Colorimetric Determination of Sulfoxy Radicals and Sulfoxy Radical Scavenging-Based Antioxidant Activity

Çiğdem Aşilioğlu; Seda Uzunboy; Sema Demirci-Çekiç; Reşat Apak

doi:10.1021/acsomega.3c03194

Colorimetric Determination of Sulfoxy Radicals and Sulfoxy Radical Scavenging-Based Antioxidant Activity

ACS Omega. 2023 Sep 27;8(40):36764-36774. doi: 10.1021/acsomega.3c03194. eCollection 2023 Oct 10.

Authors

Çiğdem Aşilioğlu¹, Seda Uzunboy², Sema Demirci-Çekiç², Reşat Apak^{2

3}

Affiliations

¹ Department of Chemistry, Institute of Graduate Studies, Istanbul University-Cerrahpaşa, Avcilar, Istanbul 34320, Turkey.
² Department of Chemistry, Faculty of Engineering, Istanbul University-Cerrahpasa, Avcilar, Istanbul 34320, Turkey.
³ Turkish Academy of Sciences (TUBA), Vedat Dalokay St. No. 112, Cankaya, Ankara 06670, Turkey.

Abstract

Sulfoxy radicals (SORs) are oxygen- and sulfur-containing species such as SO₃^•-, SO₄^•-, and SO₅^•-. They can be physiologically generated by S(IV) autoxidation with transition metal catalysis. Due to their harmful effects, the detection of both SORs and their scavengers are important. Here, a simple and cost-effective method for the determination of SORs and the scavenging activity of different antioxidant compounds was proposed. A SOR was selectively generated by combining CoSO₄·7H₂O with Na₂SO₃. To detect SOR species as a whole, 3,3',5,5'-tetramethylbenzidine (TMB) was used as the chromogenic reagent, where SOR generated in the medium caused the formation of a blue-colored diimine from TMB. Additionally, the SOR scavenging effects of a number of antioxidant compounds (AOx) belonging to different classes were investigated, among which catechin derivatives were the most effective scavengers. The obtained results were compared with those of a reference rhodamine B decolorization assay. The radical scavenging effects of the tested AOx were ranked by both assays and then compared using the Spearman statistical test to yield a very strong correlation between the two rankings. The method was applied to real samples such as catechin-rich tea, that is, white, black, and green tea, among which white tea was determined as the most effective SOR scavenger.