Search results for "Crown"
showing 10 items of 324 documents
Bis-cyclohexyl-crown-ethers as allosteric carriers
1992
Abstract Several bis-cyclohexyl-crown-ethers have been synthesized and used as carriers for alkaline cations. These compounds should all show negative allosteric cooperativity, but only 1 exhibits an odd cation transport behavior across the liquid organic membranes.
Electrochemical and spectroscopic characterization of cobalt and zinc diaza‐18‐crown‐6 porphyrins and of a zinc dioxocyclam porphyrin
2000
The synthesis and electrochemical characterization of ‘crowned’ and ‘dioxocyclam’ metalloporphyrins containing Co(II) or Zn(II) metal ions is presented. Each complex is also characterized by mass spectrometry in addition to a variety of spectroscopic techniques (UV-vis, FTIR, ESR (in the case of Co(II)) and 1H and 13CNMR spectroscopy).
Tetra-μ-chlorido-bis(18-crown-6)platinum(II)dipotassium(I)
2010
In the title compound, [K(2)PtCl(4)(C(12)H(24)O(6))(2)], the Pt(II) ion is located on an inversion centre and is coordinated by four Cl atoms, forming a square-planar geometry. The K(I) ion is coordinated by six O atoms of the crown ether and two bridging Cl atoms. The K(I) ion is displaced by 0.756 (2) Å from the mean plane of the six O atoms of the crown ether. The mol-ecules are connected by weak C-H⋯O hydrogen bonds, forming an infinite two-dimensional network parallel to the (10) plane. Intra- and inter-molecular C-H⋯Cl hydrogen bonds are also observed.
Green discoloration of the crown after internal root resorption treatment with grey mineral trioxide aggregate (MTA)
2011
Root resorption (RR) is the loss of dental hard tissues as a result of clastic activities. Internal inflammatory root resorption (IRR) is a type of RR characterized by progressive loss of tooth substance starting from the root canal wall. IRR is usually asymptomatic, slowly progressing, and detectable upon routine radiographic examination or by the clinical sign of a ‘pink spot’ when the IRR involves the crown or the coronal third of the root canal. Mineral trioxide aggregate (MTA) is a biocompatible cement that has been used successfully in pulp capping, pulpotomy, treatment of traumatized teeth with immature apices, and for treatment of root resorption. The treatment and follow-up of a ma…
The Discoloration effect of White Mineral Trioxide Aggregate (WMTA), Calcium Enriched Mixture (CEM), and Portland Cement (PC) on Human Teeth
2017
Background The aim of this study was to evaluate the discoloration induced by CEM cement, Portland cement (PC) and MTA mixed with propylene glycol (MTA-PG) in comparison to White MTA. Material and methods Ninety extracted premolar and canine teeth were resected 2 mm below the CEJ. The coronal part of crown was prepared with peeso reamer and Gates-Glidden drills, and the specimens were randomly divided into 4 experimental (n=20) and one control (n=10) groups. The tooth crowns in experimental groups 1 to 4 were filled with White MTA, PC, CEM cement and MTA-PG, respectively; and in group 5, the teeth were kept empty. After incubation, digital photographs of teeth were acquired at 4 time points…
Hydrogen-bond-mediated self-assembly of 26-membered diaza tetraester crowns of 3,5-disubstituted 1 h -pyrazole. Dimerization study in the solid state…
2011
By using an improved synthetic method reported earlier, the cyclic stannoxanes obtained from RN-diethanolamine (R = Me, Bu) and dibutyltin oxide have been reacted with 1H-pyrazole-3,5-dicarbonyl dichloride to afford 26-membered diaza tetraester crowns (1, R = Me; 3, R = Bu) and 39-membered triaza hexaester crowns (2, R = Me; 4, R = Bu). The new structures were identified from their analytical and spectroscopic (1H and 13C NMR, FAB-MS, and/or ESI-MS) data. Both diaza tetraester crowns (1 and 3), containing two 1H-pyrazole units, self-assemble into dimeric species through the formation of four hydrogen bonds involving the two NH pyrazole groups and the two tertiary amine groups of both crowns…
Simultaneous Freezing of Chirality and In−Out Conformation of a Macropentacyclic Cryptand by Protonation
2004
Compound 1, a cryptand-derived macropentacycle, is a flexible molecule that encompasses many conformations (symmetrical, unsymmetrical, and chiral ones) depending on the observation temperature (VT 1H NMR). Selective monoprotonation of this molecule leads to a totally unsymmetrical, rigidly chiral species in solution (1H NMR). Helical chirality and in-out conformation of monoprotonated 1 are observed in the solid state by X-ray diffraction analysis, as well as the proton location. The latter is bound to the endo bridgehead nitrogen atom and involved in hydrogen-bonding interactions with the three closest sulfurs. Significant induction of chirality is triggered by reaction of 1 with the opti…
Synthesis and structure of mono-bridged resorcinarene host: a ditopic receptor for ammonium guests.
2009
The synthesis and structural properties of tetramethoxy resorcinarene mono-crown-5 (1) are described. The binding characteristics of 1 toward acetylcholine and tetramethylammonium salts were investigated by 1H NMR titration. It was observed that the cavity of 1 provides a better fit to acetylcholine compared to the smaller tetramethylammonium cation, as acetylcholine is able to interact with both the crown ether moiety and the free hydroxyl groups of receptor 1 simultaneously.
Oxaaza cyclophanes in the recognition of nucleotides. The role of oxygen and electron-rich aromatic rings
2007
Dioxapolyaza cyclophanes derived from resorcinol and different polyamine chains have been studied in aqueous solution as abiotic receptors for nucleotides. The presence of the additional ethyleneoxy subunits is reflected in a higher basicity and in a significant increase in the log K values for the interaction with nucleotides relative to that of related polyazacyclophanes.
Designing binuclear transition metal complexes: a new example of the versatility of N,N′-bis(2-aminobenzyl)-4,13-diaza-18-crown-6
2005
[Abstract] N,N′-Bis(2-aminobenzyl)-4,13-diaza-18-crown-6 (L) is a versatile receptor able to adapt to the coordinative preferences of different metal cation guests. With first-row transition metal ions, L tends to form binuclear complexes but, depending on the nature of the particular metal ion, the structure of the binuclear complex may be very different. Herein we report a study of the structure and magnetic properties of the corresponding nickel(II) and cobalt(II) complexes. The X-ray crystal structure of the nickel complex (1), with formula [Ni2(L)(CH3CN)4](ClO4)4·CH3CN, shows that this compound presents a symmetric coordination environment with L adopting an anti arrangement. Each Ni(I…