Physical and chemical aspects of the interaction of molecules with external surface and structural cavities of nanomaterials.

The research work carried out during this PhD project has been aimed to the investigation of molecular surface events relevant for the catalytic formation, in mild conditions, of amide/peptide bonds from non-activated reagents adsorbed on nanomaterials. The formation of C-N bonds is among the topics of high interest in modern research in chemistry, addressing issues ranging from fine to prebiotic chemistry. The implementation of this project required the selection of both catalyst and reactants. As for the nanomaterials, the criteria of choice were simplicity, availability and low cost for possible future applications and, on the other hand, reasonable representativeness of minerals possibly present on the early Earth, and active as catalyst towards adsorbed organic molecules. On this basis the following nanoparticles of silica and titania are selected as well as a zeolite of the ZSM-10 type, with a MOZ framework. This latter material was intended as a porous host for future studies of the high pressure induced oligomerization of amino acids. This part of the work belongs to a very recent project, and then the work carried out in this respect in this PhD thesis is focused on the synthesis of zeolite particles with proper framework features. The choice of reactants was driven, on one hand, on the suitability to be studied in depth by both experimental methods and theoretical modelling, and on the other hand, by the possibility to adsorb them on surfaces of nanomaterials from the vapour phase, i.e. in highly controlled conditions. Thus, the simplest carboxylic acid, HCOOH was selected, as well as two simple primary amines (methylamine and 1-pentanamine). One of the surface reaction investigated was the oligomerization of amino acids on the nanomaterials and for this glycine, alanine, histidine, serine were selected because of the possibility to adsorb them on catalyst via a chemical vapour deposition method. In summary, in Chapter One, the study targeting the elucidation of the mechanism of the amide bond formation between non-activated carboxylic acids and amines at the surface of amorphous silica is reported. The results prepare the ground to address the occurrence of this reaction and of the oligomerization of amino acids (glycine and alanine) at the surface of α-quartz sub-micrometric particles (Chapter Two). The study of the C-N bond formation at the surface of titania nanoparticles is the object of Chapters Three to Five. In particular, Chapter Three is devoted to the investigation the structural requirements of sites expose at the surface of titania nanoparticles in order they can act as catalytic sites towards amino acid oligomerization. In Chapter Four, insights on basic aspects of the interaction of formic acid and methylamine with the 101 anatase titania surface are presented. The possibility to prepare Ser-His dipeptides starting from non-activated amino acids by using titania nanoparticle as catalyst and the possible hydrolytic activity of the obtained peptides is the object of Chapter Five. Finally, in Chapter Six, challenges, successes and problems still to be solved for and effective synthesis of large ZSM-10 particles, required for multitechniques investigations, including single crystal X-ray diffraction.