A new insight into the oxidative mechanism of caffeine and related methylxanthines in aprotic medium: May caffeine be really considered as an antioxidant?

Abstract

Beyond the experimental methods used, the discussion of the present results might provide food for thought to the wide audience working on antioxidants.

Electrochemical Oxidation of Theophylline in Organic Solvents: HPLC‐PDA‐ESI‐MS/MS Analysis of the Oxidation Products

“…Cyclic voltammetries (CVs), performed to measure the anodic potential value to be used for electrolysis, were carried out on TPh 0.02 M in solvent/supporting electrolyte at a glassy carbon (GC) electrode, at the scan rate of 200 mV s −1 . A broadened irreversible anodic peak was evidenced in all solvent/supporting electrolyte systems used, as shown in Figures a–e (red curves), in agreement with the electrochemical study on TPh in aprotic medium, topic of the previous work recently published . The anodic peak potential values were in the range of 1.3–2.0 V, vs saturated calomel electrode (SCE), the lowest value measured in water/KCl (pH=7) while the highest one was approximately the same in both ACN and DMF, all values in good agreement with literature .…”

“…Oxidation products 2 – 4 were consistent with the mono‐electronic anodic oxidation of the olefinic bond bridging the two rings of TPh molecule, in agreement with what previously proposed and supported by DFT calculation by Petrucci and coworkers, leading to a radical cation that can undergo different fate, mainly depending on medium.…”

“…Nowadays, new contexts are being proposed with positive outcomes for caffeine and TPh (Figure ), and increasing pharmaceutical and therapeutic potentialities are emerging from an always growing number of scientific reports on them. Also the antioxidant capacity of caffeine and TPh, mainly as HO ⋅ scavenger, has been discussed more recently …”

“…If few studies on the chemically induced oxidation of TPh have been reported in literature, also the electrochemical oxidation has been sparingly studied, and more recent electrochemical studies mainly aimed at analytical application …”

“…As for caffeine, by far the most thoroughly studied methylxanthine (also in organic solvents,) the few reported studies on TPh were mainly carried out in water at different pH . Major differences compared to the electrochemical behavior of caffeine were firstly evidenced, as the formation of little amounts of a dimeric form of TPh insoluble in water: a one‐electron one‐proton anodic oxidation of TPh was there supposed, and two oxidative routes were proposed for the electro‐generated radical: dimerization or further oxidation to uric acids and degradation derivatives.…”