A comprehensive study of a less harmful functionalization of multiwalled carbon nanotubes (MWCNT) was performed. The influence of ultrasonic cavitation and solid/liquid interface was indirectly evaluated by statistical characterization of MWCNT aspect ratio and degree of functionalization. MWCNT aspect ratio was determined through hundreds of electron microscopy images. Degree of functionalization of MWCNT was characterized by elemental analysis and thermogravimetry. Distribution of different oxygen-containing functional groups was assessed by potentiometric titration. MWCNT aqueous dispersions were evaluated by electrophoretic mobility and dynamic light scattering. An acid volume over 90% lower than usually reported in literature guaranteed MWCNTs with significantly larger aspect ratio, higher proportion of carboxylic groups and a more negative zeta potential in aqueous suspension. These results can be related to a more localized ultrasonic cavitation in MWCNTs/acid interface for reduced liquid volumes. This distinguished influence of ultrasonic cavitation may be a valuable contribution to more eco-friendly processes with nanomaterials.

The resistance of Annona muricata roots to the nematode Meloidogyne javanica was investigated by nuclear magnetic resonance (NMR)-based metabolomics in combination with principal component analysis (PCA). Metabolic changes in roots exposed and not exposed to the nematode were evaluated and compared. In addition, the presence of nematicidal compounds in the root extracts was investigated through in vitro assay against Meloidogyne javanica second-stage juveniles. Plants exposed to nematodes showed significant changes in their metabolism after 24 h. Several resistance-related metabolites, including dopamine, xanthine and aromatic compounds, could be identified in the roots with the joint analysis of 1D/2D NMR and the loadings of PC3 (17.8%). A.muricata root chloroform extract, containing mainly acetogenins, has shown nematostatic activity against M. javanica, suggesting that a pre-formed defense mechanism can support the reported resistance. For the first time, metabolomic studies allowed to identify induced and pre-formed defense mechanisms and their related metabolites in Annona muricata.