Crown-containing naphtho- and anthraquinones: synthesis and complexation with alkali and alkaline-earth metal cations

Novel naphtho- and anthraquinones conjugated with benzo- and dibenzo-18-crown-6 ethers were obtained. Their complexation reactions with Groups Ia and IIa metal perchlorates in acetonitrile were studied by spectrophotometric titration. In most cases, the complexation involves the crown ether moiety; the stability constant of the resulting complex decreases in the following order: Ba²⁺ > Sr²⁺ > Ca²⁺ > Na⁺. For crown-containing anthraquinone imines characterized by prototropic “imine-enamine” tautomerism, the complexation shifts the equilibrium toward the imine species, which allow these compounds to be classified among a rarely occurring type of tautomeric chromoionophores. Unlike other cations, the magnesium ions preferably interact with the heteroatoms of the anthraquinone moiety (the imine N atom, the OH group, and the carbonyl O atom of the benzamido group); the logK value reaches 4.4. The chelation to the Mg²⁺ cations and the effect of the complexation on the tautomeric equilibrium was confirmed by quantum chemical calculations.     

Complexation of di-benzyloxy ether derivatives of calix[4]arene with alkali earth metal cations

The synthesis and complexing abilities of 26,28-bis-benzyloxy-25,27-dihydroxy-5,11,17,23-tetra-tertbutyl-calix[4]arene towards alkali earth metal ions Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ in a methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed that the ligand is capable to complex all alkali earth cations by 1:1 metal to ligand ratios. The selectivity presented considering the calculated stability constants are in the order Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ towards the ligand.     

Interaction between p-tetraphenyl tetrahomodioxacalix[4]arene amide derivatives and alkali and alkaline-earth metal cations

The binding properties of four amido derivatives of p-tetraphenyl tetrahomodioxacalix[4]arene towards alkali and alkaline-earth metal cations using UV-absorption spectrophotometry, ¹H NMR and ESI-mass spectrometry techniques are reported.     

Complexation of alkaline-earth metals with bisazosubstituted chromotropic acid derivatives on fibrous ion exchanges

The method of diffuse refection has been used for the investigation of complexation reactions between Mg, Ca, Sr, and Ba ions (2+) with bisazosubstituted chromotropic acid derivatives after their sorption on a solid phase. Different adsorbents and methods of the immobilization of metal ions and organic reagent have been tested. The influence of pH on the sorption and subsequent reaction between alkaline-earth metals and organic reagents has been studied. The dependence of analytical signals on the reagent nature has been discussed. Systems have been proposed for the determination of the total concentration of Ca, Sr, and Ba and also Sr and Ba in the concentration range n × 10⁻⁴ M; these systems include the sorption of elements on the solid phase of polyacrylonitrile fiber loaded with the Chelex-100 ion exchanger from the solution with pH 7.0 ± 0.5, subsequent treatment of discs with the solutions of Carboxynitrazo or Ortanyl B and the measurement of the coefficients of diffuse refection.     

Photonics of 18-crown-6-containing styryl dye and its complexes with metal cations

Using absorption, luminescence, ¹H NMR, and laser kinetic spectroscopies, the photophysical processes and photochemical reactions of 4-[(E)-2-(2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecin-18-yl)vinyl]-1-ethylpyridinium perchlorate and its complexes with lithium, sodium, potassium, calcium, barium, silver, and lead perchlorates in MeCN have been studied. The styryl dye and its complexes with metal cations are capable of emitting normal (prompt) and delayed fluorescence and enter into the trans–cis photoisomerization reaction. The dye molecules in the triplet state participate in the processes of degradation of electronic excitation energy. Triplet–triplet absorption is observed only in the presence of lead cations with a maximum at 470 nm and the deactivation rate constant of the triplet state k = 2.5 × 10⁴ s^–1 in a deoxygenated solution.     

Ozone reactions with alkaline-earth metal cations and dications in the gas phase: room-temperature kinetics and catalysis

Room-temperature rate coefficients and product distributions are reported for the reactions of ozone with the cations and dications of the alkaline-earth metals Ca, Sr, and Ba. The measurements were performed with a selected-ion flow tube (SIFT) tandem mass spectrometer in conjunction with either an electrospray (ESI) or an inductively coupled plasma (ICP) ionization source. All the singly charged species react with ozone by O-atom transfer and form monoxide cations rapidly, k = 4.8, 6.7, and 8.7 x 10(-10) cm3 molecule(-1) s(-1) for the reactions of Ca+, Sr+, and Ba+, respectively. Further sequential O-atom transfer occurs to form dioxide and trioxide cations. The efficiencies for all O-atom transfer reactions are greater than 10%. The data also signify the catalytic conversion of ozone to oxygen with the alkaline-earth metal and metal oxide cations serving as catalysts. Ca2+ reacts rapidly with O3 by charge separation to form CaO+ and O2+ with a rate coefficient of k = 1.5 x 10(-9) cm3 molecule(-1) s(-1). In contrast, the reactions of Sr2+ and Ba2+ are found to be slow and add O3, (k >/= 1.1 x 10-11 cm3 molecule-1 s-1). The initial additions are followed by the rapid sequential addition of up to five O3 molecules with values of k between 1 and 5 x 10(-10) cm3 molecule(-1) s(-1). Metal/ozone cluster ions as large as Sr2+(O3)5 and Ba2+(O3)4 were observed for the first time.     

Complexation of common metal cations by cyanins: Binding affinity and molecular structure

The ability of diverse metal cations to form complexes with cyanin has been investigated by means of Density Functional Theory (DFT) and the Quantum Theory of Atoms in Molecules (QTAIM). The strongest preference is shown by trivalent metals which exceed that of Mg(II), indicating that ion replacement processes are suitable detoxification mechanisms for plants. Molecular structure analysis indicates that the larger the metal affinity of Cy⁻ the longer the C2-C1’ bond length and smaller ρ_b value. This is understood as upon metal complexation the Cy⁻ ligand molecular structure is more compatible with a dienolate-like structure rather than the 4′-keto-quinoidal-like structure. The weight of the former increases as stronger the binding. QTAIM charges indicate that the stronger the binding energy the larger the charge transfer from Cy⁻ to the metal, reducing its positive charge below the values indicated by the corresponding Lewis structure.     

Supramolecular organic photochemistry of crown-ether-containing styryl dyes

The data on the molecular design, spectral properties, photochemistry and complexation of photochromic crown ethers containing a C=C bond are described systematically and generalized. Prospects for the practical application of these compounds are considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp 641–665, April, 1997.     

Controlling chemistry with cations: photochemistry within zeolites

The alkali ions present in the supercages of zeolites X and Y interact with included guest molecules through quadrupolar (cation-pi), and dipolar (cation-carbonyl) interactions. The presence of such interactions can be inferred through solid-state NMR spectra of the guest molecules. Alkali ions, as illustrated in this article, can be exploited to control the photochemical and photophysical behaviors of the guest molecules. For example, molecules that rarely phosphoresce can be induced to do so within heavy cation-exchanged zeolites. The nature (electronic configuration) of the lowest triplet state of carbonyl compounds can be altered with the help of light alkali metal ions. This state switch (n pi*-pi pi*) helps to bring out reactivity that normally remains dormant. Selectivity obtained during the singlet oxygen oxidation of olefins within zeolites illustrates the remarkable control that can be exerted on photoreactions with the help of a confined medium that also has active sites. The reaction cavities of zeolites, like enzymes, are not only well-defined and confined, but also have active sites that closely guide the reactant molecule from start to finish. The examples provided here illustrate that zeolites are far more useful than simple shape-selective catalysts.     

Complexation of acyclic ligands having two terminal quinoline units with alkali metal cations

Abstract

Acyclic multidentate ligands consisting of an oligooxyethylene chain (di-, tri-, tetra-, and penta-) and two terminal rigid quinaldate end groups were newly prepared and their complexation properties with alkali metal cations were estimated by the solvent extraction method to indicate a better affinity for K⁺. Among them, the tetraethylene glycol derivative showed the highest K⁺ binding on about the same level as 18-crown-6. Their conformations in solution and in the solid state were examined by using ¹H- and ¹³C-NMR spectroscopy and X-ray crystal analyses, respectively. The better binding of K⁺ in comparison with the corresponding glymes or analogues having the same donor sites was reasonably explained by considering the effective co-ordination of the carbonyl oxygen of the ester groups and the parallel π-stacking interaction between two quinaldate surfaces.     

Complexation of lanthanide cations with ampicillin

The complexation of Ln³⁺ ions with ampicillin anions (Amp^?) in an aqueous solution at 25°C has been studied by pH titration on the background of 0.1 M KNO₃. Ln(OH)Amp⁺ complexes are formed in neutral and weakly alkaline media. The logarithm of β increases nonlinearly along the lanthanide series from 9.02 ± 0.06 for Ce(OH)Amp⁺ to 10.25 ± 0.09 for Lu(OH)Amp⁺. The structure of the Lu(OH)Amp⁺ complex was simulated by the PM6 semiempirical quantum-chemical method and the MOPAC 2009 software; the results of which impliy the formation of a chelate complex via bidentate coordination of Amp^? through the oxygen atoms of the carboxylate and β-lactam groups and the inclusion of up to five water molecules into the coordination sphere of Lu(III).     

Surface properties of catalytic aluminas modified by alkaline-earth metal cations: A microcalorimetric and IR-spectroscopic study

Lewis acidic properties of transition aluminas whose surfaces have been doped with alkaline-earth metal cations (Ca²⁺ and Ba²⁺) were studied by means of the room temperature adsorption of carbon monoxide. The vibrational features of CO adsorbed at the surface of doped aluminas were investigated by IR spectroscopy in comparison with pure parent aluminas, while the quantitative and energetic features were studied by adsorption microcalorimetry. Various CO adspecies were found to form at the surface of both pure and doped-alumina, owing to the structural heterogeneity of the Al₂O₃ surface and to the presence of alkaline-earth metal cations. The surface heterogeneity was revealed by different v_co stretching frequencies, namely v_co≈2230, 2218 and 2205 cm⁻¹ for coordinatively unsaturated tetrahedral Al³⁺ cations in different crystallographic configurations, and v_co≈2186 and 2172 cm⁻¹ for coordinatively unsaturated Ca²⁺ and Ba²⁺ cations, respectively. Heats of adsorption of ≈80, 70 and 55 kJ/mol were assigned to the formation of Al³⁺/CO complexes, ≈45 kJ/mol for Ca²⁺/CO and ≈30 kJ/mol for Ba²⁺/CO complexes. The latter value was estimated through a correlation curve existing between v_co stretching frequencies and adsorption enthalpies. This correlation, already proposed in the past for CO adsorbed on non-d/d⁰/d¹⁰ metal cations, has been revisited and confirmed here, by including Al₂O₃ data for which an apparent lack of correlation between the two parameters was first observed. With respect to pure alumina, the population of Lewis acidic sites was found to be significantly depressed by the presence of alkaline-earth cus metal cations. These acidic sites are intrinsically weaker than tetrahedral cus Al³⁺ cations, as witnessed by smaller upward shifts of the v_co stretching frequencies with respect to CO gas and lower heats of adsorption, in accordance with expectations from the charge/ionic radius ratios. Ca²⁺ cations were found to compete in adsorbing CO with Al³⁺ cations more efficiently than the larger Ba²⁺ cations. In the case of CaO/Al₂O₃ systems outgassed at 1023 K, a thin surface layer of calcium aluminate, not detected by XRD or HRTEM, was suggested to form.     

Complexation of anion exchangers based on polyimines and allyl and epoxy compounds with transition metal cations

Complexation of polymeric anion exchangers with transition metals was studied by polarographic and potentiometric titration techniques.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1693–1698.Original Russian Text Copyright © 2004 by Ergozhin, Chalov, Kovrigina, Iskakova, Nikitina.     

Confined space and cations enhance the power of a chiral auxiliary: photochemistry of 1,2-diphenylcyclopropane derivatives

Alkali ion-exchanged Y-zeolites significantly enhance asymmetric induction in the photoisomerization of a number of cis-1,2-diphenylcyclopropane derivatives containing a distant chiral auxiliary.     

Photoinduced recoordination in the complexes of bis-aza-18-crown-6-containing dibenzylidenecyclobutanone with alkali and alkaline-earth metal cations

Complexation with strong competitors (i.e., Ba²⁺, Ca²⁺, and K⁺) shortens the length of the chromophore in bis-aza-18-crown-6-containing dienones of 2,4-dibenzylenecyclo-butanone series due to the weakening of π–LP conjugation as well as disruption of the quinonoid structure in the ground state of the dye (LP is the lone electron pair of the crown nitrogen atom). In the excited state, recoordination of metal cations in the crown cavity takes place. The complexation as well as the newly discovered photorecoordination in these metal complexes may be used to control the chromophore properties of the samples.     

Role of cations and confinement in asymmetric photochemistry: enantio- and diastereo-selective photocyclization of tropolone derivatives within zeolites

Asymmetric induction in photochemical reactions has been explored using the photochemistry of tropolones as a model. Three approaches have been examined: chiral inductor, chiral auxiliary and [chiral inductor + chiral auxiliary]. All three methods gave excellent asymmetric induction in zeolite and very little or zero induction in solution. Results presented on tropolones clearly illustrate the remarkable influence that a confined space studded with cations can have on asymmetric induction. Tropolone derivatives, upon irradiation undergo 4pi-electron electrocyclization to yield a bicyclic product and a rearranged product. Enantiomeric excess up to 68% has been achieved in the cyclized product. In systems where a chiral inductor has been covalently linked, diastereomeric excess as high as 88% has been achieved within a zeolite while the same system in solution gave 10%.     

Layered hydrous manganese dioxide saturated with alkaline-earth cations: Synthesis and sorption properties

Layered compounds based on hydrous manganese dioxides (hereafter, Mn-phases) saturated with alkaline-earth cations were synthesized at 3–6°C. These phases are analogues of manganese minerals from oceanic iron-manganese sediments (vernadite, birnessite, buserite-I, an asbolan-like phase, and a hybrid phase). All the Mn-phases, as a rule, had poorly ordered structures. The sorption properties of these phases were studied with respect to alkali-metal cations (Na⁺, K⁺), an s-metal cation (Ba²⁺), a p-metal cation (Pb²⁺), and d-metal cations (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺). The exchange capacities of the Mn-phases were 0.45–1.06 mg-equiv/g for the alkali cations and 0.94–5.78 mg-equiv/g for the other cations. The phase composition of the Mn-phase did not affect the alkali cation sorption but affected the divalent cation sorption. The divalent cation exchange capacity increased from well-ordered birnessite to poorly ordered vernadite.     

Stability constants and thermodynamic data for complexes of 12-crown-4 with alkali metal and alkaline-earth cations in methanol solutions

The formation of 1:1- and 2:1-complexes of the crown ether 12C4 with mono- and bivalent cations was studied in methanol solutions by calorimetric, potentiometric and conductometric titrations. It is shown that not all donor atoms of the ligand 12C4 take part in complex formation. The accuracy of the three experimental methods are checked by comparing the results for the complexation of alkali ions with crown ether 18C6.     

Oligoether derivatives of 1-phenoxyanthraquinone: Synthesis,photochromism, and complex formation with metal cations

1-Phenoxyanthraquinone isomeric conjugates with tetraethylene glycol were prepared. Their photochromic properties and complex formation in solutions were quantitatively studied by spectrophotometry, quantum yields of the arylotropic photoisomerism and stability constants of complexes between para–ana-quinoid isomers and metal cations. The photochemical migration of a phenyl group considerably affects the complex stability thus providing the possibility to regard the synthesized compounds as photocontrolled ionophores. The structure of some complexes was investigated by X-ray diffraction (XRD) analysis and quantum-chemical simulation.