In biology, an adduct is a complex that forms when a chemical binds to a biological molecule, such as DNA or protein. DNA adducts are altered forms of DNA that occur as the result of exposure to carcinogens (in the case of smokers these would be the carcinogens present in cigarette smoke). A DNA adduct, once formed, can be repaired, resulting in a return to the original DNA structure or be mis-repaired, resulting in a mutation. Protein adducts do not have adverse biological effects but can be used as a measure of exposure to a foreign substance.
An adduct (from the Latin adductus, "drawn toward") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components, with formation of two chemical bonds and a net reduction in bond multiplicity in at least one of the reactants. The resultant is considered a distinct molecular species. Examples include the adduct between hydrogen peroxide and sodium carbonate to give sodium percarbonate, and the addition of sodium bisulfite to an aldehyde to give a sulfonate.
Adducts often form between Lewis acids and Lewis bases. A good example would be the formation of adducts between the Lewis acid borane and the oxygen atom in the Lewis bases, tetrahydrofuran (THF) or diethyl ether: BH3•THF, BH3•OEt2.
A ball-and-stick model of the Lewis adduct between BH3 and THF