Thesis title: Applications of Dissipative Dynamic Covalent Chemistry based on Transimination reactions
In this thesis, the development and applications of dissipative dynamic covalent chemistry of imines are explored. This innovative approach relies on the ability to transiently change the composition of an equilibrium system of imines (known as a dynamic library, DL) over a limited and controllable period of time.
In Chapter 1, this process is investigated by adding an activated carboxylic acid (ACA) to a DL of imines, thereby shifting the equilibrium from an initial predominance of N-aliphatic imines to N-aromatic ones. Such variation of composition is temporary, since the characteristic feature of ACAs is their tendency to undergo decarboxylation, generating in situ a base that cancels the effect previously induced by the acid. The decarboxylation reaction therefore restores the original composition, dominated by N-aliphatic imines. Moreover, the lifetime of the overexpression of N-aromatic imines can be finely tuned by varying the solvent, temperature, and the amount of ACA supplied.
In Chapter 2, this approach is extended to the design of supramolecular polymers, where ACA addition promotes the transient formation of N-aromatic imines able to self-assemble through hydrogen bonds into linear polymers. As monomers, both imines derived from 1,3-isophthalaldehyde and more complex scaffolds such as a 1,3-diformyl calix[4]arene were employed. By modulating the concentration of the transiently formed monomers, it is possible to control the extension of the supramolecular polymer thanks to the reversibility of the non-covalent interactions. Subsequent ACA decarboxylation induces polymer disassembly and restores the original, non-assembling imines.
In Chapter 3, still about the transient supramolecular polymers, the focus is the development of a new ACA, bearing two carboxylic functionalities able to decarboxylate after proton transfer. This acid, through a proton transfer reaction with bivalent amines, is capable of forming linear supramolecular polymers. The novelty of this approach lies in the fact that the ACA not only acts as an activator of the assembly, but also becomes an integral part of the polymeric backbone. Its subsequent decarboxylation leads to disassembly of the system.
Finally, in Chapter 4, the dissipative chemistry of imines is applied for the first time to colloidal systems such as gold nanoparticles, still in the context of transient self-assembly. The addition of ACA induces the transient overexpression of divalent imines, which act as cross-links between distinct nanoparticles, leading to the formation of a covalent network. The consumption of ACA via decarboxylation is then responsible for the cleavage of the imine cross-links, disaggregating the covalent nanoparticles clusters.