Periodic Reporting for period 1 - SuprAlloCat (Nanostructured Supramolecular Polymers with Allosterically Regulated Catalytic Interstices)
Periodo di rendicontazione: 2021-11-23 al 2023-11-22
-The extraordinary biological importance and impressive performance of (metallo)porphyrins in energy-related molecular activation reactions have attracted the interest of scientists from diverse fields. Increasingly sophisticated synthetic models of the heme iron porphyrin have been used to understand this complex coordination chemistry and to prepare homogeneous biomimetic catalysts. A more recent trend aims at controlling the self-assembly of porphyrinoids to produce a new family of nanoporous metal-organic frameworks (MOFs) or covalent organic frameworks (COFs) that can function as heterogeneous (photo/electro)catalysts. However, the primary self-assembly driving forces involved in the formation of MOFs and COFs based on porphyrins usually include axial coordination and cofacial π-π stacking, respectively. This is a big problem because, with the exception of the molecules sited at the crystal edges, the axial active sites around the metal center are not exposed to the relevant reagents, drastically decreasing their catalytic properties.
In this project we combined the versatility and robustness of the self-assembly approach shown in both COFs and MOFs preparation, with the well-defined nanocavities present in biological enzymes, that are responsible for accessible active sites, to prepare nanostructured systems based on co-facial (metallo)porphyrins which exhibited relevant host-guest properties, chiral induction, allosteric effects, and potential catalytic applications.
-The severe energy crisis due to the massive consumption of fossil fuels and the considerable global population growth, together with the more than evident environmental impact caused by the last two, make extreme urgency for our present society the development of a complementary set of sustainable energy and raw material resources for both the economic and the ecological point of view.
Therefore, the implementation of this kind of molecules in nanostructured systems that present an accessible catalytic pocket could result in great importance in order to achieve the same level of performance as Nature does in the very relevant field of catalysis.
-In this context, in SuprAlloCat we plan to apply some of the lessons learned from nature to target the noncovalent construction of unprecedented nanostructured supramolecular polymers with catalytic performance that would combine the broad catalytic scope of homogeneous catalysts, and the allosteric control, selectivity and activity under mild conditions of enzymes. The key to achieving such a goal relies on the development of a self-assembly strategy that will allow us to cofacially arrange metalloporphyrins at tailored interstitial distances along different dimensions, thus creating a periodic array of connected nanoreactors with well-defined, accessible (photo)catalytic sites. These self-assembled compartmentalized materials can serve as catalysts for manifold relevant chemical transformations, and in particular for regio- and enantioselective epoxide ring-opening reactions using Lewis-acid based catalysis.
In this project we combined the versatility and robustness of the self-assembly approach shown in both COFs and MOFs preparation, with the well-defined nanocavities present in biological enzymes, that are responsible for accessible active sites, to prepare nanostructured systems based on co-facial (metallo)porphyrins which exhibited relevant host-guest properties, chiral induction, allosteric effects, and potential catalytic applications.
-The severe energy crisis due to the massive consumption of fossil fuels and the considerable global population growth, together with the more than evident environmental impact caused by the last two, make extreme urgency for our present society the development of a complementary set of sustainable energy and raw material resources for both the economic and the ecological point of view.
Therefore, the implementation of this kind of molecules in nanostructured systems that present an accessible catalytic pocket could result in great importance in order to achieve the same level of performance as Nature does in the very relevant field of catalysis.
-In this context, in SuprAlloCat we plan to apply some of the lessons learned from nature to target the noncovalent construction of unprecedented nanostructured supramolecular polymers with catalytic performance that would combine the broad catalytic scope of homogeneous catalysts, and the allosteric control, selectivity and activity under mild conditions of enzymes. The key to achieving such a goal relies on the development of a self-assembly strategy that will allow us to cofacially arrange metalloporphyrins at tailored interstitial distances along different dimensions, thus creating a periodic array of connected nanoreactors with well-defined, accessible (photo)catalytic sites. These self-assembled compartmentalized materials can serve as catalysts for manifold relevant chemical transformations, and in particular for regio- and enantioselective epoxide ring-opening reactions using Lewis-acid based catalysis.
Targeting the preparation of 0D cages and 1D polymers based on co-facial porphyrins a variety of tetra- and octa- topic porphyrins P and di- topic linkers L decorated with carboxylic acid, aldehydes, amines, and amidines were synthetized.
Unfortunately, all the attempts to produce 1D polymers resulted in insoluble materials making it impossible to continue the project in this sense. Therefore, this fact produced a deviation from the original objectives, and all the efforts were then focused on 0D porphyrin cages.
Regarding the type of interaction that drives the self-assembly process the cages prepared can be classified as:
i) Amidinium-carboxylated 0D cages, assembled by H-bond interactions between complementary tetra-carboxylic acid P and bis-amidine L, that were soluble in both organic and aqueous media by varying the solubilizing groups. These cages have an accessible active site able to encapsulate guest molecules in very different solvent environments.
ii) NC imine 0D cages formed by imine condensation reaction, that is a dynamic covalent reaction, between tetra-amine Ps and bis-aldehyde Ls, and iii) CN imine 0D cages prepared by imine condensation reaction between tetra-aldehyde Ps and bis-amine Ls. The imine-based molecular cages ii) and iii) have been widely studied and manifold modifications have been introduced in their structure to achieve different objectives.
The characterization of the “original” cages revealed that from the two possible conformations, which depend on the alternance of the imine bonds, only the extended one was observed in solution experiments as well as in the solid state (single X-ray diffraction). To explore the ability of these cages to encapsulate molecules into its inner cavity, host-guest studies were performed for both NC and CN cages, concluding that due to the fixed porphyrin-porphyrin distance, the cage shown selectivity for the encapsulation of guests in the function of their size. In addition, some guest molecules were able to trigger a conformational change from extended to compact conformation.
To control the conformational equilibria slight modifications either in the structure of the porphyrin or the linker were introduced. For instance, the molecular cage CN connected by pyridine linkers allowed to switch from the extended to the compact conformation by the coordination of metal cations to the pyridine N and both imine N. Interestingly, the encapsulation of guest molecules experimented with an allosteric effect where the metal cation acts as an effector molecule.
Furthermore, by introducing hydroxyl groups at the porphyrin for the cage CN, and at the linker for the cage NC led to synthetic conformational control achieving exclusively the compact conformation.
Additionally, chiral induction was achieved by adding chiral host molecules to the “original cages” or introducing chiral moieties in the porphyrin or the linker. Finally, the imine cages are being tested as catalysts for epoxide ring-opening reactions catalyzed by metallic Lewis-acid centers.
These results have been disseminated in National and International conferences by the researchers involved, and the main results are being collected in 5 manuscripts aiming to be published in high-impact factor journals.
Unfortunately, all the attempts to produce 1D polymers resulted in insoluble materials making it impossible to continue the project in this sense. Therefore, this fact produced a deviation from the original objectives, and all the efforts were then focused on 0D porphyrin cages.
Regarding the type of interaction that drives the self-assembly process the cages prepared can be classified as:
i) Amidinium-carboxylated 0D cages, assembled by H-bond interactions between complementary tetra-carboxylic acid P and bis-amidine L, that were soluble in both organic and aqueous media by varying the solubilizing groups. These cages have an accessible active site able to encapsulate guest molecules in very different solvent environments.
ii) NC imine 0D cages formed by imine condensation reaction, that is a dynamic covalent reaction, between tetra-amine Ps and bis-aldehyde Ls, and iii) CN imine 0D cages prepared by imine condensation reaction between tetra-aldehyde Ps and bis-amine Ls. The imine-based molecular cages ii) and iii) have been widely studied and manifold modifications have been introduced in their structure to achieve different objectives.
The characterization of the “original” cages revealed that from the two possible conformations, which depend on the alternance of the imine bonds, only the extended one was observed in solution experiments as well as in the solid state (single X-ray diffraction). To explore the ability of these cages to encapsulate molecules into its inner cavity, host-guest studies were performed for both NC and CN cages, concluding that due to the fixed porphyrin-porphyrin distance, the cage shown selectivity for the encapsulation of guests in the function of their size. In addition, some guest molecules were able to trigger a conformational change from extended to compact conformation.
To control the conformational equilibria slight modifications either in the structure of the porphyrin or the linker were introduced. For instance, the molecular cage CN connected by pyridine linkers allowed to switch from the extended to the compact conformation by the coordination of metal cations to the pyridine N and both imine N. Interestingly, the encapsulation of guest molecules experimented with an allosteric effect where the metal cation acts as an effector molecule.
Furthermore, by introducing hydroxyl groups at the porphyrin for the cage CN, and at the linker for the cage NC led to synthetic conformational control achieving exclusively the compact conformation.
Additionally, chiral induction was achieved by adding chiral host molecules to the “original cages” or introducing chiral moieties in the porphyrin or the linker. Finally, the imine cages are being tested as catalysts for epoxide ring-opening reactions catalyzed by metallic Lewis-acid centers.
These results have been disseminated in National and International conferences by the researchers involved, and the main results are being collected in 5 manuscripts aiming to be published in high-impact factor journals.
The investigations in SuprAlloCat enhanced the state of the art of different fields. The rational design of the building block precursor, placing the complementary functional groups in strategy positions, efficiently led to the formation of the target self-assembled structures. Besides, the inner nanocavity between co-facial metalloporphyrins, that did not collapse even in the solid state, featured these systems with accessible active sites with applications in host-guest chemistry and catalysis. The unique arrangement shown by the imine bonds that formed the cages allowed to modulate the cage size, and therefore the porphyrin-porphyrin distance on demand, giving access to different host-guest selectivity, chiral induction, and allosteric behavior.
We now plan to apply some of the lessons learned in SuprAlloCat to face the plastic waste issue, targeting to efficiently cleave and recycle poly(ethylene-terephthalate) (PET) at mild temperatures back into the original monomers: ethylene glycol and terephthalate.
We now plan to apply some of the lessons learned in SuprAlloCat to face the plastic waste issue, targeting to efficiently cleave and recycle poly(ethylene-terephthalate) (PET) at mild temperatures back into the original monomers: ethylene glycol and terephthalate.