Question

Why does the absorbance of ABTS solution decrease after an
antioxidant is added?

Answer 1

The absorbance of ABTS solution decreases after an antioxidant is added because the antioxidant reduces the ABTS, disrupting its conjugated system, which alters its ability to absorb light and results in a color change indicative of reduced absorbance.

Step-by-step explanation:

The absorbance of an ABTS solution decreases after an antioxidant is added because antioxidants are reducing agents. ABTS, which has an extended system of conjugated pi bonds, absorbs light in the visible range, and the absorbance is seen when these bonds are intact. When an antioxidant is introduced, it donates an electron to the ABTS, which disrupts the conjugated system and reduces the molecule. This reduction alters the electronic structure of ABTS, thereby reducing its ability to absorb light at specific wavelengths, which causes the decrease in absorbance observed.

As an example, ascorbic acid (vitamin C) is a well-known antioxidant that can donate electrons to neutralize free radicals or reduce other molecules. In the presence of the antioxidant, the ABTS molecule is reduced and the characteristic color may fade, demonstrating a lower absorbance in a visible light spectrophotometry assay.

Answer 2

The antioxidant reduces the ABTS radical, causing a decrease in its absorbance. This indicates the antioxidant's ability to neutralize oxidative agents in the solution.

The decrease in absorbance of an ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) solution after adding an antioxidant is indicative of the antioxidant's ability to neutralize free radicals or oxidizing agents present in the solution.

ABTS is commonly used to measure antioxidant activity. It's initially in its radical cation form, ABTS•+, which has a characteristic blue-green color and absorbs light at a specific wavelength. When an antioxidant is introduced to the ABTS solution, it can donate electrons to the ABTS•+ radical, converting it back to its colorless reduced form, ABTS. As a result, the intensity of the blue-green color diminishes, leading to a decrease in absorbance at the specific wavelength.

This reduction in absorbance indicates the antioxidant's capacity to scavenge or neutralize free radicals or reactive oxygen species, demonstrating its antioxidative potency. Essentially, the stronger the antioxidant, the greater the decrease in absorbance observed due to its ability to counteract oxidation in the ABTS solution.