DQ (Diquat)
Definition and meaning of DQ (Diquat) in chemistry.
DQ (diquat) is a fast-acting, nonselective bipyridylium herbicide and crop desiccant that kills plant tissue on contact by generating reactive oxygen species inside chloroplasts.
In more detail
Diquat is a quaternary ammonium salt built from a fused bipyridyl (viologen-type) ring system, sold commercially as the dibromide salt. In sunlight, the diquat dication intercepts electrons from photosystem I, forming a stable radical cation that immediately reduces molecular oxygen to superoxide and other reactive oxygen species. These oxidants rupture cell membranes within hours, causing rapid wilting and browning of foliage. Because it damages only the tissue it contacts and does not translocate well to roots, diquat is valued for quick crop desiccation before harvest and for controlling submerged and floating aquatic weeds, unlike systemic herbicides such as glyphosate.
Key facts
| Field | Organic Chemistry |
|---|---|
| Formula (dibromide salt) | C12H12Br2N2 |
| Chemical class | Bipyridylium (viologen-type) quaternary ammonium herbicide |
| Mechanism | Accepts electrons from photosystem I, generating superoxide radicals |
Diquat dibromide is sprayed onto potato fields a few days before harvest to rapidly kill the leafy foliage (haulm), which stops tuber growth and makes mechanical harvesting easier.
Frequently asked questions
Is DQ (diquat) the same compound as paraquat?
No. Both are bipyridylium herbicides that kill plants by generating reactive oxygen species via photosystem I, but they are structurally distinct molecules (diquat has a fused bicyclic pyrazinediium ring) with different toxicity profiles and regulatory histories.
Why does diquat kill plants so quickly compared to glyphosate?
Diquat directly disrupts photosynthetic electron transport to produce membrane-destroying reactive oxygen species within hours, whereas glyphosate must be absorbed and translocated to block an amino acid synthesis pathway, a slower process.