Concentration Distribution Diagrams Research Articles

Metal complexes of 1,4-bis(2-hydroxyethyl) piperazine: Thermodynamic and theoretical approach.

In the present study, the acid-base equilibria of 1,4-bis(2-hydroxyethyl)piperazine (BHEB) and the formation equilibria of complexes with the metal ions Cu(II), Ni(II), Co(II) and Zn(II) are investigated using the potentiometric technique. The acid-dissociation constants of BHEP in the protonated form and the formation constants of the complexes are determined using the Miniquad-75 program in the temperature range (15oC - 35oC). The thermodynamic parameters were determined and discussed. The concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties such as atomic number, ionic radius, electronegativity, and ionization potential are investigated. The complexes were synthesized and characterized by elemental analysis and mass spectra. Density Functional Theory (DFT) calculations have been performed to study the equilibrium geometry of 1,4-bis(2-hydroxyethyl)piperazine and its complexes. The optimization of the structure of the complexes reveals that CuII and CoII complexes have distorted octahedral geometry. NiII complex has a distorted square planar geometry. ZnII complex has a distorted tetrahedral geometry. The calculated total energies, energies of highest occupied molecular orbital (HOMO), energies of lowest unoccupied molecular orbital (LUMO) and dipole moments are reported. The N---N distance for uncoordinated 1,4-bis(2-hydroxyethyl)piperazine is calculated to be 2.870 Å and decreased to 2.588 Å, 2.491 Å, 2.502 Å, 2.479 Å, and 2.552 Å for Cu(II), Co(II), Ni(II) and Zn(II) complexes respectively. Also, bonds connected to N atoms are elongated upon complex formation. The interactions with the receptors as breast cancer oxidoreductase were feasible as evidenced by Docking analysis.

Potentiometric determination of stability constants of ternary complexes of first row transition metal ions with ditopic azelaic acid dihydrazide and aspartic acid in aqueous medium

A Chemical speciation study of ternary complexes containing transition metal ions (Mn2+,Co2+,Ni2+, Cu2+ and Zn2+) with a ditopic novel ligand L ​= ​Azelaic acid dihydrazide (AZDH) and X ​= ​l-Aspartic acid of type [MmLlX xHh], (where m ​= ​1, 2; l ​= ​1; x ​= ​1, 2 and h ​= ​−2 to 5) in different ratios of M:L:X ​= ​1:1:1, 1:2:1, 2:1:1and 2:1:2 was carried out using pH -potentiometric method of data acquisition and applied to chemometric modelling methods of analysis. MINIQUAD-75 program was used for the resolution of the plausible species and their corresponding formation constants at 303 ​± ​0.1 ​K, and 0.01 ​M ionic strength. Species concentration distribution diagrams were generated using HySS program. Best-fit chemical models were selected on the basis of statistical parameters like Standard deviation (SD), U (sum of the squares of the residuals in mass balance equations), and chi-square test etc. Relatively stable ternary complexes were evaluated quantitatively using Δlog K formulation. All the formation constants for the species were compared for Irving-Williams order of stability.

Determination of Protonation Constants of Viral Inhibitor, Aurintricarboxylic Acid in SDS and CTAB Micellar Media: A Potentiometric Study

Protonation constants of a viral inhibitor, aurintricarboxylic acid were determined using potentiometric method of data acquisition followed by chemometric modelling methods of analysis in the presence of two different kinds of micellar media, CTAB, a cationic micelle and SDS, an anionic micelle. MINIQUAD75 program was used for the determination of the plausible species and their corresponding formation constants at 303 ± 0.1 K and 0.01 M ionic strength. Five formation constants were identified corresponding to five ionizable hydrogens. Species concentration distribution diagrams were generated using Origin software. Best-fit chemical models were selected on the basis of statistical parameters like standard deviation (SD), U (sum of the squares of the residuals in mass balance equations) and chi-square test. It was found that the formation constants are lower in CTAB micellar medium while there is no significant change in the presence of SDS compared to aqueous medium.

Equilibrium Studies of Binary and Ternary Complexes Involving 2-Hydroxy-1- Naphthoic Acid and Amino Acids in Dioxane–Water Mixture

Complex formation equilibria of 2-hydroxy-1-naphthoic acid with Cu2+, Ni2+, Co2+ and Mn2+ and the ternary complexes involving Cu2+, 2-hydroxy-1-naphthoic acid and some amino acids containing different functional groups are investigated. Stoichiometry and stability constants for the complexes are estimated at 25 oC and 0.1M ionic strength in 50% dioxane-water mixture. The stability of the complexes follows the trend Cu2+ > Ni2+ > Co2+ > Mn2+, which is in agreement with the Irving–Williams order of the metal ions. Ternary complexes of amino acids are formed by a simultaneous mechanism. The stabilities of ternary complexes are quantitatively compared with their corresponding binary complexes. The concentration distribution diagrams of the complexes were evaluated.

Interaction between 2-pyrrolidine-1-hydroxymethane-1,1-diphosphonic acid and palladium(II) in aqueous solutions

The structure of the 2-pyrrolidine-l-hydroxymethane-l,l-diphosphonic acid (PyrHMDP, H4L) has been determined by X-ray crystallography. Formation of the complexes between K2[PdCl4] and PyrHMDP was studied by pH-potentiometry, UV–Vis spectrophotometry and 31P, 13C and 1H NMR spectroscopy in aqueous solutions containing CKCl = 0.15 mol L−1, which corresponds to the concentration of chloride ions in intercellular fluid. The formation constants were calculated for the protonated forms of the PyrHMDP and for the [PdHLCl2]3− and [PdLCl2]4− complexes. The equilibrium concentration distribution diagram for the complexes of different composition was drawn using the formation constants of the Pd chloro-aqua complexes and the chloride concentration. In equimolar palladium complexes with PyrHMDP the ligand was coordinated in a bidentate manner via the nitrogen atom of the pyrrolidine ring and the oxygen atom of the phosphonic group forming a six-membered chelate ring.

Antibacterial and molecular study of thiourea derivative ligand and its Dimethyltin(IV) complex with the superior of its Copper(II) complex as a hepatocellular antitumor drug

1-benzoyl(1,2,4-triazol-3-yl)thiourea [BTThU] ligand and its [dimethyltin(IV), Pd(II) and Cu(II)] complexes are synthesized. The complexes are formed in molar ratio Cu(BTThU)2, DMT(BTThU)2 and Pd(BTThU)2. The characterization has been done by using different physicochemical methods as elemental analyses, IR, 1H NMR DMSO‑d6 and molar conductance measurements. The stability constants of the formed species that produced from the interaction of [BTThU] with dimethyltin(IV) [DMT], dibutyltin(IV) [DBT] and diphenyltin(IV) [DPT] were determined potentiometrically using the non-linear least-square program MINIQUAD-75 in 50% ethanol–water mixture and 0.1 M ionic strength at 25 °C. Concentration distribution diagrams for these system were evaluated. The theoretical conformational structure analyses were performed using density functional theory for thiol and thione tautomeric forms of [BTThU] ligand and its complex at B3LYP functional with 6-311G basis set for ligand and LANL2DZ basis set for complex. The theoretical vibrational frequency values of the optimized structures were calculated. The charge distribution within the ligand and its dimethyltin(IV) complex was calculated using Mulliken population analysis of [MPA] and natural population analysis [NPA]. The biological activity of BTThU ligand and its dimethyltin(IV) complex were tested in vitro against some selected species of fungi and bacteria. The hepatocellular antitumor effect of all compounds was investigated.

Spectrophotometric-chemometrics study of the effect of solvent composition and temperature on the spectral shape and shift of copper and nickel phthalocyanines in different aqueous-nonaqueous mixed solvents.

Phthalocyanines (Pcs) are green-blue colored aromatic macrocyclic compounds used extensively in the dyeing industry. The assembly phenomenon for dye molecules is directly traceable by most of the spectroscopic methods. In this investigation, the monomer-dimer equilibria of copper and nickel phthalocyanines tetra sulfonic acid tetrasodium salts (CuPcTS, NiPcTS) have been investigated by spectrophotometric and chemometrics methods in binary mixtures of H2O-DMSO and H2O-CH3CN. The dimerization constants, (KD), enthalpies and entropies of CuPcTS and NiPcTS have been calculated by studying the UV-Vis spectra at different concentrations of dyes (10-6 to 10-4molL) and in the temperature range 298-343 K and in some samples up to 353 K by multivariate curve resolution (mcr) methods. By increasing the temperature, the value ofKD decreases. The inverse temperature dependence of KD(van't Hoff equation) was used for determination of ΔH0 and ΔS0and following that ΔG0of the dimerization reactions. As a result, upon aggregation, an increase in the intensity of the new shoulder at (~600 nm) and the Q-band at (662-670 nm) and concomitant decrease of the dimer band at (630-624 nm) are observed for all of the samples in different solvents composition. Therefore, the H-dimer type of these pigments was notable, in studied binary solvents. The effect of the solvent composition, concentration dye, and temperature on the spectral responses, the exciton parameters and concentration distribution diagrams of the two pigments were studied and discussed. The density functional theory (DFT) calculations were done in the aqueous and gas phase that they were included the HOMO-LUMO energies and the simulated UV-Vis spectrum. These calculations were beneficial for studying the UV-Vis spectrum of it in the aqueous phase for checking experimental data.

Levaquin drug complexing property towards platinum and palladium metal ions: Thermodynamic studies in aqueous solutions

The experimental protonation and complex formation equilibrium constants of levaquin (LFX) with platinum(II) and palladium(II) metal ions have been investigated at 310.15K in water solutions at ionic strength of I=0.16mol·dm−3 NaNO3 using pH-potentiometric and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of LFX and the equilibrium constants of its binary complexes with the studied platinum(II) and palladium(II) metal ions in I=0.16mol·dm−3 NaNO3 water solutions were observed at different temperatures such as 298.15, 310.15, 318.15 and 328.15K. The theoretical calculations of overall protonation and stability constants of the metal ion-LFX complex species in aqueous solutions were predicted as the free energy change associated with the LFX protonation, and metal ion – LFX complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modeling. The determination of equilibrium constants were confirmed by the spectrophotometric method with the refinement by using the HypSpec program. The usage of the experimental potentiometry/spectrophotometry techniques and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (metal ions -LFX). Precisely, this theoretically predications could be useful to control the most real protonation constants of levaquin ligand in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different platinum(II) and palladium(II) metal ions towards LFX in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions - LFX complex species in solutions were estimated using HySS 2009 software.

Thermodynamic studies on metal ions – Ninhydrin – Glycine interactions in aqueous solutions

The experimental protonation and complex formation equilibrium constants of ligands (ninhydrin (NHN) and glycine (Gly)) with trivalent (iron(III), aluminium(III), and chromium (III)), divalent (copper(II), cobalt(II), nickel(II), strontium(II), manganese(II), and mercury(II)) and monovalent silver(I) metal ions have been investigated at 310.15 K in water solutions at ionic strength of 13.60 g·dm−3 NaNO3 using pH-potentiometric, UV–visible spectrophotometric, and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of NHN and the equilibrium constants of its binary complexes and ternary complexes with the studied metal ions in 13.60 g·dm−3 NaNO3 water solutions were observed at different temperatures such as (298.15, 310.15, 318.15 and 328.15) K. The theoretical calculations of overall protonation and stability constants of the metal ion-ninhydrin complex species in aqueous solutions were predicted as the free energy change associated with the ninhydrin protonation, and metal ion – ninhydrin – glycine complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modelling. The convention of the experimental Potentiometry/Spectrophotometry techniques and theoretical calculations provide a complete picture of the microscopic equilibria of the studied metal ions – ninhydrin – glycine systems. Precisely, this theoretical predication could be useful to control the most real protonation constants of ninhydrin and glycine ligands in which the binding sites change due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different metal ions towards ninhydrin and glycine in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions – ninhydrin – glycine complex species in solutions were estimated using HySS 2009 software.

Equilibrium and DFT studies of the bi- and mononuclear complexes of 4,4′-bipiperidine with Pd(2-(2-aminoethyl)-1-methylpyrrolidine)2+ and other biorelevant ligands

Optimized structure of coordinated glycinamide after peptide ionization ([Pd(AEMP)GlyA-H] + ) (H atoms are omitted for clarity) by DFT method using B3LYP/LANL2DZ functional. • The manuscript deals with speciation studies of mono and binuclear Pd(II) complexes with bio-relevant ligands. • The binuclear complexes are the third generation of antitumor complexes. Some of them are now under clinical tests. • The formation constants of the complexes formed in solution phase are determined. • Concentration distribution diagrams of the complexes were evaluated to indicate the predominated species in the biological fluids. • Molecular geometry of the complexes were investigated.

Mathematical Simulation of Multiphase Reactive Chromatography Process

In order to carry out theoretical analysis and digital simulation for multiphase reactive chromatography, the multiphase and multicomponent reaction chromatography equations are established considering the coupling effect between chemical reaction and multiphase chromatography. The multiphase - multicomponent reaction chromatography equation is solved by using the second order TVD numerical method. The reversible chromatographic process of two-phase four-component is discussed using the second order form with flux limiting factor. The fluctuation image with initial and boundary conditions is analyzed, and the formation mechanism of the wave image is discussed. The results show that after the fluid enters the chromatography, the shock wave will be generated due to the difference of the adsorption property of the component, thus affecting the concentration distribution diagram of the chromatogram.

Nicotine – Metal ion interactions in solutions: Potentiometric, cyclic voltammetry investigations and quantum chemical calculations

The experimental protonation and complex formation equilibrium constants of nicotine (NIC) with trivalent (iron (III), and chromium (III)) and divalent (copper (II), and nickel (II)) metal ions have been investigated at 310.15 oK in water solutions at ionic strength of 13.60g·dm−3 NaNO3 using pH-potentiometric and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of NIC and the equilibrium constants of its binary complexes with the studied metal ions in 13.60g·dm−3 NaNO3 water solutions were observed at different temperatures such as (298.15, 310.15, 318.15 and 328.15) K. The theoretical calculations of overall protonation and stability constants of the metal ion-nicotine complex species in aqueous solutions were predicted as the Gibbs energy change associated with the nicotine protonation, and metal ion – nicotine complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modeling. The usage of the experimental potentiometry/spectrophotometry techniques and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (metal ions -nicotinate). Precisely, this theoretically predications could be useful to control the most real protonation constants of nicotine ligand in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different metal ions towards nicotine in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions - nicotine complex species in solutions were estimated using HySS 2009 software.

Synthesis, characterization, speciation and biological studies on metal chelates of 1-benzoyl(1,2,4-triazol-3-yl)thiourea

Proton-ligand association constants of 1-benzoyl(1,2,4-triazol-3-yl)thiourea (BTTU) and its complex formation constants with some bivalent metal ions Ni(II), Co(II), Mn(II), Zn(II), and Cu(II), have been determined potentiometrically in 50% EtOH–H2O and 0.1 M NaNO3. The complexes formed in solution have a stoichiometry of 1:1 and 1:2 [M:L], where M represents the metal ion and L the BTTU ligand. The corresponding thermodynamic parameters are derived and discussed. The complexes are stabilized by enthalpy changes and the results suggest that complexation is an enthalpy-driven process. The effects of metal ion, ionic radius, electronegativity, and nature of ligand on the formation constants are discussed. The formation constants of the complexes with 3d transition metals follow the order Mn2+ < Co2+ < Ni2+ < Cu2+ > Zn2+. The metal complexes were synthesized and characterized by elemental analyses, conductance, IR, 1H NMR, and magnetic measurements. The low magnetic moment of 0.11 BM for the Cu(II) complex is suggestive of dimerization through Cu–Cu interaction. The concentration distribution diagrams of the complexes were evaluated. The ligands and their metal complexes have been screened in vitro against some bacteria and fungi.

Gibbs energies of protonation and complexation of platinum and vanadate metal ions with naringenin and phenolic acids: Theoretical calculations associated with experimental values

The Experimental thermodynamic equilibrium (pKa values) and stability (logβ) constants of vanadium and platinum binary and mixed ligand complexes involving naringenin, ferulic acid, p-coumaric acid, caffeic acid, vanillic acid, sinapic acid, and gallic acid were determined at 310.15K in 0.16mol·dm−3 KCl aqueous solutions using pH-potentiometric technique and by means of two estimation models (HYPERQUAD 2008 and Bjerrum–Calvin). The theoretical calculations of overall protonation and stability constants of the metal complex species in solution were predicted as the free energy change associated with the ligand protonation, and metal ion–ligand complex formation equilibria (species solvation/de-solvation) using ab initio and density function theory (DFT) calculations. The usage of the experimental potentiometry technique and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (vanadium/platinum–naringenin–phenolic acid). Specifically, this theoretically DFT predications would be useful to determine the most real protonation constants of the studied bioligands in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of vanadium and platinum towards naringenin, ferulic acid, p-coumaric acid, caffeic acid, vanillic acid, sinapic acid, and gallic acid in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ion complex species in solution was estimated using HySS 2009 software.

Synthesis, X-ray structure, DFT and thermodynamic studies of mono- and binuclear palladium(II) complexes involving 1,4-bis(2-hydroxyethyl)piperazine, bio-relevant ligands and 4,4′-bipiperidine

[Pd(BHEP)Cl2] (BHEp = 1,4-bis(2-hydroxyethyl)piperazine) was synthesized and characterized. The palladium center has a typical square-planar geometry with a tetrahedral distortion. The alcohol groups of the ligand do not participate in binding to Pd(II). The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program and compared with experimental results. The stoichiometry and stability constants of the complexes formed between [Pd(BHEP)(H2O)2]2+ and some selected amino acids, peptides, and DNA constituents were investigated at 25 °C and 0.1 M ionic strength. The binuclear complex [(H2O)(BHEP)Pd(Bip)Pd(BHEP)(H2O)]4+ was detected, where Bip = 4,4′-bipiperidine. Inosine, uracil, and thymine interact with the binuclear complex via substitution of both coordinated water molecules. The potentiometric results were complimented by spectroscopic measurements. The concentration distribution diagrams of the various species formed were evaluated.

Synthesis, DNA binding and complex formation reactions of 3-amino-5,6-dimethyl-1,2,4-triazine with Pd(II) and some selected biorelevant ligands

With the purpose of studying the binding behavior of Pd(II) complexes with DNA as the main biological target, and their ability to penetrate reasonably into tumour cells and destroy their replication ability, Pd(ADT)Cl2 complex was synthesized and characterized, where ADT is 3-amino-5,6-dimethyl-1,2,4-triazine. Stoichiometry and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(ADT)(H2O)2]2+ were investigated at 25°C and at constant 0.1moldm−3 ionic strength. The concentration distribution diagrams of the various species formed are evaluated. Further investigation of the binding properties of the diaqua complex [Pd(ADT)(H2O)2]2+ with calf thymus DNA (CT-DNA) was investigated by UV–vis spectroscopy. The intrinsic binding constants (Kb) calculated from UV–vis absorption studies was calculated to be 2.00×103moldm−3. The calculated (Kb) value was found to be of lower magnitude than that of the classical intercalator EB (Ethidium bromide) (Kb=1.23(±0.07)×105moldm−3) suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA. Thermal denaturation has been systematically studied by spectrophotometric method and the calculated ΔTm was nearly 5°C, supporting the electrostatic and/or groove binding mode for the interaction between the complex and CT-DNA

Erratum to: DNA Binding and Equilibrium Investigation of the Interaction of a Model Pd(II) Complex with Some Selected Biorelevant Ligands

The Pd(DAP)Cl2 complex, where DAP is 2,6-diaminopyridine, was synthesized and characterized. The stoichiometries and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(DAP)(H2O)2]2+ were investigated at 25 °C and at constant 0.1 mol·dm−3 ionic strength. The concentration distribution diagrams of the various species formed were evaluated. A further investigation of the binding properties of the diaqua complex [Pd(DAP)(H2O)2]2+ with calf thymus DNA (CT-DNA) was investigated by UV–Vis spectroscopy. The intrinsic binding constants (K b) calculated from UV–Vis absorption studies is 1.04 × 103 mol·dm−3. The calculated (K b) value was found to be of lower magnitude than that of the classical intercalator EB (ethidium bromide) (K b = 1.23 (±0.07) × 105 mol·dm−3), suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA.

Reactions of Cr3+ with aspartic acid within a wide pH range

Formation of the metal complexes of aspartic acid (Asp) with the chromium metal ion (Cr3+) in solutions using potentiometric titrations is presented within a wide pH range (∼3.5 to ∼10.5) at 25°C and I=0.10 M NaNO3. Concentration distribution diagrams revealed that the main complex formed within this pH range is the bis Cr 3+ complex. Literature stability constant values for the Cr–Asp complexes were used to construct concentration distribution diagrams. Complexes taken into consideration were the simple one-to-one complex, the bis-complex, and the bis-mono-protonated complex, namely, Cr–Asp, Cr(Asp)2, and Cr(Asp)2H. The corresponding Log β values of these complexes were 12.46, 21.86, and 24.30, respectively. UV–Vis spectra demonstrate Cr 3+–Asp binding. The UV–Vis spectra were collected from a system that reached a high level of equilibrium state (50 days’ equilibrium time).

Palladium(II) Complexes Containing Mixed Nitrogen-Sulphur Donor Ligands: Interaction of [Pd(Methionine Methyl Ester)(H2O)2](2+) with Biorelevant Ligands.

Pd(MME)Cl2 complex (MME = methionine methyl ester) was synthesised and characterized by physicochemical measurements. The reaction of [Pd(MME)(H2O)2]2+ with amino acids, peptides, or dicarboxylic acids was investigated at 25°C and 0.1 M ionic strength. Amino acids and dicarboxylic acids form 1 : 1 complexes. Peptides form both 1 : 1 complexes and the corresponding deprotonated amide species. The stability of the complexes formed was determined and the binding centres of the ligands were assigned. Effect of solvent on the stability constant of Pd(MME)-CBDCA complex, taken as a representative example, shows that the complex is more favoured in a medium of low dielectric constant. The concentration distribution diagrams of the complexes were evaluated.

Thermodynamic investigation of the binary and ternary complexes involving 1-aminocyclopropane carboxylic acid with reference to plant hormone

Abstract Complex formation equilibria of 1-aminocyclopropane carboxylic acid (ACC) and 3,3-bis(1-methylimidazol-2-yl) propionic acid (BIMP) with metal ions Cu2+, Ni2+, Co2+, Zn2+, Mn2+ and Fe2+ were investigated. ACC forms 1:1 and 1:2 complexes in addition to the hydrolysed form of the 1:1 complex, except in the case of Mn2+ and Fe2+, where the hydrolysed complex is not formed. BIMP forms 1:1 and 1:2 complexes in addition to the hydrolsed form of the 1:1 complex in the case of Mn2+ and Cu2+, however the hydrolysed complex is not detected for Ni2+, Co2+, Zn2+ and Fe2+. The concentration distribution diagrams of the complexes were determined. The Fe2+-complex with BIMP is exothermic and the thermodynamic parameters were calculated. The effect of organic solvent on the acid dissociation constants of 1-aminocyclopropane carboxylic acid (ACC) and 3,3-bis(1-methylimidazol-2-yl) propionic acid (BIMP) and the formation constants of Fe2+ complexes were investigated. Fe2+ forms a mixed-ligand complex with ACC and BIMP with stoichiometric coefficients 1:1:1. The formation constant was determined. The ternary complex is enhanced by back donation from the negatively charged 1-aminocyclopropane carboxylate to the π-system of BIMP. From the concentration distribution diagram, the ternary complex prevails in the physiological pH range.