Irving-Williams Order Research Articles

Irving-Williams Order in the Framework of Connectivity Index 3χv Enables Simultaneous Prediction of Stability Constants of Bivalent Transition Metal Complexes

Logarithms of stability constants, log K1 and log β2, of the first transition series metal mono- and bis-complexes with any of four aliphatic amino acids (glycine, alanine, valine and leucine) decrease monotonously with third order valence connectivity index, 3χv, from Cu2+ to Mn2+. While stability of the complexes with the same metal is linearly dependent on 3χv, stability constants of Mn2+, Fe2+, Co2+, and Ni2+complexes with the same ligand show a quadratic dependence on 3χv. As Cu2+ complexes deviate significantly from quadratic functions, models for the simultaneous estimation of the stability constants, yielding r = 0.999 (S.E. = 0.05) and r = 0.998 (S.E. = 0.11), for log K1 and log β2, respectively, were developed only for Mn2+, Fe2+, Co2+, and Ni2+ complexes with amino acids.

Computational study on imidazole-2-carboxaldehyde-glycylglycine and indole-3- carboxaldehyde-glycylglycine Schiff base ligands and equilibrium studies on their metal complexes

Semiempirical (AM1) calculations were carried out for the Schiff bases, imidazole-2-carboxaldehyde-glycylglycine (imal-glygly) and indole-3-carboxaldehyde-glycylglycine (indal-glygly). Five conformers of imal-glygly and indal-glygly suitable for complex formation were studied. The stable conformers were chosen for further studies. The geometrical parameters are in good agreement with the experimental values. The Schiff bases are planar with C 1 symmetry. The denticity reduction energy for imal-glygly and indal-glygly are respectively 21.04 kcal/mol and 18.24 kcal/mol. imal-glygly is a potentially tetradentate ligand capable of binding through N 4 , N 7 , N 11 /O 10 and O 15 and indal-glygly is tridentate using N 11 , N 15 /O 14 and O 19 atoms. The basisity of the hetero atoms were studied by calculating the protonation constant. The higher dipole moment values indicate that they are highly soluble in polar solvents. The ionization potential is 11.70 eV and 8.59 eV respectively for imal-glygly and indal-glygly. The chemical hardness has also been studied. Equilibrium studies were carried out for Co II , Ni II , Cu II and Zn II -imal-glygly/indal-glygly systems. M(AB) and M(AB) 2 types of complexes were formed for Co II , Ni II and Zn II systems, while Cu II forms only M(AB). The stability of the metal ions follows Irving-Williams order.

Gas phase and solution state stability of complexes L…M, where M = Cu 2+, Ni 2+, or Zn 2+ and L = R−C( [dbnd]O)NHOH (R = H, NH 2, CH 3, CF 3, or Phenyl)

The structure and gas-phase metal affinities (M = Cu 2+, Ni 2+, and Zn 2+) of formohydroxamic acid derivatives R–C( O)NHOH (R = H, NH 2, CH 3, CF 3 and Phenyl) were studied using the B3LYP/6-311+G(d,p) method of DFT theory. In order to evaluate the conformational behavior of these systems in water, we carried out CPCM-SCRF optimization calculations at the B3LYP/6-311+G(d,p) levels of theory. The obtained optimized geometries and interaction affinities of the gas and solution phase were compared. The following order of stability was found for ionic complexes of the transition metals: Cu 2+ > Ni(t) 2+ > Zn 2+. The same stability order would be expected according to the Irving–Williams order of stability constants. The high-spin complexes of the Ni 2+ were more stable than the low-spin complexes. The solvent effect reduced the observed relative stability of individual metallic complexes of substituted hydroxamic acids.

Thermo-Responsivity of the Polyacrylate-Adsorbed Metal Cation and its Hydration Structure

The thermo-responsive phase behaviour of the sodium salt of poly(acrylic acid) (PAA) was studied when its counter-ion was exchanged for a series of metal cations (PAA-metal cation complexes). The thermo-responsivity of such PAA-metal cation complexes appeared greatest for divalent metal cations capable of interacting weakly with PAA carboxylates. The thermoresponsivity was correlated with the adsorption behaviour of PAA towards such cations and the hydration structure of the complexes. The effect of metal cations on the thermo-responsivity followed the Irving-Williams order of stability. The condition of such complexes allowing the generation of thermo-responsivity was discussed.

Synthesis, characterization, potentiometric and thermodynamic studies of transition metal complexes with 1-benzotriazol-1-yl-1-[( p -methoxyphenyl) hydrazono]propan-2-one†

A new series of Mn2+ and Co2+ complexes with 1-benzotriazol-2-yl-1-[(p-methoxyphenyl)-hydrazono]propan-2-one (BMHP) were synthesized and characterized by the elemental analysis, magnetic and different spectral techniques. Proton dissociation constant of the free ligand and the stepwise stability constants of its metal complexes were determined potentiometrically in 0.1 M KC1 and 40% (v/v) ethanol–water. The dissociation constants of the free ligand and its metal complexes were determined at different temperatures and the corresponding thermodynamic parameters were calculated and discussed. The dissociation process was found to be non-spontaneous, endothermic and entropically unfavorable. The changes in the standard ΔG 0 and ΔH 0 accompanying complexation were decreased with increasing metal ionic radius but increased with increasing electronegativity, ionization enthalpy, and hydration enthalpy of the metal ion. The values of (−ΔG 0) and (−ΔH 0) were in the order: Mn2+ < Co2+ < Ni2+ < Cu2+, in accord with the Irving-Williams order. The complexes were found to be stabilized by both enthalpy and entropy changes and the results suggest that complexation is an enthalpy-driven process. The distribution diagrams of the complexes in solution were evaluated. †Presented at the 37th International Conference of Coordination Chemistry (37th ICCC), Cape Town, 13–18 August, 2006.

Properties of a new 4-imidazolyl derivative of a 14-membered tetraazamacrocyclic chelating agent

A new bis-N,N'-(5-methylimidazol-4-ylmethyl) derivative of a 14-membered tetraazamacrocycle, L1, has been synthesized. The protonation constants of this compound and the stability constants of its complexes with divalent first-row transition metal ions and Fe3+ were determined at 298.2 K in aqueous 0.10 mol dm(-3) KNO3. Compound L1 exhibits high overall basicity, which is mainly conferred by the imidazolyl groups. The complexes of the divalent first row-transition metal ions of L1 follow the Irving-Williams order of stability with the maximum for Cu2+ as expected, but a steep fall of constants is verified for the Mn2+, Fe2+ and Co2+, in one side, and for the Zn2+ complexes, in the other side. Additionally, L1 shows a large affinity for Fe3+, and the relative stability constants for its Cd2+ and Pb2+ complexes indicate that L1 may be useful for the complexometric determination of these two toxic metal ions in solutions containing both metal ions. These studies together with NMR, UV-vis and EPR spectroscopic data indicated the presence of mononuclear complexes, which adopt distorted pyramidal or octahedral geometries depending on the metal centre. The X-ray crystal structure of [Cu(HL1)](PF6)2(NO3).H2O showed that the coordination sphere of the copper centre can be described as a distorted square pyramid with the basal plane defined by three nitrogen donors of the macrocycle backbone and one nitrogen atom from one imidazolyl pendant arm. The apical position is occupied by the nitrogen atom of the macrocycle trans to the pyridine ring. To achieve this coordination environment, the macrocycle is folded along the axis defined by the two N atoms contiguous to the pyridine ring. The free methylimidazolyl arm points away from the metal centre leading to an intramolecular Cu[dot dot dot]N distance of 5.155(1) A.

Functional characterization of the dimerization domain of the ferric uptake regulator (Fur) of Pseudomonas aeruginosa

The functional properties of the recombinant C-terminal dimerization domain of the Pseudomonas aeruginosa Fur (ferric uptake regulator) protein expressed in and purified from Escherichia coli have been evaluated. Sedimentation velocity measurements demonstrate that this domain is dimeric, and the UV CD spectrum is consistent with a secondary structure similar to that observed for the corresponding region of the crystallographically characterized wild-type protein. The thermal stability of the domain as determined by CD spectroscopy decreases significantly as pH is increased and increases significantly as metal ions are added. Potentiometric titrations (pH 6.5) establish that the domain possesses a high-affinity and a low-affinity binding site for metal ions. The high-affinity (sensory) binding site demonstrates association constants (K(A)) of 10(+/-7)x10(6), 5.7(+/-3)x10(6), 2.0(+/-2)x10(6) and 2.0(+/-3)x10(4) M(-1) for Ni2+, Zn2+, Co2+ and Mn2+ respectively, while the low-affinity (structural) site exhibits association constants of 1.3(+/-2)x10(6), 3.2(+/-2)x10(4), 1.76(+/-1)x10(5) and 1.5(+/-2)x10(3) M(-1) respectively for the same metal ions (pH 6.5, 300 mM NaCl, 25 degrees C). The stability of metal ion binding to the sensory site follows the Irving-Williams order, while metal ion binding to the partial sensory site present in the domain does not. Fluorescence experiments indicate that the quenching resulting from binding of Co2+ is reversed by subsequent titration with Zn2+. We conclude that the domain is a reasonable model for many properties of the full-length protein and is amenable to some analyses that the limited solubility of the full-length protein prevents.

Complexation of some hydrazones bearing the quinoline ring: potentiometric studies

Three hydrazones (oximic: MHQ; ketonic: BHQ and phenolic: AHQ) bearing the quinoline moiety were prepared and characterized. Their dissociation constants as well as their stability constants with some transition, lanthanide and actinide metal ions have been investigated potentiometrically in 75% (v/v) dioxane-water at 303K. Also, stability constants of cobaloximes in 75% (v/v) solvent-water (solvent = dioxane, isopropanol, ethanol and methanol) as well as in 75, 70, 65, 60 and 55% (v/v) ethanol-water at 303K were evaluated. A linear regression analysis was used to evaluate the stability constants in the aqueous medium. Irving-Williams order for stability is not strictly obeyed.

Multimetal multiligand complex formation equilibria of copper(II), nickel(II) and zinc(II) with L-2-amino-3-methylbutanoic acid (valine) and nitrilotriacetic acid

Formation equilibria of homo and heterobinuclear ternary/quaternary complexes of Cu II , Ni II and Zn II with nitrilotriacetic acid (A) and valine (B) ligands in aqueous solution have been investigated. Stability constants of the complexes and the complex formation equilibria at temperature 30 ± 1° and the ionic strength I = 0.1 M (NaNO 3 ) have been determined by potentiometric method. Complexes of the type MAB (2:2:1) and M 1 M 2 AB (1: 1: 1: 1 )/( )/( 1: 1: 2: 1) have been discussed from the computer based analysis. Stability constants of binary, ternary and quaternary complexes follow the Irving-Williams order.

Interpretation of Transition Metal Sorption Behavior by Oxidized Active Carbons and Other Adsorbents

Several active carbons derived from different precursors and oxidized by different techniques have been characterized by N2 porosimetry and various titration methods. The adsorption of Cu2+, Ni2+, Co2+, Zn2+ and Mn2+ from aqueous solutions was studied using these carbons and carboxylic resin Purolite C104. The affinity series Mn2+ < Co2+ < Ni2+ < Cu2+ > Zn2+ established in adsorption experiments coincides with the Irving–Williams order and is independent of the method and extent of adsorbent oxidation, carbon precursor, porous structure, and type of adsorbent. Enhanced selectivity of adsorbents towards Cu2+ is related to the electronic structure of this ion.

Ditopic hexaazamacrocycles containing pyridine: synthesis, protonation and complexation studies

Structural studies of metal complexes of five ditopic hexaazamacrocycles containing two pyridine rings ([n]py2N4 n= 18, 20, 22, 24 and 26) have been carried out. The synthesis of macrocycles [22]- to [26]-py2N4 are also reported. The protonation constants of the last three compounds and the stability constants of their complexes with Ni2+, Cu2+, Zn2+, and Pb2+ were determined at 25 degrees C in 0.10 mol dm(-3) KNO3 in aqueous solution. Our results with [22]py2N4 show significant differences from those described previously, while [24]py2N4 has not been studied before and [26]py2N4 is a new compound. Mononuclear and dinuclear complexes of the divalent metal ions studied with [22]- to [26]-py2N4 were found in solution. The stability constants for the ML complexes of the three ligands follow the Irving-Williams order: NiL2+ < CuL2+ >> ZnL2+ > PbL2+, however for the dinuclear complexes the values for Pb2+ complexes are higher than the corresponding values for the Ni2+ and the Zn2+ complexes. The X-ray single crystal structures of the supramolecular aggregates [Cu2([20]py2N4)(H2O)4][Cu(H2O)6](SO4)3 x 3H2O and [Cu(2)([20]py(2)N4)(CH3CN)4][Ni([20]py2N4)]2(ClO4)8 x H2O, which are composed of homodinuclear [Cu2([20]py2N4])(H2O)4]4+ and [Cu2([20]py2N4])(CH3CN))4]4+, and mononuclear species, [Cu(H2O)6]2+ and [Ni([20]py2N4)]2+, respectively, assembled by an extensive network of hydrogen bonds, are also reported. In both homodinuclear complexes the copper centres are located at the end of the macrocycle and display distorted square pyramidal coordination environments with the basal plane defined by three consecutive nitrogen donors and one solvent molecule, water in and acetonitrile in . The macrocycle adopts a concertina-type conformation leading to the formation of macrocyclic cavities with the two copper centres separated by intramolecular distances of 5.526(1) and 5.508(7) A in 1a and 2a, respectively. The mononuclear complex [Ni([20]py2N4])]2+ displays a distorted octahedral co-ordination environment with the macrocycle wrapping the metal centre in a helical shape. EPR spectroscopy of the copper complexes indicated the presence of mono- and dinuclear species.

Polarographic behaviour of 3-(1-phenyl)-1-(2' -hydroxynaphthyl)-2-propen-1-one and thermodynamic parameters of complexes of bivalent transition metal ions

The electrochemical reduction behaviour of 3-(1-phenyl)-1-(2'-hydroxynaphthyl)-2-propen-1-one (PHPO) has been studied in aq. DMF media of pH 2.0 to 12.0 by d.c. polarography. Diffusion coefficient (D) of the electrode process has been calculated. The stability constants of UO 2 + 2, Cu 2 + , Zn 2 + , Co 2 + , Ni 2 + and Mn 2 + complexes of PHPO have been determined in 75% (v/v) dioxane-water, acetone-water and 2-ethoxyethanol-water mixture using the Bjerrum-Calvin pH titration technique as developed by trying and Rossottii. The stability constants are in fair agreement with Irving-Williams order. The results obtained are compared with electrochemical reduction behaviour of PHPO and also with the data available in the literature. Abnormal behaviour of the chelates was observed in acetone-water medium. The thermodynamic parameters such as free energy, enthalpy and entropy changes involved in complexation have been calculated.

Release and phase partitioning of metals from anoxic estuarine sediments during periods of simulated resuspension.

Periodically, marine sediments are subjected to physical processes which resuspend them into the water column, releasing previously sequestered metals. The role of resuspension energy and duration on release and subsequent redistribution of sediment bound metals was measured experimentally using a particle entrainment simulator. Two metal contaminated anoxic sediments with different physical and chemical characteristics were resuspended for 12 h at energies of 2 and 5 dynes cm(-2). Samples were taken at specified intervals, and the water column pH, Eh and dissolved oxygen levels were monitored continuously. Over time, metal concentrations increased in the particulate (nonfilterable > or = 1 microm) and filterable (< 1 microm) phases of the overlying water. In general, metal enrichment followed the Irving-Williams order of complex stability. Overall, the sediment's chemical and physical composition were major factors in determining the amount of metal released, more so than the level of resuspension energy applied. These results provide insight into how physical and chemical processes interact during sediment resuspension to release sediment bound metals and control their phase distribution in the water column.

A new bipodal carboxy-bis(hydroxypyridinonate) ligand.: Synthesis and complexation with copper(II), nickel(II) and zinc(II) in aqueous solution

A new tetradentate ligand having two 3-hydroxy-4-pyridinonate moieties and one carboxylate group appended to a cyclohexane backbone is reported, together with the corresponding bidentate hydroxypyridinonate pendant arm. The synthesis and characterization of these ligands, as well as their complexation properties towards the first transition series of metal ions M(II) (M=Cu, Ni, Zn) in aqueous solution, are described and discussed herein. The tetradentate ligand forms quite stable complexes with this series of metal ions and in solution, it is proved to be a much more effective chelator than the corresponding bidentate derivative. The stability constants of the complexes formed with this set of bivalent ions follow the Irving–Williams order Ni<Cu>Zn. The carboxylic group has no interaction with the metal centre, thus remaining free for potential interaction with biological ligands (e.g. proteins).

Potentiometric and spectrometric study: Copper(II), nickel(II) and zinc(II) complexes with potentially tridentate and monodentate ligands

Equilibrium and solution structural study of mixed-metal-mixed-ligand complexes of Cu(II), Ni(II) and Zn(II) with L-cysteine, L-threonine and imidazole are conducted in aqueous solution by potentiometry and spectrophotometry. Stability constants of the binary, ternary and quaternary complexes are determined at 25 ±1°C and in I= 0.1 M NaClO4. The results of these two methods are made selfconsistent, then rationalized assuming an equilibrium model including the species H3A, H2A, A, BH, B, M(OH), M(OH)2, M(A), MA(OH), M(B), M(A)(B), M2(A)2(B), M2(A)2(B-H), M1M2(A)2(B) and M1M2(A)2(B-H) (where the charges of the species have been ignored for the sake of simplicity) (A = L-cysteine, L-threonine, salicylglycine, salicylvaline and BH = imidazole). Evidence of the deprotonation of BH ligand is available at alkalinepH. N1H deprotonation of the bidentate coordinated imidazole ligand in the binuclear species atpH > 70 is evident from spectral measurements. Stability constants of binary M(A), M(B) and ternary M(A)(B) complexes follow the Irving-Williams order.

Studies of copper(ii)-binding to bacterioferritin and its effect on iron(ii) oxidationBased on the presentation given at Dalton Discussion No. 4, 10–13th January 2002, Kloster Banz, Germany.

The iron-storage protein bacterioferritin (BFR) from Escherichia coli consists of twenty four identical subunits, each containing a dinuclear metal ion-binding site (the ferroxidase centre) at which iron(II) is oxidised to iron(III) and dioxygen is reduced. Other metal ions that are commonly found in biological systems bind to the ferroxidase centre, including manganese(II), cobalt(II) and zinc(II). In this work, copper(II)-binding to BFR and its effect on iron(II) oxidation kinetics were studied by a combination of gel filtration–copper(II) binding assay, optical, magnetic and kinetic methods. Data indicate that two copper(II) ions bind per subunit with a Kd of ≈ 2.0 × 10−5 M and establish the order of divalent metal ion binding as Cu(II) < Co(II) < Zn(II), i.e. it does not follow the Irving–Williams order. A number of lower affinity copper(II)-binding sites were also detected. The presence of copper(II) was found to significantly enhance the rate of iron(II) oxidation and subsequent core formation. This effect does not arise from copper(II) bound at the ferroxidase centre but, rather, is due to displaced copper(II). The nature of the displaced copper is discussed.

Acid and metal ion promoted hydrolysis of [ N-( o-carboxyphenyl)iminodiacetato](picolinato)chromate(III) complex: a mechanistic study

The sodium salt of the [ N-( o-carboxyphenyl)iminodiacetato]picolinatochromate(III) complex has been synthesised and characterised. In acidic media, the complex has been shown to aquate to diaqua[ N-( o-carboxyphenyl)imminodiacetato]chromium(III) and picolinic acid as the ultimate products. The enhanced kinetic stability exhibited by the aromatic amino acid (cida) may be attributed to (i) resonance interaction of the carboxyl and tertiary nitrogen group with the phenyl ring resulting in a shortening of the bond distance and thus leading to a closer approach of the chelate donor groups, (ii) the presence of a larger number (two five-membered and one six-membered ring) of chelate rings in the ligated amino acid, in comparison to only one five-membered metal–picolinato ring. The variation of the observed pseudo-first-order rate constants with perchloric acid concentration suggests the operation of two concurrent uncatalysed and acid-catalysed pathways. The reaction exhibits a solvent deuterium isotope effect k D/ k H=1.5 at 45 °C. The solvent deuterium isotope effect is consistent with a rapid pre-equilibrium protonation followed by rate-determining ring opening and excludes a mechanism involving concerted attack by [H 3O +]. The metal ions, Cu 2+, Ni 2+, and Zn 2+, promoted hydrolysis in weakly acidic medium has been studied as a function of metal ion concentration and temperature. The metal ion catalysed aquation is proposed to take place through a rapid pre-equilibrium step to form a binuclear complex with the M 2+ ion, followed by the cleavage of the CrO bond in a slow rate-determining step. The catalytic efficiency of the metal ion follows the Irving–Williams order of stability and also parallels the log k M-pic values.

Thermodynamics of Dissociation and Metal Complexation of 3-Nitro-1,5-Diphenylformazan

Thermodynamic parameters for dissociation of 3-nitro-1,5-diphenylformazan and its complexation by some divalent metal ions were determined in a 50%(v/v) dioxane–water mixture at constant ionic strength (0.1 M KCl) using an automatic potentiometric technique. The changes in the standard Gibbs energy ΔGo and enthalpy ΔHo accompanying the complexation were found to decrease with increasing metal ionic radius and to increase with the electronegativity, the ionization enthalpy, and the enthalpy of hydration. The order of −ΔGo and −ΔHo values were found to be Mn2+ Zn2+, in accordance with the Irving–Williams order. The complexes were stabilized by both enthalpy and entropy changes and the results suggest that the complexation is an enthalpy-driven process. The transition-series contraction energy Er(Mn–Zn) and the ligand field stabilization energy δ H were calculated from the enthalpy changes.

High concentrations of complexed metals in the guts of deposit feeders

Sediment particles passing through the guts of deposit feeders are subject to an environment unusually rich in dissolved organic material, especially proteinaceous materials, capable of binding metals. Concentrations of many heavy metals are high in gut fluids of various deposit feeders from pristine environments. Concentrations of Cu and Cd show strong correlations with total acid‐hydrolyzed amino acids (TAHAA) in gut fluids in a cross‐phyletic survey of 35 deposit feeder species. Similar correspondence with TAHAA obtains among individuals, along longitudinal gut sections, and among molecular weight fractions. Multiple incubations of sediments with a commercial protein solution having similar TAHAA concentration as gut fluid solubilized many metals, showing convergence toward similar composition as gut fluid. Adherence of gut‐dissolved metal concentrations to the Irving‐Williams order suggests that the rich milieu of soft ligands contained in gut fluids provides a mechanism for mobilization of softer metals in sediments.

Trace metal composition of colloidal organic material in marine environments

Marine colloidal material (1 kDa–0.2 μm) was isolated by cross-flow ultrafiltration followed by diafiltration and freeze-drying from surface waters of the Gulf of Mexico and the Middle Atlantic Bight (MAB), as well as from estuarine waters of Galveston Bay. Elemental characterization of isolated colloidal material included organic carbon (OC) and selected trace metal (Cu, Pb, Zn, Cd, Co, Ni, Cr, Be, Fe, Al, Mn, V, Ba, and Ti) determinations. It was found that levels of these metals in marine colloids ranged from <0.1 to ∼50 μg/g colloidal matter, except for Fe which generally had a concentration >120 μg/g. Most metals (Cu, Pb, Zn, Ni, Al, Mn, V, and Ti) had an average concentration >1 μg/g while concentrations of Cd, Co and Be were usually <1 μg/g. Metal concentrations (μg/g) in isolated colloids were, in general, higher in Galveston Bay than in the Gulf of Mexico, suggesting either high abundance of trace metals in estuarine waters or differences in organic matter composition. Higher colloidal metal concentrations in the MAB than in the Gulf of Mexico might be due to higher terrestrial inputs in the MAB. Colloidal metal concentrations (μg/g) were generally lower than those in average soils, continental crust and suspended particles. However, metal/aluminum ratios (Me/Al) in isolated marine colloids were significantly higher than those for average soils and continental crust. Most importantly, colloids had a metal composition and metal/OC ratio (Me/C) similar to humic substances and marine plankton, suggesting that marine colloids largely originate from planktonic sources and are composed of predominately organic components. The Me/C ratios of Galveston Bay colloids followed the sequence of Cu>Ni, Cr, Zn>Mn>Co>Pb, Cd, which is similar to the Irving–Williams order except for Mn, suggesting that the interaction of metals with marine colloids is determined by the affinity of metals for specific organic ligands.