Sulfur (US English) or sulphur

Sulfur (US English) or sulphur is the chemical element with atomic number 16. In theperiodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow crystalline solid when at room temperature. Sony VAIO VGN-CS120J/Q Battery

Chemically, sulfur can react as either an oxidant or reducing agent. It oxidizes most metals and severalnonmetals, including carbon, which leads to its negative charge in most organosulfur compounds, but it reduces several strong oxidants, such as oxygen and fluorine. It is also the lightest element to easily produce stable exceptions to the octet rule.Sony VAIO VGN-CS120J/R Battery

In nature, sulfur can be found as the pure element and as sulfide and sulfate minerals. Elemental sulfur crystals are commonly sought after by mineral collectors for their brightly colored polyhedron shapes. Being abundant in native form, sulfur was known in ancient times, mentioned for its uses in ancient Greece, China and Egypt.Sony VAIO VGN-CS190JTB Battery

Sulfur fumes were used as fumigants, and sulfur-containing medicinal mixtures were used as balms and antiparasitics. Sulfur is referenced in the Bibleas brimstone in English, with this name still used in several nonscientific terms.[2] Sulfur was considered important enough to receive its own alchemical symbol. Sony VAIO VGN-CS190JTP Battery

It was needed to make the best quality of black gunpowder, and the bright yellow powder was hypothesized by alchemists to contain some of the properties of gold, which they sought to synthesize from it. In 1777,Antoine Lavoisier helped convince the scientific community that sulfur was a basic element, rather than a compound.Sony VAIO VGN-CS190JTQ Battery

Elemental sulfur was once extracted from salt domes where it sometimes occurs in nearly pure form, but this method has been obsolete since the late 20th century. Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas and petroleum. Sony VAIO VGN-CS190JTR Battery

The element's commercial uses are primarily in fertilizers, because of the relatively high requirement of plants for it, and in the manufacture of sulfuric acid, a primary industrial chemical. Other well-known uses for the element are in matches, insecticides and fungicides. Sony VAIO VGN-CS190JTW Battery

Many sulfur compounds are odiferous, and the smell of odorized natural gas, skunk scent, grapefruit, and garlic is due to sulfur compounds. Hydrogen sulfide produced by living organisms imparts the characteristic odor to rotting eggs and other biological processes.Sony VAIO VGN-CS190NAB Battery

Sulfur is an essential element for all life, and is widely used in biochemical processes. In metabolic reactions, sulfur compounds serve as both fuels and respiratory (oxygen-replacing) materials for simple organisms. Sulfur in organic form is present in the vitamins biotin and thiamine, the latter being named for the Greek word for sulfur.Sony VAIO VGN-CS190NAC Battery

Sulfur is an important part of many enzymes and in antioxidant molecules like glutathione and thioredoxin. Organically bonded sulfur is a component of all proteins, as the amino acids cysteine and methionine. Disulfide bonds are largely responsible for the mechanical strength and insolubility of the protein keratin, found in outer skin, hair, and feathers, and the element contributes to their pungent odor when burned.Sony VAIO VGN-CS190NAD Battery

Physical

Sulfur forms polyatomic molecules with different chemical formulas, with the best-known allotrope being octasulfur, cyclo-S8. Octasulfur is a soft, bright-yellow solid with only a faint odor, similar to that of matches.[3] It melts at 115.21 °C, boils at 444.6 °C and sublimes easily.Sony VAIO VGN-CS190NBB Battery

At 95.2 °C, below its melting temperature, cyclo-octasulfur changes from ?-octasulfur to the ?-polymorph.The structure of the S8ring is virtually unchanged by this phase change, which affects the intermolecular interactions. Between its melting and boiling temperatures, octasulfur changes its allotrope again, turning from ?-octasulfur to ?-sulfur, again accompanied by a lower density but increased viscosity due to the formation of polymers.Sony VAIO VGN-CS190NCA Battery

At even higher temperatures, however, the viscosity decreases as depolymerization occurs. Molten sulfur assumes a dark red color above 200 °C. The density of sulfur is about 2 g·cm?3, depending on the allotrope; all of its stable allotropes are excellent electrical insulators.Sony VAIO VGN-CS190NCB Battery

Chemical

Sulfur burns with a blue flame concomitant with formation of sulfur dioxide, notable for its peculiar suffocating odor. Sulfur is insoluble in water but soluble in carbon disulfide and, to a lesser extent, in other nonpolar organic solvents, such as benzene andtoluene. Sony VAIO VGN-CS190NCC Battery

The first and the second ionization energies of sulfur are 999.6 and 2252 kJ·mol?1, respectively. Despite such figures, S2+ is rare, S4, 6+ being more common. The fourth and sixth ionization energies are 4556 and 8495.8 kJ·mol?1, the magnitude of the figures caused by electron transfer between orbitals; these states are only stable with strong oxidants as fluorine, oxygen, and chlorine.Sony VAIO VGN-CS50B/W Battery

Allotropes

Sulfur forms more than 30 solid allotropes, more than any other element. Besides S8, several other rings are known. Removing one atom from the crown gives S7, which is more deeply yellow than S8. HPLC analysis of "elemental sulfur" reveals an equilibrium mixture of mainly S8, but with S7 and small amounts of S6.Sony VAIO VGN-CS51B/W Battery

Larger rings have been prepared, including S12 and S18.

Amorphous or "plastic" sulfur is produced by rapid cooling of molten sulfur—for example, by pouring it into cold water. X-ray crystallography studies show that the amorphous form may have a helical structure with eight atoms per turn. Sony VAIO VGN-CS52JB/W Battery

The long coiled polymeric molecules cause the brownish substance to be elastic, and in bulk this form has the feel of crude rubber. This form is metastable at room temperature and gradually reverts to crystalline molecular allotrope, which is no longer elastic. This process happens within a matter of hours to days, but can be rapidly catalyzed.Sony VAIO VGN-CS60B/P Battery

Isotopes

Sulfur has 25 known isotopes, four of which are stable: 32S (95.02%), 33S (0.75%), 34S (4.21%), and 36S (0.02%). Other than 35S, with a half-life of 87 days and formed in cosmic ray spallation of 40Ar, the radioactive isotopes of sulfur have half-lives less than 170 minutes.Sony VAIO VGN-CS60B/Q Battery

When sulfide minerals are precipitated, isotopic equilibration among solids and liquid may cause small differences in the ?S-34 values of co-genetic minerals. The differences between minerals can be used to estimate the temperature of equilibration.Sony VAIO VGN-CS60B/R Battery

The ?C-13 and ?S-34 of coexisting carbonates and sulfides can be used to determine the pH and oxygen fugacity of the ore-bearing fluid during ore formation.

In most forest ecosystems, sulfate is derived mostly from the atmosphere; weathering of ore minerals and evaporites contribute some sulfur. Sony VAIO VGN-CS61B/P Battery

Sulfur with a distinctive isotopic composition has been used to identify pollution sources, and enriched sulfur has been added as a tracer in hydrologic studies. Differences in the natural abundances can be used in systems where there is sufficient variation in the 34S of ecosystem components. Sony VAIO VGN-CS61B/Q Battery

Rocky Mountain lakes thought to be dominated by atmospheric sources of sulfate have been found to have different ?34S values from lakes believed to be dominated by watershed sources of sulfate.

Natural occurrence

32S is created inside massive stars, at a depth where the temperature exceeds 2.5×109 K, by the fusion of one nucleus of silicon plus one nucleus of helium.Sony VAIO VGN-CS61B/R Battery

As this is part of the alpha process that produces elements in abundance, sulfur is the 10th most common element in the universe.

Sulfur, usually as sulfide, is present in many types of meteorites. Ordinary chondrites contain on average 2.1% sulfur, and carbonaceous chondrites may contain as much as 6.6%.Sony VAIO VGN-CS62JB/P Battery

It is normally present as troilite (FeS), but there are exceptions, with carbonaceous chondrites containing free sulfur, sulfates and other sulfur compounds. The distinctive colors of Jupiter'svolcanic moon Io are attributed to various forms of molten, solid and gaseous sulfur.Sony VAIO VGN-CS62JB/Q Battery

On Earth, elemental sulfur can be found near hot springs and volcanic regions in many parts of the world, especially along thePacific Ring of Fire; such volcanic deposits are currently mined in Indonesia, Chile, and Japan. Such deposits are polycrystalline, with the largest documented single crystal measuring 22×16×11 cm.Sony VAIO VGN-CS62JB/R Battery

Historically, Sicily was a large source of sulfur in the Industrial Revolution.

Significant deposits of elemental sulfur, believed to have been (and are still being) synthesised by anaerobic bacteria on sulfate minerals like gypsum, exist in salt domes along the coast of the Gulf of Mexico, and in evaporites in eastern Europe and western Asia. Native sulfur may be produced by geological processes alone.Sony VAIO VGN-CS71B/W Battery

Fossil-based sulfur deposits from salt domes have until recently been the basis for commercial production in the United States, Poland, Russia, Turkmenistan, and Ukraine. Such sources are now of secondary commercial importance, and most are no longer worked.Sony VAIO VGN-CS72JB/W Battery

Common naturally-occurring sulfur compounds include the sulfide minerals, such as pyrite (iron sulfide), cinnabar (mercury sulfide), galena (lead sulfide), sphalerite (zinc sulfide) and stibnite (antimony sulfide); and the sulfates, such as gypsum (calcium sulfate), alunite (potassium aluminium sulfate), and barite (barium sulfate). Sony VAIO VGN-CS90HS Battery

On Earth, just as upon Jupiter's moon Io, elemental sulfur occurs naturally in volcanic emissions, including emissions from hydrothermal vents.

Production

Sulfur may be found by itself and historically was usually obtained in this way, while pyrite has been a source of sulfur via sulfuric acid.Sony VAIO VGN-CS90NS Battery

The Sicilian process was used in ancient times to obtain sulfur from rocks present in volcanic regions ofSicily: sulfur deposits were piled and stacked in brick kilns built on sloping hillsides, with airspaces between them. Then, powdered sulfur was put on top of the deposit and ignited, causing the deposits to melt down the hills. Sony VAIO VGN-CS90S Battery

Today's sulfur production is as a side product of other industrial processes such as oil refining; in these processes, sulfur often occurs as undesired or detrimental compounds that are extracted and converted to elemental sulfur. As a mineral, native sulfur under salt domes is thought to be a fossil mineral resource, produced by the action of ancient bacteria on sulfate deposits. Sony VAIO VGN-CS91HS Battery

It was removed from such salt-dome mines mainly by the Frasch process. In this method, superheated water was pumped into a native sulfur deposit to melt the sulfur, and then compressed air returned the 99.5% pure melted product to the surface. Sony VAIO VGN-CS91NS Battery

Throughout the 20th century this procedure produced elemental sulfur which required no further purification. However, due to a limited number of such sulfur deposits and the high cost of working them, this process for mining sulfur has not been employed in a major way anywhere in the world since 2002.Sony VAIO VGN-CS91S Battery

Today, sulfur is produced from petroleum, natural gas, and related fossil resources, from which it is obtained mainly ashydrogen sulfide. Organosulfur compounds, undesirable impurities in petroleum, may be upgraded by subjecting them tohydrodesulfurization, which cleaves the C–S bonds:Sony VAIO VGN-CS92DS Battery

R-S-R + 2 H2 ? 2 RH + H2S

The resulting hydrogen sulfide from this process, and also as it occurs in natural gas, is converted into elemental sulfur by theClaus process. This process entails oxidation of some hydrogen sulfide to sulfur dioxide and then the comproportionation of the two:Sony VAIO VGN-CS92JS Battery

3 O2 + 2 H2S ? 2 SO2 + 2 H2O

SO2 + 2 H2S ? 3 S + 2 H2O

Owing to the high sulfur content of the Athabasca Oil Sands, stockpiles of elemental sulfur from this process now exist throughoutAlberta, Canada. Another way of storing sulfur is as a binder for concrete, the resulting product having many desirable properties. The price of sulfur increased from 2007 to 2008, and decreased thereafter.Sony VAIO VGN-CS92XS Battery

Compounds

Common oxidation states of sulfur range from ?2 to +6. Sulfur forms stable compounds with all elements except the noble gases.

Sulfides

Treatment of sulfur with hydrogen gives hydrogen sulfide. When dissolved in water, hydrogen sulfide is mildly acidic:Sony VAIO VGN-FW11E Battery

H2S HS– + H+

Hydrogen sulfide gas and the dissolved sulfide and hydrosulfide anions are extremely toxic to mammals, due to their inhibition of the oxygen-carrying capacity of hemoglobin and certain cytochromes in a manner analogous to cyanide and azide (see below, underprecautions).Sony VAIO VGN-FW11L Battery

Reduction of elemental sulfur gives polysulfides, which consist of chains of sulfur atoms terminated with S– centers:

2 Na + S8 ? Na2S8

This reaction highlights arguably the single most distinctive property of sulfur: its ability to catenate (bind to itself by formation of chains). Sony VAIO VGN-FW11M Battery

Protonation of these polysulfide anions gives the polysulfanes, H2Sx where x = 2, 3, and 4. Ultimately reduction of sulfur gives sulfide salts:

16 Na + S8 ? 8 Na2S

The interconversion of these species is exploited in the sodium-sulfur battery. The radical anion S3– gives the blue color to the mineral lapis lazuli.Sony VAIO VGN-FW11S Battery

Elemental sulfur can be oxidized, for example, to give bicyclic S82+.

Oxides and oxyanions

The principal sulfur oxides are obtained by burning sulfur:

S + O2 ? SO2

2 SO2 + O2 ? 2 SO3

Other oxides are known, e.g. sulfur monoxide and disulfur mono- and dioxides, but they are unstable.Sony VAIO VGN-FW11ZU Battery

The sulfur oxides form numerous oxyanions with the formula SOn2–. Sulfur dioxide and sulfites (SO2?3) are related to the unstable sulfurous acid (H2SO3). Sulfur trioxide and sulfates (SO2?4) are related to sulfuric acid. Sulfuric acid and SO3 combine to give oleum, a solution of pyrosulfuric acid (H2S2O7) in sulfuric acid.Sony VAIO VGN-FW139E/H Battery

Peroxides convert sulfur into unstable such as S8O, a sulfoxide. Peroxymonosulfuric acid (H2SO5) and peroxydisulfuric acids (H2S2O8), made from the action of SO3 on concentrated H2O2, and H2SO4 on concentrated H2O2 respectively.Sony VAIO VGN-FW140AE Battery

Thiosulfate salts (S2O2?3), sometimes referred as "hyposulfites", used in photographic fixing (HYPO) and as reducing agents, feature sulfur in two oxidation states. Sodium dithionite, (S2O2?4), contains the more highly reducing dithionite anion. Sodium dithionate(Na2S2O6) is the first member of the polythionic acids (H2SnO6), where n can range from 3 to many.Sony VAIO VGN-FW140D Battery

Halides and oxyhalides

The two main sulfur fluorides are sulfur hexafluoride, a dense gas used as nonreactive and nontoxic propellant, and sulfur tetrafluoride, a rarely used organic reagent that is highly toxic. Their chlorinated analogs are sulfur dichloride and sulfur monochloride.Sony VAIO VGN-FW140E Battery

Sulfuryl chloride and chlorosulfuric acid are derivatives of sulfuric acid; thionyl chloride (SOCl2) is a common reagent inorganic synthesis.

Pnictides

The most important S–N compound is the cage tetrasulfur tetranitride (S4N4). Sony VAIO VGN-FW140E/H Battery

Heating this compound gives polymeric sulfur nitride((SN)x), which has metallic properties even though it does not contain any metal atoms. Thiocyanates contain the SCN? group. Oxidation of thiocyanate gives thiocyanogen, (SCN)2 with the connectivity NCS-SCN. Phosphorus sulfides are numerous, the most important commercially being the cages P4S10 and P4S3.Sony VAIO VGN-FW140E/W Battery

Metal sulfides

Many if not most minerals occur as sulfides. The principal ores of copper, zinc, nickel, cobalt, molybdenum and others are sulfides. These materials tend to be dark-colored semiconductors that are not readily attacked by water or even many acids. Sony VAIO VGN-FW140FE Battery

They are formed, both geochemically and in the laboratory, by the reaction of hydrogen sulfide with metal salts to form the metal sulfides. The mineral galena (PbS) was the first demonstrated semiconductor and found a use as a signal rectifier in the cat's whiskers of early crystal radios.Sony VAIO VGN-FW140N Battery

The iron sulfide called pyrite, the so-called "fool's gold," has the formula FeS2. The upgrading of these ores, usually by roasting, is costly and environmentally hazardous. Sulfur corrodes many metals via the process called tarnishing.

Some of the main classes of sulfur-containing organic compounds include the following:Sony VAIO VGN-FW140N/W Battery

• Thiols or mercaptans (as they are mercury capturers as chelators) are the sulfur analogs of alcohols; treatment of thiols with base gives thiolate ions.
• Thioethers are the sulfur analogs of ethers.
• Sulfonium ions have three groups attached to a cationic sulfur center. Dimethylsulfoniopropionate (DMSP) is one such compound, important in the marine organicsulfur cycle.Sony VAIO VGN-FW145E Battery
• Sulfoxides and sulfones are thioethers with one and two oxygen atoms attached to the sulfur atom, respectively. The simplest sulfoxide, dimethyl sulfoxide, is a common solvent; a common sulfone is sulfolane.
• Sulfonic acids are used in many detergents.Sony VAIO VGN-FW145E/W Battery

Some inorganic compounds with carbon–sulfur bonds are known. Carbon disulfide, a volatile colorless liquid at standard conditions, is structurally similar to carbon dioxide; it is used as a solvent to make polymers. Whereas carbon monoxide is highly stable, carbon monosulfide is unstable and has only been observed as a gas and in the interstellar medium.Sony VAIO VGN-FW160AE Battery

Organosulfur compounds are responsible for the some of the unpleasant odors of decaying organic matter. They are used in the odoration of natural gas and cause the odor of garlic and skunk spray. Not all organic sulfur compounds smell unpleasant at all concentrations:Sony VAIO VGN-FW160D Battery

the sulfur-containing monoterpenoid grapefruit mercaptan in small concentrations is responsible for the characteristic scent of grapefruit, but has a generic thiol odor at larger concentrations. Sulfur mustard, a potentvesicant, was used in World War I as a disabling agent.Sony VAIO VGN-FW160E Battery

Sulfur can be used in organics as a structural component to harden synthetic polymers, in a way similar to the biological use of disulfide bridges to reinforce proteins (see biological below). In the most common type of industrial "curing" or hardening and strengthening of natural rubber,Sony VAIO VGN-FW160E/H Battery

elemental sulfur is heated with the rubber to the point that chemical reactions form disulfide bridges between isoprene units of the polymer. This process, patented in 1843, historically changed rubber into a major industrial product. The process was named vulcanization after the Roman god of the forge and volcanism, in honor of both the heat and sulfur used. Sony VAIO VGN-FW160F/E Battery

Although vulcanization is applied to other polymers, and sometimes with crosslinking agents other than sulfur, variants of sulfur/rubber vulcanization continue to be used in producing automobile tires and other elastomer products.Sony VAIO VGN-FW170J/H Battery

Antiquity

Being abundantly available in native form, sulfur (Latin sulphur) was known in ancient times and is referred to in the Torah (Genesis). English translations of the Bible commonly referred to burning sulfur as "brimstone", giving rise to the name of 'fire-and-brimstone' sermons, Sony VAIO VGN-FW180AE Battery

in which listeners are reminded of the fate ofeternal damnation that await the unbelieving and unrepentant. It is from this part of the Bible that Hell is implied to "smell of sulfur" (likely due to its association with volcanic activity). According to the Ebers Papyrus, a sulfur ointment was used in ancient Egypt to treat granular eyelids.Sony VAIO VGN-FW180D Battery

Sulfur was used for fumigation in preclassical Greece;[31] this is mentioned in the Odyssey.[32] Pliny the Elder discusses sulfur in book 35 of his Natural History, saying that its best-known source is the island of Melos. He mentions its use for fumigation, medicine, and bleaching cloth.Sony VAIO VGN-FW180E Battery

A natural form of sulfur known as shiliuhuang was known in China since the 6th century BC and found in Hanzhong. By the 3rd century, the Chinese discovered that sulfur could be extracted from pyrite. Chinese Daoists were interested in sulfur's flammability and its reactivity with certain metals, yet its earliest practical uses were found in traditional Chinese medicine.Sony VAIO VGN-FW180E/H Battery

A Song Dynasty military treatise of 1044 AD described different formulas for Chinese black powder, which is a mixture of potassium nitrate (KNO3), charcoal, and sulfur.

Early alchemists gave sulfur its own alchemical symbol which was a triangle at the top of a cross. Sony VAIO VGN-FW180FU Battery

In traditional medical skin treatment which predates modern era of scientific medicine, elemental sulfur has been used mainly as part of creams to alleviate various conditions such as scabies, ringworm, psoriasis, eczema and acne. The mechanism of action is not known, although elemental sulfur does oxidize slowly to sulfurous acid, which in turn (through the action of sulfite) acts as a mild reducing and antibacterial agent. Sony VAIO VGN-FW190EBH Battery

Modern times

In 1777, Antoine Lavoisier helped convince the scientific community that sulfur was an element, not a compound. With the sulfur from Sicily being principally controlled by the French market, a debate ensued about the amount of sulfur France and Britain got. This led to a bloodless confrontation between the two sides in 1840.Sony VAIO VGN-FW190ECH Battery

In 1867, sulfur was discovered in underground deposits inLouisiana and Texas. The highly successful Frasch process was developed to extract this resource.

In the late 18th century, furniture makers used molten sulfur to produce decorative inlays in their craft. Sony VAIO VGN-FW190EDH Battery

Because of the sulfur dioxide produced during the process of melting sulfur, the craft of sulfur inlays was soon abandoned. Molten sulfur is sometimes still used for setting steel bolts into drilled concrete holes where high shock resistance is desired for floor-mounted equipment attachment points. Pure powdered sulfur was used as a medicinal tonic and laxative.Sony VAIO VGN-FW190NAH Battery

With the advent of the contact process, the majority of sulfur today is used to make sulfuric acid for a wide range of uses, particularly fertilizer.

Spelling and etymology

Sulfur comes from the Old French soufre, apparently referring from a root meaning "to burn".Sony VAIO VGN-FW190NBH Battery

The element was traditionally spelled sulphur in the United Kingdom (since the 14th century), most of the Commonwealth including India, Malaysia, South Africa, and Hong Kong, along with the rest of the Caribbean and Ireland. Sulfur is used in the United States, while both spellings are used in Canada and the Philippines.Sony VAIO VGN-FW190NCH Battery

However, the IUPAC adopted the spelling sulfur in 1990, as did the Royal Society of Chemistry Nomenclature Committee in 1992.The Qualifications and Curriculum Authority for England and Wales recommended its use in 2000, and it now appears in GCSE exams.Sony VAIO VGN-FW190NDH Battery

The Oxford Dictionaries note that "In chemistry... the -f- spelling is now the standard form in all related words in the field in both British and US contexts"

In Latin, the word is variously written sulpur, sulphur, and sulfur (the Oxford Latin Dictionary lists the spellings in this order). Sony VAIO VGN-FW190NEH Battery

It is an original Latin name and not a Classical Greek loan, so the ph variant does not denote the Greek letter ? (phi). Sulfur in Greek is thion (?????), whence comes the prefix thio-. The simplification of the Latin words p or ph to an f appears to have taken place towards the end of the classical period.Sony VAIO VGN-FW198U/H Battery

Sulfuric acid

Elemental sulfur is mainly used as a precursor to other chemicals. Approximately 85% (1989) is converted to sulfuric acid (H2SO4):

2 S + 3 O2 + 2 H2O ? 2 H2SO4

With sulfuric acid being central importance to the world's economies, its production and consumption is an indicator of a nation's industrial development.Sony VAIO VGN-FW260J/B Battery

For example with 36.1 million metric tons in 2007, the United States produces more sulfuric acid every year than any other inorganic industrial chemical. The principal use for the acid is the extraction of phosphate ores for the production of fertilizer manufacturing. Sony VAIO VGN-FW280J/H Battery

Other applications of sulfuric acid include oil refining, wastewater processing, and mineral extraction.

Other large scale sulfur chemicals

Sulfur reacts directly with methane to give carbon disulfide, which is used to manufacture cellophane and rayon. One of the direct uses of sulfur is invulcanization of rubber, where polysulfides crosslink organic polymers. Sony VAIO VGN-FW290JRB Battery

Sulfites are heavily used to bleach paper and as preservatives in dried fruit. Manysurfactants and detergents, e.g. sodium lauryl sulfate, are produced are sulfate derivatives. Calcium sulfate, gypsum, (CaSO4·2H2O) is mined on the scale of 100 million tons each year for use in Portland cement and fertilizers.Sony VAIO VGN-FW290JTB Battery

When silver-based photography was widespread, sodium and ammonium thiosulfate were widely used as "fixing agents." Sulfur is a component of gunpowder.

Fertilizer

Sulfur is increasingly used as a component of fertilizers. The most important form of sulfur for fertilizer is the mineral calcium sulfate.Sony VAIO VGN-FW290JTH Battery

Elemental sulfur is hydrophobic (that is, it is not soluble in water) and therefore cannot be directly utilized by plants. Over time, soil bacteria can convert it to soluble derivatives which can then be utilized by plants. Sulfur improves the use efficiency of other essential plant nutrients, particularly nitrogen and phosphorus.Sony VAIO VGN-FW290JTW Battery

Biologically produced sulfur particles are naturally hydrophilic due to a biopolymer coating. This sulfur is therefore easier to disperse over the land (via spraying as a diluted slurry), and results in a faster release.

Plant requirements for sulfur are equal to or exceed those for phosphorus.Sony VAIO VGN-FW355J/H Battery

It is one of the major nutrients essential for plant growth, root nodule formation of legumes and plants protection mechanisms. Sulfur deficiency has become widespread in many countries in Europe. Because atmospheric inputs of sulfur will continue to decrease, the deficit in the sulfur input/output is likely to increase, unless sulfur fertilizers are used.Sony VAIO VGN-FW373J/B Battery

Fine chemicals

Organosulfur compounds are used in pharmaceuticals, dyestuffs, and agrochemicals. Many drugs contain sulfur, early examples being antibacterial sulfonamides, known as sulfa drugs. Sulfur is a part of many bacterial defense molecules. Most ?-lactamantibiotics, including the penicillins, cephalosporins and monolactams contain sulfur.Sony VAIO VGN-FW30B Battery

Magnesium sulfate, known as Epsom salts when in hydrated crystal form, can be used as a laxative, a bath additive, an exfoliant,magnesium supplement for plants, or (when in dehydrated form) as a desiccant.Sony VAIO VGN-FW50B Battery

Fungicide and pesticide

Elemental sulfur is one of the oldest fungicides and pesticides. "Dusting sulfur," elemental sulfur in powdered form, is a common fungicide for grapes, strawberry, many vegetables and several other crops. It has a good efficacy against a wide range of powdery mildew diseases as well as black spot.Sony VAIO VGN-FW51B/W Battery

In organic production, sulfur is the most important fungicide. It is the only fungicide used in organically farmed apple production against the main disease apple scab under colder conditions. Biosulfur (biologically produced elemental sulfur with hydrophilic characteristics) can be used well for these applications.Sony VAIO VGN-FW51MF Battery

Standard-formulation dusting sulfur is applied to crops with a sulfur duster or from a dusting plane. Wettable sulfur is the commercial name for dusting sulfur formulated with additional ingredients to make it water miscible. It has similar applications and is used as a fungicide against mildew and other mold-related problems with plants and soil.Sony VAIO VGN-FW51MF/H Battery

Elemental sulfur powder is used as an "organic" (i.e. "green") insecticide (actually an acaricide) against ticks and mites. A common method of use is to dust clothing or limbs with sulfur powder.

Diluted solutions of lime sulfur (made by combinding calcium hydroxide with elemental sulfur in water), are used as a dip for pets to destroy ringworm (fungus),mange and other dermatoses and parasites.Sony VAIO VGN-FW51ZF Battery

Bacteriocide in winemaking and food preservation

Small amounts of sulfur dioxide gas addition (or equivalent potassium metabisulfite addition) to fermented wine to produce traces of sulfurous acid (produced when SO2 reacts with water) and its sulfite salts in the mixture, has been called "the most powerful tool in winemaking."Sony VAIO VGN-FW51ZF/H Battery

The sulfites absorb oxygen to inhibitaerobic bacterial growth after the yeast-fermentation stage in winemaking, that otherwise would turn ethanol into acetic acid and thus cause the wine to "sour." Without this preservative step, indefinite refrigeration of the product before consumption is usually required. Sony VAIO VGN-FW52JB Battery

Similar methods go back into antiquity but modern historical mentions of the practice go to the fifteenth century. The practice is used by large industrial wine producers and small organic wine producers alike.

Sulfur dioxide and various sulfites have been used for their antioxidant antibacterial preservative properties in many other parts of the food industry also.Sony VAIO VGN-FW54FB Battery

The practice has declined since reports of a allergy-like reaction of some persons to sulfites in foods.

Protein and organic cofactors

Sulfur is an essential component of all living cells. It is the seventh or eighth most abundant element in the human body by weight, being about as common aspotassium, and a little more common than sodium or chlorine.Sony VAIO VGN-FW70DB Battery

A 70 kg human body contains about 140 grams of sulfur.

In plants and animals, the amino acids cysteine and methionine contain most of the sulfur. The element is thus present in all polypeptides, proteins, and enzymesthat contain these amino acids. Disulfide bonds (S-S bonds) formed between cysteine residues in peptide chains are very important in protein assembly and structure. Sony VAIO VGN-FW71DB/W Battery

These covalent bonds between peptide chains confer extra toughness and rigidity.For example, the high strength of feathers and hair is in part due to their high content of S-S bonds and their high content of cysteine and sulfur. Eggs are high in sulfur because large amounts of the element are necessary for feather formation, and the characteristic odor of rotting eggs is due to hydrogen sulfide.Sony VAIO VGN-FW72JGB Battery

The high disulfide bond content of hair and feathers contributes to their indigestibility and to their characteristic disagreeable odor when burned.

Homocysteine and taurine are other sulfur-containing acids that are similar in structure, but which are not coded by DNA, and are not part of the primary structureof proteins. Sony VAIO VGN-FW73JGB Battery

Many important cellular enzymes use prosthetic groups ending with -SH moieties to handle reactions involving acyl-containing biochemicals: two common examples from basic metabolism are coenzyme A and alpha-lipoic acid. Two of the 13 classical vitamins, biotin and thiamine contain sulfur, with the latter being named for its sulfur content. Sony VAIO VGN-FW74FB Battery

Sulfur plays an important part, as a carrier of reducing hydrogen and its electrons, for cellular repair of oxidation. Reducedglutathione, a sulfur-containing tripeptide, is a reducing agent through its sulfhydryl (-SH) moiety derived from cysteine.Sony VAIO VGN-FW81HS Battery

The thioredoxins, a class of small protein essential to all known life, using neighboring pairs of reduced cysteines to act as general protein reducing agents, to similar effect.

Methanogenesis, the route to most of the world's methane, is a multistep biochemical transformation of carbon dioxide. This conversion requires several organosulfur cofactors.Sony VAIO VGN-FW81NS Battery

These include coenzyme M, CH3SCH2CH2SO3–, the immediate precursor to methane.

Metalloproteins and inorganic cofactors

Inorganic sulfur forms a part of iron-sulfur clusters as well as many copper, nickel, and iron proteins. Most pervasive are the ferrodoxins, which serve as electron shuttles in cells. Sony VAIO VGN-FW81S Battery

In bacteria, the important nitrogenase enzymes contains an Fe-Mo-S cluster, is a catalyst that performs the important function of nitrogen fixation, converting atmospheric nitrogen to ammonia that can be used by microorganisms and plants to make proteins, DNA, RNA, alkaloids, and the other organic nitrogen compounds necessary for life.Sony VAIO VGN-FW82DS Battery

Sulfur metabolism

Sulfur may serve as energy (chemical food) source for bacteria that use hydrogen sulfide (H2S) in the place of water as the electron donor in a primitivephotosynthesis-like process in which oxygen is the electron receptor. Sony VAIO VGN-FW82JS Battery

The photosynthetic green sulfur bacteria and purple sulfur bacteria and some chemolithotrophsuse elemental oxygen to carry out such oxidization of hydrogen sulfide to produce elemental sulfur (S0), oxidation state = 0. Primitive bacteria which live around deep ocean volcanic vents oxidize hydrogen sulfide in this way with oxygen: Sony VAIO VGN-FW82XS Battery

see giant tube worm for an example of large organisms (via bacteria) making metabolic use of hydrogen sulfide as food to be oxidized.

The so-called sulfate-reducing bacteria, by contrast, "breathe sulfate" instead of oxygen. They use sulfur as the electron acceptor, and reduce various oxidized sulfur compounds back into sulfide, often into hydrogen sulfide. Sony VAIO VGN-FW83DS Battery

They can grow on a number of other partially oxidized sulfur compounds (e. g. thiosulfates, thionates, polysulfides, sulfites). The hydrogen sulfide produced by these bacteria is responsible for some of the smell of intestinal gases (flatus) and decomposition products.Sony VAIO VGN-FW83JS Battery

Sulfur is absorbed by plants via the roots from soil as the sulfate and transported as a phosphate ester. Sulfate is reduced to sulfide via sulfite before it is incorporated into cysteine and other organosulfur compounds. Sony VAIO VGN-FW83XS Battery

SO42– ? SO32– ? H2S ? cysteine

Precautions

Elemental sulfur is non-toxic, as generally are the soluble sulfate salts, such as Epsom salts. Soluble sulfate salts are poorly absorbed and laxitive. However, when injected parenterally, they are freely filtered by the kidneys and elimimated with very little toxicity in multi-gram amounts.Sony VAIO VGN-FW90HS Battery

When sulfur burns in air it produces sulfur dioxide. In water, this gas produces sulfurous acid and sulfites which are antioxidants, inhibiting the growth of aerobic bacteria, and allowing it to be used as a food additive in small amounts. However, at high concentrations these acids harm the lungs, eyes or other tissues.Sony VAIO VGN-FW90NS Battery

In organisms without lungs such as insects or plants, it otherwise prevents respiration in high concentrations. Sulfur trioxide (made by catalysis from sulfur dioxide) and sulfuric acidare similarly highly corrosive, due to the strong acids that form on contact with water.Sony VAIO VGN-FW90S Battery

The burning of coal and/or petroleum by industry and power plants generates sulfur dioxide (SO2), which reacts with atmospheric water and oxygen to produce sulfuric acid (H2SO4) and sulfurous acid (H2SO3). These acids are components of acid rain, which lower the pH of soil and freshwater bodies, Sony VAIO VGN-FW91NS Battery

sometimes resulting in substantial damage to the environment and chemical weathering of statues and structures. Fuel standards increasingly require sulfur to be extracted from fossil fuels to prevent the formation of acid rain. This extracted sulfur is then refined and represents a large portion of sulfur production.Sony VAIO VGN-FW91S Battery

In coal fired power plants, the flue gases are sometimes purified. In more modern power plants that use synthesis gas the sulfur is extracted before the gas is burned.

Hydrogen sulfide is as toxic as hydrogen cyanide and kills by the same mechanism, although hydrogen sulfide is less likely to result in surprise poisonings from small inhaled amounts, due to its more disagreeable warning odor. Sony VAIO VGN-FW92DS Battery

However, although very pungent at first awareness to the human nose, hydrogen sulfide quickly deadens the sense of smell, so potential victims breathing larger and larger quantities of it may be unaware of its presence until severe symptoms occur (these can then quickly lead to death). Dissolved sulfide and hydrosulfide salts are also toxic by the same mechanism.Sony VAIO VGN-FW92JS Battery

The sulfur cycle are the collection of processes by which sulfur moves to and from minerals (including the waterways) and living systems. Such biogeochemical cycles are important in geology because they affect many minerals. Biogeochemical cycles are also important for life because sulfur is an essential element, being a constituent of many proteins and cofactors.Sony VAIO VGN-FW93DS Battery

Steps of the sulfur cycle are:

• Mineralization of organic sulfur into inorganic forms, such as hydrogen sulfide (H2S), elemental sulfur, as well as sulfide mineralss.
• Oxidation of hydrogen sulfide, sulfide, and elemental sulfur (S) to sulfate (SO42–).Sony VAIO VGN-FW93JS Battery
• Reduction of sulfate to sulfide.
• Incorporation sulfide into organic compounds (including metal-containing derivatives).

These are often termed as follows:

Assimilative sulfate reduction (see also sulfur assimilation) in which sulfate (SO42–) is reduced by plants, fungi and variousprokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH.Sony VAIO VGN-FW93XS Battery

Desulfurization in which organic molecules containing sulfur can be desulfurized, producing hydrogen sulfide gas (H2S, oxidation state = –2). An analogous process for organic nitrogen compounds is deamination.

Oxidation of hydrogen sulfide produces elemental sulfur (S8), oxidation state = 0. This reaction occurs in the photosynthetic green and purple sulfur bacteria and some chemolithotrophs. Often the elemental sulfur is stored as polysulfides.Sony VAIO VGN-FW94FS Battery

oxidation of elemental sulfur by sulfur oxidizers produces sulfate.

Dissimilative sulfur reduction in which elemental sulfur can be reduced to hydrogen sulfide.

Dissimilative sulfate reduction in which sulfate reducers generate hydrogen sulfide from sulfate.Sony VAIO VGN-FW94GS Battery

Sulfur sources and sinks

Sulfur is found in oxidation states ranging from +6 in SO4 to -2 in sulfides. Thus elemental sulfur can either give or receive electrons depending on its environment. Igneous rocks such as pyrite (FeS2) comprised the original pool of sulfur on earth. Sony VAIO VGN-FW94HS Battery

Owing to the sulfur cycle, the amount of mobile sulfur has been continuously increasing through volcanic activity as well as weathering of the crust in an oxygenated atmosphere.[1] Earth’s main sulfur sink is the oceans as SO2, where it is the major oxidizing agent. Sony VAIO VGN-G118CN Battery

When SO4 is assimilated by organisms, it is reduced and converted to organic sulfur, which is an essential component of proteins. However, the biosphere does not act as a major sink for sulfur, instead the majority of sulfur is found in seawater or sedimentary rocks especially pyrite rich shales and evaporite rocks (anhydrite andbaryte).Sony VAIO VGN-G118GN/B Battery

The amount of sulfate in the oceans is controlled by three major processes:

1. input from rivers

2. sulfate reduction and sulfide reoxidation on continental shelves and slopes

3. burial of anhydrite and pyrite in the oceanic crust.Sony VAIO VGN-G118GN/T Battery

There is no significant amount of sulfur held in the atmosphere with all of it coming from either sea spray or windblown sulfur rich dust,[4] neither of which is long lived in the atmosphere. In recent times the large annual input of sulfur from the burning of coal and other fossil fuels adds a substantial amount SO2 which acts as an air pollutant. Sony VAIO VGN-G118TN/B Battery

In the geologic past, igneous intrusions into coal measures have caused large scale burning of these measures, and consequential release of sulfur to the atmosphere. This has led to substantial disruption to the climate system, and is one of the proposed causes of the great dying.Sony VAIO VGN-G118TN/S Battery

Dimethylsulfide [(CH3)2S or DMS] is produced by the decomposition of dimethylsulfoniopropionate DMSP) from dying phytoplankton cells in the shallow levels of the ocean, and is the major biogenic gas emitted from the sea, where it is responsible for the distinctive “smell of the sea” along coastlines.Sony VAIO VGN-G11VN/T Battery

DMS is the largest natural source of sulfur gas, but still only has a residence time of about one day in the atmosphere and a majority of it is redeposited in the oceans rather than making it to land. However, it is a significant factor in the climate system, as it is involved in the formation of clouds.Sony VAIO VGN-G11VN/TC Battery

Biologically and thermochemically driven sulfate reduction

Sulfur can be reduced both biologically and thermochemically. Dissimilatory sulfate reduction has two different definitions:

1. the microbial process that converts sulfate to sulfide for energy gain, and

2. a set of forward and reverse pathways that progress from the uptake and release of sulfate by the cell to its conversion to various sulfur intermediates, and ultimately to sulfide which is released from the cell.Sony VAIO VGN-G11XN/B Battery

Sulfide and thiosulfate are the most abundant reduced inorganic sulfur species in the environments and are converted to sulfate, primarily by bacterial action, in the oxidative half of the sulfur cycle. Bacterial sulfate reduction (BSR) can only occur at temperature from 0 up to 60–80 °C because above that temperature almost all sulfate-reducing microbes can no longer metabolize. Sony VAIO VGN-G1AAPS Battery

Few microbes can form H2S at higher temperatures but appear to be very rare and do not metabolize in settings where normal bacterial sulfate reduction is occurring. BSR is geologically instantaneous happening on the order of hundreds to thousands of years.Sony VAIO VGN-G1AAPSA Battery

Thermochemical sulfate reduction (TSR) occurs at much higher temperatures (160–180 °C) and over longer time intervals, several tens of thousands to a few million years.

The main difference between these two reactions is obvious, one is organically driven and the other is chemically driven. Sony VAIO VGN-G1AAPSB Battery

Therefore the temperature for thermochemical sulfate reduction is much higher due to the activation energy required to reduce sulfate. Bacterial sulfate reductions requires lower temperatures because the sulfur reducing bacteria can only live at relatively low temperature (below 60 °C). Sony VAIO VGN-G1AAPSC Battery

BSR also requires a relatively open system; otherwise the bacteria will poison themselves when the sulfate levels rise above 5–10%.

The organic reactants involved in BSR are organic acids which are distinctive from the organic reactants needed for TSR. In both cases sulfate is usually derived from the dissolution of gypsum or taken directly out of the seawater. Sony VAIO VGN-G1ABNS Battery

The factors that control whether BSR or TSR will occur are temperature, which is generally a product of depth, with BSR occurring in shallower levels than TSR. Both can occur within the oil window. Their solid products are similar but can be distinguished from one another petrographically, due to their differing crystal sizes, shapes and reflectivity.Sony VAIO VGN-G1KAP Battery

?34S

Although 25 isotopes are known for sulfur, only four are stable and of geochemical importance. Of those four, two (32S, light and 34S, heavy) comprise (99.22%) of S on Earth. The vast majority (95.02%) of S occurs as 32S with only 4.21% in 34S. The ratio of these two isotopes is fixed in our solar system and has been since its formation. Sony VAIO VGN-G1KBN Battery

The bulk Earth sulfur isotopic ratio is thought to be the same as the ratio of 22.22 measured from the Canyon Diablo troilite (CDT), a meteorite. That ratio is accepted as the international standard and is therefore set at ?0.00. Deviation from 0.00 is expressed as the ?34S which is a ratio in per mill (‰).Sony VAIO VGN-G1KBNA Battery

Positive values correlate to increased levels of 34S, whereas negative values correlate with greater 32S in a sample.

Formation of sulfur minerals through non-biogenic processes does not substantially differentiate between the light and heavy isotopes, therefore sulfur values ingypsum or baryte should be the same as the overall ratio in the water column at their time of precipitation. Sony VAIO VGN-G1LAP Battery

Sulfate reduction through biologic activity strongly differentiates between the two isotopes because of the more rapid enzymic reaction with 32S. Sulfate metabolism results in an isotopic depletion of -18‰, and repeated cycles of oxidation and reduction can result in values up to -50 ‰. Average present day seawater values of ?34S are on the order of +21‰.Sony VAIO VGN-G1LBN Battery

Throughout geologic history the sulfur cycle and the isotopic ratios have coevolved with the biosphere becoming overall more negative with the increases in biologically driven sulfate reduction, but also show substantial positive excursion. In general positive excursions in the sulfur isotopes mean that there is an excess of pyrite deposition rather than oxidation of sulfide minerals exposed on land. Sony VAIO VGN-G218LN/T Battery

Evolution of the sulfur cycle

The isotopic composition of sedimentary sulfides provides primary information on the evolution of the sulfur cycle. The total inventory of sulfur compounds on the surface of the Earth (nearly 1022g S) represents the total outgassing of sulfur through geologic time.Sony VAIO VGN-G218N/B Battery

Rocks analyzed for sulfur content are generally organic-rich shales meaning they are likely controlled by biogenic sulfur reduction. Average seawater curves are generated from evaporites deposited throughout geologic time because again, since they do not discriminate between the heavy and light sulfur isotopes, they should mimic the ocean composition at the time of deposition.Sony VAIO VGN-G21XP/B Battery

4.6 billion years ago (Ga) the Earth formed and had a theoretical ?34S value of 0. Since there was no biologic activity on early Earth there would be no isotopic fractionation. All sulfur in the atmosphere would be released during volcanic eruptions. When the oceans condensed on Earth, the atmosphere was essentially swept clean of sulfur gases, owing to their high solubility in water. Sony VAIO VGN-G2AANS Battery

Throughout the majority of the Archean (4.6–2.5 Ga) most systems appeared to be sulfate-limited. Some small Archean evaporite deposits require that at least locally elevated concentrations (possibly due to local volcanic activity) of sulfate existed in order for them to be supersaturated and precipitate out of solution.Sony VAIO VGN-G2AAPS Battery

3.8–3.6 Ga marks the beginning of the exposed geologic record because this is the age of the oldest rocks on Earth. Metasedimentary rocks from this time still have an isotopic value of 0 because the biosphere was not developed enough (possibly at all) to fractionate sulfur.Sony VAIO VGN-G2AAPSA Battery

3.5 Ga anoxyogenic photosynthesis is established and provides a weak source of sulfate to the global ocean with sulfate concentrations incredibly low the ?34S is still basically 0. Shortly after, at 3.4 Ga the first evidence for minimal fractionation in evaporitic sulfate in association with magmatically derived sulfides can be seen in the rock record. Sony VAIO VGN-G2AAPSB Battery

This fractionation shows possible evidence for anoxygenic phototrophic bacteria.

2.8 Ga marks the first evidence for oxygen production through photosynthesis. This is important because there cannot be sulfur oxidation without oxygen in the atmosphere. Sony VAIO VGN-G2AAPSC Battery

This exemplifies the coevolution of the oxygen and sulfur cycles as well as the biosphere.

2.7–2.5 Ga is the age of the oldest sedimentary rocks to have a depleted ? 34S which provide the first compelling evidence for sulfate reduction. Sony VAIO VGN-G2KAN Battery

2.3 Ga sulfate increases to more than 1 mM; this increase in sulfate is coincident with the “Great Oxygenation Event", when redox conditions on Earth’s surface are thought by most workers to have shifted fundamentally from reducing to oxidizing.Sony VAIO VGN-G2KANA Battery

This shift would have led to an incredible increase in sulfate weathering which would have led to an increase in sulfate in the oceans. The large isotopic fractionations that would likely be associated with bacteria reduction are produced for the first time. Although there was a distinct rise in seawater sulfate at this time it was likely still only less than 5–15% of present-day levels.Sony VAIO VGN-G2KBNA Battery

At 1.8 Ga, Banded iron formations (BIF) are common sedimentary rocks throughout the Archean and Paleoproterozoic; their disappearance marks a distinct shift in the chemistry of ocean water. BIFs have alternating layers of iron oxides and chert. Sony VAIO VGN-NR160E/S Battery

BIFs only form if the water is be allowed to supersaturate in dissolved iron (Fe2+) meaning there cannot be free oxygen or sulfur in the water column because it would form Fe3+ (rust) or pyrite and precipitate out of solution.Sony VAIO VGN-NR160E/T Battery

Following this supersaturation, the water must become oxygenated in order for the ferric rich bands to precipitate it must still be sulfur poor otherwise pyrite would form instead of Fe3+. It has been hypothesized that BIFs formed during to the initial evolution of photosynthetic organisms that had phases of population growth, causing over production of oxygen. Sony VAIO VGN-NR160E/W Battery

Due to this over production they would poison themselves causing a mass die off, which would cut off the source of oxygen and produce a large amount of CO2 through the decomposition of their bodies, allowing for another bacterial bloom. After 1.8 Ga sulfate concentrations were sufficient to increase rates of sulfate reduction to greater than the delivery flux of iron to the oceans.Sony VAIO VGN-NR180E/S Battery

Along with the disappearance of BIF, the end of the Paleoproterozoic also marks the first large scale sedimentary exhalative deposits showing a link between mineralization and a likely increase in the amount of sulfate in sea water. In the Paleoproterozoic the sulfate in seawater had increased to an amount greater than in the Archean, but was still lower than present day values.Sony VAIO VGN-NR180E/T Battery

The sulfate levels in the Proterozoic also act as proxies for atmospheric oxygen because sulfate is produced mostly through weathering of the continents in the presence of oxygen. The low levels in the Proterozoic simply imply that levels of atmospheric oxygen fell between the abundances of the Phanerozoic and the deficiencies of the Archean.Sony VAIO VGN-NR290E/S Battery

750 million years ago (Ma) there is a renewed deposition of BIF which marks a significant change in ocean chemistry. This was likely due to snowball earth episodes where the entire globe including the oceans was covered in a layer of ice cutting off oxygenation.Sony VAIO VGN-NR290E/T Battery

In the late Neoproterozoic high carbon burial rates increased the atmospheric oxygen level to >10% of its present day value. In the Latest Neoproterozoic another major oxidizing event occurred on Earth’s surface that resulted in an oxic deep ocean and possibly allowed for the appearance of multicellular life.Sony VAIO VGN-NR298E/S Battery

During the last 600 million years, seawater SO4 has varied between +10 and +30‰ in ?34S, with an average value close to that of today. This coincides with atmospheric O levels reaching something close to modern values around the Precambrian–Cambrian boundary.Sony VAIO VGN-NR460E/L Battery

Over a shorter time scale (10 million years) changes in the sulfur cycle are easier to observe and can be even better constrained with oxygen isotopes. Oxygen is continually incorporated into the sulfur cycle through sulfate oxidation and then released when that sulfate is reduced once again.Sony VAIO VGN-NR460E/P Battery

Since different sulfate sources within the ocean have distinct oxygen isotopic values it may be possible to use oxygen to trace the sulfur cycle. Biological sulfate reduction preferentially selects lighter oxygen isotopes for the same reason that lighter sulfur isotopes are preferred. Sony VAIO VGN-NR498E/L Battery

By studying oxygen isotopes in ocean sediments over the last 10 million years were able to better constrain the sulfur concentrations in sea water through that same time. They found that the sea level changes due to Plioceneand Pleistocene glacial cycles changed the area of continental shelves which then disrupted the sulfur processing, Sony VAIO VGN-NR498E/S Battery

lowering the concentration of sulfate in the sea water. This was a drastic change as compared to preglacial times before 2 million years ago.

Economic importance

Sulfur is intimately involved in production of fossil fuels and a majority of metal deposits because of its ability to act as an oxidizing or reducing agent. Sony VAIO VGN-NR498E/T Battery

The vast majority of the major mineral deposits on Earth contain a substantial amount of sulfur including, but not limited to: sedimentary exhalative deposits(SEDEX), Mississippi Valley-Type (MVT) and copper porphyry deposits. Iron sulfides, galena and sphalerite will form as by-products of hydrogen sulfide generation, Sony VAIO VGN-NR498E/W Battery

as long as the respective transition or base metals are present or transported to a sulfate reduction site. If the system runs out of reactive hydrocarbons economically viable elemental sulfur deposits may form. Sulfur also acts as a reducing agent in many natural gas reservoirs and generally ore forming fluids have a close relationship with ancient hydrocarbon seeps or vents.Sony VAIO VGN-NR50 Battery

Important sources of sulfur in ore deposits are generally deep-seated, but they can also come from local country rocks, sea water, or marine evaporites. The presence or absence of sulfur is one of the limiting factors on both the concentration of precious metals and its precipitation from solution.Sony VAIO VGN-NR50B Battery

pH, temperature and especially redox states determine whether sulfides will precipitate. Most sulfide brines will remain in concentration until they reach reducing conditions, a higher pH or lower temperatures.

Ore fluids are generally linked to metal rich waters that have been heated within a sedimentary basin under the elevated thermal conditions typically in extensional tectonic settings. Sony VAIO VGN-NR51 Battery

The redox conditions of the basin lithologies exert an important control on the redox state of the metal-transporting fluids and deposits can form from both oxidizing and reducing fluids. Metal-rich ore fluids tend to be by necessity comparatively sulfide deficient, so a substantial portion of the sulfide must be supplied from another source at the site of mineralization. Sony VAIO VGN-NR51B Battery

Bacterial reduction of seawater sulfate or a euxinic (anoxic and H2S-containing) water column is a necessary source of that sulfide. When present, the ?34S values of barite are generally consistent with a seawater sulfate source, suggesting barite formation by reaction between hydrothermal barium and sulfate in ambient seawater.Sony VAIO VGN-NR52 Battery

Once fossil fuels or precious metals are discovered and either burned or milled, the sulfur become a waste product which must be dealt with properly or it can become a pollutant. There has been a great increase in the amount of sulfur in our present day atmosphere because of the burning of fossil fuels. Sony VAIO VGN-NR52B Battery

Sulfur acts as a pollutant and an economic resource at the same time.

Human Impact

Human activities have had a major effect on the global sulfur cycle. The burning of coal, natural gas, and other fossil fuels has greatly increased the amount of S in the atmosphere and ocean and depleted the sedimentary rock sink.Sony VAIO VGN-NR71B Battery

Without human impact sulfur would stay tied up in rocks for millions of years until it was uplifted through tectonic events and then released through erosion and weathering processes. Instead it is being drilled, pumped and burned at a steadily increasing rate. Over the most polluted areas there has been a 30-fold increase in sulfate deposition.Sony VAIO VGN-NR71B2 Battery

Although the sulfur curve shows shifts between net sulfur oxidation and net sulfur reduction in the geologic past, the magnitude of the current human impact is probably unprecedented in the geologic record. Human activities greatly increase the flux of sulfur to the atmosphere, some of which is transported globally. Sony VAIO VGN-NR72B Battery

Humans are mining coal and extracting petroleum from the Earth’s crust at a rate that mobilizes 150 x 1012 gS/yr, which is more than double the rate of 100 years ago. The result of human impact on these processes is to increase the pool of oxidized sulfur (SO4) in the global cycle, at the expense of the storage of reduced sulfur in the Earth’s crust. Sony VAIO VGN-NS10E/S Battery

Therefore, human activities do not cause a major change in the global pools of S, but they do produce massive changes in the annual flux of S through the atmosphere.

When SO2 is emitted as an air pollutant, it forms sulfuric acid through reactions with water in the atmosphere. Sony VAIO VGN-NS10J/S Battery

Once the acid is completely dissociated in water thepH can drop to 4.3 or lower causing damage to both man-made and natural systems. According to the EPA acid rain is a broad term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere containing higher than normal amounts of nitric and sulfuric acids. Sony VAIO VGN-NS10L/S Battery

Distilled water (water without any dissolved constituents), which contains no carbon dioxide, has a neutral pH of 7. Rain naturally has a slightly acidic pH of 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a very weak acid. Around Washington, D.C., however, the average rain pH is between 4.2 and 4.4. Sony VAIO VGN-NS110E/L Battery

Since pH is on a log scale dropping by 1 (the difference between normal rain water and acid rain) has a dramatic effect on the strength of the acid. In the United States, roughly 2/3 of all SO2 and 1/4 of all NO3 come from electric power generation that relies on burning fossil fuels, like coal.Sony VAIO VGN-NS110E/S Battery

Stratospheric sulfur aerosols are sulfur-rich particles which exist in the stratosphere region of the Earth's atmosphere. The layer of the atmosphere in which they exist is known as the Junge layer, or simply the stratospheric aerosol layer. These particles consist of a mixture of sulfuric acid and water. Sony VAIO VGN-NS110E/W Battery

They are created naturally, such as by photochemical decomposition of sulfur-containing gases, e.g. carbonyl sulfide. When present in high levels, e.g after a strong volcanic eruption such as Mount Pinatubo, they produce a cooling effect, by reflecting sunlight, and by modifying clouds as they fall out of the stratosphere.Sony VAIO VGN-NS115N/S Battery

This cooling may persist for a few years before the particles fall out.

An aerosol is a suspension of fine solid particles or liquid droplets in a gas. The sulfate particles or sulfuric acid droplets in the atmosphere are about 0.1 to 1.0 micrometer (a millionth of a meter) in diameter.Sony VAIO VGN-NS11ER/S Battery

Sulfur aerosols are common in the troposphere as a result of pollution with sulfur dioxide from burning coal, and from natural processes. Volcanos are a major source of particles in the stratosphere as the force of the volcanic eruption propels sulfur-containing gases into the stratosphere.Sony VAIO VGN-NS11E/S Battery

The relative influence of volcanoes on the Junge layer varies considerably according to the number and size of eruptions in any given time period, and also of quantities of sulfur compounds released. Onlystratovolcanoes containing primarily granitic rocks are responsible for these fluxes, as basaltic rock erupted in shield volcanoes doesn't result in plumes which reach the stratosphere.Sony VAIO VGN-NS11J/S Battery

Creating stratospheric sulfur aerosols deliberately is a proposed geoengineering technique which offers a possible solution to some of the problems caused by global warming. However, this will not be without side effects and it has been suggested that the cure may be worse than the disease.Sony VAIO VGN-NS11L/S Battery

Natural sulfur aerosols are formed in vast quantities from the SO2 ejected by volcanoes, which may be injected directly into the stratosphere during very large (Volcanic Explosivity Index, VEI, of 4 or greater) eruptions. A comprehensive analysis, dealing largely with tropospheric sulfur compounds in the atmosphere, is provided by Bates et al.Sony VAIO VGN-NS11MR/S Battery

The IPCC AR4 says explosive volcanic events are episodic, but the stratospheric aerosols resulting from them yield substantial transitory perturbations to the radiative energy balance of the planet, with both shortwave and longwave effects sensitive to the microphysical characteristics of the aerosols.Sony VAIO VGN-NS11M/S Battery

As of 2009 there have been no explosive and climatically significant volcanic events since Mt. Pinatubo and consequently stratospheric aerosol concentrations are at the lowest concentrations since the satellite era and global coverage began in about 1980.Sony VAIO VGN-NS11SR/S Battery

During periods lacking volcanic activity (and thus direct injection of SO2 into the stratosphere), oxidation of COS (carbonyl sulfide) dominates the production of stratospheric sulfur aerosol.

Chemistry

The chemistry of stratospheric sulfur aerosols varies significantly according to their source.Sony VAIO VGN-NS11S/S Battery

Volcanic emissions vary significantly in composition, and have complex chemistry due to the presence of ash particulates and a wide variety of other elements in the plume.

The chemical reactions affecting both the formation and elimination of sulfur aerosols are not fully understood.Sony VAIO VGN-NS11ZR/S Battery

It is difficult to estimate accurately, for example, whether the presence of ash and water vapour is important for aerosol formation from volcanic products, and whether high or low atmospheric concentrations of precursor chemicals (such as SO2 and H2S) are optimal for aerosol formation. Sony VAIO VGN-NS11Z/S Battery

This uncertainty makes it difficult to determine a viable approach for geoengineering uses of sulfur aerosol formation.

Scientific study

Understanding of these aerosols comes in large part from the study of volcanic eruptions, notably Mount Pinatubo in thePhilippines, which erupted in 1991 when scientific techniques were sufficiently far advanced to study the effects carefully.Sony VAIO VGN-NS12M/S Battery

The formation of the aerosols and their effects on the atmosphere can also be studied in the lab. Samples of actual particles can be recovered from the stratosphere using balloons or aircraft.

Computer models can be used to understand the behaviour of aerosol particles, and are particularly useful in modelling their effect on global climate.Sony VAIO VGN-NS12M/W Battery

Biological experiments in the lab, and field/ocean measurements can establish the formation mechanisms of biologically derived volatile sulfurous gases.

Effect on climate

It has been established that emission of precursor gases for sulfur aerosols is the principle mechanism by which volcanoes cause episodic global cooling.Sony VAIO VGN-NS12S/S Battery

The Intergovernmental Panel on Climate Change AR4 regards stratospheric sulfate aerosols as having a low level of scientific understanding.

The aerosol particles form a whitish haze in the sky. This creates a global dimming effect, where less of the sun's radiation is able to reach the surface of the Earth.Sony VAIO VGN-NS21M/P Battery

This leads to a global cooling effect. In essence, they act as the reverse of a greenhouse gas, which tends to allow visible light from the sun through, whilst blocking infra-red emitted from the Earth's surface and its atmosphere. The particles also radiate infra red energy directly, as they lose heat into space.Sony VAIO VGN-NS21M/W Battery

Effects on light transmission through the atmosphere

All aerosols both absorb and scatter solar and terrestrial radiation. This is quantified in the Single Scattering Albedo (SSA), the ratio of scattering alone to scattering plus absorption (extinction) of radiation by a particle. Sony VAIO VGN-NS21S/S Battery

The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber.Sony VAIO VGN-NS21S/W Battery

Aerosols, natural and anthropogenic, can affect the climate by changing the way radiation is transmitted through the atmosphere. Direct observations of the effects of aerosols are quite limited so any attempt to estimate their global effect necessarily involves the use of computer models. Sony VAIO VGN-NS21Z/S Battery

The Intergovernmental Panel on Climate Change, IPCC, says: While the radiative forcing due to greenhouse gases may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modelling studies that are difficult to verify at the present time.Sony VAIO VGN-NS31M/P Battery

However, they are mostly talking about tropospheric aerosol.

Effect on ozone

The aerosols have a role in the destruction of ozone due to surface chemistry effects. Destruction of ozone has in recent years created large holes in the ozone layer, initially over the Antarctic and then theArctic. Sony VAIO VGN-NS31M/W Battery

These holes in the ozone layer have the potential to expand to cover inhabited and vegetative regions of the planet, leading to catastrophic environmental damage.

Ozone destruction occurs principally in polar regions, but the formation of ozone occurs principally in the tropics.Sony VAIO VGN-NS31S/S Battery

Ozone is distributed around the planet by the Brewer-Dobson circulation.Therefore, the source and dispersal pattern of aerosols is critical in understanding their effect on the ozone layer.

Effect on sky appearance

Aerosols scatter light, which affects the appearance of the sky and of sunsets. Changing the concentration of aerosols in theatmosphere can dramatically affect the appearance of sunsets. Sony VAIO VGN-NS31Z/P Battery

A change in sky appearance during the year without a summer(attributed to the eruption of Mount Tambora) was the inspiration for the paintings of J. M. W. Turner. Further volcanic eruptions and geoengineering projects involving sulfur aerosols are likely to affect the appearance of sunsets significantly,and to create a haze in the sky.Sony VAIO VGN-NS31Z/S Battery

Effect on the biosphere

Aerosol particles are eventually deposited from the stratosphere onto land and ocean. Depending on the volume of particles descending, the effects may be significant to ecosystems, or may not be. Modelling of the quantities of aerosols used in likelygeoengineering scenarios suggest that effects on terrestrial ecosystems from deposition is not likely to be significantly harmful.Sony VAIO VGN-NS31Z/W Battery

Geoengineering

The ability of stratospheric sulfur aerosols to create this global dimming effect has made them a possible candidate for use in geoengineering projects to limit the effect and impact of climate change due to rising levels of greenhouse gases. Delivery of precursor gases such as H2S and SO2 by artillery, aircraft andballoons has been proposed.Sony VAIO VGN-NS38M/P Battery

Understanding of this proposed technique is partly based on the fact that it is the adaptation of an existing atmospheric process. The technique is therefore potentially better understood than are comparable (but purely speculative) geoengineering schemes. Sony VAIO VGN-NS38M/W Battery

It is also partly based on the speed of action of any such solution deployed, in contrast to carbon sequestration projects such as carbon dioxide air capture which would take longer to work. However, gaps in understanding of these processes exist, for example the effect on stratospheric climate and on rainfall patterns, and further research is needed.Sony VAIO VGN-NS130E/L Battery

This technique has been studied more extensively than most other geoengineering techniques, and is suggested by commentators including Tom Wigley.

In chemistry, a disulfide bond (Br.E. disulphide bond) is a covalent bond, usually derived by the coupling of two thiol groups.Sony VAIO VGN-NS130E/S Battery

The linkage is also called anSS-bond or disulfide bridge. The overall connectivity is therefore R-S-S-R. The terminology is widely used in biochemistry. In formal terms, the connection is a persulfide, in analogy to its congener, peroxide (R-O-O-R), but this terminology is obscure and is no longer used (except in reference to R-S-S-H or H-S-S-H compounds).Sony VAIO VGN-NS130E/W Battery

Properties

The disulfide bond is strong, with a typical bond dissociation energy of 60 kcal/mole. Being about 40% weaker than C-C and C-H bonds, the disulfide bond is thus often the "weak link" in many molecules.Sony VAIO VGN-NS140E/L Battery

Furthermore, reflecting the polarizability of divalent sulfur, the S-S bond is susceptible to scission by polar reagents, both electrophiles and especially nucleophiles:

RS-SR + Nu- ? RS-Nu + RS-

The disulfide bond is about 2.05 Å in length, about 0.5 Å longer than a C-C bond. Rotation about the S-S axis is subject to a low barrier.Sony VAIO VGN-NS140E/S Battery

Disulfides show a distinct preference for dihedral angles approaching 90°. When the angle approaches 0° or 180°, then the disulfide is a significantly better oxidant.

Disulfides where the two R groups are the same are called symmetric, examples being diphenyl disulfide and dimethyl disulfide. When the two R groups are not identical, the compound is said to be an unsymmetric or mixed disulfide.Sony VAIO VGN-NS140E/W Battery

Although the hydrogenation of disulfides is usually not practical, the equilibrium constant for the reaction provides a measure of the standard redox potential for disulfides:

RSSR + H2 ? 2 RSH

This value is about -250 mV vs NHE (pH = 7). By comparison, the standard reduction potential for ferrodoxins is about -430 mV.Sony VAIO VGN-NS190J/L Battery

Formation of disulfides

Disulfide bonds are usually formed from the oxidation of sulfhydryl (-SH) groups, especially in biological contexts. The transformation is depicted as follows:

2 RSH ? RS-SR + 2 H+ + 2 e-

A variety of oxidants promote this reaction including air and hydrogen peroxide. Sony VAIO VGN-NS190J/S Battery

Such reactions are thought to proceed via sulfenic acid intermediates. In the laboratory, iodine in the presence of base is commonly employed to oxidize thiols to disulfides. Several metals, such as copper(II) and iron(III) complexes affect this reaction. Alternatively, disulfide bonds in proteins often formed by thiol-disulfide exchange:Sony VAIO VGN-NS190J/W Battery

RS-SR + R'SH R'S-SR + RSH

Such reactions are mediated by enzymes in some cases and in other cases are under equilibrium control, especially in the presence of a catalytic amount of base.

The alkylation of alkali metal di- and polysulfides gives disulfides. "Thiokol" polymers arise when sodium polysulfide is treated with an alkyl dihalide. Sony VAIO VGN-NS235J/L Battery

In the converse reaction, carbanionic reagents react with elemental sulfur to afford mixtures of the thioether, disulfide, and higher polysulfides. These reactions are often unselective but can be optimized for specific applications.

Many specialized methods have been developed for forming disulfides, usually for applications in organic synthesis. Reagents that deliver the equivalent of "RS+" react with thiols to give asymmetrical disulfidesSony VAIO VGN-NS235J/P Battery

RSH + R'SNR"2 ? RS-SR' + HNR"2, where R"2N = phthalimido

Scission of disulfides

The most important reaction of disulfide bonds is their cleavage, which occurs via reduction. A variety of reductants can be used.Sony VAIO VGN-NS235J/S Battery

In biochemistry, thiols such asmercaptoethanol (b-ME) or dithiothreitol (DTT) serve as reductants, the thiol reagents are used in excess to drive the equilibrium to the right:

RS-SR + HOCH2CH2SH HOCH2CH2S-SCH2CH2OH + 2 RSH

The reductant Tris(2-carboxyethyl)phosphine (TCEP) is useful, beside being odorless compared to b-ME and DTT, Sony VAIO VGN-NS235J/W Battery

because it is selective, working at both alkaline and acidic conditions (unlike DTT), is more hydrophilic and more resistant to oxidation in air. Furthermore, it is often not needed to remove TCEP before modification of protein thiols .

In organic synthesis, hydride agents are typically employed for scission of disulfides, such as sodium borohydride. More aggressive, alkali metals will effect this reaction:Sony VAIO VGN-NS240E/L Battery

RS-SR + 2 Na ? 2 NaSR

These reactions are often followed by protonation of the resulting metal thiolate:

NaSR + HCl ? HSR + NaCl

Thiol-disulfide exchange is a chemical reaction in which a thiolate group -S? attacks a sulfur atom of a disulfide bond -S-S-. Sony VAIO VGN-NS290J/L Battery

The original disulfide bond is broken, and its other sulfur atom (green atom in Figure 1) is released as a new thiolate, carrying away the negative charge. Meanwhile, a new disulfide bond forms between the attacking thiolate (red atom in Figure 1) and the original sulfur atom (blue atom in Figure 1).Sony VAIO VGN-NS290J/S Battery

Thiolates, not thiols, attack disulfide bonds. Hence, thiol-disulfide exchange is inhibited at low pH (typically, below 8) where the protonated thiol form is favored relative to the deprotonated thiolate form. (The pKa of a typical thiol group is roughly 8.3, but can vary due to its environment.)Sony VAIO VGN-NS50B/L Battery

Thiol-disulfide exchange is the principal reaction by which disulfide bonds are formed and rearranged in a protein. The rearrangement of disulfide bonds within a protein generally occurs via intra-protein thiol-disulfide exchange reactions; a thiolate group of a cysteine residue attacks one of the protein's own disulfide bonds. Sony VAIO VGN-NS50B/W Battery

This process of disulfide rearrangement (known as disulfide shuffling) does not change the number of disulfide bonds within a protein, merely their location (i.e., which cysteines are bonded). Disulfide reshuffling is generally much faster than oxidation/reduction reactions, which change the number of disulfide bonds within a protein.Sony VAIO VGN-NS51B/L Battery

The oxidation and reduction of protein disulfide bonds in vitro also generally occurs via thiol-disulfide exchange reactions. Typically, the thiolate of a redox reagent such as glutathione or dithiothreitol attacks the disulfide bond on a protein forming a mixed disulfide bond between the protein and the reagent. Sony VAIO VGN-NS51B/P Battery

This mixed disulfide bond when attacked by another thiolate from the reagent, leaves the cysteine oxidised. In effect, the disulfide bond is transferred from the protein to the reagent in two steps, both thiol-disulfide exchange reactions.

The in vivo oxidation and reduction of protein disulfide bonds by thiol-disulfide exchange is facilitated by a protein called thioredoxin. Sony VAIO VGN-NS51B/W Battery

This small protein, essential in all known organisms, contains two cysteine amino acid residues in a vicinal arrangement (i.e., next to each other), which allows it to form an internal disulfide bond, or disulfide bonds with other proteins. As such, it can be used as a repository of reduced or oxidized disulfide bond moieties.Sony VAIO VGN-NS52JB/L Battery

Other reactions of disulfides

Many specialized organic reactions have been developed for disulfides, again mainly associated with the scission of the S-S bond, which is usually the weakest bond in a molecule. In the Zincke disulfide cleavage reactions, disulfides are cleaved to give the to a sulfenyl halide by reaction with bromine or chlorine.Sony VAIO VGN-NS52JB/P Battery

Occurrence in proteins

Disulfide bonds play an important role in the folding and stability of some proteins, usually proteins secreted to the extracellular medium. Since most cellular compartments are reducing environments, in general, disulfide bonds are unstable in the cytosol, with some exceptions as noted below, unless a sulfhydryl oxidase is present.Sony VAIO VGN-NS52JB/W Battery

Disulfide bonds in proteins are formed between the thiol groups of cysteine residues. The other sulfur-containing amino acid, methionine, cannot form disulfide bonds. A disulfide bond is typically denoted by hyphenating the abbreviations for cysteine, e.g.,Sony VAIO VGN-NS70B/W Battery

when referring toRibonuclease A the "Cys26-Cys84 disulfide bond", or the "26-84 disulfide bond", or most simply as "C26-C84"[10]where the disulfide bond is understood and does not need to be mentioned. The prototype of a protein disulfide bond is the two-amino-acid peptide cystine, Sony VAIO VGN-NS71B/W Battery

which is composed of two cysteine amino acids joined by a disulfide bond (shown in Figure 2 in its unionized form). The structure of a disulfide bond can be described by its ?ss dihedral angle between the C? ? S? ? S? ? C? atoms, which is usually close to ±90°.

The disulfide bond stabilizes the folded form of a protein in several ways:Sony VAIO VGN-NS72JB/W Battery

1) It holds two portions of the protein together, biasing the protein towards the folded topology. That is, the disulfide bond destabilizes the unfolded form of the protein by lowering its entropy.

2) The disulfide bond may form the nucleus of a hydrophobic core of the folded protein, i.e., local hydrophobic residues may condense around the disulfide bond and onto each other through hydrophobic interactions.Sony VAIO VGN-NS90HS Battery

3) Related to #1 and #2, the disulfide bond link two segments of the protein chain, the disulfide bond increases the effective local concentration of protein residues and lowers the effective local concentration of water molecules. Since water molecules attack amide-amidehydrogen bonds and break up secondary structure, a disulfide bond stabilizes secondary structure in its vicinity.Sony VAIO VGN-NS92JS Battery

For example, researchers have identified several pairs of peptides that are unstructured in isolation, but adopt stable secondary and tertiary structure upon forming a disulfide bond between them.

A disulfide species is a particular pairing of cysteines in a disulfide-bonded protein and is usually depicted by listing the disulfide bonds in parentheses, e.g., the "(26-84, 58-110) disulfide species".Sony VAIO VGN-NS92XS Battery

A disulfide ensemble is a grouping of all disulfide species with the same number of disulfide bonds, and is usually denoted as the 1S ensemble, the 2S ensemble, etc. for disulfide species having one, two, etc. disulfide bonds. Thus, the (26-84) disulfide species belongs to the 1S ensemble, whereas the (26-84, 58-110) species belongs to the 2S ensemble. Sony VAIO VGN-NW11S/S Battery

The single species with no disulfide bonds is usually denoted as R for "fully reduced". Under typical conditions, disulfide reshuffling is much faster than the formation of new disulfide bonds or their reduction; hence, the disulfide species within an ensemble equilibrate more quickly than between ensembles.Sony VAIO VGN-NW11S/T Battery

The native form of a protein is usually a single disulfide species, although some proteins may cycle between a few disulfide states as part of their function, e.g.,thioredoxin. In proteins with more than two cysteines, non-native disulfide species may be formed, which are almost always unfolded.Sony VAIO VGN-NW11Z/S Battery

As the number of cysteines increases, the number of nonnative species increases factorially. The number of ways of forming pdisulfide bonds from n cysteine residues is given by the formula.

For example, an eight-cysteine protein such as ribonuclease A has 105 different four-disulfide species, only one of which is the native disulfide species. Sony VAIO VGN-NW11Z/T Battery

Isomerases have been identified that catalyze the interconversion of disulfide species, accelerating the formation of the native disulfide species.

Disulfide species that have only native disulfide bonds (but not all of them) are denoted by des followed by the lacking native disulfide bond(s) in square brackets. Sony VAIO VGN-NW21EF/S Battery

For example, the des[40-95] disulfide species has all the native disulfide bonds except that between cysteines 40 and 95. Disulfide species that lack one native disulfide bond are frequently folded, in particular, if the missing disulfide bond is exposed to solvent in the folded, native protein.Sony VAIO VGN-NW21JF Battery

In order to analyze the structure of proteins, it is often necessary to break disulfide bonds. This reduction of disulfide bonds can be accomplished by treatment with 2-mercaptoethanol, dithiothreitol, or tris(2-carboxyethyl)phosphine.

In prokaryotes and archaea

Disulfide bonds play an important protective role for bacteria as a reversible switch that turns a protein on or off when bacterial cells are exposed to oxidationreactions.Sony VAIO VGN-NW21MF Battery

Hydrogen peroxide (H2O2) in particular could severely damage DNA and kill the bacterium at low concentrations if not for the protective action of the SS-bond. Archaea typically have fewer disulfides than higher organisms.

In eukaryotes

In eukaryotic cells, in general, disulfide bonds are formed in the lumen of the RER (rough endoplasmic reticulum) but not in the cytosol.Sony VAIO VGN-NW21MF/W Battery

This is due to the oxidative environment of the ER and the reducing environment of the cytosol (see glutathione). Thus disulfide bonds are mostly found in secretory proteins, lysosomal proteins, and the exoplasmic domains of membrane proteins.Sony VAIO VGN-NW21ZF Battery

Notable exceptions to this rule include a number of cytosolic proteins which have cysteine residues in proximity to each other that function as oxidation sensors; when the reductive potential of the cell fails, they oxidize and trigger cellular response mechanisms.Sony VAIO VGN-NW31EF/W Battery

Vaccinia virus also produces cytosolic proteins and peptides that have many disulfide bonds; although the reason for this is unknown presumably they have protective effects against intracellular proteolysis machinery.

Disulfide bonds are also formed within and between protamines in the sperm chromatin of many mammalian species.Sony VAIO VGN-NW31JF Battery

Disulfides in regulatory proteins

As disulfide bonds can be reversibly reduced and re-oxidized, the redox state of these bonds has evolved into a signaling element. In chloroplasts, for example, the enzymatic reduction of disulfide bonds has been linked to the control of numerous metabolic pathways as well as gene expression. Sony VAIO VGN-NW320F/B Battery

The reductive signaling activity has been shown, thus far, to be carried by the ferredoxin thioredoxin system, channeling electrons from the light reactions of photosystem I to catalytically reduce disulfides in regulated proteins in a light dependent manner.Sony VAIO VGN-NW320F/TC Battery

In this way chloroplasts adjust the activity of key processes such as the Calvin-Benson cycle, starchdegradation, ATP production and gene expression according to light intensity.

In hair and feathers

Over 90% of the dry weight of hair comprises proteins called keratins, which have a high disulfide content, from the amino acid cysteine. Sony VAIO VGN-NW35E Battery

The robustness conferred in part by disulfide linkages is illustrated by the recovery of virtually intact hair from ancient Egyptian tombs. Feathers have similar keratins and are extremely resistant to protein digestive enzymes. Different parts of the hair and feather have different cysteine levels, leading to harder or softer material. Sony VAIO VGN-NW380F/S Battery

Manipulating disulfide bonds in hair is the basis for the permanent wave in hairstyling. Reagents that affect the making and breaking of S-S bonds are key, e.g., ammonium thioglycolate. The high disulfide content of feathers dictates the high sulfur content of bird eggs. Sony VAIO VGN-NW380F/T Battery

The high disulfide content of hair and feathers contributes to the disagreeable odor that results when they are burned.

In industry

Disulfide and (polysulfide) bonds are the crosslinking groups that result from the vulcanization of rubber. In analogy to the role of disulfides in proteins, the S-S linkages in rubber are crosslinkers, and strongly affect the rheology of the material.Sony VAIO VGN-NW50JB Battery

Related compounds

Thiosulfoxides are orthogonally isomeric with disulfides, having the second sulfur branching from the first and not partaking in a continuous chain. i.e. -S(=S)- rather than -S-S-.

Disulfide bonds are analogous but more common than related peroxides and diselenide bonds.Sony VAIO VGN-NW51FB/N Battery

Intermediate compounds of these also exist, for example, thioperoxides, also known as oxadisulfide bonds, have formula R1OSR2(equivalently R2SOR1). These are isomeric to sulfoxides in a similar manner to the above; i.e. -S(=O)- rather than -S-O-.Sony VAIO VGN-NW51FB/W Battery

Thiuram disulfides, with the formula (R2NC(S)S)2, are disulfides but they behave distinctly because of the thiocarbonyl group.

Compounds with three sulfur atoms, e.g., CH3S-S-SCH3, are called trisulfides, or trisulfide bonds.Sony VAIO VGN-NW70JB Battery,Sony VAIO VGN-NW71FB/N Battery,Sony VAIO VGN-NW71FB/W Battery,Sony VAIO VGN-NW91FS Battery,Sony VAIO VGN-NW91GS Battery,Sony VAIO VGN-NW91VS Battery