4-(8-Quinolylazo)-1-Aminonaphtalene as a Metallochromic Indicator for Cu(II), Ni (II) and Hg(II)

Abstract

The dissociation constant of 4–(8-quinolylazo)- l -aminonaphtalene (QAN) and conditional formation constants of its complexes with Cu(II), Ni(II) and Hg(II) were measured spectrophotometrically. The use of QAN as metallochromic indicator in copper, nickel and mercury titrations with EDTA was studied. QAN improves PAN and XO results in Cu(II) and Hg(II) titrations and is comparable to Murexide in Ni(II) titration.     

Potentiometric study of Cd(II) and Pb(II) complexation with two high molecular weight poly(acrylic acids); comparison with Cu(II) and Ni(II)

The cadmium (II) or lead (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×10⁵ and 3×10⁶) was investigated in dilute aqueous solution (NaNO₃ 0.1 mol l⁻¹; 25°C). Potentiometric titrations were carried out to determine the stability constants of the MA and MA₂ complex species formed. Bjerrum’s method, modified by Gregor et al. (J. Phys. Chem. 59 (1955) 34–39), for the study of polymeric acids was used. The results were compared to those previously obtained in the same conditions with copper (II) and nickel (II) . It appeared that the two polymers under study present similar binding properties and that the stability constants of the complex species formed increased in the following order, depending on the metal ion: Ni(II)β₁₀₂ was found to be close to 7.0) and allowed the formation of the predominant PbA₂ species in a quite large pH domain. Finally, the greater stability of PAA complexes compared to those of their monomeric analogs, glutaric and acetic acids, was confirmed.     

Complex Formation of Acetic Acid with Ca(II) and Mg(II) Under Physiological Conditions

Potentiometric titrations of aqueous acetic acid alone and in the presence of Ca(II) or Mg(II) ions have been carried out under physiological conditions at the temperature 37 °C and ionic strength 0.15 mol⋅dm⁻³ (NaCl) at different ligand-to-metal ratios. Changes in pH were monitored with a glass electrode calibrated daily in terms of the hydrogen ion concentrations. Titration data within the pH range 2.5 to 6.6 were analyzed to determine stability constants using the SUPERQUAD program. Different combinations of complexes were considered during the calculation procedure for both systems, but evidence was found only for mononuclear ML and ML₂ species. Speciation calculations based on the corresponding constants were then used to simulate the species’ distributions.     

Complexation of copper(II) with azo derivatives of benzoylacetone

1-Phenyl-2-[2-hydroxy-3-sulfo-5-nitrophenylazo]butadione-1,3 (H₂L) was synthesized from benzoylacetone. The dissociation constants of the reagent were determined (pK ₁ = 4.98 ± 0.03 and pK ₂ = 8.53 ± 0.01). Stability constants of some metal complexes with this reagent were determined by potentiometric and conductometric titrations. The stability of these complexes decreased in the following order: Fe > Cu > UO₂ > Ni > Co > Zn > Cd > Mn > Mg > Ca. The copper(II) H₂L complex with a stoichiometry of 1: 2 was studied by photometry. ε = 1.4 × 10⁴, Beer is law was obeyed in the copper concentration range from 0.25 to 3.07 μg/mL. The effect of foreign ions and masking agents on complexation was studied. A procedure for the photometric determination of copper(II) in seawater was developed.     

Compleximetric titrations of iron(III) and iron(II) with triethylenetetraminehexaacetic acid

The stability constants of the iron(II) complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from measured pH and redox potentials. The values of the cumulative constants obtained were: log β_FeL= 15.37, log β_FeHL = 23.83, log β_FeH2L = 28.0, log β_Fe2L = 24.73. On the basis of these values and the previously determined constants ofiron(III) complexes, the possibilities of titrating iron(III) and iron(II) with TTHA were investigated. Depending on the experimental conditions, either FeL or Fe₂L formed. Actual titrations were in agreement with the developed theory. The influence of aluminium and titanium on titrations of iron(III) solutions was elucidated.     

Interaction of Cu(II) and Cd(II) ions with DNA from Spirulina platensis

Equilibrium dialysis and atomic absorption analysis were used to obtain adsorption isotherms and determine the stoichiometric binding constants of Cu(II) and Cd(II) ions to DNA from Spirulina platensis in solutions. The stoichiometric constants of Cu(II) and Cd(II) ions with DNA from S. platensis in 3 mM NaCI are 15.56⋅10⁴ and 14.40⋅10⁴, respectively. Effect of ionic strength and DNA GC content on binding constants of Cu(II)- and Cd(II)-DNA complexes were studied out. It was showed that the binding constants of Cu(II)- and Cd(II)-DNA complexes decrease with increase of ionic strength. The empirical dependences of logK on the GC content has been derived for Cd(II)- and Cu(II)-DNA complexes.     

Binding of Cu(II) to poly(methacrylic acid)

The binding of Cu(II) ions to partly neutralized poly(methacrylic acid) (PMA) has been investigated by potentiometric titration and dialysis to determine the stoichiometry the Cu–PMA complexes formed. Partly ionized PMA was titrated with solutions of the metal ion to enable a large range of metal ion/polymer ratios to be studied. Combination of the results from these two techniques at ionic strength 0.1 indicates that at very low Cu(II)/polymer ratios, a 4:1 complex exists, but at higher ratios the complex breaks down to give a mainly 2:1 coordination with some 1:1 binding. Conductance titrations support these results. Viscometric titrations show strong interactions between the metal and polymer, preventing the full extension of the polyion at high degrees of ionization, and spectrophotometric titrations support the existence of at least two types of complexes in the solution.     

Studies on some salicylaldehyde Schiff base derivatives and their complexes with Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II)

The formation constants of some transition metal ions Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II) binary complexes containing Schiff bases resulting from condensation of salicylaldehyde with aniline (I), 2-aminopyridine (II), 4-aminopyridine (III) and 2-aminopyrimidine (IV) were determined pH-metrically in ethanolic medium (80%, v/v). The formation constants were determined for all binary complexes. The important infrared (IR) spectral bands corresponding to the active groups in the four ligands and the solid complexes under investigation were studied. The solid complexes have been synthesized and studied by thermogravimetric analysis. The thermal dehydration and decomposition of these complexes were studied kinetically using the integral method applying the Coats-Redfern equation. It was found that the thermal decomposition of the complexes follow second order kinetics. The thermodynamic parameters of the decomposition are also reported. The electronic absorption spectra of the investigated ligands were carried out to determine the pK(a) values spectrophotometrically.     

A Thermodynamic Study Of N,N,N',N'-Tetrakis(2-Hydroxyethyl)-Ethylenediamine Complexes With Nickel(II), Copper(II), And Zinc (II)

Abstract

Thermodynamic parameters have been determined by poten-tiometric techniques for complex ions formed by N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine TKED, with nickel (II), copper(II), and zinc(II) ions. The formation constants, enthalpy, and free energy data for the complexes exhibited values qualitatively consistent with predicted ligand field stabilization trends for these cations. The general expected stability of the complexes in the order Ni(II) < Cu(II) > Zn(II) is observed.     

Cu(II), Zn(II), AND Pb(II) STABILITY CONSTANTS OF CYCLAM AMPHIPHILES

Abstract

1-Hexadecyl-1,4,8,11-tetraazacyclotetradecane (hexadecyl cyclam) and 1-(3,7,11,15-tetramethyl) hexadecyl-1,4,8,11-tetraazacyclotetradecane (tetramethylhexadecyl cyclam) have been synthesized and their deprotonation and ligand-metal formation constants, K, determined for Cu(II), Zn(II) and Pb(II). The coupling of a long hydrocarbon chain to a ring nitrogen decreased the general ability of the cyclam ring to complex with metal ions. The greatest effect appeared to be for Cu(II) decreasing from a pK of 27 for cyclam to about 17. The titrations were fitted by HYPERQUAD and the concentrations of the intermediate complexes obtained as a function of pH. Metal-ligand complexes LMH₂ ⁴⁺, LMH₂₊ and LM₂₊ can coexist through a wide pH range. We have also calculated a composite metal-binding constant, K′, to reflect more accurately the overall ability of these ligands to bind a metal at any particular pH. K′, which is 14.6 for (hexadecyl cyclam)-Cu(II), is constructed from the concentrations of all the metal-chelated species at pH = 7. Generally, K′ is much lower than K.     

Synthesis, characterization of a novel calixarene having dipyridyl pendants and study of its complexes with Cu(II) and Co(II)

Two dipyridyl pendants were attached to the 1,3 positions of a calix[4]arene, with the purpose of having a ligand able to complex Cu(II) and Co(II). Indeed, the new ligand, fixed in its 1,3-alternate conformation, forms stable complexes with both Co(II) and Cu(II), as shown by UV-vis titrations carried out in acetonitrile. However, the data analysis clearly shows that the ligand forms with the two metal ions complexes having different stoichiometries.     

Three-ring, branched cyclam derivatives and their interaction with nickel(II), copper(II), zinc(II) and cadmium(II)

The interaction of two symmetrically branched tris-cyclam derivatives based on 1,3,5-trimethylenebenzene and phloroglucinol cores with nickel(II), copper(II), zinc(II) and cadmium(II) is reported. All four metal ions yield solid complexes in which the metal : ligand ratio is 3 : 1. For both ligand types, spectrophotometric titrations confirm the formation of nickel(II) and copper(II) complexes of similar 3 : 1 stoichiometry in dimethyl sulfoxide. Visible spectral, electrochemical, magnetic moment, ESR and NMR studies have been performed to probe the nature of the respective complexes. Where appropriate, the results from the above metal-ion studies are compared with those from parallel investigations in which the corresponding (substituted) mono-cyclam analogues were employed as the ligands. A structural determination employing a poorly diffracting crystal of the trinuclear nickel(II) complex of the tris-cyclam ligand incorporating a 1,3,5-trimethylenebenzene core was successfully carried out with the aid of a synchrotron radiation source. A nickel ion occupies each cyclam ring in a square-planar coordination arrangement, with each cyclam ring adopting the stable trans-III configuration.     

The Interaction of Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) with Mixed Donor Macrocycles Containing Pendant Carboxylic Acid Functions

The syntheses of mixed oxygen-nitrogen donor macrocycles incorporating two or three pendant carboxylic acid groups are described. Potentiometric titrations in water (I = 0.1; KNO₃) at 25°C have been used to determine the stability constants for the 1: 1 (metal:ligand) complexes of Co(II). Ni(II), Cu(II), Zn(II), and Cd(II). The constants obtained are compared with the previously determined values for the corresponding complexes of the unsubstituted macrocyclic precursors. The results of these studies indicate that each carboxylate function participates in binding to the central metal. For some metal-ion/ligand systems there is evidence that ring size effects influence the overall stability patterns and that, in such cases, both the ether oxygens as well as the tertiary amines of the macrocyclic rings appear to bind to the metal.     

Acid equilibria of semi-methylthymol blue and formation constants of cobalt(II), nickel(II), copper(II) and zinc(II) complexes with semi-methylthymol blue

Potentiometric and spectrophotometric studies on Semi-Methylthymol Blue (SMTB or H(4)L) have been performed. The acid-base and Co(II), Ni(II), Cu(II) and Zn(II)-ligand reaction stoichiometries were determined, and the formation constants of the corresponding proton and metal complexes, and the molar absorptivities were calculated. Evidence was found for the formation of 1:1 Co(II), Ni(II) and Cu(II) complexes, and 1:1 and 1:2 Zn(II) complexes. Cu(II) formed the hydroxo-complex, Cu(OH)L(3-), but no hydroxo-complexes of the other metal ions were observed. Suggestions are made concerning the probable structure of the complexes.     

Potentiometric determination of stability constants of inorganic cyclophosphate complexes with copper(II), cadmium(II) and lead(II) ions

The stability constants of the complexes of cyclophosphate anions and copper(II), cadmium(II) and lead(II) ions were determined by potentiometry with the use of ion-selective electrodes. For each metal ion, the stability constant of the 1:1 complex increases linearly with the charge on the phosphate ion. For the same cyclophosphate ion, the stability constants also increase with increase in the crystal radii of the cation, i.e. in the order: Cu²⁺ < Cd²⁺ < Pb²⁺. These results suggest that the complex formed is a typical outer-sphere type based on electrostatic forces.     

Colorimetric recognition of Cu(II) by (2-dimethylaminoethyl)amino appended anthracene-9,10-diones in aqueous solutions: deprotonation of aryl amine NH responsible for colour changes

Chromogenic receptors 2 and 3 undergo distinct colour changes from magenta to blue on gradual addition of Cu(II) and can be used as colorimetric probes for spectrophotometric and visual analysis of Cu(II) in the presence of biological metal ions Na(I), K(I), Mg(II), Ca(II), Fe(II), Zn(II) etc. in aqueous solution (methanol-water 1 : 1 v/v). On addition of Cu(II), both 2 and 3 exhibit a bathochromic shift of Delta lambda(max) = 114 nm for 2 and Delta lambda(max)= 150 and 265 nm for receptor 3. The protonation constants and formation constants of Cu(II) complexes of receptors 2 and 3 (at pH 7) and the effect of pH on formation of these complexes has been determined by the combination of UV-vis-pH titrations of receptors 2 and 3 and their Cu(II) complexes. These results and the emergence of only one peak at 610 nm for 2 and two distinct absorption peaks at 715 and 800 nm for 3 on addition of Cu(II) unambiguously point to mono- and di-deprotonation for 2 and 3, respectively.     

Mn(II) complexes of novel hexadentate AAZTA-like chelators: a solution thermodynamics and relaxometric study

Three novel chelators based on the 6-amino-6-methylperhydro-1,4-diazepine scaffold and possessing three pendant N-acetic or N-α-methylacetic acid have been synthesised. The ligands contain six donor atoms for complexation of Mn(II) ions and thus potentially leave an additional site for coordination of a water molecule. The protonation constants of the ligands and the stability constants of their complexes formed with Mn(II) ion were determined by pH-potentiometric titrations in 0.15 M NaCl solution at 25 °C and compared to those of the parent AAZTA ligand (AAZTA = 6-amino-6-methylperhydro-1,4-diazepine tetraacetic acid). In spite of the similar value of the total basicity (Σlog K), the values of the stability constants of the Mn(II)AAZTA-like complexes are more than three orders of magnitude lower than that of MnAAZTA (log K(MnL) = 14.19). A detailed (1)H and (17)O NMR relaxometric study was carried out on the Mn(II) complexes in aqueous solution as a function of pH, temperature and magnetic field strength. The (1)H NMRD profiles of all the complexes show a similar shape, typical of low-molecular weight systems, but amplitudes that markedly differ to indicate a different degree of hydration. A similar behaviour is shown by the (17)O NMR transverse relaxation rates and chemical shift data as a function of temperature. The experimental data can be rationalised by considering the presence in solution of a mixture of two isomeric species differing in coordination number (7 and 6) and in the number (1 and 0) of bound water molecules. Whereas this type of coordination equilibrium has been previously reported for lanthanide(III) complexes, it is observed for the first time on Mn(II) chelates.     

Coordination mode and reactivity of nickel(II) with vitamin B6

This contribution presents a selection of results obtained using spectrophotometric and potentiometric titrations. For several reasons, the investigated equilibria present particular challenges to traditional analysis techniques. Equilibrium constants and UV–vis absorption spectra for different ligands in the complexation process of Ni(II) with pyridoxamine (pm), pyridoxal (pl) and pyridoxine are reported. The gradual and cumulative stability constants occurring in aqueous solution are presented for all complexes studied. Additionally, crystal-field parameters were calculated for two nickel(II) complexes synthesized, [Ni(pm)₂]Cl₂ and [Ni(pl)₂]Cl₂, respectively. The minimum inhibitory concentration and minimal bactericidal/fungicidal concentration values for Ni(II) complexes studied were obtained at 25 °C for 24–48 h. The activity data show that the complexes are more potent antimicrobials than the parent ligands.     

Synthesis and Thermodynamic Investigation of 4-Amino-6-Hydroxy-2-Mercapto Pyrimidine (AHMP) Complexes with Some Selected Divalent Metal(II) Ions

The synthesis and characterization of zinc(II), cadmium(II), lead(II), mercury(II) and phenylmercury(II) complexes of 4-amino-6-hydroxy-2-mercapto pyrimidine (AHMP) are reported. The stoichiometry of the complexes was found to be 1:2 except for the phenylmercury(II) complex where the ratio is 1:1. Characterization of these complexes was carried out by means of elemental analyses, IR and ¹H NMR measurements. In these complexes the ligand is bonded to the metal through its sulfur atom. The potentiometric results showed the formation of 1:1 and 1:2 complexes and the corresponding stability constants were determined for both Zn(II) and Cd(II) ions. The high insolubility of mercury(II), phenylmercury(II) and lead(II) complexes prevented the determination of their stability constants. The concentration distribution of the complexes in solution was evaluated. The effect of temperature on the dissociation constant of AHMP and the formation constants of both the Zn-AHMP and Cd-AHMP complexes were studied and the thermodynamic parameters were calculated.     

Complexation of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid with Fe(II), Co(II), and Ni(II) in aqueous solution

In a search for environment-friendly metal chelating ligands for industrial applications, the protonation and complex formation equilibria of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid (BCA6) with Fe(II), Co(II), and Ni(II) ions in aqueous 0.1 M NaCl solution were studied at 25°C by potentiometric titration. The model for complexation and the stability constants of different complexes were determined for each metal ion using SUPERQUAD. In all cases, complex formation was dominated by stable ML^4? complexes.