Iodide

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"i-" redirects here. For the Internet-related prefix i-, see Wiktionary's entry i-.

An iodide ion is an iodine atom with a −1 charge [1]. Compounds with iodine in formal oxidation state −1 are called iodides. This can include ionic compounds such as caesium iodide or covalent compounds such as phosphorus triiodide. This is the same naming scheme as is seen with chlorides and bromides. The chemical test for an iodide compound is to acidify the aqueous compound by adding some drops of acid, to dispel any carbonate ions present, then adding lead(II) nitrate, yielding a bright yellow precipitate of lead iodide. Most ionic iodides are soluble, with the exception of yellow silver iodide and yellow lead iodide. Aqueous solutions of iodide dissolve iodine better than pure water due to the formation of complex ions:

I−(aq) + I2(s) ⇌ I3−(aq)

The color of new triiodide ions formed is brown.

Contents

Examples

Examples or common iodides include:

Iodide as an antioxidant

Iodide can function as an antioxidant as it is a reducing species that can detoxify reactive oxygen species such as hydrogen peroxide. Over three billion years ago, blue-green algae were the most primitive oxygenic photosynthetic organisms and are the ancestors of multicellular eukaryotic algae (1). Algae that contain the highest amount of iodine (1-3 % of dry weight) and peroxidase enzymes, were the first living cells to produce poisonous oxygen in the atmosphere [2][3]. Therefore algal cells required a protective antioxidant action of their molecular components, in which iodides, through peroxidase enzymes, seem to have had this specific role [4][5] [6]. In fact, iodides are greatly present and available in the sea, where algal phytoplankton, the basis of marine food-chain, acts as a biological accumulator of iodides, selenium, (and n-3 fatty acids) [7][8] [9]:

Antioxidant biochemical mechanism of iodides [10]

2 I− → I2 + 2 e− (electrons) = −0.54 Volt ;
2 I− + Peroxidase + H2O2 + 2 Tyrosine → 2 Iodo-Tyrosine + H2O + 2 e− (antioxidants);
2 e− + H2O2 + 2 H+ (of intracellular water-solution) → 2 H2O

Antioxidant biochemical mechanism of iodides, probably one of the most ancient mechanisms of defense from poisonous reactive oxygen species:

2 I− + Peroxidase + H2O2 + Tyrosine, Histidine, Lipids, Carbons -> Iodo-Compounds + H2O + 2 e− (antioxidants)

Iodo-Compounds: Iodo-Tyrosine, Iodo-Histidine, Iodo-Lipids, Iodo-Carbons.

Clinical Use

Iodide (>6mg/day) can be used to treat patients with hyperthyroidism due to its ability to block the release of thyroid hormone (TH), known as the Wolff-Chaikoff Effect, from the thyroid gland. In fact, prior to 1940, iodides were the predominant antithyroid agents. In large doses, iodides inhibit proteolysis of thyroglobulin. This permits TH to be synthesized and stored in colloid, but not released into the bloodstream.

Of note, this treatment is seldom used today as a stand-alone therapy despite the rapid improvement of patients immediately following administration. The major disadvantage of iodide treatment lies in the fact that excessive stores of TH accumulate, slowing the onset of action of thioamides (TH synthesis blockers). Additionally, the functionality of iodides fade after the initial treatment period. An "escape from block" is also a concern, as extra stored TH may spike following discontinuation of treatment.

See also

HI He
LiI BeI2 BI3 CI4 NI3 I2O4 I2O5 I4O9 IF IF3 IF5 IF7 Ne
NaI MgI2 AlI3 SiI4 PI3 S ICl ICl3 Ar
KI CaI2 Sc TiI4 V Cr MnI2 Fe Co NiI2 CuI ZnI2 Ga2I6 GeI2 GeI4 As Se IBr Kr
RbI SrI2 Y ZrI4 Nb Mo Tc Ru Rh Pd AgI CdI2 InI3 SnI4 SnI2 SbI3 TeI4 I Xe
CsI BaI2 Hf Ta W Re Os Ir Pt AuI HgI2 TlI PbI2 Bi Po At Rn
Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo
↓
La Ce Pr Nd Pm SmI2 Eu Gd TbI3 Dy Ho Er Tm Yb Lu
Ac ThI4 Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr


References

  1. ^ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 
  2. ^ Küpper FC, Feiters MC, Meyer-Klaucke W, Kroneck PMH, Butler A (2002) Iodine Accumulation in Laminaria (Phaeophyceae): an Inorganic Antioxidant in a Living System? Proceedings of the 13th Congress of the Federation of European Societies of Plant Physiology, Heraklion, Greece, September 2-6, p. 571
  3. ^ Küpper FC, Schweigert N, Ar Gall E, Legendre J-M, Vilter H, Kloareg B (1998) Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide. Planta 207:163-171
  4. ^ Ar Gall, E., Küpper, F.C. & Kloareg, B. (2004). A survey of iodine content in Laminaria digitata. Botanica Marina 47: 30-37.
  5. ^ Küpper FC et al. (2008) Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry. Proc Natl Acad Sci U S A. May 5 . N PMID: 18458346
  6. ^ Venturi S, Donati FM, Venturi A, Venturi M. Environmental iodine deficiency: A challenge to the evolution of terrestrial life? Thyroid. 2000 Aug;10(8):727-9. PMID: 11014322
  7. ^ Venturi S. and Venturi M. “Iodine and Evolution”. DIMI-MARCHE NEWS, Dipartimento Interaziendale di Medicina Interna della Regione Marche (Italy), published on-line, Feb. 8, 2004: http://web.tiscali.it/iodio/
  8. ^ Venturi S, Donati FM, Venturi A, Venturi M, Grossi L, Guidi A. Role of iodine in evolution and carcinogenesis of thyroid, breast and stomach. Adv Clin Path. 2000 Jan;4(1):11-7. PMID: 10936894
  9. ^ Venturi S, Venturi M. Evolution of Dietary Antioxidant Defences. European EPI-Marker. 2007, 11, 3 :1-12
  10. ^ Venturi S, Venturi M. Iodide, thyroid and stomach carcinogenesis: evolutionary story of a primitive antioxidant? Eur J Endocrinol. 1999 Apr;140(4):371-2. N PMID: 10097259

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  • This page was last modified on 29 August 2008, at 13:15.

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