Synthesis Of Novel Tweezers Receptors And Their Anion Recognition Properties

Nowadays, supramolecular chemistry has become a chemistry inter-subject because of the close correlation with life sciences. Supramolecular chemistry is the chemistry which is not about the simple molecule, but about the structures and functions of the system of supramolecular chemistry. Molecular recognition is the process that host molecular form binding with guest molecular selectively and produce some special function, which is an important research area in supramolecular chemistry. Molecular recognition includes the recognition of neutral molecules, cations and anion. Anion has become a hotspot of supramolecular chemistry research, which has played an important role in biology, pharmacy, catalysis and environmental science. The development of anion coordination chemistry is delayed compared with neutral molecules and cations. It is therefore necessary to construct novel anion receptors. In this thesis, we have synthesized some novel tweezers receptors based on carbonyl thiourea and thiosemicarhazide frameworks and studied on their anion recognition properties. The major contents are as follows:Firstly, researches in the development of anion recognition were briefly reviewed. The coordination chemistry of anions has received little attention over the last 30 years when compared to that devoted to coordination chemistry of cations. Therefore a number of anion recognition systems have been reported. The content of this chapter includes: (i) The concept of supramolecular chemistry, molecular recognition, anion recognition and the interaction of anions and receptors, (ii) The new research progress of tweezers receptors by no covalent interactions existed in recent years, (iii) The background and design of the theme.Secondly, with solid-liquid phase transfer catalyst polyglycol-400(PEG-400), seven 1,3-benzenedicarbonyl thiourea receptors have been prepared by classical method and free-solvent gridding method at room temperature and characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR. The result shows that free-solvent gridding method is clean, efficient, safe and environmental protection, and it is an excellent method of preparation of these receptors. The binding properties of the receptors with anions such as F^-, Cl^-, Br^-, I^-, CH₃COO^-, HSO₄^- and NO₃^- in DMSO were examined by UV-Vis and ¹H NMR spectroscopy methods. The results showed that the receptors had a better selectivity for F^- and CH₃COO^-, but no evident binding with Cl^-, Br^-, I^-, HSO₄^- and NO₃^-. In addition, the results showed that with compare to single thiourea receptors, the tweezers receptors have better anion recognition ability with the skeleton, and the association constants followed the trend: F^-> CH₃COO^-, while regularly the receptors had different binding ability with the two anions because of the electronic effect. The UV-Vis data indicated that a 1:1 stoichiometry complex was formed between compounds and anions, while ¹H NMR titrations confirmed hydrogen interaction between the receptors and anions.Thirdly, with phase transfer catalyst polyglycol-400(PEG-400), eight 1,3 -benzenedicarbonyl thiosemicarhazide receptors have been prepared in the conditions of solid-liquid phase transfer catalysis and characterized. Compared with the classical method, solid-liquid phase transfer catalysis has many advantages, such as easy approach, soft reaction condition, and clean, efficient, high production. The binding properties of the receptors with anions such as F^-, Cl^-, Br^-, I^- and CH₃COO^- in DMSO were examined by UV-Vis and ¹H NMR spectroscopy methods. The results showed that the receptors had a better selectivity for F^- and CH₃COO^-, but no evident binding with Cl^-, Br^- and I^-. In addition, the results showed that the carbonyl thiosemicarhazide tweezers receptors have more bingding points of receptors and ainions, better recognition ability, and larger binding constant, and the association constants followed the trend: F^- > CH₃COO^-, while regularly the receptors had different binding ability with the two anions because of the electronic effect. The UV-Vis data indicated that a 1:1 stoichiometry complex was formed between compounds and anions, while ¹H NMR titrations confirmed hydrogen interaction between the receptors and anions.