Synthesis And Performance Studies Of Novel Quinoline-based Fluorescent Chemosensors For Mental Ions

Metal ions exists widely in the biological systems and environment, deficit orsurplus of some metal ions may damage human health and accumulation of anexcessive amount can cause pollution. Owing to the advantages of simplicity, highselectivity and sensitivity, instantaneous response, low cost and non-destructivecharacter of fluorescence chemosensors, which have potential use in biological,medicinal and environmental research. For an efficient fluorescent sensor, a highselectivity towards an ion and with good water solubility are required. Moreover,most of the reported sensors suffer from poor water solubility, which restrict theirpractical application in the field of biology. Thus many researchers are activelyengaged in the development of novel aqueous soluble chemosensors with highselectivity and sensitivity is cruicial for the detection of mental ions in theenvironment and biological systems.In the present paper, three fluorescent zinc ion chemosensors, two fluorescentaluminium ion chemosensors and one colorimetric chemosensor for copper ion werereported according to molecular recognition and sensing mechanism. Specific contentas follows:First,8-aminoquinoline derivatives have been used traditionally as fluorogenicagents for the chemical assay of zinc ion because of its nitrogen-rich donor sites, andcarbohydrates are highly soluble in water and have good biocompatibility. Three newfluorescent chemosensors (1,2and3) were synthesized, which have high selectivitytoward zinc ion in an aqueous HEPES buffer (pH7.2). Their signaling mechanismwere researched by spectroscopic studies.Second, a colorimetric chemosensor (L2) by coupling quinoline-2-carbaldehydewith4-(dimethylamino)benzohydrazide was synthesized. The sensor exhibits asignificantly red-shifted absorption band and a color change response from colorlessto red only toward copper ion, which can be easily observed by eye. The1:1bindingmode was proposed based on UV-vis titrations, ESI-MS and X-ray analysis.Third,2-hydroxy-1-naphthaldehyde has been widely used as an ideal fluorophore for its short fluorescence lifetime, low fluorescence quantum yield, and the salicylfunctional group of2-hydroxy-1-naphthaldehyde is a popluar reaction counterpart fornucleophilic addition reactions due to its carbonyl group which is activated by aphenolic hydrogen through an intramolecular hydrogen bond. Two aluminium ionselective chemosensors (C1and C2) based on2-hydroxy-1-napthaldehyde weredesigned, which were visible-excited fluorescent sensor and a1:1stoichiometrycomplex were formed between the sensors and aluminium ion. In addition, C2exhibits sensitive fluorescence turn-on response specific to Al3+in100%aqueoussolution over a wide range of pH values (4.5-8.0) highly, and the fluorescenceresponse is visible under natural light.