Sulfation (sometimes spelledsulphation inBritish English) is thechemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions ofsulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the installation of a sulfate-like group on a substrate leads to substantial changes.
Sulfation is a process used to remove "sulfur" from the combustion of fossil fuels. The goal is to minimize the pollution by the combusted gases. Combustion of sulfur-containing fuels releasessulfur dioxide, which, in the atmosphere, oxidizes to the equivalent ofsulfuric acid, which is corrosive. To minimize the problem, the combustion is often conducted in the presence of calcium oxide or calcium carbonate, which, directly or indirectly, bind sulfur dioxide and some oxygen to givecalcium sulfite.[1] The net reaction is:
or the net reaction is sulfation, the addition of SO3:
In the idealized scenario, the calcium sulfate (gypsum) is used as a construction material or, less desirably, deposited in a landfill.
Sulfation is widely used in the production of consumer products such as detergents, shampoos, and cosmetics. Since the sulfate group is highly polar, its conjugation to a lipophilic "tail" gives surfacant-like properties. Well known sulfates aresodium lauryl sulfate andsodium laureth sulfate.[2]
Alkylsulfate are produced from alcohols by reaction withchlorosulfuric acid:[3]
Alternatively, alcohols can be sulfated to the half sulfate esters usingsulfur trioxide. The reaction proceeds by initial formation of thepyrosulfate:
Several million tons of fatty acid sulfates are produced in this way annually. The most common example issodium dodecylsulfate (SDS) derived fromlauryl alcohol.[4]
In biology, sulfation is typically effected bysulfotransferases, which catalyze the transfer of the equivalent of sulfur trioxide to substrate alcohols and phenols, converting the latter to sulfate esters.[5][6] The source of the SO3 group is usually3'-phosphoadenosine-5'-phosphosulfate (PAPS). When the substrate is an amine, the result is asulfamate. Sulfation is one of the principal routes forpost-translational modification of proteins.[7]
Sulfation is involved in a variety of biological processes, including detoxification, hormone regulation, molecular recognition, cell signaling, and viral entry into cells.[6] It is among the reactions inphase II drug metabolism, frequently effective in rendering axenobiotic less active from apharmacological andtoxicological standpoint, but sometimes playing a role in the activation of xenobiotics (e.g.aromatic amines, methyl-substitutedpolycyclic aromatic hydrocarbons). Sulfate is part ofsulfolipids, such assulfatides, which constitute 20% of thegalactolipids inmyelin. Another example of biological sulfation is in the synthesis of sulfonatedglycosaminoglycans, such asheparin,heparan sulfate,chondroitin sulfate, anddermatan sulfate. Sulfation is also a possibleposttranslational modification of proteins.
Tyrosine sulfation is aposttranslational modification in which atyrosine residue of a protein is sulfated by atyrosylprotein sulfotransferase (TPST) typically in theGolgi apparatus. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated. Sulfation occurs in animals and plants but not inprokaryotes or in yeasts. Sulfation sites are tyrosine residues exposed on the surface of the protein typically surrounded by acidic residues. The function of sulfation remains uncertain.[7]
Very limited evidence suggests that the TPST genes are subject to transcriptional regulation and tyrosineO-sulfate is very stable and cannot be easily degraded by mammalian sulfatases. TyrosineO-sulfation is an irreversible processin vivo. An antibody called PSG2 shows high sensitivity and specificity for epitopes containing sulfotyrosine independent of the sequence context. New tools are being developed to study TPST's, using synthetic peptides and small molecule screens.[8]
Many edible seaweeds are composed on highly sulfated polysaccharides.[9]The evolution of several sulfotransferases appears to have facilitated the adaptation of the terrestrial ancestors of seagrasses to a new marine habitat.[10][11]
