4. The reaction was stopped by the addition of SDS (final concentration of 1.35%), and lipid peroxidation products were measured by the addition of acetic acid/HCl buffer, pH 3.4 and 0.6% TBA, pH 6.0.

The color reaction was developed by incubating tubes in boiling water for 60 min. TBARS levels were measured at 532 nm. The radical scavenging activities of the compounds were determined as previously described (Brand-Williams et al., 1995). Each compound was tested at 6.25, 12.5, 25, 50, 100, 200, and 400 μM in 10% DMSO. Seven different concentrations of ascorbic acid (6.25; 12.5; 25; 50; 100; 200; 400 μM) were used as positive controls. DPPH (diluted Ipilimumab mouse in ethanol) was added to final concentration of 0.3 mM and allowed to react at room temperature for 30 min in dark GSK2118436 cell line conditions. The absorbance was measured at 518 nm using Spectra Max Plate Reader®

M2 (Molecular Devices), Sunnyvale, California, USA. The total antioxidant potential of the mono- and diselenides was evaluated by the phosphomolybdenum method as previously described (Prieto et al., 1999). A sample solution aliquot in ethanol (0.3 ml) was combined in a vial with reagent solution (0.6 M sulfuric acid, 28 mM sodium phosphate and 4 mM ammonium molybdate, 3 ml). The compounds were tested a concentration of 400 μM. The vials were capped and incubated in a water bath at 95 °C for 90 min. After cooling the mixture to room temperature, the absorbance was measured at 695 nm against a blank control. The GPx catalytic activity of mono- and diselenides was evaluated utilizing 10 mM benzenethiol (PhSH) as a substrate, as previously described (Iwaoka and Tomoda, 1994). The H2O2 reduction was monitored at 305 nm for 150 s. The compounds were tested at concentrations of 200 and 400 μM.

DMSO was used as a negative control (vehicle). Thiol oxidase activity of 200 and 400 μM concentrations of the compounds (C1–C4) was determined in a medium containing 10 mM Tris/HCl buffer (pH 7.4) and 1 mM glutathione or PhSH. An aliquot of 100 μL was removed at different time points (0, 30, 60 and 120 min) and added to a solution containing 0.5 mM DTNB and 10 mM Tris/HCl buffer (in the absence of thiol oxidation a maximum of 100 nmol of –SH/ml can be found). The absorbance of each sample Cell Penetrating Peptide was measured at 412 nm (Ellman, 1959). The reduction of mono- and diselenides (15 μM) by rat hepatic TrxR was performed by a modification of the method previously described by Holmgren and Bjornstedt (1995). TrxR was mixed with a medium containing 10 mM Tris–HCl, 1 mM EDTA, pH 7.5, in the presence or absence of selenide compounds and then, the reaction was started by adding NADPH (final concentration 120 μM). The Fe(II)-chelating ability of compounds was determined using a modified method of Puntel et al. (2005). Freshly prepared 500 μmol/L Fe(II) (150 μL) was added to a reaction mixture containing 168 μL of 0.1 mol/L Tris–HCl (pH 7.4), 218 μL saline and the compounds (100 μM).