The Design, Synthesis Of Novel Porphyrin, Rhodamine Derivatives And Their Application In Fluorescent Probes And Ion-selective Eletrodes

Fluorescent probes can transfer molecular recognition events into fluorescence signals, which make a bridge between the molecular analytes and the analyst as an observer. It has been of current interest in analytical chemistry owing to its high sensitivity, nice selectivity, observation in situ (fluorescence imaging), remote sensing with the application of fiber optics, and so on. Many of the heavy and transition metal (HTM) ions are known as fluorescent quenchers via enhancement of spin-orbit coupling (e.g., Hg²⁺) or energy or electron transfer (e.g., paramagnetic Cu²⁺). Most of the reported fluorescent chemosensors for these cations are based on a fluorescence quenching mechanism, and the quenching is not only disadvantageous for a high signal output upon complexation but also limits their applications in the biology community. Design and synthesis highly sensitive and selective chemsensor with fluorescence enhancement for HTM cations is still one of the difficult and hot spots for organic and analytical chemists. Ratiometric measurements involve the observation of changes in the ratio of the intensities of the absorption or the emission at two wavelengths. Ratiometric fluorescent probes have the important feature in that they permit signal rationing and thus increase the dynamic range and provide built-in correction for environmental effects. The NIR fluorescence probe offers several advantages over the visible fluorescence probe: (a) it is poorly absorbed by biomolecules, so it can penetrate deeply into tissues; (b) there is also less auto-fluorescence in this region, and so the characteristics of the NIR dyes are favorable for in vivo imaging. Ion-selective electrode (ISE), an old member of the electrochemical sensor family, has attracted research interest for many years due to their accuracy, simplicity, low cost, and high selectivity, etc. However, the reported electrodes generally exhibit long response time, narrow working concentration range or moderate selectivity. Searching for novel molecular recognition ionophores with high selectivity, short response time, and the ablity to applied in real samples for ISEs, therefore, remains task of theoretical and practical significance.Taking the aforementioned reasonings as research objectives, this thesis mainly finished two research tasks as follows:In part I, to improve the sensitivity, selectivity and application in biology community of fluorescence probe, series of novel fluorescent probes based on rhodamine, porphyrin or near-infrared dye were developed as a fluorescent recognition system. These sensors were used for the detection of mercury cations and copper cations. The detection signals involve fluorescence enhancement, ratiometric and fluorescence quenching.1. In chapter 2, a new fluorescent probe, 8-quinolinealdehyde thiorhodamine B hydrazone (QL-RDM), was developed and displayed selective Hg(II)-amplified absorbance and fluorescence emission above 500 nm in mixed N, N-dimethylform- amide(DMF) neutral buffered media. It was designed to chelate with metal ions via its S atoms, imino and quinoline N atoms. The signal change of the probe is based on a specific metal ion induced reversible ring-opening mechanism of a rhodamine B thiohydrazide. Compound QL-RDM was synthesized via a one-step reaction by refluxing of rhodamine B thiohydrazide with 8-quinolinecarbaldehyde in absolute alcohol. It is a colorless, non-fluorescent compound, and upon mixing Hg²⁺ in its DMF-water (1:1, v/v) solution, the spirolactam ring of QL-RDM was opened, which resulted in a dramatic increase in both fluorescence intensity and absorbance of the mixing solution. With the experimental conditions optimized, the probe exhibits a dynamic response concentration range for Hg²⁺ from 1.0×10-8 to 1.0×10-5 M, with a detection limit of 8.5×10-9 M. The fluorescent probe exhibits high selectivity over other common metal ions, and pH independent in medium condition. It was also used for imaging of Hg²⁺ in living cells with satisfied results.2. In chapter 3, a highly sensitive fluorescent probe based on picoline-containing Rhodamine 6G derivative (PL-RDM) for selective detection of copper ion in mixed ethanol aqueous media was developed and prepared. Addition of 10 equiv. of Cu²⁺ causes 80-fold fluorescence enhancement and an increase in absorption intensity at 529 nm, which indicates that synthesized chemosensor effectively avoided the fluorescence quenching for the paramagnetic nature of Cu²⁺ via its strong binding capability towards Cu²⁺. With the experimental conditions optimized, the probe exhibits a dynamic response range for Cu²⁺ from 8.0×10^-7 to 1.0×10^-5 M, with a detection limit of 3.0×10^-7 M. The response of the chemosensor for Cu²⁺ is instantaneous and reversible. Most importantly, both the color and fluorescence changes of the chemosenor are remarkably specific for Cu²⁺ in the presence of other heavy and transition metal ions (even existing in high concentration), which meet the selective requirements for biomedical and environmental monitoring application. The proposed chemosensor has been used for direct measurement of Cu²⁺ content in river water samples and imaging of Cu²⁺ in living cells with satisfied results, further demonstrating its value of the practical applications in environmental and biological systems.3. In chapter 4, quinolin-8-ol-p-[10, 15,20-triphenyl-5-porphyrinyl]benzoate (QL-TPP) was synthesized for the first time and developed as a ratiometric fluorescent chemosensor for recognition of Hg²⁺ ions in aqueous ethanol with high selectivity. The QL-TPP-Hg²⁺ complexation quenches the fluorescence of porphyrin at 646 nm and induces a new fluorescent enhancement at 603 nm. The fluorescent response of QL-TPP towards Hg²⁺ seems to be caused by the binding of Hg²⁺ ion with the quinoline moiety, which was confirmed by the absorption spectra and 1H NMR spectrum. The fluorescence response fits a Hill coefficient of 1 (1.0308), indicating the formation of a 1:1 stoichiometry for the QL-TPP-Hg²⁺ complex. The analytical performance characteristics of the chemosensor were investigated. The sensor shows a linear response toward Hg²⁺ in the concentration range of 3×10^-7 to 2×10^-5 M with a limit of detection of 2.2×10-8 M. Chemosensor QL-TPP shows excellent selectivity to Hg²⁺ over transition metal cations except Cu²⁺, which quenches the fluorescence of QL-TPP to some extent when it exists at equal molar concentration. Moreover, the chemosensor are pH-independent in 5.0-9.0 and show excellent selectivity for Hg²⁺ over transition metal cations.4. In chapter 2, 3 and 4, the fluorophore selected excitation profiles in the ultraviolet or visible region which can damage living samples and cause interfering autofluorescence from native cellular molecules. The light in the near-infrared (NIR) region around 650-900 nm can penetrate more deeply into tissues, which is of great importance to study living organism imaging. Moreover, it has the further advantage that autofluorescence is not observed upon NIR excitation. Heptamethine cyanine dyes, one of the important kinds of near-infrared (NIR) dyes, have been widely used in various fields and have been employed as fluorescent labels in fluorescence imaging studies of biological mechanisms. And a few probes based on heptamethine cyanines dyes have been employed to detect metal ions or small molecules. In chaper 5, a new Near-infrared dye derivative, 2-(2-aminoethyl)pyridine-tricarbocyanine (AEP-TCC) was first synthesized and developed as a fluorescent probe to recognize Cu(II) in CH3CN/H2O (1:1, v/v) solution with high selectivity. The response of the probe is based on the fluorescence quenching of fluorophore upon binding to Cu(II). The analytical performance characteristics of the proposed Cu(II)-sensitive probe were investigated. The probe can be applied to the quantification of Cu(II) with a linear concentration range covering from 4.8×10^-7 to 1.6×10^-4M with a detection limit of 9.3×10-8 M. The experiment results show that the response of AEP-TCC to Cu(II) is pH independent in medium condition (pH 6.0-8.0), and exhibits excellent selectivity towards Cu(II) over other common metal cations. In part II, to improve the response speed, sensitivity and selectivity of ISEs, a series of novel ion-selective electrodes based on corrole or porphyrin were developed and used for the detection of silver cations and molybdate.5. Corroles are ring contracted analogues of porphyrins that retain the tetrapyrrolic, 18-Ï€-electron aromatic porphyrinoid nucleus. Different from the structure of H2TPP with two protons on the tetrapyrrolic nucleus, there are three protons on the tetrapyrrolic nucleus of H3(tpfc). This kind of structure might cause the distortion of the corrole macrocycle, which is thought to result in increasing exposure of the pyrrole nitrogen lone pairs to solvent and be favorable for metal ion binding comparing to H2TPP. Up to date, however, corroles are scarcely reported, as sensing materials for chemical sensors in analytical chemistry. In chapter 6, a new highly selective silver(I) electrode was prepared with a PVC membrane using 5,10,15-tris(pentafluorophenyl)corrole as an electroactive material, 2-nitrophenyl octyl ether (o-NPOE) as a plasticizer and sodium tetraphenylborate (NaTPB) as an additive in the percentage ratio of 3:3:62:32 (corrole:NaTPB:o-NPOE:PVC, w:w). The electrode exhibited linear response with a near Nernstian slope of 54.8 mV/decade within the concentration range of 5.1×10-6 to 1.0×10^-1 M silver ions, with a working pH range from 4.0 to 8.0, and a fast response time (<30 s). Selectivity coefficients for Ag(I) relative to a number of interfering ions were investigated. The electrode is highly selective for Ag(I) ions over a large number of mono-, bi-, and tri-valent cations. Common interferents like Hg²⁺ and Cd²⁺ show very low interfering effect on the silver assay, which is valuable property of the proposed electrode. Several electroactive materials and solvent mediators have been compared and the experimental conditions were optimized. The sensor was applied to the determination of silver in real ore samples with satisfied results.6. Monometalloporphyrin has only one central metal, while the metalloporphyrin dimer has two central metals in a molecule, which might coordinate with two guests. Moreover, the lipophilicity of monometalloporphyrin is worse than that ofμ-oxo-bridged metalloporphyrin dimer. So An electrode based on monometalloporphy- rin might show better response characteristics than those of theμ-oxobridged metalloporphyrin dimer in terms of the working concentration range and the slope. In chapter 7, a novel high selective potentiometric sensor for molybdate was prepared with PVC membrane utilizingμ-oxobis[5,10,15,20-tetra(p-methyl-phenyl)porphinato- manganese(III)] [Mn(p-Me)TPP]2O] as an electroactive material and 2-nitrophenyl octyl ether (o-NPOE) as a plasticizer in the percentage ratio of 3:65:32, [Mn(p-Me)TPP]2O:o-NPOE:PVC (w:w). The sensor exhibited a linear response with a Nernstian slope of 30.5 mV /decade within a concentration range of 2.1×10-6 to 1.0×10^-1 M MoO₄^2-, with a working pH range from 5.0 to 12.5, and a fast response time of less than 15 s. The electrode showed improved selectivity toward molybdate with respect to common coexisting anions compared to monometalloporphyrin counterparts. Several electroactive materials and solvent mediators were compared and the experimental conditions were optimized. The sensor is preliminary applied to the assay of MoO₄^2- in corrosion inhibitor samples with satisfactory results.