Extraction of Sodium and Potassium Perchlorates with Dibenzo-18-crown-6 into Various Organic Solvents. Quantitative Elucidation of Anion Effects on the Extraction-Ability and -Selectivity

The constants for overall extraction into various diluents of low dielectric constants (K_ex) and aqueous ion-pair formation (K_MLA) of dibenzo-18-crown-6 (DB18C6)–sodium and potassium perchlorate 1:1:1 complexes (MLA) were determined at 25°C. The K_ex value was analyzed by the four underlying equilibrium constants. The K_MLA values were determined by applying our established method to this DB18C6/alkali metal perchlorate extraction system. The K_M(DB18C6)A value of the perchlorate is much greater for K⁺ than for Na⁺, and is much smaller than that of the picrate. The K_MLA value makes a negative contribution to the extractability of DB18C6 for MClO₄, whereas the value of the MLA distribution-constant does a major one. The partition behavior of M(DB18C6)ClO₄ obeys the regular solution theory. However, the M(DB18C6)ClO₄ complexes in the diluent of high dipole moment somewhat undergo the dipole–dipole interaction. DB18C6 always shows high extraction selectivity for KClO₄ over NaClO₄, which is governed largely by the much greater K_MLA value for K⁺ than for Na⁺. The K⁺ extraction-selectivity of DB18C6 over Na⁺ for perchlorate ions is comparable to that for picrate ions. By comparing this perchlorate system with the picrate one, the anion effects on the extraction-efficiency and -selectivity of DB18C6 for Na⁺ and K⁺ was discussed in terms of the fundamental equilibrium constants.     

The determination of crown–cation complexation behavior in dioxane/water mixtures by conductometric studies

Using conductance measurements, an attempt has been made to gain detailed information about the specific molecular interactions of crown compounds with metal ions in a 1,4-dioxane/water binary system. Analyses of the transport data of dioxane/water mixtures yielded the mobility of the crown compound action complexes and the ion-pair dissociation constant of the crown compound–electrolyte complex. Binary mixed aqueous solvents are frequently employed in broad areas of chemistry. Their applicability ranges from synthetic and mechanistic studies in organic chemistry to biophysical chemistry, with emphasis on molecular interactions in biologically significant structures. Stability constants of crown compound complexes are determined by various methods, such as potentiometry (with ion selective electrodes), polarography, voltammetry, spectrophotometry, nuclear magnetic resonance, calorimetry and solubility. In this study the conductometry measurements have been carried out with high precision at optimal concentrations in dioxane/water systems. Structures of crown–cation complexes in dioxane/water mixtures are estimated from the conductance parameters (κ, Λ and α) as well as the complex formation constant, K_e = (Λ_MAm − Λ) / (Λ − Λ_MaLbAm) [L]. The conductance behavior of Na⁺, K⁺ chlorides and Na⁺ perchlorates with 18-crown-6, 15-crown-5, and 12-crown-4 have been studied in various dioxane/water systems (50%, 80%, and 85%) at 25°C. The all experimental studies have been made by the ratio 1 : 1 of the metal-ion and the crown ether, K_e. For the calculations, Excel. 5.0 was used as an application program. Copyright © 1998 John Wiley & Sons, Ltd.     

Dibenzo-18-crown-6-tricarbonylchromium compounds. Synthesis and substituent derived reversal of ion extraction selectivity

Mono- and bis-(tricarbonylchromium) compounds of dibenzo-18-crown-6 have been synthesized. The compounds exhibit a decreased ability to extract alkali metal salts into organic solvents, indicating an overall electron withdrawal from the oxygen crown by the Cr(CO)₃ substituents. For the disubstituted compound, the normal selectivity for K⁺ over Na⁺ is reversed.     

Extraction of sodium picrate into nitrobenzene in the presence of dicyclohexyl-18-crown-6

From extraction experiments and -activity measurements, the extraction constant corresponding to the equilibrium Na⁺(aq)+A^–(aq)+L(nb)NaL⁺(nb)+A^–(nb) taking place in the two-phase water-nitrobenzene system (A^–=picrate, L= dicyclohexyl-18-crown-6; aq-aqueous phase, nb=nitrobenzene phase) was evaluated as logK _ex(NaL⁺, A^–)=2.6.Further, the stability constant of the dicyclohexyl-18-crown-6-sodium complex in nitrobenzene saturated with water was calculated: _nb(NaL⁺)=7.8.     

Stabilization of a K+-(bis-Cage-Annulated 20-Crown-6) Complex by Bidentate Picrate

Bis-cage-annulated 18-crown-6 and 20-crown-6 macrocyclic ethers (i.e., 1 and 2, respectively) have been synthesized, and their alkali metal picrate extraction profiles have been determined. Host system 1 proved to be a significantly more avid alkali metal cation complexant than 2 and somewhat more avid than 18-crown-6. Both 1 and 18-crown-6 display modest selectivity toward K⁺ and Rb⁺. A stable host–guest complex was prepared by slow evaporation of a CH₂Cl₂–hexane solution of an equimolar mixture of 2 and potassium picrate. The X-ray crystal structure of this complex reveals that picrate anion functions as a bidentate ligand therein. The gas-phase interaction energy between the 2 K⁺ complex and picrate anion was calculated to be ca. –64.9 kcal mol^–1, thereby indicating that participation of picrate anion as an additional bidentate ligand results in significant stabilization of complex 10.     

New ditopic receptors for alkylammonium ion complexation

New receptor molecules have been synthesized in which ,-bis-(4-hydroxyphenyl)-1,4-diisopropylbenzene is linked to 1,10-diaza-18-crown-6, 1,10-diaza-21-crown-7 or 1,13-diaza-24-crown-8 units by ethylene or 1,4-butylene bridges. Binding abilities of the new receptors and the model compoundN,N-didecyl-1,10-diaza-18-crown-6 toward alkali metal cations and alkylammonium ions were assessed by picrate extraction. Spectral evidence for inclusion of alkylammonium ions within the receptor cavity was obtained by¹H NMR spectroscopy. From a¹H NMR titration experiment conducted in CDCL₃–CD₃OD (91), a relatively strong inclusion complex (K _a 900M^–1) of the receptor having a 1,10-diaza-18-crown-6 subunit and ethylene spacers with propylammonium picrate was observed.     

HYBRID PHOSPHINE-CROWN ETHER LIGANDS: THE STUDY OF BENZO-15-CROWN-5 AND N-PHENYLAZA-15-CROWN-5 AND -18-CROWN-6 FUNCTIONALIZED WITH Ph2P-

Abstract

Methods for the preparation of the 4-diphenylphosphino derivatives of N-phenylaza-15-crown-5 and -18-crown-6 are described. The properties of these systems and the 4′-diphenylphosphino derivative of benzo-15-crown-5 have been examined by way of picrate ion extraction abilities and IR spectra of their Ni(CO)₃L (L = these phosphines) complexes. All three have abilities to extract Na⁺ and K⁺ that are comparable to benzo-15-crown-5. The IR studies (ν_CO, A₁ band) indicate that the azacrown systems have better ability than the benzocrown system to increase the electron density on the nickel center. Further, the addition of alkali metal ions, Na⁺ and K⁺, to the Ni(CO)₃L solutions results in maximum shifts of ca 1.5 cm^?1 for the former systems and 0.7 cm^?1 for the latter system. A rationale for this observation is presented in terms of Hammett substituent constants. Finally, an X-ray structure of the phosphine oxide of the phenylaza-15-crown-5 derivative is presented. A prominent feature of the structure is that the nitrogen atom is essentially planar with the result that the crown ether ring is large and not preorganized for coordination of spherical ions.     

Polysalt complexes of poly(vinylbenzo-18-crown-6) and of poly(crown acrylate)s with polyanions

Macrocyclic polyether or crown ether ester derivatives of acrylic and methacrylic acid were synthesized and polymerized. The cation binding properties of the polymers determined by extraction of picrate salts were similar to those obtained for poly(crown ether)s derived from styrene. In the presence of a crown-complexable cation both polymers form insoluble polysalt complexes with sodium carboxymethylcellulose, potassium poly(styrene sulfonate), and potassium polyacrylate. The extent of precipitation depends on the type and concentration of cation as well as on the ratio polyanion to poly(crown ether). The precipitate appears to have an equal number of positive and negative charges. An insoluble hydrogen-bonded complex is formed in the absence of salt when poly(vinylbenzo-18-crown-6) and poly(acrylic acid) are mixed in 0.01M HCl. Organic solutes bound to the poly(crown ether)s, which occur in an aqueous mixture of poly(vinylbenzo-18-crown-6) and picrate anions, are precipitated with the poly(crown ether) when the polysalt complex is formed.     

Fluorescence of auramine O and its binding to poly(vinylbenzo-18-crown-6) and to polyvinylbenzoglyme in water

Binding of the cationic dye auramine O (AuO) to the polysoap-type polymers poly(vinylbenzo-18-crown-6) (P18C6) and polyvinylbenzoglyme (PVBG) in water were studied by fluorimetry and dialysis. The quantum yield of P18C6-bound AuO was found to be 0.028, the value being 0.018 for AuO bound to PVBG. The intrinsic binding constants were found to be 2.2 × 10⁴M^?1 (P18C6) and 1.2 × 10⁴M^?1 (PVBG), the respective first binding constants being 317 and 63M^?1. Addition of crown-ether-complexable cations such as K⁺, Tl⁺, or Cs⁺ converts the neutral poly(crown ether) into a polycation, causing repulsion of the cationic dye and a strong decrease in the AuO fluorescence. AuO fluorescence was also studied in the absence of polymer in ether solvents, giving θ values of 0.011 and 0.018 in THF and dioxane. Traces of water rapidly form a nonfluorescent species. Solutions of AuO in water without polymer present exhibit very strong fluorescence on addition of BPh₄ anions owing to formation of AuO⁺, BPh₄^? ion pairs and higher aggregates.     

Stability of crown-ether complexes with alkali-metal ions in ionic liquid-water mixed solvents

Stability constants of sodium and cesium ion complexes with 18-crown-6 (18C6) and dibenzo-18-crown-6 (DB18C6) in N-butyl-4-methyl-pyridinium tetrafluoroborate [BMP][BF₄] aqueous solutions were measured using the ²³Na and ¹³³Cs NMR technique at 23 °C. To the best of our knowledge, the estimated values of stability constants reported in this study are the first such values given for ionic liquid solutions. The cationic exchange between the free and complexed species is rapid, and only formation of the 1:1 complexes [M(18C6)]⁺ and [M(DB18C6)]⁺ (M = Na⁺, Cs⁺) were observed. The complex formation constants demonstrated a strong dependence on the [BMP][BF₄] concentration. For [M(18C6)]⁺, in solutions with a 0.33–0.70 mole fraction of water in [BMP][BF₄], lg K values are found to be more than one unit higher than the lg K values measured in pure aqueous solutions, although no information concerning the influence of [BMP][BF₄] on the complex formation selectivity could be observed. DB18C6 complexes revealed significantly lower stability under the same conditions. An extrapolation to zero water content gave the lg K = 2.42 for [Cs(18C6)]⁺ in [BMP][BF₄]. It was discovered that when added to water, [BMP][BF₄] increases the solubility of crown ethers and decreases the solubility of alkali metal nitrates. Complex formation with crown ethers enhances the solubility of alkali metal salts in [BMP][BF₄].     

Synthesis,characterization, and photochemistry of the supramolecules formed from chromium(III) thiocyanato anion associated with crown ethers

A series of anionic chromium(III) thiocyanato complexes with metal crown ether cations have been prepared and characterized. These complexes have the form [Crown-M]₂⁺[Cr(NCS)₅(H₂O)]²⁻ and [Crown-M]₃⁺[Cr(NCS)₆]³⁻, where M=Na⁺, K⁺, or NH₄⁺ and crown represents the crown ether. The crown ethers are 15-crown-5, B-15-crown-5, 18-crown-6, DB-18-crown-6, and DB-24-crown-8, where B- and DB- stand for benzo- and dibenzo-, respectively. The complexes are stable for at least 20 h in the dark in dimethylformamide(DMF) or in acetonitrile, and they release thiocyanate slowly, k=(0.71–2.67)×10⁻⁹ mol/(L s) in acetonitrile in the dark. Photoanation of thiocyanate was observed for the complexes in DMF and in acetonitrile. The quantum yields of thiocyanate release in DMF and in acetonitrile are reported. The quantum yields were in the range 0.05 to 0.52 mol einstein⁻¹ and were solvent and wavelength dependent. In general, larger quantum yields were observed in DMF than in acetonitrile. The photoreaction mechanism is discussed.     

Sodium and potassium benzeneazophosphonate complexes with crown ethers: Solid-state microwave synthesis, characterization and biological activity

The eco-friendly synthesis, spectroscopic (IR, MS, ¹H and ¹³C NMR) study and biological (cytostatic, antiviral) activity of sodium and potassium benzeneazophosphonate complexes, obtained by reaction in the solid state under microwave irradiation of the alkali salts of ethyl [α-(4-benzeneazoanilino)-N-benzyl]phosphonic acid and [α-(4-benzeneazoanilino)-N-4-methoxybenzyl]phosphonic acid with crown ethers containing 18-membered (dibenzo-18-crown-6 and bis(4′-di-tert-butylbenzo)-18-crown-6), 24-membered (dibenzo-24-crown-8) and 30-membered (dibenzo-30-crown-10) macrocyclic rings, have been described. The simple work-up solvent free reaction is an efficient green procedure for the formation of mononuclear crown ether complexes in which the sodium/potassium ion is bound to oxygen atoms of the macrocycle and the phosphonic acid oxygen. The free crown ethers, alkali benzeneazophosphonate salts and their complexes were evaluated for their cytostatic activity in vitro against murine leukemia L1210, murine mammary carcinoma FM3A and human T-lymphocyte CEM and MT-4 cell lines, as well as for their antiviral activity against a wide variety of DNA and RNA viruses. The investigated compounds showed no specific antiviral activity, whereas all the free crown ethers and their complexes demonstrated cytostatic activity, which was especially pronounced in the case of bis(4′-di-tert-butylbenzo)-18-crown-6 and its complexes.     

Nitro derivatives of <Emphasis Type="Italic">N</Emphasis>-alkylbenzoaza-15-crown-5: synthesis,structures, and complexation with metal and ammonium cations

A number of N-alkylnitrobenzoaza-15-crown-5 with the macrocycle N atom conjugated with the benzene ring were obtained. The structural and complexing properties of these compounds were compared with those of model nitrobenzo- and N-(4-nitrophenyl)aza-15-crown-5 using X-ray diffraction, ¹H NMR spectroscopy, and DFT calculations. The macrocyclic N atom of benzoazacrown ethers are characterized by a considerable contribution of the sp3-hybridized state and a pronounced pyramidal geometry; the crownlike conformation of the macrocycle is preorganized for cation binding, which facilitates complexation. The stability constants of the complexes of crown ethers with the NH₄ ⁺, EtNH₃ ⁺, Na⁺, K⁺, Ca²⁺, and Ba²⁺ ions were determined by 1H NMR titration in MeCN-d₃. The most stable complexes were obtained with alkaline-earth metal cations, which is due to the higher charge density at these cations. The characteristics of the complexing ability of N-alkylnitrobenzoaza-15-crown-5 toward alkaline earth metal cations are comparable with analogous characteristics of nitrobenzo-15-crown-5 and are much better than those of N-(4-nitrophenyl)aza-15-crown-5.     

Solvent effects on extraction of potassium picrate with benzo-18-crown-6. A new equation for the determination of ion-pair formation of crown ether-metal salt complexes in water

In order to determine the ion-pair formation constant of a crown ether-metal salt 1:1:1 complex in water, an equation is derived from regular solution theory and its predictions are verified experimentally by the solvent extraction method using benzo-18-crown-6 (B18C6), potassium picrate (KA), and various diluents of low dielectric constant. The distribution constants of B18C6 itself and the overall extraction constants of KA with B18C6 were determined at 25±0.2°C. The distribution constants of the neutral K(B18C6)A complex were calculated from these data. The literature value for the complex-formation constant of K(B18C6)⁺ in water and the ion-pair formation constant (K _K(B18C6)A ) for K(B18C6)A in water determined in this study were log K _K(B18C6)A =3.12±0.23 at 25°C). The distribution behavior of B18C6 and K(B18C6)A is explained in terms of regular solution theory. The molar volumes V (cm³·mol^–1) and solubility parameters (cal^1/2-cm^–3/2) are as follows: V _B18C6 =249±36; V _K(B18C6)A =407±56; _B18C6 = 11.5 ± 0.5; and _K(B18C6)A = 11.5 ± 0.5.     

Preparation and X-ray structures of complexes of 18-membered crown ethers with polyfunctional guests: Urea and (O-alkyliso)uronium salts

The preparation and X-ray structure determinations of six complexes of urea and (O-n-butyliso)uronium salts with crown ethers are presented. Urea forms isostructural 5:1 adducts with 18-crown-6 (1) and aza-18-crown-6 (2), in which two urea molecules are each hydrogen bonded to two neighbouring hetero atoms of the macroring. The remaining urea molecules form two-dimensional layers alternating with crown ether layers. In both complexes the macroring has theg ⁺ g ⁺ a ag ^– a ag ^– a g ^– g ^– a ag ⁺ a ag ⁺ a conformation withC _i symmetry. In the solid 1:1 complex of O-n-butylisouronium picrate with 18-crown-6 (3) two types of conformations of the macroring were observed: theg ⁺ g ⁺ a ag ^– a ag ⁺ a ag ^– g ^– ag ^– a ag ⁺ a conformation with approximateC _m symmetry and to a lesser extent theg ⁺ g ⁺ a ag ^– a ag ⁺ a g ⁺ g ⁺ a ag ^– a ag ⁺ a conformation with approximateC ₂ symmetry. Both conformations allow the guest to form three hydrogen bonds to the macrocyclic host. Three complexes of 18-crown-6 and uronium salts have been prepared and characterized by X-ray crystallography. The 1:1 complexes with uronium nitrate (4) and uronium picrate (5) both exhibit the sameC ₂ conformation and the same hydrogen bonding scheme as in the least occupied form of the previous complex. A 1:2 complex with uroniump-toluenesulphonate (6) has a different hydrogen bonding scheme (two hydrogen bonds per cation to neighbouring oxygen atoms of the macroring) and a different conformation of the host molecule (theag ⁺ a ag ^– a ag ⁺ a ag ^– a ag ⁺ a ag ^– a conformation with almostD _3d symmetry). An attempt to prepare a solid uronium nitrate complex with diaza-18-crown-6 in the same way as the 18-crown-6·uronium nitrate (1:1) complex did not yield the expected result. Instead X-ray analysis revealed that the uronium ion is dissociated, resulting in the nitrate salt of the diprotonated diaza crown ether (7). Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82058 (26 pages).     

Cation-complexation-induced aggregation and specific ion conduction of lipophilic crowned azobenzenes

Lipophilic azobenzene derivatives incorporating a monoazacrown or oligooxyethylene moiety were employed as a component of ion-conducting composite films containing a polyester elastomer and an alkali metal (Li⁺, Na⁺, K^–) perchlorate. Composite films of monoaza-15-crown-5-containing azobenzene1 exhibited ionic conductivities following the order of Na > Li > K, reflecting the cation-binding selectivity of the 15-crown-5 ring. The ion-conducting behavior of composite films of1 is quite different from that of composite films containing a 1 : 1 mixture of an azobenzene derivative without any crown moiety andN-phenyl-monoaza-15-crown-5 (ionic conductivity order of Li > Na > K >). It was suggested that cation and anion migration is predominant in the LiClO₄ and NaClO₄ systems, respectively. The specific ion conduction can be attributed to ordered aggregation of1 induced by cation complex formation of its crown moiety. Azobenzene derivatives incorporating a monoaza-12-crown-4, monaza-18-crown-6, or oligooxyethylene moiety cannot afford such aggregate formation and specific ion-conduction as is seen in the1 system.     

Conductance study of the complexation of substituted and lariat 16-crown-5 derivatives with alkali metal ions in nonaqueous solvents

Formation constants (K _ML) of 1:1 complexes of 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L16C5) and 15,15-dimethyl-16-crown-5 (DM16C5) with alkali metal ions were determined in acetonitrile (AN) and propylene carbonate (PC) by conductometry at 25°C. Except for the case of Li⁺-and K⁺-16C5 complexes in PC, the selectivity sequences of L16C5 and DM16C5 are identical with those of the parent crown ether 16-crown-5 (16C5) regardless of the solvent (AN, PC, methanol) (Na¹ > Li⁺ > K⁺ > Rb⁺ > Cs⁺), which show the size-fit correlation. The selectivities of L16C5 and DM16C5 for the alkali metal ions are governed not by the sidearms but by the cavity size. The stability of the crown ether complex is dependent not on the dielectric constant but largely on the donor number of the solvent. TheK _ML(M₁ ⁺)/K _ML(M₂ ⁺) ratio of L16C5 or 16C5 varies very much with the solvent in the cases of M₁=Na, M₂=K and M₁=Na, M₂=Li, but that of DM16C5 is almost constant regardless of the solvent.     

Inhibition of Na+, K+-ATPase in the presence of crown ethers: modulation of ionic composition or pharmacological effects

It is believed that the biological effects of chelating agents such as crown ethers are largely related to their ability to form complexes with ions and/or to facilitate ion transport across membranes. Specific influences are rarely related. Here we present the evidence that even one of the simplest representatives of the crown ether super-family, 1,4,7,10,13,16-hexaoxacyclooctane (18-crown-6), is able to affect the activity of Na⁺, K⁺-ATPase directly. Using nonlinear regression fitting to kinetic data we have found that the crown ether diminishes the apparent Michaelis constant, K _m , and the maximal rate of ATP hydrolysis, V _m , acting as noncompetitive inhibitors. The apparent dissociation constants, K _i , for the crown interaction with the free ATPase and with the enzyme-substrate complex were established to be of 77 ± 3 mM and 21 ± 2 mM, respectively. So 18-crown-6 possesses weak but “direct” pharmacological activity on Na⁺, K⁺-ATPase hinders the formation of enzyme–substrate complex and detains the enzyme in this state.     

Thermodynamics of Complex Formation and Solvation in the System NaCl-18-crown-6-Water-Dioxane

Stability constants of Na⁺ complexes with 18-crown-6-ether and thermodynamic characteristics of the complex formation in water and mixed water-dioxane solvents (0.2, 0.4, 0.6, and 0.8 wt. fraction of dioxane, 283-318 K) were determined by the method of EMF of galvanic circuits without transfer. Comparative thermodynamic analysis of the complex 18-crown-6Na⁺ formation reactions in water-dioxane, water-acetonitrile, water-acetone, water-methanol, and water-2-propanol mixtures was carried out. Contributions of the Gibbs energies of transfer (G _t) of 18-crown-6Na⁺, Na⁺, and the ligand to the increase in the stability of the complexes on replacement of water by mixed water-dioxane solvents were estimated. It was shown that the increase in the stability of sodium crown ether complexes primarily depends on solvation of the complex cation and desolvation of the central cation. Changes in the conformational Gibbs energy of the ligand and quantitative parameters of selective solvation of the reagents were estimated.     

Molecular clips based on diphenylglycoluril and benzocrown ethers: promising complexing agents for the alkali metal cations

The interaction of new molecular clips containing diphenylglycoluril and benzocrown ethers moieties with alkali metals ions was studied. Stability constants were determined by spectrophotometric titrations with chloride salts in methanol. Complex stability and cation binding selectivity were shown to be dependent on the size of the crown ether moiety. The “sandwich-type” 1:1 (clip to cation) complexes and the “classical” 1:2 complexes were found. Their ratio varies depending on the molecular clips nature and on the cation type. It was found an unexpected selectivity of the molecular clip with benzo-15-crown-5 moieties toward K⁺ and Rb⁺ cations. The molecular structure of the clip complex with benzo-15-crown-5 fragments and sodium picrate was determined by X-ray crystallography. The crystal structure and solution-state structure were proven to be similar.