Influence of polar solvents upon the complex formation of 18-crown-6 with cations in chloroform

The complex formation of crown ethers with cations in nonpolar medium with small amounts of polar solvents added has been studied. The goal has been to get deeper insight into the influence of solvation (hydration) of the salts for the formation of complexes with the macrocyclic ligand 18-crown-6 (18C6). A linear dependence of the reaction enthalpy for complex formation between 18C6 and alkali metal cations in chloroform in the presence of water or methanol has been observed. The presence of acetonitrile or acetone has had no influence upon the measured reaction enthalpies. The influence of methanol on the complex formation between 18C6 and alkali metal cations in chloroform is weaker than in the case of water. This underpins the selective solvation of alkali cations in chloroform after the addition of small amounts of water or methanol. The experiments have been performed using calorimetric titrations.     

Extraction and determination of crown ethers from water samples using a membrane disk and gas chromatography

A method for rapid extraction and determination of some crown ethers in aqueous matrices using octadecyl-bonded silica membrane disks and gas chromatography is presented. Extraction efficiency and the influence of vacuum pressure. pH, and type and least amount of eluting solvent used to extract the crown ethers from the membrane disks were evaluated. Extraction efficiencies > 95% were obtained for benzo-15-crown-5, benzo-18-crown-6 and dicyclohexyl-18-crown-6 using 5 ml of acetonitrile as eluting solvent. The limit of detection of the proposed method for the determination of the crown ethers is reported.     

Influence of ligand structure and solvent effects on complexation of neutral guests by several crown ethers

The formation of complexes between crown ethers and acetonitrile, chloroform, and nitromethane were investigated in carbon tetrachloride at 25°C. A significant influence of the ring size on the selectivity of the host is evident. The host 18-crown-6 forms complexes for which the reaction enthalpy and entropy are quite high. Host molecules with benzene side groups form complexes of lower reaction enthalpy and entropy and therefore the complexes formed are less stable than that of the analogous crown ethers without aromatic groups. Solvent effects on the stability constant K, the reaction enthalpy H, and the reaction entropy S were studied for the complexation of malonitrile by 18-crown-6. The reaction enthalpy and entropy values change in accordance with the dielectric constant of the solvent used, but no overall effect on complex stability with change in solvent dielectric constant was observed.     

Thermodynamic Data for Complex Formation Between Cucurbituril and Alkali and Alkaline Earth Cations in Aqueous Formic Acid Solution

Complex formation, between alkali and alkaline earth cations and the macrocyclic ligands cucurbituril and 18-crown-6, was studied by calorimetric titration in aqueous formic acid solution (50 vol.%). The solubility of cucurbituril strongly depends on the concentration of formic acid. At low and very high formic acid concentrations, the solubility of cucurbituril is low. For both ligands the formation of proton complexes influence the complexation reactions with cations. Thus, the complex formation in most cases is favored by entropic contributions. Only in the case of the Ba²⁺ ion stability constants and reaction enthalpies could be measured at lower formic acid concentrations. Using a highly sensitive calorimeter, the stability constants and reaction enthalpies for the reaction of Na⁺ and Ba²⁺ with cucurbituril in aqueous solution could be determined.     

丙二胺18冠6醚包合物的合成、晶体结构及介电性质

丙二胺盐酸盐,18冠6醚和三价的氯化铁在甲醇溶液中反应,产生了1个新的超分子包合物,[(C₃N₂H₁₂)·(18-Crown-6)₂][Fe₂OCl₆](1)。双质子化的丙二胺包含2个-NH₃⁺取代基团,阳离子-NH₃⁺基团和冠醚的氧原子间通过N-H…O氢键作用,形成了1个三明治式的超分子结构。化合物1的介电常数分别在不同温度和频率下进行了测量,结果表明没有出现介电异样,也就是说,在测量温度范围内,1应该没有结构相变发生。     

Synthesis and study of crown ether-appended boron dipyrrin chemosensors for cation detection

Boron dipyrrin (BDP) bearing crown ethers of varying cavity sizes, namely, 15-crown-5, 18-crown-6, and 21-crown-7, at the meso-position are synthesized and employed as chemosensors for cation detection in solution. In the absence of metal cations, the emission of the BDP moiety is found to be quenched to some extent by an intramolecular charge transfer (ICT) process from the donor oxygen atoms to the acceptor BDP unit. Coordination of metal ions to the oxygen donor atoms in the crown ether cavity inhibits intramolecular charge transfer to the BDP acceptor, leading to cation-induced fluorescence enhancement. The fluorescence enhancement is systematically probed as a function of crown ether cavity and metal ion sizes to achieve metal ion selectivity.     

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.     

冠醚配合物热力学性质的研究——Ⅷ 无水硝酸镧与若干冠醚在乙腈中的量热滴定

稀土离子与冠醚反应的热函至今报道不多。仅1977年Izatt等用量热滴定对稀土氯化物在甲醇中与18-冠-6的反应热函进行过研究。他们发现轻稀土从La~(3+)至Gd~(3+)与冠醚反应是吸热反应,而重稀土从Tb~(3+)至Lu~(3+)与冠醚反应却没有热量产生或△H近于零。此外他们还得出了若干反常结果,我们认为,反应热量的大小与稀土盐和有机溶剂的含水量有密切关系,因三价稀土离子电荷高,牛径又不大,水合能力强,在不严格去水的条件下,所得的△H和稳定常数不甚可靠。为此,我们研究了无水硝酸镧与18-冠-6(18C6),2,3,11,12-二环已基-18-冠-6(DC-18C6),及2,3-苯并-11-甲基-18-冠-6(BC1-18C6)在无水乙腈中的配位反应,得出与Izatt等不同的结果。实验表明,所有冠醚与La~(3+)的反应均为放热反应,它们有较大的热函和较高的稳定性。     

Thermodynamics of Amino Acid Methyl Ester Hydrochlorides—Crown Ether Complexes in Methanol at 25°C

Stability constants, free energies, and enthalpies and entropies of the complexation of L-alanine methyl ester hydrochloride (L-Ala-HCl), L-phenylalanine methyl ester hydrochloride (L-Phe-HCl), and valine methyl ester hydrochloride (L-Val-HCl) with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexano-18-crown-6 (DC18C6), and dicyclohexano-24-crown-8 (DC24C8) in methanol are reported for 20°C. No significant variation in the stability constants and free energies of complexation is observed, indicating that the various crown ethers are poorly selective in binding the amino acids. However, the nature of the crown ether and the amino acid and their pattern of substitution cause a remarkable variation in the enthalpies and entropies of complexation. This indicates a strong enthalpy–entropy compensation effect. The enthalpy–entropy compensation effect for the crown ether complexes of the amino acid methyl ester hydrochlorides reported herein is compared with that of the crown ethers complexes of the amino alcohols and the free amino acid. It is found that the enthalpy–entropy compensation effect holds equally for the three classes of complexes.     

Conductance studies of salt solutions in the presence of poly(vinylbenzo crown ethers)

The conductance of acetone and methyl ethyl ketone solutions of tetraphenylborate salts in the presence of homopolymers and styrene copolymers of vinylbenzo-15-crown-5 and vinylbenzo-18-crown-6 was studied, and the results compared with data obtained for crown ethers. Polycations are formed on binding cations to the poly(crown ethers), and the conductance behavior of the polyelectrolytes depends on the nature of the cation-crown complex and the spacing between crown moieties which in turn determines the charge density on the polymer chain. The compositions of the crown-cation complexes were determined for crown ethers. The complex formation constants of sodium and potassium cations to poly(vinylbenzo-18-crown-6) were found to change as more cations bind to the chain. This is not the case for the copolymers where the crown ligands are spaced farther apart. A mixture of poly(vinylbenzo-15-crown-5) and 10^?3M potassium tetraphenylborate in methyl ethyl ketone or acetone has a minimum conductance at a crown to cation ratio of 3.0, but the conductance rapidly increases on addition of crown ether. This was used to qualitatively determine the binding efficiency of a series of crown ethers since the rate of increase in the conductance is a measure of the binding ability of the crown ether to the cation.     

Complexation of silver(I) with different substituted diaza-18-crown-6 ethers in methanol

A large number of derivatives of the diaza-18-crown-6 ligand have been synthesized and characterized. These derivatives have different alkyl or aryl side arms at the nitrogen donor atoms of the macrocyclic diazacrown ether. In some side chains additional donor atoms are available. These diazacrown ethers are used as ligands for the complexation of Ag^I in MeOH. The complexation reactions have been studied using potentiometric and calorimetric methods. The thermodynamic data show the absence of a lariat effect. The increase of the values of the reaction enthalpies are due only to changes in solvation of the different ligands.     

The Complexation of Amino Acids by Crown Ethers and Cryptands in Methanol

Complex formation between several crown ethers and the cryptand (222) and -amino acids in methanol was studied by calorimetric titration. The ligand structure and the donor atoms of the ligands play an important role in determining the measured values of the reaction enthalpies and entropies. However, with the exception of the diaza crown ether (22) all stability constants are of the same order of magnitude. The enthalpic and entropic contributions to the stabilities of the complexes formed compensate each other. In methanolic solution the amino acids exist in their zwitterionic form. This equilibrium can be influenced. Under acidic, neutral or basic conditions different values of the reaction enthalpies are measured for the complexation of some amino acids with 18-crown-6. These results demonstrate that the concentration of the zwitterionic form of the -amino acids can be influenced. Thus the reaction between macrocyclic and macrobicyclic ligands and amino acids should be described by at least two different reaction schemes.     

Fencing of Photoinduced Electron Transfer in Nonconjugated Bichromophoric System by β-cyclodextrin Nanocavity

²³Na NMR measurements were employed to monitor the stability of Na⁺ ion complexes with 18-crown-6 (18C6), dicycloxyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6), 15-crown-5 (15C5) and benzo-15-crown-5 (B15C5) in binary acetonitrile–dimethylformamide mixtures of varying composition. In all cases, the variation of ²³Na chemical shift with [crown]/[Na⁺] mole ratios indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation which relates the observed chemical shifts to the formation constants. It was found that, in pure acetonitrile, the stabilities of the resulting 1:1 complexes vary in the order 15C5>DC18C6>B15C5>18C6>DB18C6, while in pure dimethylformamide the stability order is DC18C6>18C6>15C5>B15C5>DB18C6. The observed changes in the stability order could be related to the specific interactions between some crown ethers and acetonitrile. It was found that, in the case of all complexes, an increase in the percentage of dimethylformamide in the solvent mixtures would significantly decrease the stability of the complexes.     

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.     

Excess enthalpies and apparent molar volumes of aqueous solutions of crown ethers and cryptand(222) at 25°C

The enthalpies of dilution and densities of aqueous solutions of 12-crown-4, 15-crown-5, 18-crown-6, 1,10-diaza-18-crown-6 and cryptand (222) were measured at 25°C. The excess enthalpies and enthalpic coefficients of solute-solute interactions were calculated by the McMillan-Mayer theory formalism. Values for the apparent molar volumes at infinite dilution were determined by extrapolation. The contributions of the-CH₂CH₂O-group to values of h₂ and to the limiting partial molar volume were calculated for the series of crown ethers studied. It is concluded that the hydrophobic hydration and the hydrophobic solute-solute interaction are predominant in the solutions investigated.     

The complexation of the ammonium ion by 18-crown-6 in different solvents and by noncyclic ligands,crown ethers and cryptands in methanol

The complexation of the ammonium ion with the macrocyclic ligand 18-crown-6 was studied using calorimetric and potentiometric titrations in different solvents. In water and dimethyl sulphoxide the stability constants had the lowest values compared with all other solvents examined. No specific interactions between the ammonium ion and solvent molecules were observed. Crown ethers formed more stable complexes in methanol with the ammonium ion than diaza crown ethers. The most stable complexes were formed with cryptands. The highest values of the stability constants for the reaction with macrocyclic and macrobicyclic ligands were measured if the dimensions of the ammonium ion and of the cavities were nearly identical.     

The effect of carbonyl carbon atom replacement in acetone molecule (ACN) by sulfur atom (DMSO)

The enthalpies of solution of cyclic ethers: 1,4-dioxane, 12-crown-4 (12C4), and 18-crown-6 (18C6) in water–acetone mixtures have been measured within the whole mole fraction range at 298.15 K. Based on the obtained data, the effect of base–acid properties of water–acetone mixtures on the solution enthalpy of cyclic ethers in this mixed solvent has been analyzed. The strong dependence of the enthalpy of solution (solvation) of cyclic ethers on basic properties of mixed solvent has been observed. The effects of carbonyl atom replacement in acetone (ACN) molecule by sulfur atom (DMSO molecule) and base–acid properties of mixed solvent on the solvation process of cyclic ethers have been analyzed.     

Synthesis and characterization of novel ionophores of double-armed penta-crown ethers

Unique structures of novel ionophores of double-armed penta-crown ethers were successfully synthesized. Diaza 18-crown-6 was designed as the parent crown ring. The penta-crown ethers were prepared by the reaction of trimethylolpropane triacrylate (TMPTA) with diaza 18-crown-6 and further with 1-aza crown ethers through the Michael reaction. The newly synthesized penta-crown ethers were characterized by ¹H NMR, ¹³C NMR, FAB mass spectrum, IR and elemental analyses, respectively.     

Thermodynamic Data for the Formation of 1:1 and 2:1 Complexes of α,ω-Diamino Dihydrochlorides with 18-Crown-6 in Aqueous Solution

Calorimetric titrations are used to study the interactions between the crown ether 18-crown-6 and several α,ω-diamino dihydrochlorides in aqueous solution. These complexes are formed by ion-dipole interactions between the positively charged nitrogen atoms and the oxygen donor atoms of the crown ether. Depending on the experimental conditions, the formation of 1:1 or 2:1 complexes (ligand:diamines) can be studied. The solvation of the ligand and the amines are responsible for the observed thermodynamic values. The number of water molecules released during the reaction were calculated from the determined reaction entropies. Formation of 1:1 complexes distorts the solvation shell around the molecules. As a result, the number of solvent molecules released during the formation of the 2:1 complexes is slightly smaller than the number released from formation of the 1:1 complex. No experimental evidence is observed for the formation of complexes between one crown ether and two protonated amino groups.     

Formation Constants of Complexes of Monovalent Cations with Benzocrown Ethers in Nitromethane

The complexation reactions between the macrocyclic polyethers dibenzo-18-crown-6, benzo-18-crown-6, benzo-15-crown-5 and polyethers bearing a stilbene unit with alkali metal and silver cations have been studied conductometrically in nitromethane. The formation constants of 1 : 1 and 1 : 2 (metal : ligand) complexes were determined and found to decrease with increasing cation diameter. The stability of the stilbene crown – metal cation complexes is lower than for complexes of other investigated crown ethers with analogous cations. There seem to be some effects of double bond-silver ion interactions.