Search results for "Crown Compounds"
showing 10 items of 10 documents
Complexation of the potassium ion by diaza crown compounds in aqueous solutions
1988
The conductance behavior of potassium nitrate in water with and without 1,7,10,16-tetraoxa-4,13-diazacyclooctandecane[2.2] and 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-8.8.8-exacosane[2.2.2] macrocyclic ligands have been studied in order to analyze the complexation behavior of potassium cations in water. The absence of the complexation found in the [2.2] system is discussed in terms of the ligand structural features (presence of hydrogen bond donor and acceptor sites). The ion pair association constant of potassium cryptate as obtained from conductance measurements is also reported and discussed.
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…
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.
A thermodynamic insight into the recognition of hydrophilic and hydrophobic amino acids in pure water by aza-scorpiand type receptors.
2014
Interactions of different hydrophilic (His, Asp, Glu,) and hydrophobic (Ala, Phe, Tyr, Trp) amino acids in water with a scorpiand aza-macrocycle (L1) containing a pyridine group in the ring and its derivative (L2) bearing a naphthalene group in the tail have been analysed by potentiometric and calorimetric measurements. Theoretical calculations corroborate that major attractive forces that hold the adduct together are hydrogen bonds and salt-bridges, even though other interactions such as π-stacking or NH(+)⋯π may contribute in the case of hydrophobic amino acids and L2. Calorimetric measurements indicate that the interactions between L1 and the different amino acids are principally driven …
X-Ray and NMR Studies on Host-Guest Inclusion Complex Formation between Crown Ethers and Pyridinium Compounds
1998
Aromatic–aromatic, π–π, and cation–π interactions can be exploited in the preparation of molecular complexes between benzene-substituted crown ethers and pyridium cations. These complexes have been studied in the gas phase, in solution, and in the solid state; the structure of one of the complexes is depicted on the right.
Tuning the Basicity of Synergic Bimetallic Reagents: Switching the Regioselectivity of the Direct Dimetalation of Toluene from 2,5‐ to 3,5‐Positions
2008
Meta-meta metalation: Remarkably, toluene can be directly dimanganated or dimagnesiated at the 3,5-positions using bimetallic bases with active Me3SiCH2 ligands (see scheme, blue). In contrast, n-butyl ligands lead to 2,5-metalation (red). tmp=2,2,6,6-tetramethylpiperidide.
Direct C-H metalation with chromium(ii) and iron(ii): transition- metal host/benzenediide guest magnetic inverse-crown complexes
2009
Check M(etal)ate: The chessboard and the figures represent a special reaction in which different low-polarity metals can metalate arenes directly when they are brought into the right position. In a combination of queen (sodium) and knight (chromium or iron), it is possible for the knight (usually the weaker piece) to make a direct deadly hit on the king (benzene) in this game of elemental chess. Fil: Alborés, Pablo. Johannes Gutenberg Universitat Mainz; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Carrella, Luca M.. Johannes Gutenberg Universitat Mainz; Alemania Fil: Clegg, William. University of Newcastle; Reino Unido Fil: García Álvarez, Pablo. Univ…
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…
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.
Kronenethersubstituierte 1,4-Distyrylbenzole und ihre Komplexierung mit Alkalipikraten
2000
Crown Ether Substituted 1,4-Distyrylbenzenes and their Complexation with Alkali Picrates The 1,4-distyrylbenzenes 8 and 9, which contain two crown ether units, each, were prepared by Wittig—Horner reactions. Their complexation tendencies with alkali picrates (Li—Cs) in water/dichloromethane were investigated. Potas sium ions give the strongest complexes. Generally monomo-lecular 1:1-complexes are formed; however, [K-8] + [Pik]—, [K-9]+ [Pik]— and [Rb-8] + [Pik]— generate aggregates, for which a stairway structure is proposed.