Xenon Compounds

 

"It was initially believed that the noble gases could not form compounds due to their full valence shell of electrons that rendered them very chemically stable and unreactive."

"All noble gases have full s and p outer electron shells (except helium, which has no p sublevel), and so do not form chemical compounds easily. Because of their high ionization energy and almost zero electron affinity, they were not expected to be reactive."

"In 1933 Linus Pauling predicted that the heavier noble gases would be able to form compounds with fluorine and oxygen. Specifically, he predicted the existence of krypton hexafluoride and xenon hexafluoride (XeF₆), speculated that XeF₈ might exist as an unstable compound, and suggested that xenic acid would form perxenate salts.^[1][2] These predictions proved quite accurate, although subsequent predictions for XeF₈ indicated that it would be not only thermodynamically unstable, but kinematically unstable.^[3] As of 2009, XeF₈ has not been made, although the octafluoroxenon(VI) anion (XeF₈²⁻) has been observed."

Pyrene

"Pyrene is a polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is C₁₆H₁₀. This colourless solid is the smallest peri-fused PAH (one where the rings are fused through more than one face). Pyrene forms during incomplete combustion of organic compounds. "

"Pyrene was first isolated from coal tar, where it occurs up to 2% by weight. As a peri-fused PAH, pyrene is much more resonance-stabilized than its five-member-ring containing isomer fluoranthene. Therefore, it is produced in a wide range of combustion conditions. For example, automobiles produce about 1 μg/kg."

"Oxidation with chromate affords perinaphthenone and then naphthalene-1,4,5,8-tetracarboxylic acid. It undergoes a series of hydrogenation reactions, and it is susceptible to halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity."

Rhodopsin

"Rhodopsin, also known as visual purple, is a biological pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light, enabling vision in low-light conditions.^[1] Exposed to light, the pigment immediately photobleaches, and it takes about 30 minutes^[2] to regenerate fully in humans."

"Rhodopsin consists of the protein moiety opsin and a reversibly covalently bound cofactor, retinal. Opsin, a bundle of seven transmembrane helices connected to each other by protein loops, binds retinal (a photoreactive chromophore), which is located in a central pocket on the seventh helix at a lysine residue. Retinal lies horizontally with relation to the membrane. Each outer segment disc contains thousands of visual pigment molecules. About half the opsin is within the lipid bilayer. Retinal is produced in the retina from Vitamin A, from dietary beta-carotene. Isomerization of 11-cis-retinal into all-trans-retinal by light induces a conformational change (bleaching) in opsin continuing with metarhodopsin II, which activates the associated G protein transducin and triggers a second messenger cascade."

Crown Ethers

"Crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups. The Ball-and-stick model of the 18-crown-6 potassium complex in crystalline (18-crown-6)potassium chlorochromate, [K(C12H24O6)][CrClO3]most common crown ethers are oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., -CH₂CH₂O-. Important members of this series are the tetramer (n = 4), the pentamer (n = 5), and the hexamer (n = 6). The term "crown" refers to the resemblance between the structure of a crown ether bound to a cation, and a crown sitting on a person's head. The first number in a crown ether's name refers to the number of atoms in the cycle, and the second number refers to the number of those atoms that are oxygen. Crown ethers are much broader than the oligomers of ethylene oxide; an important group are derived from catechol."

"Crown ethers strongly bind certain cations, forming complexes. The oxygen atoms are well situated to coordinate with a cation located at the interior of the ring, whereas the exterior of the ring is hydrophobic. The resulting cations often form salts that are soluble in nonpolar solvents, and for this reason crown ethers are useful in phase transfer catalysis. The denticity of the polyether influences the affinity of the crown ether for various cations. For example, 18-crown-6 has high affinity for potassium cation, 15-crown-5 for sodium cation, and 12-crown-4 for lithium cation. The high affinity of 18-crown-6 for potassium ions contributes towards its toxicity."

Acetone

"Acetone is the organic compound with the formula (CH₃)₂CO, a colorless, mobile, flammable liquid, the simplest example of the ketones."

"Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory. About 6.7 million tonnes were produced worldwide in 2010, mainly for use as a solvent and production of methyl methacrylate and bisphenol A.^[7][8] Familiar household uses of acetone are as the active ingredient in nail polish remover and as paint thinner. It is a common building block in organic chemistry."

"Acetone is naturally produced and disposed of in the human body as a result of normal metabolic processes. It is normally present in blood and urine. Diabetic people produce it in larger amounts. Reproductive toxicity tests show that it has low potential to cause reproductive problems. In fact, the body naturally increases the level of acetone in pregnant women, nursing mothers and children because their higher energy requirements lead to higher levels of acetone production. Ketogenic diets that increase acetone in the body are used to reduce epileptic attacks in infants and children who suffer from recalcitrant refractory epilepsy."

Chloral Hydrate

"Chloral hydrate is a sedative and hypnotic drug as well as a chemical reagent and precursor. The name chloral hydrate indicates that it is formed from chloral (trichloroacetaldehyde) by the addition of one molecule of water. Its chemical formula is C₂H₃Cl₃O₂."

"It was discovered through the chlorination of ethanol in 1832 by Justus von Liebig in Gießen.^[2][3] Its sedative properties were first published in 1869 and subsequently, because of its easy synthesis, its use was widespread.^[4] It was widely used recreationally and misprescribed in the late 19th century. Chloral hydrate is soluble in both water and alcohol, readily forming concentrated solutions. A solution of chloral hydrate in alcohol called "knockout drops" was used to prepare a Mickey Finn. More reputable uses of chloral hydrate include its use as a clearing agent for chitin and fibers and as a key ingredient in Hoyer's mounting medium, which is used to prepare permanent or semipermanent microscope slides of small organisms, histological sections, and chromosome squashes."

"It is, together with chloroform, a minor side-product of the chlorination of water when organic residues are present in the water, though concentrations rarely exceed 5 micrograms per litre (µg/L)."

Niacin

"Niacin (also known as vitamin B₃, nicotinic acid and vitamin PP) is an organic compound with the formula C₆H₅NO₂ and, depending on the definition used, one of the forty to eighty essential human nutrients."

"Niacin is one of five vitamins associated with a pandemic deficiency disease: niacin deficiency (pellagra), vitamin C deficiency (scurvy), thiamin deficiency (beriberi), vitamin D deficiency (rickets), vitamin A deficiency (night blindness and other symptoms)."

"Niacin has been used to increase levels of HDL cholesterol in the blood and has been found to modestly decrease the risk of cardiovascular events in a number of controlled human trials. However, in a recent trial AIM-HIGH, a slow-release form of niacin was found to have no effect on cardiovascular event and stroke risk in a group of patients with LDL levels already well-controlled by a statin drug, and the trial was halted prematurely on evidence that niacin addition actually increased stroke risk in this group.^[2] The role of niacin in treating cardiovascular risk remains under debate."

Cyclooctatetraene

"1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane, with the formula C₈H₈. It is also known as [8]annulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of its stoichiometric relationship to benzene, COT has been the subject of much research and some controversy."

"Unlike benzene, C₆H₆, however, cyclooctatetraene, C₈H₈, is not aromatic, although its dianion, C₈H₈^2- (cyclooctatetraenide), is. Its reactivity is characteristic of an ordinary polyene, i.e. it undergoes addition reactions. Benzene, by contrast, characteristically undergoes substitution reactions, much as alkanes do, not additions."

Nitrosamines

"Nitrosamine occurs in latex products such as balloons,^[1] and in many foods and other consumables. Nitrosamines from condoms are not expected to be of toxicological significance."

"In foods, nitrosamines are produced from nitrites and secondary amines, which often occur in the form of proteins. Their formation can occur only under certain conditions, including strongly acidic conditions such as that of the human stomach. High temperatures, as in frying, can also enhance the formation of nitrosamines. The presence of nitrosamines may be identified by the Liebermann's reaction."

"Under acidic conditions the nitrite forms nitrous acid (HNO₂), which is protonated and splits into the nitrosonium cation N≡O⁺ and water: H₂NO₂⁺ = H₂O + NO⁺. The nitrosonium cation then reacts with an amine to produce nitrosamine."

"These processes lead to significant levels of nitrosamines in many foodstuffs, especially beer, fish, and fish byproducts, and also in meat and cheese products preserved with nitrite pickling salt. The U.S. government established limits on the amount of nitrites used in meat products in order to decrease cancer risk in the population.^{[citation needed]} There are also rules about adding ascorbic acid or related compounds to meat, in order to inhibit nitrosamine formation."

"Nitrosamines can also be found in tobacco smoke, American dip snuff and to a much lesser degree, snus. (127.9 PPM for American dip snuff compared to 2.8 PPM in Swedish snuff or snus)."

Piperdine

"Piperidine (Azinane after the Hantzsch–Widman nomenclature) is an organic compound with the molecular formula (CH₂)₅NH. This heterocyclic amine consists of a six-membered ring containing five methylene units and one nitrogen atom. It is a colorless fuming liquid with an odor described as ammoniacal, pepper-like;^[2] the name comes from the genus name Piper, which is the Latin word for pepper.^[3] Piperidine is a widely used building block and chemical reagent in the synthesis of organic compounds, including pharmaceuticals."

"Piperidine itself has been obtained from black pepper,^[6] from Psilocaulon absimile N.E.Br (Aizoaceae),^[7] and in Petrosimonia monandra."

"The piperidine structural motif is present in numerous natural alkaloids. These include piperine, which gives black pepper its spicy taste. This gave the compound its name. Other examples are the fire ant toxin solenopsin,^[9] the nicotine analog anabasine of the Tree Tobacco (Nicotiana glauca), lobeline of the indian tobacco, and the toxic alkaloid coniine from poison hemlock, which was used to put Socrates to death."