The new optical test system for semi-quantitative determination of antioxidant capacity using complexes of the iron with 2,2'-bipyridine derivatives.

This work introduces the semi-quantitative optical test system for determining the antioxidant capacity (AOC) of various substances using coordination compounds as model oxidizers. The test system consists of the plastic plate with paper sensors impregnated with a model oxidant, and the calibration strip. In order to determine AOC, the sensor color must be compared with the color of the calibration strip. For more accurate color identification, a Python-based software has been developed. Iron complexes with 2,2'-bipyridine and its derivatives were used as the model oxidant. Directed synthesis of 2,2'-bipyridine derivatives was carried out using various modifications of the "1,2,4-triazine" methodology in order to select a model oxidizing agent, which must have high stability under assay conditions, a high molar absorptivity coefficient, and good solubility in solvents. It was shown that complex-forming ability, especially with Fe(III), increases when halogens are introduced into the 2,2'-bipyridine. Characteristics of the complex compounds were evaluated both in solution and in thin layers. Promising complex compounds were identified. Properties of the complexes, such as high stability, contrast, and solubility, enable their use in portable devices and ensure reliable results. AOC was determined for a number of model antioxidant solutions, ethanol extracts of plant materials, and supplements, containing ascorbic acid and α-tocopherol, using the test system. Comparative studies with spectrophotometry using selected complex showed a high level of concordance between the results. Thus, the semi-quantitative test system allows for express and accurate in site analysis. It can be used for analyzing a wide variety of substances.