Definition

A nonmetallic element of the halogen group that is represented by the atomic symbol I, atomic number 53, and atomic weight of 126.90. It is a nutritionally essential element, especially important in thyroid hormone synthesis. In solution, it has anti-infective properties and is used topically. Elemental iodine (I2) is poisonous if taken orally in larger amounts; 2?3 grams of it is a lethal dose for an adult human.; Elemental iodine is an oxidizing irritant and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine are capable of causing tissue damage if use for cleaning and antisepsis is prolonged.; In many ways, 129I is similar to 36Cl. It is a soluble halogen, fairly non-reactive, exists mainly as a non-sorbing anion, and is produced by cosmogenic, thermonuclear, and in-situ reactions. In hydrologic studies, 129I concentrations are usually reported as the ratio of 129I to total I (which is virtually all 127I). As is the case with 36Cl/Cl, 129I/I ratios in nature are quite small, 10?14 to 10?10 (peak thermonuclear 129I/I during the 1960s and 1970s reached about 10?7). 129I differs from 36Cl in that its halflife is longer (15.7 vs. 0.301 million years), it is highly biophilic, and occurs in multiple ionic forms (commonly, I? and IO3?) which have different chemical behaviors. This makes it fairly easy for 129I to enter the biosphere as it becomes incorporated into vegetation, soil, milk, animal tissue, etc.; Iodic acid (HIO3) and its salts are strong oxidizers. Periodic acid (HIO4) cleaves vicinal diols along the C-C bond to give aldehyde fragments. 2-Iodoxybenzoic acid and Dess-Martin periodinane are hypervalent iodine oxidants used to specifically oxidize alcohols to ketones or aldehydes. Iodine pentoxide is a strong oxidant as well.; Iodine (pronounced /?a?.?da?n/ EYE-o-dyne, /?a?.?d?n/ EYE-o-d?n, or in chemistry /?a?.?di?n/ EYE-o-deen; from Greek: ????? iodes 'violet'), is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons. Chemically, iodine is the second least reactive of the halogens, and the second most electropositive halogen, trailing behind astatine in both of these categories. However, the element does not occur in the free state in nature. As with all other halogens (members of Group 17 in the periodic table), when freed from its compounds iodine forms diatomic molecules (I2).; Iodine forms many compounds. Potassium iodide is the most commercially significant iodine compound. It is a convenient source of the iodide anion; it is easier to handle than sodium iodide because it is not hygroscopic. Sodium iodide is especially useful in the Finkelstein reaction, because it is soluble in acetone, while potassium iodide is poorly so. In this reaction, an alkyl chloride is converted to an alkyl iodide. This relies on the insolubility of sodium chloride in acetone to drive the reaction:; Iodine is a common general stain used in thin-layer chromatography. It is also used in the Gram stain as a mordant, after the sample is treated with crystal violet.; Iodine is an essential trace element for life, the heaviest element commonly needed by living organisms, and the second-heaviest known to be used by any form of life (only tungsten, a component of a few bacterial enzymes, has a higher atomic number and atomic weight). Iodine's main role in animal biology is as constituents of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These are made from addition condensation products of the amino acid tyrosine, and are stored prior to release in an iodine-containing protein called thyroglobulin. T4 and T3 contain four and three atoms of iodine per molecule, respectively. The thyroid gland actively absorbs iodide from the blood to make and release these hormones into the blood, actions which are regulated by a second hormone TSH from the pituitary. Thyroid hormones are phylogenetically very old molecules which are synthesized by most multicellular organisms, and which even have some effect on unicellular organisms.; Iodine is an essential trace element. Chemically, iodine is the least reactive of the halogens, and the most electropositive halogen after astatine. However, iodine does not occur in the free state in nature. As with all other halogens , when freed from its compounds iodine forms diatomic molecules (I2).; Iodine and its compounds are primarily used in medicine, photography, and dyes. Iodine is required for the production of thyroid hormones, which are essential for normal brain development, and the fetus, newborn, and young child are particularly vulnerable to iodine deficiency. Physiologically, iodine exists as an ion in the body. The iodine requirement increases during pregnancy and recommended intakes are in the range of 220-250 microg/day. Monitoring iodine status during pregnancy is a challenge. New recommendations from World Health Organization suggest that a median urinary iodine concentration >250 microg/L and <500 microg/L indicates adequate iodine intake in pregnancy. Based on this range, it appears that many pregnant women in have inadequate intakes. Thyroid-stimulating hormone concentration in the newborn is a sensitive indicator of mild iodine deficiency in late pregnancy. The potential adverse effects of mild iodine deficiency during pregnancy are uncertain. Controlled trials of iodine supplementation in mildly iodine-deficient pregnant women suggest beneficial effects on maternal and newborn serum thyroglobulin and thyroid volume, but no effects on maternal and newborn total or free thyroid hormone concentrations. There are no long-term data on the effect of iodine supplementation on birth outcomes or infant development. New data from well-controlled studies indicate that iodine repletion in moderately iodine-deficient school-age children has clear benefits: it improves cognitive and motor function; Iodine under standard conditions is a shiny grey solid. It can be seen apparently sublimating at standard temperatures into a violet-pink gas that has an irritating odor. This halogen forms compounds with many elements, but is less reactive than the other members of its Group VII (halogens) and has some metallic light reflectance.; Iodine-129 (129I; half-life 15.7 million years) is a product of cosmic ray spallation on various isotopes of xenon in the atmosphere, in cosmic ray muon interaction with tellurium-130, and also uranium and plutonium fission, both in subsurface rocks and nuclear reactors. Artificial nuclear processes, in particular nuclear fuel reprocessing and atmospheric nuclear weapons tests, have now swamped the natural signal for this isotope. Nevertheless, it now serves as a groundwater tracer as indicator of nuclear waste dispersion into the natural environment. In a similar fashion, 129I was used in rainwater studies to track fission products following the Chernobyl disaster.; The most common compounds of iodine are the iodides of sodium (NaI) and potassium (KI) and the iodates (KIO3), as elemental iodine is mildly toxic to all living things. Normal iodine is an essential precursor for the manufacture of thyroid hormone.; it also increases concentrations of insulin-like growth factor 1 and insulin-like growth factor-binding protein 3, and improves somatic growth. (PMID: 17956157)

Description

Iodine is a chemical element that has the symbol I and atomic number 53. Chemically, iodine is the second least reactive of the halogens, and the second most electropositive halogen; trailing behind astatine in both of these categories. However, the element does not occur in the free state in nature. As with all other halogens, when freed from its compounds iodine forms diatomic molecules. Iodine naturally occurs in the environment chiefly as a dissolved iodide in seawater, although it is also found in some minerals and soils. Iodine is an essential trace element for life, mainly as constituents of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Iodine-131 is used in nuclear medicine both diagnostically and therapeutically. Examples of its use in radiation therapy include the treatment of thyrotoxicosis and thyroid cancer. Diagnostic tests exploit the mechanism of absorption of iodine by the normal cells of the thyroid gland. Iodine-131 is also used as a radioactive label for radiopharmaceuticals that can be used for imaging and therapy. (L1845, L1846)

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