AbstractThe antimicrobial and growth-stimulating activities of nine protic ionic liquids (PILs)—tris(2-hydroxyethyl)ammonium salts (protatranes) of cinnamic, benzoic, salicylic, oxalic, malonic, succinic, malic and citric acids—were investigated for the first time. It was found that tris(2-hydroxyethyl)ammonium salts of cinnamic, benzoic and malonic acids have a positive impact on seeds germination and growth characteristics of garden cress (Lepidium sativum L.) sprouts. All the investigated PILs exhibited selective activity against Staphylococcus aureus bacteria. PILs based on tris(2-hydroxyethyl)ammonium malate with the melting point of 41°C were isolated as crystals to perform a comparative study of the crystal structure by single-crystal X-ray diffraction. In contrast to cations in tris(2-hydroxyethyl)ammonium succinate, cations in malate have a tricyclic endo conformation that is most typical of tris(2-hydroxyethyl)ammonium salts.