Hydroxy and amidinium containing acyclic and interlocked anion receptors

Abstract

This thesis reports the synthesis of acyclic, macrocyclic and interlocked anion receptors containing hydroxy and amidinium motifs, and describes how these receptors interact with anions in competitive organic solutions. Chapter One introduces the area of supramolecular chemistry with a specific focus on the fields of anion coordination, anion templation and the synthesis of interlocked species. Chapter Two details the synthesis of a cationic acyclic hydroxy based receptor, which showed interesting reactivity towards borate counter ions to furnish borate-containing zwitterions. Studies into the anion binding capabilities of this receptor and related acyclic hydroxy containing systems demonstrated that these simple acyclic hydroxy receptors can strongly associate with chloride and sulfate in competitive aqueous media. Chapter Three describes the synthesis of two neutral catechol containing [2]catenanes templated by a spiroborate linkage, the syntheses of the analogous macrocycles and a neutral acyclic catechol containing model receptor. The anion binding capabilities of these acyclic, macrocyclic and interlinked receptors are reported and then further analysed using computational semi-empirical molecular dynamics simulations. These studies demonstrated that these neutral hydroxy containing [2]catenanes can associate with oxyanions with moderate affinity even in aqueous media, though it appears that these interactions are hindered by the lack of preorganisation within the system. Chapter Four reports the synthesis of two cationic hydroxy containing [2]rotaxanes and compares their anion binding abilities to a previously reported analogous [2]rotaxane without hydroxy groups. Along with 1H NMR solution anion binding studies, the binding modes of these three [2]rotaxanes to various anions was thoroughly investigated through semi-empirical molecular dynamics studies. The binding studies and computational data highlighted that, depending on the substitution of the hydroxy groups, the affinity and selectivity of the [2]rotaxanes towards chloride was either enhanced or decreased compared to the analogous non-hydroxy containing [2]rotaxane. The semi-empirical molecular dynamics studies indicated that this was due to preorganisation of the binding pocket, with the hydroxy groups binding to the macrocycle to stabilise the binding cavity. Chapter Five details synthesis towards multiple cationic acyclic amidinium based anion receptors for subsequent clipping to form the [2]catenane analogues. Unfortunately, due to synthetic difficulties, [2]catenation was not successful and analysis of the potential anion binding abilities of these receptors could not be conducted. Chapter Six summarizes the major conclusions of this thesis. Chapter Seven reports the experimental procedures used in this work for the synthesis and characterization of novel compounds, as well as the corresponding characterisation data. Anion binding data, computational methods, and computational time traces are also detailed, as well as crystallographic data. Chapter Eight contains the references cited within Chapters One to Seven.