Jodination

Jodination, commonly spelled iodination in English, is the chemical process of introducing iodine into a substrate. It is used in organic synthesis, biochemistry, and radiochemistry to modify molecules, enable detection, or adjust biological activity. While the exact spelling varies by language, the underlying concept is the same: the addition or incorporation of iodine into a molecule.

In organic chemistry, iodination is usually accomplished by electrophilic iodination or radical methods. Electrophilic iodination uses I2 or N-iodosuccinimide (NIS) with a catalyst to generate an electrophilic iodine that adds to double bonds or substitutes on arenes. Alkenes yield iodoalkanes or halohydrins depending on water; alkynes form vinyl iodides. Radical iodination uses initiators to abstract hydrogen and install iodine, with selectivity guided by substrate and conditions.

In biochemistry, iodination describes enzymatic incorporation of iodine into tyrosine residues to form monoiodotyrosine and diiodotyrosine, a key step in thyroid hormone biosynthesis. The reaction is catalyzed by thyroid peroxidase and requires iodide and hydrogen peroxide.

In radiochemistry, isotopes such as I-125 and I-131 are used to label biomolecules for imaging or therapy. Reagents like chloramine-T, Iodogen, or Bolton-Hunter facilitate the labeling under controlled conditions. Safety and regulatory controls are essential due to iodine's toxicity and the radiological hazards.

See also iodination, halogenation, radiolabeling.