Avan Aslı Neslihan, Demirci Çekiç Sema, Uzunboy Seda, Apak Reşat
Department of Chemistry, Faculty of Engineering, Istanbul University, 34320 Istanbul, Turkey.
Turkish Academy of Sciences (TUBA) Piyade St. No. 27, 06690 Çankaya Ankara, Turkey.
Int J Mol Sci. 2016 Aug 12;17(8):1325. doi: 10.3390/ijms17081325.
Development of easy, practical, and low-cost spectrophotometric methods is required for the selective determination of phenolic antioxidants in the presence of other similar substances. As electron transfer (ET)-based total antioxidant capacity (TAC) assays generally measure the reducing ability of antioxidant compounds, thiols and phenols cannot be differentiated since they are both responsive to the probe reagent. In this study, three of the most common TAC determination methods, namely cupric ion reducing antioxidant capacity (CUPRAC), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt/trolox equivalent antioxidant capacity (ABTS/TEAC), and ferric reducing antioxidant power (FRAP), were tested for the assay of phenolics in the presence of selected thiol and protein compounds. Although the FRAP method is almost non-responsive to thiol compounds individually, surprising overoxidations with large positive deviations from additivity were observed when using this method for (phenols + thiols) mixtures. Among the tested TAC methods, CUPRAC gave the most additive results for all studied (phenol + thiol) and (phenol + protein) mixtures with minimal relative error. As ABTS/TEAC and FRAP methods gave small and large deviations, respectively, from additivity of absorbances arising from these components in mixtures, mercury(II) compounds were added to stabilize the thiol components in the form of Hg(II)-thiol complexes so as to enable selective spectrophotometric determination of phenolic components. This error compensation was most efficient for the FRAP method in testing (thiols + phenols) mixtures.
需要开发简便、实用且低成本的分光光度法，以在存在其他类似物质的情况下选择性测定酚类抗氧化剂。基于电子转移（ET）的总抗氧化能力（TAC）测定通常测量抗氧化剂化合物的还原能力，由于硫醇和酚类对探针试剂均有响应，因此无法区分它们。在本研究中，测试了三种最常见的TAC测定方法，即铜离子还原抗氧化能力（CUPRAC）、2,2'-联氮双（3-乙基苯并噻唑啉-6-磺酸）二铵盐/特洛克斯等效抗氧化能力（ABTS/TEAC）和铁还原抗氧化能力（FRAP），用于在选定的硫醇和蛋白质化合物存在下测定酚类。尽管FRAP方法单独对硫醇化合物几乎无响应，但在将该方法用于（酚类+硫醇）混合物时，观察到了令人惊讶的过氧化现象，与加和性有很大的正偏差。在所测试的TAC方法中，对于所有研究的（酚类+硫醇）和（酚类+蛋白质）混合物，CUPRAC给出了最具加和性的结果，相对误差最小。由于ABTS/TEAC和FRAP方法分别对混合物中这些组分产生的吸光度加和性有小的和大的偏差，因此添加汞（II）化合物以Hg（II）-硫醇配合物的形式稳定硫醇组分，从而能够选择性分光光度法测定酚类组分。在测试（硫醇+酚类）混合物时，这种误差补偿对FRAP方法最为有效。
