Oxidation of copper(II)-coordinated diethylenetriamine by hexacyanoferrate(III) ion. A kinetic investigation

The stoichiometry and kinetics of the reaction between [Cu(dien)(OH)]⁺ and [Fe(CN)₆]³⁻ in aqueous alkaline medium are described. The rate equation − (d[Fe(III)]/dt = {k₁[OH⁻]²[[Cu(dien)(OH)]⁺] + k₂[OH⁻] × [[Cu(dien)(OH)]⁺]²}([Fe(III)]/[Fe(II)]) (Fe(III) = [Fe(CN)₆]³⁻; Fe(II) = [Fe(CN)₆]⁴⁻, the 4:4:1 OH⁻/Fe(III)/[Cu(dien)(OH)]⁺ stoichiometric ratio and the nature of the ultimate products identified in the reaction solution suggest the fast formation of a doubly deprotonated Cu(III)-diamido complex which slowly undergoes an internal redox process where the ligand is oxidised to the Schiff base H₂NCH₂CH₂NCHCHNH.The [[Cu(dien)(OH)]⁺]² term in the rate equation is explained with the formation of a transient μ-hydroxo mixed-valence Cu dimer. A two-electron internal reduction of the Cu(III) complex yielding a Cu(I) intermediate is suggested to account for the presence of monovalent copper in a precipitate which forms at relatively high reactant concentrations and in the absence of dioxygen.     

Iron and nickel complexes with heterocyclic ligands: Stability,synthesis, spectral characterization,antimicrobial activity,acute and subacute toxicity

The synthesis and characterization by elemental analysis, emission atomic spectroscopy, TG measurements, magnetic measurements, FTIR, ¹H NMR, UV–visible spectra and conductivity of a series of iron (II) and nickel (II) complexes with two heterocyclic ligands (L¹(SMX): sulfamethoxazole and L²(MIZ): metronidazole) used in pharmaceutical field and with a new ligand derived benzoxazole (L³(MPBO): 2-(5-methylpyridine-2-yl)benzoxazole), were reported. The formulae obtained for the complexes are: [M(L¹)₂ Cl₂]·nH₂O, [M(L²)₂Cl₂(H₂O)₂]·H₂O and [M(L³)₂(OH)₂]·nH₂O. Stability constants of these complexes have been determined by potentiometric methods in water–ethanol (90:10, v/v) mixture at a 0.2 mol L^?1 ionic strength (NaCl) and at 25.0 ± 0.1 °C. Sirko program was used to determine the protonation constants as well as the binding constants of three species [ML₂H₂]²⁺, [ML₂] and [ML]²⁺. The antimicrobial activity of the ligands and complexes was evaluated in vitro against different human bacteria and fungi using agar diffusion method.Iron sulfamethoxazole complex showed a remarkable inhibition of bacteria growth especially on Staphylococcus aureus and P. aeruginosa. The iron metronidazole complex is active against yeasts especially on Candida tropicalis strain. Nickel complexes presented different antibacterial and antifungal behavior's against bacteria and fungal.The acute toxicity study revealed that the iron complexes are not toxic at 2000 mg/kg dose orally administrated.LD₅₀ for nickel complexes was determined using graphical method.No significant differences in the body weights between the control and the treated groups of both rat sexes in subacute toxicity study using for iron complexes. Hematological and clinical blood chemistry analysis revealed no toxicity effects of the iron complexes. Pathologically, neither gross abnormalities nor histopathological changes were observed for these complexes.     

Metal chelates with biological activity. Part 4. Solution properties of iron(III)-histidinehydroxamic acid

Reactions of carbon monoxide with iron(II) diethyldithiocarbamate and iron(II) ethylxanthate were followed using solution IR spectroscopy. In DMF and CH₃CN solutions, the only Fe—dithiocarbamate—carbon monoxide complex observed was cis-[Fe(CO)₂(dedtc)₂]. This complex formed rapidly and appeared to be very stable, resisting displacement of the coordinated CO molecules by other ligands. Fe(exa)₂ showed very little coordination of CO in DMF solution, but in CH₃CN solution formed the complex cis-[Fe(CO)₂(exa)₂] rapidly via the monocarbonyl intermediate [Fe(CO)(exa)₂CH₃CN]. In CHCl₃ solution, in the presence of CO and added bases, a series of complexes, [Fe(CO)(exa)₂L], where L = pyridine, pyrrolidine, diethylamine and triphenylphosphine, was formed. However, with the exception of [Fe(CO)(exa)₂(ø₃P)], these monocarbonyl complexes were unstable with respect to disproportionation to cis-[Fe(CO)₂(exa)₂] and [Fe(exa)₂L₂]. No mixed-ligand monocarbonyl complexes were observed with Fe(dedtc)₂.     

A hexanuclear iron(III) complex [Fe6O2(OH)2(PhCOO)10(hedmp)2]·3CH3CN assembled from 2-hydroxyethyl-3,5-dimethyl pyrazole

In order to assemble polynuclear iron(III) complexes, the coordination chemistry of the 2-hydroxyethyl-3,5-dimethylpyrazole (hedmp-H) ligand has been investigated. Reaction of hedmp-H with trinuclear iron carboxylate precursor [Fe₃O(PhCOO)₆(H₂O)₃]Cl in acetonitrile yielded the hexanuclear Fe(III) complex [Fe₆O₂(OH)₂(PhCOO)₁₀(hedmp)₂]·3CH₃CN (1). This aggregate has been characterized by employing various analytical techniques, spectroscopic studies and single crystal X-ray diffraction. Detailed magnetic susceptibility measurements revealed that 1 displays an S_T = 5 ground state.     

Studies on metal carboxylates. VIII. Reactions of acetylacetonates of the first row transition elements with pyridine-2,6-dicarboxylic acid

The acetylacetonates VO(acac)₂, M(acac)₃, where M = V, Mn or Fe and [M′(acac)₂]_n, where M′ = Co, Ni or Cu, have been reacted with pyridine-2,6-dicarboxylic acid (dipicH₂) in acetone to afford the complexes VO(dipic)·2H₂O, M(acac)(dipic)·xH₂O [M = V, Mn or Fe and x = 1 or 0] and M₂(dipic) (dipicH)₂·yH₂O [M = Co, Ni or Cu and y = 2 or 0]. The cobalt(II) and nickel(II) complexes are converted to polymeric [M(dipic)]_n in ethanol and all three complexes formulated as M₂(dipic)(dipicH)₂ react with 2,2′2″-terpyridyl to yield M(dipic)(terpy)·3H₂O. The vanadium(III) complex V(acac)(dipic) is oxidized to VO(dipic)·4H₂O in aqueous solution via the vanadium(III) intermediate V(OH)(dipic)·2H₂O. Tentative structural conclusions are drawn for certain of these new complexes based upon room temperature spectral and magnetic measurements. The characterization of these complexes has included selected studies of their X-ray photoelectron spectra.     

Synthesis, crystal structure and characterization of alkali metal hydroxoantimonates

Several alkali metal hydroxoantimonates, K₂[Sb(O)(OH)₅], Na[Sb(OH)₆], Cs[Sb(OH)₆] and Cs₂[Sb₂(μ-O)₂(OH)₈] were isolated from aqueous solutions and characterized by single crystal and powder X-ray diffraction studies and by FTIR and thermal analysis. Crystal structures involving [Sb(O)(OH)₅]²⁻ were never anticipated before, and this is also the first disclosure of a dinuclear antimonate [Sb₂(μ-O)₂(OH)₈]²⁻. Aqueous antimonate solutions of different pH were studied by high resolution electrospray mass spectrometry showing pH indifferent spectra and predominance of the mono and dinuclear antimonate species at pH 4-10.     

The kinetics of the complex formation between iron(III)-ethylenediaminetetraacetate and hydrogen peroxide in aqueous solution

The kinetics of the formation of the purple complex [Fe^III(EDTA)O₂]³⁻, between Fe^III-EDTA and hydrogen peroxide was studied as a function of pH (8.22-11.44) and temperature (10-40 °C) in aqueous solutions using a stopped-flow method. The reaction was first-order with respect to both reactants. The observed second-order rate constants decrease with an increase in pH and appear to be related to deprotonation of Fe^III-EDTA ([Fe(EDTA)H₂O]⁻ ⇔ Fe(EDTA)OH]²⁻ + H⁺). The rate law for the formation of the complex was found to be d[Fe^IIIEDTAO₂]³⁻/dt=[(k₄[H⁺]/([H⁺] + K₁)][Fe^III-EDTA][H₂O₂], where k₄=8.15±0.05×10⁴ M⁻¹ s⁻¹ and pK₁=7.3. The steps involved in the formation of [Fe(EDTA)O₂]³⁻ are briefly discussed.     

Effect of complex formation by taxifolin and naringenin with Cu(i) ions on the distribution of the components of complexes in the octanol–water system

The interaction of two structurally close flavanones: taxifolin and naringenin with copper(I) ions and its effect on the distribution of flavonoids and the corresponding ions in a biphasic system octanol–water have been studied. It has been shown that these polyphenols form complexes with copper ions of different stoichiometric ratio depending on the pH of medium (5.4, 7.4, and 9.0). The interaction of the flavonoids with copper ions leads to an increase in the fraction of polyphenols in the water phase at all pH values examined. The fraction of metal ions in octanol in the presence of both taxifolin and naringenin is maximal in the range of neutral pH values. The parameters obtained in the study, such as the partition coefficient and the coefficient of distribution in a biphasic system octanol–water (logP and logD) form the physicochemical basis necessary for the estimation of the bioavailability of flavonoids and the corresponding metal ions upon their combined consumption.     

Imidazole,imidazolate, and hydroxide complexes of (protoporphyrin IX)iron(III) and its dimethyl ester as model systems for ferric hemoproteins: Electron paramagnetic resonance and electronic spectral study

The EPR and electronic spectral changes upon titration of systems consisting of (protoporphyrin IX)iron(III) chloride (Fe(PPIX)Cl) or its dimethyl ester (Fe-(PPIXDME)Cl) and imidazole derivatives with tetrabutylammonium hydroxide solution have been measured at 77 and 298 °K in various solvents. The EPR and electronic spectra of the melt of Fe(PPIXDME)Cl in imidazole derivatives have been also measured. The imidazole derivatives studied here were imidazole and 4-methyl-, 4-phenyl-, 2-methyl-, 2,4-dimethyl-, 1-methyl-, and 1-acetylimidazole. The spectral changes upon addition of hydroxide were markedly different between the systems containing NH imidazoles (BH), with a dissociable proton, and those containing NR imidazoles (BR), without it. In the former systems, five spectral species were successively formed at 77 °K and were assigned to following complexes: [Fe(P)(BH)₂]⁺, Fe(P)(BH)(B), [Fe(P)(B)₂]^?, Fe(P)(BH)(OH), and [Fe(P)(B)(OH)]^?, where P is PPIX or PPIXDME. In the latter systems, initial complex, [Fe(P)(BR)₂]⁺, was found to be changed to final complex, Fe(P)(BR)(OH), through an intermediate at 77 °K. At 298 °K, both systems were found to react with hydroxide to finally form Fe(P)(OH). The crystal field parameters were evaluated using the EPR g values in low-spin complexes studied here and in hemoproteins. The five regions corresponding to five low-spin complexes could be distinguished in crystal field diagrams.     

Towards a model of non-equilibrium binding of metal ions in biological systems

We have used a systems biology approach to address the hitherto insoluble problem of the quantitative analysis of non-equilibrium binding of aqueous metal ions by competitive ligands in heterogeneous media. To-date, the relative proportions of different metal complexes in aqueous media has only been modelled at chemical equilibrium and there are no quantitative analyses of the approach to equilibrium. While these models have improved our understanding of how metals are used in biological systems they cannot account for the influence of kinetic factors in metal binding, transport and fate. Here we have modelled the binding of aluminium, Al(III), in blood serum by the iron transport protein transferrin (Tf) as it is widely accepted that the biological fate of this non-essential metal is not adequately described by experiments, invitro and insilico, which have consistently demonstrated that at equilibrium 90% of serum Al(III) is bound by Tf. We have coined this paradox ‘the blood-aluminium problem’ and herein applied a systems biology approach which utilised well-found assumptions to pare away the complexities of the problem such that it was defined by a comparatively simple set of computational rules and, importantly, its solution assumed significant predictive capabilities. Here we show that our novel computational model successfully described the binding of Al(III) by Tf both at equilibrium and as equilibrium for Al_Tf was approached. The model predicted significant non-equilibrium binding of Al by ligands in competition with Tf and, thereby, provided an explanation of why the distribution of Al(III) in the body cannot be adequately described by its binding and transport by Tf alone. Generically the model highlighted the significance of kinetic in addition to thermodynamic constraints in defining the fate of metal ions in biological systems.     

New Fe starting materials: preparation, characterisation and structural features of iron halide complexes with alcohol ligands

The new mononuclear [FeCl₂(HOPrⁱ)₄] (1), polymeric [{Cl₃Fe(μ-Cl)Fe(HOPrⁱ)₄}_n] (2) and binuclear [I₂Fe(μ-I)₂Fe(PrⁱOH)₄] (3) iron(II) complexes have been synthesized in high yields in propan-2-ol or toluene/propan-2-ol mixtures at room temperature. Magnetic moment measurements, ⁵⁷Fe Mössbauer spectroscopy data and the results of semi-empirical quantum mechanical calculations confirmed the high-spin configuration of the iron(II) centres, which were shown to be four- and/or six-coordinate by single crystal X-ray diffraction analyses. Intermolecular hydrogen bonding was observed in the solid state structure of 1, intramolecular interactions in 2, while both intra- and intermolecular association was seen in 3. Long iron-(μ-halide) bonds suggest the possibility of complex dissociation in solution and facile ligand substitution in 2 and 3.     

Enantioselective DNA binding of iron(II) complexes of methyl-substituted phenanthroline

The enantioselective binding of [Fe(4,7-dmp)₃]²⁺ (dmp: 4,7-dimethyl-1,10-phenantroline) and [Fe(3,4,7,8-tmp)₃]²⁺ (tmp: 3,4,7,8-tetramethyl-1,10-phenanthroline) to calf-thymus DNA (ct-DNA) has been systematically studied by monitoring the circular dichroism (CD) spectral profile of the iron(II) complexes in the absence and presence of ct-DNA. The effect of salt concentration and temperature on the degree of enantioselectivity of the ct-DNA binding of the iron(II) complexes, i.e. the molar ratio of Δ- to Λ-enantiomer in the solution or vice versa has been rigorously evaluated. It is noticeable that Δ-[Fe(4,7-dmp)₃]²⁺ and Λ-[Fe(3,4,7,8-tmp)₃]²⁺ are preferentially bound to ct-DNA as reflected in their opposite CD spectral profiles. The preferential binding of the Λ-enantiomer of [Fe(3,4,7,8-tmp)₃]²⁺ to ct-DNA compared to that of the Δ-enantiomer is associated with the bulkiness of the ancillary ligands due to substitution of four hydrogen atoms in 1,10-phenanthroline for four methyl groups. The determination of enantiomeric inversion constant (K_inv) at various salt concentrations has revealed that the degree of enantioselectivity is salt concentration dependent, indicating that electrostatic interaction is involved in the enantioselective binding of the iron(II) complexes to ct-DNA. Although [Fe(4,7-dmp)₃]²⁺ and [Fe(3,4,7,8-tmp)₃]²⁺ exhibit an opposite pattern in the CD spectra, the degree of their enantioselectivity (K_inv) is not different from each other significantly. A thermodynamic study on the enantioselective binding of [Fe(4,7-dmp)₃]²⁺ to ct-DNA using the van’t Hoff plot of ln K_inv versus 1/T has demonstrated that the enthalpy change (ΔH°) in the inversion process from the Λ- to Δ-enantiomer of [Fe(4,7-dmp)₃]²⁺ ct-DNA is positive, indicating that the process is endothermic and thus entropically driven.     

Acid activation of titanium alkoxide systems - Structural characterisation of Ti(IV) sulfonyl-imide complexes

Treatment of [Ti(OⁱPr)₄] with the sulfonyl-imine systems Tos₂NH ([(p-Me-C₆H₄SO₂)₂NH]) and Tf₂NH ([(CF₃SO₂)₂NH]) results in the formation of the new Lewis acidic titanium sulfonyl-imide complexes [Ti(OⁱPr)₂(O,O′-Tos₂N)₂] (1) and [Ti(OⁱPr)₂(HOⁱPr)₂(O-Tf₂N)₂] (2), respectively. The molecular structures of the complexes have been determined by single crystal X-ray diffraction. The reaction of [Ti(OⁱPr)₃(OAr)] (Ar = 2,6-di-tert-butyl-4-methyl phenyl) with Tf₂NH results in the formation of the dimeric complex [Ti(OⁱPr)₃(O,O′-Tf₂N)]₂ (3), which has also been structurally characterised. The ability of the complexes to catalyst the Friedel-Crafts acylation of anisole has also been assessed.     

Heterometallic complex formation on p-sulfonatothiacalix[4]arene platform resulting in pH- and redox-modification of [Ru(bpy)3] luminescence

The pH-dependent heterometallic complex formation with p-sulfonatothiacalix[4]arene (TCAS) as bridging ligand in aqueous solutions was revealed by the use of spectrophotometry, nuclear magnetic relaxation and fluorimetry methods. The novelty of the structural motif presented is that the appendance of emission metal center ([Ru(bpy)₃]²⁺) is achieved through the cooperative non-covalent interactions with the upper rim of TCAS. The second metal block (Fe(III), Fe(II) and Mn(II)), bound with the lower rim of TCAS in the inner sphere coordination mode is serving as quencher of [Ru(bpy)₃]²⁺ emission. The difference between the complex ability of Fe(III) and Fe(II) ions provides pH conditions for redox-dependent emission of [Ru(bpy)₃]²⁺.     

Oxidation of thiocyanate by iron(V) in alkaline medium

The oxidation of thiocyanate by iron(V) (Fe(V)) was studied as a function of pH in alkaline solutions by a premix pulse radiolysis technique. The rates decrease with an increase in pH. The rate law for the oxidation of SCN⁻ by Fe(V) was obtained as −d[Fe(V)]/dt = k₁₀{[H⁺]²/([H⁺]² + K₂[H⁺] + K₂K₃)}[Fe(V)][SCN⁻], where k₁₀ = 5.72 ± 0.19 × 10⁶ M⁻¹ s⁻¹, pK₂ = 7.2, and pK₃ = 10.1. The reaction precedes via a two-electron oxidation, which converts Fe(V) to Fe(III). Thiocyanate reacts approximately 10³× faster with iron(V) than does with iron(VI).     

Isokinetic Relationship in the Oxidation of Cuprous Stellacyanin by Cobalt(III) Complexes

Rate parameters have been obtained for the oxidation of cuprous stellacyanin by cobalt(III) ions of the form cis(N)-[CoN₂O₄]^?, including cis(N)-[Co(NTA)(gly)]^?, cis(N)-[Co(IDA)₂]^?, [Co(en)(ox)₂]^?(μ 0.5 M(phosphate), pH 7.0), and Co(EDTA)^?(μ 0.1 M(NaCl), pH 7.2, 0.001 M phosphate). An excellent isokinetic correlation between the activation parameters ΔH^≠ and ΔS^≠ exists for the reactions of aminopolycarboxylatocobalt(III) ions with reduced stellacyanin (β = 300 ± 12 K; correlation coefficient = 0.995). It is concluded that enthalpy-entropy compensation in these reactions may be understood in terms of differing orientations preferred by the various oxidants in forming precursor complexes with the reduced blue protein. While ΔH^≠ and ΔS^≠ values for electron transfer from stellacyanin to cis(N)-[CoN₂O₄]^? ions vary over ranges of 10.7 kcal/mol and 34 cal/mol-deg, respectively, room temperature rate constants are relatively constant (3.6–34.5 M^?1 sec^?1), as expected from Marcus theory for outer sphere electron transfer.     

Syntheses, structures, and magnetic properties of three Fe(II) complexes with reduced radical ligands

Three new Fe(II) complexes [Fe(HIM2py)₂(SCN)₂] (1), [Fe(HIM2py)₂(H₂O)₂](ClO₄)₂ · 2H₂O (2), and [Fe(HIM2py)₂(4,4-bipy)](ClO₄)₂ · 3CH₃CH₂OH (3) (4,4-bipy = 4,4′-bipyridine, HIM2py = 1-hydroxyl-2(2′-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole) have been synthesized and characterized structurally as well as magnetically. The X-ray analysis reveals that HIM2py ligands are coordinated to the metal ions as an unusual six-membered didentate chelate with the κ²N(py), O(HIM) mode. Fe(II) ions in complex 3 are bridged by 4,4-bipy, leading to a 1D chain structure. The magnetic behavior of complex 3 is investigated, showing weak antiferromagnetic interactions.     

Dinuclear complexes with a μ-cyano ligand. Part X. Synthesis and characterization of several derivatives of cis-diaquaamminecobalt(III) complexes. Influence of pH

Six new dinuclear complexes, derived from cis-[Co(H₂O)₂(NH₃)₄]³⁺, cis-[Co(H₂O)₂(en)₂]³⁺ and [M(CN)₄^2? (M = Ni, Pd, Pt) were prepared and characterized by means of chemical analysis, electronic and IR measurements. The influence of the pH on the rate of the reaction was studied for the two derivatives of [Pd(CN)₄]^2?, showing that the best conditions to obtain the dinuclear compounds are at pH near 6, where the predominant species are cis-[Co(OH)(H₂O)(amine)₂]²⁺. The [Pt(CN)₄]^2? derivatives show PtPt interactions both in the solid state and in solution.     

Iron(III) nitrate complexes with linear pentacoordinate ligands and their base hydrolysis products

The complexes, Fe(saldpt)NO₃, [Fe(salmedpt)]₂(NO₃)(OH), Fe(saldien)NO₃, and Fe(salmedien)NO₃·CH₂Cl₂, have been prepared. Solid state properties (IR spectra, Mössbauer spectra and magnetic moments) and solution properties (electronic spectra, PMR spectra, conductivities and cyclic voltammograms) have been measured. The saldpt and saldien compounds when reacted with aqueous KOH formed Fe(saldpt)sal and Fe(saldien)OC₂H₅·H₂O. Single crystals of Fe(saldpt)sal were prepared and examined. Crystal data: Fe(saldpt)sal: monoclinic, space group P2₁/c(#14), a=12.486(5), b=18.502(8), c=10.870(5) Å, β=104.23(3)°, V=2434(2) ų, Z=4, D_c=1.40 g cm⁻³, R=0.0473 (R_w=0.0681) for 317 parameters and 2107 data with F_o² > 3σ(F_o²).     

Synthesis of water-soluble dinuclear metal complexes [metal = cobalt(II) and nickel(II)] and their behavior in solution

Two dinuclear metal complexes, [Co₂(bhmp)(MeCO₂)₂]ClO₄ · 2H₂O (1) and [Ni₂(bhmp)(MeCO₂)₂]ClO₄ · 2H₂O (2), were synthesized with a dinucleating ligand, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [H(bhmp)]. Both complexes were easily soluble in water as well as in DMF. Electronic spectra for both complexes were measured in both solvents and analyzed using the angular overlap model (AOM). From the electronic spectra and molar conductance, both complexes were determined to exist as [M₂(bhmp)(MeCO₂)₂]⁺ (M = Co^II or Ni^II) in DMF, dissociating perchlorate ions. On the other hand, in water, it was concluded that the acetate ions were partially dissociated and each complex existed as a mixture of some dissociated species, such as [M₂(bhmp)(MeCO₂)(H₂O)₂]²⁺ and [M₂(bhmp)(H₂O)₄]³⁺ (M = Co^II or Ni^II). Such dissociation was also confirmed by precipitation of the dissociated species when NaBPh₄ was added into an aqueous solution of the nickel complex.