Antioxidant Activity Evaluation Assay Based on Peroxide Radicals Generation and Potentiometric Measurement

Determination of Photoinduced Radical Generation Quantum Efficiencies by Combining Chemical Actinometry and 19F NMR Spectroscopy

We introduce a general and relatively straightforward protocol aimed at determining the absolute photoinduced radical generation efficiency via NMR monitoring. This approach relies on the use of a radical scavenger probe that combines a nitroxide moiety that specifically reacts with radicals and a trifluoromethyl group used as a ¹⁹F NMR signaling unit. Using an LED source, whose fluence is precisely determined by a chemical actinometry procedure also described herein, the method is used to determine the radical photogeneration quantum yields of three well-known polymerization initiators: azobisisobutyronitrile (AIBN), 4,4'-bis(N,N-diethylamino)benzophenone (BDEBP, a derivative of Michler's ethyl ketone), and 2,4,6-trimethylbenzoyl diphenylphosphine oxide (MAPO). The overall good agreement with values previously reported in the literature proves the robustness of this new method. We then extended the study to the precise measurement of the quantum yield of free-radical photogeneration on a newly synthesized photoinitiator used for two-photon direct laser writing. This study highlights the potential of this methodology for the quantitative determination of photoinduced radical generation efficiency used in many fields of applications.

An integrated approach to the investigation of antioxidant properties by potentiometry

An analytical methodology is proposed for a comprehensive study of antioxidant properties of various objects based on the implementation of various mechanisms of antioxidant action. In order to interpret results regarding the action of antioxidants in living organisms it is proposed to adhere to certain requirements for research methods of antioxidant properties, for oxidizing agents of a radical and non-radical nature. The developed integrated approach consists in using the potentiometry method and is based on the antioxidant capacity determination which is founded on the interaction of antioxidants with the К₃[Fe(CN)₆] by the ET-mechanism and the conjugation mechanism and the antiradical capacity determination based on the interaction of antioxidants with peroxyl radicals by the HAT-mechanism. Individual antioxidants of natural origin, plant materials extracts as well as synthesized 6-nitro-1,2,4-triazoloazin containing polyphenols fragments, which are complex conjugated structures, have been investigated. It has been shown that in the antioxidants study it is advisable to use the integrated approach that will allow to evaluate antioxidant properties from the point of view of various antioxidants action mechanisms.

Novel Potentiometric 2,6-Dichlorophenolindo-phenolate (DCPIP) Membrane-Based Sensors: Assessment of Their Input in the Determination of Total Phenolics and Ascorbic Acid in Beverages

In this work, we demonstrated proof-of-concept for the use of ion-selective electrodes (ISEs) as a promising tool for the assessment of total antioxidant capacity (TAC). Novel membrane sensors for 2,6-dichlorophenolindophenolate (DCPIP) ions were prepared and characterized. The sensors membranes were based on the use of either Cu^II-neocuproin/2,6-dichlorophenolindo-phenolate ([Cu(Neocup)₂][DCPIP]₂) (sensor I), or methylene blue/2,6-dichlorophenolindophenolate (MB/DCPIP) (sensor II) ion association complexes in a plasticized PVC matrix. The sensors revealed significantly enhanced response towards DCPIP ions over the concentration range 5.13 × 10⁻⁵–1.0 × 10⁻² and 5.15 × 10⁻⁵–1.0 × 10⁻² M at pH 7 with detection limits of 6.3 and 9.2 µg/mL with near-Nernstian slope of −56.2 ± 1.7 and −51.6 ± 2 mV/decade for sensors I and II, respectively. The effects of plasticizers and various foreign common ions were also tested. The sensors showed enhanced selectivity towards DCPIP over many other phenolic and inorganic ions. Long life span, high potential stability, high reproducibility, and fast response were also observed. Method validation was also verified by measuring the detection limit, linearity range, accuracy, precision, repeatability and between-day-variability. The sensors were introduced for direct determination of TAC in fresh and canned juice samples collected from local markets. The obtained results agreed fairly well with the data obtained by the standard method.

New antiradical capacity assay with the use potentiometric method

For the first time, the dependence of a redox potential change during a reaction of peroxyl radical generation and their interaction with antioxidants was studied. A regular change of a potential is due to oxidation of an antioxidant by initiating peroxyl radicals accompanied by an electron transfer. An original direct method for determining induction periods, inhibition coefficients and an antiradical capacity using the potentiometric method is proposed. Using the proposed approach the induction periods and the inhibition coefficients of various OH, NH, SH containing antioxidants were determined. The antiradical capacity of a herbal extract was studied. A high degree of correlation with a DPPH assay was obtained. RSD results obtained using the proposed approach do not exceed 7%.

Electrochemical Methods for Total Antioxidant Capacity and its Main Contributors Determination: A review

Backround: The present review focuses on electrochemical methods for antioxidant capacity and its main contributors assessment. The main reactive oxygen species, responsible for low density lipoprotein oxidation, and their reactivity are reminded. The role of antioxidants in counteracting the factors leading to oxidative stress-related degenerative diseases occurence, is then discussed. Antioxidants can scavenge free radicals, can chelate pro-oxidative metal ions, or quench singlet oxygen. When endogenous factors (uric acid, bilirubin, albumin, metallothioneins, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-S-transferase) cannot accomplish their protective role against reactive oxygen species, the intervention of exogenous antioxidants (vitamin C, tocopherols, flavonoids, carotenoids etc) is required, as intake from food, as nutritional supplements or as pharmaceutical products.

Literature study: The main advantages of electrochemical methods with respect to traditional, more laborious instrumental techniques are described: sensitivity, rapidity, simplicity of the applied analytical procedure which does not require complicated sample pre-treatment etc.

The paper reviews minutiously the voltammetric, amperometric, biamperometric, potentiometric and coulometric methods for total antioxidant capacity estimation. For each method presented, the electroactivity and the mechanism of electro-oxidation of antioxidant molecules at various electrodes, as well as the influences on the electroactive properties are discussed. The characteristics of the developed methods are viewed from the perspective of the antioxidant molecule structure influence, as well as from the importance of electrode material and/or surface groups standpoint.

The antioxidant molecule-electrode surface interaction, the detection system chosen, the use of modifiers, as well as the nature of the analysed matrix are the factors discussed, which influence the performances of the studied electrochemical techniques.

Conclusions: The electrochemical methods reviewed in this paper allow the successful determination of the total antioxidant capacity and of its main contributors in various media: foodstuffs and beverages, biological fluids, pharmaceuticals. The advantages and disadvantages of the electrochemical methods applied to antioxidant content and antioxidant activity assay are treated and interpreted, in the case of various analysed matrixes. Combining advanced materials with classical electrode construction, provides viable results and can constitute an alternative for the future.