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Sulfonium Compounds
In organic chemistry, a sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively-charged ion (a "cation") featuring three organic substituents attached to sulfur. These organosulfur compounds have the formula . Together with a negatively-charged counterion, they give sulfonium salts. They are typically colorless solids that are soluble in organic solvent. Synthesis Sulfonium compounds are usually synthesized by the reaction of thioethers with alkyl halides. For example, the reaction of dimethyl sulfide with iodomethane yields trimethylsulfonium iodide: : + → The reaction proceeds by a nucleophilic substitution mechanism (SN2). Iodide is the leaving group departs. The rate of methylation is faster with more electrophilic methylating agents, such as methyl trifluoromethanesulfonate. Inversion Sulfonium ions with three different substituents are chiral owing to their pyramidal structure. Unlike the isoelectronic oxonium ions (R3O+), chiral sulfonium ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methionine
Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical role in the metabolism and health of many species, including humans. It is encoded by the codon AUG. Methionine is also an important part of angiogenesis, the growth of new blood vessels. Supplementation may benefit those suffering from copper poisoning. Overconsumption of methionine, the methyl group donor in DNA methylation, is related to cancer growth in a number of studies. Methionine was first isolated in 1921 by John Howard Mueller. Biochemical details Methionine (abbreviated as Met or M; encoded by the codon AUG) is an α-amino acid that is used in the biosynthesis of proteins. It contains a carboxyl group (which is in the deprotonated −COO− form under biological pH conditions), an amino group (which is in the protonated fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cations
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. The net charge of an ion is not zero because its total number of electrons is unequal to its total number of protons. A cation is a positively charged ion with fewer electrons than protons while an anion is a negatively charged ion with more electrons than protons. Opposite electric charges are pulled towards one another by electrostatic force, so cations and anions attract each other and readily form ionic compounds. Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. In the case of physical ionization in a fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Onium Compounds
In chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake for the class, is ammonium, , the protonated derivative of ammonia, . The name onium is also used for cations that would result from the substitution of hydrogen atoms in those ions by other groups, such as organic radicals, or halogens; such as tetraphenylphosphonium, . The substituent groups may be divalent or trivalent, yielding ions such as iminium and nitrilium. A simple onium ion has a charge of +1. A larger ion that has two onium ion subgroups is called a double onium ion, and has a charge of +2. A triple onium ion has a charge of +3, and so on. Compounds of an onium cation and some other anion are known as onium compounds or onium salts. Onium ions and onium compounds are inversely analogous to ions and ate complexes: *Lewis bas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoacid
Photoacids are molecules which become more acidic upon absorption of light. Either the light causes a photodissociation to produce a strong acid or the light causes photoassociation (such as a ring forming reaction) that leads to an increased acidity and dissociation of a proton. There are two main types of molecules that release protons upon illumination: photoacid generators (PAGs) and photoacids (PAHs). PAGs undergo proton photodissociation irreversibly, while PAHs are molecules that undergo proton photodissociation and thermal reassociation. In this latter case, the excited state is strongly acidic, but reversible. Photoacid generators An example due to photodissociation is triphenylsulfonium triflate. This colourless salt consists of a sulfonium cation and the triflate anion. Many related salts are known including those with other noncoordinating anions and those with diverse substituents on the phenyl rings. The triphenylsulfonium salts absorb at a wavelength of 233&n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triphenylsulfonium Triflate
Photoacids are molecules which become more acidic upon absorption of light. Either the light causes a photodissociation to produce a strong acid or the light causes photoassociation (such as a ring forming reaction) that leads to an increased acidity and dissociation of a proton. There are two main types of molecules that release protons upon illumination: photoacid generators (PAGs) and photoacids (PAHs). PAGs undergo proton photodissociation irreversibly, while PAHs are molecules that undergo proton photodissociation and thermal reassociation. In this latter case, the excited state is strongly acidic, but reversible. Photoacid generators An example due to photodissociation is triphenylsulfonium triflate. This colourless salt consists of a sulfonium cation and the triflate anion. Many related salts are known including those with other noncoordinating anions and those with diverse substituents on the phenyl rings. The triphenylsulfonium salts absorb at a wavelength of 233&n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TASF Reagent
The TASF reagent or tris(dimethylamino)sulfonium difluorotrimethylsilicate is a reagent in organic chemistry with structural formula (CH3)2N)3Ssup>+ 2Si(CH3)3sup>−. It is an anhydrous source of fluoride and is used to cleave silyl ether protective groups. Many other fluoride reagents are known, but few are truly anhydrous, because of the extraordinary basicity of "naked" F−. In TASF, the fluoride is masked as an adduct with the weak Lewis acid trimethylsilylfluoride (FSi(CH3)3). The sulfonium cation ((CH3)2N)3S+ is unusually non-electrophilic due to the electron-donating properties of the three (CH3)2N substituents. This compound is prepared from sulfur tetrafluoride: :3 (CH3)2NSi(CH3)3 + SF4 → 2 (CH3)3SiF + (CH3)2N)3Ssup>+ 2Si(CH3)3sup>− The colorless salt precipitates from the reaction solvent, diethyl ether. Structure The cation (CH3)2N)3Ssup>+ is a sulfonium ion. The S-N distances are 1.612 and 1.675 pm. The N-S-N angles are 99.6°. The anion is 2Si(CH ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TASF
The TASF reagent or tris(dimethylamino)sulfonium difluorotrimethylsilicate is a reagent in organic chemistry with structural formula (CH3)2N)3Ssup>+ 2Si(CH3)3sup>−. It is an anhydrous source of fluoride and is used to cleave silyl ether protective groups. Many other fluoride reagents are known, but few are truly anhydrous, because of the extraordinary basicity of "naked" F−. In TASF, the fluoride is masked as an adduct with the weak Lewis acid trimethylsilylfluoride (FSi(CH3)3). The sulfonium cation ((CH3)2N)3S+ is unusually non-electrophilic due to the electron-donating properties of the three (CH3)2N substituents. This compound is prepared from sulfur tetrafluoride: :3 (CH3)2NSi(CH3)3 + SF4 → 2 (CH3)3SiF + (CH3)2N)3Ssup>+ 2Si(CH3)3sup>− The colorless salt precipitates from the reaction solvent, diethyl ether. Structure The cation (CH3)2N)3Ssup>+ is a sulfonium ion In organic chemistry, a sulfonium ion, also known as sulphonium ion or sulfanium ion, is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ylide
An ylide or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms have full octets of electrons. The result can be viewed as a structure in which two adjacent atoms are connected by both a covalent and an ionic bond; normally written X+–Y−. Ylides are thus 1,2-dipolar compounds, and a subclass of zwitterions. They appear in organic chemistry as reagents or reactive intermediates. The class name "ylide" for the compound should not be confused with the suffix "-ylide". Resonance structures Many ylides may be depicted by a multiple bond form in a resonance structure, known as the ylene form, while the actual structure lies in between both forms: : The actual bonding picture of these types of ylides is strictly zwitterionic (the structure on the right) with the strong Coulombic attraction between the " ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimethylsulfoniopropionate
Dimethylsulfoniopropionate (DMSP), is an organosulfur compound with the formula (CH3)2S+CH2CH2COO−. This zwitterionic metabolite can be found in marine phytoplankton, seaweeds, and some species of terrestrial and aquatic vascular plants. It functions as an osmolyte as well as several other physiological and environmental roles have also been identified. DMSP was first identified in the marine red alga '' Polysiphonia fastigiata''. Biosynthesis In higher plants, DMSP is biosynthesized from ''S''-methylmethionine. Two intermediates in this conversion are dimethylsulfoniumpropylamine and dimethylsulfoniumpropionaldehyde. In algae, however, the biosynthesis starts with the replacement of the amino group in methionine by hydroxide. Degradation DMSP is broken down by marine microbes to form two major volatile sulfur products, each with distinct effects on the environment. One of its breakdown products is methanethiol (CH3SH), which is assimilated by bacteria into protein su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
S-Methylmethionine
''S''-Methylmethionine (SMM) is a derivative of methionine with the chemical formula ( CH3)2S+CH2CH2CH(NH3+)CO2−. This cation is a naturally-occurring intermediate in many biosynthetic pathways owing to the sulfonium functional group. It is biosynthesized from L-methionine which is first converted to ''S''-adenosylmethionine. The subsequent conversion, involving replacement of the adenosyl group by a methyl group is catalyzed by the enzyme methionine ''S''-methyltransferase. ''S''-methylmethionine is particularly abundant in plants, being more abundant than methionine. ''S''-Methylmethionine is sometimes referred to as ''vitamin U'', but it is not considered a true vitamin. The term was coined in 1950 by Garnett Cheney for uncharacterized anti-ulcerogenic factors in raw cabbage juice that may help speed healing of peptic ulcers. Biosynthesis and biochemical function ''S''-Methylmethionine arises via the methylation of methionine by ''S''-adenosyl methionine (SAM). The copr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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