Ternary Complex Species Research Articles

Circular Dichroism Spectroscopic Studies on Solution Chemistry of M(II)-Monensinates in Their Competition Reactions

The chirality of the polyether ionophore monensic acid A can be successfully used to study its coordination ability in solution. A complementary approach to gain new insights into the complexation chemistry of the antibiotic (studied previously by circular dichroism (CD) spectroscopy in the ultraviolet range (UV-CD)) is presented. (1) Methods: The CD spectroscopy in the visible (VIS-CD) and near-infrared (NIR-CD) range is applied to evaluate the affinity of deprotonated monensic acid A (monensinate A) towards Ni(II) or Co(II) cations in methanolic solution. Competition experiments between a variety of colorless divalent metal ions for binding the ligand anion were also performed. (2) Results: The stability constants of the species observed in binary Ni(II)/Co(II)-monensinate systems and their distribution were reevaluated with the VIS- and NIR-CD techniques. The data confirmed the formation of mono and bis complexes depending on the metal-to-ligand molar ratio. The studies on the systems containing two competing divalent metal cations exclude the formation of ternary complex species but provide an opportunity to also calculate the stability constants of Zn(II), Mg(II), and Ca(II) monensinates. (3) Conclusions: The advantages of CD spectroscopy in the VIS-NIR range (“invisible” ligand and metal salts, “visible” chiral complex species) simplify the experimental dataset evaluation and increase the reliability of computed results.

Ternary copper(II) complexes with 1,10‑phenanthroline and various aminoacidates: A spectroscopic and voltammetric study in aqueous solution

Ternary copper(II) complexes with 1,10‑phenanthroline and the aminoacids l‑arginine, l‑aspartic acid, l‑histidine, l‑glutamic acid, l‑glutamine, l‑leucine, l‑lysine, l‑methionine, l‑phenylalanine, l‑tryptophan, l‑tyrosine, l‑valine, were studied in aqueous solution by means of UV–Vis-NIR spectrophotometry, EPR spectroscopy either at room or at low temperatures, and Square Wave Voltammetry. From the experimental data it is possible to conclude that most of these ternary complexes show a pseudo-octahedral geometry with a CuN3O in plane chromophore and two oxygen atoms coming from water molecules perpendicularly bound to the equatorial plane. An exception to this general behaviour is given by the ternary copper(II) complex with 1,10‑phenanthroline and histidine at pH value near the neutrality because of the terdentate nature of histidine when it coordinates by means of its histamine-like mode. In this case, evidence for a probable square-based pyramidal stereochemistry is given in support. At pH values around 5 the histidine behaves as bidentate ligand coordinating by its glycine-like mode, so as the copper(II) ternary complex with 1,10‑phenathroline shows the pseudo-octahedral geometry found for all the ternary complexes with the other aminoacids. Moreover the ternary complex species with histidine at pH 5 and 7 are in equilibrium with each other as a function of the aqueous solution pH value and the temperature. In fact, the examination of low temperature EPR spectra at pH near 7 revealed not only a square-based pyramid complex but also products of decomposition. These results were also confirmed by the trend found in the formal redox potentials by the voltammetric measurements on many of these ternary complexes.

Multilinear analysis of Time-Resolved Laser-Induced Fluorescence Spectra of U(VI) containing natural water samples

Natural waters’ uranium level monitoring is of great importance for health and environmental protection. One possible detection method is the Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), which offers the possibility to distinguish different uranium species. The analytical identification of aqueous uranium species in natural water samples is of distinct importance since individual species differ significantly in sorption properties and mobility in the environment. Samples originate from former uranium mine sites and have been provided by Wismut GmbH, Germany. They have been characterized by total elemental concentrations and TRLFS spectra. Uranium in the samples is supposed to be in form of uranyl(VI) complexes mostly with carbonate (CO3 2− ) and bicarbonate (HCO3 − ) and to lesser extend with sulphate (SO4 2− ), arsenate (AsO4 3− ), hydroxo (OH− ), nitrate (NO3 − ) and other ligands. Presence of alkaline earth metal dications (M = Ca2+ , Mg2+ , Sr2+ ) will cause most of uranyl to prefer ternary complex species, e.g. Mn (UO2 )(CO3 )3 2n-4 (n ∊ {1; 2}). From species quenching the luminescence, Cl− and Fe2+ should be mentioned. Measurement has been done under cryogenic conditions to increase the luminescence signal. Data analysis has been based on Singular Value Decomposition and monoexponential fit of corresponding loadings (for separate TRLFS spectra, the “Factor analysis of Time Series” (FATS) method) and Parallel Factor Analysis (PARAFAC, all data analysed simultaneously). From individual component spectra, excitation energies T 00 , uranyl symmetric mode vibrational frequencies ω gs and excitation driven U-Oyl bond elongation ΔR have been determined and compared with quasirelativistic (TD)DFT/B3LYP theoretical predictions to cross -check experimental data interpretation.

Complex Formation Study of Binary and Ternary Complexes Including 2,3-Dihydroxybenzoic Acid, N-acetylcysteine and Divalent Metal Ions

The binary and ternary complex stability constants between 2,3-dihydroxybenzoic acid (DA) and N-acetylcysteine (Nac) with the divalent metal ions (M) Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ were studied in aqueous solution at 310.15 K and an ionic medium of 0.15 mol·dm−3 NaCl. The complexes’ stability constants (log10 β), refined from the potentiometric data using the Hyperquad2008 program, indicate that the ternary complexes are more stable than the binary complexes. The stability constants were supported by additional computation, refined from the spectrophotometric data using the Hypspec program. The values of the ternary complex stability relative to their binary complex (Δlog10 K) and the disproportionation constant (log10 X) indicate that formation of ternary complex species [M(DA)(Nac)]3− is more favorable than that of species formed by two identical ligands, [M(DA)2]4− or [M(Nac)2]2−. For the investigated M, the stability of complexes follows the trend Cu2+ > Zn2+ > Ni2+ > Co2+ > Mn2+.

Equilibrium studies of ternary systems containing some selected transition metal ions, triazoles and aromatic carboxylic acids

Solution equilibria of the binary and ternary complex systems of the divalent transition metal ions Cu2+, Ni2+, Zn2+, and Co2+ with 1,2,4-triazole (TRZ), 3-mercapto-1,2,4-triazole (TRZSH), and 3-amino-1,2,4-triazole (TRZAM) and aromatic carboxylic acids (phthalic, anthranilic, salicylic, and 5-sulfosalicylic acid) have been studied pH-metrically at (25.0±0.1) °C, and a constant ionic strength I=1×10−1 mol L−1 NaNO3 in an aqueous medium. The potentiometric titration curves show that binary and ternary complexes of these ligands are formed in solution. The stability constants of the different binary and ternary complexes formed were calculated on the basis of computer analysis of the titration data. The relative stability of the different ternary complex species is expressed in terms of Δ log K values, log X and R. S.% parameters. The effect of temperature of the medium on both the proton-ligand equilibria for TRZAM and phthalic acid and their metal-ligand equilibria with Cu2+, Ni2+, and Co2+ has been studied along with the corresponding thermodynamic parameters. The complexation behavior of ternary complexes is ascertained using conductivity measurements. In addition, the formation of ternary complexes in solution has been confirmed by using UV-visible spectrophotometry.

Thermodynamics of binary and ternary interactions in the tin(II)/phytate system in aqueous solutions, in the presence of Cl− or F−

An extensive study of the tin(II)/phytate (Phy) system was carried out in NaNO3(aq), at different ionic strengths (0.10⩽I/mol·L−1⩽1.00) and temperatures (278.15⩽T/K⩽328.15), by potentiometric and voltammetric techniques. The stability and formation enthalpy changes of six SnHqPhy species were determined. To better characterise this system, some potentiometric titrations were also carried out in mixed ionic media (NaNO3(aq)+NaCl(aq) and NaNO3(aq)+NaF(aq)) at total ionic strength I=1.00mol·L−1. The formation of some ternary mixed SnHqPhyCl and SnHqPhyF species (charges omitted for simplicity) was found. The formation enthalpies of the complex species were calculated, at I=0.40mol·L−1 in NaNO3(aq), by the dependence of stability constants on temperature obtained by potentiometric titrations, in the range 278.15⩽T/K⩽328.15. The complex formation process is endothermic, and the main contribution to tin(II) complexation by phytate is entropic in nature. For example, for the SnPhy species we have, at T=298.15K and I=0.40mol·L−1 in NaNO3(aq): ΔH=57.7±2.8kJmol·L−1, ΔG=−99.9±1.7kJmol·L−1, and TΔS=158±3kJmol·L−1. The ionic strength dependence of the formation constants of the simple tin(II)/phytate species, was modelled by the Debye–Hückel and the SIT approaches. The sequestering ability of phytate towards tin(II) was evaluated by calculating the pL0.5 values (i.e., the total ligand concentration necessary to bind 50% of cation present in trace) at different ionic strengths, ionic media, and pH. The sequestering ability increases with increasing the pH, whilst it decreases with increasing the ionic strength (the same behaviour shown by the stability constants). Moreover, taking into account the different sequestering ability of phytate towards tin(II) in the different ionic media, the trend: pL0.5=5.70 (in NaNO3(aq)+NaF(aq))>pL0.5=5.16 (in NaNO3(aq)+NaCl(aq))>pL0.5=4.86 (in NaNO3(aq)) was observed at pH 8.1 and I=1.00mol·L−1. This is due to the presence of a second ligand (Cl− or F−) that stabilizes the complex species with the formation of ternary complex species. Some empirical relationships were also found.

Characterization of HDEHP-lanthanide complexes formed in a non-polar organic phase using 31P NMR and ESI-MS

HDEHP (di-2-ethylhexylphosphoric acid) is one of the extractant molecules most intensively used in liquid-liquid extraction systems. Of particular interest in this investigation is its application in the TALSPEAK process, which is among the methods currently considered to be ready for technological deployment for the separation of trivalent actinides (Am(III) and Cm(III)) from lanthanide (Ln(III)) cations. However, several fundamental features of the chemistry of this separation system are not well understood. It has become clear that the lactic acid (LacH), which is employed as a buffer in the aqueous phase, plays a very complex role in the biphasic chemistry of the system. In this study, Nuclear Magnetic Resonance ((31)P NMR) was used to investigate the rate of HDEHP (AH) exchange occurring in the binary complexes Ln(AHA)(3) (Ln = La and Sm), which are usually considered to be the predominant species present in a non-polar organic phase (1,3-diisopropylbenzene). The rate data indicate considerably faster ligand exchange kinetics for La(AHA)(3) than is seen for Sm(AHA)(3), with a corresponding shift from a dissociative interchange to an associative process. With the introduction of lactic acid (LacH) and higher concentrations of lanthanides into the system, ternary complexes (Ln(3+)-HDEHP-lactate) become dominant, as demonstrated using (31)P NMR and Electrospray Ionization Mass Spectrometry (ESI-MS). Lactate partitioning experiments indicate that the amount of lactate extracted is correlated with the concentration of Ln(3+). The terminal ternary complex species appears to have the general stoichiometry 1 : 2 : 1 (Ln(3+) : HDEHP : lactate). The detection of bimetallic ternary complexes (by ESI-MS) with La(3+) and the observation of multiple phosphorus environments (by NMR) suggest the presence of polymetallic complexes with the general formula (LaA(2)Lac)(n). A model is proposed in which DEHP(-) molecules bridge two metal ions.

Studies on some ternary complexes of copper(II) involving an amino penicillin drug

Multiple equilibrium studies by pH-metric measurements in the ternary copper(II) complexes with ampicillin(amp) as ligand A and glycine(gly), dl-2-aminobutanoic acid(2aba), dl-3-aminobutanoic acid(3aba), 1,2-diaminopropane(dp), 1,3-diaminopropane(tp), dl-2,3-diaminopropanoic acid(dapa), dl-2,4-diaminobutanoic acid(daba) &dl-2,5-diaminopentanoic acid(ornithine)(orn) as ligands B show the presence of CuABH, CuAB or CuAH−1 B ternary complex species. In the CuAB species the binding of the ligands A and B is similar to their binding in their respective binary complexes. In CuABH−1 species the deprotonation occurs with amp(A) ligand. The ΔlogK values indicate higher stabilities for the ternary complexes than the binary species. The CuAB species with B=gly, 2aba, dapa & orn have been isolated and characterized. The conductivity measurements indicate that the complexes are non-electrolytes. Magnetic susceptibility and electronic spectral data suggest a square pyramidal geometry for CuAB with B=gly/2aba complexes and distorted octahedral geometry for CuAB with B=dapa/orn. The vibrational spectra are interpreted to find the mode of binding of ligand to metal. The TG/DTA studies reveal that the complexes decompose in three steps, indicating non-involvement of hydrated or coordinated water molecules in the complex. The cyclic voltammograms indicate a quasi reversible Cu2+/Cu+ couple. The antimicrobial activity and CT-DNA cleavage ability of the complexes show higher activity for ternary complexes.

Ternary Complex Formation between Vanadium(III), Dipicolinic Acid and Picolinic Acid in Aqueous Solution

Ternary complex species formed by the V3+ cation with the picolinic acid (Hpic, HL) and dipicolinic acid (H2dipic, H2L) ligands in aqueous solutions have been studied potentiometrically (25 °C, I=3.0 mol⋅dm−3 KCl ionic medium) and by spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the experimental emf (H) data, taking into account the hydrolytic V(III) species and the binary V3+–picolinic acid and V3+–dipicolinic acid complexes, shows that under the investigated conditions the following ternary complexes are formed: [V(dipic)(pic)], [V(dipic)(pic)(OH)]− and [V(dipic)(pic)2]−. The stability constants of the ternary complexes were determined by potentiometric measurements whereas the spectrophotometric measurements were done in order to obtain a qualitative characterization of the complexes formed in aqueous solution.

Identifing Unique Conformational Forms of Phosphofructokinase Using Fluorescence Phasor Analysis

The two main parameters, phase angle and modulation, determined in frequency-domain fluorescence measurements, can be acquired with high precision. Unfortunately, when analyzing systems with complex decay mechanisms, error is often introduced by the imperfect modeling of this complexity. For questions that do not require a precise understanding of those mechanisms, the phasor approach allows a description of the system utilizing only the raw phase angle and modulation data with a corresponding improvement in reproducibility. In this investigation, we used phasor plots to describe the allosteric enzyme phosphofructokinase from E. coli (EcPFK). In our approach, we perform a direct transformation of the phase angle and modulation to the S and G function coordinates described in a Cartesian system as determined at an individual excitation modulation frequency. EcPFK contains a single tryptophan at position 311. Despite this simple composition, conventional fluorescence lifetime measurements of EcPFK exhibit complex decay behavior. The goal of this investigation is to describe the four species involved in the allosteric coupling between the substrate, fructose-6-phosphate (F6P) and the allosteric inhibitor, phosphoenolpyruvate (PEP), using the phasor approach. These four forms are: apo-EcPFK, EcPFK-F6P, PEP-EcPFK, and PEP-EcPFK-F6P). Special interest is on the ternary complex species (PEP-EcPFK-F6P) that is not considered in classic two-state models that attempt to explain the origin of allosteric behavior. The best results were obtained by exciting at 300 nm and collecting the fluorescence response at frequencies between 40 to 70 MHz. Our results show the presence of four unique conformations that correspond to the different ligated states of the enzyme. Notably, the ternary complex exhibits a unique phasor value, independent of whether it was formed by titrating the substrate followed by the inhibitor or vice versa. Supported by NIH Grant GM33216 and Welch Foundation Grant A1548.

Solution Equilibria of Ternary Systems Involving Transition Metal Ions, Hydroxamic Acids, and Bioligands

The formation of ternary complexes of the Cu(II), Co(II), Ni(II), and Zn(II) metal ions with some hydroxamic acids (acetohydroxamic acid, Aha; benzohydroxamic acid, Bha; salicylhydroxamic acid, Sham; and N-phenylbenzohydroxamic acid, N-PhBha) and some bioligands (α-alanine, α-ala; l-valine, l-val; norvaline, norval; aspartic acid, aspart; glutamic acid, glut; asparagines, asperg; histamine, Him; and imidazole, imid) was investigated using the potentiometric technique at 25 °C and I = 0.10 mol·dm−3 NaNO3. The stability constants of these ternary systems were calculated. The order of stability of the ternary complexes in terms of the nature of metal ions, hydroxamic acids, and bioligands was investigated and discussed as well as the values of Δ log K and log X for the ternary systems. The concentration distribution curves of the various binary and ternary complex species in solution were evaluated. The effect of temperature of the medium on both the ionization process of Aha, Sham, aspart, and glut and the ...

New Insights into M(II)−Hydroxamate Interactions: The Electro-Analytical Behavior of Metal(II) Complexes Involving Monohydroxamic Acids and Diamines in an Aqueous Medium

The binary and ternary systems of Cu(II), Co(II), Ni(II), Zn(II), Cd(II), Mn(II), Mg(II), and Ca(II) metal ions with the hydroxamic acids, acetohydroxamic acid (Aha), benzohydroxamic acid (Bha), and salicylhydroxamic acid (Sham), and diamines, ethylenediamine (en), 1,3-diaminopropane (dapr), and o-phenylenediamine (o-pda), were investigated potentiometrically at 25 °C and I = 0.10 mol·dm−3 (NaNO3) in aqueous solution. The acid−base properties of the ligands were investigated. The potentiometric titration curves show that the ternary complexes are formed in a stepwise manner. The stability constants of the binary and ternary complexes were calculated on the basis of computer analysis of titration data. The order of stability of the binary and ternary complexes in terms of the nature of hydroxamic acids, diamines, and metal ions was investigated and discussed. The relative stability of ternary complex species is expressed in terms of Δlog K and % R.S. parameters. The distribution of binary and ternary complexes in solution was evaluated. Evaluation of the effect of temperature of the medium on both the ionization process of the ligands and complex formation for the M(II)−en−Sham (M(II) = Cu(II), Co(II), and Ni(II)) ternary systems has been studied along with the corresponding thermodynamic parameters. The complexation behavior of ternary complexes is ascertained using conductivity measurements. In addition, confirmation of the formation of ternary complexes in solution has been performed using cyclic voltammetry measurements.

Ternary complex formation of Eu(III) and Am(III) with pyridine-2,6-dicarboxylate in aqueous solutions

Ternary hydroxo complex formation of Eu(III) with pyridine-2,6-dicarboxylate (PDA) was investigated by potentiometry and fluorescence spectrophotometry. Curves of equilibrium pH versus amount of OH − added showed that the pH for the precipitation of Eu(III) was decreased due to the formation of ternary hydroxo complex, EuOHL(s) (L = PDA), which was confirmed by the enhancement of fluorescence intensity of Eu(III) in precipitate with PDA excitation wavelength. The ternary hydroxo complex species was also confirmed by the analysis of concentrations of the Eu(III), OH − and PDA in the precipitate. Solubility products of EuOHL(s) and Eu(OH) 3 were determined as p K sp 0 = 19.2 ± 0.2 and 24.5 ± 0.1, respectively. Similar behavior for the ternary hydroxo complex formation was observed for trace 241Am(III) added to Eu(III).

Formation constants of some ternary lanthanide(III) chelates with vitamin U and oxine

Formation of 1: 1: 1 ternary complex species (MAL) has been inferred and the relevant equilibrium has been established from pH measurements on the interaction of M 3+ ions [M = La III , Pr III , Sm III and Gd III ] with ligand A [HA = oxine] in the presence of the ligand L [HL = vitamin U] in aqueous medium at ionic strength of 0.2 and at varying temperatures 25 °C and 35 °C.

Complexation Equilibria of Zn(II), Pb(II) and Cd(II) with Reduced Glutathione (GSH) and Biologically Important Zwitterionic Buffers

The interaction of zinc(II), lead(II), and cadmium(II) with Glutathione (S-L-glutamyl-Lcysteinylglycine) as primary ligand and zwitterionic buffers (N-[2-Hydroxyethyl]piperazine-N′-[2-ethanesulfonic acid]) (HEPES) and (N-Hydroxyethyl]piperazine-N′-[2-hydroxy-propanesulfonic acid]) (HEPPSO) as secondary ligands were studied by potentiometric-pH titration in 1:1:1 ratio at 25.0 °C and I = 0.1 mol.dm−3 (KNO3). The formation constants of different normal and protonated binary and ternary complex species were calculated. Formation constants for the monohydroxy, and dihydroxy complexes for the binary systems M(II) + HEPES and M(II) + HEPPSO have been evaluated. The distribution curves for the various complex species as a function of pH were constructed.

Equilibrium studies on binary and ternary complexes of palladium and cadmium with some nitrogen and oxygen donor ligands

The metal-ligand equilibrium reactions involving palladium(II), cadmium(II) and 1,2-dihydroxybenzene, 1-amino-2-naphthol-4-sulfonic acid, 8-amino-1-naphthol-3,6-disulfonic acid, o-aminophenol and 4,5-dihydroxybenzene-1,3-disulfonic acid have been studied in solution at 25 and at ionic strength of 0.10 M (KNO 3 ). Formation of the binary, ternary and hydroxo complex species has been inferred in solution and the corresponding equilibrium constants have been evaluated and discussed.

Studies on ternary complexes of nickel(II) involving ligands with nitrogen, sulfur or oxygen as donor groups

Analysis of the pH-titration data in the Ni I I -1,2-diaminopropane/1,3-diaminopropane(A)-L-cysteine, D-penicillamine and L-cysteic acid(B) systems show the presence of NiAB ternary species in addition to the binary species HA, H 2 A, NiAH, NiA, NiA 2 H, NiA 2 , NiA 3 , HB, H 2 B, H 3 B, NiB, NiB 2 H and NiB 2 , The coordination of ligands A and B in both the binary and ternary complex species are similar and the ternary species tetracoordinated. The NiAB species have a square-planar structure.

Complexes of Vitamin B6. 23. Interaction of Some Tertiary Ligating Amino Acids with the Binary Complexes of Ni(II) or Cu(II) and Pyridoxamine

Binary and ternary complexes involved in the systems pyridoxamine (PM), glutamic acid (Glu), or aspartic acid (Asp) plus Ni(II) or Cu(II) were studied in solution at 0.15 M ionic strength and 25 °C by pH-metric, absorpiometric, and polarographic techniques. The differential pulse polarographic technique was used to study the reduction properties of these complexes. EPR was used to confirm the presence of binary and ternary complex species in the Cu(II) systems. The stoichiometry and formation constants of the binary and ternary complex species were determined by the SUPERQUAD program. Ternary species of the types 1:1:1:r and 1:2:1:r (PM/Glu or Asp/M/H) were found to exist in the pH range ∼3 to ∼10.

Coupled transport of Zn(II) through a supported liquid membrane containing bis(2,4,4-trimethyl pentyl) phosphinic acid in kerosene. I. A model for the rate process involving binary and ternary complex species

Since many divalent metal ions form more than one complex species with organic extractants, the transport process of such metal ions through a supported liquid membrane (SLM) containing similar extractants as carriers, may involve more than one species. A model has therefore been proposed to describe the rate of transport of more than one metal complex species, using Zn(II)-cyanex 272 system as a typical example, through SLM under different conditions. The overall rate process takes into account the basic interfacial chemical reactions, besides diffusion through the aqueous boundary layer as well as through the organic membrane phase. However, the model is flexible enough to describe the rate of transport of a single permeating species also.

Extraction Equilibria of Nickel(II) with 3-Mercapto-1,5-Diarylformazans in the Presence of 2,2′-Bipyridyl or 1,10-Phenanthroline

Abstract The equilibria associated with nickel(II) extraction from aqueous solutions with 3-mercapto-1,5-diarylformazans (dithizone analogues, RPh-N=N-C(=S)NH-NH-PhR; H2R2Dz) in the presence of 2,2′-bipyridyl or 1,10-phenanthroline (L) has been investigated. The reactions between H2R2Dz and [NiL]2+, [NiL2]2+ and [NiL3]2+ were also studied and found to give identical ternary nickel(II) complexes, Ni(HR2Dz)2L. The absorption spectral characteristics of ternary complex species extracted from perchlorate solutions were found to be different from those of the corresponding ternary complex species extracted from chloride, acetate, phosphate or sulfate solutions. The reaction equilibria between binary nickel(II) 3-mercapto-1,5-diarylformazan complexes, Ni(HR2Dz)2 and 2,2′-bipyridyl or 1,10-phenanthroline were also investigated and the formation constants of the ternary complex species were calculated. The effect of substituents R, on the extraction or formation constants of the ternary complexes are discussed and correlated with Hammett′s σ+ values.