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Sulfur

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Sulfur or sulphur (see spelling differences) is a chemical element with symbol S and atomic number 16. 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 at room temperature. Chemically, sulfur reacts with all elements except for nitrogen and the noble gases.

Elemental sulfur occurs naturally as the element (native sulfur), but most commonly occurs in combined forms as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, and Egypt. Sulfur is referred to in the Bible as brimstone.

Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas and petroleum. The element's largest commercial use (after mostly being converted to sulfuric acid) is to produce sulfate and phosphate fertilizers, because of the relatively high requirement of plants for sulfur and phosphorus. Sulfuric acid is also a primary industrial chemical outside fertilizer manufacture. Other uses for the element are in matches, insecticides and fungicides. Many sulfur compounds are odoriferous, and the smell of odorized natural gas, skunk scent, grapefruit, and garlic is due to organosulfur compounds. Hydrogen sulfide imparts the characteristic odor to rotting eggs and other biological processes.

Sulfur. Spelling and etymology.

Characteristics

Production. Compounds. History. Applications. Biological role. Precautions. Ultra-low-sulfur diesel. Ultra-low-sulfur diesel (ULSD) is diesel fuel with substantially lowered sulfur content.

Ultra-low-sulfur diesel

As of 2006, almost all of the petroleum-based diesel fuel available in UK, Europe and North America is of a ULSD type. There is not a single standard set of specifications and as the government mandated standard becomes progressively more strict so does the definition. The move to lower sulfur content is expected to allow the application of newer emissions control technologies that should substantially lower emissions of particulate matter from diesel engines.[1] This change occurred first in the European Union and is now happening in North America.[1] New emissions standards, dependent on the cleaner fuel, have been in effect for automobiles in the United States since model year 2007. ULSD has a lower energy content due to the heavy processing required to remove large amounts of sulfur from oil, leading to (1 to 2%) lower fuel economy.

Using it requires more costly oil.[2] Africa[edit] Kenya[edit] Sulfur assimilation. Sulfate reduction and assimilation in plants (APS, adenosine 5'-phosphosulfate; Fdred, Fdox, reduced and oxidized ferredoxin; RSH, RSSR, reduced and oxidized glutathione; SQDG, sulfoquinovosyl diacylglycerol) Sulfur is an essential element for growth and physiological functioning of plants.

Sulfur assimilation

However, its content strongly varies between plant species and it ranges from 0.1 to 6% of the plants' dry weight. Sulfates taken up by the roots are the major sulfur source for growth, though it has to be reduced to sulfide before it is further metabolized. Root plastids contain all sulfate reduction enzymes, but the reduction of sulfate to sulfide and its subsequent incorporation into cysteine predominantly takes place in the shoot, in the chloroplasts.

Stratospheric sulfur aerosols. Stratospheric sulfur aerosols are sulfur-rich particles which exist in the stratosphere region of the Earth's atmosphere.

Stratospheric sulfur aerosols

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. 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.[1] This cooling may persist for a few years before the particles fall out. Methionine. Methionine (/mɛˈθaɪ.ɵniːn/ or /mɛˈθaɪ.ɵnɪn/; abbreviated as Met or M) is a non-polar α-amino acid with a straight side chain that possess a S-methyl thioether (i.e.

Methionine

C–S–C bonding) at the γ-carbon. It has the chemical formula HO2CCH(NH2)CH2CH2SCH3. It is an essential amino acid in all metazoa.,[3] and is coded by the initiation codon AUG which also indicates mRNA's coding region where translation into protein begins. Methionine: a proteinogenic amino acid[edit] Disulfide. In inorganic chemistry disulfide usually refers to the corresponding anion S22−, or −S–S−, for example in disulfur dichloride.

Disulfide

Organic disulfides[edit] Properties[edit] The disulfide bonds are strong, with a typical bond dissociation energy of 60 kcal/mole (251 kJ mol−1). However, being about 40% weaker than C–C and C–H bonds, the disulfide bond is often the "weak link" in many molecules. Furthermore, reflecting the polarizability of divalent sulfur, the S–S bond is susceptible to scission by polar reagents, both electrophiles and especially nucleophiles:[1] 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. Disulfides where the two R groups are the same are called symmetric, examples being diphenyl disulfide and dimethyl disulfide. 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: Synthesis[edit] [edit]

Cysteine. Cysteine (abbreviated as Cys or C)[3] is a semi-essential proteinogenic amino acid with the formula HO2CCH(NH2)CH2SH.

Cysteine

It can be synthesized in humans to some extent.[4] It is encoded by the codons UGU and UGC. The thiol side chain in cysteine often participates in enzymatic reactions, serving as a nucleophile. The thiol is susceptible to oxidization to give the disulfide derivative cystine, which serves an important structural role in many proteins.