Spectrophotometric study of complexation of dibenzopyridino-18-crown-6 with some transition and post-transition metal ions in DMSO solution using murexide as a metallochromic ligand

The complexation reaction of dibenzopyridino-18-crown-6 (DBPY 18C6) with Co²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Hg²⁺, and Ag⁺ have been studied in DMSO at 25°C by the spectrophotometric method. Murexide was used as a competitive colored ligand. The stoichiometry of metal ion-murexide and metal ions with DBPY18C6 complexes were estimated by mole ratio and continuous variation methods and emphasized by the KINFIT program. The stoichiometry of all the complexes was found to be 1: 1 (metal ion/ligand). The order of stability constants for the obtained metal ion-murexide complexes (1: 1) varies in the order Cu²⁺ > Cd²⁺ > Co²⁺ ∼ Pb²⁺ > Zn²⁺ > Ag⁺ > Hg²⁺. This trend shows that the transition metal ions clearly obey the Irving-Williams role. For the post-transition metal ions, the ionic radius and soft-hard behavior was the major affects in varying of this order. The dibenzopyridino-18-crown-6 complexes with the used metal ions vary as Ag⁺ > Pb²⁺ > Cu²⁺ > Cd²⁺ > Hg²⁺ > Zn²⁺ > Co²⁺. The article is published in the original.     

Simultaneous Titration of Ternary Mixtures of Pb(II), Cd(II) and Cu(II) with Potentiometric Electronic Tongue Detection

An automatic titration method is reported to resolve ternary mixtures of transition metals (Pb²⁺, Cd²⁺ and Cu²⁺) employing electronic tongue detection and a reduced number of pre‐defined additions of EDTA titrant. Sensors used were PVC membrane selective electrodes with generic response to heavy‐metals, plus an artificial neural network response model. Detection limits obtained were ca. 1 mg L^?1 for the three target ions and reproducibilities 3.0 % for Pb²⁺, 4.1 % for Cd²⁺ and 5.2 % for Cu²⁺. The system was applied to contaminated soil samples and high accuracy was obtained for the determination of Pb²⁺. In the determination Cd²⁺ and Cu²⁺, sample matrix showed a significant effect.     

ICT-based Cu(II)-sensing 9,10-anthraquinonecalix[4]crown

A series of calix[4]arene-based chromogenic sensors bearing the 9,10-anthraquinone moiety have been synthesized and examined for their abilities to recognize various cations such as Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Cd²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Co²⁺, and Cu²⁺ by UV-vis spectroscopy. In acetonitrile, the presence of Cu²⁺ induces the formation of the 1:1 ligand/metal complex, which exhibits a new absorption band centered at 450 nm, and leads to an obvious color change from yellow to red.     

Die Chelate von Co(II), Ni(II), Cu(II), Zn(II) und Cd(II) mit Malonsäurehydrazid und dessen Arylidenderivaten

The metal chelates formed by the reaction of Co²⁺, Cu²⁺, Ni²⁺, Zn²⁺, and Cd²⁺ with malonic hydrazide and its arylidene derivatives are investigated. The i.r.-absorption spectra of the solid compounds supported the tetradentate character of these compounds; they also show that the ligand still attained the keto form. The shift of the C=O, C=N bands is utilized in determining the coordination bond length. The stoichiometry of the metal complexes, as studied by spectrophotometric and conductometric methods, is found to be metal ion: ligand =11. The apparent formation constants of the malonic hydrazide complexes are also determined.

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Study of Complex Formation between 5,7‐Diiodo‐8‐hydroxyquinoline and Zn2+, Cd2+, Pb2+ and Tl+ Cations in Binary Non‐Aqueous Solvents Using Square Wave Polarography Technique (SWP)

The complexation reaction between Zn²⁺, Pb²⁺, Cd²⁺ and Tl⁺ cations by 5,7‐diiodo‐8‐hydroxyquinoline (IQN) was studied in the Dimethylformamide /Acetonitril (DMF‐AN) binary system using square wave polarography technique. The stoichiometry and stability of the complexes were determined by monitoring the shifts in half‐wave or peak potential of the polarographic waves of metal ions against the ligand concentration. The stoichiometry of the complexes was found to be 1:1. The results obtained show that there is an inverse relationship between the formation constant of the complexes and the donor number of solvent base on the Guttmann donocity scale. In all cases the formation constants increased with increasing amounts of AN in these binary systems. The selectivity order for IQN complexes with the cations is Zn²⁺ > Pb²⁺ > Cd²⁺ > Tl⁺.     

Competitive Potentiometric Study of the Thermodynamics of Complexation of Some Transition and Heavy Metal Ions with Dibenzopyridino-18-crown-6 in Methanol using Ag+ Ion as a Probe

The complexation of dibenzopyridino-18-crown-6 with some transition and heavy metal ions in methanol solution at various temperatures was studied by a competitive potentiometric method using a Ag⁺/Agelectrode system. The stoichiometry and stability of the resulting complexes were computed by the MINIQUAD program. The stability of the resulting complexes varied in the order Ag⁺ > Pb²⁺ > Tl⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺. The enthalpy and entropy of the resulting 1:1 complexeswere evaluated from the temperature dependence of the stability constants.The complexes of all cations were enthalpy-stabilized but entropy-destabilized,except for Ag⁺ and Pb²⁺ ions,which were also entropy-stabilized.     

Synthesis,structure, and solvent-extraction properties of tridentate oxime ligands and their cobalt(II), nickel(II), copper(II), zinc(II) complexes

Synthesis of four different types of ligands Ar[COC(NOH)R] _n (Ar = biphenyl, n = 1, HL¹; Ar = biphenyl, n = 2, H₂L²; Ar = diphenylmethane, n = 1, HL³; Ar = diphenylmethane, n = 2, H₂L⁴; R = furfurylamine in all ligands) and their dinuclear Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ complexes is reported herein. These compounds were characterized by elemental analysis, ICP-OES, FT-IR spectra, and magnetic susceptibility measurements. The ligands were further characterized by ¹H NMR. The results suggest that dinuclear complexes of HL¹ and HL³ have a metal to ligand mole ratio of 2: 2 and dinuclear complexes H₂L² and H₂L⁴ have a metal to ligand mole ratio of 2: 1. Square pyramidal or octahedral structures are proposed for complexes of oxime ligands. Furthermore, extraction abilities of the four ligands were also evaluated in chloroform using selected transition metal picrates such as Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺. The ligands show strong binding ability towards Hg²⁺ and Cu²⁺ ions.     

The Copper(II)‐Catalyzed Oxidation of Glutathione

The kinetics and mechanisms of the copper(II)‐catalyzed GSH (glutathione) oxidation are examined in the light of its biological importance and in the use of blood and/or saliva samples for GSH monitoring. The rates of the free thiol consumption were measured spectrophotometrically by reaction with DTNB (5,5′‐dithiobis‐(2‐nitrobenzoic acid)), showing that GSH is not auto‐oxidized by oxygen in the absence of a catalyst. In the presence of Cu²⁺, reactions with two timescales were observed. The first step (short timescale) involves the fast formation of a copper–glutathione complex by the cysteine thiol. The second step (longer timescale) is the overall oxidation of GSH to GSSG (glutathione disulfide) catalyzed by copper(II). When the initial concentrations of GSH are at least threefold in excess of Cu²⁺, the rate law is deduced to be ?d[thiol]/dt=k[copper–glutathione complex][O₂]^0.5[H₂O₂]^?0.5. The 0.5^th reaction order with respect to O₂ reveals a pre‐equilibrium prior to the rate‐determining step of the GSSG formation. In contrast to [Cu²⁺] and [O₂], the rate of the reactions decreases with increasing concentrations of GSH. This inverse relationship is proposed to be a result of the competing formation of an inactive form of the copper–glutathione complex (binding to glutamic and/or glycine moieties).     

Out-cage metal ion coordination by novel benzoazacrown bisamides with carboxyl,pyridyl and picolinate pendant arms

A new series of macrocyclic diamides with carboxyl, pyridyl and picolinate pendant arms have been synthesized and the stability constants of their complexes with Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ in water were determined. Complexes with a stoichiometry of 1 : 1 (M: L) were found for all ligands with the exception of 15-membered crown ethers with one pendant carboxyl or pyridine group. The ligand containing two picolinate backbone groups exhibits the highest values of the stability constants for all studied cations (logβ_ML?=?12.5–15.7). X-ray study of free ligands showed that the introduction of benzene and amide fragments into the macrocyclic moiety provides a flatten open structure of the ligand. The crystallographic analysis of Cu²⁺ and Zn²⁺ complexes revealed the external coordination of the metal atom by amine N atoms of the macrocycle and heteroatoms of the pendant groups.     

Stability studies on 1:1 or 1:3 stoichiometry complexes of hexaza tripods with zinc(II), copper(II), nickel(II) and cobalt(II)

The coordination properties of two C₃-symmetry hexaza tripods, 1,3,5-tri(2,5-diazahexyl)benzene (L1) and 1,3,5-tri(2,5-diazaheptyl)benzene (L2), towards Zn²⁺, Cu²⁺, Ni²⁺ and Co²⁺ ions, studied by potentiometric techniques, are reported. Both ligands form quite stable complexes either in a 1:1 or 1:3 M:L stoichiometry, presenting a preferential coordination order: Zn²⁺ < Cu²⁺ > Ni²⁺ > Co²⁺. It is observed that the different configurations of metal complexes are achieved due to the fact that tripodal ligands are flexible and not constrained into a rigid geometry.     

Cation Complexation by a Lower Rim Calix(4)arene Derivative: Structural,Electrochemical and Thermodynamic Studies

The synthesis and characterization (¹H and ¹³C NMR) of a partially substituted lower rim p-tert-butylcalix(4)arene, namely, 5,11,17,23-tetra-4-tert-butyl-25,27-bis(diethylphosphate amino)ethoxy-26,28-dihydroxycalix[4]arene (1), are reported. The solution thermodynamics of the ligand in a variety of solvents at 298.15?K was investigated through solubility (hence standard Gibbs energy of solution) measurements while the calorimetric technique was used to derive the standard solution enthalpy. These data were used to calculate the standard entropy of solution. An enthalpy–entropy compensation effect is shown and, as a result, slight variations are observed in the transfer Gibbs energies of this ligand from the reference to other solvents. ¹H NMR, conductance and calorimetric measurements were carried out to establish the degree of interaction of the ligand with univalent (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and Ag⁺) and bivalent (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, Zn²⁺) cations in acetonitrile, methanol, N,N-dimethylformamide and propylene carbonate. No complexation was found between this ligand and univalent cations in these solvents. As far as the bivalent cations are concerned, interaction between 1 and these cations was found only in acetonitrile. The versatile behaviour of this ligand with bivalent cations in this solvent is reflected by the formation of complexes of different stoichiometry. Thus the interaction of 1 with alkaline-earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) and Pb²⁺ metal cations leads to the formation of 1:2 (cation:ligand) complexes. However, for other bivalent metal cations (Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺) the complex stoichiometry was found to be 1:1. The results are discussed in terms of the key role played by acetonitrile in processes involving calix[4]arene derivatives.     

Study of Cd2+ complexation by the glutathione fragments Cys-Gly (CG) and gamma-Glu-Cys (gamma-EC) by differential pulse polarography

A differential pulse polarographic study of the Cd2+/gamma-Glu-Cys and Cd2+/Cys-Gly systems assisted by the alternating least-squares multivariate curve resolution (MCR-ALS) method was carried out to obtain a better understanding of the different metal affinities of the complexation sites on glutathione (GSH). The simultaneous analysis of the titration of peptide with metal and of metal with peptide allowed the resolution of the Cd2+/Cys-Gly system, whereas in the analysis of the Cd2+/gamma-Glu-Cys system the analysis of a single titration experiment was sufficient. The analysis of the shape of the resulting pure voltammograms and concentration profiles of the resolved components suggested the presence of two different types of bound Cd2+ in the two systems considered, that could be attributed to Cd2+ bound to one or two sulfur atoms to form complexes of stoichiometry 1:1 and 1:2. respectively.     

Removal of Cd(II), Cu(II), and Pb(II) by adsorption onto natural clay: a kinetic and thermodynamic study

In this work, we study the elimination of three bivalent metal ions (Cd²⁺, Cu²⁺, and Pb²⁺) by adsorption onto natural illitic clay (AM) collected from Marrakech region in Morocco. The characterization of the adsorbent was carried out by X-ray fluorescence, Fourier transform infrared spectroscopy and X-ray diffraction. The influence of physicochemical parameters on the clay adsorption capacity for ions Cd²⁺, Cu²⁺, and Pb²⁺, namely the adsorbent dose, the contact time, the initial pH imposed on the aqueous solution, the initial concentration of the metal solution and the temperature, was studied. The adsorption process is evaluated by different kinetic models such as the pseudo-first-order, pseudo-second-order, and Elovich. The adsorption mechanism was determined by the use of adsorption isotherms such as Langmuir, Freundlich, and Temkin models. Experiments have shown that heavy metals adsorption kinetics onto clay follows the same order, the pseudo-second order. The isotherms of adsorption of metal cations by AM clay are satisfactorily described by the Langmuir model and the maximum adsorption capacities obtained from the natural clay, using the Langmuir isotherm model equation, are 5.25, 13.41, and 15.90 mg/g, respectively for Cd(II), Cu(II), and Pb(II) ions. Adsorption of heavy metals on clay is a spontaneous and endothermic process characterized by a disorder of the medium. The values of ΔH are greater than 40 kJ/mol, which means that the interactions between clay and heavy metals are chemical in nature.     

Assessing effects of pH,metal ion and natural organic matter on identification and determination of reduced glutathione by cathodic stripping voltammetry

The effects of pH, metal ions (i.e. Cu²⁺, Cd²⁺, Pb²⁺ and Zn²⁺) and natural organic matter (i.e. Suwannee River natural organic matter standard [SRNOM]) on determination of thiol (i.e. reduced glutathione [GSH]) by cathodic stripping voltammetry were evaluated. pH was the most critical parameter to influence GSH voltammogram (i.e. peak shape, position and height). In presence of Cu and Cd, secondary peaks were found at [metal]/GSH > 1 due to formation of GSH complexes at pH = 8.0 (Cu and Cd) and 2.5 (Cu only). On the other hand, Pb showed negligible influence on GSH voltammogram at pH 8.0 and 2.5 within [Pb]/[GSH] = 0.01–2.0. Zn significantly reduced GSH peak height at pH 2.5 at [Zn]/[GSH] = 0.01–2.0. SRNOM peak significantly overlapped with GSH peak at pH 8.0 and [SRNOM] > 1 mg L^?1 but was clearly separated from the GSH peak at pH 2.5. However, at pH 2.5, the presence of metal ions and/or SRNOM significantly underestimated GSH concentration (recovery = 21–69%), likely due to metal complexation with GSH and/or SRNOM adsorption onto Hg electrode. The effects of metal ions were minimised by the addition of EDTA. The interference induced by SRNOM adsorption was reduced as the [SRNOM] was reduced to 1 mg L^?1 and the recovery was improved to 98%.     

Structural studies on cadmium(II), cobalt(II), copper(II), nickel(II) and zinc(II) complexes of 1-malonyl-bis(4-phenylthiosemicarbazide)

Summary Several new complexes of the title ligand (H₂MPTS) with Co^II, Ni^II, Cu^II, and Cd^II have been prepared. Structural assignments of the complexes have been made based on elemental analysis, molar conductivity, magnetic moment and spectral (i.r.,¹H n.m.r., reflectance) studies. The compounds are non-conductors in dimethylsulphoxide. The neutral molecule is coordinated to the metal(II) sulphate as a bidentate ligandvia the two carbonyl groups. The ligand reacts with the metal(II) chlorides with the liberation of two hydrogen ions, behaving as a bianionic quadridentate (NONO) donor. Enolization is confirmed by the pH-titration of H₂ MPTS and its metal(II) complexes against NaOH. A distorted octahedral structure is proposed for the Cu^II complex, while a square planar structure is suggested for both Co^II and Ni^II complexes. The stoichiometry of the complexes formed in EtOH and buffer solutions, their apparent formation constants and the ranges for obedience to Beer's law are reported for Co^II, Ni^II and Cu^II ions. The ligand pK values are calculated. The antimicrobial activity of H₂ MPTS and its Co^II, Ni^II, Cu^II and Mn^II complexes is demonstrated.     

A highly selective turn-on fluorescent chemosensor for copper(II) ion

A new pyrene derivative (1) containing a diaminomaleonitrile moiety exhibits high selectivity for Cu²⁺ detection. Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence values for the system. The apparent association constant (K_a) of Cu²⁺ binding in chemosensor 1 was found to be 5.55×10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5-7.5.     

Highly selective colorimetric naked-eye Cu2+ detection using new bispyrazolone silver nanoparticle-based chemosensor

In this work, we have successfully developed novel silver nanoconjugates of pyrazolone analogue and screened its chemosensing potential in aqueous medium. Bispyrazolone silver nanoparticles (Bispyra-AgNPs) were synthesised and characterised through FTIR, UV-visible spectroscopy and atomic force microscopy. The sensing ability was explored towards Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Li⁺, Pb²⁺, La³⁺, Hg²⁺, Mg²⁺, Ni²⁺ and Ba²⁺ metal ions, respectively. Bispyra-AgNPs showed a highly quenching potential in selective recognition of Cu²⁺and colour of the solution immediately turned from yellow to purple, after the addition of Cu²⁺ in to the solution. The developed method also displayed a remarkable selectivity for Cu²⁺ over others interfering metal ions. The binding ratio and stoichiometry of host-guest complex was found to be 1:1 and determined by Job’s method. The propose method is facile and sensitive to detect Cu²⁺ with detection limit of 10 µM.     

Complexation and thermodynamic studies of oxathiadibenzocrown ethers with Cu2+, Pb2+, Zn2+ and Cd2+ ions

A thermodynamic study of the complexation of Cu²⁺, Pb²⁺, Zn²⁺ and Cd²⁺ ions with 1 and 2 in acetonitrile has been carried out. The study was conducted in the temperature range 283–308 K using a conductometric technique. The observed molar conductivity, Λ, was found to decrease significantly for mole ratios [L]_t/[M]_t less than unity in all cases. A model involving 1:1 stoichiometry has been used to analyze the conductivity data. The stability constant, K, for each 1:1 complex was determined from the conductivity data by using a nonlinear least-squares curve fitting procedure. The results show that compound 1 has no peak selectivity for any of the metal cations, while compound 2 selectively associates with Cu²⁺ and Pb²⁺. Complexes of 1 have the following stability order Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺  and Pb²⁺ > Cu²⁺ for the complexes of 2. The ?H° and ?S° values for the complexation process were obtained from the slope and intercept of the Van’t Hoff plots respectively. All ?G° values were negative and were determined from the Gibbs–Helmholtz equation and the significance of these values is discussed.     

The use of ESI-MS to probe the binding of divalent cations to calmodulin

Proteins have evolved with distinct sites for binding particular metal ions. This allows metalloproteins to perform a myriad of specialized tasks with conformations tailor-made by the combination of its primary sequence and the effect on this of the ligated metal ion. Here we investigate the selectivity of the calcium trigger protein calmodulin for divalent metal ions. This ubiquitous and highly abundant protein exists in equilibrium between its apo and its holo form wherein four calcium ions are bound. Amongst its many functions, calmodulin modulates the calcium concentration present in cells, but this functional property renders it a target for competition from other metal ions. We study the competition posed by four other divalent cations for the calcium binding sites in calmodulin using electrospray ionization mass spectrometry (ESI-MS). We have chosen two other group II cations Mg²⁺, Sr²⁺, and two heavy metals Cd²⁺, Pb²⁺. The ease with which each of these metals binds to apo and to holo CaM[4Ca] is described. We find that each metal ion has different properties with respect to calmodulin binding and competition with calcium. The order of affinity for apo CaM is Ca²⁺ ≫ Sr²⁺ ∼ Mg²⁺ > Pb²⁺ ∼ Cd²⁺. In the presence of calcium the affinity alters to Pb²⁺ > Ca²⁺ > Cd²⁺ > Sr²⁺ > Mg²⁺. Once complexes have been formed between the metal ions and protein (CaM:[xM]) we investigate whether the structural change which must accompanies calcium ligation to allow target binding takes place for a given CaM:[xM] system. We use a 20 residue target peptide, which forms the CaM binding site within the enzyme neuronal nitric-oxide synthase. Our earlier work (Shirran et al. 2005) [1] has demonstrated the particular selectivity of this system for CaM:4Ca²⁺. We find that along with Ca²⁺ only Pb²⁺ forms complexes of the form CaM:4M²⁺:nNOS. This work demonstrates the affinity for calcium above all other metals, but also warns about the ability of lead to replace calcium with apparent ease.     

Preparation of guanidinylated carboxymethyl chitosan and its application in the diffusive gradients in thin films (DGT) technique for measuring labile trace metals in water

ABSTRACT

Guanidinylated carboxymethyl chitosan (GCMCS) was prepared via the guanidinylation of carboxymethyl chitosan (CMCS). A device employing the diffusive gradients for thin films (DGT) technique was made using a GCMCS aqueous solution as the binding agent and a cellulose acetate dialysis membrane (CADM) as the diffusion phase to measure labile Cu²⁺, Pb²⁺ and Cd²⁺ in water. The percentage uptake (U%) values of labile Cu²⁺, Pb²⁺ and Cd²⁺ in a synthetic water sample were almost consistent with the theoretical values at 101.6 ± 2.8%, 104.6 ± 6.1% and 95.9 ± 4.4%, respectively. The optimum pH ranges for the measurement of labile Cu²⁺, Pb²⁺ and Cd²⁺ were 3.0–7.0, 3.0–7.0 and 4.0–8.0, respectively. The ionic strength mainly affected the diffusion of metal ions in the CADM. The diffusion rates decreased with increasing concentrations of NaNO₃ solutions. The application of GCMCS-DGT in natural water and industrial wastewater showed that dissolved organic carbon (DOC) only affects metal species, and the accurate determination of labile Cu²⁺, Pb²⁺ and Cd²⁺ can be achieved when the diffusion coefficients of these metal ions in the diffusion phase have been determined. GCMCS is suitable for DGT application as a chelating agent for metal ions.