Cucurbiturils, tetrahedral capsules, and porous systems: synthesis, functionalization, and applications

Taking a cue from the principles developed by the founding fathers of supramolecular chemistry, the PhD program consists of four lines of research that develop in a multidisciplinary plan starting from alternative and more environmentally friendly synthesis methodologies. During the first year a new synthetic strategy was developed for the preparation of cucurbit[7] uril through the use of molecular models to increase the yield of CB[7] compared to the classical syntheses reported so far. The conversion of the imidazole models into magnetic liquid facilitated the separation of CB[7], which, in general, is time-consuming and costly in terms of time and money. Subsequently, CB[7] was used as a supramolecular reactor for the synthesis, in some cases, of stereocontrolled isoxazolidine substituted by exploiting the 1,3-dipolar cycloaddition reaction. The reaction was carried out under "GREEN" conditions using water and microwaves. Remaining in the context of the use of water as a reaction solvent, in the second part of the first year and the beginning of the second year of the doctorate a tetrahedral capsule was exploited as a nanoreactor for the realization of dehydration reactions in water for synthesis of nitrones. During the second year a new supramolecular system was developed capable of adsorbing a significant amount of carbon dioxide. This system was developed starting from the cucurbit[6]uril, which was functionalized with 12 chains of 1-(ethyl)-3-methyl-1H-imidazol-3-ium bromide. The presence of the positively charged imidazole groups made possible the formation of cation-dipole interactions between the positively charged side chain of a functionalized CB[6] and the carbonyl dipole of another functionalized CB[6]. This network of interactions led to the formation of further interstices, in addition to the cavities of the macrocycles, which transformed the system into a supramolecular nanosponge. Furthermore, the adsorbed CO2 was used to perform the carboxylation of phenylacetylene was easily and satisfactorily accomplished. Finally, following the current topic of environmental awareness, in the development of new advanced materials that are both ecological and capable of exhibiting the properties targeted for the required application. It was developed a straightforward and rapid synthetic methodology to synthesize a new hybrid, ecological and reusable material starting from cheap materials such as loofah and halloysite. The composite showed a significantly greater ability to absorb and retain carbon dioxide than non-contaminated materials. This underlines the synergistic effect of the two materials, which also possess a greater adsorption capacity than the BEA and MOR zeolites, which are currently used in the industrial field for gas adsorption and require more prolonged and more expensive synthetic processes. Moreover, the synergistic effect of the materials is evident in the greater carrying capacity of resveratrol compared to individual materials. This study opens another way towards developing hybrid, organic-inorganic materials, applicable in multiple fields and at the same time eco-sustainable and economical.