DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is an algicide and herbicide of the aryl urea class that inhibits

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. It was introduced by Bayer in 1954 under the trade name of Diuron.

History

In 1952, chemists at E. I. du Pont de Nemours and Company patented a series of aryl urea derivatives as herbicides. Several compounds covered by this patent were commercialized as herbicides: monuron (4-chlorophenyl),

chlortoluron Chlortoluron or chlorotoluron are the common names for an organic compound of the phenylurea class of herbicides used to control broadleaf and annual grass weeds in cereal crops. History In 1952, chemists at E. I. du Pont de Nemours and Company pa ...

(3-chloro-4-methylphenyl) and DCMU, the (3,4-dichlorophenyl) example. Subsequently, over thirty related urea

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with the same mechanism of action reached the market worldwide.

Synthesis

As described in the du Pont patent, the starting material is a substituted aryl

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

, an

aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine. It is an industrially significant commodity chemical, as well as a versatile start ...

, which is treated with

phosgene Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, es ...

to form its isocyanate derivative. This is subsequently reacted with dimethylamine to give the final product. :Aryl-NH₂ + COCl₂ → Aryl-NCO :Aryl-NCO + NH(CH₃)₂ → Aryl-NHCON(CH₃)₂

Mechanism of action

DCMU is a very specific and sensitive inhibitor of photosynthesis. It blocks the Q_B plastoquinone binding site of

photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photos ...

, disallowing the electron flow from photosystem II to plastoquinone. This interrupts the photosynthetic

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couple ...

in photosynthesis and thus reduces the ability of the plant to turn light energy into chemical energy (

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and reductant potential). DCMU only blocks electron flow from photosystem II, it has no effect on photosystem I or other reactions in photosynthesis, such as light absorption or carbon fixation in the Calvin cycle. However, because it blocks electrons produced from water oxidation in PS II from entering the plastoquinone pool, "linear" photosynthesis is effectively shut down, as there are no available electrons to exit the photosynthetic electron flow cycle for reduction of NADP⁺ to NADPH. In fact, it was found that DCMU not only does not inhibit the cyclic photosynthetic pathway, but, under certain circumstances, actually stimulates it. Because of these effects, DCMU is often used to study energy flow in

Toxicity

DCMU (Diuron) has been characterized as a known/likely human carcinogen based on animal testing.

References

{{Herbicides Herbicides Ureas Toxicology Anilines Chlorobenzenes Carcinogens