Complex Formation Of Crown Ethers Research Articles

Entropy Effects in Intermolecular Associations of Crown-Ethers and Cyclodextrins with Amino Acids in Aqueous and in Non-Aqueous Media.

The analysis of the ratios of entropy and enthalpy characteristics and their contributions to the change in the Gibbs energy of intermolecular interactions of crown ethers and cyclodextrins with amino acids is carried out. Two different types of macrocycles were chosen for examination: crown ethers with a hydrophilic interior and cyclodextrins with a hydrophobic inner cavity and a hydrophilic exterior. The thermodynamics of complex formation of crown ethers and cyclodextrins with amino acids in water and aqueous-organic solvents of variable composition was examined. The contributions of the entropy solvation of complexes of 18-crown-6 with glycine, alanine, phenylalanine to the change in the entropy of complexation in water-ethanol and water-dimethyl sulfoxide solvents was calculated and analyzed. It was found that the ratios of the entropy and enthalpy solvation of the reagents for these systems have similar trends when moving from water to aqueous-organic mixtures. The relationship between the thermodynamic characteristics and structural features of the complexation processes between cyclodextrins and amino acids has been established. The thermodynamic enthalpy–entropy compensation effect was revealed, and its features for complexation of cyclodextrins and 18-crown-6 were considered. It was concluded that, based on the thermodynamic parameters of molecular complexation, one could judge the mode of the formation of complexes, the main driving forces of the interactions, and the degree of desolvation.

Complex formation of crown ethers with α-amino acids: Estimation by NMR spectroscopy

Complex formation of 18-crown-6 and dibenzo crowns with glycine, leucine, and norleucine was studied by NMR spectroscopy. The efficiency of non-valence interactions with participation of different active centers of the host and guest molecules is determined by solvation effects, mutual arrangement of benzene rings in dibenzo crowns, and the presence of bulky aliphatic substituents in the α-amino acid. The complexation of dibenzo crowns with α-amino acids in acid medium involves a system of different non-valence interactions, the most efficient of which are NH 3 + ... O hydrogen bond between the ammonium group in the guest molecule and ether oxygen atoms in the host molecule and dipole-dipole interaction between the guest ammonium group and host benzene ring (NH 3 + ... Ar). The efficiency of NH 3 + ... O hydrogen bonding decreases in going from 18-crown-6 to dibenzo crowns due to distortion of symmetry of the macroring cavity and violation of geometric complementarity of some ether oxygen atoms. The integral efficiency of non-valence interactions in the system dibenzo crown-α-amino acid was estimated on a quantitative level by 1H NMR relaxation technique.

Variation of thermodynamic parameters of crown ether-metal complex formation and reactant solvation in binary nonaqueous solvent mixtures

General trends in the variation of thermodynamic parameters of complex formation of crown ethers with d-metal ions in binary nonaqueous solvent mixtures were determined. An equation was proposed for predicting variation of the stability of coordination compounds upon replacement of one nonaqueous solvent by another on the basis of the change in the Gibbs energy of solvation of the central ion. Calculation of the Gibbs energies for the formation of the [Ag18C6]+ ion in acetonitrile and a number of nonaqueous solvents confirmed the predictive ability of the proposed equation.

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.

Complex Formation of Crown Ethers and Cations in Water−Organic Solvent Mixtures: The Thermodynamic Functions of Complex Formation of Benzo-15-crown-5 with Na+ in Water + Ethanol at 298.15 K

The enthalpies of solution of benzo-15-crown-5 ether in ethanol + water and ethanol + water + sodium iodide systems have been measured at T = 298.15 K. The values of standard enthalpies of solution of benzo-15-crown-5 ether are positive in the mixtures of water and ethanol within the whole range of mixture composition. The equilibrium constants of complex formation of benzo-15-crown-5 ether with a sodium cation have been determined by conductivity measurements at T = 298.15 K. In the process of complex formation, ethanol molecules show their hydrophobic properties.

Erratum to: Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XI. Effects of the Preferential Solvation of Benzo-15-Crown-5 and Acid-Base Properties of the Mixtures on the Thermodynamic Functions for Complex Formation of Benzo-15-Crown-5 with Na+ in Propan-1-ol–Water Mixtures at 298.15 K

The thermodynamic functions of complex formation of benzo-15-crown-5 ether (B15C5) and sodium cation (Na+) in the mixtures of propan-1-ol (PrOH) with water at 298.15 K have been calculated from experimental measurements. The equilibrium constants of B15C5/Na+ complex formation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method. The complexes are enthalpy stabilized but entropy destabilized in the PrOH–H2O mixtures. The effects of preferential solvation of B15C5 by molecules of the organic solvent, solvation of the sodium cation, as well as the acid-base properties of propan-1-ol–water mixtures on the complex formation processes are discussed.

Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XII. Effect of the Acid–Base Properties of the Mixture on the Thermodynamic Functions of Complex Formation of Benzo-15-Crown-5 with Na+ in Water–Methanol Mixtures at 298.15 K

The enthalpies of solution of benzo-15-crown-5 ether in methanol–water mixtures and methanol–water–sodium iodide systems have been measured at 298.15 K. The values of standard enthalpies of solution of benzo-15-crown-5 ether are positive in the mixtures of water and methanol within the whole range of mixture composition. The equilibrium constants of complex formation of benzo-15-crown-5 ether with the sodium cation have been determined by conductivity measurements at 298.15 K. The thermodynamic functions of the formation of these complexes have been calculated. The Gibbs energy of complex formation depends on the base–acid properties of methanol–water mixture.

Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XI. Effects of the Preferential Solvation of Benzo-15-Crown-5 and Acid-Base Properties of the Mixtures on the Thermodynamic Functions for Complex Formation of Benzo-15-Crown-5 with Na+ in Propan-1-ol–Water Mixtures at 298.15 K

Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XI. Effects of the Preferential Solvation of Benzo-15-Crown-5 and Acid-Base Properties of the Mixtures on the Thermodynamic Functions for Complex Formation of Benzo-15-Crown-5 with Na+ in Propan-1-ol–Water Mixtures at 298.15 K

The effect of carbonyl carbon atom replacement in acetone molecule (ACN) by sulfur atom (DMSO): Part II. Thermodynamic functions of complex formation of crown ethers with Na+ in mixed solvents

The thermodynamic functions of complex formation of benzo-15-crown-5 ether (B15C5) and sodium cation (Na+) in acetone–water mixtures at 298.15 K have been calculated. The equilibrium constants of B15C5/Na+ complex formation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by the calorimetric method. The complexes are enthalpy-stabilized but entropy-destabilized in acetone–water mixtures. The effects of hydrophobic hydration, preferential solvation of B15C5 by a molecule of water and acetone, respectively and the solvation of Na+ on the complex formation processes have been discussed. The calculated thermodynamic functions of B15C5/Na+ complex formation and the effect of benzene ring on the complex formation have been compared with analogous data obtained in dimethylsulfoxide–water mixtures. The effect of carbonyl atom replacement in acetone molecule by sulphur atom (DMSO molecule) on the thermodynamic functions of complex formation has been analysed.

Influence of temperature and crown ether complex formation on the charge partitioning between z and c fragments formed after electron capture by small peptide dications

Electron capture by peptide dications results in N–C α bond cleavage to give c + and z or c and z + fragments. In this work we have investigated how crown ether (18-crown-6 = CE) complex formation and a change in the internal energy affect the charge division between the z and c fragments. Both complex formation and a high temperature have the effect of breaking internal ionic hydrogen bonds. The crown ether complex also lowers the probability of internal proton transfer between the two fragments, and reduces the recombination energy of the charged group it targets. The systems under study were doubly protonated di- and tripeptides, [AK+2H] 2+, [AR+2H] 2+, [KK+2H] 2+ and [GHK+2H] 2+ (A = alanine, K = lysine, R = arginine, G = glycine and H = histidine). For crown ether complexes the formation of z + ions was always preferred over c + ions. In the case of [GHK+2H] 2+, the bare ion dissociated into z 2 + + c 1 and z 1 + c 2 + from cleavage of the first and second N–C α bond, respectively, whereas z 1 + fragment ions had higher yield than c 2 + for [GHK+2H] 2+(CE). The internal energy of the ions was changed by storing them in a 22-pole ion trap in which they were equilibrated to a temperature between −60 and 90 °C in collisions with helium gas. The average internal energy increased by about 0.4 eV from the lowest to the highest temperature for the dipeptides and 0.6 eV for the tripeptide. More fragmentation occurred at the higher temperature, as observed by an increase in the formation of b + and y + ions after breakage of the peptide bond of vibrationally hot even-electron cations and from secondary reactions of z + radical cations within the time window of the experiment. However, the z + to c + partitioning was not found to depend significantly on temperature in the measured range. In addition the decay of [GHK+H] +/[GHK+2H] + and [AK+H] + formed after electron capture by [GHK+2H] 2+ and [AK+2H] 2+ was found to occur on a microsecond to millisecond timescale. The data are well described by a power-law decay, which implies that the internal energy distribution is broad after electron capture and/or hydrogen loss.

Complex Formation of Crown Ethers and Cryptands with Alkali Metal and Ammonium Ions in Chloroform

The complex formation between different crown ethers and the cryptand [222] with alkali metal and ammonium ions in chloroform has been investigated by means of calorimetric titrations. The stability constants, reaction enthalpies and entropies for complex formation in chloroform have been determined. The complexation of alkali metal ions is favored by enthalpic contributions and influenced by both the ligand and the nature of the cation. The reaction enthalpies for complex formation of different ammonium salts with cryptand [222] are higher compared to the corresponding values for the reaction with different 18-crown-6 derivatives in chloroform due to the complete encapsulation of ammonium ion by the cryptand [222]. The benzo group attached to the crown ethers and the nature of the anion borne by the ammonium ion influence complex formation of ammonium with crown ethers. In the case of ammonium salts, competitive measurements have been carried out to underline the influence of the anion upon the complex formation. From the reaction enthalpies for complexation of ammonium ions, the contributions for the formation of hydrogen bonds are calculated using experimental data.

Complex formation of crown ethers with cations in water–organic solvent mixtures: Part X. Thermodynamics of interactions between Na + ion and 15-crown-5 ether in acetone–water mixtures at 298.15 K

The thermodynamic functions of complex formation of 15-crown-5 ether (15C5) with sodium cation (Na +) in the mixtures of water with acetone at 298.15 K have been calculated. The equilibrium constants of complex formation of 15C5 with Na + have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by the calorimetric method. The complexes are enthalpy-stabilized but entropy-destabilized in acetone–water mixtures. The effects of hydrophobic hydration, preferential solvation of 15C5 by a molecule of organic solvent and solvation of Na + on the complex formation processes have been discussed.

Complex formation of crown ethers and cryptands with Ba 2+ in the biphasic system chloroform/water studied by titration calorimetry

Calorimetric titrations have been performed in the liquid biphasic system chloroform/water. The reactions between salts in aqueous in different crown ethers and a cryptand in chloroform solution have been studied. After saturation of each solvent with the other no heats of mixing are detected. The values of the stability constants are related to different individual reaction steps during the complex formation. The experimental values show that the complex formation itself is not measured. Other steps e.g. transfer of the salt from one solvent to the other are responsible for the calculated values. On the other hand the overall reaction enthalpies show a significant contribution resulting from the interactions between the ligands and the cation or salt. A more detailed discussion is not possible at the moment.

Complex formation of crown ethers with cations in the (water + organic solvent) mixtures: Part IX. Thermodynamics of interactions of Na + ion with benzo-15-crown-5 ether in {(1 − x)DMA + xH 2O} at T = 298.15 K

The thermodynamic functions of complex formation of benzo-15-crown-5 ether with sodium cation in {(1 − x)DMA + xH 2O} at T = 298.15 K have been calculated. The equilibrium constants of complex formation of benzo-15-crown-5 ether with sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by calorimetric method at T = 298.15 K. The complexes are enthalpy stabilized and entropy destabilized. A simple model has been proposed to describe the relationship between the thermodynamic functions of complex formation of crown ethers with sodium cation and the structural and energetic properties of the mixed water–organic solvent. The linear enthalpy–entropy relationship for complex formation is also presented. The solvation enthalpy of the complex in {(1 − x)DMA + xH 2O} is discussed.

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VIII. Thermodynamic of Interactions of Na+Ion with 15-Crown-5 and Benzo-15-Crown-5 Ethers in the Mixtures of Water with Hexamethylphosphortriamide at 298.15 K

The equilibrium constants of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15 K. The thermodynamic functions of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation in the mixtures of water with hexamethylphosportriamide at 298.15 K have been calculated. The extent of complex formation in this mixed solvent depends on the enthalpic effect. In water–hexamethylp- hosportriamide mixtures with medium and low water content, the complex of crown ethers with the sodium cation is not formed because of the strong solvation of sodium cation and crown ethers molecules; this implies that the entropy of complex formation is more negative than the enthalpy of complex formation.

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VII. Thermodynamic of Interactions of Na+ Ion with 15-Crown-5 Ether in the Mixture of Water with N,N-Dimethylacetamide at 298.15 K

The thermodynamic functions of the complex formation of 15-crown-5 ether with sodium cation in mixtures of water with N,N-dimethylacetamide at 298.15 K are calculated. The equilibrium constants of complex formation of 15-crown-5 ether with sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15 K. The complexes are enthalpy-stabilized but entropy-destabilized in this mixed solvent. A quantitative dependence of the excess molar enthalpy and entropy of complex formation on the structural and energetic properties of interactions between water and organic solvent molecules in the mixtures of water with N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide has been found. The linear entropy–enthalpy relationship for complex formation is also presented. The solvation enthalpy of the complex in the water–N,N-dimethylacetamide mixtures is discussed.

Complex formation of crown ethers with cations in the (water + organic solvent) mixtures. Part VI. Thermodynamic of interactions of Na + ion with benzo-15-crown-5 ether in {(1− x)DMF + xH 2O} at 298.15 K

The equilibrium constants of complex formation of benzo-15-crown-5 ether with sodium cation in {(1− x)DMF + xH 2O} were calculated using conductometric measurements. The thermodynamic functions of complex formation, the transfer enthalpy of complex from DMF to mixed solvent and the influence of benzene ring on the process of complex formation were calculated and discussed together with the same function in {(1− x)DMSO + xH 2O}. A good relationship between the enthalpy and entropy of complex formation was observed.

Complex formation of crown ethers with cations in the water-organic solvent mixtures. Part V. Thermodynamic of interactions of Na + ion with 15-crown-5-ether in the mixtures of water with N,N-dimethylformamide at 298.15 K

The equilibrium constants of complex formation of 15-crown-5-ether with sodium iodide have been determined by conductivity measurements in the mixtures of water with N,N-dimethylformamide-water-sodium iodide system have been measured at 298.15 K. The N,N-dimethylformamide at 298.15 K. Standard enthalpies of solution of crown ether in the thermodynamic functions of complex formation of 15-crown-5-ether with sodium iodide are discussed. The complex formation in this mixed solvent depends on the enthalpic effect. The linear enthalpy-entropy relationship for complex formation is presented. The transfer enthalpy of the complex from pure N,N-dimethylformamide to the examined mixtures were calculated and discussed.

Complex formation of crown ethers with cations in water-organic solvent mixtures.: Part II. Thermodynamics of interactions of Na + ion with benzo-15-crown-5 ether in the mixtures of water with dimethylsulfoxide at 298.15 K

The equilibrium constants of complex formation of crown ether (benzo-15-crown-5 ether) with sodium cation have been determined by molar conductance at various molar ratios of benzo-15-crown-5 ether and sodium iodide in the mixtures of water with dimethylsulfoxide at 298.15 K. The solution enthalpy of benzo-15-crown-5 ether in the dimethylsulfoxide-water-sodium iodide system has been measured at 298.15 K. The thermodynamic functions of complex formation of benzo-15-crown-5 ether with sodium iodide were calculated. The linear enthalpy-entropy relationship for complex formation was discussed. The transfer enthalpy of the benzo-15-crown-5 ether/Na + complex from pure dimethylsulfoxide to the examined mixtures was calculated and discussed. The contribution of the benzene ring in the thermodynamic functions of complex formation and in the standard enthalpy of complex solvation was analysed.

Complex Formation of Crown Ethers with Cations in Water–Organic Solvent Mixtures. Part IV. Thermodynamics of Interaction of Na+Ion with Benzo-15-crown-5 Ether in the Mixtures of Water with Acetonitrile at 298.15 K

Abstract The equilibrium constants of complex formation of crown ether (benzo-15-crown-5 ether) with sodium cation have been determined by molar conductance at various molar ratios of benzo-15-crown-5 ether and sodium iodide in the mixtures of water with dimethylsulfoxide at 298.15 K. The solution enthalpy of benzo-15-crown-5 ether in the dimethylsulfoxide-water-sodium iodide system has been measured at 298.15 K. The thermodynamic functions of complex formation of benzo-15-crown-5 ether with sodium iodide were calculated. The linear enthalpy-entropy relationship for complex formation was discussed. The transfer enthalpy of the benzo-15-crown-5 ether/Na + complex from pure dimethylsulfoxide to the examined mixtures was calculated and discussed. The contribution of the benzene ring in the thermodynamic functions of complex formation and in the standard enthalpy of complex solvation was analysed.