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.     

Influence of the composition of aqueous dimethylsulfoxide solvent on thermodynamics of complexing between 18-crown-6-ether and D,L-alanine

Standard thermodynamic parameters (logK ^o, ??_r H ^o, T??_r S ^o) of complexing 18-crown-6 ether (18C6) with D,L-alanine (Ala) in mixed water-dimethysulfoxide (H₂O-DMSO) solvents are calculated on the basis of calorimetric titration results. A rise in the DMSO concentration in mixed solvent is found to increase stability and increase the exothermicity of the formation of [Ala-18C6] molecular complex. Changes in the reaction energetic are shown to be determined by changes in the solvation state of 18C6 that is the characteristic of the reactions of molecular complex formation between 18C6 and D,L-alanine or glycine in water-organic solvents.     

Study of complexation process between N-phenylaza-15-crown-5 with yttrium cation in binary mixed solvents

The complexation reaction between Y³⁺ cation with N-phenylaza-15-crown-5(Ph-N15C5) was studied at different temperatures in acetonitrile–methanol (AN/MeOH), acetonitrile–propanol (AN/PrOH), acetonitrile–1,2 dichloroethane (AN/DCE) and acetonitrile–water (AN/H₂O) binary mixtures using the conductometric method. The results show that in all cases, the stoichiometry of the complex is 1:1 (ML). The values of formation constant of the complex which were determined using conductometric data, show that the stability of (Ph-N15C5.Y)³⁺ complex in pure solvents at 25?°C changes in the following order: PrOH?>?AN?>?MeOH and in the case of binary mixed solutions at 25?°C it follows the order: AN–DCE?>?AN–PrOH?>?AN–MeOH?>?AN–H₂O. The values of standard thermodynamic quantities (?H _c ^° and ?S _c ^° ) for formation of (Ph-N15C5.Y)³⁺ complex were obtained from temperature dependence of the formation constant using the van’t Hoff plots. The results show that in most cases, the complex is entropy and enthalpy stabilized and these parameters are influenced by the nature and composition of the mixed solvents. In most cases, a non-linear behavior was observed for variation of log K_f of the complex versus the composition of the binary mixed solvents. In all cases, an enthalpy–entropy compensation effect was observed for formation of (Ph-N15C5.Y)³⁺ complex in the binary mixed solvents.     

Study of complexation process between 4′-nitrobenzo-15-crown-5 and yttrium(III) cation in binary mixed non-aqueous solvents using conductometric method

The complexation reaction of macrocyclic ligand (4??-nitrobenzo-15C5) with Y³⁺ cation was studied in acetonitrile-methanol (AN-MeOH), acetonitrile-ethanol (AN-EtOH), acetonitrile-dimethylformamide (AN-DMF) and ethylacetate-methanol (EtOAc-MeOH) binary mixtures at different temperatures using conductometry method. The conductivity data show that in all solvent systems, the stoichiometry of the complex formed between 4??-nitrobenzo-15C5 and Y³⁺ cation is 1: 1 (ML). The stability order of (4??-nitrobenzo-15C5). Y³⁺ complex in pure non-aqueous solvents at 25°C was found to be: EtOAc > EtOH > AN ?? DMF > MeOH, and in the case of most compositions of the binary mixed solvents at 25°C it was: AN??MeOH ?? AN-EtOH > AN-DMF > EtOAc-MeOH. But the results indicate that the sequence of the stability of the complex in the binary mixed solutions changes with temperature. A non-linear behavior was observed for changes of logK _f of (4??-nitrobenzo-15C5 · Y³⁺) complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent interactions and also the hetero-selective solvation of the species involved in the complexation reaction. The values of thermodynamic parameters (??H _c ^? and ??S _c ^? ) for formation of the complex were obtained from temperature dependent of the stability constant using the van??t Hoff plots. The results represent that in most cases, the complex is both enthalpy and entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.     

Complexation ability of kryptofix 22DD with lanthanum (III) cation in some binary mixed non-aqueous solvents

The complex formation between lanthanum (III) cation with kryptofix 22DD was studied in acetonitrile–dimethylformamide (AN–DMF), acetonitrile–methanol (AN–MeOH), acetonitrile–ethylacetate (AN–EtOAc) and acetonitrile–ethanol (AN–EtOH) binary solvent solutions at different temperatures by using conductometric method. The conductance data show that in all cases, the stoichiometry of the complex formed between the macrocyclic ligand and the metal cation is 1:1 [ML]. The stability order of (kryptofix 22DD.La)³⁺ complex in the studied binary solvent solutions at 25 °C was found to be: AN–EtOAc>AN–EtOH>AN–MeOH>AN–DMF and in the case of pure non-aqueous solvents at 25 °C was: EtOAc>EtOH>MeOH>AN>DMF. A non-linear behavior was observed for changes of logK_f of (kryptofix 22DD.La)³⁺ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the preferential solvation of the species involved in the complexation reaction. The values of standard thermodynamic parameters (?H _c°, ?S _c°) for formation of (kryptofix 22DD.La)³⁺ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots.The results show that in most cases, the (kryptofix 22DD.La)³⁺ complex is enthalpy destabilized, but entropy stabilized and the values of these thermodynamic quantities for formation of the complex are quite sensitive to the nature and composition of the mixed solvents solution.     

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.     

The state of 5,10,15,20-tetraphenyl-21H,23H-porphine rhenium(V) complexes in solutions of acids

The spectral properties (UV/Vis, IR, ¹H NMR) and stability of diverse forms of 5,10,15,20-tetraphenyl-21H,23H-porphine rhenium(V) complexes in neutral and protolytic solvents have been studied. Quantitative characteristics have been obtained for the reactions of formation and interconversion of the μ-oxo dimeric and monomeric rhenium(V) complex species in the benzene-AcOH system and dissociation at the coordination center of the H⁺-associated form of the monomeric rhenium(V) complex in mixed H₂O-H₂SO₄ solvents in a wide range of component concentrations. It has been shown that the stability of the coordination center of the rhenium(V) complexes sharply depends on the nature of a second acido ligand, in addition to the coordinated porphyrin.     

Trans-Effect in Kinetics of Reactions of Mixed Solvates of Cu(II) Acetate with Tetraphenyltetrabenzoporphine in Organic Solvents

The kinetics of complex formation of tetraphenyltetrabenzoporphine with Cu(II) and Zn(II) acetates is studied in individual and mixed coordinating solvents on the basis of DMSO, DMF, and Py. The substantial increase in CuAc₂ reactivity in mixed solvents is explained by the trans-effect of ligands in composition of the metal solvate sphere.     

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.     

Controlling the surface composition of PCBM in P3HT/PCBM blend films by using mixed solvents with different evaporation rates

The surface composition of poly(3-hexylthiophene-2,5-diyl) and fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) blend films could be changed by controlling the film formation process via using mixed solvents with different evaporation rates. The second solvent, with a higher boiling point than that of the first solvent and much better solubility for PCBM than P3HT, is chosen to mix with the first solvent with a lower boiling point and good solubility for both PCBM and P3HT. The slow evaporation rate of the second solvent provides enough time for PCBM to diffuse upwards during the solvent evaporation. Thus, the weight ratio of PCBM and P3HT (m _PCBM/m _P3HT) at surface of the blend films was varied from ca. 0.1 to ca. 0.72, i.e., it increases about seven times by changing from single solvent to mixed solvents. Meanwhile, the mixed solvents were in favor to form P3HT naonofiber network and enhance phase separation of P3HT/PCBM blend films. As a result, the power conversion efficiency of the device from mixed solvents with slow evaporation process was about 1.5 times of the one from single solvents.     

Study of Kryptofix5 Complexation with La<Superscript>3+</Superscript> Cation in Several Individual and Binary Nonaqueous Solvents Using Conductometric Method

Complexatio of the La³⁺ cation with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane(Kryptofix5) was studied in pure solvents acetonitrile (AN), methanol (MeOH), nitrobenzene (NB), tetrahydrofuran (THF), methyl acetate (MeOAC) and in various binary solvent mixtures of AN–MeOH, AN–NB, AN–THF, and AN–MeOAC systems at different temperatures using the conductometric method. The stoichiometry of the complex was found to be 1 : 1 (ML). In all cases, the variation of the log kf with composition of the solvent was non-linear. This behavior is probably due to a change in the structure of these binary mixed solvents as the composition of the medium is varied. The stability order of the complex in pure nonaqueous solvents at 25°C increases in the order: AN > THF > MeOAC > MeOH > NB. The values of thermodynamic data (ΔH _c °,ΔS _c °) formation of (Kryptofix5.La)³⁺ complex are definitely solvent dependent.     

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)]⁺.     

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.     

Solvent influence upon complexation of N-phenylaza-15-crown-5 with UO2 2+ cation in binary mixed non-aqueous solvents

The complexation reaction of N-phenylaza-15-crown-5 (PhA15C5) with UO₂ ²⁺ cation was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–butanol (AN–BuOH), acetonitrile–dimethylformamide (AN–DMF) and methanol–propylencarbonate (MeOH–PC) binary solutions, at different temperatures by conductometry method. The conductance data show that the stoichiometry of the complex formed between PhA15C5 with UO₂ ²⁺ cation in most cases is 1:1 [M:L], but in some solvent systems a 1:2 [M:L₂] complex is formed in solutions. The results revealed that, the stability constant of (PhA15C5·UO₂)²⁺ complex in the binary mixed solvents varies in the order: AN–BuOH>AN–MeOH>AN–DMF. In the case of the pure organic solvents, the sequence of the stability of the complex changes as: AN>PC>BuOH>DMF. A non-linear relationship was observed for changes of logK_f of (PhA15C5·UO₂)²⁺ complex versus the composition of the binary mixed solvents. The corresponding standard thermodynamic parameters (ΔH_c°, ΔS_c°) were obtained from temperature dependence of the stability constant. The results show that the values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents.     

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.     

Spectrophotometric and spectroscopic studies of charge transfer complexes of p-toluidine as an electron donor with picric acid as an electron acceptor in different solvents

The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as carbon tetrachloride, chloroform, dichloromethane acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in non-polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (K_CT), molar extinction coefficient (?_CT), standard free energy (ΔG^o), oscillator strength (f), transition dipole moment (μ_EN), resonance energy (R_N) and ionization potential (I_D). The results indicate that the formation constant (K_CT) for the complex was shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents that were used.     

Spectroscopic studies of multiple charge transfer complexes of p-toluidine with π-acceptor picric acid in different polar solvents

The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in less polar solvent is high. The stoichiometry of the complex was found to be 1: 1 ratio by straight line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (K _CT), molar extinction coefficient (?_CT), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (μ_EN), resonance energy (R _N) and ionization potential (I _D). The results indicate that the formation constant (K _CT) for the complex were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used.     

A conductometric study of complexation reaction between dibenzo-24-crown-8 with yttrium cation in some binary mixed non-aqueous solvents

The complexation reaction of macrocyclic ligand, dibenzo-24-crown-8 (DB24C8) with Y⁺³ cation was studied in some binary mixtures of methanol (MeOH), ethanol (EtOH), acetonitrile (AN) and tetrahydrofuran (THF) with dimethylformamide (DMF) at different temperatures using the conductometric method. The conductance data show that in all solvent systems, the stoichiometry of the complex formed between DB24C8 and Y⁺³ cation is 1:1 (ML). The stability order of (DB24C8.Y)⁺³ complex in pure non-aqueous solvents was found to be: AN > EtOH > MeOH > DMF. A non-linear behaviour was observed for changes of log K_f of (DB24C8.Y)⁺³ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the heteroselective solvation of the species involved in the complexation reaction. The obtained results show that the stability of (DB24C8.Y)⁺³ complex is sensitive to the mixed solvents composition. The values of thermodynamic parameters (?H°_c and ?S°_c) for formation of (DB24C8.Y)⁺³ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The results show that in most cases, the (DB24C8.Y)⁺³ complex is enthalpy destabilized but entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.     

A thermodynamic study of complexation process between <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-dipyridoxylidene(1,4-butanediamine) and Cd<Superscript>2+</Superscript> in some binary mixed solvents using conductometry

Complexation of the Cd²⁺ ion with N,N′-dipyridoxylidene(1,4-butanediamine) Schiff base was studied in pure solvents including acetonitrile (AN), ethanol (EtOH), methanol (MeOH), tetrahydrofuran (THF), dimethylformamide (DMF), water (H₂O), and various binary solvent mixtures of acetonitrile–ethanol (AN–EtOH), acetonitrile–methanol (AN–MeOH), acetonitrile–tetrahydrofuran (AN–THF), acetonitrile–dimethylformamide (AN–DMF), and acetonitrile–water (AN–H₂O) systems at different temperatures using the conductometric method. The conductance data show that the stoichiometry of complex is 1: 1 [ML] in all solvent systems. A non-linear behavior was observed for changes of log K_f of [Cd(N,N′-dipyridoxylidene(1,4-butanediamine)] complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions. The results show that the thermodynamics of complexation reaction is affected by the nature and composition of the mixed solvents.     

Thermodynamic study of complex formation between Kryptofix-5 and Sn2+ in several individual and binary non-aqueous solvents using a conductometric method

The complex formation between 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix-5) and Sn²⁺ ions was studied in pure acetonitrile (AN), dimethylformamide (DMF), 1,4-dioxane (DOX), and methanol (MeOH) and in acetonitrile-1,4-dioxane (AN-DOX), acetonitrile-dichloromethane (AN-DCM), acetonitrile-methanol (AN-MeOH), and acetonitrile-dimethylformamide (AN-DMF) binary mixed solvent solutions at different temperatures using conductometric method. 1: 1 [ML] complex is formed between the metal cation and ligand in most solvent systems but in the cases of AN-MeOH (MeOH = 90 mol %) binary mixture and in pure MeOH a 2: 1 [M₂L] complex was observed, that is the stoichiometry of complexes may be changed by the nature of the medium. The stability order of the (Kryptofix-5·Sn)²⁺ complex in the studied binary mixed solvent solutions at 25°C was found to be AN-DOX > AN-DCM > AN-MeOH > AN-DMF and in the case of pure solvents at 25°C the sequence was the following: AN > DMF > DOX. A non-linear behavior was observed for changes of logK _f of (Kryptofix-5·Sn)²⁺ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent intractions and also by the preferential solvation of the f species involved in the complexation reaction. The values of standard enthalpy changes (ΔH _c ^○ ) for complexation reactions were obtained from the slope of the Van’t Hoff plots and the changes in standard entropy (ΔS _c ^○ ) were calculated from the relationship ΔG _{c, 298.15} ^○ = ΔH _c ^○ ? 298.15ΔS _c ^○ . The results show that in most cases, the (Kryptofix-5·Sn)²⁺ complex is both enthalpy and entropy stabilized.