Ácidos escuarámicossíntesis, caracterización y aplicaciones

Abstract

ABSTRACT This PhD thesis describes squaramic acids and their application in different fields related to Supramolecular Chemistry. These compounds are a little known type of squaric acid derivatives. Specifically, the work described herein is divided into five chapters. Chapter 1. The general introduction provides an overview of Supramolecular Chemistry and its main current fields of application. More specifically, squaric acid derivatives and their use as active centers for recognition and supramolecular aggregation phenomena, the main topic on which this report is, are described. Chapter 2. In this chapter an effective method of microwave-assisted synthesis of squaramic acids derived from both aliphatic and aromatic amines is developed in yields ranging from 41 to 92%. The acid properties of the most representative compounds have been characterized by spectrophotometric titrations, obtaining pKa values between 0.9 and 2.0. Chapter 3. In a first phase, long-chain squaramic acids have been synthesized, and their ability to chemically adsorb on aluminum surfaces has been studied. This chapter provides basic information for a subsequent implementation of squaramic acids in coated materials. The coatings obtained have been studied through a wide range of techniques, such as contact angle measurements, microscopy techniques, grazing angle IR spectroscopy and mass spectrometry. Contact angle measurements have shown the formation of a layer which provides hydrophobicity to the surface, comparable to that obtained with carboxylic acids of similar chain lengths. The aromaticity of the squaramate group has allowed for detecting and monitoring the formation of the molecular layer by UV-vis reflectance spectroscopy, a technique not widely used in this field. In addition, the coatings obtained exhibit a higher resistance to desorption by immersion in isopropanol than those carried out with carboxylic acids. Chapter 4. In this chapter a squaramide-squaramate based receptor has been designed for the detection of zwitterionic molecules such as miltefosine. The structure of this receptor gives rise to an ensemble of the squaramide and squaramate groups that allows its self-aggregation, preventing the formation of complexes with competitive anions like halides. Chapter 5. The self-aggregation capacity of squaramates has been used for the design of squaramide-squaramate-based hydrogels. The high acidity of the squaramic acid ensures its ionization over a wide pH range, allowing its use as a hydrophilic part of a low molecular weight hydrogelator. The introduction of the -NO2 and -CF3 groups into the arylsquaramide leads to the modulation of the resulting properties of the hydrogels, causing marked differences in the thermal stability, mechanical properties and morphology of the fibers. Thus, the nitroderivative hydrogel turn out to be injectable, thixotropic, and undergoes an irreversible shrinking process in the presence of saline solutions. In addition, substantial amounts of zwitterionic biomolecules can be charged inside the hydrogel (up to 240: 1 excess molar ratio), which can subsequently be released into the medium in a controlled manner.