Riconoscimento di metaboliti batterici, batteri Gram-negativi e della loro parete cellulare tramite recettori calix[4]arenici

This thesis deals with the study of calix[4]arenes receptors, in particular their synthesis and first interaction studies with bacterial metabolites, Gram-negative bacteria and their artificial models of cell wall. The first chapter of this thesis is a general introduction of the topic of bacteria recognition and how can be made with supramolecular receptors, such as calix[4]arenes, or other multivalent ligands. Among the techniques that can be used to study this interaction, a focus is set on the quartz crystal microbalance, a mechanical system that is able to assess the presence of an interaction by detecting a variation in the mass that is set on the sensor surface. Chapter 2 is about the interaction of two negatively charged calix[4]arenes with four biogenic polyamines (1,4-diamino butane, 1,6-diamino hexane, spermidine and spermine), and the study of this interaction has been carried out via 1H NMR titrations, resulting in a complex system with multiple equilibria occurring. To clarify the system fluorescence titrations were performed, consenting to determine the association constants of the complexes formed. The third chapter is about the synthesis of derivatives of two calix[4]arenes already studied in this research group, bearing four methyl-L-proline and four methyl-L-phenylalanine at the upper rim respectively. These receptors have proven to be selective ligands for Gram-negative bacteria, opening the possibility to be exploited for multiple applications. Two derivatives that have been synthetized possess alkyl chains at the lower rim, that will consent to study if the ligand properties of the macrocycle changed upon alkylation of the phenolic groups. The other two derivatives possess alkyl chains that terminate with an azide, allowing the attachment of the calixarene to the surface. The synthetic strategy employed has not led to the products, and for time reasons I was not able to find a suitable strategy. Moreover, two models of the calixarenes with a monovalent amino acid moiety have been synthetized, with an azide on the other end to allow the linkage to the surface and study another type of multivalent surface. Chapter 4 concerns about the work carried out in a six-months research period in University of Twente, the Netherlands, where quartz crystal microbalance was used to study the multivalent interactions between zwitterionic surfaces and Gram-negative bacterial membrane models. In the first model the supported lipid bilayers were used as models for the Gram-negative bacteria cell wall and on the surface solutions of methyl-L-proline and methyl-L-phenylalanine calix[4]arenes were flowed: the interaction was not detected with this system. Given that only the two monovalent calixarene models were successfully obtained, these were the sole molecules immobilized on a surface in the second approach. By subsequently introducing a vesicle solution over the modified surface, the interaction between the vesicles and the calixarene-functionalized surface was examined. Chapter 5 is a preliminary study on a new project, the SAMBA project, where the aim is to obtain nano-objects made of polymers with different shapes, bearing units of calix[4]arenes with properties of Gram-negative bacteria ligands. This work represents a preliminary investigation into the feasibility of conducting RAFT polymerization by anchoring the RAFT agent to the lower rim of calix[4]arene. After synthesizing calixarenes functionalized with between one and four RAFT agent units, polymerization was carried out using the calixarene with two RAFT agents, yielding the polymers subsequently analyzed.