Oregano Essential Oil Interactions with Photogenerated Singlet Molecular Oxygen.

Essential oils are a mixture of volatile compounds, products of the secondary metabolism of plants. Once extracted, they can be deteriorated losing their organoleptic and therapeutic properties due to various environmental factors, being light exposure in aerobic conditions the main cause. In this work, the oregano essential oil extraction and characterization from Origanum vulgare plants grown in the experimental field of the FTU-UNSL and its photodegradation in MeOH:H2 O 60:40 v/v solvent were studied. Characterization by EIMS and NIST Mass Spectrometry indicates the main compounds of oregano essential oil, quantified in the extracted oil by GC-MS, are carvacrol (7.14%) and thymol (47.37%). Degradation of essential oil and its two major components can be caused by reactive oxygen species photogenerated from endogenous sensitizers as riboflavin. Our results suggest degradation occurs involving singlet molecular oxygen. Interaction of carvacrol and thymol with singlet oxygen is mainly a physical process, while essential oil has an important reactive component, which indicates there might be other constituents which could contribute to reactive photoprotection. The effect of simultaneous presence of oregano essential oil and tryptophan amino acid-used as a photooxidizable model under riboflavin-photosensitizing conditions-was studied in order to evaluate the possible photoprotection exerted by the essential oil.

Experimental and Theoretical Study of the Stability of the Complex Fisetin-Cu(II) and A Comparative Study of Free Ligand and Complex Interaction with Molecular Singlet Oxygen.

In this work, the flavonol fisetin was selected in order to study its reactivity against Cu(II), a metal ion of interest in biological media and industry. The stoichiometry and apparent formation constant of the complex in ethanolic medium at 25°C were evaluated using spectrophotometric techniques. The resulting stoichiometry was a 1:1 ligand:metal complex, and a log K = 5.17 ± 0.12 was determined. Since two possible chelation sites can be proposed for the complex formation, quantum chemistry calculations were performed on these structures. Calculations suggest that the hydroxyl-keto site is more stable for the complex formation than the catechol site. Flavonoids could exert protection against oxidative damage caused by reactive oxygen species, and this biological activity could be affected by chelation with metal ions. This led us to perform a study on the interaction of both, free flavonoid and complex, with reactive oxygen species. Our results showed both compounds quench molecular singlet oxygen photogenerated with visible light, mainly in a physical fashion. In order to analyze a possible protective effect of flavonoid and its complex against oxidative damage in biological environments, the amino acid tryptophan was selected as a model oxidation system. Free flavonoid does not have a marked protective effect, whereas its complex showed a relevant protective effect.