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.     

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.     

Coordination properties of some nickel(II) monophosphono dipeptides species in aqueous solution: The role of phosphonic oxygen in complex stabilization and ligand-fields analysis

Equilibrium studies on the nickel(II) complexes of oxygen and nitrogen donor ligand (monophosphono dipeptides: 1- (N-l-leucylamino)methylphosphonic acid – Leu-Gly(P), and a thioether sulfur donor ligands (monophosphono dipeptides: 1-N-(glycyloamino)-2-(S-benzylthio)ethanephosphonic acid – Gly-(Bz)Cys(P), d(−) and Gly-(Bz)Cys(P), d(+) were performed by potentiometric titration and NIR–Vis spectroscopy. Additionally, the ligand-field parameters (CFM/AOM) were estimated and discussed in the tetragonal distortion framework. The lowest tetragonal distortion was observed in the case of the [NiHL] species, whereas the strongest in the case of [NiL₂] species. In the latter species the ligand-field analysis confirms the coordination of the deprotonated phosphonic groups to the metal ions in both axial positions. In the case of nickel(II) complexes with Gly-(Bz)Cys(P), d(−) or Gly-(Bz)Cys(P), d(+) additional interaction between sulfur donor atom and nickel(II) was suggested.     

Synthesis, structural and magnetic properties of diphenoxo-bridged binuclear mixed-ligand Cu(II) complexes

The copper(II) complexes [Cu₂(phen)₂(HL¹)₂] (ClO₄)₂ (1) and [Cu₂(phen)₂(HL²)₂] (ClO₄)₂ (2) synthesized from two potentially tridentate ligands N-(2-hydroxybenzyl) propanolamine (H₂L¹) and N-(5-methyl-2-hydroxybenzyl) propanolamine (H₂L²) have centrosymmetric bis(μ₂-phenoxo)-bridged dicopper(II) structures. Variable temperature magnetic measurements have revealed the existence of relatively weak antiferromagnetic interactions (1: 2J=−212.5, 2: 2J=−337.0 cm⁻¹) with respect to the bridging angles (1: θ=101.47(18)°, 2: θ=102.79(12)°). The results suggest that the distortion index of the Cu(II) atoms (1: τ=0.73, 2: τ=0.53) may be the major factor governing the spin coupling between the copper(II) centers of these diphenoxo-bridged binuclear complexes. The coordination moieties of complex 1 are connected into a 1D linear structure via intermolecular hydrogen bonds between alkoxyl, amine, and perchlorate groups.     

Studies on the mixed-ligand complexes of copper(II) with gallic acid and pyridine carboxylic acids and their benzologues

Summary The ternary complex formation of copper(II) with gallic acid (gal) and 2-hydroxy nicotinic acid (hyna), 2-mercapto nicotinic acid (mena), salicylic acid (sa) or thiosalicylic acid (tsa) as a second ligand in a 1:1:1 molar ratio has been investigated in 40% (v/v) ethanol using spectrophotometric andpH titration methods. The solution equilibria of the ternary systems have been determined and the stability constants of the mixed complexes has been evaluated. Considering all parameters, the Cu-gal-sa ternary system was proved as a suitable, rapid, and sensitive spectrophotometric indicator for determining traces of copper.The ternary system containingsa obeysBeer's law up to 3.4 µg·ml^–1 copper. The optimum range for the determination of copper (Ringbom) atpH 6.0 ranges from 0.63 to 1.74 µg·ml^–1 of copper. The molar absorptivity of the ternary complex is 1.3×10⁴l·mol^–1·cm^–1.

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Untersuchungen anmixed-ligand — Komplexen von Kupfer(II) mit 3,4,5-Trihydroxybenzoesäure und Pyridincarbonsäuren und ihren C-Homologen

Zusammenfassung Die Bildung ternärer Komplexe von Kupfer(II) mit 3,4,5-Trihydroxybenzoesäure (gal) und 2-Hydroxynicotinsäure (hyna), 2-Mercaptonicotinsäure (mena), Salicylsäure (sa) oder Thiosalicylsäure (tsa) in einem molaren Verhältnis von 1:1:1 wurde mittels spektrophotometrischer und potentiometrischer Methoden in 40% (v/v) Ethanol untersucht. Die Lösungsgleichgewichte der termären Systeme und die Stabilitätskonstanten der gemischten Komplexe wurden bestimmt. Unter Berücksichtigung aller Parameter erwies sich das termäre System Cu-gal-sa als geeigneter schneller und empfindlicher Indikator zur Spurenanalyse von Kupfer.Dassa enthaltende ternäre System gehorcht demBeerschen Gesetz bis zu einer Kupferkonzentration von 3.4 µg·ml^–1. Der optimale Bereich zur Bestimmung von Kupfer (Ringbom) beipH 6.0 erstreckt sich von 0.63 bis 1.74 µg Cu pro ml. Die molare Extinktion des ternären Komplexes beträgt 1.3×10⁴l·mol·cm^–1.

     

Chromotropism studies on copper(II) compounds. Part II. Dinuclear copper(II) complexes with triply-bridged hydroxo,acetate, and halo ligands

Abstract

Two triply-bridged dinuclear copper(II) complexes of formula [LCu(μ-OH)(μ-OAc)(μ-X)CuL]X?0.5H₂O where L is a bidentate ligand of N-(pyridine-2-ylmethyl)propane-2-amine and X=Cl, 1 and Br, 2 were synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–Vis, EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar. The complexes show a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₂X chromophore in which both copper(II) ions are connected by a hydroxo bridge and a triatomic syn-syn carboxylato bridge in equatorial positions and a halide ion bridge at the axial site. The chromotropism behavior of the complexes, including solvato-, thermo-, and halochromism, were investigated in detail. Their halochromism was investigated in the pH range of 2.0–11.0 by visible absorption spectroscopy. The reversible color variations from blue to colorless are attributable to deprotonation and protonation of the ligands. The complexes show reversible thermochromism in solution due to dissociation and recombination of ligands to copper ions.     

Mixed-ligand complexes of palladium(II) involving propane 1,2,3-triamine as primary ligand and amino acids,peptides, or DNA units as secondary ligands

Summary The acid-base equilibria of propane 1,2,3-triamine (PTA) and the formation equilibria of binary and ternary complexes of palladium(II) withPTA as primary ligand and amino acid, peptide, and DNA subunits as secondary ligand have been investigated. Pd(II) is found to form a 1:1 complex withPTA. The ternary complexes are formed in a stepwise mechanism, wherebyPTA first binds to Pd(II) and then ligates to the secondary ligand. The hydrolysis of the Pd-PTA complex and the deprotonation of the amide residues in the peptide complexes are discussed in relation to physiological conditions.

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Gemischte Palladium(II)-Komplexe mit Propan-1,2,3-triamin als Primärligand und Aminosäuren, Peptiden oder DNA-Einheiten als Sekundärliganden

Zusammenfassung Das Säure-Basen-Gleichgewicht von Propan-1,2,3-triamin (PTA) und die Bildungsgleichgewichte von binären und ternären Komplexen von Pd(II) mitPTA als Primärligand und Aminosäuren, Peptiden und DNA-Einheiten als Sekundärliganden wurden untersucht. Pd(II) bildet mitPTA einen 1:1-Komplex. Die ternären Komplexe werden stufenweise gebildet, wobeiPTA zuerst an Pd(II) koordiniert; dann erfolgt die Bindung an den Sekundärliganden. Die Hydrolyse des Pd-PTA-Komplexes und die Deprotonierung der Amide in den Peptidkomplexen werden im Zusammenhang mit physiologischen Bedingungen diskutiert.

     

EPR Spectra of Copper(II) Complexes with N,N-Dialkyl Amino Acids. The Influence of Water dissolved in Organic Solvents on the Copper(II) Coordination Sphere

EPR spectra of four bis(N,N-dialkyl-L-α-aminoacidato) copper(II) complexes were studied with the aim to determine the effect of the water molecules dissolved in organic solvents on the electronic states of copper(II). It was shown that water dissolved in methylene chloride or dioxan influence the copper(II) electronic states. If the amino acid side chains are long enough to form the aliphatic intramolecular van der Waals contacts, the water molecules will induce the change in the conformation of the whole complex.     

Syntheses,equilibrium, and structural studies of copper(II) and nickel(II) complexes with a tripodal alanine-based ligand

A heptadentate ligand, tris[(L)-alanyl-2-carboxamidoethyl]amine (H₃trenala), has been synthesized as its tetrahydrochloride salt; its protonation constants and the stability constants of the copper(II) and nickel(II) chelates have been determined by potentiometry. Mononuclear species with protonated, neutral, or deprotonated forms of the ligand, [Cu(H₅trenala)]⁴⁺, [M(H₄trenala)]³⁺, [M(H₃trenala)]²⁺, [M(H₂trenala)]⁺, and [M(Htrenala)] (M?=?Cu²⁺ and Ni²⁺) have been detected in all cases, while only Cu²⁺ gives dinuclear [Cu₂(H₂trenala)]²⁺, [Cu₂(Htrenala)]²⁺, [Cu₂(trenala)]⁺, and [Cu₂(trenala)(OH)] species. Two dinuclear copper(II) complexes have been prepared and characterized by spectroscopic techniques (IR, UV-Vis, mass electro-spray) and thermogravimetric analysis.     

Cyanide thermodynamics 2. Stability constants of copper(I) cyanide complexes in aqueous acetonitrile mixtures

The stability (formation) constants of the binary Cu(I)-CN⁻ complexes have been measured in five aqueous mixtures containing from 10% to 70% v/v acetonitrile (MeCN) by glass electrode potentiometry at 25 °C and an ionic strength of l M (NaClO₄). The constants show monotonic increases with MeCN concentration, the changes being greatest for the higher order complexes, consistent with the unfavourable solvation of CN ⁻ in these mixtures. The sparing solubility of CuCN(s) prevented determination of the stability constant for CuCN ⁰ (soln.) at low MeCN concentrations.     

Ternary complexes in solution. Comparison of the coordination tendency of some polybasic oxygen acids toward the binary complexes of Cu(II) andAMP,ADP orATP

Summary Potentiometric equilibrium measurements have been made at 25±0.1°C (=0.1 mol dm^–3 KNO₃) for the interaction of adenosine-5-mono-, -di- and -triphosphate (AMP,ADP andATP) and Cu(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP, and secondary ligand acid, have been refined with the SUPERQUAD computer program. In some systems logK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. In some Cu(II) ternary systems the interligand interactions between the coordinate ligands, possibly H bond formation, have been found to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increase in the orderAMP <ADP <ATP. With respect to the secondary ligands, the formation constants of the mixed ligand complexes decrease in the order succinic > maleic > tartaric > malic > citric > oxalic acid.

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Ternäre Komplexe in Lösung. Vergleich der Koordinationstendenz einiger polybasischer Sauerstoffsäuren gegenüber binären Komplexen von Cu(II) mitAMP,ADP oderATP

Zusammenfassung Es wurden potentiometrische Gleichgewichtsmessungen bei 25±0.1°C bei =0.1 mol dm^–1 KNO₃ durchgeführt, um die Wechselwirkung von Adenosin-5-mono-, -di- und triphosphat mit Cu(II) und biologisch relevanten Sekundärliganden wie Äpfel-, Malein-, Bernstein-, Wein-, Zitronen- und Oxalsäure im Verhältnis 1:1:1 festzustellen. Aus den potentiometrischenpH-Titrationskurven ergaben sich verschiedene 1:1:1 gemischte Ligandenkomplexe. Anfänglich abgeschätzte Komplexbildungskonstanten der Komplexe und Säuredissoziationskonstanten vonAMP,ADP undATP und den Sauerstoffsäuren wurden mittels des Computerprogramms SUPERQUAD verfeinert. In einigen Systemen ist logK positiv, demzufolge sind die ternären Komplexe stabiler als die korrespondierenden binären. In einigen ternären Cu(II)-Komplexen bestehen zwischen den Liganden Wechselwirkungen, vermutlich auf der Basis von stabilitätsfördernden Wasserstoffbrückenbindungen. Die Stabilitäten der gemischten Komplexe steigen in der ReihenfolgeAMP <ADP <ATP. Bezüglich der Sekundärliganden ergibt sich für die Bildungskonstanten der ternären Komplexe die Reihung Bersteinsäure > Maleinsäure > Weinsäure > Äpfelsäure > Zitronensäure > Oxalsaure.

     

Complexation of copper(I) by thiourea in acidic aqueous solution

The interaction of copper(II) and copper(I) with thiourea(Tu) has been investigated by UV and visible spectrophotometry. Over the range of concentrations of copper(I) and Tu(0.1–20)×10^–3 mol-dm^–3 in acid aqueous solutions there are two complexes, CuTu₂ ⁺ (log ₂=11.1) and the other has the ratio Cu/Tu=1/1 with the likely composition Cu₂Tu₂ ²⁺ with log ₂₂=18.5. By the determination of copper(0) solubility in acid thiourea solution and potentiometric measurements it was shown that the potential of the copper electrode is that of a non-equilibrium (corrosive) electrode.     

Molecular complexes of hydrazides with copper(II)

Summary The reaction of substituted hydrazides with copper(II) chloride was investigated in the solid state or in solution in order to account for substituent effects. Spectroscopic results and values of the formation constants indicate the occurrence of strong complexes.

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Molekulare Komplexe von Hydraziden mit Kupfer(II)

Zusammenfassung Die Reaktionen von substituierten Hydraziden mit Kupfer(II)chlorid wurden im Festzustand und in Lösung untersucht. Die spektroskopischen Ergebnisse und die Werte der Bildungskonstanten zeigen die Koordinierung zu starken Komplexen an.

     

EPR study on the charge-transfer photochemistry of the bromide mixed-ligand dithiocarbamate complex of copper(II)

The EPR technique has been used to study the photolysis of the mixed-ligand complex Cu^II(Et₂dtc)Br in a 1:1 solvent mixture of chloroalkane and alcohol, where the chloroalkane is CCl₄, CHCl₃ or CH₂Cl₂ and the alcohol is MeOH, EtOH, i-PrOH or i-BuOH, in comparison with Cu^II(Et₂dtc)Cl photolysis in CHBr₃:ROH. It was found that while Cu^II(Et₂dtc)Br photolysis in chloroalkane:ROH yielded Cu^II(Et₂dtc)Cl as an intermediate, the opposite conversion of Cu^II(Et₂dtc)Cl to Cu^II(Et₂dtc)Br proceeded via Cu^II(Et₂dtc)Cl photolysis in CHBr₃:ROH. The final photolytic products in both cases were tetraethylthiuramdisulphide and the corresponding copper(II) salt (CuCl₂ or CuBr₂, respectively). The results obtained by EPR allowed to get some insight into the behaviour of the primary photolytic products towards both components of the mixed solvent.     

Restricting the versatile metal-binding behaviour of adenine by using deaza-purine ligands in mixed-ligand copper(II) complexes

In order to deepen our understanding of the versatile behaviour of adenine (Hade) as ligand, we have synthesized four novel ternary copper(II) complexes having two deazaadenine ligands, namely 4-azabenzimidazole (H4abim) or 7-azaindole (H7azain) as N1,N6-dideazaadenine or N1,N6,N7-trideazaadenine, respectively. The related compounds were studied by thermal, spectral and single crystal X-ray diffraction methods. In [Cu(NBzIDA)(H4abim)]_n (1) the recognition between H4abim and the (N-benzyliminodiacetate)-copper(II) chelate only displays the formation of the Cu–N7(purine-like) bond, in contrast to Hade behaviour in [Cu(NBzIDA-like)(Hade)(H₂O)]·H₂O (Cu–N3(Hade) bond reinforced by N9–H···O(IDA-like) interaction). In [Cu(EIDA)(H7azain)(H₂O)] (2, EIDA = N-ethyliminodiacetate ligand), [Cu(NBzIDA)(H7azain)(H₂O)] (3) and [Cu(μ₂-SO₄)(H7azain)₂(H₂O)₂]_n (4), H7azain binds Cu(II) centre by the Cu–N3(purine-like) bond, reinforced by a N9–H···O(IDA-like or sulfate) intra-molecular interligand interaction.     

Thermal and photochemical reactions of copper(II) dithiocarbamate mixed-ligand complexes with chloroalkanes

Thermal and/or photochemical conversion of a series of copper(II) complexes containing mixed dithiocarbamato–alcohol ligands, Cu^II(Et₂dtc)⁺ . . . Y⁻ (Y=ClO₄⁻, NO₃⁻), into Cu^II(Et₂dtc)Cl in chloroalkane/alcohol solutions, where chloroalkane=CCl₄, CHCl₃ or CH₂Cl₂ and alcohol=MeOH, EtOH or i-BuOH, proceeds in chloroalkanes. Both reactions follow a similar pathway which is more effective the stronger the acceptor properties of chloroalkanes and the weaker the coordinating abilities of alcohols are. A detailed reaction mechanism is proposed which well fits the experimental results obtained by EPR and UV–VIS spectra and quantum yields.     

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.     

Mixed ligand complexes of copper(II) iminodiacetate with di- and tripeptides in solution

Calorimetric, potentiometric, and spectrophotometric studies on mixed ligand complexes of copper(II) iminodiacetate and simple di- and tripeptides (GlyGly, αAlaαAla, αAlaβAla, βAlaβAla, αAlaAsn, GlyGlyGly, AlaGlyGly) have been carried out in aqueous solution at 298.15 K and ionic strength of I = 0.5 (KNO₃). The thermodynamic parameters of formation of various mixed complexes have been determined. The probable coordination modes of the complex and peptide molecules in the mixed ligand complexes are discussed.     

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.