Optical Chemosenors With Selective Recognition For Anions In Aqueous Solution: Synthesis And Sensing Properties

One goal of supramolecular chemistry is the development of general design strategies for optical chemical sensors to bind anions selectively in the physiological condition. This subject is in the forefront of supramolecular chemistry and still a challenging task. The key issue for achieving the task is to overcome the effect of the highly competitive media to the molecular recognition. In this thesis, some preorganized synthetic receptors with complementary scaffolding structure and suitable binding sites to the biologically active targets have been designed and synthesized. The effect of the protic solvent to the molecular recognition have been weakened by the stronger intermolecular interactions between receptors and the guests, such as multi-hydrogen bonds, electrostatic interactions and coordination bond. The selective recognitions of hydrophilic biologically active guests have been achieved with these artificial receptors.Fluorescence, UV-vis absorption, NMR and Mass spectroscopies have been applied in this work to investigate the molecular recognitions of these artificial receptors to different guests in the protic solvents and explore molecular recognition mechanism. This research will be helpful for understanding biological process and searching useful artificial receptors or chemosensors for biologically active materials.This dissertation consists of seven chapters.Chapter 1 is an overview of the recent work in the area of anion recognition in protic solvent. In light of this introduction, the design strategies of this thesis are outlined.In chapter 2, a new fluorescent chemosensor (Ⅱ-1) bearing guanidiniocarbonyl pyrrole moiety has been synthesized. The anion binding properities ofⅡ-1 are studied in DMSO by using fluorescence, UV-vis, NMR spectroscopies and CV. AsⅡ-1 containing two unequivalent recognition sites,Ⅱ-1 binds fluoride ion in two steps. The first step contributes to the high association constant, and the second is responsible for the dramatic fluorescence enhancement. By combination the two complexation steps,Ⅱ-1 bind fluoride ion with highly sensitivity and selectivity. The recognition of fluoride is also studied in aqueous solution. By comparision of the binding behavior in DMSO and aqueous DMSO solution, we can draw the conclusion that the NH in 5 position of guanidiniocarbonyl pyrrole is of great importance for fluorescence sensing of the artifical receptors.In chapter 3, two 4-amino-1,8-naphthalimide based fluorescent chemosensors (Ⅲ-1,Ⅲ-2) bearing guanidiniocarbonyl pyrrole moiety have been synthesized. The recognition properties ofⅢ-1 andⅢ-2 are studied in 90% water/DMSO with nucleotide acid and inorganic anions as substrates. The rational preorganisation ofⅢ-1 provides excellent shape, size and charge complementarity to pyrophosphate (PPi), which makes it exhibit remarkable selectivity for PPi in aqueous solution over other anions, including its analogues (ATP, ADP, AMP).Ⅲ-2 shows both PET and ICT characters in the process of ATP recognition. Upon addition of ATP, the fluorescence ofⅢ-2 is quenched and blue shifted.In chapter 4, one-armed and two-armed fluorescent chemosensors (Ⅳ-1,Ⅳ-4) containing guanidiniocarbonyl pyrrole and anthracene moieties have been synthesized. An intramolecular FRET is existed inⅣ-1. When sulfite is added, receptor 1 interacts with sulfite through a combination of ion pairing and multiple hydrogen bonds. Upon irradiation, the sulfite-Ⅳ-1 complex undergoes photochamical reaction of anthracene, which inhibits the FRET process, inducing the formation of ratiometric fluorescence. The photophysical properties indicate thatⅣ-4 shows an ideal photoinduced electron transfer (PET) behavior upon anion recognition. The receptorⅣ-4 strongly binds oxalate over other dicarboxylates in 90% H2O/DMSO solution.In chapter 5, two guanidiniocarbonyl pyrroles bearing nitro group (Ⅴ-1 andⅤ-2) have been designed and synthesized. Anion binding studies are carried out using UV-vis spectroscopy. As chromogenic anion receptor,Ⅴ-1 exhibits high selectivity for F- in DMSO through a remarkable color change from colorless to orange.Ⅴ-2 strongly binds CO32- in 10% H2O-DMSO solution through a combination of multi-interactions. Upon the addition of CO32- toⅤ-2, the color of the solution changes from yellowish to yellow, which could be detected by naked eyes.In chapter 6, a tweezer-like receptor bearing two guanidiniocarbonyl pyrrole side chains combined with coordinatively unsaturated Cu(Ⅱ) (Ⅵ-1) has been synthesized. The anion sensing properties for multi-carboxylates are investigated by using indicator displacement assays. By combination of metal coordination, ion pairing, multiple hydrogen bonds and geometrical complementarity, the receptor exhibits good selectivity for citrate and N(CH2COOH)3 in highly competitive media, the binding constants are up to 105 M-1. In theⅥ-1-pyrocatechol violet colormetric sensing ensemble, citrate could displace the pyrocatechol violet to the bulk solvents, which makes the color change between yellow and deep blue, achieving naked-eye detection.In chapter 7, a series of tweezer-type receptors (Ⅶ-1,Ⅶ-2,Ⅶ-3) bearing anthracene, pyrene, laurent’s acid as fluorophores have been synthesized, and their binding properities for nucleotide acid are studied in aqueous CH3CN solution.Ⅶ-1 exhibits selective fluorescent enhancement for ATP and ADP.Ⅶ-2 shows ratiometric fluorescence for ATP, ADP and AMP, while a totally different fluorescent behavior is observed for PPi and Pi, which could differentiate nucleotide acid from inorganic phosphate. The interactions betweenⅦ-3 and nucleotide acids are rather weak, soⅦ-3 could not be used for nucleotide acid recognition.