*2.6. Superoxide Anion Radical Scavenging Capacity Assay*

Superoxide anion radicals were generated with xanthine/XO and determined as described in a previous paper of ours [31]. EGCG and the POSS–EGCG conjugate were first dissolved in the mixed solvent of DMSO and DPBS (pH 7.4) and diluted with DPBS. To measure the superoxide anion radical scavenging capacity, xanthine (30 μg/mL) was added to DPBS containing ethylenediaminetetraacetic acid (EDTA, 15 μg/mL), XO (40 milliunits/mL), NBT (130 μg/mL), and various concentrations of test sample. Changes in the absorbance at 560 nm over 10 min were recorded as a measure of the changing number of superoxide anion radicals.

The superoxide anion radical scavenging capacity of samples was determined according to the following formula.

$$\text{L'superoxoide anion radical scavenging capacity } (\%) = \frac{\text{Abs}\_{\text{control}} - \text{Abs}\_{\text{sample}}}{\text{Abs}\_{\text{control}}} \times 100\%$$

where Abscontrol is the absorbance of control in the absence of sample and Abssample is the absorbance in the presence of samples.
