Kelp Keeps Iodide As An Antioxidant

Iodine was first discovered in kelp two centuries ago, but its bioactive chemical form and function have remained a mystery. Now, a research team led by Frithjof C. Küpper of the Scottish Association for Marine Science, in Scotland, has determined that iodide ions are stored in kelp cell walls and serve as antioxidants when they are released in response to exposure to ozone or aqueous oxidants such as hydrogen peroxide (Proc. Natl. Acad. Sci. USA 2008, 105, 6954). The researchers used X-ray absorption spectroscopy to identify I^- as the chemical species. Extended X-ray absorption fine structure spectroscopy indicated that I^- is not surrounded by water but rather forms noncovalent associations with biomolecules such as carbohydrates, polyphenols, and proteins. The group further found that in response to oxidative stress kelp releases I^- into the surrounding water, where it may react with O₃ to form I₂ and O₂. Photolysis of I₂ on the seaweed surface may then contribute to the formation of aerosol particles over kelp fields in the daytime.