Study On Synthesis Of Optical Chemosensors And Their Selective Recognition And Optical Sensing Abilities To Anions

Anions exist vastly in the nature and biosystem and play important roles in the maintaining of the humans and other organisms. Due to the importance of anions in pharmacy and biological science, the design and synthesis of efficient anion receptors attracts intensive interest of scientist and become a significant issue in the field of supramolucular chemistry. Compared with cation, anion has its own feature (larger dimension, complicated geometric structure and high hydration energy) that make the recognition of anions difficult and challenging.However, despite of these obvious difficulties, variety species of anion selective receptors have been developed in the recent years. Based on the theory of preorganization of the receptor and the complementary structure between the host and guest, the supramolecular complex was usually formed utilizing the hydrogen bonding, electrostatic interaction, hydrophobic effect or Van der Waals force. Receptors have optical response to anions make the anion sensing process much sensitive and convenient using the detection of UV-vis or fluorescent signals.Chiral recognition is one of the most fundamental and significant process in living system. The study of enantiometric recognition of biological important substrate is a very important research area since it can provide valuable information for understanding the mechanism of interaction in biological system, and for developing useful molecular devices in biochemical and pharmaceutical studies, catalysis and sensing.Many important biological anions existed in the aqueous solution, for many reported receptors, their binding ability to both chiral and achiral anion guest have been studied by 1H NMR, UV-vis spectra, fluorescence and electrochemical analysis. But most of the receptors are mainly studied in the organic solvent such as chloroform, CH3CN and DMSO. For the competing effect of the water, receptors of these kinds based on hydrogen bonding have little interaction with guests in the aqueous solution. The synthesis and study of water soluble receptor became a challenging work in the recent years.In this thesis, for the recognition of anions, a series of novel artificial receptors were synthesized, including four receptors based on thiourea and seven metal-ligand complex receptors. Their binging properties to anions (chiral dicarboxylates and biological important anions) were evaluated by UV-vis, fluorescence emission, 1HNMR, MS and circular dichlorisim methods.In charpter 1, describes the mechanism of the anion sensing and various types of anion receptors. Review the research progress of fluorescent and colorimetric anion receptors and their recognition abilities to anion guests.In charpter 2, through introduce the chial alanine, thiourea and signal units to the pyridine or benzyl skeleton, novel chiral receptorsâ…¡-1,â…¡-2,â…¡-3,â…¡-4 were synthesized. Their discriminating abilities to chiral carboxylate anion enantiomers were examined by the UV-vis and fluorescent spectral and 1H NMR study. These receptors formed the 1:1 shoichiometriy complex with anion guests through the multiple hydrogen bonding interactions. PET sensorsâ…¡-1 andâ…¡-2 showed different fluorescence response to each anion enantiomers, and have certain chiral recognition abilities. For the electron-withdrawing effect of the p-nitrophenyl groups, the colorimetric sensorsâ…¡-3 andâ…¡-4 showed much stronger binding abilities to anion guests. Especially for the receptorâ…¡-3, it shows a good recognition ability to mandelate and alanine anions, it can be used for discriminating these two chiral anions by the different colure changes. By split the Boc-NH signals of racemic glutamate and aspartate by 1H NMR, the receptorâ…¡-3 can be used in the detecting the ee. value of these two anions.In charpter 3, two chiral fluorescent receptorsâ…¢-1 andâ…¢-2 were synthesized. Receptorâ…¢-1 andâ…¢-2 showed a good selective binding ability to Cu2+. The hostâ…¢-1-Cu2+ complex revealed an excellent enantioselective recognition ability to L-/D-mandelate anions in aqueous solution (Kass(L)/Kass(D)=15.2) and formed 1:1 stoichiometry complex. The obvious different changes in the fluorescence intensity of the interaction between theâ…¢-1-Cu2+ and enantiomers of mandelate exhibited that hostâ…¢-1-Cu2+ can be used as a good enantioselective fluorescent chemosensor for the chiral mandelate anions in the physiological pH condition.In chapter 4, two receptorsâ…£-1 andâ…£-2 were synthesized. Metal complexâ…£-1-Zn2+ showed good binding abilities to phosphate and pyrophosphate anions in aqueous solution and formed 1:1 stochiometric complex with anion guest. Receptorâ…£-2 showed a selective recognition ability to metal ions such as Cd2+, Zn2+ and Cu2+ in aqueous solution with different fluorescent changes. The metal complex receptorsâ…£-2 -Eu3+ andâ…£-2-Tb3+ exhibited an excellent selective recognition ability and quenching response to the pyrophosphate anions (PPi) in the water solution (10mM HEPES buffer, H2O/MeOH=9:1). The better preorganization structure of the metal-complex receptorsâ…£-2-Eu3+ andâ…£-2-Tb3+, and larger charge density of anion guest may be responsible for the selective recognition of PPi anion. The good fluorescent response in the interaction between host and guest illustrate that these two receptors may be used as the fluorescent chemosensor for the PPi anion in the physiological pH condition.In charpter 5, two dinuclear metal complexâ…¤-1-2Zn2+ andâ…¤-1-2Cu2+ were synthesized and used as the receptor to anions. With the addition of equal amount of pyrocatechol violet (PV) as the indicator to theâ…¤-1-2Zn2+ orâ…¤-1-2Cu2+ solution, the complexâ…¤-1-2Zn2+(PV) orâ…¤-1-2Cu2+(PV) were formed with a dark blue color. While the pyrophosphate anion was added to the mixture, the color was changed to bright yellow, which indicate that PV was displaced by PPi from the ternary complex. The color of the complex was not changed when other anions were added even in the same amounts. It is clear that the pre-organized structure of the receptorsâ…¤-1-2Zn2+ andâ…¤-1-2Cu2+, and that the space complementary between receptor and anion guest resulted in the selective recognition for PPi. The obvious different changes of color and CD spectra indicated that two receptorsâ…¤-1-2Zn2+ andâ…¤-1-2Cu2+ may be used as efficient PPi sensors in aqueous solution.In charpter 6, the lanthanide metal complexesâ…¥-1-Tb3+,â…¥-2-Tb3+,â…¥-1-Eu3+ andâ…¥-2-Eu3+ were synthesized. Their recognition abilities to anion guests were examined by the lanthanide emission spectrum through the excitation of the pyridine unite of the ligand. Through the non-linear curve fitting, the receptor formed the 1:1 stoichiometry complex anion guest. These four receptors showed selectively fluorescent quenching to the fluoride anions in aqueous solution.