Crystal engineering strategies for a healthier environment: solid-state syntheses and characterization of organic/inorganic co-crystals and host-guest systems with improved stability and performance activities

In a society increasingly aware of and concerned about environmental issues, chemistry is being asked to promote sustainability through the development of processes less impacting on the environment and of products environmentally friendly. In this context, the field of chemistry referred as crystal engineering can play a major role in the quest for sustainability. By exploiting sustainable synthetic methodologies - first of all the mechanochemical method - crystal engineering can guide solid-state modifications in order to obtain crystalline materials with an improved sustainable character. This doctoral research activity addressed the synthesis and characterization of environmentally friendly crystalline materials. Two different lines of research were undertaken: • Optimization of materials of agrochemical interest, mainly through the co-crystallization method. The first systems investigated were urea-based co-crystals, designed (i) to improve the chemical-physical properties of urea by reducing its water solubility/dissolution rate and (ii) to exert an inhibition activity towards the soil enzymes urease and ammonia monooxygenase (AMO). The work resulted in the publication of three papers, which are presented in Chapter 2. A further development of this research project concerned the synthesis and characterization of crystalline materials based on AMO inhibitors, aimed to modulate the physico-chemical properties of such inhibitors in terms of water solubility, thermal stability, and inhibition activity. The experiments discussed in Chapter 3 are quite promising: a paper has been submitted upon invitation, and two more manuscripts are in preparation. • Improvement in the photostability of organic UV filters commonly used in sunscreen formulations through their inclusion into β-cyclodextrin. The inclusion complexes of β-cyclodextrin with the UV filters avobenzone and octinoxate were synthesized and proved to possess the desired properties. The results led to the publication of a paper, which is presented in Chapter 4.