Optically, chemically and electrically active (supra)molecular systems: from solution to liposomes and protein nanopores

This thesis deals with the characterization of stimuli-responsive molecular and supramolecular systems in different environments, including biomimetic settings such as liposomes and protein nanopores. A substantial portion of the work centers on the investigation of the recently introduced photochromic compound Donor-Acceptor Stenhouse adduct (DASA). Chapter 2 delves into their fundamental photochemical properties and isomerization behavior in organic solution. Their response to both optical and chemical stimulation, probed through photophysical and photochemical techniques, reveals an intriguing multiresponsive behavior. Chapter 3 details parallel studies on the preparation and characterization of liposomal vesicles doped with DASAs, aiming at obtaining an optically active system for potential applications in controlled drug delivery. As it will be shown, the pronounced polarity contrast between DASAs isomeric forms enables the incorporation of DASA into the liposomal membrane and subsequent release of the molecule into the aqueous compartment upon visible light irradiation. Chapter 4 delves into the electrophysiological studies conducted on a transmembrane protein nanopore, α-hemolysin. Two approaches to influence by external stimulus the current flowing through the protein are presented. The first involves a novel bioconjugation strategy developed using reactions inspired by DASA synthetic preparation, while the second approach introduces the macrocycle cucurbituril within the pore, acting as a molecular adapter. This study thus represents an advance in understanding modification strategies of biomimetic ion channels. On a separated research line, in Chapter 5 is presented the characterization of supramolecular host-guest complexes formed in organic solution between calixarene macrocycle/capsule hosts and bipyridinium guests using photophysical techniques. Calixarene-based structures functionalized with urea receptors emerge as excellent heteroditopic hosts, as it will be shown through the thermodynamic and kinetic analysis of their complexes. Overall, these projects collectively contribute to advancing the understanding of the supramolecular chemistry of these systems and pave the way for future studies in this intriguing field.