Manganese is also used in portland cement mixtures. Manganese is an important element for human health, essential for development, metabolism, and the antioxidant system. Nevertheless, excessive exposure or intake may lead to a condition known as manganism, a neurodegenerative disorder that causes dopaminergic neuronal death and symptoms similar to Parkinson's disease. The classes of enzymes that have manganese cofactors is large and includes oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The reverse transcriptases of many retroviruses (though not lentiviruses such as HIV) contain manganese. The best-known manganese-containing polypeptides may be arginase, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD).
Methylcyclopentadienyl manganese tricarbonyl ferrocene, which has also been used as an additive to gasoline. Although of no practical value, the related compound cyclopentadienyl manganese tricarbonyl (CH)Mn(CO) is also well studied. Up to two of the CO ligands in MMT can be replaced with thiocarbonyl groups, as illustrated by the compounds (CHCH)Mn(CS)CO and (CHCH)Mn(CS)(CO). The human and environmental health impacts that may result from the use of MMT will be a function of exposure to either: (1) MMT in its original, unchanged, chemical form and/or (2) manganese combustion products emitted from vehicles operating on gasoline containing MMT as an octane improver. The general public