Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

Ceric ammonium nitrate (CAN) or Ce^IV(NH₄)₂(NO₃)₆ is often used in artificial water oxidation and generally considered to be an outer-sphere oxidant. Herein we report the spectroscopic and crystallographic characterization of [(N4Py)Fe^III-O-Ce^IV(OH₂)(NO₃)₄]⁺ ( 3 ), a complex obtained from the reaction of [(N4Py)Fe^II(NCMe)]²⁺ with 2 equiv CAN or [(N4Py)Fe^IV=O]²⁺ ( 2 ) with Ce^III(NO₃)₃ in MeCN. Surprisingly, the formation of 3 is reversible, the position of the equilibrium being dependent on the MeCN/water ratio of the solvent. These results suggest that the Fe^IV and Ce^IV centers have comparable reduction potentials. Moreover, the equilibrium entails a change in iron spin state, from S=1 Fe^IV in 2 to S=5/2 in 3 , which is found to be facile despite the formal spin-forbidden nature of this process. This observation suggests that Fe^IV=O complexes may avail of reaction pathways involving multiple spin states having little or no barrier.     

A Thermodynamic Study on the Binding of Cobalt(II) and Iron(III) Ions with Bovine Carbonic Anhydrase II at Different Temperatures

A thermodynamic study on the interaction of bovine carbonic anhydrase II, CAII, with cobalt(II) and iron(III) ions was made using isothermal titration calorimetry (ITC) at 300.15 K and 310.15 K in Tris buffer solutions at pH=7.5. The enthalpies of interaction of Co²⁺+ CAII and Fe³⁺+ CAII are reported and analyzed in terms of the extended solvation theory. The results indicate that there are three identical and non-cooperative binding sites for Co²⁺ and Fe³⁺ ions. Binding of these ions with CAII occurs exothermically with dissociation equilibrium constants of 87.15 and 91.00 μmol⋅L⁻¹ at 300.15 K, for Co²⁺ and Fe³⁺, respectively.     

What Determines the Selectivity of Arginine Dihydroxylation by the Nonheme Iron Enzyme OrfP?

The nonheme iron enzyme OrfP reacts with l -Arg selectively to form the 3R,4R-dihydroxyarginine product, which in mammals can inhibit the nitric oxide synthase enzymes involved in blood pressure control. To understand the mechanisms of dioxygen activation of l -Arg by OrfP and how it enables two sequential oxidation cycles on the same substrate, we performed a density functional theory study on a large active site cluster model. We show that substrate binding and positioning in the active site guides a highly selective reaction through C³−H hydrogen atom abstraction. This happens despite the fact that the C³−H and C⁴−H bond strengths of l -Arg are very similar. Electronic differences in the two hydrogen atom abstraction pathways drive the reaction with an initial C³−H activation to a low-energy ⁵σ-pathway, while substrate positioning destabilizes the C⁴−H abstraction and sends it over the higher-lying ⁵π-pathway. We show that substrate and monohydroxylated products are strongly bound in the substrate binding pocket and hence product release is difficult and consequently its lifetime will be long enough to trigger a second oxygenation cycle.     

Phenol Oxidation by a Nickel(III)–Fluoride Complex: Exploring the Influence of the Proton Accepting Ligand in PCET Oxidation

In order to gain insight into the influence of the H⁺-accepting terminal ligand in high-valent oxidant mediated proton coupled electron transfer (PCET) reactions, the reactivity of a high valent nickel–fluoride complex [Ni^III(F)(L)] ( 2 , L=N,N’-(2,6-dimethylphenyl)-2,6-pyridinecarboxamidate) with substituted phenols was explored. Analysis of kinetic data from these reactions (Evans–Polanyi, Hammett, and Marcus plots, and KIE measurements) and the formed products show that 2 reacted with electron rich phenols through a hydrogen atom transfer (HAT, or concerted PCET) mechanism and with electron poor phenols through a stepwise proton transfer/electron transfer (PT/ET) reaction mechanism. The analogous complexes [Ni^III(Z)(L)] (Z=Cl, OCO₂H, O₂CCH₃, ONO₂) reacted with all phenols through a HAT mechanism. We explore the reason for a change in mechanism with the highly basic fluoride ligand in 2 . Complex 2 was also found to react one to two orders of magnitude faster than the corresponding analogous [Ni^III(Z)(L)] complexes. This was ascribed to a high bond dissociation free energy value associated with H−F (135 kcal mol⁻¹), which is postulated to be the product formed from PCET oxidation by 2 and is believed to be the driving force for the reaction. Our findings show that high-valent metal–fluoride complexes represent a class of highly reactive PCET oxidants.     

Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Catalytic hydrogenation of nitroaromatics is an environment-benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)_x deposition on Pt nanocrystals to give Fe(OH)_x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the Fe^III-OH-Pt interfaces. While H₂ activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the Fe^III-OH-Pt interfaces. In situ IR, X-ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe³⁺/Fe²⁺ redox couple facilitates the hydrodeoxygenation of the -NO₂ group during hydrogenation catalysis. Benefitting from Fe^III-OH-Pt interfaces, the Fe(OH)_x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.     

Aliphatic Hydroxylation by a Bis(µ-oxo)dicopper(III) Complex

By using molecular oxygen bis(μ-oxo)dicopper(III) complexes can be produced from Cu(I) complexes with ligand L(X) (L(X)=p-substituted N-ethyl-N-[2-(2-pyridyl)ethyl]-2-phenylethylamine; X=OMe, Me, H, Cl, NO(2)) in which the benzylic position of the ligand is activated and hydroxylated by the Cu(2)O(2) core (see reaction scheme). Detailed characterization of this new C-H bond activation reaction by the bis(μ-oxo)dicopper(III) core reveals important information on the fundamental chemistry underlying copper monooxygenase reactivity.     

Interaction of the La(III)–Morin Complex with Human Serum Albumin

Journal of Solution Chemistry - Lanthanum (La) is one of the most reactive rare earth elements, whose carbonate had been approved by the FDA for marketing as a treatment drug for hyperphosphatemia....     

Use of Metal Ions for the Estimation of the Efficiency of Antibody–Antigen Interactions

The applicability of Co(II), Ni(II), Fe(III), and Cr(III) ion labels to the immunochemical determination of ribonuclease, Candida albicans, Trichophyton rubrum, and Phoma betaeantigens was studied. The catalytic waves of hydrogen evolution, which occur in transition metal solutions in the presence of protein compounds, were used as analytical signals. The maximum catalytic effect depends on the pH, buffer capacity, and nature of buffer solution and on the nature of antigen to be determined. A new procedure was proposed for the immunochemical determination of the ribonuclease antigen using Co(II) ions as a label. The conditions of the formation and degradation of the antibody–antigen immune complex were found. The linear analytical range for the ribonuclease antigen was 0.005–1.0 mg/mL.     

Biophysical Studies on the Site-Selective Binding of a Synthesized Selenium–Quercetin Complex on a Protein

A selenium?Cquercetin complex (SEQC) was synthesized and its structure was identified by IR, LC-MS and ¹H-NMR. Its biochemical effects on bovine serum albumin (BSA) were studied by measuring its molecular spectra including three-dimensional fluorescence, ultraviolet and circular dichroism (CD) spectra. The interaction of SEQC and BSA is discussed in terns of fluorescence quenching and F?rster??s non-radiation energy transfer theory. The thermodynamic parameters $\Delta H^{\uptheta}$ , $\Delta G^{\uptheta}$ , and $\Delta S^{\uptheta}$ were calculated at different temperatures and the results indicate that the interaction is an endothermic as well as an entropy generating process. The binding site was explored by the fluorescence probe technique using warfarin and ibuprofen as markers. It was found that around body temperature hydrophobic forces maintained the average distance from the tryptophan residue in domain?II of BSA (donor) to SEQC (acceptor) at 3.76 nm. The conformational changes of BSA were investigated by three-dimensional fluorescence and circular dichroism spectra.     

Photo-and Electro-luminescence of the New Ternary Europium(III) Complex

In recent years, the interest in developing luminescent lanthanide complexes has been greatly stimulated by their potential use in electroluminescent displays1. Europium complexes appear most attractive in view of the high photoluminescent efficiency and the high monochromatic red light that are widely exploited in full-color displays2. It has been approved that the second ligand plays an important role in europium complexes, the synergistic complexation of the second ligand can not only lead …     

Rearrangement of a P4 Butterfly Complex—The Formation of a Homoleptic Phosphorus–Iron Sandwich Complex

The versatile coordination behavior of the P₄ butterfly complex [{Cp′′′Fe(CO)₂}₂(μ,η^1:1-P₄)] ( 1 , Cp′′′=η⁵-C₅H₂^tBu₃) towards different iron(II) compounds is presented. The reaction of 1 with [FeBr₂⋅dme] (dme=dimethoxyethane) leads to the chelate complex [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:2-P₄){FeBr₂}] ( 2 ), whereas, in the reaction with [Fe(CH₃CN)₆][PF₆]₂, an unprecedented rearrangement of the P₄ butterfly structural motif leads to the cyclo-P₄ moiety in {(Cp′′′Fe(CO)₂)₂(μ₃,η^1:1:4-P₄)}₂Fe][PF₆]₂ ( 3 ). Complex 3 represents the first fully characterized “carbon-free” sandwich complex containing cyclo-P₄R₂ ligands in a homoleptic-like iron–phosphorus-containing molecule. Alternatively, 2 can be transformed into 3 by halogen abstraction and subsequent coordination of 1 . The additional isolated side products, [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:2-P₄){Cp′′′Fe(CO)}][PF₆] ( 4 ) and [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:4-P₄){Cp′′′Fe}][PF₆] ( 5 ), give insight into the stepwise activation of the P₄ butterfly moiety in 1 .     

Probing the Interaction Between a Surfactant–Cobalt(III) Complex and Bovine Serum Albumin

The mechanism of binding of the surfactant–cobalt(III) complex, cis-[Co(phen)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂⋅3H₂O (phen = 1,10-phenanthroline, C₁₄H₂₉NH₂ = tetradecylamine) with bovine serum albumin (BSA) was investigated by UV–vis absorption, circular dichroism (CD) and fluorescence spectroscopic techniques. The results of fluorescence titration revealed that the surfactant–cobalt(III) complex quenched the intrinsic fluorescence of BSA through a combination of static and dynamic quenching. The apparent binding constant (K _a) and number of binding sites (n) were calculated below and above the critical micelle concentration (CMC). The thermodynamic parameters determined by the van’t Hoff analysis of the constants (ΔH ^∘=14.87 kJ⋅mol⁻¹; ΔS ^∘=152.88 J⋅mol⁻¹⋅K⁻¹ below the CMC and 25.70 kJ⋅mol⁻¹ and 243.14 J⋅mol⁻¹⋅K⁻¹, respectively, above the CMC) clearly indicate that the binding is entropy-driven and enthalpically disfavored. Based on F?rster’s theory of non-radiation energy transfer, the binding distance, r, between donor (BSA) and the acceptor (surfactant–cobalt(III) complex) was evaluated. UV–vis, CD and synchronous fluorescence spectral results showed that the binding of the surfactant–cobalt(III) complex to BSA induced conformational changes in BSA.     

Fine tuning of the Cd(II)–bis(benzimidazole) networks by changing carboxylate anions

Three new polymeric frameworks, [Cd(bbbi)(ita)(H₂O)]?·?H₂O (1), [Cd(bbbi)(fma)] (2), and [Cd(bbbi)(fma)(H₂O)]?·?2H₂O (3) (bbbi?=?1,1-(1,4-butanediyl)bis-1?H-benzimidazole, H₂ita?=?itaconic acid, and H₂fma?=?fumaric acid), have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 is a 2-D (4,4) network containing infinite 1-D zigzag Cd(II)-bbbi chains linked by auxiliary ita ligands. In the structure of 2, infinite 1-D linear Cd(II)-bbbi chains are linked by fma ligands to generate an undulated 2-D (4,4) network. In 3, an in situ ligand transformation occurred with malate converted to H₂fma by dehydration. Thus, a 2-D (4,4) grid network constructed from bbbi and fma was obtained. The carboxylates with different substituents play an important role in the formation of the final frameworks and coordination modes of Cd(II). Thermal stability and luminescent properties of 1–3 were investigated.     

Applications of Inorganic Ion Exchangers: II—Adsorption of Some Heavy Metal Ions from Their Aqueous Waste Solution Using Synthetic Iron(III) Titanate

Adsorption of Zn²⁺ and Cd²⁺ ions from aqueous waste solutions on iron(III) titanate as inorganic ion exchange material was investigated to determine the effect of contact time, pH of solution and the reaction temperatures. Batch kinetic studies were carried out and showed that the time of equilibrium for both Zn²⁺ and Cd²⁺ ions was attained within three hours, and the order of kinetic reaction is the first order reaction. Batch distribution coefficients of Zn²⁺ and Cd²⁺ ions on iron(III) titanate as a function of pH have been studied at 25, 40 and 60 ± 1°C. From the obtained results we found that the K _d values decreased with increasing reaction temperatures. Enthalpy change (H) values for Zn²⁺ and Cd²⁺ ions were found to be –8.19 and –22.49 kJ/mol, respectively. The data of adsorption of Zn²⁺ and Cd²⁺ ions at various concentrations were fitted with the Freundlich isotherm. Finally, separation of the above mentioned cations on iron(III) titanate in a column was performed.     

Adsorptive Voltammetric Measurement of Trace Level of Iron(III) with 4–(2–Pyridylazo) Resorcin

Abstract

The polarographic behavior of the complex of iron–4– (2–pyridylazo) resorcin(PAR) was studied. In HAc– NaAc– EDTA buffer solution, the complex can be adsorped on a hanging mercury drop electrode giving a sensitive adsorptive complex reduction peak with a peak potential at -0.36V(vs. SCE). Optimum experimental conditions were found by the use of 0.08mol/L HAc, 0.06mol/L NaAc, 5.0 × 10^?3mol/L EDTA and 1.0 × 10^?5mol/L PAR. With preconcentration for 60s, the derivative peak height of the complex compound is linearly proportional to the concentration for Fe in the range from 1.0 × 10^?9mol/L to 1.0 × 10^?7mol/L. For a 2–min pre–concentration time, the detection limit found was 2.0 × 10^?10mol/L. This method has high sensitivity and selectivity. It has been applied to the determination of trace iron in food and water samples without any pre–separation step.     

Polymorphism of the Double Octa(ε-caprolactam)europium(III) Hexa(isothiocyanato)chromate(III) Complex

Russian Journal of Coordination Chemistry - A new structural polymorph of the compound [Eu(ε-C6H11NO)8][Cr(NCS)6] was isolated from the solid product mixture obtained in the reaction of EuCl3,...