Synthesis of Two N,N′-bis(N,N-dialkylamide) Derivatives of Diethylenetriaminepentaacetic Acid and the Stabilities of Their Complexes with Gd3+, Ca2+, Cu2+, and Zn2+

Two bis(N,N-dialkylamide) derivatives of DTPA [(carboxymethyl)iminobis (ethylenenitrilo) tetraacetic acid], DTPA-BDMA = the bis(N,N-dimethylamide) and DTPA-BDEA = the bis(N,N-diethylamide) were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1 °C. Stability and selectivity constants were measured to evaluate the possibility of using the corresponding gadolinium(III) complexes for magnetic resonance imaging contrast agents. The stability constants of gadolinium(III), copper(II), zinc(II), and calcium(II) complexes with DTPA-BDMA and DTPA-BDEA were investigated quantitatively by potentiometry. The stability constant for gadolinium(III) complexes is larger than those for Ca(II), Zn(II), and Cu(II) complexes. The selectivity constants and modified selectivity constants of the amides for Gd³⁺ over endogenously available metal ions were calculated. Effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media is assessed by comparing pM values at physiological pH 7.4. Spin-lattice relaxivity values R₁ for Gd(III) complexes were also determined. The observed relaxivity values were found to decrease with increasing pH in the acid range below pH 4 and relaxivity values became invariant with respect to pH changes over the range of 4–10. ¹⁷O NMR shifts showed that the [Dy(DTPA-BDMA)] and [Dy(DTPA-BDEA)] complexes had one inner-sphere water molecule. Water proton spin-lattice relaxation rates for the [Gd(DTPA-BDMA)] and [Gd(DTPA-BDEA)] complexes were also consistent with one inner-sphere gadolinium(III) coordination position.     

Chromium(III): Extra nonlability of its 1:1 chelates of polycarbonylic ligands

Decomplexation rates of chromium(III) chelates of dicarbonylic and tricarbonylic ligands in aqueous solution have been evaluated. Results show an extreme nonlability of these metal complexes that does not depend on the chelating ligand structure. A more extensive analysis including structurally similar complexes of first‐row transition metal ions [Ni(II), Co(II), and Cu(II)] shows decomplexation rate values at least 10⁴ times higher than the rate constants of previously mentioned chromium metal complexes. Correlations between the decomplexation rate constants and the deprotonation capability of the enol tautomer suggest that the decomplexation rates of a structurally similar 1:1 chelate of quoted metal ions may be predicted from the ligand dissociation constant. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 178–183, 2000     

Synthesis of Two Derivatives of 3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic Acid and the Stabilities of Their Complexes with Ca2+, Cu2+, Zn2+, Dy3+ and Gd3+

Two N‐2‐hydroxy‐1‐phenylethyl and N‐2‐hydroxy‐2‐phenylethyl derivatives of DTPA (3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic acid), DTPA‐H1P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐1‐phenylethyl‐3,6,9‐triazaundecanedioic acid, and DTPA‐H2P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐2‐phenylethyl‐3,6,9‐triazaundecanedioic acid were synthesized. Their protonation constants were determined by Potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1°C. The formations of lanthanide(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constant for Gd(III) complex is larger than those for Ca(II), Zn(II) and Cu(II) complexes with these two ligands. The selectivity constants and modified selectivity constants of the DTPA‐H1P and DTPA‐H2P for Gd(III) over endogenously available metal ions were calculated. Comparing pM values at physiological pH 7.4 assesses effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media. The observed water proton relaxivity values of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? became constant with respect to pH changes over the range of 4‐10. ¹⁷O NMR shifts showed that the [Dy(DTPA‐H1P)]^? and [Dy(DTPA‐H2P)]^? complexes at pH 6.30 had 1.91 and 2.28 inner‐sphere water molecules, respectively. Water proton spin‐lattice relaxation rates of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? complexes were also consistent with the inner‐sphere Gd(III) coordination.     

Synthesis of new ionic β-cyclodextrin polymers and characterization of their heavy metals retention

In this study, a new aqueous insoluble ionic β-cyclodextrin polymer (PYR), synthesized by reaction of β-cyclodextrin with pyromellitic anhydride [1], is characterized by IR spectroscopy, showing typical cyclodextrin and carboxylic absorptions. pH-metric titrations of the acidic functions with standard NaOH solutions followed by a refinement of protonation constants, with specific software for equilibrium in solution, have been performed. Through this approach, the pK _a values of the functional groups have been calculated. The complexation capabilities of PYR towards metal ions [Al(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Cd(II), Pt(IV), Tl(I), and U(IV)] have been evaluated in aqueous solution (pH 3–5). The retention is mainly pH dependent and higher than 70% for Al(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Cd(II) and U(IV). For Tl(I) and Pt(IV) the retention is about 60% and 40% respectively.     

Metal chelates of salicyl-4-aminoantipyrine

The formation constants of salicyl-4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (SAAP) complexes with 3d transition metal ions [Cu(II), Ni(II), Co(II), Zn(II) and Mn(II)] have been determined in 60% ethanol-water medium ofμ = 0.1M (NaCl) at 25°C. It is observed that the formation constants for chelates with 3d transition metals follow the order Mn(II) < Co(II) < Ni(II) < Zn(II) < Cu(II). The effects of metal ions, ionic radii, electronegativities and ionization potentials on chelate formation constants are discussed. Complexes of UO₂(II) and Pd(II) have been synthesized and characterised by elemental analysis, electrolytic conductance, IR spectra and magnetic measurements. The ligand forms the complexes PdLCl and UO₂L₂,2H₂O, where L is a uninegatively charged tridentate ligand (ONO donor sets).     

The sorption of thiocyanate ions on complex-forming ionites

The ligand sorption of thiocyanate ions on several complex-forming ionites was studied. The ionites were preliminarily transformed into metal forms by saturation with copper(II) ions. ANKB-2 amphoteric ionite in the Cu form had the strongest affinity for thiocyanate ions. The optimum conditions for their extraction were pH ∼ 2 and solution ionic strength 1. IR spectroscopy was used to study the ligand sorption of SCN⁻ ions by ANKB-2 ionite in the Cu form. The stability constants of thiocyanate ionite copper complexes were calculated from formation function [`(n)] \bar n .     

Optical and chromaticity parameters of transition metal complexes with 1-nitroso-2-naphthol-3,6-disulfonic acid in the presence of surfactants

Optimal conditions for the complexation of transition metal ions [Cu(II), Ni(II), Co(II, III), and Fe(II, III)] with 1-nitroso-2-naphthol-2,6-disulfonic acid have been determined by spectrophotometry in the presence of cationic (cetylpyridinium and cetyltrimethylammonium bromides) and nonionic (OP-10, neonol) surfactants. The introduction of nonionic surfactants does not influence the optical parameters of the system, while the introduction of cationic ones leads to hyperchromic and hypsochromic (for the system Fe(III)-NRS-surfactant) effects. The stoichiometric ratios determined by the method of isomolar series and treatment of the saturation curves of cationic surfactants at pH 4.0 are Me(II): R: surfactant = 1: 2: 4, Me(III): R: surfactant = 1: 3: 6. The molar absorption coefficients and chromaticity parameters of ternary complexes have been determined. A 2–5-fold increase in the molar absorption coefficients and chromaticity functions as compared to binary systems has been revealed.     

Speciation of the Ternary Complexes of Vanadium(III)–Dipicolinic Acid with the Amino Acids Glycine,Proline, <Emphasis Type="Italic">α</Emphasis>-Alanine and <Emphasis Type="Italic">β</Emphasis>-Alanine Studied in 3.0 mol⋅dm<Superscript>−3</Superscript> KCl at 25 °C

In this paper we present speciation results for the ternary vanadium(III)–dipicolinic acid (H₂dipic) systems with the amino acids glycine (Hgly), proline (Hpro), α-alanine (Hα-ala), and β-alanine (Hβ-ala), obtained by means of electromotive forces measurements emf(H) using 3.0 mol⋅dm⁻³ KCl as the ionic medium and a temperature of 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid base reactions of the ligands, which were kept fixed during the analysis. In the vanadium(III)–dipicolinic acid–glycine system, formation of the ternary [V(Hdipic)(Hgly)]²⁺, [V(dipic)(Hgly)]⁺, [V(dipic)(gly)], [V(dipic)(gly)(OH)]⁻ and [V(dipic)(gly)(OH)₂]²⁻ was observed; in the case of the vanadium(III)–dipicolinic acid–proline system the ternary complexes [V(Hdipic) (Hpro)]²⁺, [V(dipic)(Hpro)]⁺, [V(dipic)(pro)] and [V(dipic)(pro)(OH)]⁻ were observed; in the vanadium(III)–picolinic acid–α-alanine were observed [V(Hdipic)(Hα-ala)]²⁺, [V(dipic) (Hα-ala)]⁺, [V(dipic)(αala)], [V(dipic)(α-ala)(OH)]⁻ and [V(dipic)(α-ala)(OH)₂]²⁻; and in the vanadium(III)–dipicolinic acid–β-ala system the complexes [V(dipic) (Hβ-ala)]⁺, [V(dipic)(β-ala)], [V(dipic)(β-ala)(OH)]⁻ and [V(dipic)(β-ala)(OH)₂]²⁻ were observed. Their respective stability constants were determined, and we evaluated values of Δlog ₁₀ K″ in order to understand the relative stability of the ternary complexes compared to the corresponding binary ones. The species distribution diagrams are briefly discussed as a function of pH.     

Complexation behaviour of benzilmono(Iepidyl)hydrazone (BLH) toward bivalent metal ions: A potentiometric study

Potentiometric investigations on metal complexes of various bivalent metal ions, viz. UO₂(II), Cu(II), Ni(II), Co(II), Cd(II), Pb(II), Zn(II) and Mn(II) with benzilmonol(lepidy!)hydrazone (BLH) have been carried out at different ionic strengths and at different temperatures in order to determine stability constants of the complexes. Thermodynamic parameters ΔC, ΔH and ΔS have also been evaluated from temperature coefficient data. The effect of varying the dielectric constant of the medium on the stability constants of complexes has also been investigated at 30±0.5°C and μ = 0.1MNaCl. Thermodynamic stability constants and thermodynamic stabilization energies for the first transition metals have also been discussed.     

Correlation between hydration and deprotonation in hexaaqua metal complexes

The hydration energy of metallic cations determined with density functional calculations using a double-numerical plus p-polarization basis set, related to the acidity constants of hexaaqua metal complexes, was investigated in the present study. From the results calculated by Vosko-Wilk-Nusair (VWN), Becke-Perdew (BP) and Becke-Lee-Yang-Parr (BLYP) density functionals, a global linear correlation with the observed acidity constants in both main group [Mg(II), Ca(II) and Al(III)] and (post-)transition group [Mn(II), Zn(II), Cd(II), Sc(III), Cr(III), Fe(III), Ga(III) and In(III)] hexaaqua metal complexes has been established:

VWN density functional: pK_a = 16.5760 + 0.0173E_hydr kcal mol⁻¹

BP density functional: pK_a = 15.7329 + 0.0182E_hydr kcal mol⁻¹

BLYP density functional: pK_a = 15.9448 + 0.0185E_hydr kcal mol⁻¹