visual determination without the need of any sophisticated instruments. This method can be used for simple qualitative and quantitative determination of Cu2+, the probe can also be applied in bioimaging, which has potential application in the near futuer.