Poly(methylene blue)-modified electrode for indirect electrochemical sensing of OH radicals and radical scavengers

ABSTRACT A new modified electrode for indirect sensing of OH· and radical scavengers was described. The electrochemical polymerization of methylene blue in aqueous solutions and the properties of the resulting films on a glassy carbon electrode were carried out using cyclic voltammetry. A surface coverage of 1.11 × 109mol cm2 was obtained, revealing a complete surface coverage of the polymeric film on the electrode surface. OH· was able to destroy the poly(methylene blue) film by exposure to a Fenton solution. The loss of the electrochemical signal of the residual polymeric film attached to the electrode surface was related to the extent of its dissolution. The applicability of the sensor was demonstrated by evaluating the OH radical scavenging effect on different concentrations of ascorbic acid. The obtained radical scavenging capacity were 31.4%, 55.7%, 98.9% and 65.7% for the ascorbic acid concentrations of 5, 10, 30 and 50 mM, respectively.

Qualitative and quantitative analysis of the phenolic content of Connarus var. angustifolius, Cecropia obtusa, Cecropia palmata and Mansoa alliacea based on HPLC-DAD and UHPLC-ESI-MS/MS

ABSTRACT The phenolic content of the medicinal species Connarus perrottetti var. angustifolius Radlk., Connaraceae, Cecropia obtuse Trécul, Cecropia palmata Willd., Urticaceae; and Mansoa alliacea (Lam.) A.H.Gentry, Bignoniaceae, collected in three different years was evaluated. Plant infusions and hydroalcoholic, butanol and ethyl acetate extracts were analyzed by high-performance liquid chromatography with diode array detection. In order to endorse these results, analysis by electrospray mass spectrometry was also performed. Were identified: gallic acid, catechin, caffeic acid, ferulic acid, rutin, quercitrin and resveratrol. C. perrottetti showed greater diversity of polyphenols. M. alliacea had the higher concentration of caffeic acid even though it was found in all species. Catechin was the major antioxidant, but was not detected in M. alliacea. However, we discuss the popular use of these species, as well as their phenolic constitution and the interannual distribution of phenolic compounds.