Mixed complex formation of copper(II) with 2,2′, 2″-terpyridine and some tridentate ligands in aqueous solution

Summary The formation of copper(II) ternary complexes [Cu(tpy)(L)] (tpy = 2,2,2-terpyridine; L = oxydiacetate, thiodiacetate, iminodiacetate or dipicolinate) has been studied by potentiometric measurements in aqueous solution at 25° and I = 0.1 mol dm^–3 (NaNO₃ or NaClO₄). All the systems investigated also form protonated species of the [Cu(tpy)(L)H]⁺ type. The effect of the different heteroatoms (donor atoms) in the ligands L (i.e. O, S or N), other than oxygens of the carboxylic groups, on the stability of the mixed complexes has been evaluated and compared with the trends observed for the analogous complexes of copper(II) with 2,2-bipyridine (bpy).The stabilization of ternary complexes of copper(II) with respect to the different coordination levels is also discussed.     

Thermodynamic study of Cd(II) complex formation with tripodal N-donor ligands in DMSO

The complex formation of Cd(II) with N-donor ligands in dimethylsulfoxide (DMSO) is investigated by means of potentiometry and titration calorimetry. The ligands considered in this work are tripodal polyamines and polypyridines: 2,2′,2″-triaminotriethylamine (TREN), tris(2-(methylamino)ethyl)amine (Me₃TREN), tris(2-(dimethylamino)ethyl)amine (Me₆TREN), tris[(2-pyridyl)methyl]amine (TPA) and 6,6′-bis-[bis-(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine (BTPA). These ligands are characterized by a systematic modification of the donor groups to relate their structure to the thermodynamics of the complexes formed. The TREN and Me₃TREN ligands form highly stable species. The stability of the complex formed with the fully methylated Me₆TREN is much lower than with other polyamines and the enthalpic and entropic terms suggest an incomplete coordination to the metal ion. In general, the TPA ligand forms complexes less stable than TREN and Me₃TREN as a result of the combination of higher structural rigidity of TPA and lower basicity of pyridine moiety with respect to primary and secondary amines. Pyridine-containing ligands display, in general, a less unfavorable formation entropy than tripodal polyamines here considered. In particular, TPA forms a more stable 1:1 species with respect to Me₆TREN due to the entropic term, being the enthalpy less negative. The ligand BTPA is able to form only a monometallic complex, where the metal ion is likely to be encapsulated as indicated by the obtained thermodynamic parameters.     

Four copper(II) complexes with potentially tetradentate tripodal ligands

The four title Cu^II compounds are chloro­[(2‐furyl­methyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′]copper(II) perchlorate, [CuCl(C₁₇H₁₇N₃O)]ClO₄, (I), chloro{2‐[bis(2‐pyridyl­methyl)­amino]­ethano­lato‐N,N′,N′′,O}­copper(II) hemi­[tetra­chloro­copper(II)], [CuCl(C₁₄H₁₇N₃O)][CuCl₄]_1/2, (II), chloro­[(2‐morpholino­ethyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′,N′′′]copper(II) perchlorate, [CuCl(C₁₈H₂₄N₄O)]ClO₄, (III), and chloro­[(2‐piperidinyl­ethyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′,N′′′]­copper(II) hexa­fluoro­phosphate, [CuCl(C₁₉H₂₆N₄)]­PF₆, (IV). They have tripodal potentially tetradentate ligands. In (I), the O atom of the furan moiety weakly coordinates to the Cu atom at a distance of 2.750 (3) Å.     

Thermodynamics of mixed-ligand complex formation of copper (II) ethylenediaminetetraacetate with hexamethylenediamine in an aqueous solution

The mixed-ligand complex formation in the system Cu²⁺−Edta⁴⁻−(CH₂)₆(NH₂)₂ (L), where L is hexamethylenediamine has been calorimetrically, pH-potentiometrically and spectrophotometrically studied in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO₃). The thermodynamic parameters of formation of the CuEdtaL²⁻, CuEdtaHL⁻ (CuEdta)₂L⁴⁻ and (CuEdta)₂En⁴⁻ complexes have been determined. The most probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand complexes was discussed.     

Cadmium(II) N-acetylcysteine complex formation in aqueous solution

The complex formation between Cd(II) ions and N-acetylcysteine (H(2)NAC) in aqueous solution was investigated using Cd K- and L(3)-edge X-ray absorption and (113)Cd NMR spectroscopic techniques. Two series of 0.1 M Cd(II) solutions with the total N-acetylcysteine concentration c(H2NAC) varied between 0.2-2 M were studied at pH 7.5 and 11.0, respectively. At pH = 11 a novel mononuclear [Cd(NAC)(4)](6-) complex with the average Cd-S distance 2.53(2) ? and the chemical shift δ((113)Cd) = 677 ppm was found to dominate at a concentration of the free deprotonated ligand [NAC(2-)] > 0.1 M, consistent with our previous reports on cadmium tetrathiolate complex formation with cysteine and glutathione. At pH 7.5 much higher ligand excess ([HNAC(-)] > 0.6 M) is required to make this tetrathiolate complex the major species. The (113)Cd NMR spectrum of a solution containing c(Cd(II)) = 0.5 M and c(H2NAC) = 1.0 M measured at 288 K showed three broad signals at 421, 583 and 642 ppm, which can be attributed to CdS(3)O(3), CdS(3)O and CdS(4) coordination sites, respectively, in oligomeric Cd(II)-NAC species with single thiolate bridges between the cadmium ions.     

Temperature effect on the heats of copper(II) ion complex formation with L-phenylalanine in aqueous solution

The heats of complex formation in the L-phenylalanine-copper(II) ion system in aqueous solution were determined calorimetrically at 288.15, 298.15, and 308.15 K for an ionic strength of 0.5 (KNO₃ supporting electrolyte). The thermodynamic parameters of formation of phenylalaninatocopper(II) complexes were calculated for various temperatures.     

Complex formation equilibria of L-Amino-Acid amides with copper(II) in aqueous solution

Protonation and Cu(II) complexation equilibria of L -phenyhilaninamide, N²-methyl-L-phenylalaninamide, N², N²-dimethyl-L-phenylalaninamide, L -valinamide, and L -prolinamide have been studied by potentiometry in aqueous solution. The formation constants of the species observed, CuL²⁺, CuL, CuLH, CuL₂H and CuL₂H_?2, are discussed in relation to the structures of the ligands. Possible structures of bisamidato complexes are proposed on the ground of VIS and CD spectra. Since Cu(II) complexes of the present ligands (pH range 6–8) perform chiral resolution of dansyl- and unmodified amino acids in HPLC (reversed phase), it is relevant for the investigation of the resolution mechanism to know which are the species potentially involved in the recognition process.     

Mercury(II) penicillamine complex formation in alkaline aqueous solution

The complex formation between mercury(II) and penicillamine (H(2)Pen = 3,3'-dimethyl cysteine) in alkaline aqueous solutions (pH approximately 2) has been investigated with extended X-ray absorption fine structure (EXAFS) and 199Hg NMR spectroscopy. By varying the penicillamine concentration (C(H(2)Pen) = 0.2-1.25 M) in approximately 0.1 M Hg(II) solutions, two coexisting major species [Hg(Pen)2](2-) and [Hg(Pen)3](4-) were characterized with mean Hg-S bond distances 2.34(2) and 2.44(2) A, respectively. The [Hg(Pen)2](2-) complex with two deprotonated penicillamine ligands forms an almost linear S-Hg-S entity with two weak chelating Hg-N interactions at the mean Hg-N distance 2.52(2) A. The same type of coordination is also found for the corresponding [Hg(Cys)2](2-) complex in alkaline aqueous solution with the mean bond distances Hg-S 2.34(2) A and Hg-N 2.56(2) A. The relative amounts of the [Hg(Pen)2](2-) and [Hg(Pen)3](4-) complexes were estimated by fitting linear combinations of the EXAFS oscillations to the experimental spectra. Also their (199)Hg NMR chemical shifts were used to evaluate the complex formation, showing that the [Hg(Pen)3](4-) complex dominates already at moderate excess of the free ligand ([Pen(2-)] > approximately 0.1 M).     

Kinetics and mechanism of interaction of Pt(II) complex with bio-active ligands and in vitro Pt(II)-sulfur adduct formation in aqueous medium: bio-activity and computational study

Kinetics of interaction between [Pt(pic)(H₂O)₂](ClO₄)₂, 2 (where pic = 2-aminomethylpyridine) with the selected ligands DL-methionine (DL-meth) and DL-penicillamine (DL-pen) have been studied spectrophotometrically in aqueous medium separately as a function of [2] as well as [ligand], pH and temperature at constant ionic strength. The association equilibrium constants (K_E) for the outer sphere complex formation have been evaluated together with the rate constants for the two subsequent steps. Activation parameters (enthalpy of activation ΔH^≠ and entropy of activation ΔS^≠) were calculated from the Eyring equation. An associative mechanism of substitution is proposed for both reactions on the basis of the kinetic observations, evaluated activation parameters, and spectroscopic data. Structural optimizations, HOMO-LUMO energy calculation, and Natural Bond Orbital (NBO) analysis of 2–4 were carried out with Density Functional Theory. Bonding mode of thiol and thio-ether is confirmed by spectroscopic analyses and NBO calculation. Cytotoxic properties of 2–4 were explored on A549 carcinoma cell lines; DNA-binding properties of the complexes were also investigated by gel electrophoresis.     

Kinetics and mechanism of formation of square-planar copper(II) and nickel(II) complexes of ethylenebisbiguanide in aqueous acetate buffer media

Summary The kinetics of formation of square-planar Cu^II and Ni^II complexes of the quadridentate ligand, ethylenebisbiguanide, have been studied spectrophotometrically in aqueous HOAc–NaOAc buffer, at ionic strength 0.2 mol dm^–3, in the 25–35°C temperature range. The observed rate constants for the formation reactions are independent of pH (and of OAc^– concentration) in the pH range used (3.6–4.8 for Cu^II and 5.0–5.8 for Ni^II) where the product complexes form stoichiometrically, but show first-order dependence on the ligand concentration;i.e. k_obs=k_f[L]_total. At 25°C k_f values (dm³ mol^–1s^–1) are 35.2±0.4 for Cu^II and (8.4±0.1)×10^–3 for Ni^II. The mechanism of the reactions is discussed.     

Kinetics of the dissolution of copper metal in aqueous solutions containing unsaturated organic ligands and copper(II)

The kinetics of the dissolution of copper metal in an aqueous solution containing copper(II) and an unsaturated organic ligand was followed by using an automated flow-injection analysis technique to determine the concentration of copper(I) in solution as a function of time. The results suggest that the rate of dissolution of the copper metal is dependent on electron transfer between the copper(II) and copper atoms on the surface of the copper metal, and on the stabilization of copper(I) by the unsaturated organic ligand in solution.     

Kinetics of complexation of nickel (II) and copper (II) with some azophenol derivatives in aqueous nonionic surfactant solution

The kinetics of formation of 11 complexes of nickel(II) and copper(II) ions with some azophenol derivatives in aqueous and micellar solution of a nonionic surfactant, Triton X-100, have been studied by a stopped-flow spectrophotometric method. Second order rate constants for the reactions were determined at 298 K and ionic strength 0.1 (NaClO₄) in aqueous solution. In the surfactant solution, the pseudo-first-order rate constants for the complexation reactions,k_obs, decreased with increasing the concentration of Triton X-100. This observation was explained by the assumption that the chelating reagents distribute between the micelle of the surfactant and bulk aqueous phase and rate-controlling reactions occur only in the bulk aqueous phase. On the basis of the relation betweenk_obs and the concentration of the surfactant, the partition constants of the reagents between micellar and aqueous phases were determined.     

Mixed complex formation of lead(II) and mercury(II) ethylenediaminetetraacetates with thiourea in an aqueous solution

The formation of mixed-ligand complexes HgEdtaThio²⁻, HgEdtaS₂O₃⁴⁻, PbEdtaThio²⁻, and Pb(Thio) _i ²⁺, i = 1, 2; Thio is thiourea) was studied by calorimetry, pH metry, and ¹H and ¹³C NMR spectroscopy. The thermodynamic parameters (logK, Δ _r G ⁰, Δ _r H, and Δ _r S) for the formation of the complexes at 298.15 K and the ionic strength I = 0.5(NaClO₄) were determined. The most probable coordination mode of the ligands in the mixed complex was considered.     

Thermodynamics of complex formation of Cu(II) ethylenediaminetetraacetate with ethylenediamine in aqueous solution

The formation of mixed-ligand complexes in the system Cu²⁺-Edta^4?-En was studied by the calorimetric and pH-potentiometric methods at 298.15 K and I = 0.5(KNO₃). The thermodynamic characteristic of the CuEdtaEn^2? complex formation were determined.     

Complex formation studies on copper(II) and zinc(II) with asparagine and aspartic acid in aqueous solution

The complex equilibria of the systems copper—aspartic acid, zinc—aspartic acid, copper—asparagine, and zinc—asparagine have been studied by computer analysis of potentiometric data.     

Fe(II)三脚架多咪唑配合物的合成与性质表征

三脚架结构配体与过渡金属离子形成的配合物具有较高的热力学稳定性、动力学惰性及特殊的配位模式,显示出优良的物理和化学性质,因而在化学、生物和材料等领域具有潜在的应用价值.三脚架有机多胺自1926年F.G.Mann等合成了Ni与三(3-氨基乙基)胺的配合物后,以后有很多类似结构的出现.