The determination of the stability constants of mixed ligand complexes of adenine and amino acids with Ni(II) by potentiometric titration method

A potentiometric titration technique has been used to determine the stability constants for the various complexes of Ni(II) with adenine (A) as primary ligand and selected amino acids (L) as secondary ligands. Ternary complexes of amino acids are formed in a stepwise mechanism, whereby (A) binds to Ni(II), followed by interaction with ligand (L), whereas thiol-containing ligands form ternary complexes through a simultaneous mechanism. The formation constants of the complexes were determined at 25 °C and ionic strength 0.1 M NaNO₃. The relative stabilities of the ternary complexes are compared with those of the corresponding binary complexes in terms of Δlog K values. The concentration distribution of the complexes are evaluated.     

Potentiometric studies on mixed-ligand complexes of cobalt(II) and nickel(II) with amino acids as primary ligands and imidazole as secondary ligand

Summary The formation constants of mixed-ligand complexes of cobalt(II) and nickel(II) with glycine, DL--alanine and DL-valine as primary ligands and imidazole as secondary ligand have been determined potentiometrically under physiological-like conditions (T=37°C and I=0.15 M KNO₃). The proton association constants of the free ligands and the stability constants for binary systems involving the amino acids and imidazole were also determined under identical conditions, and the experimental pH-titration data were analysed using the computer SUPERQUAD program. The relative stability of the ternary complex as compared to that of the corresponding binary complexes has been quantitatively expressed in terms of log K and log X values.     

pH-Metric studies on the binary and ternary complexes of oxovanadium(IV)

The interaction of oxovanadium(IV) with some hydroxy acids, salicylic (SA), 5-sulphosalicylic (SSA) and 8-hydroxyquinoline-5-sulphonic (HQSA) acids, has been studied potentiometrically. Further, pH-metric studies of the ternary systems, VO²⁺?HQSA-dicarboxylic or hydroxy acids (where dicarboxylic acids = phthalic and maleic acids and hydroxy acids =SA andSSA) have been carried out and the formation of 1∶1∶1 mixed complexes inferred from the potentiometric curves. The equilibrium, chelate formation and hydrolysis constants have been calculated in the case of binary systems. The ternary complexes have been found to be more stable as indicated by their formation constants.     

Solution Equilibria and Thermodynamic Studies of Complexation of Divalent Transition Metal Ions with Some Triazoles and Biologically Important Aliphatic Dicarboxylic Acids in Aqueous Media

The formation of binary and ternary complexes of the divalent transition metal ions Cu^II, Ni^II, Zn^II, and Co^II with some triazoles [1,2,4-triazole (TRZ), 3-mercapto-1,2,4-triazole, and 3-amino-1,2,4-triazole], and the biologically important aliphatic dicarboxylic acids adipic, succinic, malic, malonic, maleic, tartaric, and oxalic acid, was investigated in aqueous solutions using the potentiometric technique at 25 °C and I = 0.10 mol·dm^?3 NaNO₃. The formation of 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes was inferred from the corresponding titration curves. The formation of ternary complexes occurs in a stepwise manner with the carboxylic acids acting as primary ligands. The ionization constants (pK _a) of the investigated ligands were redetermined and used for determining the stability constants of the binary and ternary complexes formed in solution. The order of stability of the ternary complexes was investigated in terms of the nature of the triazole, carboxylic acid and metal ion used. The ?log₁₀ K values, percent relative stabilization, and log₁₀ X for the ternary complexes have been evaluated and discussed. The concentration distributions of the various species formed in solution were evaluated. The ionization constants of TRZ and malic acid and stability constants of their binary and ternary complexes with Cu^II, Ni^II, and Co^II metal ions were studied at four different temperatures (15, 25, 35, and 45 °C) and the corresponding thermodynamic parameters have been evaluated and discussed. The complexation behavior of ternary complexes was ascertained using conductivity measurements. In addition, the formation of ternary complexes in solution has been confirmed by using UV–visible spectrophotometry.     

Complexes of vitamin B6—XVIII. Ternary and quaternary complexes involving pyridoxamine,glycylglycine and imidazole and some bivalent metal ions

The formation constants of ternary and quaternary complexes containing the ligands pyridoxamine, glycylglycine and imidazole with Co(II), Ni(II), Zn(II) and Cd(II) were determined by pH-metric titration in 0.15 M NaNO₃ at 37°C using the MINIQUAD-75 program. It has been shown that the logarithms of the ternary formation constants are linear increasing functions of the sum of the logarithms of the first protonation constants of the ligands, but the log K^I (MLH_m+ML′H_m⇌^KIMLL′H_s) are linear decreasing functions. It has been shown that deprotonation of the peptidic group is prohibited in ternary and quaternary metal complexes. It is also found that the imidazole moiety favourably ligates the ternary complexes rather than the bare metal ions.     

Thermodynamique des complexes metalliques ternaires des amino acides: Etude du systeme Ni(II)—Glycine—DL-α-alanine

Standard enthalpies and entropies of formation for binary and ternary Ni(II) complexes with glycine and DL-α-alanine were calorimetrically determined at 25°C in aqueous solution (I = 1 M NaClO₄). The evolution of these values from binary to ternary complexes is discussed on the basis of the stabilization characterizing the stability constants of the ternary species which have been previously calculated under the same experimental conditions.     

Stability constants of mixed ligand complexes of lead(II) with 1-(aminomethyl) cyclohexane acetic acid and α-amino acids

Formation of binary and ternary complexes of lead(II) ions with 1-(aminomethyl) cyclohexane acetic acid and some biologically important α-amino acids, such as glycine, l-alanine, l-valine, l-leucine, l-isoleucine, l-phenylalanine and l-proline was investigated using the potentiometric technique at 32 °C. The properties of mixed ligands were investigated and discussed. The acidity constants of the ligands and their stability constants were determined in 50% (v/v) DMSO-water medium under experimental conditions. The ternary complex formation was found to occur in a stepwise manner. The stability of ternary complexes was investigated and compared with that of the corresponding binary complex in terms of the parameters, Δ log K and log X. The concentration distribution of various species formed in the mixed ligand systems was evaluated.     

Potentiometric studies on mixed-ligand complexes of copper(II) and zinc(II) with some amino acids (glycine,DL-α-alanine and DL-valine) as primary ligands and imidazole as a secondary ligand

Summary Mixed-ligand complexes of Cu^II and Zn^II with glycine(GL), DL--alanine (AL) and DL-valine (VL) as primary ligands and imidazole (IM) as secondary ligand have been studied potentiometrically under physiological conditions (t=37° C and I=0.15 M KNO₃). The experimental pH-titration data were analysed with aid of the SUPERQUAD computer program in order to evaluate formation constants of binary and ternary systems involying amino acids (AA) and IM. The relative stability of each of the ternary complexes was compared with that of corresponding binary complexes in terms of log K and log X values.     

The effect of ligand donor atoms on ternary complex stability

Formation constants of mixed ligand complexes of Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺,with cyadine-5′-monophosphoric acid (CMP) and various primary ligands such as 1,10-phenanthroline(phen), glycylglycine(glygly) and salicylic acid (sal) have been determined in aqueous solution at 35°C and 0.1 M (KNO₃) by potentiomeric measurements. The acid dissociation constants of all the above mentioned ligands together with their 1 : 1 binary metal complex formation constants were also measured at 35°C. In general all the 1 : 1 binary complexes follow the Irving-Williams order of stability. Further the binary metal complexes of primary ligands are more stable than their ternary complexes with CMP. For ternary complexes, Δ(log K) values seem to change from positive to highly negative as the coordinating atoms of the primary ligands were varied from N,N to N,O^? to O^?O^?. The higher stability of ternary complexes involving phen is due to its Π-bonding interaction with the above metal ions and the relative decrease in the stability of other ternary systems is due to the coulombic repulsion of donor oxygen atoms of primary and secondary ligands. Thus for ternary complexes the stabilities follow a decreasing order of M-phen-CMP > M-glygly-CMP > M-sal-CMP.     

Nickel(II) derivatives of N-benzyliminodiacetate(2−) ligands,with and without imidazole: Synthesis,crystal structure and properties

In an attempt to prepare binary and ternary compounds, we have obtained two molecular complexes [Ni(MEBIDA or MOBIDA)(H₂O)₃]·nH₂O (n = 0 or 1) and two iso-type salts [Ni(Him)₆][Ni(MEBIDA or MOBIDA)₂]·4H₂O [MEBIDA = N-(p-methylbenzyl)iminodiacetate(2−) and MOBIDA = N-(p-methoxybenzyl)iminodiacetate(2−) ligands, Him = imidazole]. Our results are discussed with regard to related copper(II) and nickel(II) compounds. The reasons for which these chelating ligands produce nickel(II) salts instead of ternary compounds remain unclear since other iminodiacetate-like ligands give true ternary Ni(II) compounds with imidazole and other N-heterocyclic ligands.     

Thermo acoustic and spectral investigations of charge transfer interaction between aromatic amine and ketones

Ultrasonic velocity (u), density (ρ) and coefficient of viscosity (η) were measured for ternary mixtures containing aniline (ANI) as common component and acetophenone (ACP), 4-chloroactophenone (ClACP) and 4-methylacetophenone (MACP) as other components in n-hexane medium in the concentration range 0.025-0.2 M. The measurements were made at four different temperatures, namely, 293, 298, 303 and 308 K and at atmospheric pressure. The experimental results have been used to calculate various acoustical parameters and excess parameters. The trend in these parameters with concentration establishes that (i) strong intermolecular interactions exist in these mixtures and (ii) formation of charge transfer complexes through hydrogen bonding between primary amine and aromatic ketones. The formation of complexes has also been confirmed by optical spectroscopy at 303 K. The formation constants of the charge transfer complexes determined using Benesi-Hildebrand equation (spectroscopic method) are comparable with those obtained using Kannappan equation (ultrasonic method). It is observed that the stability of the complexes is influenced by the structure of the component molecules. In order to assess the thermodynamic stability of the complexes, free energy of formation (ΔG), enthalpy of formation (ΔH) and entropy changes (ΔS) are computed.     

Complexation Equilibria and Determination of Stability Constants of Binary and Ternary Nickel(II) Complexes with Amino Acids (Glycine, α-Alanine, β-Alanine and Proline) and Dipicolinic Acid as Ligands

In this paper we report the formation of binary and ternary nickel(II) complexes involving dipicolinic acid (H₂Dipic) as the primary ligand and some selected amino acids {glycine (HGly), ?-alanine (H?-Ala), ??-alanine (H??-Ala) and proline (HPro)} as secondary ligands. These complexes were studied at 25?°C by means of electromotive force measurements, emf(H), using 1.0?mol?dm^?3 NaCl as the ionic medium. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the nickel(II) cation and the acid/base reactions of the ligands whose equilibrium constants were kept fixed during the analysis. In the study of the binary nickel(II)?Camino acids systems the species [NiL]⁺, NiL₂ and [NiL₃]^? were observed, and in the case of the ternary nickel(II)?Cdipicolinic acid?Camino acids systems the complexes Ni(Dipic)HL, [Ni(Dipic)L] ^? and [Ni(Dipic)L(OH)]^2? were observed. The respective stability constants were determined, and the species distribution diagrams, as a function of pH, are briefly discussed.     

A spectrofluorimetric study of binary fluorophore-cyclodextrin complexes used as chiral selectors

Six binary complexes between three fluorophores (pyrene, xanthone and anthraquinone) and β-cyclodextrin (β-CD) or heptakis-(6-amino)-(6-deoxy)-β-cyclodextrin (am-β-CD) were tested at two pH values (8.0 and 9.0) as chiral selectors for three α-amino acids chosen as model. The conditional constant (β_2T) values for ternary complexes (fluorophore-CD-amino acid), determined by means of fluorescence spectroscopy, showed that the binary complexes are suitable receptors for chiral recognition. The effect of α-amino acids on stability and stoichiometric ratio of the binary complexes has also been studied. The binary complexes were in most cases stabilized by adding the ternary agent. The trend of stoichiometric ratios found is supported by variations in fluorescence spectra. Those relative to pyrene (Py) show little changes going from binary to ternary complexes, while those recorded in the presence of xanthone (Xan) give the most significant variations underlining a deep reorganization of guest. Anthraquinone (Aq) shows an intermediate behavior.     

Equilibrium studies of the binary and ternary complexes involving tetracycline and amino acid or DNA constituents

The acid-base equilibria of tetracycline and its copper(II) complex formation equilibria are investigated in dioxane-water mixtures. The ternary complexes of copper(II) with tetracycline as primary ligand and amino acid or DNA constituent as secondary ligand are studied in 50% dioxane-water solution. The formation constants of the ternary and binary complexes with amino acids or DNA constituents are determined. The concentration distribution of the various complex species are evaluated. Probable mode of chelation with tetracycline and DNA constituents is discussed.     

Studies on Complexation of Resorcinol with Some Divalent Transition Metal Ions and Aliphatic Dicarboxylic Acids in Aqueous Media

The binary and ternary complexes of Cu²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions with resorcinol (R) as primary ligand and some biologically important aliphatic dicarboxylic acids (adipic, succinic, malic, malonic, maleic, tartaric and oxalic acids) as secondary ligands were studied in aqueous solution at 25 °C and I=0.1 mol⋅dm⁻³ NaNO₃ using the potentiometric technique. The formation of different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes is inferred from the corresponding potentiometric pH-titration curves. The ternary complex formation was found to take place in a stepwise manner. The protonation constants of the ligands were determined and used for determining the stability constants of the different complexes formed in aqueous solutions. The lower stability of the 1:2 binary complexes compared to the corresponding 1:1 systems of all ligands studied were in accordance with statistical considerations. The order of stability of the complexes formed in solution was investigated in terms of the nature of the resorcinol, carboxylic acid, and metal ion used. The values of Δlog ₁₀ K, percentage of relative stabilization (% R.S.), and log ₁₀ X for mixed-ligand complexes studied have been evaluated and discussed. The concentration distribution of the various species formed in solution was evaluated. The mode of chelation of the ternary complexes was ascertained by conductivity measurements.     

Stabilities of the Ternary Complexes of Copper(II) with Substituted 1,10-Phenanthrolines and Some Amino Acids in Aqueous Solution

In this study the binary and ternary complexes of copper(II) with substituted 1,10-phenanthrolines [s-phen: 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (dmphen) and 5-nitro-1,10-phenanthroline (nphen)] and l-amino acids [aa: l-phenylalanine (phe), l-tyrosine (tyr) and l-tryptophan (trp)] have been investigated using potentiometric methods in 0.1 mol·L^?1 KCl aqueous ionic media at 298.2 K. The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Cu(II) with the ligands were calculated from the potentiometric data using the “BEST” software package. It was inferred that the aromatic 1,10-phenanthrolines act as a primary ligand in the ternary complexes, while the oxygen and nitrogen donor-containing amino acids are secondary ligands. The observed values of Δlog₁₀ K indicate that the ternary complexes are more stable than the binary ones, suggesting no interaction takes place between the ligands in the ternary complexes. The magnitudes of the measured stability constants of all of the ternary complexes are in the order [Cu(s-phen)(trp)]⁺ > [Cu(s-phen)(tyr)]⁺ > [Cu(s-phen)(phe)]⁺, which is identical to the sequence found for the binary complexes of Cu(II) with the amino acids. When the substituted 1,10-phenanthroline is changed, the stability constants of the ternary complexes decrease in the following order: [Cu(dmphen)(aa)]⁺ > [Cu(phen)(aa)]⁺ > [Cu(nphen)(aa)]⁺.     

Equilibrium and spectroscopic studies of ternary cadmium(II) and mercury(II) complexes with CMP and triamines

Formation of ternary Cd(II) and Hg(II) complexes with cytidine 5′-monophosphate (CMP) and triamines has been studied. Complexes M(CMP)(H _x PA) and M(CMP)(PA) (M?=?Cd, Hg; PA?=?polyamine) were detected and overall stability constants and equilibrium constants for their formation determined. The mode of coordination in the complexes has been proposed on the basis of the equilibrium and ¹³C, ³¹P NMR and IR studies. In the Hg(II) systems, metalation involves the donor endocyclic N(3) atom, the CMP phosphate group and nitrogen donor atoms of PA. Relative to the Hg/CMP binary systems, the presence of a polyamine in ternary systems does not change the metal–nucleotide mode of coordination. In ternary systems including Hg(II) ions, the occurrence of noncovalent interactions has not been detected. Cd(II) ions form molecular complexes as well as protonated species. Introduction of a polyamine to the Cd/CMP system changes the coordination mode of the nucleotide. The phosphate group of CMP is inactive in binary complexes (metalation by the N(3) atom) but is involved in coordination in heteroligand species. In contrast to other polyamines studied, in the system including 1,7-diamino-4-azaheptane (3,3-tri), the phosphate group of CMP in Cd(CMP)(H3,3-tri) does not participate in metalation but is engaged in intramolecular noncovalent interactions that stabilize the complex.     

The effect of boronic acid-positioning in an optical glucose-sensing ensemble

The quenching of the anionic dye 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine) with three different boronic acid-substituted benzyl viologens was determined, and the fluorescence signal modulation obtained upon addition of glucose to the dye/quencher system was also studied. The benzyl viologen that contains boronic acids in the ortho-position (o-BBV) was found to display unique behavior, which can be rationalized by a charge neutralization mechanism facilitated by an intramolecular interaction between sp³ boronate and the quaternary nitrogen of the viologen. Potentiometric titration and ¹¹B NMR spectroscopy were used to generate pH profiles for the boronic acids, which provide additional evidence for the proposed mechanism.     

Studies of new phosphothreonine complexes formed in binary and ternary systems including biogenic amines and copper(II)

Binary and ternary systems of copper(II) with O-phospho-L-threonine (Thr-P) and biogenic amines (putrescine or spermidine or spermine) have been investigated. The studies were performed in aqueous solution. Overall stability constants of the complexes were determined by pH-metric study and the coordination sites were identified by ³¹P NMR, visible and electron paramagnetic resonance spectroscopies. Results of the equilibrium and spectral studies have shown that in the phosphothreonine binary system Cu(HThr-P), Cu(Thr-P) and Cu(Thr-P)(OH) are formed. In the binary system at low pH, only the phosphate group is involved in coordination but at higher pH, the efficiency of ?PO₄ ^2? is low and the amine and carboxylate are the main sites of coordination. Formation of complexes was established in ternary systems with all bioamines studied. In these systems the reaction centers of phosphothreonine are the same as in the binary systems: phosphate, carboxylate and amine. Additionally, amine groups from the polyamines (PAs) are involved in the complex formation. Besides the heteroligand complexes with intermolecular interactions, also molecular complexes with the protonated bioamine in the outer coordination sphere appeared. In these molecular species, PA was involved in non-covalent interactions with the anchoring phospho-threonine complex.     

Binary and ternary complexes of Cd(II) involving triethylenetetramine and selected amino acids and DNA units

The formation equilibria of the binary complex of cadmium(II) with triethylenetetramine (Trien) and of ternary complexes Cd(Trien)L, where L refers to amino acids, DNA constituents and related compounds have been investigated. Cd(II) was found to form a highly stable complex with Trien. The acid-base equilibria of Cd(Trien)²⁺ were characterized. Ternary complexes of amino acids and DNA constituents are formed through stepwise mechanism, whereby Trien binds to Cd(II), followed by interaction with ligand (L), whereas thiol-containing ligands form ternary complexes through a simultaneous mechanism. The formation constants of the complexes were determined at 25 °C and , = 0.1M NaNO₃. The participation of different ligand functional groups in the complex-formation was examined.