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Molecular Redox Reactions

Defines molecular redox reactions.

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Foods with Superpowers?

Foods with Superpowers?

Credit: Kyle McDonald
Source: http://www.flickr.com/photos/kylemcdonald/3443105556/
License: CC BY-NC 3.0

Blueberries, beets, kale, and various other foods are sometimes marketed as health-promoting “superfoods.” One of the most common reasons for a food to receive this label is that it contains a high level of antioxidants. What exactly are antioxidants, and why might they be good for our health?

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  • Oxygen-based free radicals will forcibly remove electrons from nearby molecules, including DNA, proteins, and cellular membranes. These molecules then become free radicals themselves, which may result in a chain reaction.
  • Antioxidants neutralize free radicals by providing a source of electrons. The unpaired electron that remains on the antioxidant molecule is stabilized, either by resonance or by being on a larger atom like sulfur. This results in a much less reactive free radical that is less likely to cause oxidative damage.
  • When attacking another molecule, free radicals often remove an H+ ion along with an electron. For oxygen-based radicals, this transfer of a hydrogen atom (one proton plus one electron) results in the formation of a new O-H bond.
  • It should be noted that, although damage from free radicals has been linked to aging and various diseases, it is still not clear whether consuming large amounts of antioxidants has beneficial effects on your health.
  • "Superfood" has become a marketing term used by food companies to sell more products. Since there is no regulations regarding the naming of "superfoods", do not be fooled by savvy marketing. 
  • Credit: Esperluette
    Source: http://www.flickr.com/photos/esperbot/8506627580/
    License: CC BY-NC 3.0

    Food companies are cashing in on the demand for "superfoods" [Figure2]

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With the links below, learn more about bond energies, free radicals, and antioxidants. Then answer the following questions.

  1. A typical free radical reaction might involve an OH radical (in which oxygen has only 7 valence electrons) taking a hydrogen atom from a C-H bond in a nearby organic molecule, leaving behind an unpaired electron on the carbon atom. The net result is the formation of an O-H bond at the expense of a C-H bond. Calculate the approximate change in enthalpy for this reaction.
  2. Our bodies produce their own antioxidant molecules, the most important of which is probably glutathione. Each molecule of glutathione has an S-H bond that can act as a sacrificial hydrogen atom donor, thus preventing the rupturing of C-H bonds in molecules that serve various other functions. Calculate the approximate change in enthalpy when an OH radical removes a hydrogen atom from glutathione.
  3. After glutathione reacts with a free radical, it is still left with an unpaired electron on the sulfur atom. Why is this sulfur-based radical unlikely to react with any nearby C-H bonds? Use a calculation to support your answer.
  4. What are some potential adverse side effects of having excessively high levels of antioxidants in your body?

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Image Attributions

  1. [1]^ Credit: Kyle McDonald; Source: http://www.flickr.com/photos/kylemcdonald/3443105556/; License: CC BY-NC 3.0
  2. [2]^ Credit: Esperluette; Source: http://www.flickr.com/photos/esperbot/8506627580/; License: CC BY-NC 3.0

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