Antimicrobial Activity of the Thio-Cyclized Lippia citriodora Leaf Essential Oil Cultivated in Algeria

Abstract

The essential oil of Lippia citriodora extracted by hydrodistillation from dry leaves with a yield of 0.3 % which characterization by TLC, UV-Vis, and IRTF analyses make it possible to distinguish the presence of aldehydes functions within the chemical composition. The GC-MS has permitted to confirm and to identify the neral and the geranial in appreciable proportions in the chemical composition of Lippia citriodora essential oil. The thionation of the carbonyl compounds of the essential oil has led to the transformation of the carbonyl compounds into corresponding thiones. The UV-Vis spectroscopy and the FT-IR spectra have shown the disappearance of the aldehyde function and its replacement by thione and thiol functions in solution by tautomery. The GC-MS has permitted to identify the formation of unsaturated cyclic compounds such as the 2-Isopropyl-5-methyl-cyclohexa-2,5-dienethione, the 6-Isopropyl-3-methyl-cyclohexa-2,4-dienethione and the 5-Isopropenyl-2-methyl-cyclohex-2-enethione, as well as an aromatic compound namely the thiothymol (2-Isopropyl-5-methyl-benzenethiol).The antibacterial and especially antifungal activity of the essential oil of Lippia citriodora has been greatly improved with the replacement of the oxygen by the sulphur and therefore the increase of the hydrophobic character and the volatility of the chemical composition of the oil.