Abstract
Il presente progetto mira ad ampliare i limiti degli attuali sistemi artificiali dissipativi, utilizzando combustibili chimici per spingere un sistema chimico fuori dal suo equilibrio, inducendo dissipativamente modifiche specifichea. Il tipo e la quantità di combustibile aggiunto permetteranno di controllare la scala temporale di tale modifica. Questo obiettivo generale sarà articolato in quattro sezioni: I) la progettazione di una macchina molecolare autonoma che "respira" (si muove ripetutamente avanti e indietro) simile a un organismo vivente, sotto l’azione di un alcol riducente (furfurale) e dell’ossigeno atmosferico come combustibili; II) la progettazione di librerie dinamiche complesse di immine/ammine che modificano temporaneamente la loro composizione sotto l’azione di un acido carbossilico attivato (ad esempio, l’acido 2-fenil-2-cianopropanoico e i suoi derivati) come combustibile; III) la progettazione di un polimero responsivo che cambia il proprio stato fisico nel tempo sotto l’azione dello stesso combustibile chimico, in una transizione complessiva sol-gel-sol, tramite un controllo dissipativo dei legami a base di immine tra le catene polimeriche; IV) la progettazione di una macchina molecolare che, in modo dissipativo, compie un movimento accoppiato a una modifica strutturale sotto l’azione di un combustibile chimico, inducendo una modulazione controllata nel tempo del suo segnale EPR.
Results achieved
The project focused on the development of dissipative chemical systems, spanning from molecular machines to transient supramolecular polymers. These systems operate under non-equilibrium conditions, where a chemical fuel temporarily drives them away from equilibrium until fuel consumption restores the initial state. Two complementary strategies were pursued: redox-driven processes based on nitroxide radical catalysts and acid–base processes fueled by activated carboxylic acids (ACAs). The collaboration between the University of Bologna and Sapienza University of Rome combined expertise in supramolecular chemistry, catalysis, radical chemistry, and dynamic covalent systems to address fundamental questions in fuel-driven molecular systems. A major achievement was the development of novel nitroxide-containing rotaxanes capable of reversible redox cycling during catalytic alcohol oxidation. These interlocked molecules demonstrated that mechanically trapped nitroxide radicals can reversibly interconvert with oxoammonium species while catalyzing oxidation reactions, establishing a platform for future dissipative molecular machines in which catalytic turnover may be coupled to controlled mechanical motion. Parallel investigations also clarified the influence of the mechanical bond on the electronic properties of radical-containing interlocked molecules, revealing significant effects on spin coupling and transition-metal electronic states. The project also successfully established several fuel-driven dissipative systems based on activated carboxylic acids. These include transient supramolecular polymers formed through reversible transamination reactions, where covalent imine-based monomers are temporarily converted into supramolecular assemblies held together by crown ether–ammonium interactions before spontaneous disassembly upon fuel consumption. A second important result was the realization of transient chirality transfer, where chiral information generated by an activated carboxylic acid is temporarily transferred to a zinc complex, producing a time-dependent circular dichroism signal that disappears once the fuel is exhausted. Additional studies demonstrated dissipative control over boron–nitrogen dynamic libraries, expanding the generality of dissipative dynamic covalent chemistry. Beyond the original objectives, the project generated several complementary advances. Supramolecular nanoconfinement inside resorcinarene capsules enabled otherwise inaccessible cyclization reactions, including the synthesis of medium-sized rings that cannot be efficiently produced in bulk solution. Mechanistic investigations also clarified how substrate orientation controls the activity of supramolecular oxidation catalysts, providing valuable insight into structure–reactivity relationships. Although the majority of the planned objectives were achieved, some activities required modifications due to synthetic challenges. The synthesis of certain molecular machine architectures proved more demanding than anticipated, leading to the redesign of several systems. In particular, one aliphatic nitroxide macrocycle underwent irreversible ring opening during redox cycling and therefore could not function as originally envisioned, although it unexpectedly displayed excellent sensing properties toward metal and organic cations. Similarly, the originally proposed transient gelation system and transient EPR modulation were replaced by chemically different but conceptually equivalent systems involving transient supramolecular polymers and transient chirality transfer. These alternative approaches successfully fulfilled the fundamental objectives of temporal control, reversibility, and fuel-driven behavior while simultaneously opening new research directions. The project also provided important mechanistic understanding of dissipative dynamic covalent chemistry. Detailed thermodynamic and kinetic investigations established the operating principles governing transient imine-based systems and directly supported the development of the transient supramolecular polymer. This knowledge is expected to facilitate future efforts aimed at overcoming the remaining synthetic and characterization challenges associated with more complex polymeric systems. Looking forward, the research team expects to complete the original long-term goals by exploiting the expertise acquired during the project. New molecular designs are currently being developed to overcome the synthetic limitations encountered in constructing dissipative molecular machines capable of transient EPR modulation. Alternative architectures, including relocating the nitroxide unit within the rotaxane framework, are expected to improve spectroscopic monitoring of mechanical motion. Similarly, the experience gained in polymer synthesis and characterization is anticipated to enable realization of the originally envisioned transient polymeric materials. Overall, the project successfully established new concepts in dissipative chemistry, molecular machines, supramolecular polymers, and dynamic covalent systems. Importantly, deviations from the original work plan did not compromise the scientific objectives but instead generated broader and more impactful discoveries. The strong synergy between the Bologna and Rome research units, together with seven high-quality peer-reviewed publications, full compliance with Open Access and DNSH principles, and the development of innovative methodologies, provides a solid foundation for future research in adaptive, fuel-driven molecular systems with long-term scientific relevance.Project details
Unibo Team Leader: Marco Lucarini
Unibo involved Department/s:
Dipartimento di Chimica "Giacomo Ciamician"
Coordinator:
ALMA MATER STUDIORUM - Università di Bologna(Italy)
Total Eu Contribution: Euro (EUR) 164.902,00
Total Unibo Contribution: Euro (EUR) 83.843,00
Project Duration in months: 24
Start Date:
16/10/2023
End Date:
31/12/2025
