New complex iron with various functionalized 2,2'-bipyridine derivatives in evaluation of total lipophilic and hydrophilic antioxidant capacity by the potentiometry

The potentiometric approach for determining the integral antioxidant capacity was developed. The reaction of antioxidants with new complexes of the iron with target functionalized 2,2'-bipyridine derivatives was used as a signal-forming reaction. The approach allows the joint determination of hydrophilic and lipophilic antioxidants, which is especially important in the analysis of plant samples with a complex composition. A number of new 2,2'-bipyridine derivatives have been synthesized. It has been shown that the complexing ability, especially with Fe(III), is increased by introducing halogens into the structure of 2,2'-bipyridine. The solubility of the complexes in polar solutions is increased by introducing the triethylene glycol fragment into the 2,2'-bipyridine at the aryl substituent in the C5 position. The electrochemical behavior of the complexes with Fe(II) and Fe(III) was studied. The metal - ligand ratios and stability constants of the complexes were estimated by the voltammetric method (the values of the conditional stability constants ranged from 1∙10⁸ to 5∙10¹⁰). Individual antioxidants with different solubilities and cereal extracts, containing antioxidants of different hydrophilicity, were studied by the potentiometric method using promising synthesized complexes. Recovery is about 100%. Relative standard deviation for promising complexes does not exceed 9%. Since the synthesized complexes have a color, they were used in the spectrophotometric method for correlation studies. In addition, the spectrophotometric method using the stable 2,2'-diphenyl-1-picrylhydrazyl radical was chosen as a comparison method. It has been shown that spectrometry using both new complex compounds and the 2,2'-diphenyl-1-picrylhydrazyl radical has limitations in the analysis of colored samples. Since food products are colored, this complicates the analysis by optical methods. Correlations between methods were established in cases of uncolored extracts. Thus, the developed potentiometric approach is not only simple and informative, but can also be used for a wider range of objects.