Oxalat

Oxalate is the dianion derived from oxalic acid, with the chemical formula C2O4^2-. It also denotes the salts and esters of oxalic acid. In chemistry, oxalate often acts as a bidentate ligand, capable of forming chelate rings with a variety of metals to give metal oxalate complexes. Common oxalate salts include calcium oxalate (CaC2O4) and sodium oxalate (Na2C2O4).

In nature, oxalate occurs widely in plants and is frequently deposited as calcium oxalate crystals in tissues. This storage form can deter herbivory and protect plants from certain stresses. Foods of plant origin commonly contain oxalate at varying levels, including spinach, rhubarb, beets, nuts, and tea. Dietary oxalate availability varies with food type and preparation.

In humans and other animals, oxalate is produced endogenously and excreted primarily through urine. It can bind minerals such as calcium to form calcium oxalate, which is the main constituent of kidney stones. Excess urinary oxalate may result from high dietary intake, impaired metabolism, or certain genetic disorders such as primary hyperoxaluria. Oxalate also acts as an anti-nutrient by reducing the absorption of minerals like calcium and iron when present in high concentrations.

Applications in chemistry and materials science include the use of oxalate and its salts as chelating agents and ligands in coordination chemistry. Metal oxalates are studied for their crystal structures and properties, and calcium oxalate has long been a focus in medical contexts due to its role in kidney stone formation.