Graphene oxide (GO) is an attractive nanomaterial for many applications. Controlling the functionalization of GO is essential for the design of graphene-based conjugates with novel properties. But, the chemical composition of GO has not been fully elucidated yet. Due to the high reactivity of the oxygenated moieties, mainly epoxy, hydroxyl and carboxyl groups, several derivatization reactions may occur concomitantly. The reactivity of GO with amine derivatives has been exploited in the literature to design graphene-based conjugates, mainly through amidation. However, in this study we undoubtedly demonstrate using magic angle spinning (MAS) solid-state NMR that the reaction between GO and amine functions occurs via ring opening of the epoxides, and not by amidation. We also prove that there is a negligible amount of carboxylic acid groups in two GO samples obtained by a different synthesis process, hence eliminating the possibility of amidation reactions with amine derivatives. This work brings additional insights into the chemical reactivity of GO, which is fundamental to control its functionalization, and highlights the major role of MAS NMR spectroscopy for a comprehensive characterization of derivatized GO.

2D transition metal dichalcogenide MoS2 nanosheets are increasingly attracting interests due to their promising applications in materials science and biomedicine. However, their biocompatibility and their biodegradability have not been thoroughly studied yet. Here, we investigated the biodegradability of exfoliated pristine and covalently functionalized MoS2 (f-MoS2). First, biodegradability of these nanomaterials was evaluated using plant horseradish peroxidase and human myeloperoxidase. The results revealed that the enzymatic degradability rate of MoS2 and f-MoS2 was slower than in the case of the simple treatment with H2O2 alone.In parallel, high biocompatibility of both pristine and f-MoS2 nanosheets was found up to 100 µg mL -1 both in cell lines (HeLa and Raw264.7) and primary immune cells. In addition, no immune cell activation and minimal pro-inflammatory cytokine release were observed in RAW264.7 and human monocyte-derived macrophages, suggesting a negligible cellular impact of such materials. Furthermore, the effects of degraded MoS2 and partially degraded f-MoS2 products on cell viability and activation were studied in cancer and immune cells. A certain cytotoxicity was measured at the highest concentrations. Finally, to prove that the