
	Where results make sense

Topic: Crown ether

Related Topics

Ether

Charles Pedersen

Complex (chemistry)

Dimethyl ether

Chemical synthesis

Ligand

Tetrahydrofuran

Petroleum ether

Cation

Chemical reaction

Inorganic chemistry

DuPont

Polyethylene glycol

Naphtha

Israeli terrorism

In the News (Fri 4 Dec 09)

Northern Trust

Marvin Harrison

Peter Chernin

Gary Locke

Match Play

Penelope Cruz

Mickey Rourke

AR Rahman

Danny Boyle

Hugh Jackman

	DuPont.com: Crown Ether (Site not responding. Last check: 2007-11-03)
		A crown ether is a molecule containing hydrogen, carbon and oxygen atoms.
		The original crown ether discovered by Charles Pedersen has six oxygen atoms exposed along the inside wall of the ring.
		Crown ethers also have potential to be used as "scavengers" to remove certain elements like radioactive strontium from the environment or to regulate concentrations of sodium in the blood.
	www.dupont.com /corp/science/crownether.html (270 words)

	Crown Ether Complexation
		The common names of these ethers include a number as a prefix to designate the total number of atoms in the ring and a number as a suffix to designate the number of oxygen atoms in the ring.
		Crown ethers may be used as phase-transfer catalysts and as agents to promote solubility of inorganic salts in organic solutions.
		The crown ether dissolves in benzene, the potassium ion complexes with the crown ether, and the permanganate is forced to dissolve in the benzene in order to ion-pair with the potassium ion.
	www.thecatalyst.org /experiments/jones/jones.html (551 words)

	Crown ether uranyl halide complexes - Patent 4186175
		Water is not a suitable liquid as it causes the inventive crown ether complexes to dissociate.
		The amount of liquid diluent used in admixing the uranyl halide and crown ether in accordance with this invention is not considered to be critical.
		Preferably the crown ether complexes are precipitated from the liquid and recovered by filtration.
	www.freepatentsonline.com /4186175.html (3985 words)

	[No title]
		Although the activity of the enzyme lyophilized in the absence of crown ether is different due to differences in hydrophobicity and thermodynamic water activity of the media, the activation factor is almost identical in the three cases.
		Crown ether induced activation is shown to be generally applicable for various enzymes, and different types of enzyme preparations, with a wide variety of solvents, reaction conditions, and reactions.
		Figure 3 Crown ether activation (V0(18-crown-6)/V0) for the peptide bond formation catalyzed by cross-linked subtilisin Carlsberg crystals in acetonitrile as a function of the amount of 18-crown-6 present during soaking and drying of the enzyme crystals.
	homepages.strath.ac.uk /~cdbs05/engberg.htm (4822 words)

	The Actinide Research Quarterly: 3rd quarter 1998
		Crown ether ligands have the ability to selectively bind metal ions of a characteristic size; thus, it's not surprising that crown ether ligands have been considered as potential extractants for actinide ions.
		Crown ether ligands have been shown to afford actinide extraction in hydrocarbon-water systems, and many of these studies invoke the standard cavity-size argument to explain the observed results.
		Indeed, the majority of reports on actinide crown ether complexes reveal that the crown ether ligand prefers to reside in the outer sphere of the actinide ion and engage in second-sphere hydrogen bonding between the crown ether oxygen atoms and water molecules coordinated to the actinide metal center (as illustrated in V).
	www.lanl.gov /source/orgs/nmt/nmtdo/AQarchive/98fall/crown_ether.html (1080 words)

	Crown ether - Wikipedia, the free encyclopedia
		The crown ethers are notable for their ability to strongly solvate cations.
		The fields of anionic synthetic reagents, phase transfer catalysts, biological ion transfer, and other emerging disciplines benefited profoundly from the discovery of crown ether.
		Aza analogues of crown ethers exist as well notably cyclen.
	en.wikipedia.org /wiki/Crown_ether (502 words)

	Synergism in Crown Ether Research (Site not responding. Last check: 2007-11-03)
		Although the discovery of crown ethers by Pedersen in 1967 opened up many opportunities for selective separations of metal ions, it wasn't until the discovery of synergistic extraction by crown ethers at Oak Ridge National Laboratory that many practical industrial and analytical applications were made possible.
		Below is a depiction of synergistic extraction of Cs ion from a mixture by a crown ether in synergistic combination with a sulfonic acid extractant.
		The problem arises in that the extraction by the crown ether used alone is often prohibitively weak, because this requires the co-extraction of a negative ion (called an anion) and anions present in most solutions of interest are inextractable.
	www.ornl.gov /sci/casd/csg/highlights/synergism.html (322 words)

	Qwika - similar:Ether
		The essential repeating unit of any simple crown ether is ethyleneoxy, i.e., -CH2CH2O-, which repeats twice in dioxane and six times in 18-crown-6.
		The Williamson reaction is a nucleophilic substitution in which the alkoxide ion displaces the halide, forming an ether and an inorganic salt.
		The Ether Dome was the operating room of the Bulfinch Building at Massachusetts General Hospital in Boston.
	www.qwika.com /rels/Ether (1546 words)

	PNNL News and Publications
		Environmental Molecular Sciences Laboratory, which is operated for DOE by its Pacific Northwest Laboratory, are looking at the possibility of using molecules known as crown ethers to bind to highly radioactive pollutants such as cesium and strontium.
		Scientists believe that once the crown ethers attach themselves to the radioactive isotopes, the molecules could be used to separate the highly radioactive contaminants from the large volume of liquid waste.
		One crown ether, called 18-crown-6, has been widely studied and is known to have a preference to bind to potassium in water.
	www.pnl.gov /news/1994/94-21.htm (873 words)

	Banita White Brown (Site not responding. Last check: 2007-11-03)
		Lariat ethers are derivatives of crown ether macrocycles which contain a sidearm appended to the macroring.
		The sidearm(s) is attached to a nitrogen atom of an aza or diaza crown ether molecule.
		In this case, the cation binding properties of the crown ether may be coupled with the binding properties of phenanthroline.
	www.chem.uncc.edu /FACULTY/BROWN/grad.htm (360 words)

	18-Crown-6
		18-Crown-6 is an example of a crown ether, which is a large cyclic polyether.
		Crown ethers are available in a variety of sizes and are named according to the number of atoms in the ring.
		Crown ethers are useful as complexing agents that help polar inorganic salts (like KF) dissolve in nonpolar organic solvents (like benzene).
	www.sunybroome.edu /~wovkulich_m/18-Crown-6.htm (362 words)

	ILL : ANNUAL REPORT 2001
		Multiple, cooperative hydrogen bonds in labile crown ether complexes are frequently more important in determining overall structure in the solid state than direct interactions with metal centres [1].
		Thus, crown ethers are remarkably effective in the isolation of strong hydrogen bond acceptors such as the hydrated proton (oxonium ion) [2].
		The hydrogen bond distances involving the water protons and the crown ether increase significantly as the temperature rises.
	www.ill.fr /AR-01/p-40.htm (1038 words)

	Crown Demo - Perturbation of Ion in Crown Ether (Vacuum) (Site not responding. Last check: 2007-11-03)
		This is because, with current methods, one must choose ionic parameters consistent with either water or the atom types in the crown molecule: it is impossible to allow the ion to act according to different nonbonded constants with different atoms.
		In the case of the crown, the issue could be crucial if the waters provide much of the free energy difference between different ion complexes; consider the structural finding that waters can fit in the ring with smaller ions.
		Thus the initial crown conformation would be expected to mostly affect the Na+ -> K+ perturbation, and the K+ -> Na+ result would be expected to vary depending on whether the crown happened to fold as the ion shrank.
	darkwing.uoregon.edu /~eshamay/AmberTutorial/crown_ether/pert/index.html (992 words)

	Pseudocrown Ether Membranes
		Crown ethers themselves are hard to work with on industrial scales because they are expensive, and toxic.
		Recovery of all of the crown ethers is very important both from an economic point of view as well as for safety.
		The ability to produce pseudocrown ether membranes would be an economical and safe means of removing metals from organic and aqueous sources.
	stripe.colorado.edu /~bowmanc/PROJECTS/BJE/BJE.html (648 words)

	Method of separating isomers of a crown ether compound to recover cis-syn-cis isomer from dicyclohexyl 18-crown 6. - ...
		The mode for separation used in the method of the invention is based on the solubility difference in the organic solvent used of the cis-syn-cis isomer and the complex formed between the cis-anti-cis isomer and uranyl nitrate.
		The quantity of uranyl nitrate to be used depends in particular on the nature of the crown compound, the precipitation conditions and the isomer B content of the mixture.
		In this example, 1 g of an isomer mixture of DCH18C6, namely of the crown compound of formula (I) with n=2 containing 47% of the cis-anti-cis isomer and 53% of the cis-syn-cis isomer, is dissolved in 3 ml of heptane and 1.5 ml of uranyl nitrate UO.sub.2 (NO.sub.3).sub.2.6H.sub.2 O is added to this under agitation.
	www.freepatentsonline.com /5082955.html (2811 words)

	The MSDS HyperGlossary: Ether
		Ether is also used as shorthand to refer to one of the most common ethers, diethyl ether, shown above.
		Ethers are particularly prone to formation of dangerous peroxides.
		The term "petroleum ether" is an old term used to refer to a mixture of hydrocarbons with a specific boiling point range.
	www.ilpi.com /msds/ref/ether.html (512 words)

	[No title] (Site not responding. Last check: 2007-11-03)
		Armed crown ethers intoduce guest-ligating sidearms to the crown rings to form dynamic and three dimentional complexes which are attracting increased interest as intelligent molecules.
		These compounds, 1-6, have nitrogen atoms at their crown rings, and via the introduction of sidearms by reaction with electrophiles, can be transformed in to armed crown ethers exhibiting new functionality.
		Synthesis of chromogenic crown ethers and liquid-liquid extraction of alkali metal ions
	www.tciamerica.com /news/page/armedcrown.html (205 words)

	Chapter 16 : Crown Ethers (Site not responding. Last check: 2007-11-03)
		These ethers are called "crown ethers" due to their shape.
		This allows ionic systems such as KF to be dissolved in organic solvents and used as reagents where the metal ion is in a complex, but the anion is unsolvated or naked and therefore quite reactive.
		Varying the size of the crown ether varies the cavity size and some metal ions fit better than others.
	www.chem.ucalgary.ca /courses/351/Carey5th/Ch16/ch16-1-2.html (224 words)

	Crown Ethers (Site not responding. Last check: 2007-11-03)
		The outside of the crown ether consists mostly of C-H bonds, and is therefore nonpolar.
		This region of the crown ether should associate with other nonpolar molecules.
		From this map we can see that the positive charge is distributed over a very large area, and that the center of the crown ether is negatively charged.
	www2.chem.ucla.edu /~harding/crownethers.html (242 words)

	Crown Ether Demo (Site not responding. Last check: 2007-11-03)
		In this demo, we build a simple crown ether, put a Na+ ion in it, equilibrate the system (and use this to explore vacuum dynamics), and perturb the ion (first Na+ -> K+, then K+ -> Cs+), analyzing the trajectories.
		Since the atomic charges were derived in the distant past, the 1-4 charge-scaling factor SCEE is set to 2.0 in all simulations, even though the crown vdw and bonding parameters are from the newer Cornell et al.
		Mechanism and thermodynamics of ion selectivity in aqueous solutions of 18-crown-6 ether - a molecular dynamics study.
	amber.scripps.edu /tutorial/crown_ether/index.html (297 words)

	Novel Process Employs Crown Ethers for Removing Technetium
		Although it had been well known that crown ethers possess the ability to efficiently extract sodium salts by binding the sodium ion, a key question of interest at ORNL concerns what factors determine which salt would be extracted selectively from a mixture of sodium salts.
		The transfer of either of these metal ions into the solvent by the crown ether must also be accompanied by a negatively charged ion.
		When the solvent is contacted with water, the sodium pertechnetate may be released into the water, regenerating the crown ether for further extraction cycles.
	www.ornl.gov /sci/casd/csg/highlights/srtalk.html (637 words)

	ZQLiu
		For crown ether, the macro cycle effect plays a very important role.
		Due to the crown shape, the electron lone pairs of Oxygen are conflicting each other at the center of crown ether.
		That raises the energy of un-bind crown ether.
	www.chem.northwestern.edu /~lambert/Zhongqiang.htm (286 words)

	Jean-Marie Lehn Summary
		Lehn, Pedersen and Cram shared the 1987 Nobel Prize in chemistry for their work in "elucidating mechanisms of molecular recognition, which are fundamental to enzymic catalysis, regulation, and transport." Through their combined efforts, they have made it possible to create synthetically molecules and enzymes with enormous pharmacological and research applications.
		Jean-Marie Lehn shared the 1987 Nobel Prize in chemistry for his contributions to the field of supramolecular or host-guest chemistry, particularly for his development of the crown ethers known as a cryptands and his work on synthesizing artificial enzymes.
		The shape of the crown ether, he found, allowed it easily to capture, or bind with, a metal ion.
	www.bookrags.com /Jean-Marie_Lehn (1862 words)

	Organic Chemistry Nomenclature
		Pederson synthesized about 60 different crown ethers in the 1960s, and found that the size of the central "cavity" determined which metal ions would be complexed most strongly, depending on their size.
		Modified crown ethers with some of the oxygen atoms replaced by nitrogen atoms are called cryptands.
		The concept of size- and shape-selective trapping, complexing, and catalysis, analogous in some respects to the use of crown ethers, has been extended to using natural and synthetic inorganic zeolites (aluminosilicates) as selective adsorbents.
	accurapid.com /journal/20org.htm (850 words)

	Dimethyl ether - Wikipedia, the free encyclopedia
		Dimethyl ether, also known as methoxymethane, oxybismethane, methyl ether, wood ether, and DME, is a colorless gaseous ether with an ethereal odor.
		And used in conjunction with propane to create a chemical reaction in which cryogenic freezing is used for the removal of common warts found on the human body.
		Dimethyl ether is also a clean-burning alternative to liquified petroleum gas, liquified natural gas, diesel and gasoline.
	en.wikipedia.org /wiki/Dimethyl_ether (157 words)

	Metallacrown Project
		A typical crown ether is a cyclic oligomer with a -C-C-O- repeat unit forming the macrocyclic ring.
		Crown ethers are classic ligands (composed of a cyclic polyether structure) that selectively sequester monovalent alkali metals and divalent alkali earths.
		Metallacrowns, unlike many similar cyclic sequestering agents, such as porphyrins, texaphyrins and crown ethers, can be synthesized in one or two steps, with high yields of 40%-95%.
	www.umich.edu /~vlpecgrp/Mcrowns/crown.html (2625 words)

	EXAFS studies of CsBr-dibenzo-18-crown-6 ether solutions
		Crown ethers represent a good first choice for XAFS structural studies because they have well-defined first and second shell environments.
		Additionally, the oxygen functional groups and bond distances can be easily manipulated by choice of specific crown ether molecules.
		The ability of XAFS to elucidate the structural environment of Cs within the crown ether complex will be useful in additional investigations in which the Cs is selectively bound within a cage of electronegative oxygen donors including humic and other organic substances, colloidal clay minerals and ion selective exchange resins used to treat nuclear wastes.
	www.uga.edu /srel/Reprint/1940.htm (174 words)

	[No title] (Site not responding. Last check: 2007-11-03)
		The metallacrown is neutral since the 3+ charge of V(V)O is balanced by the oxygen atoms of the triply deprotonated ligand, salicylhydroxamic acid.
		Though the metal-oxygen bond is lengthened as compared to that of the carbon-oxygen bonds of the crown ether (~1.9 A for the metallacrown, 1.3 for the crown ether A), the angles of the connectivity also change making up for the change in bond length (90
		These two changes combined to give an overall size similar to that of the crown ethers.
	www-personal.umich.edu /~vlpec/Mcrowns/9MC3.html (315 words)

	www.somewhereville.com » Blog Archive » Synthetic, Structural And Theoretical Investigations Of Alkali ...
		The crystal cells of these two complexes are far larger than computational resources would handle now (and definitely when the project started), but they’d be easily handled on better equipment (such as an 8-processor box with a terabyte or so of scratch space).
		Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH
		Interestingly, the lone pair at germanium is not pointed towards the alkali metal, rather two of the three hydrides are approaching the alkali metal center to display M-H interactions.
	www.somewhereville.com /?p=56 (574 words)

Try your search on: Qwika (all wikis)