New data on iodine in seaweed

Randy Holmes-Farley

Reef Chemist
Premium Member
Shows it is used as an antioxidant in kelp:

Full article is here:

http://www.pnas.org/cgi/reprint/0709959105v1



Proc Natl Acad Sci U S A. 2008 May 13;105(19):6954-8. Epub 2008 May 5.

Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry.

Küpper FC, Carpenter LJ, McFiggans GB, Palmer CJ, Waite TJ, Boneberg EM, Woitsch S, Weiller M, Abela R, Grolimund D, Potin P, Butler A, Luther GW 3rd, Kroneck PM, Meyer-Klaucke W, Feiters MC.

Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll PA37 1QA, Scotland, United Kingdom. fck@sams.ac.uk

Brown algae of the Laminariales (kelps) are the strongest accumulators of iodine among living organisms. They represent a major pump in the global biogeochemical cycle of iodine and, in particular, the major source of iodocarbons in the coastal atmosphere. Nevertheless, the chemical state and biological significance of accumulated iodine have remained unknown to this date. Using x-ray absorption spectroscopy, we show that the accumulated form is iodide, which readily scavenges a variety of reactive oxygen species (ROS). We propose here that its biological role is that of an inorganic antioxidant, the first to be described in a living system. Upon oxidative stress, iodide is effluxed. On the thallus surface and in the apoplast, iodide detoxifies both aqueous oxidants and ozone, the latter resulting in the release of high levels of molecular iodine and the consequent formation of hygroscopic iodine oxides leading to particles, which are precursors to cloud condensation nuclei. In a complementary set of experiments using a heterologous system, iodide was found to effectively scavenge ROS in human blood cells.
 
<a href=showthread.php?s=&postid=12546246#post12546246 target=_blank>Originally posted</a> by fatrip
that is pretty neat...but what are reactive oxygen species? lol...

An unbalanced oxygen(s) ion(s) ( peroxides, and other oxygen ions) with an imbalance in valance electrons. This makes them highly reactive to further bonding.

Hopefully Randy chimes in here :)
 
Interesting bit from the article, which I would not have expected:

"indicating that the iodide ion in Laminaria is not surrounded by a complete shell of water oxygens but instead is noncovalently associated with biomolecules such as carbohydrates, polyphenols, or proteins."

That may imply a mechanism for iodide to be removed by skimming. I had assumed that iodide did not bind strongly to organics in seawater, and so had previously assumed it had to be skimmed as covalent organoiodine forms, but that may not be the case.
 
Okay, non-covalently I can understand, but what is meant by "associated" in this case? Something like hydrogen bonds?
 
<a href=showthread.php?s=&postid=12552481#post12552481 target=_blank>Originally posted</a> by bertoni
Okay, non-covalently I can understand, but what is meant by "associated" in this case? Something like hydrogen bonds?

You've got the right idea. In this case H-bonds are impossible because the iodide doesn't have hydrogen ;) Here we'd be talking more along the lines of electrostatic attraction.
 
<a href=showthread.php?s=&postid=12557283#post12557283 target=_blank>Originally posted</a> by madadi
so is this more of a reason we should dose iodine, especially if we have a large skimmer?

This just shows what brown algaes use iodine for. It doesn't say anything about iodine depletion in our tanks, or uses in corals ;)
 
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