Carbon dioxide basic water illustrates this property, in which case hydroxide is the nucleophile. Other nucleophiles react as well. For example, carbanions as provided by Grignard reagents and organolithium compounds react with to give carboxylates: In metal carbon dioxide complexes, serves as a ligand, which can facilitate the conversion of to other chemicals. The reduction of to CO is ordinarily a difficult and slow reaction: Photoautotrophs (i.e. plants and cyanobacteria) use the energy contained in sunlight to photosynthesize simple sugars from absorbed from the air and water: The redox potential for this reaction near pH 7 is about −0.53 V "versus" the
Carbon dioxide to prevent oxidation, though it has the problem that it can dissolve into the wine, making a previously still wine slightly fizzy. For this reason, other gases such as nitrogen or argon are preferred for this process by professional wine makers. Carbon dioxide is often used to "stun" animals before slaughter. "Stunning" may be a misnomer, as the animals are not knocked out immediately and may suffer distress. It is one of the most commonly used compressed gases for pneumatic (pressurized gas) systems in portable pressure tools. Carbon dioxide is also used as an atmosphere for welding, although in the