Crystal engineering of co-crystals and host-guest systems for environmentally friendly applications: sunscreens stabilization, pollutant sequestering and herbicide reformulation.

Solid state engineered materials have proven to be useful and suitable tools in the quest of new materials. In this thesis different crystalline compounds were synthesized to provide more sustainable products for different applications, as in cosmetics or in agrochemistry, to propose pollutants removal strategy or to obtain materials for electrocatalysis. Therefore, the research projects presented here can be divided into three main topics: (i) sustainable preparation of solid materials of widely used active ingredients aimed at the reduction of their occurrence in the natural environment. The systems studied in this section are cyclodextrins host-guest compounds, obtained via mechanochemical and slurry synthesis. The first chemicals studied are sunscreens inclusion complexes, that proved to have enhanced photostability and desired photoprotection. The same synthetic methods were applied to obtain inclusion complexes of bentazon, a herbicide often found to leach in groundwaters. The resulting products showed to have desired water solubility properties. The same herbicide was also adsorbed on amorphous calcium phosphate nanoparticles, to obtain a biocompatible formulation of this agrochemical. This herbicide could benefit by the adsorption on nanoparticles for what concerns its kinetic release in different media as well as its photostability. (ii) Sustainable synthesis of co-crystals based on polycyclic aromatic hydrocarbons, for the proposal of a sequestering method with a resulting material with enhanced properties. The co-crystallization via mechanochemical means proved that these pollutants can be sequestered via simple solvent-free synthesis and the obtained materials present better photochemical properties when compared to the starting co-formers. (iii) Crystallization from mild solvents of nanosized materials useful for the application in electrocatalysis. The study of compounds based on nickel and cobalt metal ions resulted in the obtainment of 2D and 1D coordination polymers. Moreover, solid solutions were obtained. These crystals showed layered structures and, according to preliminary results, they can be exfoliated.

Development of new collagen cross-linkers for adhesive bonding stabilization

Aims: This thesis aimed to investigate the influence of different collagen cross-linkers, as separate primers or contained within desensitizing agents, on the longevity of dental restorations and on the dentinal enzymatic activity immediately, or after aging in vitro. Methods: A series of studies was conducted using several different cross-linking molecules and several adhesive systems. Four studies investigated the longevity of the hybrid layer by means of microtensile bond strength test, and the enzymatic activity using gelatin and in situ zymography, immediately or after 1 year of aging in the artificial saliva. The first study tested samples bonded with or without a cross-linking agent, that were previously aged for 5 years. The degradation of the hybrid layer was observed using transmission electron microscopy, the enzymatic activity in the hybrid layer using in situ zymography. Raman spectroscopy was used to investigate whether the active substance was still within the hybrid layer after 5 years. Results: The results of the studies showed that collagen cross-linkers were efficient in preserving bond strength after aging in vitro when used as separate primers on demineralized or partially demineralized dentin. In the cases when the cross-linker was utilized on mineralized dentin, bond strength results were higher than in the control groups immediately and after aging, however, no difference in enzymatic activity was detected after aging. Conclusions: The tested cross-linker molecules used as separate primers in etch-and-rinse and self-etch adhesives seem to be clinically applicable, since the procedure is not overly time-consuming and seems to preserve the hybrid layer over time. As for the cross-linkers contained in the desensitizing agent, when utilized before the adhesive procedures, it has shown to increase the bond strength of self-etch adhesives, but further studies are needed to better understand its effect on the enzymatic activity and crosslinking effects on mineralized dentin.