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Assessment of antioxidant potential of phenolic compounds present in popular medicinal herbs

Over the years, various studies have shown that natural compounds present in herbs have many health promoting effects, such as reduction in risk of cardiovascular and neurodegenerative diseases. One of the most popular explanations ascribes these effects to antioxidant activity (scavenging of free radicals) of polyphenolic compounds present not only in medicinal herbs, but also in fruit and vegetables. Polyphenols undergo colon metabolism, during which many of the structurally diverse molecules are broken down into a common set of simple phenols, which are also widely present in herbs. Because polyphenols generally have low bioavailability, their biological activity could be associated with their colon catabolites, present in circulation at higher concentrations (µM value, which could be sufficient for in vivo antioxidant activity). Polyphenolic profile of selected medicinal herbs (Angelica L., Mentha spicata L., Rosmarinus officinalis L., Salvia officinalis L., Verbena officinalis L., etc.) was determined using the Phenol-Explorer database. Antioxidant activity of selected polyphenols and their catabolites (such as quercetine and coffeic acid, to name a few) was studied by DFT method using the M06-2X/6-311++G(d, p) level of theory and the SMD continuum solvation model. Two mechanisms of free radical scavenging, hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET), were determined to be thermodynamically probable and competitive mechanisms in aqueous and non- aqueous media. The Gibbs free energy change for HAT/SPLET mechanism of studied compounds with a selection of free radicals was also calculated. Obtained results indicate these compounds as efficient deactivators of free radicals with different characteristics, what could explain some of health beneficial effects of medicinal herbs.

medicinal herbs, polyphenols, DFT, HAT, SPLET

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