Search results for "Crown"
showing 10 items of 324 documents
Ion-Induced Stretching of Low Generation Dendronized Polymers with Crown Ether Branching Units
2009
Synthesis of the first (G1) and second generation (G2) dendronized macromonomers MG1 and MG2 with the dibenzo-24-crown-8 moiety as branching unit is reported. The corresponding dendronized polymers, the polymethacrylates PG1 and PG2, were synthesized by free radical polymerization using AIBN as initiator at 60−80 °C. Static and dynamic light scattering revealed a significant chain expansion upon complexation of these polymers’ crown ether side chains with K+ ions. It is concluded that electrostatic repulsion does not significantly contribute to the chain expansion because of excessive counterion binding even well below the Manning limit, as evidenced by 19F NMR and 1H−19F NOE experiments. R…
Electron-transfer reduction of selected alcohols with alkalide K−, K+(15-crown-5)2 via organometallic intermediates
2004
Abstract The course of the reaction of alkalide K − , K + (15-crown-5) 2 1 with selected alcohols depends on the kind of alcohol and the mode of substrate delivery. In the case of methanol, potassium methoxide formed initially undergoes destruction at the excess of 1 . It results in potassium oxide and methylpotassium. The latter opens the crown ether ring giving potassium tetraethylene glycoxide vinyl ether and methane. A similar course of the process is observed for propanol. Potassium glycidoxide is the main product formed in the reaction of 1 with glycidol. Its oxirane ring is opened at the excess of 1 . Organopotassium alkoxides, i.e., potassium potassiomethoxide and dipotassium potass…
Crown ethers derived from bicyclocalix[4]arenes as chromoionophores
2001
The synthesis of calix[4]arenes in which opposite phenolic units are connected by a poly(oxyethylene) bridge at the narrow rim and a 2,6-dimethylene-4-nitrophenol bridge at the wide rim is reported. For two derivatives with tetra- (4) and penta(oxyethylene) (5) bridges UV-Vis spectrophotometric studies were carried out in buffered solution in the presence of alkali metal ions. Their complexation was associated with changes in their UV-Vis spectra, especially with an increase of the absorption band at 450 nm. For 4 and 5 this was most intense in the presence of potassium and caesium ions, respectively, indicating that the calixarene with the shorter crown ether bridge is selective towards po…
Synthesis and Characterization of a Soluble Bimetallic Oxalate-Based Bidimensional Magnet: [K(18-crown-6)]3[Mn3(H2O)4{Cr(ox)3}3]
2006
The "templating" K crown ether cation allows for the preparation of soluble layered oxalate-based bimetallic magnets, as in [K(18-crown-6]3{Mn3(H2O)4[Cr(ox)3]3}, with an unprecedented bidimensional polymeric anionic network that involves both oxalato bridges and H bonds. As in other 2D oxalate-bridged compounds, the compound behaves as a soft ferromagnet, with the onset of magnetic ordering occurring at 3.3 K.
Intramolecularly Coordinated Bis(crown ether)-Substituted Organotin Halides as Ditopic Salt Receptors
2013
The synthesis of the bis(crown ether)-substituted organostannanes X2Sn(CH2-[16]-crown-5)2 (3, X = I; 4, X = Br; 5, X = Cl; 6, X = F) and X2Sn(CH2-[13]-crown-4)2 (10, X = I; 11, X = Br; 12, X = F) is reported. The compounds have been characterized by 1H, 13C, 19F, and 119Sn NMR spectroscopy, elemental analyses, and electrospray ionization mass spectrometry (ESI-MS). Single-crystal X-ray diffraction analyses reveal a distorted-octahedral cis,cis,trans configuration of the tin atoms in compounds 4–6 and 10–12 as a result of intramolecular O→Sn coordination. The ability of the host molecules to form mono- and ditopic complexes with various halide salts in different solvents, including water, ha…
Controlling Multivalent Interactions in Triply-Threaded Two-Component Superbundles
2003
We have investigated the (1)H NMR spectra, the absorption spectra, the fluorescence spectra and decays, and the electrochemical properties of i). a tritopic receptor in which three benzo[24]crown-8 macrorings are fused onto a triphenylene core, ii). a trifurcated trication wherein three dibenzylammonium ions are linked 1,3,5 to a central benzenoid core, and iii). their 1:1 adduct which constitutes a triply-threaded, two-component supramolecular bundle. X-Ray crystallography has established the precise geometry of this paucivalent recognition motif in the solid state. In addition to [N(+)-H...O] hydrogen bonding and [C-H...O] interactions between the NH(2) (+) centers on the three dibenzylam…
The First Examples of a Crown Ether Intramolecularly Encapsulating Mono- and Diorganotin Dications: Synthesis and Structures of [PhSnCH2([16]crown-5)…
2010
The reaction of silver perchlorate with [PhI 2 SnCH 2 ([16]crown-5)] (1) and [I 3 SnCH 2 ([16]crown-5)] (2) gave the organotin(IV)-substituted crown ether complexes [PhSnCH 2 ([16]crown-5)][ClO 4 ] 2 (3) and [HOSnCH 2 ([16]crown-5)][Y] 2 (4: Y= ClO 4 , 5: Y=CF3 S 03 ) , respectively. All compounds have been isolated as air-stable materials and characterised by 1 H, 13 C, 119 Sn and 119 Sn MAS (5) NMR spectroscopy, ESIMS spectrometry, elemental analysis and by single-crystal X-ray diffraction analysis. The molecular structures of 3-5 show that the tin(IV) cation fits perfectly into the crown ether cavity and is coordinated by the five oxygen atoms of the ring to give a pentagonal bipyramidal…
Efficient Self-Assembly of Di-, Tri-, Tetra-, and Hexavalent Hosts with Predefined Geometries for the Investigation of Multivalency
2015
Coordination-driven self-assembly of differently shaped di- to hexavalent crown-ether host molecules is described. A series of [21]crown-7- and [24]crown-8-substituted bipyridine and terpyridine ligands was synthetized in a "toolbox" approach. Subsequent coordination to 3d transition metal and ruthenium(II) ions provides an easy and fast access to host assemblies with variable valency and pre-defined orientations of the crown-ether moieties. Preliminary isothermal calorimetry (ITC) titrations provided promising results, which indicated the host complexes under study to be suitable for the future investigation of multivalent and cooperative binding. The hosts described herein will also be su…
Structure and Conformational Studies of Aza-Crown 8-Amino-BODIPY Derivatives: Influence of Steric Hindrance on Their Photophysical Properties
2017
Herein, we report the synthesis, X-ray crystal structure and photophysical studies of six new 8-amino-BODIPY derivatives containing crown or azo-crown ether moieties. The influence of steric hindrance, caused by the crown ether, on the planarity of the BODIPY core and its relationship with the fluorescent properties has been established. 1H NMR spectroscopic studies were undertaken to clarify the changes in fluorescence observed in the presence of ZnII.
Influence of negative allosteric cooperativity in cation transport.
1992
Abstract The bis-macrocyclic ether5 seems to have a negative allosteric cooperativity and is able to transport double the amount of Na+ and K+ cations as monocyclic systems. This compound could be used as a simple model of the plasma membrane Na+−K+ ATPase which actively pumps Na+ out and K+ into the cell, respectively.