Crown-6 Moieties Research Articles

Nanostructuring with Surfactants: The Self-Assembly of a New Poly(thiophene-phenylene) Conjugated Polymer Bearing Azacrown Ether Pendant Groups.

We report the synthesis of a new conjugated polymer bearing crown ether moieties, poly[(N(1-aza-[18]crown-6)carbamido)thiophene-2,5-diyl-alt-1,4-phenylene] (BG2). In water, BG2 forms a dispersion with a slightly cloudy appearance. We have studied the effect of adding surfactants, with different polar head groups, on these polymer-polymer aggregates. Special attention is given to the system with the anionic surfactant, sodium dodecyl sulfate (SDS). The combination of photophysical techniques with electrical conductivity, NMR (1H, 13C, and 27Na), DFT calculations, molecular dynamics simulations, and small-angle neutron scattering (SANS) provides a detailed picture on the behavior of the SDS/BG2 system in aqueous solution and in thin films. NMR, electric conductivity, and DFT results suggest that hydrophilic interactions occur between the polar headgroup of the surfactant (OSO3- Na+) and the aza-[18]-crown-6 moiety. DFT calculations confirmed the capability of BG2 to form stable complexes with the Na+ cations, where the cation can be either inside the azacrown cavity or sandwiched between the cavity and the polymer chain, which seem to determine the position of the surfactant hydrocarbon chain and, therefore, be responsible for the disruption of the BG2 aggregates and subsequent increase in the photoluminescence quantum yields. SANS measurements, made with hydrogenated and deuterated SDS in D2O, clearly show how micron-sized aggregates of BG2 are broken down by SDS and then how BG2 becomes preferentially incorporated within joint colloidal particles of BG2 and SDS with increasing [SDS]/[BG2] molar ratio.

Protonation of calix[4]arene-(2,3-naphthylene-crown-6,crown-6): Experimental and theoretical study

On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H3O+ (aq) + 1·Na+ (nb) ⇄1·H3O+ (nb) + Na+ (aq) occurring in the two–phase water–nitrobenzene system (1 = calix[4]arene-(2,3-naphthylene-crown-6,crown-6); aq = aqueous phase, nb = nitrobenzene phase) was determined as log Kex(H3O+,1·Na+) = −0.2 ± 0.1. Further, the stability constant of the 1·H3O+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb(1·H3O+) = 5.9 ± 0.2. Finally, applying quantum chemical DFT calculations, the most probable structure of the cationic complex species 1·H3O+ was derived. In the resulting complex, the “central” cation H3O+ is bound by three strong hydrogen bonds to two phenoxy oxygen atoms and to one ethereal oxygen from the crown-6 moiety of the parent ligand 1. The interaction energy, E(int), of the considered 1·H3O+ complex was found to be −416.0 kJ/mol, confirming the formation of this cationic species as well.

Calix[4]arene-(2,3-naphthylene-crown-6,crown-6) as an extraordinarily efficient macrocyclic receptor for the univalent thallium cation

On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Tl+ (aq) + 1·Cs+ (nb) 1·Tl+ (nb) + Cs+ (aq) taking place in the two-phase water–nitrobenzene system (1 = calix[4]arene-(2,3-naphthylene-crown-6,crown-6); aq = aqueous phase, nb = nitrobenzene phase) was determined as log Kex(Tl+,1·Cs+) = 0.3 ± 0.1. Further, the extremely high stability constant of the 1·Tl+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb(1·Tl+) = 10.0 ± 0.2. Finally, applying quantum mechanical calculations, the most probable structure of the cationic complex species 1·Tl+ was derived. In the resulting complex, the ‘central’ cation Tl+ is bound by eight strong bonds to six oxygen atoms of the crown-6 moiety and to two carbons from the respective two benzene rings of the parent ligand 1 via cation-π interaction. The interaction energy, E(int), of the considered 1·Tl+ complex was found to be −305.7 kJ/mol, also confirming the formation of this cationic species.

Tuning electron donor-acceptor hybrids by alkali metal complexation.

A zinc phthalocyanine endowed with four [18]-crown-6 moieties, ZnPcTeCr, has been prepared and self-assembled with either pyridyl-functionalized perylenebisimides (PDI-Py) or fullerenes (C60-Py) to afford a set of novel electron donor-acceptor hybrids. In the case of ZnPcTeCr, aggregation has been circumvented by the addition of potassium or rubidium ions to lead to the formation of monomers and cofacial dimers, respectively. From fluorescence titration experiments, which gave rise to mutual interactions between the electron donors and the acceptors in the excited state, the association constants of the respective ZnPcTeCr monomers and/or dimers with the corresponding electron acceptors were derived. Complementary transient-absorption experiments not only corroborated photoinduced electron transfer from ZnPcTeCr to either PDI-Py or C60-Py within the electron donor-acceptor hybrids, but also the unexpected photoinduced electron transfer within ZnPcTeCr dimers. In the electron donor-acceptor hybrids, the charge-separated-state lifetimes were elucidated to be close to 337 ps and 3.4 ns for the two PDI-Pys, whereas the longest lifetime for the photoactive system that contains C60-Py was calculated to be approximately 5.1 ns.

Two-photon probes for metal ions based on phenylaza[18]crown-6 ethers and 1,2,3-triazoles as π-linkers.

Selective response: Two new cation-responsive two-photon absorption (2PA) dyes containing phenylaza[18]crown-6 moieties and 1,2,3-triazole units as π-linkers are described. One of the dyes (see picture) without cations exhibits a 2PA cross-section of 190 GM. Through binding of cations, the 2PA cross-section is reduced or enhanced.

Effect of Mutual Position of Electron Donor and Acceptor on Photoinduced Electron Transfer in Supramolecular Chlorophyll–Fullerene Dyads

In this study we have explored the influence of mutual position of chlorin electron donor and fullerene C60 electron acceptor on photoinduced electron transfer. Two zinc-chlorin-aza-[18]crown-6 compounds and three pyrrolidino[60]fullerenes with alkyl aminium and varying coordinative moieties were synthesized and used for self-assembling of a set of complexes via two-point binding. The aza[18]crown6 moieties were connected to chlorins via amide linker either at 13(4) or 17(4) position, hence, being attached on different sides of the chlorin plane. Furthermore, in the former case, the linker holds the crown closely spaced, whereas, in the latter, the linker gives more space and conformational freedom for the crown with respect to the chlorin macrocycle. The coordinative moieties at fullerene site, 3-pyridine, 4-pyridine, and 3-furan, were built by utilizing the Prato reaction. The two-point binding drove the molecules into specific complex formation by self-assembling; aminium ion was chelated by crown ether, while zinc moiety of chlorin was coordinated by pyridine and furan. Such pairing resulted in distinct supramolecular chlorin-fullerene dyads with defined distance and orientation. The performed computational studies at DFT level in solution, with TPSS-D3/def2-TZVP//def2-SVP, indicated different geometries and binding energies for the self-assembling complexes. Notably, the computations pointed out that for all the studied complexes, the donor-acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C60. The selective excitation of chlorin chromophore revealed efficient emission quenching in all dyads. The ultrafast spectroscopy studies suggested a fast and efficient photoinduced charge transfer in the dyads. The lifetimes of the charge separated states range from 55 to 187 ps in o-dichlorobenzene and from 14 to 60 ps in benzonitrile. Expectedly, the electron transfer rate was found to be critically dependent on the donor-acceptor distance; additionally, the mutual orientation of these entities was found to have significant contribution on the rate.

Molecular motion in pyridazinium/crown ether supramolecular cation salts of a nickel dithiolene complex

Supramolecular cations formed by monoprotonated pyridazinium cations and cis-anti-cis-dicyclohexano[18]-crown-6 (DCH[18]-crown-6) or dibenzo[18]-crown-6 (DB[18]-crown-6) were introduced into [Ni(dmit)2]− salts (where dmit2− = 2-thione-1,3-dithiole-4,5-dithiolate). X-ray crystal structure analysis of (pyridazinium+)(DCH[18]-crown-6)[Ni(dmit)2]− (1) revealed a chair-type conformation of the DCH[18]-crown-6 moiety. A V-shaped conformation of the DB[18]-crown-6 moiety was observed in (pyridazinium+)(DB[18]-crown-6)2[Ni(dmit)2]−(H2O)2 (2). Nitrogen atoms in the pyridazinium cations interacted with the oxygen atoms of the DCH[18]-crown-6 and DB[18]-crown-6 through N–H+O hydrogen bonds, forming 1:1 and 1:2 supramolecular structures, respectively. Sufficient space for molecular motions of the pyridazinium cations, namely flip-flop and in-plane rotations, exists in salt 1. Disorder in nitrogen atoms was observed by X-ray analysis, indicating dynamic motion of the pyridazinium cation, namely flip-flop motion and in-plane motion. A potential energy calculation further supported the possibility of dynamic motion of cations in the crystal. By contrast, the flip-flop motion of the pyridazinium group in salt 2 is restricted by the two nearest-neighbouring DB[18]-crown-6 molecules. Weak antiferromagnetic intermolecular interactions between the [Ni(dmit)2]− anions in the two-dimensional layers of salt 1 were observed, resulting in alternating antiferromagnetic Heisenberg chain-type magnetic susceptibility. Quasi-one-dimensional intermolecular interactions between the [Ni(dmit)2]− anions were observed in salt 2, whose magnetic behaviour followed the Bonner–Fisher model.

Chlorophyll tailored 20-trifluoroacetamide and its azacrown derivative as pH sensitive colorimetric sensor probe with response to AcO−, F− and CN− ions

Chlorophyll derivatives were functionalized with a trifluoroamide (TFA) group to obtain colorimetric ion sensors. Prior to this, a NO2BF4*pyridine based, chlorin nitration method was developed. The base strength dependent sensing of AcO−, F− and CN− ions was detected in aqueous media, which was enhanced in nonprotic solvents by an integration of the ditopic chelation capable amine crown-6 moiety.

Synthesis, crystal structures and competitive binding property of a family of functionalized calix[4]arene ionophores

Abstract A family of calix-crown hybrid molecules incorporating crown-4, crown-5 and crown-6 moieties as ionophore has been synthesized to evaluate their competitive complexing and extracting ability towards different alkali and alkaline earth metal ions. Selectivity of these ionophores towards Li+, Na+, K+, Ca2+, Mg2+ and Sr2+ has been evaluated with aqueous solution containing equimolar mixture of these ions. The concentration of metal ion in the extract (organic phase) has been estimated by ion chromatographic assay. Two of the ionophores show strong complexation with Na+ and K+, whereas the third ionophore exhibits no complexation with any metal ions used in this study. Association constants (Ka) for the binding of Na+ and K+ with two of these ionophores have been determined spectrophotometrically. Molecular structures of the Na+ and K+ complexes of these ionophores have been established by single crystal X-ray study. 1H NMR study of the ionophores and their complexes has also been carried out to investigate conformational behavior of the ionophores and their metal complexes in solution. Results have been discussed in light of various factors contribute to determine ion-selectivity.

Synthesis of Triptycene-Derived Macrotricyclic Host Containing Two Dibenzo-[18]-crown-6 Moieties and Its Complexation with Paraquat Derivatives: Li+-Ion-Controlled Binding and Release of the Guests in the Complexes

A new triptycene-derived macrotricyclic host containing two dibenzo-[18]-crown-6 moieties was synthesized and shown to form 1:1 complexes with paraquat derivatives in solution, in which the guests all thread the central cavity of the host. However, it was interestingly found that, depending on the paraquat derivatives with different functional groups, the host can form stable 1:1 or 1:2 complexes in different complexation modes in the solid state, which is significantly different from those of the macrotricyclic host containing two dibenzo-[24]-crown-8 moieties. The formation of the complexes was also proved by the ESI MS and electrochemical experiments. Moreover, it was found that the binding and release of the guests in the complexes could be easily controlled by the addition and removal of lithium ions.

Effect of Axial Ligation or π–π‐Type Interactions on Photochemical Charge Stabilization in “Two‐Point” Bound Supramolecular Porphyrin–Fullerene Conjugates

Two types of structurally well-defined, self-assembled zinc porphyrin-fullerene conjugates were formed by "two-point" binding strategies to probe the effect of axial ligation or pi-pi-type interactions on the photochemical charge stabilization in the supramolecular dyads. To achieve this, meso-tetraphenylporphyrin was functionalized to possess one or four [18]crown-6 moieties at different locations on the porphyrin macrocycle while fullerene was functionalized to possess an alkyl ammonium cation, and a pyridine or phenyl entities. As a result of the crown ether-ammonium cation complexation, and zinc-pyridine coordination or pi-pi-type interactions, stable zinc porphyrin-fullerene conjugates with defined distance and orientation were formed. Evidence for the zinc-pyridine complexation or pi-pi-type interactions was obtained from the spectral and computational studies. Steady-state and time-resolved emission studies revealed efficient quenching of the zinc-porphyrin singlet excited state in these dyads, and the measured rates of charge separation, k(CS) were found to be slightly better in the case of the dyads held by axial coordination and crown ether-cation complexation. Nanosecond transient absorption studies provided evidence for the electron transfer reactions, and these studies also revealed charge stabilization in these dyads. The lifetimes of the radical ion pairs were found to depend upon the type of porphyrins utilized to form the dyads, that is, porphyrin possessing the crown ether moiety at the ortho position of one of the phenyl rings yielded prolonged charge stabilized states. Addition of pyridine to the supramolecular dyads eliminated the zinc-pyridine coordination or pi-pi-type interactions of the "two-point" bound systems due to the formation of a new zinc-pyridine axial bond thus giving a unique opportunity to probe the effect of axial coordination or pi-pi interactions on k(CS) and k(CR). Under these conditions, the measured electron transfer rates revealed faster k(CS) and slower k(CR) as compared to those obtained in the absence of added pyridine. The evaluated lifetimes of the radical ion-pairs were found to be hundreds of nanoseconds and were longer in the presence of pyridine.

Synthesis and properties of calix[4]crown-6 functionalized polymers

Calix[4]crown-6-2,4-bis(4-aminobutyl ether), which has a crown-6 moiety at the 1,3-position and amino function at the 2,4-position, was prepared as an intermediate for the subsequent synthesis of calix[4]crown-6-containing polyamide and polyimide using adipoyl chloride and 1,2,4,5-benzenetetracarboxylic dianhydride. The chemical structures were characterized by IR,1H NMR spectroscopy and elemental analysis, and some of their physical properties, including their thermal behavior, were examined. The ion binding characteristics of the monomer and polymers for alkali metal and alkali earth metal ions were measured by liquid-liquid extraction from the aqueous phase into the organic phase. It has been observed that polyamide has a high binding ability towards various metal cations as compared to polyimide, which showed cesium ion selectivity.

Synthesis and binding properties of a calix[4]crown-6-functionalized polymeric ion acceptor

Calix[4]crown-6-2,4-bis(2-hydroxyethyl ether) (2), which has crown-6 moieties at the 1- and 3-positions and hydroxyethyl functions at the 2- and 4-positions, was prepared for the syntheses of polyester3 and polyurethane4 by reactions with adipoyl chloride and hexamethylene diisocyanate, respectively. The ion binding characteristics of monomer2 and polymers3 and4 toward alkali and alkali earth metal ions were measured by liquid-liquid extraction from the aqueous phase into the organic phase. We observed that the polyurethane4 has a higher binding affinity toward various metal cations when compared to polyester3, which exhibits cesium ion selectivity.

Solvent extraction of heavy metals with macrocyclic ligands based on calix[4]arenes

Ligand 1, a calix[4]arene-based compound with a crown-6 moiety, efficiently extracts the heavy metal ions Hg2+ and Pb2+ from weakly acidic solutions due to their compatible ion radius. The CO2H groups are essential for the metal extraction, as seen from a comparison with the corresponding ester compound 2. Ligand 3 as a crown-5 is also capable of extracting smaller cations such as Zn2+ and Cd2+ from weakly acidic solutions. Compound 5, bearing four CO2H groups, shows quantitative extraction for Hg2+ and Pb2+ at pH values above 2.5 and 2.8, respectively. Extraction takes place to some extent even if water-soluble organic complexing reagents are present in the aqueous phase, such as EDTA. Quantitative back-extraction is achieved by using 0.75 M HNO3.

Complexation of alkali cations by calix[4]crown ionophores: Conformation and solvent dependent Na+/Cs+binding selectivity and extraction: MD simulations in the gas phase, in water and at the chloroform-water interface

Abstract Calix[4]arenes bridged by crown5 and crown6 moieties represent a promising class of ionophores for big alkali cations. We present a theoretical demonstration of the possible modulation of the hostguest complementarity and recognition via the conformation of the host, and the solvent. Molecular dynamics and free energy calculations are reported for the 1,3-dimethoxy-p-tert-butyl and the p-H-derivatives in the cone, 1,3-alternate, and partial cone conformations, simulated in the gas phase and in water. In the gas phase, a decrease in binding affinity is calculated for the three forms of the complexes, from Na+ to Cs+. Intrinsically, the largest ions prefer clearly the 1,3-alternate conformers, while Na+ prefers slightly the cone conformers. In aqueous solution, the change in free energy for mutating the Na+ calix[4]-crown6 complex to the Cs+ complex depends markedly on the conformation of the calixarene, and is about 12 kcal/mol weaker for the 1,3-alternate than for the cone form. Taking into accou...

Liquid crystalline polyesteramides containing crown ether units in the mesogenes

Main chain liquid crystalline polyesteramides containing dibenzo-[18]-crown-6 moieties have been synthesized. Shown by polarisation microscopy and x-ray investigations, these polymers tend to form a mesophase with a layered structure,e.g. smectic A or smectic C type.