Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Activated Carboxylic Acids for the Operation of pH-Responsive Supramolecular Systems

This thesis illustrates the results of the research I carried out during my PhD, which was focused on the employment of Activated Carboxylic Acids (ACAs) as chemical fuels for the dissipative operation of pH responsive supramolecular systems. This particular topic is part of a wider research field, which aims to artificially reproduce the characteristic features of living systems. Part A of the thesis gives an overview about recent advancements in this field. In particular, Chapter 1 briefly describes some examples found in Nature from which scientists took inspiration for the design of artificial systems with life like properties, such as adaptation and self regulation. Two main characteristics can be envisaged in this context: the high dynamicity and the ability to harness energy from the environment to accomplish fundamental tasks. Chapter 2 shows how supramolecular chemistry has been used so far to develop structures and systems that achieved, at least in part, the high dynamicity, recognition ability and selectivity of their natural counterparts. On the other hand, some of the strategies employed so far to design systems able to dissipate energy in order to provide a certain output, e.g. self assembly, catalysis, or a mechanical movement, are presented in Chapter 3, with particular focus on the employed chemical fuels. Among these, ACAs have been conveniently used to trigger transient pH variation, thus allowing to control pH responsive supramolecular systems, as described in Part B. Here, the state of the art of the ACAs topic is presented, drawing the attention on their mechanisms of operation, weaknesses, and strengths. During my PhD, I focused my research on broadening the field of application of ACAs, employing them to trigger the dissipative operation of other pH responsive supramolecular systems. Chapter 5 presents the results, obtained in collaboration with Casnati and Baldini’s group, and concerning the first application of an ACA, namely 2 cyano 2 phenilpropanoic acid, to control in a dissipative fashion the conformational equilibria of the calix[4]arene scaffold. Chapter 6 and 7 deal with the use of nitroacetic acid, a highly reactive and water-soluble ACA, to trigger the dissipative operation of supramolecular systems in water. Firstly, the host guest interaction between  cyclodextrin and an aminoacid was controlled over time, and secondly, in collaboration with Ricci’s group, nitroacetic acid was used to program the operation of DNA based pH responsive nanodevices. Moving back to organic solvents, Chapter 8 shows how ACAs can be used to control over time the distribution of components in dynamic library of imines, a useful tool to design highly dynamic systems based on covalent bonds. Finally, in Chapter 9 the results obtained during my six months stay in Mainz hosted by Walther group, are presented, showing how ACAs can be employed not only to control nanoscopic pH responsive supramolecular systems, but also macroscopic hydrogel based devices.