Squaramides (3,4-diaminocyclobutene-1,2-diones) are known to be strong hydrogen bond donors, and recently have been demonstrated to show unusual responses to anions and the potential to adopt secondary structures. In the first part of the project, a small molecule version of a fluorene-based poly(squaramide) was synthesized to gain insights into the mechanism of the “turn-on” fluorescence response of the polymer in the presence of mono-basic phosphate anions. In the second part, mono and dipyridyl squaramides are examined. Pyridyl squaramides were discovered to form strong intramolecular hydrogen bonds, making the folding process more favorable than their urea counterparts. They are particularly interesting as their urea analogues are capable of taking up helical conformations when folded. The folding properties of these pyridyl squaramides in a range of solvents, and the influence of added anions on the folding process, are described herein.

Squaramides (3,4-diaminocyclobutene-1,2-diones) are known to be strong hydrogen bond donors, and recently have been demonstrated to show unusual responses to anions and the potential to adopt secondary structures. In the first part of the project, a small molecule version of a fluorene-based poly(squaramide) was synthesized to gain insights into the mechanism of the “turn-on” fluorescence response of the polymer in the presence of mono-basic phosphate anions. In the second part, mono and dipyridyl squaramides are examined. Pyridyl squaramides were discovered to form strong intramolecular hydrogen bonds, making the folding process more favorable than their urea counterparts. They are particularly interesting as their urea analogues are capable of taking up helical conformations when folded. The folding properties of these pyridyl squaramides in a range of solvents, and the influence of added anions on the folding process, are described herein.

The application of neutral dicopper helicates to the encapsulation of a number of anions was investigated. Two dicopper salen derived helicates were studied which contained phenolic and either iminophenyl (1) or oxime (2) donor groups. UV-visible spectroscopy was used to determine the binding stoichiometry and formation constants of the anion complexes. Complex binding was supported by electrospray ionisation mass spectrometry. Receptor 1 possessed a remarkable selectivity for sulfate in isopropanol (IPA) for which a log K value of 5.07 ± 0.24 was obtained. Receptor 2 bound all anions studied more strongly than 1. Crystal structural data supports the proposition that there is a steric barrier to contraction of 1 from the bulky iminophenyl groups. Receptor 2 was not restricted by the small oxime moieties allowing for optimum copper-anion interactions.

L’any 2002 tres grups de recerca, entre ells el nostre grup, van demostrar teòricament que la interacció entre anions i anells aromàtics electrodeficients, anomenada interacció anió–, era favorable. Des de llavors s’ha dut a terme un intens estudi de la seva naturalesa física fins la total comprensió. Aquesta tesi es basa amb l’estudi de la interacció anió– des de tres punts de vista. Primerament, la investigació es basa en el disseny teòric de motius estructurals per donar lloc a un receptor on la interacció anió– siga molt favorable, per posteriorment avaluar la força de la interacció experimentalment en dissolució. A continuació, es va analitzar la interrelació entre un gran nombre de combinacions d’interaccions no covalents. A partir d’aquest estudi es defineixen nous conceptes i es proposen diferents formules per calcular efectes de cooperativitat. Finalment, hem anat un pas més enllà en l’estudi de la interacció analitzant: 1) l’impacte de la interacció anió– a sistemes biològics; 2) la influència de modificacions a l’anió sobre la naturalesa física de la interacció. / In 2002 three research groups, among them our research group, theoretically demonstrated that the interaction between anions and electron-deficient aromatic rings, named anion– interaction, was favourable. Since then, an intense study of its physical nature has been performed to understand it completely. This thesis is based on the study of the anion– interaction from three points of view. Firstly, theoretical design of binding units to build a receptor and to obtain the most favourable binding based on anion– interactions. The binding properties of these receptors have been experimentally assessed in solution. Secondly, we have studied the interplay between a great combination of noncovalent interactions. From this study, new concepts and formula to calculate cooperativity effects have been described. Finally, we have study one step further the anion– interaction analysing: 1) the impact of anion– interaction in biological systems; 2) how the modifications in the anion influence the physical nature of the interaction.