Plants synthesize antioxidant compounds as a defense mechanism against reactive oxygen species. Recently, plant-derived antioxidant compounds have attracted attention due to the increasing consumer awareness in the heath industry. However, traditional methods for measuring the antioxidant activity of these compounds are time-consuming and costly. Therefore, our study constructed a quantitative structure-activity relationship (QSAR) model that can predict antioxidant activity using graph convolutional networks (GCN) from plant structural data. The accuracy (Acc) of the model reached 0.6 and the loss reached 0.03. Although with lower accuracy than previously reported QSAR models, our model showed the possibility of predicting DPPH antioxidant activity in a wide range of plant compounds (phenolics, polyphenols, vitamins, etc.) based on their graph structure.

Essential oils or phytochemicals that are naturally synthesized by plants have received much attention as alternative pest control strategy. They are composed of highly volatile compounds which are less toxic to human but highly toxic to pests such as insects, microorganisms and nematodes. Until now, many researchers have evaluated the toxicities of essential oils and phytochemicals in Korea. Among them some of essential oils are formulated as repellents against mosquitoes. However, even such a broad research, the mode of action of essential oils is still unclear. To develop more effective and environmental friendly natural pesticides and to help understand the mode of action of essential oils, we have investigated the structureactivity relationship (SAR) between the chemical components of bio-active essential oils and nematode as well as insect pests. SAR of short-chain aliphatic compounds and ester analogues and pine wood nematode, Brusaphelenchus xylophilus; and salicylate analogues and adzuki been weevil, Callosobruchus chinensis are discussed here.

Maize weevil is one of the most common and critical storage pest in the world. In this study, the insecticidal activity of the methanol extracts derived from Caesalpinia sappan was evaluated against adults of maize weevil, using by direct contact and fumigant methods. Based on the two methods, ethyl acetate fraction of the C. sappan extracts had 100% mortality against Maize weevil adults at 10 mg. The biological constituent of C. sappan extract was isolated by various chromatographic techniques and identified as juglone. On the basis of 72 h LD50 values, in the direct contact bioassay, the insecticidal activity of juglone (0.010 mg/cm2) was the most effective, followed by 1,4-NQ (0.018 mg/cm2) and menadione (0.087 mg/cm2). In a fumigant bioassay, the insecticidal activity of juglone (0.014 mg/cm2) was the most effective, followed by 1,4-NQ (0.015 mg/cm2) against maize weevil adults. On the other hand, menadione, lawsone, and 2-methoxy-1,4-NQ observed no insecticidal activity or weak. These results suggested that active compound of C. sappan materials could be used as biological control agent against maize weevil. Therefore, further research should be performed to the structure activity relationship of juglone and compared with its derivatives.

Nematicidal activity of aliphatic compounds was tested against pien wood nematode, Bursaphelenchus xylophilus. There was a significant difference in nematicidal activity among function groups. In a test with alkanols and 2-alkenols, compounds with C8-C11 chain length showed 100% nematicidal activity at 0.5 mg/mL concentration. C6-C10 2-alkenals exhibited >95% nematicidal activity, but the other compounds with C11-C14 chain length showed weak activity. Nematicidal activity of alkanoic acids with C7-C11 chain length was strong. Whole compounds belonging to hydrocarbons, alkanals and alkanoic acetate showed weak nematicidal activity at 0.5 mg/mL concentration. Nematicidal activity of compounds which showed strong nematicidal activity at 0.5 mg/mL concentration was tested at a lower concentration. At 0.25 mg/mL concentration, whole compounds except C8 alkanol, C8 2-alkenol and C7 alkanoic acid showed >80% nematicidal activity. C9-C11 alkanols, C10-C11 2-alkenols, C8-C9 2-alkenals and C9-C10 alkanoic acids showed >80% nematicidal activity at 0.125 mg/mL concentration. Only C11 alkanol exhibited strong nematicidal activity at 0.0625 mg/mL concentration