Potentiometric studies of binary and ternary complexes of Zn(II) with triethylenetetramine as primary ligand and selected amino acids and DNA units as secondary ligands

The acid-base equilibria of triethylenetetramine. (Trien) and the formation equilibria of binary and ternary complexes of Zn(II) with Trien as primary ligand and some selected arnino acids and DNA units as secondary ligands have been investigated. The results showed the formation of a 11 Zn (Trien)²⁺ complex. At higher pH, the Zn (Trien)²⁺ complex is hydrolysed to give Zn (Trien) (OH)⁺ and Zn(Trien)(OH)₂ complexes. The fraction of the monohydroxo species attains a maximum of 81.3% at pH 10. The stability constantsK _Zn(Trien)A ^Zn(Trien) for the ternary complexes were determined. Histidine coordinates in a histamine-like way. Lysine and ornithine ligate by the two amino groups. Serine and methionine are bound in a glycine-like mode. However, penicillamine, cysteine and glutathione ligate partly like mercaptoethylamine and partly like mercaptopropionic acid. In the case of DNA complexes, inosine is bound through the n₁ atom. However, uracil, undine, thymine and thymidine ligate through the N₃ atom. The relative stabilities of ternary complexes are compared with those of the corresponding binary complexes in terms of logK values. The concentration distribution diagrams of the complexes are evaluated.     

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.     

Interaction of dipropyltin(IV) with amino acids,peptides, dicarboxylic acids and DNA constituents

Interaction of dipropyltin(IV) with selected amino acids, peptides, dicarboxylic acids or DNA constituents was investigated using potentiometric techniques. Amino acids form 1?:?1 and 1?:?2 complexes and, in some cases, protonated complexes. The amino acid is bound to dipropyltin(IV) by the amino and carboxylate groups. Serine is complexed to dipropyltin(IV) with ionization of the alcoholic group. A relationship exists between the acid dissociation constant of the amino acids and the formation constants of the corresponding complexes. Dicarboxylic acids form both 1?:?1 and 1?:?2 complexes. Diacids forming five- and six-membered chelate rings are the most stable. Peptides form complexes with stoichiometric coefficients 111(MLH), 110(ML) and 11-1(MLH_?1)(tin: peptide: H⁺). The mode of coordination is discussed based on existing data and previous investigations. DNA constituents inosine, adenosine, uracil, uridine, and thymine form 1?:?1 and 1?:?2 complexes and the binding sites are assigned. Inosine 5′-monophosphate, guanosine 5′-monophosphate, adenosine 5′-monophosphate and adenine form protonated species in addition to 1?:?1 and 1?:?2 complexes. The protonation sites and tin-binding sites were elucidated. Cytosine and cytidine do not form complexes with dipropyltin(IV) due to low basicity of the donor sites. The stepwise formation constants of the complexes formed in solution were calculated using the non-linear least-square program MINIQUAD-75. The concentration distribution of the various complex species was evaluated as a function of pH.     

Mixed ligand complexes of [Pd(terpy)(H2O)]2+ with some selected amino acids,peptides, DNA and related ligands

Stability constants of the ternary palladium(II) complexes of triamine 2,2′:6′,2″-terpyridine (terpy) and some amino acids, peptides, DNA constituents or thiols were determined at 25 °C and at constant 0.1 mol dm⁻³ ionic strength, adjusted using NaNO₃. The coordination sites are pH-dependent. The results show the formation of binuclear species, 210. The speciation diagrams of various complex species were evaluated as a function of pH. Good correlations were found between the stability constants of the complexes and basicity of ligands.     

Coordination modes of histidine- or methioninehydroxamic acids in copper(II) mixed-ligand complexes with ethylenediamine in aqueous solution

The stability constants and coordination modes of the mixed-ligand complexes formed by copper(II) ion and ethylenediamine as a primary ligand and methioninehydroxamic acid (Metha) or histidinehydroxamic acid (Hisha) as a secondary ligand L were determined by potentiometric titration, UV–Vis and EPR spectroscopy. The obtained results suggest the formation of mixed-ligand species in basic solution with 4N coordination – both amine and hydroxamic nitrogens of Metha or Hisha (NH₂, N_ha) and two amine nitrogens of en (2 × NH₂) in the equatorial plane.     

Equilibrium investigation of complex formation reactions involving copper(II), nitrilo-tris(methyl phosphonic acid) and amino acids,peptides or DNA constitutents. The kinetics,mechanism and correlation of rates with complex stability for metal ion promoted hydrolysis of glycine methyl ester

The complex formation reactions of [Cu(NTP)(OH₂)]^4? (NTP?=?nitrilo-tris(methyl phosphonic acid)) with some selected bio-relevant ligands containing different functional groups, are investigated. Stoichiometry and stability constants for the complexes formed are reported. The results show that the ternary complexes are formed in a stepwise mechanism whereby NTP binds to copper(II), followed by coordination of amino acid, peptide or DNA. Copper(II) is found to form Cu(NTP)H _n species with n?=?0, 1, 2 or 3. The concentration distribution of the various complex species has been evaluated. The kinetics of base hydrolysis of glycine methyl ester in the presence of copper(II)-NTP complex is studied in aqueous solution at different temperatures. It is proposed that the catalysis of GlyOMe ester occurs by attack of OH^? ion on the uncoordinated carbonyl carbon atom of the ester group. Activation parameters for the base hydrolysis of the complex [Cu(NTP)NH₂CH₂CO₂Me]^4? are, ΔH^±?=?9.5?±?0.3?kJ?mol^?1 and ΔS^±?=??179.3?±?0.9?J?K^?1?mol^?1. These show that catalysis is due to a substantial lowering of ΔH^±.     

Palladium (II) complexes chelated by 1-substituted-4-pyridyl-1H-1,2,3-triazole ligands as catalyst precursors for selective ethylene dimerization

A series of neutral as well as cationic palladium methyl complexes bearing 1-substituted-4-pyridyl-1H-1,2,3-triazole ligands were prepared and fully characterized by a range of analytical techniques. Conventional and 2D NMR spectroscopy as well as single-crystal X-ray diffraction analysis unambiguously determined the molecular structure of the complexes. The neutral complexes activated by methylaluminoxane were found to be effective catalysts in the ethylene dimerization reaction. The catalyst performance of the in-situ-generated active species was compared with the discrete cationic complexes of the same ligand scaffold. Activities and selectivities for the two systems were remarkably similar, pointing to similarities in the nature of the active species. Both catalytic systems showed a strong correlation of activity and selectivity with the nature of the ligand scaffold. Highest activities were attained when electron-withdrawing groups were incorporated into the triazole ring, while increasing steric bulk in the ortho-position on the pyridyl ring of the ligand led to the almost exclusive dimerization of ethylene with selectivities up to 94% observed toward 1-butene.     

Unexpected formation of the copper(II) dinuclear mixed-ligand species in the ternary system of N,N,N′,N″,N″-pentamethyldiethylenetriamine with methionine- or histidinehydroxamic acids in aqueous solution

Equilibrium studies of the mixed-ligand complexes of the copper(II) ion with pentamethyldiethylenetriamine (N,N,N′,N″,N″-pentamethyl-[bis(2-aminoethyl)amine], Me₅dien) as a primary ligand and methioninehydroxamic acid (2-amino-4-(methylthio)butanehydroxamic acid, Metha) or histidinehydroxamic acid (2-amino-3-(4′-imidazolyl)propanehydroxamicacid, Hisha) as a secondary ligand L were performed by potentiometric titration, UV–Vis and EPR spectroscopy. The results show that in these ternary systems the dinuclear [Cu₂(Me₅dien)L₂H₋₁]⁺ mixed-ligand species is formed as a predominant one in the basic solution. The monouclear [Cu(Me₅dien)L]⁺ species is formed in low concentration. Our spectroscopic results indicate that the geometry of these mixed-ligand five-coordinate complexes is strongly distorted towards trigonal-bipyramidal.     

Anticancer metallopharmaceutical agents based on mixed‐ligand palladium(II) complexes with dithiocarbamates and tertiary organophosphine ligands

Mixed‐ligand palladium(II) complexes of the type [(DT)Pd(PR₃)Cl], where DT = diethyldithiocarbamate (1), dibutyldithiocarbamate (2,3), dipropyldithiocarbamate (4,5), bis(2‐methoxyethyl)dithiocarbamate; PR₃ = benzyldiphenylphosphine (1,4), diphenyl‐o‐tolylphosphine (2), diphenyl‐t‐butylphosphine (3), P‐chlorodiphenylphosphine (5) and triphenylphosphine (6), have been synthesized and characterized by elemental analyses and FT‐IR, Raman and multinuclear NMR spectroscopy. The structures of compounds 1 and 2 were determined by single‐crystal X‐ray diffraction (XRD) measurements and these analyses showed that the complexes have pseudo square‐planar geometry around the Pd(II) and that the dithiocarbamate ligand is bound in a bidentate fashion, while the remaining two positions are occupied by a tertiary organophosphine and a chloride ligand. The anticancer studies showed that the Pd(II) complexes are highly active against cisplatin‐resistant DU145 human prostate carcinoma (HTB‐81) cells with the highest activity shown by compound 6 (IC₅₀ = 2.12 µm ). The redox behavior and ds‐DNA‐denaturing ability of the complexes were studied by cyclic voltammetry and two reduction and one oxidation waves were observed. The decrease in the reduction peak currents illustrated the consumption of the mixed‐ligand drug by the DNA molecule. Copyright © 2013 John Wiley & Sons, Ltd.     

Mixed ligand complexes of palladium(II) with diethylenetriamine as a primary ligand and amino acids as secondary ligands

Summary Equilibrium studies of mixed ligand complexes of palladium(II) containing diethylenetriamine as a primary ligand and amino acids as secondary ligands were made by the pH titration method at 25° C and ionic strengthM=0.1. Different equilibrium constants, characteristic of binary and mixed ligand complexes were calculated and the chelation mode was deduced from conductivity measurements.     

Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine,diethylenetriamine or N,N,N′,N″,N″-pentamethyldiethylenetriamine in aqueous solution

Solution equilibrium studies on the Cu(II)–polyamine–histidine ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N″,N″-pentamethyldiethylenetriamine (Me₅dien)) have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods. The obtained results suggest the formation of the mixed-ligand complexes with [Cu(A)(His)]⁺ stoichiometry in all studied systems. Additionally, in the systems with dien and Me₅dien protonated [Cu(A)(H–His)]²⁺ species also exists in acid solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(His)]⁺, the geometry slightly deviated from square pyramidal for the [Cu(dien)(His)]⁺ and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me₅dien)(His)]⁺ species. The coordination modes in these mixed-ligand complexes are discussed.     

Syntheses and characterization of nickel(II), zinc(II) and palladium(II) complexes derived from three pyrazole-based polydentate ligands

Two pyrazole-based polydentate ligands, 1,3-bis(5-methyl-3-phenylpyrazol-1-yl)-propan-2-ol (Hmppzpo) and 1,3-bis(5-methyl-3-p-isopropylphenylpyrazol-1-yl)-propan-2-ol (Hmcpzpo), have been synthesized. A third ligand, 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-2-ol (Hdmpzpo), has been synthetically modified. Seven new M(II) coordination compounds of general formula M₂L₂X₂ (M?=?Zn, Ni; X?=?NO₃ or ClO₄; L?=?dmpzpo, mppzpo or mcpzpo) or MLX (M?=?Pd; L?=?dmpzpo; X?=?Cl) were synthesized and structurally characterized by elemental analysis and FT-IR analysis. The crystal structures of [Zn₂(μ-dmpzpo-O,N,N′)₂(NO₃)₂]?·?2H₂O (1?·?2H₂O), [Ni₂(μ-dmpzpo-O,N,N′)₂(CH₃CN)₂](ClO₄)₂ (2) and Pd(μ-dmpzpo-N,N′)Cl₂ (4) were determined by single-crystal X-ray crystallography. The crystal structures show that complexes 1?·?2H₂O and 2 are center-symmetric dinuclear compounds, with two metal ions bridged by two alkoxo groups and each metal ion with a distorted square-pyramidal environment. The palladium complex, 4, displayed square-planar coordination geometry around the Pd(II) ion with trans arrangement.     

Synthesis and characterization of novel water-soluble zinc(II) Schiff-base complexes derived from amino acids and salicylaldehyde-5-sulfonates

New water-soluble zinc(II) Schiff-base complexes derived from amino acids (glycine, L-phenylalanine, and L-valine) and salicylaldehyde-5-sulfonates (sodium salicylaldehyde-5-sulfonate and sodium 3-methoxy-salicylaldehyde-5-sulfonate) have been synthesized. The complexes were characterized by elemental analysis, IR, electronic, ¹H?NMR, and ¹³C?NMR spectra. In the IR spectra of the complexes, the large difference between the asymmetric ν_as(COO) and symmetric ν_s(COO) carboxylate stretch, Δν(ν_as(COO)–ν_s(COO)) of 199–247?cm^?1, indicates monodentate coordination of the carboxylate group. Spectral data showed that in these complexes the ligand is a tridentate ONO moiety, coordinating to the metal through its phenolic oxygen, imine nitrogen, and carboxyl oxygen.     

Synthesis,characterization, equilibrium studies,and biological activity of complexes involving copper(II), 2-aminomethylthiophenyl-4-bromosalicylaldehyde Schiff base,and selected amino acids

Ternary complexes of copper(II) with 2-aminomethylthiophenyl-4-bromosalicylaldehyde (ATS) and some amino acids have been isolated and characterized by elemental analyses, IR, magnetic moment, molar conductance, UV–vis, mass spectra, and ESR. The proposed general formulas of the prepared complexes are [Cu(ATS)(AA)]·nH₂O (where AA?=?glycine, alanine, and valine). The low molar conductance values suggest the non-electrolytic nature of the complexes. IR spectra show that ATS is coordinated to copper in a bidentate manner through azomethine-N and phenolic-OH. The amino acids also are monobasic bidentate ligands via amino and ionized carboxylate groups. The magnetic and spectral data indicate the square-planar geometry of Cu(II) complexes. The geometry of the Cu(II) complexes has been fully optimized using parameterized PM3 semiempirical method. The Cu–N bond length is longer than that of Cu–O in the isolated complexes. Also, information is obtained from calculations of molecular parameters for all complexes including net dipole moment of the metal complexes, values of binding energy, and lipophilicity value (log P). The antimicrobial activity studies indicate significant inhibitory activity of complex 3 against the selected types of bacteria. The mixed ligand complexes have also been studied in solution state. Protonation constants of ATS and amino acids were determined by potentiometric titration in 50% (v/v) DMSO–water solution at ionic strength of 0.1?M NaCl. ATS has two protonation constants. The binary and ternary complexes of copper(II) involving ATS and some selected amino acids (glycine, alanine, and valine) were examined. Copper(II) forms [Cu(ATS)], [Cu(ATS)₂], [Cu(AA)], [Cu(AA)₂], and [Cu(ATS)(AA)] complexes. The ternary complexes are formed in a simultaneous mechanism.     

Synthesis and characterization of some potential antitumor palladium(II) complexes of 2-aminomethylbenzimidazole and amino acids

The stoichiometry and stability constants of complexes formed between [Pd(AMBI)(H₂O)₂]²⁺ (AMBI?=?2-(aminomethyl)-benzimidazole) with some selected bio-relevant ligands containing different functional groups were investigated at 25°C and 0.1?mol?L^?1 ionic strength. The ligands used are imidazole, cysteine, glutathione (GSH), threonine, aspartic acid, 1,1-cyclobutane dicarboxylic acid (CBDCA) and lysine. The stoichiometry and stability constants of the formed complexes were reported and the concentration distribution of the various complex species was evaluated as a function of pH. The results show ring opening of CBDCA and monodentate complexation of the DNA constituent with the formation of [Pd(AMBI)(CBDCA–O)DNA], where (CBDCA–O) represents cyclobutane dicarboxylate coordinated by one carboxylate oxygen. The equilibrium constant of the displacement reaction of coordinated inosine, as a typical DNA constituent, by glutathione, as a typical thiol ligand, was investigated. The effect of dioxane on the formation constant of CBDCA with Pd(AMBI)²⁺ is reported. Five new palladium(II) complexes of the formula [Pd(AMBI)(AA)] ^{n +} (where AMBI?=?2-aminomethyl benzimidazole, AA is an anion of glycine, alanine, cysteine, methionine, and serine) have been synthesized. These palladium(II) complexes have been ascertained by elemental, molar conductance, infrared and ¹H-NMR spectroscopy. The isolated Pd(II) complexes were screened for their antibacterial and cytotoxic activities and the results are discussed.     

Synthesis and DNA cleavage properties of ternary Cu(II) complexes containing histamine and amino acids

The ternary complexes of [Cu^II(Hist)(Tyr)]⁺1 and [Cu^II(Hist)(Trp)]⁺2 have been synthesized, structurally characterized and their DNA binding and cleavage abilities probed. The intrinsic binding constants (K_b) for complexes/CT-DNA were also determined (K_b = 2.7 × 10² for complex 1 and K_b = 2.2 × 10² for complex 2). These complexes exhibit their nuclease activity on plasmid DNA, which seems to depend on the nature of the aromatic moiety. The DNA hydrolytic cleavage rate constants were also determined for complexes 1 and 2, which are 0.91 and 0.79 h⁻¹, respectively.     

Copper(II) complexation by (pyridinyl)aminomethane-1,1-diphosphonic acid derivatives; spectroscopic and potentiometric studies

The complex formation between copper(II) and (pyridinyl)aminomethane-1,1-diphosphonic acid derivatives was studied by means of pH-potentiometry, spectroscopic methods (UV-Vis, EPR) and mass spectrometry (MS). The bisphosphonate ligands form polynuclear Cu₃H_xL₃ (x = 4 ,3, 2, 1, 0, −1) species besides the mononuclear 1:1 and 1:2 metal-to-ligand molar ratio complexes. Two phosphonate groups are basic binding sites for the metal ion. It is suggested that in the polynuclear complexes the ligands adopt chelating and bridging modes via the four oxygen atoms of the two phosphonate groups.     

Synthesis and characterization of water-soluble zinc(II) Schiff-base complexes derived from amino acids and 3-formyl-4-hydroxybenzyl-triphenylphosphonium chloride

Tridentate Schiff-base ligands derived from condensation of 3-formyl-4-hydroxybenzyl-triphenylphosphonium chloride with glycine, L-alanine, L-valine, L-leucine and L-phenylalanine in the presence of Zn(OAc)₂ · 2H₂O form five new water-soluble Zn(II) complexes, which were characterized by elemental analyses, IR, electronic absorption and ¹H, ¹³C NMR spectroscopies. In the IR spectra of the complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequencies is larger than ～210 cm^?1, which implies that the carboxylate groups are monodentate. UV-Vis electronic absorption studies show that Zn(II) functions as a trap for the Schiff-base intermediate. Schiff-base complexes formation were confirmed by the appearance of new signals in the ¹H NMR for the azomethine hydrogen at ～8 ppm and condensed L-amino acids at 3.4–3.8 ppm (C(3)–H). These complexes are formed through coordination of the ONO from the carboxyl, imino and phenoxy groups of the ligands to Zn(II).     

Palladium(II) and platinum(II) complexes of bidentate 2-pyridyl-1,2,3-triazole “click” ligands: Synthesis,properties and X-ray structures

The synthesis and characterization of palladium(II) and platinum(II) complexes of isomeric bidentate 2-pyridyl-1,2,3-triazole “click” ligands is reported. The complexes have been fully characterized by elemental analysis, HRESI-MS, IR, UV–Vis, ¹H and ¹³C NMR spectroscopy. Additionally, the molecular structures of the Pd(II) and Pt(II) complexes of the 2-[(4-phenyl-1H-1,2,3-triazol-1-yl)methyl]pyridine ligand are confirmed by X-ray crystallography. Solution studies indicate the 2-(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine ligand forms more stable complexes with Pd(II) and Pt(II) than the isomeric 2-[(4-phenyl-1H-1,2,3-triazol-1-yl)methyl]pyridine ligand.     

Preparation and separation of mixed-ligand Fe(II) complexes containing 1,10-phenanthroline-5,6-dione as ligand

The synthesis, separation, and characterization of mixed-ligand iron(II) complexes containing 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione (pdon), and NCS^? are reported. The mixed-ligand complexes [Fe(phen)(pdon)₂]²⁺ and [Fe(phen)₂(pdon)]²⁺ were prepared from iron(II) sulfate hepta hydrate and both ligands. The mixture of both complexes formed regardless the ratio of the ligands or the reaction time; therefore, the complexes were separated successfully on the reversed phase (RP) Develosil RP-Aqueous [C30] 5?µm, 150?×?4.6?mm column by two different methods. The first method was the ion paired RP chromatography performed under gradient elution with acetonitrile–water containing 0.001?mol?L^?1 KPF₆ aqueous as mobile phases. The second method was the RP chromatography performed under gradient elution with methanol and water as mobile phases. The gradient elution with water–methanol as eluents was preferred for the semi preparative separations allowing one to use the complexes without further purification upon separation, different than the first method and its variations so far. Three complexes (5, 6, and 7) were characterized by electrospray ionization mass spectrometry, NMR, UV-Vis, and IR.