Azacrown Derivatives Research Articles

Metal Complexation of Calix[4]azacrown Derivatives – Evidence for Communication Between Upper and Lower Functionalised Rims

The coordination chemistry of calix[4]azacrowns obtained from the reaction of a diester calix[4]arene with diethylenetriamine provided unusual copper(II) and manganese(II) complexes in which calix[4]azacrown acts as a bidentate N,O-donor ligand, in some cases, but as a unidentate N-donor ligand, in other cases. The first example of a binuclear ruthenium(II)/manganese(II) complex, involving the calix[4]arene framework as the bridging ligand, is also reported. The calix[4]arene framework consists of a bipyridyl unit connected at the upper rim of the calix[4]arene, through an amide linkage, and an azacrown unit at the lower rim, also connected through amide groups. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Optical and electrochemical cations recognition and release from N-azacrown carbazoles

Two azacrown derivatives of carbazole have been prepared and their dipole moments in the excited state were estimated from solvatochromism. Their complexation constant K with calcium and sodium cations have been determined from the absorption spectra, the fluorescence spectra and, independently, from the first oxidation potential shift, as a function of the concentration in sodium and calcium perchlorates, when K is lower than 105. The fluorescence spectra of the calcium and sodium complexes in acetonitrile show two bands different from the fluorescence of the free probes, one from the excited complex similar to the fluorescence of the protonated probes and the other one from the nitrogen decoordinated cation complexes. These results are typical for moderatly polar crowned merocyanines with the ionophore acting as an electron-donor substituent. The stepwise decoordination rate of the calcium and sodium cations from the nitrogen atom of the fluorophore is competitive with the rate constant of fluorescence which accounts for the multiple fluorescence but does not allow a distant diffusion of the cations. From the study of the longer lived radical-cation of the azacrown carbazoles, generated electrochemically, the metal cations are completely released from the azacrown receptor as revealed by the unsensitivity of the second oxidation potential to the perchlorate salts. From the probe-cation pair with the higher association constant (log K > 6) the oxidation peak for the complex allows to estimate the decrease of K upon the oxidation of the probe to be a value of K •+/K = 8 × 10-4.

Complex formation between azacrown derivatives of dibenzylidenecyclopentanone and alkali-earth metal ions

The complex formation of 2,5-bis[4-(1,7,10,13-tetraoxa-4-azacyclopentadec-4-yl)benzylidene]cyclopentanone and several model compounds, prospective metal-sensitive fluorescent probes, with Mg2+, Ca2+, and Ba2+ ions in acetonitrile was studied. The azacrown derivatives of dibenzylidenecyclopentanone have two complex formation centers, azacrown cycle and carbonyl group. The sequence of binding to these sites is different for different ions. The efficient ejection of the Ca2+ and Ba2+ ions from their complexes with azacoronands was observed in the excited state, whereas in the case of the Mg2+ ion, this process occurred only partially.

A Conformational Phase Transition in a Langmuir Film of an Amphiphilic Azacrown

We have used grazing-incidence X-ray diffraction, X-ray reflectivity, and Brewster-angle microscopy to study an amphiphilic azacrown derivative at the air−water interface. The compound studied has a ring-shaped, flexible core with six alkyl chains attached. As the density is increased, the molecules undergo a phase transition from a face-on structure, with the alkyl tails extending away from the interface, to a thicker edge-on structure, with the tails extending radially away from the core. Concomitant with this rearrangement, the film develops long-range in-plane structural order.

Bis-Azacrown Derivative of Di-Benzilidene-Cyclopentanone as Alkali Earth Ion Chelating Probe: Spectroscopic Properties, Proton Accepting Ability and Complex Formation with Mg2+ and Ba2+ Ions

1,3- bis-[4-(N-aza-15-crown-5)-benzylidene]cyclopentanone-2 ( I), a ketocyanine dye, was synthesized. The electronic absorption and emission spectra, protolytic interactions in aqueous alcohol media and complex formation with alkali earth metals in acetonitrile were studied for the dye ( I) and for several model compounds. It was shown that protonation of both dialkylamino groups of all compounds studied takes place at closely similar pH values. The complexation of alkali earth metals with azacrown derivative ( I) takes place at azacrown moieties and the carbonyl group. The sequence of binding to these sites is different for Mg2+ and Ba2+ ions. The effective ejection of Ba2+ ion out of the azacrown cycle was observed in the excited state, though, as in the case of Mg2+ ion, such process occurred only partially. The results obtained suggest that this azacrown derivative of dibenzylidene cyclopentanone is sensitive to alkali earth ions and has prospects for different biologically oriented applications.

Induction of liquid crystalline phases in linear polyamines by complexation of transition metal ions

In this paper, we describe the preparation and characterization of polyamine–copper complexes based onN-alkylated polyethyleneimines which were obtained by polymer analogous reduction of the corresponding N-acylated polymers. Liquid crystalline properties of the originating linear polyamides are lost in the resulting polyamines which show a higher conformational mobility. In analogy to low molecular mass azacrown derivatives, the complexation of transition metal ions, here copper(ii), may reinduce liquid crystalline behavior. The structure formation in the liquid crystalline state is discussed based on X-ray investigations.

Formation of Hexagonal Columnar Mesophases by Linear and Branched Oligo- and Polyamides

The formation of columnar mesophases by N-acylated azacrown derivatives may be seen as a consequence of their discoid molecular geometry. Viewing these materials as cyclic oligomers, they are just one example of the various molecular architectures that may be realized based on the N-acylated ethylenamine fragment. By using linear oligoamides, the hexagonal columnar packing is preserved, the monotropic nature of the mesophase reflecting the higher flexibility of the systems. The corresponding polymers are accessible by polymer analogous acylation of linear poly(ethylenimine), in which a high conversion of the amino groups and a low polydispersity of the final polymers can be achieved. The resulting polyamides form enantiotropic mesophases with a hexagonal columnar structure proven by polarizing microscopy, DSC investigations, and X-ray studies. A helically folded structure of the polymer main chain is proposed whereby this structural motif is probably induced by the packing of the alkyl side chains. Based ...

Induction of liquid crystalline phases in N-alkylated poly(ethyleneimine)s by transition metal complexation

A liquid crystalline mesophase is induced by complexation of copper(II) nitrate with an N-alkylated poly(ethyleneimine) obtained by reduction of the corresponding polyamide, in analogy to low molecular mass azacrown derivatives.