The aim of the current study was the valorization of hesperidin, the dominant flavonoid in citrus processing waste, by microwave-assisted synthesis of hesperidin-Mg complex, improving its antioxidant activity and insecticidal potential. Here we show, for the first time, that microwave-assisted synthesis of [Mg(hesp)2(phen)]OAc (1) (hesp: hesperidin, phen: phenanthroline) improve the reaction rate and yield. The nuclear magnetic resonance (NMR) experiments proved to be powerful tools for the identification of three isomers in metal complexes. Moreover, we explore the insecticidal potential of 1 and [Mg(phen)2(Isov)]OAc (2) (Isov : isovanillic acid) complexes against three insects. Complex 1 killed 80% of adults whitefly at 0.14 μmol L-1, and 2 76% at 0.36 μmol L-1. There was a total mortality of Spodoptera frugiperda with 2 at 0.39 μmol L-1, and 83% with 1 at 0.14 μmol L-1. Both have similar activity, and represent a novel group of insecticide for Bemisia tabaci and S. frugiperda; nevertheless, the benefits of both as Myzus persicae repellent require further evaluation.

Citrus biomass is a source of biobased products and presents extensive chemical diversity. Among the structural macromolecules, lignins have been used in resins, bioplastics, and nanoencapsulation. Brazil has a large source of lignins, which are orange trees removed from groves that need to be renewed. However, the knowledge about these lignins is limited and little explored. Thus, this work aimed to evaluate the lignins from Citrus sinensis and to provide information on the interesting use of orange trees as a source of macromolecules. The lignins were isolated from the trunk, central and secondary roots from the orange tree by Technical Association of the Pulp and Paper Industry (TAPPI)-methods. The lignin contents for the extractive-free samples were 19.8 ± 0.19, 21.9 ± 0.36, and 19.5 ± 0.41% (m/m) in the trunk, central and secondary roots, respectively. Infrared (IR) and 13C nuclear magnetic resonance (NMR) analyses confirmed typical bands and chemical shifts to syringyl and guaiacyl units. These results are consistent with the features of lignins previously reported for orange tree branches and hardwood roots. The greatest amount of lignin in the orange tree was found in the central root. The lignins extractive-free by TAPPI-T264 cm-97 presented low solubility in organic solvents, due to their compaction and folding, which was confirmed by 13C NMR in the solid-state, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

The purification of the hexanic extract from the leaves of a native variety of mahogany collected in Santarém (Pará, Brazil) afforded eight new phragmalin limonoids along with eight known compounds. This variety, according to field observations, should be considered resistant against the specialist insect Hypsipyla grandella, that attacks the terminal shoots only of juvenile mahogany and not of matured ones. After observing that four phragmalin limonoids were present just in mature leaves, we carried out two bioassays, one of them using a fraction from hexanic extract of mature leaves and another using a mix of four limonoids. The results of the bioassay using the isolated limonoids showed a direct effect on the larvae of H. grandella, suggesting that these limonoids act as inhibitors of larvae growth. This should be the reason why larvae choose the young leaves for their development.

Insecticidal activity of essential oils of Pelargonium graveolens, Lippia alba and compounds geraniol, linalool, 1,8-cineole, limonene, carvone, citral and Azamax® were evaluated against Spodoptera frugiperda. Topical application assay showed essential oil of P. graveolens has acute toxicity against Spodoptera frugiperda larvae (third instar) with LD50 1.13 µg/mg per insect and LD90 2.56 µg/mg per insect. Three essential oils of L. alba also exhibited insecticidal activity with LD50 ranging from 1.20 to 1.56 µg/mg per insect and LD90 from 2.60 to 3.75 µg/mg per insect. Geraniol, linalool, carvone and citral caused significant mortality of 30, 90, 84 and 64% respectively, compared to negative control. The bioinsecticide, Azamax®, caused lower mortality than the compounds of the essential oils.