Equilibrium Studies of Binary and Ternary Complexes Involving Tricine and Some Selected a-Amino Acids

The formation equilibria for the binary complexes of Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Mn^II, Pb^II, Th^IV, UO₂^II, and Ce^III with tricine and for the ternary complexes involving some -amino acids (glycine, -alanine, proline, serine, asparagine, and aspartic acid) were investigated using pH-metric technique. The formation of binary and ternary complexes was inferred from the pH-metric titration curves. It was deduced that tricine acts as a primary ligand in the ternary complexes involving the monocarboxylic amino acids (glycine, -alanine, proline, serine, and asparagine), whereas it behaves as a secondary ligand in the ternary systems containing the dicarboxylic aspartic acid. The ternary complex formation was found to take place in a stepwise manner. The stability constants of the complexes formed in aqueous solutions were determined potentiometrically under the experimental conditions (t=25°C, I=0.1moldm^–3 NaNO₃). The order of stability of the ternary complexes in terms of the nature of the amino acids is investigated and discussed. The values of log K for the ternary complexes have been evaluated and discussed. Evaluation of the effects of ionic strength and temperature of the medium on the stability of the ternary system M^II-tricine--alanine (M^II=Co^II, Ni^II, and Cu^II) has been studied. The thermodynamic parameters were calculated and discussed.     

Equilibrium Studies of Binary and Ternary Complexes Involving Tricine and Some Selected α-Amino Acids

Summary. The formation equilibria for the binary complexes of Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Mn^II, Pb^II, Th^IV, UO₂^II, and Ce^III with tricine and for the ternary complexes involving some -amino acids (glycine, -alanine, proline, serine, asparagine, and aspartic acid) were investigated using pH-metric technique. The formation of binary and ternary complexes was inferred from the pH-metric titration curves. It was deduced that tricine acts as a primary ligand in the ternary complexes involving the monocarboxylic amino acids (glycine, -alanine, proline, serine, and asparagine), whereas it behaves as a secondary ligand in the ternary systems containing the dicarboxylic aspartic acid. The ternary complex formation was found to take place in a stepwise manner. The stability constants of the complexes formed in aqueous solutions were determined potentiometrically under the experimental conditions (t=25°C, I=0.1moldm^–3 NaNO₃). The order of stability of the ternary complexes in terms of the nature of the amino acids is investigated and discussed. The values of log K for the ternary complexes have been evaluated and discussed. Evaluation of the effects of ionic strength and temperature of the medium on the stability of the ternary system M^II-tricine--alanine (M^II=Co^II, Ni^II, and Cu^II) has been studied. The thermodynamic parameters were calculated and discussed.     

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.     

Mixed Ligand Complex Formation Reactions and Equilibrium Studies of Cu(II) with Bidentate Heterocyclic Alcohol (N,O) and Some Bio-Relevant Ligands

The formation equilibria of copper(II) complexes and the ternary complexes Cu(HMI)L (HMI=4-Hydroxymethyl-imidazole, L=amino acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results showed the formation of Cu(HMI)L and Cu(HMI,H₋₁)(L) complexes. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog ₁₀ K and log ₁₀ X. The effect of the side chains of amino acid ligands (Δ_R) on complex formation was discussed. The concentration distributions of various species formed in solution were also evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants are investigated. The effects of dioxane as a solvent, on the protonation constant of HMI and the formation constants of Cu^II–HMI complexes, were discussed.     

Complexes of vitamin B6 XII : Mixed ligand complexes of some divalent metal ions with pyridoxamine and histidine

Potentiometric pH titrations (I = 0.15 M NaNO₃; 37°C) have been employed to study the various complex equlibria in the systems involving pyridoxamine and histidine with Co(II), Ni(II), Cu(II), and Zn(II). The stoichiometry and formation constants of different species have been determined with the aid of MINIQUAD-75. The complexes obtained were mostly protonated and positively charged. The formation of the ternary species is discussed in terms of the binary species. They were also correlated with the quaternary species involving pyridoxamine, glycine, and imidazole. Spectral analysis of the complex solutions of different compositions are also reported. The relevance of these ternary complex equilibria to some biological functions is discussed.     

Potentiometric Studies on Binary and Ternary Complexes of Di- and Trivalent Metal Ions Involving Some Hydroxamic Acids, Amino Acids, and Nucleic Acid Components

Summary. Formation of binary and ternary complexes of Cu^II, Co^II, Ni^II, Zn^II, Fe^III, Al^III, and Cr^III metal ions with some selected aliphatic and aromatic hydroxamic acids and some biologically important amino acids or nucleic acid components was investigated using the potentiometric technique at 25°C and I=0.10moldm^–3 NaNO₃. The acid-base properties of the ligands were investigated and discussed. The acidity constants of the ligands were determined and used for determining the stability constants of the complexes formed in aqueous medium under the experimental conditions. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The order of stability of the ternary complexes in terms of the nature of hydroxamic acid, amino acid, nucleic acid component and metal ions was investigated and discussed as well as the values of log K and log X for the ternary systems. The concentration distribution of the various complex species in solution was evaluated. In addition, evaluation of the effect of temperature of the medium on the stability of the ternary system M^III – benzohydroxamic acid – L-histidine or adenine (M^III=Fe^III, Al^III, and Cr^III) has been studied. The thermodynamic parameters were calculated and discussed.     

Chelated complexes of cadmium(II), cobalt(II), copper(II), mercury(II), nickel(II), uranyl(II) and zinc(II) with benzil bis(4-phenylthiosemicarbazone)

Summary Complexes of Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Hg^II and UO ₂ ^II with benzil bis(4-phenylthiosemicarbazone), H₂BPT, have been synthesized and their structures assigned based on elemental analysis, molar conductivity, magnetic susceptibility and spectroscopic measurements. The i.r. spectra suggest that the ligand behaves as a binegative quadridentate (NSSN) (Co^II, Cu^II, Hg^II and UO ₂ ^II complexes) or as a binegative quadridentate-neutral bidentate chelating agent (Ni^II, Zn^II and Cd^II complexes). Octahedral structures for the Co^II and Ni^II complexes and square-planar structure for the Cu^II complex are suggested on the basis of magnetic and spectral evidence. The crystal field parameters (Dq, B and _B) for the Co^II complex are calculated and agree fairly well with the values reported for known octahedral complexes. The ligand can be used for the microdetermination of Ni^II ions of concentration in the 0.4–6×10^–4 mol l^–1 range and the apparent formation constant for the species generated in solution has also been calculated.     

Solvent Role on Cobalt(II) Dioxygen Carriers Based on Simple Polyamine Ligands

The kinetics and thermodynamics of O₂ addition to Co^II complexes containing the simple triamine ligand (L) diethylenetriamine (=N‐(2‐aminoethyl)ethane‐1,2‐diamine; dien) or N,N″‐dimethyldiethylenetriamine (=N‐methyl‐N′‐[2‐(methylamino)ethyl]ethane‐1,2‐diamine; dmdien) in the aprotic solvent dimethyl sulfoxide (DMSO) were studied by UV/VIS spectrophotometry, potentiometry, and O₂ absorption measurements. A parallel investigation on the anaerobic formation of Co^II complexes with dmdien, as well as on their reactivity towards O₂, was carried out in aqueous 0.1M NaClO₄ solution. [CoL]²⁺ and [CoL₂]²⁺ were the common species formed under anaerobic conditions in both aqueous and DMSO solutions. Under aerobic conditions, O₂ adducts of different stoichiometry were formed: a superoxo complex [CoL₂O₂]²⁺ in DMSO and dimeric species in H₂O. The role of the reaction medium as well as effects of N‐alkylation of the triamine ligand in the formation and reactivity of the [Co^II(triamine)] complexes are discussed.     

N-Phthaloylglycinate ternary complexes with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) metal ions and aromatic mono,bi and tridentate amines

Complexes of N-phthaloylglycinate (N-phthgly) and Co^II, Ni^II, Cu^II, Zn^II and Cd^II containing imidazole (imi), N-methylimidazole (mimi), 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen), and tridentate amines such as 2,2,2-terpyridine (terpy) and 2,4,6-(2-pyridyl)s-triazine (tptz), were prepared and characterized by conventional methods, i.r. spectra and by thermogravimetric analysis. For imi and mimi ternary complexes, the general formula [M(imi/mimi)₂(N-phthgly)₂]·nH₂O, where M = Co^II, Ni^II, Cu^II and Zn^II applies. For Cd^II ternary complexes with imi, [Cd(imi)₃(N-phthgly)₂]·2H₂O applies. For the bi and tridentate ligands, ternary complexes of the formula [M(L)(N-phthgly)₂]·nH₂O were obtained, where M = Co^II, Ni^II, Cu^II and Zn^II; L = bipy, phen, tptz and terpy. In all complexes, N-phthgly acts as a monodentate ligand, coordinating metal ions through the carboxylate oxygen, except for the ternary complexes of Co^II, Ni^II and Cu^II with mimi and Cu^II and Zn^II with imi, where the N-phthgly acts as a bidentate ligand, coordinating the metal ions through both carboxylate oxygen atoms.     

Ternary complexes of N-(2-acetamido)iminodiacetic acid and some aromatic acids. Isolation and stability constants in solution

Summary Ternary 1:1:1 complexes of Y^III, Co^II, Ni^II, Cu^II, La^III, Ce^III and UO ₂ ²⁺ with N-(2-acetamido)iminodiacetic acid (H₂ADA) as primary ligand and salicylic, anthranilic or phthalic acid as secondary ligand are described. The complexes of Co^II and Cu^II were isolated and characterized by microanalysis, molar conductance measurements, thermal analysis, i.r. and u.v.-vis. spectra. The formation constants of the 111 ternary complexes were determined potentiometrically in 20% (w/w) EtOH-H₂O at 24 °C. The stabilities of the 111 M ⁿ⁺ :ADA^2–:aromatic acid ternary complexes are higher than those of the corresponding 11 M ⁿ⁺ :aromatic acid binary complexes.     

Metal(II) Ion Complexes with 5‐(Pyrazin‐2‐yl)‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thione; Synthesis,Structural Characterization,Acid‐base,and Complexing Properties in Solution

The study reports the synthesis of complexes Co(HL)Cl₂ ( 1 ), Ni(HL)Cl₂ ( 2 ), Cu(HL)Cl₂ ( 3 ), and Zn(HL)₃Cl₂ ( 4 ) with the title ligand, 5‐(pyrazin‐2‐yl)‐1,2,4‐triazole‐5‐thione (HL), and their characterization by elemental analyses, ESI‐MS (m/z), FT‐IR and UV/Vis spectroscopy, as well as EPR in the case of the Cu^II complex. The comparative analysis of IR spectra of the metal ion complexes with HL and HL alone indicated that the metal ions in 1 , 2 , and 3 are chelated by two nitrogen atoms, N(4) of pyrazine and N(5) of triazole in the thiol tautomeric form, whereas the Zn^II ion in 4 is coordinated by the non‐protonated N(2) nitrogen atom of triazole in the thione form. pH potentiometry and UV/Vis spectroscopy were used to examine Co^II, Ni^II, and Zn^II complexes in 10/90 (v/v) DMSO/water solution, whereas the Cu^II complex was examined in 40/60 (v/v) DMSO/water solution. Monodeprotonation of the thione triazole in solution enables the formation of the L:M = 1:1 species with Co^II, Ni^II and Zn^II, the 2:1 species with Co^II and Zn^II, and the 3:1 species with Zn^II. A distorted tetrahedral arrangement of the Cu^II complex was suggested on the basis of EPR and Vis/NIR spectra.     

Fac-mer equilibria of coordinated iminodiacetate (IDA2?) in ternary CuII(ida)(H?1B)? complex formation (B = imidazole, benzimidazole) in aqueous solution

pH potentiometric and spectrophotometric investigations on the complex formation equilibria of Cu^II with iminodiacetate (ida²⁻) and heterocyclic N-bases, viz. imidazole and benzimidazole (B), in aqueous solution in binary and ternary systems using different molar ratios of the reactants indicated the formation of complexes of the types, Cu(ida), Cu(ida)(OH)⁻, (ida)Cu(OH)Cu(ida)⁻, Cu(B)²⁺, Cu(H^-1B)⁺, Cu(ida)(H₋₁B)⁻, (ida)Cu(B)Cu(ida) and (ida)Cu(H₋₁B)Cu(ida)⁻. Formation constants of the complexes at 25 ±1° at a fixed ionic strength,I = 0.1 mol dm⁻³ (NaNO₃) in aqueous solution were evaluated and the complex formation equilibria were elucidated with the aid of speciation curves. Departure of the experimental values of the reproportionation constants(ΔlogK _cu) of ternary Cu(ida)(H₋₁B)⁻ complexes from the statistically expected values, despite their formation in appreciable amounts at equilibrium, were assigned tofac(f)-mer(m) equilibria of the ida²⁻ ligand coordinated to Cu^II, as the N-heterocyclic donors, (H₋₁B)⁻, coordinatetrans- to the N-(ida²⁻) atom in the binary Cu(ida) _f complex to form the ternary Cu(ida) _m (H₋₁B)⁻ complexes     

Complexes of a tridentate ONS Schiff base. Synthesis and biological properties

Several new complexes of a tridentate ONS Schiff base derived from the condensation of S-benzyldithiocarbazate with salicylaldehyde have been characterised by elemental analyses, molar conductivity measurements and by i.r. and electronic spectra. The Schiff base (HONSH) behaves as a dinegatively charged ligand coordinating through the thiolo sulphur, the azomethine nitrogen and the hydroxyl oxygen. It forms mono-ligand complexes: [M(ONS)X], [M=Ni^II, Cu^II, Cr^III, Sb^III, Zn^II, Zr^IV or U^VI with X = H₂O, Cl]. The ligand produced a bis-chelated complex of composition [Th(ONS)₂] with Th^IV. Square-planar structures are proposed for the Ni^II and Cu^II complexes. Antimicrobial tests indicate that the Schiff base and five of the metal complexes of Cu^II, Ni^II, U^VI, Zn^II and Sb^III are strongly active against bacteria. Ni^II and Sb^III complexes were the most effective against Pseudomonas aeruginosa (gram negative), while the Cu^II complex proved to be best against Bacillus cereus (gram positive bacteria). Antifungal activities were also noted with the Schiff base and the U^VI complex. These compounds showed positive results against Candida albicans fungi, however, none of them were effective against Aspergillus ochraceous fungi. The Schiff base and its zinc and antimony complexes are strongly active against leukemic cells (CD₅₀ = 2.3–4.3 μg cm⁻³) while the copper, uranium and thorium complexes are moderately active (CD₅₀ = 6.9–9.5 μg cm⁻³). The nickel, zirconium and chromium complexes were found to be inactive. This revised version was published online in June 2006 with corrections to the Cover Date.     

Solution studies on trace metal ion interactions with adenine as primary ligand and 5-halouracils as secondary ligands

The interaction of trace metal ions, viz. Mn^II, Co^II, Ni^II, Cu^II, Zn^II and Cd^II with adenine (A) as primary ligand and 5-halouracils, viz. 5-bromouracil (5BrU) and 5-iodouracil (5IU) as secondary ligands (L) has been studied at 25±0.1°C and at constant ionic strength (=0.1M NaNO₃), in an aqueous medium using Bjerrum–Calvin's pH-titration technique as adopted by Irving and Rossotti for binary (ML), and by Chidambaram and Bhattacharya for ternary (MAL) systems respectively. The experimental pH-titration data were analyzed with the aid of the BEST computer program in order to evaluate formation constants of various intermediate complex species formed in binary and ternary systems involving nucleobases (viz. A, 5BrU and 5IU). The relative stability of each ternary complex was compared with that of the corresponding binary complexes in terms of logK values.     

Structural studies on cadmium(II), cobalt(II), copper(II), nickel(II) and zinc(II) complexes of 1-malonyl-bis(4-phenylthiosemicarbazide)

Summary Several new complexes of the title ligand (H₂MPTS) with Co^II, Ni^II, Cu^II, and Cd^II have been prepared. Structural assignments of the complexes have been made based on elemental analysis, molar conductivity, magnetic moment and spectral (i.r.,¹H n.m.r., reflectance) studies. The compounds are non-conductors in dimethylsulphoxide. The neutral molecule is coordinated to the metal(II) sulphate as a bidentate ligandvia the two carbonyl groups. The ligand reacts with the metal(II) chlorides with the liberation of two hydrogen ions, behaving as a bianionic quadridentate (NONO) donor. Enolization is confirmed by the pH-titration of H₂ MPTS and its metal(II) complexes against NaOH. A distorted octahedral structure is proposed for the Cu^II complex, while a square planar structure is suggested for both Co^II and Ni^II complexes. The stoichiometry of the complexes formed in EtOH and buffer solutions, their apparent formation constants and the ranges for obedience to Beer's law are reported for Co^II, Ni^II and Cu^II ions. The ligand pK values are calculated. The antimicrobial activity of H₂ MPTS and its Co^II, Ni^II, Cu^II and Mn^II complexes is demonstrated.     

Complex formation equilibria between mercury(II) complexes of pencillamine and glutathione and transition metal ions

Summary The interaction between Hg^II complexes of the thiols pencillamine and glutathione and some transition metal ions has been investigated potentiometrically. Mixedmetal complexes of the forms Hg(ps)₂M and Hg(gs)₂M (where M=Co or Ni), were detected. The complexes formed between glutathione disulphide with bivalent metal ions Zn^II, Ni^II, Co^II and Cd^II have also been studied. Zn^II and Ni^II form the complexes M(gssg)H and M(gssg), while Co^II and Cd^II form only the fully deprotonated complex M(gssg). The formation constants of the complexes were determined at 25°C and I=0.1 M (NaNO₃). The concentration distribution of various complex species as a function of pH was evaluated.     

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.     

Metal chelates with some cellulose derivatives; part IV. Structural chemistry of HEC complexes

Reactions of hydroxyethyl cellulose (HEC) with Cr ^III, Ni^II, Co^II, or Cu^II chlorides in aqueous medium yielded complexes with formulae [M(HEC)Cl _m .n H ₂O], wherem =1 or 2 and n=2 or 3. HEC acted as a uninegatively charged bidentate ligand in the case of Cr^III and Ni^II, and as a neutral ligand in the case of Co^II and Cu^II complexes. The spectra showed that the binding sites in Cr^III and Ni^II complexes were the ether oxygen between two ethoxyl groups and the oxygen of the hydroxyl group; while in the Co^II and Cu^II complexes the binding sites were the oxygen of ethoxyl groups and the primary alcoholic O atom of glucopyranose rings. These complexes would most likely exhibit octahedral geometry with Cr^III, Ni^II, and Co^II, but square planar configuration in the case of the Cu^II complex. The ligand parameters of the Cr^III, Ni^II, and Co^II metal chelates were calculated in different solvents and at different temperatures. The thermal stability of the above complexes was investigated and the overall thermodynamics functions G⁰, H⁰, and S⁰, associated with complex formation, were estimated.     

Synthesis and Characterization of New Water‐Soluble Hydrides of RuII: A Step towards Dinitrogen Activation?

The basic aqueous coordination chemistry of Ru^II has been studied using the catalytically important TPPTS phosphine (TPPTS=trisodium salt of 3,3′,3″‐phosphinetriylbenzenesulfonic acid) and small gas molecules (H₂, CO, N₂) as ligands. As a result, new water‐soluble ruthenium mixed hydride complexes, presumably key species in many industrial catalytic processes, have been formed and identified. The Ru^II mixed hydrides were synthesized, and their formation was followed in situ by multinuclear NMR spectroscopy, pressurizing aqueous Ru^II? TPPTS systems with H₂ and CO gas in sapphire NMR tubes. The formation equilibrium of these complexes is highly dependant on the temperature and the gas pressures. Under 50 atm of N₂, the unique [RuH(CO)(N₂)(TPPTS)₂(H₂O)]⁺ complex has been identified, which could be the first step toward dinitrogen activation.     

The synthesis,spectroscopic and thermal study of oxamic acid compounds of some metal(II) ions

Summary The preparation of oxamic acid complexes of general formula M(H₂NCOCOO)₂·xH₂O (M = Mn^II, Co^II, Ni^II, Cu^II or Zn^II; x = 1 for Cu^II, x = 2 for the other metals) is reported. The i.r. and Raman spectra are discussed considering a trans-octahedral structure, formed by five-membered chelate rings with the amide oxygen and one carboxylic oxygen as donor atoms. The apical positions are occupied by water molecules. The thermal degradation process is very similar for the different complexes, first losing H₂O in one or different steps, then the fragments of the organic ligand to give the metal oxide as residue. The thermal degradation of the Cu^II and Zn^II compounds results in the formation of a new polymeric compound by deprotonation of the primary amide function in an endothermic process, the polymer further decomposes to form the metal oxide.