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Hexaaza-18-crown-6
Hexaaza-18-crown-6 is the macrocyclic ligand with the formula (CH2CH2NH)6. A white solid, this compound has attracted attention as the N6-analogue of 18-crown-6. It functions as a hexadentate ligand in coordination chemistry. It is the parent hexaaza-crown ether. Its protonated derivatives bind anions via multiple hydrogen bonds.{{cite journal , doi=10.1016/j.inoche.2008.01.028, title=Binding of Fluoro-Containing Anions to Hexaazamacrocyclic Ligand: Competitive Interactions of Fluoride and Tetrafluoroborate Anions with Hexaprotonated [18]aneN6, year=2008, last1=Fonari, first1=Marina S., last2=Ganin, first2=Eduard V., last3=Gelmboldt, first3=Vladimir O., last4=Basok, first4=Stepan S., last5=Luisi, first5=Brian S., last6=Moulton, first6=Brian, journal=Inorganic Chemistry Communications, volume=11, issue=5, pages=497–501 References [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aza-crown Ether
In organic chemistry, an aza-crown ether is an aza analogue of a crown ether (cyclic polyether). That is, it has a nitrogen atom (amine linkage, or ) in place of each oxygen atom (ether linkage, ) around the ring. While the parent crown ethers have the formulae , the parent ''aza''-crown ethers have the formulae , where n = 3, 4, 5, 6. Well-studied aza crowns include triazacyclononane (n = 3), cyclen (n = 4), and hexaaza-18-crown-6 (n = 6). File:Me3TACN.png, 1,4,7-Trimethyl-1,4,7-triazacyclononane, a tridentate ligand used in coordination chemistry. File:Cyclam.png, Cyclam is a tetraaza crown ether with alternating and linkers between amine centers. File:Plerixafor.svg, Plerixafor, a derivative of cyclam, is used to treat lymphoma and multiple myeloma. File:Cryptand.svg, 2.2.2-Cryptand is an aza-crown of the mixed ether-amine variety. Synthesis The synthesis of aza crown ethers are subject to the challenges associated with the preparation of macrocycles. The 18-membered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macrocyclic Ligand
In coordination chemistry, a macrocyclic ligand is a macrocyclic ring having at least nine atoms (including all hetero atoms) and three or more donor sites that serve as ligands that can bind to a central metal ion. Crown ethers and porphyrins are prominent examples. Macrocyclic ligands exhibit high affinity for metal ions. History Porphyrins and phthalocyanines have long been recognized as potent ligands in coordination chemistry as illustrated by numerous transition metal porphyrin complexes and the commercialization of copper phthalocyanine pigments. In the 1960s the synthesis of macrocylic ligands received much attention. One early contribution involved the synthesis of the "Curtis macrocycles", in which a metal ion serves as a template for ring formation. Polyether macrocycles - or "crown" ligands - were also developed at that time. A few years later, three-dimensional analogs of crown ethers called " cryptands" were reported by Lehn and co-workers. Macrocyclic effect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
18-crown-6
18-Crown-6 is an organic compound with the formula [C2H4O]6 and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a ligand for some metal cations with a particular affinity for potassium cations (binding constant in methanol: 106 M−1). The point group of 18-crown-6 is S6. The dipole moment of 18-crown-6 varies in different solvent and under different temperature. Under 25 °C, the dipole moment of 18-crown-6 is in cyclohexane and in benzene. The synthesis of the crown ethers led to the awarding of the Nobel Prize in Chemistry to Charles J. Pedersen. Synthesis This compound is prepared by a modified Williamson ether synthesis in the presence of a templating cation: It can be also prepared by the oligomerization of ethylene oxide: :(CH2OCH2CH2Cl)2 + (CH2OCH2CH2OH)2 + 2 KOH → (CH2CH2O)6 + 2 KCl + 2 H2O It can be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexadentate Ligand
A hexadentate ligand in coordination chemistry is a ligand that combines with a central metal atom with six bonds. One example of a hexadentate ligand that can form complexes with soft metal ions is TPEN. A commercially important hexadentate ligand is EDTA. The denticity of hexadentate ligands is often denoted with the prefix κ6. Topology The way the donor atoms are joined together in the molecule is its topology. Some topologies are simple, such as the linear or ring shapes. The molecule can also be branched, either at a donor atom, or at a non-donor atom. Example shapes are the tripod, and amplector, with a bifurcation at each end. Rigid molecules can be used to force unusual coordination such as trigonal prism In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc .... F. Lions identif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coordination Chemistry
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many metal-containing compounds, especially those that include transition metals (elements like titanium that belong to the Periodic Table's d-block), are coordination complexes. Nomenclature and terminology Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly. The atom within a ligand that is bonded to the central metal atom or ion is called the donor atom. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A polydentate (multiple bonded) ligand is a molecule or ion that bonds to the central atom through several of the ligand's atoms; ligands with 2, 3, 4 or even 6 bonds to the central atom are common. These compl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyamines
A polyamine is an organic compound having more than two amino groups. Alkyl polyamines occur naturally, but some are synthetic. Alkylpolyamines are colorless, hygroscopic, and water soluble. Near neutral pH, they exist as the ammonium derivatives. Most aromatic polyamines are crystalline solids at room temperature. Natural polyamines Low-molecular-weight linear polyamines are found in all forms of life. The principal examples are the triamine spermidine and the tetraamine spermine. They are structurally and biosynthetically related to the diamines putrescine and cadaverine. Polyamine metabolism is regulated by the activity of the enzyme ornithine decarboxylase (ODC). Polyamines are found in high concentrations in the mammalian brain. File:Spermidine-2D-skeletal.svg, spermidine File:Spermine.svg, spermine Synthetic polyamines Several synthetic polyamines are used in chemical industry and the research laboratory. They are mainly of interest as additives to motor oil and as co-rea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethyleneamines
Ethyleneamines are a class of amine compounds containing ethylene (-CH2CH2-) linkages between amine groups. These compounds are generally colorless, low-viscosity liquids with a fishy amine odor. They are primarily used as building block chemicals and in epoxy resin curing agent chemistry. Production There are two main routes for the production of ethyleneamines, the reaction between ethylene dichloride and ammonia, and the reductive amination of monethanolamine. World capacity of ethyleneamines for the year 2001 was estimated to be 385,000 tonnes/year, with the majority comprising the ethylene dichloride route. In the ethylene dichloride route, the initial product of this reaction is ethylenediamine. In the presence of excess ethylene dichloride, the initial ethyleneamine is extended by one ethylene unit. The terminal alkyl chloride reacts with ammonia to give the amine, and the polyamine chain can be extended further in this fashion. Addition of a polyamine to the initial react ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chelating Agents
Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are called chelants, chelators, chelating agents, or sequestering agents. They are usually organic compounds, but this is not a necessity, as in the case of zinc and its use as a maintenance therapy to prevent the absorption of copper in people with Wilson's disease. Chelation is useful in applications such as providing nutritional supplements, in chelation therapy to remove toxic metals from the body, as contrast agents in MRI scanning, in manufacturing using homogeneous catalysts, in chemical water treatment to assist in the removal of metals, and in fertilizers. Chelate effect The chelate effect is the greater affinity of chelating ligands for a metal ion than that of similar nonchelating (monodentate) ligands for the same metal. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macrocycles
Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry. Synthesis The formation of macrocycles by ring-closure is called macrocylization. Pioneering work was reported for studies on terpenoid macrocycles. The central challenge to macrocyclization is that ring-closing reactions do not favor the formation of large rings. Instead, small rings or polymers tend to form. This kinetic problem can be addressed by using high-dilution reactions, whereby intramolecular processes are favored relative to polymerizations. Some macrocyclizations are favored using template reactions. Templates are ions, molecules, surfaces etc. that bind and pre-organize compounds, guiding them toward formation of a particular ring size. The crown ethers are often generated in the presence of an alkali metal cation, whic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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