In biochemistry, the term pyrophosphate (PPi) is used to refer to chemical compounds that encompass the esters, salts, and anion of pyrophosphoric acid. The latter, being a negatively charged anhydrous acid of phosphate, becomes reactive when heated. When suspended in water, however, the anion of pyrophosphoric acid also readily triggers the division of water molecules into hydrogen and hydroxide ions in a process called pyrophosphorolysis, which yields inorganic phosphate. Specifically, this involves the conversion of cellular adenosine triphosphate (ATP) to adenosine monophosphate (AMP).
Variances in energy load in phosphorylation reactions with proteins and other organic molecules produce different forms of pyrophosphate. The final result will always contain one of these ions, however. For instance, farnesyl pyrophosphate is obtained through the synthesis of hydrocarbons known as terpenes. Dimethylallyl pyrophosphate is a byproduct of mevalonic acid.
While these compounds are essential for normal cellular functioning in virtually all living organisms, they also play an important role in industrial chemistry. For example, disodium pyrophosphate is used in the processing of leather to prevent oxidation that may lead to staining from ferrous oxides. It is also used to improve the fluidity of cement and petroleum when added to act as a plasticizer. This substance is also added to leavened baked goods and to canned meats and seafood as a chelating agent to regulate pH of the preserving solution.
Sodium pyrophosphate has many applications in the food industry as a chelant and thickening agent. In combination with cornstarch, it is a primary ingredient in Bakewell Baking Powder, which gained notoriety during WW II when regular baking powder became scarce. This powder is still sold today as a gluten-free alternative to baking powder and cream of tartar. It is also a common food additive found in frozen foods, ready-made puddings, and some soy-based products.
This powder is also useful as a dispersion agent and oxidation preventative. In fact, it was once commonly used in laundry detergents to remove and deter the re-deposition of stains. This practice was largely discontinued in the 1970s, however, due to the negative environment impact of releasing phosphates into waterways. It is still used as a stain deterrent in commercial toothpaste, though, in addition to assisting in the removal of tartar and plaque from teeth.
Calcium pyrophosphate is also an additive to dental floss and toothpaste, although this chemical compound is best known for facilitating an arthritic condition called calcium pyrophosphate deposition disease (CPDD) due to an accumulation of dihydrate crystals in the synovial fluid and tissue that surround the joints. As a result, inflammation occurs, producing pain and impaired movement. While the exact mechanism behind this disease it is not yet clear, it is suspected that it may be related to elevated levels of ATP.