Dependence of the thermodynamic characteristics of the complexation of alanine-18-crown-6 on the composition of water-ethanol solvent

Standard thermodynamic parameters (Δ_r G○, Δ_r H○, TΔ_r S○) for the complexation reaction of 18-crown-6 ether (18C6) with D,L-alanine (Ala) in mixed water-ethanol (H₂O-EtOH) solvents are calculated from the data of calorimetric titrations performed at T = 298.15 K. It is established that an increase in the concentration of EtOH in mixed solvent leads to a rise in stability and an increase in the exothermicity of [Ala18C6] molecular complex formation; changes in the energetics of reaction upon a change in the solvent composition are determined by changes in the solvation state of 18C6, which is typical of the reactions of molecular complex formation of 18C6 with D,L-alanine and glycine in water-organic solvents.     

Molecular complexation of some amino acids and triglycine with 18-crown-6 ether in H2O-EtOH solvents at 298.15 K

The influence of composition of H₂O-EtOH solvent on the reaction of formation of a molecular complex of 18-crown-6 ether (18C6) with triglycine (3Gly) has been studied at 298.15 K by a thermochemical method. The standard thermodynamic parameters (Δ_r G°, Δ_r H°, and TΔ_r S°) of the reaction of [3Gly18C6] complex formation in water-ethanol (H₂O-EtOH) solvents having an EtOH mole fraction of 0.0, 0.1, 0.15, 0.2, 0.25, 0.30, and 0.50 have been calculated from the data of calorimetric measurements performed on a TAM III titration microcalorimeter. It has been found that an increase in EtOH concentration in the mixed solvent results in an increase in stability of [3Gly18C6] and in an enhancement in exothermicity of its formation reaction. The water-ethanol solvent has an analogous effect on the stability and energetics of the reactions of formation of molecular complexes of 18C6 with glycine, D,L-alanine, and L-phenylalanine.     

Molecular complex formation between l-phenylalanine and 18-crown-6 in H2O–DMSO solvents studied by titration calorimetry at T = 298.15 K

The standard thermodynamic parameters (Δ_r G°, Δ_r H°, TΔ_r S°) of the reaction of molecular complex formation between 18-crown-6 ether (18C6) and l-phenylalanine (Phe), [Phe18C6], have been obtained from calorimetric titration experiments carried out by means of the microcalorimetric system TAM III (TA Instruments, USA) at T = 298.15 K in water–dimethylsulfoxide (H₂O–DMSO) solvents. Results show that the increase of the DMSO concentration in the mixed solvents brings about an increase of the [Phe18C6] complex stability and of the exothermicity of the reaction of complex formation.     

Calorimetric investigation of the complex formation reaction of 18-crown-6 ether with d,l-alanine in water–ethanol mixtures

The standard thermodynamic parameters (Δ_r G°, Δ_r H°, and TΔ_r S°) of the reaction of molecular complex formation of 18-crown-6 ether (18C6) with d,l-alanine (Ala), [Ala18C6], have been obtained from calorimetric titration experiments carried out using the microcalorimetric system TAM III (TA Instruments, USA) at T = 298.15 K in water–ethanol (H₂O–EtOH) solvents at X _EtOH = 0 ÷ 0.6 mol fractions. Results show that the increase of the EtOH concentration in solvent brings about an increase of the [Ala18C6] complex stability and of the exothermicity of the reaction of complex formation. The solvation contributions of 18C6, Ala, [Ala18C6] to Δ_r G° and Δ_r H° at various X _EtOH values are also analyzed.     

Effect of solvation on the thermodynamics of formation for 18-crown-6 ether complexes with glycine and triglycine in water-ethanol solutions at 298 K

Using data from calorimetric titration, standard thermodynamic parameters logK ^○, Δ_r G ^○, Δ_r H ^○, and TΔ_r S ^○ of the formation of 18-crown-6 ether (18C6) molecular complex with triglycine (3Gly), [3Gly18C6] in H₂O-EtOH solvents with contents of ethanol x ranging between 0.0 and 0.5 mole fractions are calculated. Increasing the concentration of EtOH in the solvent is found to raise the reaction’s exothermicity from ?5.9 to ?21.0 kJ mol^?1 and logK ^○ [3Gly18C6] from 1.10 to 2.53. A comparative analysis of the effect the composition of H₂O-EtOH solvent has on the reactions of [3Gly18C6] and [Gly18C6] formation is performed. As in case of [Gly18C6] formation, the changes in the complex’s enthalpy of solvation Δ_tr H ^○([3Gly18C6]) are close to the Δ_tr H ^○(18C6) parameter and differ considerably from the Δ_tr H ^○(3Gly) value, testifying to the crucial role 18C6 plays in changing the [3Gly18C6] state of solvation. The ratio between solvation contributions from reagents to Δ_tr G ^○ of [3Gly18C6] formation is found to differ from that the one between the corresponding contributions to Δ_tr H _r ^o : in transferring from water to H₂O-EtOH mixtures, the increase in the positive Δ_tr G ^○(18C6) values is slight and therefore negligible when compared to Δ_tr G ^○(3Gly).     

The enthalpies of solution of DL-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (298.15 K) of DL-α-alanine in water-organic solvent mixtures were measured at organic component concentrations x ₂ = 0–0.4 mole fractions. The organic solvents used were acetonitrile (ACN), formamide (FA), N,N-dimethylformamide (DMFA), and N,N-dimethylsulfoxide (DMSO). The standard enthalpies of solution Δ_sol H ^o, solvation Δ_solv H ^o, and transfer (Δ_tr H ^o) of DL-α-alanine from water to mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics was considered. The solution of DL-α-alanine in the mixtures studied was endothermic over the whole range of organic component concentrations. The Δ_sol H ^o, Δ_tr H ^o, and Δ_solv H ^o values as functions of x ₂ can pass extrema (DMSO and DMFA), be almost independent of mixed solvent composition (FA), or be exothermic and monotonic functions (ACN). The enthalpy coefficients of pair interactions (h _xy ) between DL-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft equation was used to correlate the h _xy values with the properties of organic solvents.     

Thermodynamic characteristics of alanine-18-crown-6 ether complexes in binary water-acetone solvents

The formation of 18-crown-6 ether (18C6) complexes with D,L-alanine (Ala) in mixed wateracetone solvents with 0.0, 0.08, 0.17, 0.22, and 0.30 mole fractions of acetone (T = 298.15 K) was investigated by means of calorimetry. Thermodynamic characteristics of the reaction of the molecular [Ala18C6] complex formation (Δ_r G°, Δ_r H°, and TΔ_r S°) were calculated on the basis of calorimetric data. Analysis of solvation contributions of reagents into the enthalpy of the [Ala18C6] formation reaction showed that the changes in the reaction energy when the solvent composition is varied are determined by the changes in the solvate state of 18C6.     

Thermodynamics of complex formation in mixed solvents <Emphasis Type="Italic">K</Emphasis> and Δ<Emphasis Type="Italic">H</Emphasis> for the formation reaction of [Gly18C6] at 298.15 K

The influence of H₂O–EtOH and H₂O–Acetone mixed solvents at various compositions on the thermodynamics of complex formation reaction between crown ether 18-crown-6 (18C6) and glycine (Gly) was studied. The standard thermodynamic parameters of the complex [Gly18C6] (log K°, Δ_r H°, Δ_r S°) were calculated from thermochemical data at 298.15 K obtained by titration calorimetry. The complex stability and its formation enthalpy increase with increasing the non aqueous component concentration in both mixed solvents. The thermodynamic data were discussed on the basis of the solvation thermodynamic approach and the solvation contributions of the reagents and of the complex to the complex stability were analyzed.     

Effects of Solvent Composition and Temperature on K+–18-Crown-6 Complexation in Acetonitrile–Water Mixed Solvents

Complexation of K⁺ by 18-crown-6 ether (18C6) in pure water and in acetonitrile–water mixed solvents containing 0.1 mol-dm^{? 3} (C₂H₅)₄NCl has been systematically studied by isothermal titration calorimetry (ITC) at 293, 298, and 303 K. The formation constant K of the 1:1 [K(18C6)]⁺ complex and the complexation enthalpy Δ _rH were simultaneously determined from the titration data. The logK and Δ _rH(kJ-mol^{? 1}) values at 298 K are 2.04, ?26.2 in pure water and 2.23, ?25.0; 2.61, ?24.2; 2.95, ?23.8; 3.48, ?21.0; 3.85, ?19.4; 4.36, ?18.7; and 5.73, ?17.0 in the mixed solvents at x _AN (mole fraction of acetonitrile) of 0.043, 0.135, 0.258, 0.448, 0.578, 0.759, and 1.0, respectively. The change in heat capacity for the complex formation, Δ C _p °, was also determined by the temperature dependence of Δ _rH. Whereas the Δ C _p ° is (57 ± 11) and (63 ± 20) J-mol^{? 1}-K^{? 1} in pure water and in the solvent mixture at x _AN = 0.043, respectively, it decreases with increasing x _AN. The Δ C _p ° values are ?(48 ± 11), ?(110 ± 25), ?(354 ± 40), ?(359 ± 24), and ?(304 ± 30) J-mol^{? 1}-K^{? 1} at x _AN = 0.135, 0.258, 0.448, 0.578, and 0.759, respectively. The changes in complexation thermodynamics (Δ Δ _rG, Δ Δ_rH, and Δ Δ _r S) are discussed in terms of the corresponding transfer thermodynamics of K⁺, 18-crown-6, and [K(18C6)]⁺ upon transferring from water to acetonitrile–water mixed solvents. It was found that hydrophobic solvation of the complex [K(18C6)]⁺ plays an important role in complex formation occurring in water and in the water-rich mixed solvent. Moreover, changes in solvent structure significantly affect the transfer enthalpy and entropy of each species, i.e., K⁺, 18-crown-6, and [K(18C6)]⁺. The observed monotonous changes in the complexation Gibbs energy, enthalpy, and entropy with solvent composition are due to the effective compensation of the Δ _trG, Δ _trH, and Δ _tr S for K⁺ with those for 18-crown-6 and [K(18C6)]⁺.     

The Heats of Mixing of Aqueous Solutions of Dipeptides with Solutions of Nitric Acid and Potassium Hydroxide over the Temperature Range 288.15–308.15 K

The heats of interaction of D,L-α-alanyl-D,L-valine, β-alanyl-β-alanine, and α-alanyl-β-alanine with solutions of nitric acid and potassium hydroxide were determined calorimetrically at 288.15, 298.15, and 308.15 K and solution ion strengths of 0.5, 1.0, and 1.5 in the presence of KNO₃ and LiNO₃. The heat effects of step dissociation of the dipeptides were calculated using the RRSU universal program. The standard thermodynamic characteristics (Δ_r H ^o, Δ_r G ^o, Δ_r S ^o, and ΔC _p ^o) of proton interaction with the ligands specified were determined. The data obtained were analyzed in terms of Herny concepts. The thermodynamic characteristics of ionization correlated with the structural features of the dipeptides.     

Effect of solvation on the thermodynamics of the formation of molecular complexes of 18-crown-6 ether with glycine in water-dimethylsulfoxide solutions

Complexation of the 18-crown-6 ether (18C6) with glycine (Gly) in mixed H₂O-DMSO solvents with the composition of 0.1, 0.2, and 0.25 mole fraction of DMSO (T = 298.15 K) was studied calorimetrically. Thermodynamic characteristics of the reaction of the formation of the molecular Gly18C6 complex (Δ_r G°, Δ_r H°, TΔ_r S°) were calculated from the calorimetric data. It was established that the change in the stability of the Gly18C6 complex is mainly determined by the predominance of the enthalpy component of the Gibbs energy over the entropy component. It was shown during the analysis of the enthalpy contributions of the reagents to the enthalpy of the reaction of the formation of Gly18C6 that the change in the enthalpy of the reaction upon a change the solvent composition was due to changes in the solvation state of 18C6.     

Conductance Studies on Complex Formation Between Aza-18-Crown-6 with Ag+, Hg2+ and Pb2+ Cations in DMSO–H2O Binary Solutions

The complexation reactions between Ag⁺, Hg²⁺ and Pb²⁺ metal cations with aza-18-crown-6 (A18C6) were studied in dimethylsulfoxide (DMSO)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complexes in most cases is 1:1(ML), but in some cases 1:2 (ML₂) complexes are formed in solutions. A non-linear behaviour was observed for the variation of log K _f of the complexes vs. the composition of the binary mixed solvents. Selectivity of A18C6 for Ag⁺, Hg²⁺ and Pb²⁺ cations is sensitive to the solvent composition and in some cases and in certain compositions of the mixed solvent systems, the selectivity order is changed. The values of thermodynamic parameters (ΔH _c^o, ΔS _c^o) for formation of A18C6–Ag⁺, A18C6–Hg²⁺ and A18C6–Pb²⁺ complexes in DMSO–H₂O binary systems were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

A Thermodynamic Study of Complex Formation Between 18-Crown-6 with T1 + , Hg 2+ and Ag + Metal Cations in Some Binary Mixed Non-aqueous Solvents Using the Conductometric Method

The complexation reactions betweenT1⁺, Hg²⁺ andAg⁺ metal cations with 18-Crown-6 (18C6)were studied in acetonitrile (AN)-methanol (MeOH) andbenzonitrile (BN)-methanol (MeOH) binary mixtures at differenttemperatures using the conductometric method. The conductance datashow that the stoichiometry of the complexes in most cases is1 : 1 (ML), but in the case of theTl⁺ cation, in addition to a1 : 1 complex, a 1 : 2 (ML₂)complex is formed in solutions. A non-linear behaviourwas observed for the variation of log K_fof the complexes vs the composition of the binary mixed solvents. The stability of 18C6 complexes with T1⁺, Hg²⁺ and Ag⁺ cations is sensitive to solvent composition and in some cases, the stability order is changed with changingthe composition of the mixed solvents. The values of the thermodynamic parameters (Δ H_c°, Δ S_c°) for formation of 18C6-T1⁺, 18C6-Hg⁺² and the 18C6-Ag⁺ complexes were obtained from the temperature dependence of the stability constants and the results show that the thermodynamics of the complexationreactions is affected by the nature and composition of the mixed solvents and in most cases, the complexes are enthalpy destabilized but entropy stabilized.     

Thermodynamic behavior of complexation process between dibenzo-18-crown-6 and K+, Ag+, NH 4 + , and Hg2+ cations in ethylacetate-dimethylformamide binary media

The complexation reactions between K⁺, Ag⁺, NH₄⁺, and Hg²⁺ cations and the macrocyclic ligand, dibenzo-18-crown-6 (DB18C6), were studied in ethylacetate (EtOAc)-dimethylformamide (DMF) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry of all the complexes is 1:1. A non-linear behavior was observed for the variation of log K _f of the complexes versus the composition of binary mixed solvents, which was discussed in terms of heteroselective solvation and solvent-solvent interactions in binary solutions. It was found that the stability order of the complexes changes with changing the composition of the mixed solvents. The sequence of stabilities for the K⁺, Ag⁺, NH₄⁺, and Hg²⁺ complexes with DB18C6 in EtOAc-DMF binary solutions (mol. % DMF 25.0) and (mol. % DMF 50.0) at 25°C is (DB18C6-Ag)⁺ > (DB18C6-K)⁺ > (DB18C6-Hg)²⁺ > (DB18C6-NH₄)⁺, but in the cases of pure DMF and a binary solution of EtOAc-DMF (mol. % DMF 75.0) is (DB18C6-K)⁺ > (DB18C6-Hg)²⁺ > (DB18C6-Ag)⁺ ≈ (DB18C6-NH₄)⁺. The values of thermodynamic quantities (ΔH _c ^o, ΔS _c ^o) for these complexation reactions have been determined from the temperature dependence of the stability constants, and the results show that the thermodynamics of the complexation reactions is affected by the nature and composition of the mixed solvents and, in all cases, positive values of ΔS _c ^o characterize the formation of these complexes. In addition, the experimental results show that the values of entropies for the complexation reactions between K⁺, Ag⁺, NH₄⁺, and Hg²⁺ cations and DB18C6 in EtOAc-DMF binary solutions do not change monotonically with the solvent composition. The text was submitted by the authors in English.     

Synthesis of homoleptic tris(organo-chelate)iridium(III) complexes by spontaneous ortho-metallation of electronrich olefin-derived N,N′-diarylcarbene ligands and the X-ray structures of fac-[Ir{CN(C6H4Me-p) (CH2)2NC6H3Me-p}3] and mer-Ir{CN(C6H4Me-p)(CH2)2NC6H3Me-p}2 {CN(C6H4Me-p)(CH2)2NC6H4Me-p}Cl (a product of HCl cleavage)

Treatment of [{Ir(COD)(μ-Cl)}₂] with excess of the electron-rich olefin [$\text{CN(Ar)(CH}{}_2\text{)}{}_2\text{N}$Ar]₂ (abbreviated as (L^Ar)₂, Ar = C₆H₄Me-p or C₆H₄OMe-p) affords the ortho-metallated tricycle [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₃], which for Ar = C₆H₄Me-p (Ia) with HCL yields [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₂(L^Ar)]Cl (IV); X-ray data show that in IV there is an unexpectedly close Ir?C(o-aryl) contact (2;52(1) Å) involving the “free” L^Ar which compares with an IrC(o-aryl) distance of 2.09(3) Å in Ia or 2.07(3) Å in the ortho-metallated L^Ar ligand of complex IV.     

The enthalpies of solution of L-α-alanyl-L-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (T = 298.15 K) of L-α-alanyl-L-α-alanine in aqueous-organic solvents (acetonitrile, 1,4-dioxane, acetone, formamide, N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, and N,N-dimethylsulfoxide) were measured at organic component concentrations x ₂ = 0–0.3 mole fractions. The standard enthalpies of solution (Δ_sol H ^o) and transfer (Δ_tr H ^o) of the peptide from water into mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics is considered. The enthalpy pair interaction coefficients h _xy between L-α-alanyl-L-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft four-parameter equation was used to reveal correlation between the h _xy values and the properties of organic solvents.     

Thermodynamics of formation for the 18-crown-6-triglycine molecular complex in water-dimethylsulfoxide solvents

The effect of a water-dimethylsulfoxide (DMSO) solvent on the formation of a molecular complex of 18-crown-6 (18C6) with triglycine (diglycylglycine, 3Gly) is studied via calorimetric titration. It is found that switching from water to an H₂O-DMSO mixture with DMSO mole fraction of 0.30 is accompanied by a monotonic increase in the stability of [3Gly18C6] complex, from logK ^° = 1.10 to logK ^° = 2.44, and an increase in the exothermicity of the reaction of its formation, from ?5.9 to ?16.9 kJ/mol. It is shown that the [3Gly18C6] complex exhibits enthalpy stabilization with negative values of enthalpy and entropy over the investigated range of H₂O-DMSO solvents. Analysis of the reagents’ solvation characteristics reveals that the increase in the reaction’s exothermicity of transfer is due to differences in the solvation of [3Gly18C6] and 18C6 with a small solvation contribution from 3Gly. It is concluded that the change in the Gibbs energy of the reaction 3Gly_solv + 18C6_solv ? [3Gly18C6]_solv is due to differences in the change in the solvation state of the complex and the peptide (Δ_tr G ^°([3Gly18C6])-Δ_tr G ^°(3Gly)).     

Complexation study of dibenzo-18-crown-6 with UO2 2+ cation in binary mixed non-aqueous solutions

The complexation reaction of macrocyclic ligand, dibenzo-18-crown-6 (DB18C6) with UO₂ ²⁺ cation was studied in ethylacetate-1,2-dichloroethane (EtOAc/DCE), acetonitrile-1,2-dichloroethane (AN/DCE), methanol-1,2-dichloroethane (MeOH/DCE) and ethanol-1,2-dichloroethane (EtOH/DCE) binary solutions at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complex formed between DB18C6 and UO₂ ²⁺ cation is affected by the nature of the solvent systems. A non-linear behaviour was observed for changes of log K _f of (DB18C6.UO₂)⁺² complex versus the composition of the binary mixed solvents. The values of thermodynamic quantities (?S°_c, ?H°_c) for formation of (DB18C6.UO₂)⁺² complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The results show that in most cases, the complex is enthalpy stabilized and in all cases entropy stabilized and both parameters are affected by the nature and composition of the mixed solvents. In addition, the complex formation between dicyclohexyl-18-crown-6 (DCH18C6) and UO₂ ²⁺ cation was studied in pure AN and the results were compared with those of the (DB18C6.UO₂)⁺² complex.     

A Polarographic Study of Tl + , Pb 2 and Cd 2+ Complexes with Dicyclohexano-18-Crown-6 in Some Binary Mixed Solvents

The complexes of Tl⁺, Pb²⁺ and Cd²⁺ cations with the macrocyclic ligand, dicyclohexano-18-crown-6\linebreak(DC18C6) were studied in water/methanol (H₂₊O/MeOH), water/1-propanol (H₂₊O/1-PrOH), water/acetonitrile (H₂₊O/AN), water/dimethylformamide (H₂₊O/DMF), dimethylformamide/acetonitrile (DMF/AN), dimethylformamide/methanol (DMF/MeOH), dimethylformamide/1-propanol (DMF/1-PrOH) and dimethylformamide/nitromethane (DMF/NM) mixed solvents at 22 °C using differential pulse polarography (DPP), square wave polarography and conductometry. In general, the stability of the complexes was found to decrease with increasing concentration of water in aqueous/non-aqueous mixed solvents with an inverse relationship between the stability constants of the complexes and the concentration of DMF in non-aqueous mixed solvents. The results show that the change in stability of DC18C6.Tl⁺, vs the composition of solvent in DMF/AN and DMF/NM mixed solvents is apparently different from that in DMF/MeOH and DMF/1-PrOH mixed solvents. While the variation of stability constants of the DC18C6.Tl⁺ and DC18C6.Pb²⁺ complexes vs the composition of H₂₊O/AN mixed solvents is monotonic, an anomalous behavior was observed for variations of log K_f vs the composition of H₂₊O/1-PrOH and H₂₊O/MeOH mixed solvents. The selectivity order of the DC18C6 ligand for the cations was found to be Pb²⁺ > Tl⁺ > Cd²⁺.     

Study of Complex Formation Between Dicyclohexano-18-Crown-6 (DCH18C6) with Mg 2+, Ca2+, Sr 2+, and Ba2+ Cations in Methanol–Water Binary Mixtures Using Conductometric Method

The complexation reactions between Mg²⁺,Ca²⁺,Sr²⁺ and Ba²⁺ metal cations with macrocyclic ligand, dicyclohexano-18-crown-6 (DCH18C6) were studied in methanol (MeOH)–water (H₂O) binary mixtures at different temperatures using conductometric method . In all cases, DCH18C6 forms 1:1 complexes with these metal cations. The values of stability constants of complexes which were obtained from conductometric data show that the stability of complexes is affected by the nature and composition of the mixed solvents. While the variation of stability constants of DCH18C6-Sr ²⁺ and DCH18C6-Ba²⁺versus the composition of MeOH–H₂O mixed solvents is monotonic, an anomalous behavior was observed for variations of stability constants of DCH18C6-Mg²⁺ and DCH18C6-Ca²⁺ versus the composition of the mixed solvents. The values of thermodynamic parameters (ΔH_c°, ΔS_c°) for complexation reactions were obtained from temperature dependence of formation constants of complexes using the van’t Hoff plots. The results show that in most cases, the complexation reactions are enthalpy stabilized but entropy destabilized and the values of thermodynamic parameters are influenced by the nature and composition of the mixed solvents. The obtained results show that the order of selectivity of DCH18C6 ligand for metal cations in different concentrations of methanol in MeOH–H₂O binary system is: Ba²⁺>Sr²⁺>Ca²⁺> Mg²⁺.