| Molecular recognition is one of the most important subjects in supramolecular chemistry, and it comprises neutral molecule, anion and cation recognition. Because of the important roles of Mg2+, Zn2+ and Cu2+ in many biological and environment processes, their recognition by synthetic fluorescent receptors have drawn much attention. Due to high sensitivity, intrinsic simplicity, remote sensing capacity and living imaging analysis, fluorescent receptors have been rapidly developed for Mg2+, Zn2+ and Cu2+.Based on the fluorescence signaling mechanisms of photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) for recognition Mg2+, the majority of the recognition units for Mg2+ could form a rigid or flexible cavity around Mg2+, which match well with the shape and size of Mg2+. The 3d10electron configuration of Zn2+ do not make energy and electron-transfer processes take place so the fluorescence of fluorophores could not be quenched by Zn2+ and the fluorescent receptors for Zn2+ are mainly depended on fluorescence enhancement, based on the mechanism of PET, ICT and the C=N isomerization develpoed recently. Due to the efficient fluorescence quenching capability of Cu2+, detection of Cu2+ by fluorescent receptors is operated mainly in fluorescence quenching mode. Considering to the sensitivity reason, receptors showing fluorescence enhancement as a result of Cu2+ binding are to be favored over those exhibiting fluorescence quenching and fluorescent receptors for Cu2+ based on fluorescence enhancement have received particular attention. The mainly principles for the fluorescence enhancement by Cu2+ are depended on the mechanism of PET fluorescent chemodosimeter and so on.2-hydroxybenzaldehyde acylhydrazone are known as good ligands for metal ions, therefore, a series of fluorescent receptors benzylidene-4-phenylsemicarbazide derivatives were designed and examied in this thesis, which includes three chapters.Chapter 1 briefly summaries the research progresses in the fluorescent receptors for Mg2+, Zn2+ and Cu2+. The fluorescent receptors for Mg2+ and Zn2+ are introduced by the kinds of recognition units, while fluorescent receptors for Cu2+ was introduced according to the methods of fluorescence quenching and fluorescence enhancement. The research to be carried out is mentioned in the same chapter.Chapter 2 describes materials equipments and methods involved in this thesis. Synthetic details and characterization of receptors molecules are provided.Chapter 3 reported absorption and fluorescence spectral properties of the synthesized receptors and their response to metal ions in ACN and in H2O-ACN binary solvents.1-(2-hydroxybenzylidene)-4-phenylsemicarbazide(receptor 1) was examined as receptor for alkali metals and alkaline earth metals ions. It was found that, in ACN, receptor 1 could bind to Mg2+ and Ca2+ in a similar coordination manner in the ground state, while Ba2+, Na+ and K+ could not bind to receptor 1 in the similar coordination manner. Only Mg2+ induces remarkable enhancement in the fluorescence of receptor 1, by an enhancement of up to 212 fold. The fluorescence enhancement was due to the inhibition of C=N isomerization of receptor 1 arising from the Mg2+ binding. Job plots, computational data,1H NMR spectra and IR spectra testified receptor 1 complexation with Mg2+ via its carbonyl O, imino N and 2-hydroxy O atoms in a 1:1 stoichiometry binds. Then receptor 1 was examied as a receptor for Mg2+ in acetonitrile-water binary solvents. The research showed only Mg2+ could induce fluorescence enhancement of receptor 1 in 10% H2O-ACN (v/v) mixture, while other metal ions have no effect. It was therefore concluded that receptor 1 could be employed as a potential fluorescent receptor for Mg2+ in aqueous solution.Recepror 1 was examied as a receptor for heavy and transition metal ions. It was found that, in ACN, only Zn2+ induces remarkable enhancement in the fluorescence of receptor 1, by an enhancement of up to 214 fold. The fluorescence enhancement was due to the inhibition of C=N isomerization of receptor 1 arising from the Zn2+binding. Job plots, computational data and IR spectra testified receptor 1 complexation with Zn2+ via its carbonyl O, imino N and 2-hydroxy O atoms in a 1:1 stoichiometry binds. Then receptor 1 was examied as a receptor for Zn2+ in 10% H2O-ACN (v/v) buffered by lOmM Tris-HC1 (pH=8.56). It was found receptor 1 could bind metal ions such as Zn2+, Cu2+, Mg2+, Hg2+ and Ni2+ in a similar coordination manner in the ground state, but only Zn2+ induces remarkably enhancement in the fluorescence of receptor 1. The fluorescence enhancement factors of receptor 1 in 10% H2O-ACN (v/v) mixture was lower than in pure acetonitrile, but the selectivity was higher than in pure acetonitrile based on eliminating the interfere of Mg2+. We also studied the effect of pH and the volume proportion between water and acetonitrile on the fluorescence intensity of receptor 1 and complex 1-Zn2+1-(2-methoxybenzylidene)-4-phenylsemicarbazide (receptor 2) and benzylidene-4-phenyl-semicarbazide(receptor 3) were examined as receptors for metal ions.It was found only Cu2+ induces remarkably enhancement in the fluorescence of receptor 2 and recepror 3, while other metal ions have no effect on the fluorescence of receptor 2 and receptor 3. This is bacsuse Cu2+ could promote the oxidation reaction of receptor 2 and receptor 3 in ACN, respectively, which make receptor 2 and receptor 3 exhibit a particular selectivity for Cu2+... |
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