Oxidation of mixed-valence CoIII/FeII complexes reversed at high pH: A kinetico-mechanistic study of water oxidation

The outer-sphere oxidation of Fell in the mixed-valence complex trans-[(LCoNCFeII)-Co-14S-N-III(CN)(6)](-), being L-14S an N3S2 macrocylic donor set on the cobalt(III) center, has been studied. The comparison with the known processes of N-5 macrocycle complexes has been carried out in view of the important differences occurring on the redox potential of the cobalt center. The results indicate that the outer-sphere oxidation reactions with S2O82- and [Co(ox)(3)](3-) involve a great amount of solvent-assisted hydrogen bonding that, as a consequence from the change from two amines to sulfur donors, are more restricted. This is shown by the more positive values found for DeltaS(double dagger) and DeltaV(double dagger). The X-ray structure of the oxidized complex has been determined, and it is clearly indicative of the above-mentioned solvent-assisted hydrogen bonding between nitrogen and cyanide donors on the cobalt and iron centers, respectively. trans-[(LCoNCFeIII)-Co-14S-N-III(CN)(6)], as well as the analogous N-5 systems trans-[(LCoNCFeIII)-Co-14-N-III(CN)(6)], trans-[(LCoNCFeIII)-Co-15-N-III-(CN)(6)], and cis-[(LCoNCFeIII)-Co-n-N-III(CN)(6)], Oxidize water to hydrogen peroxide at pH > 10 with a rather simple stoichiometry, i.e., [(LCoNCFeIII)-Co-n-N-III(CN)(5)] + OH- - [(LCoNCFeII)-Co-n-N-III(CN)(5)](-) + 1/2H(2)O(2). In this way, the reversibility of the iron oxidation process is achieved. The determination of kinetic and thermal and pressure activation parameters for this water to hydrogen peroxide oxidation leads to the kinetic determination of a cyanide based OH- adduct of the complex. A second-order dependence on the base concentration is associated with deprotonation of this adduct to produce the final inner-sphere reduction process. The activation enthalpies are found to be extremely low (15 to 35 kJ mol(-1)) and responsible for the very fast reaction observed. The values of DeltaS(double dagger) and DeltaV(double dagger) (-76 to -113 J K-1 mol(-1) and -5.5 to -8.9 cm(3) mol(-1), respectively) indicate a highly organized but not very compressed transition state in agreement with the inner-sphere one-electron transfer from O2- to Fe-III.

Iron catalysed assembly of an asymmetric mixed-ligand triple helicate

The 2-pyridinecarbaldehyde isonicotinoyl hydrazone (HPCIH) family of ligands are typically tridentate N,N,O chelators that exhibit very high in vitro activity in mobilizing intracellular Fe and are promising candidates for the treatment of Fe overload diseases. Complexation of ferrous perchlorate with HPCIH in MeCN solution gives the expected six-coordinate complex Fe-II(PCIH)(2). However, complexation of Fe-II with 2-pyridinecarbaldehyde picolinoyl hydrazone (HPCPH, an isomer of HPCIH) under the same conditions leads to spontaneous assembly of an unprecedented asymmetric, mixed-ligand dinuclear triple helical complex Fe-2(II)(PCPH)(2)(PPH), where PPH2- is the dianion of bis(picolinoyl) hydrazine. The X-ray crystal structure of this complex shows that each ligand binds simultaneously to both metal centres in a bidentate fashion. The dinuclear complex exhibits two well separated and totally reversible Fe-III/II redox couples as shown by cyclic voltammetry in MeCN solution.

Novel one-dimensional structures and solution behaviour of copper(II) bromide and chloride complexes of a new pentapyridyldiamine ligand

Copper(II) bromide and chloride complexes of the new heptadentate ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (L) have been prepared. For the bromide complexes, chains of novel, approximately C-2-symmetric, chiral [Cu-2(L)Br-2](2+) 'wedge-shaped' tectons are found. The links between the dicopper tectons and the overall chirality and packing of the chains are dictated by the bromide ion content, not the counter anion. In contrast, the chloride complexes exhibit linked asymmetric [Cu-2(L)Cl-3](+) tectons with distinct N3CuCl2 and N4CuCl2 centres in the solid. The overall structures of the dicopper bromide and chloride units persist in solution irrespective of the halide. The redox chemistry of the various species is also described.

Pressure and temperature effects on metal-to-metal charge transfer in cyano-bridged Co-III-Fe-II complexes

The effects of pressure and temperature on the energy (E-op) of the metal-to-metal charge transfer (MMCT, Fe-II --> Co-III) transition of the cyano-bridged complexes trans - [(LCoNCFe)-Co-14(CN)(5)](-) and cis-[(LCoNCFe)-Co-14(CN)(5)](-) (where L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in E-op due to both pressure and temperature were found to be less than the shifts in the energy difference (E degrees) between the Co-III-Fe-II and Co-II-Fe-III redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of Co-II, are discussed in order to account for this trend. To study the effect of pressure on Co-III electronic absorption bands, a new cyano-bridged complex, trans - [(LCoNCCo)-Co-14(CN)(5)], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans -[(LCoNCFe)-Co-14(CN)(5)] center dot 5H(2)O.

Complexes of cytotoxic chelators from the dipyridyl ketone isonicotinoyl hydrazone (HPKIH) analogues

In an effort to better understand the antiproliferative effects of the tridentate hydrazone chelators di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) and di-2-pyridyl ketone benzoyl hydrazone (HPKBH), we report the coordination chemistry of these ligands with the divalent metal ions, Mn, Co, Ni, Cu, and Zn. These complexes are compared with their Fe-II analogues which were reported previously. The crystal structures of Co(PKIH)(2), Ni(PKIH)(2), Cu(PKIH)(2), Mn(PKBH)(2), Ni(PKBH)(2), Cu(PKBH)(2), and Zn(PKBH)(2) are reported where similar bis-tridenate coordination modes of the ligands are defined. In pure DMF, all complexes except the Zn-II compounds exhibit metal-centered M-III/II (Mn, Fe, Co, Ni) or M-II/I (Cu) redox processes. All complexes show ligand-centered reductions at low potential. Electrochemistry in a mixed water/DMF solvent only elicited metal-centered responses from the Co and Fe complexes. Remarkably, all complexes show antiproliferative activity against the SK-N-MC neuroepithelioma cell line similar to (HPKIH) or significantly greater than that of the (HPKBH) ligand which suggests a mechanism that does not only involve the redox activity of these complexes. In fact, we suggest that the complexes act as lipophilic transport shuttles that allow entrance to the cell and enable the delivery of both the ligand and metal which act in concert to inhibit proliferation.

Molecular regulation of iron uptake in pseudomonas aeruginosa

The microbial demand for iron is often met by the elaboration of siderophores into the surrounding medium and expression of cognate outer membrane receptors for the ferric siderophore complexes. Conditions of iron limitation, such as those encountered in vivo, cause Pseudomonas aeruginosa to express two high-affinity iron-uptake systems based on pyoverdin and pyochelin. These systems will operate both in the organism's natural habitat, soil and water, where the solubility of iron at neutral pH is extremely low, and in the human host where the availability of free iron is too low to sustain bacterial growth due to the iron-binding glycoproteins transferrin and lactoferrin. Cross-feeding and radiolabelled iron uptake experiments demonstrated that pyoverdin biosynthesis and uptake were highly heterogeneous amongst P.aeruginosa strains, that growth either in the presence of pyoverdin or pyochelin resulted in induction of specific IROMPs, and that induction of iron uptake is siderophore-specific. The P.aeruginosa Tn5 mutant PH1 is deficient in ferripyoverdin uptake and resistant to pyocin Sa, suggesting that the site of interaction of pyocin Sa is a ferripyoverdin receptor. Additional Tn5 mutants appeared to exploit different strategies to achieve pyocin Sa-resistance, involving modifications in expression of pyoverdin-mediated iron uptake, indicating that complex regulatory systems exist to enable these organisms to compete effectively for iron. Modulation of expression of IROMPs prompted a study of the mechanism of uptake of a semi-synthetic C(7) α-formamido substituted cephalosporin BRL 41897A. Sensitivity to this agent correlated with expression of the 75 kDa ferri-pyochelin receptor and demonstrated the potential of high-affinity iron uptake systems for targeting of novel antibiotics. Studies with ferri-pyoverdin uptake-deficient mutant PH1 indicated that expression of outer membrane protein G (OprG), which is usually expressed under iron-rich conditions and repressed under iron-deficient conditions, was perturbed. Attempts were made to clone the oprG gene using a degenerate probe based on the N-terminal amino acid sequence. A strongly hybridising HindIll restriction fragment was cloned and sequenced, but failed to reveal an open reading frame correspondmg to OprG. However, there appears to be good evidence that a part of the gene codmg for the hydrophilic membrane-associated ATP-binding component of a hitherto uncharacterised periplasmic- binding-protein-dependent transport system has been isolated. The full organisation and sequence of the operon, and substrate for this putative transport system, are yet: to be elucidated,

Synthesis and magnetic properties of Fe-Mn-Cr multinuclear complexes with 4-amino-1,2,4-triazole and oxalate ligands

A multinuclear Fe-Mn-Cr complex with 4-amino-1,2,4-triazole (NH2trz) and oxalate (ox) ligands has been synthesized successfully. The formula of the [Fe(NH2trz)3][ClO4][MnCr(ox)3].4H2O complex has been obtained based on the metal and C, H, N contents. The presence of water molecules, metal-ligand bonding and bridge ligand in the multinuclear complex has been confirmed by its infrared spectrum. The compound crystallizes in the hexagonal system with cell parameters of a = b = 18.695 Å and c = 57.351 Å. The compound shows a gradual spin crossover for iron(II) in the [Fe(NH2trz)3]2+ with transition temperature (T1/2) of 205 K. The antiferromagnetic interaction between Cr(III) and Mn(II) ions in the [MnCr(ox)3]n n- network is observed from the Weiss constant (θ) of –2.3 K.

Conformational analysis of the natural iron chelator myo-inositol 1,2,3-trisphosphate using a pyrene-based fluorescent mimic

myo-Inositol phosphates possessing the 1,2,3-trisphosphate motif share the remarkable ability to completely inhibit iron-catalysed hydroxyl radical formation. The simplest derivative, myo-inositol 1,2,3-trisphosphate [Ins(1,2,3)P3], has been proposed as an intracellular iron chelator involved in iron transport. The binding conformation of Ins(1,2,3)P3 is considered to be important to complex Fe3+ in a 'safe' manner. Here, a pyrene-based fluorescent probe, 4,6-bispyrenoyl-myo-inositol 1,2,3,5-tetrakisphosphate [4,6-bispyrenoyl Ins(1,2,3,5)P4], has been synthesised and used to monitor the conformation of the 1,2,3-trisphosphate motif using excimer fluorescence emission. Ring-flip of the cyclohexane chair to the penta-axial conformation occurs upon association with Fe3+, evident from excimer fluorescence induced by π-π stacking of the pyrene reporter groups, accompanied by excimer formation by excitation at 351 nm. This effect is unique amongst biologically relevant metal cations, except for Ca 2+ cations exceeding a 1:1 molar ratio. In addition, the thermodynamic constants for the interaction of the fluorescent probe with Fe3+ have been determined. The complexes formed between Fe 3+ and 4,6-bispyrenoyl Ins(1,2,3,5)P4 display similar stability to those formed with Ins(1,2,3)P3, indicating that the fluorescent probe acts as a good model for the 1,2,3-trisphosphate motif. This is further supported by the antioxidant properties of 4,6-bispyrenoyl Ins(1,2,3,5)P4, which closely resemble those obtained for Ins(1,2,3)P3. The data presented confirms that Fe3+ binds tightly to the unstable penta-axial conformation of myo-inositol phosphates possessing the 1,2,3-trisphosphate motif. © 2010 The Royal Society of Chemistry.

Highly efficient and reusable CNT supported iron(II) catalyst for microwave assisted alcohol oxidation

The highly efficient eco-friendly synthesis of ketones (yields over 99%) from secondary alcohols is achieved by combination of [FeCl2{eta(3)-HC(pz)(3)}] (pz = pyrazol-1-yl) supported on functionalized multi-walled carbon nanotubes and microwave irradiation, in a solvent-free medium. The carbon homoscorpionate iron(II) complex is the first one of this class to be used as catalyst for the oxidation of alcohols.

Soybean ferritin expression in saccharomyces cerevisiae modulates iron accumulation and resistance to elevated iron concentrations.

Fungi, including the yeast Saccharomyces cerevisiae, lack ferritin and use vacuoles as iron storage organelles. This work explored how plant ferritin expression influenced baker's yeast iron metabolism. Soybean seed ferritin H1 (SFerH1) and SFerH2 genes were cloned and expressed in yeast cells. Both soybean ferritins assembled as multimeric complexes, which bound yeast intracellular iron in vivo and, consequently, induced the activation of the genes expressed during iron scarcity. Soybean ferritin protected yeast cells that lacked the Ccc1 vacuolar iron detoxification transporter from toxic iron levels by reducing cellular oxidation, thus allowing growth at high iron concentrations. Interestingly, when simultaneously expressed in ccc1Δ cells, SFerH1 and SFerH2 assembled as heteropolymers, which further increased iron resistance and reduced the oxidative stress produced by excess iron compared to ferritin homopolymer complexes. Finally, soybean ferritin expression led to increased iron accumulation in both wild-type and ccc1Δ yeast cells at certain environmental iron concentrations.

I) Improving low photocurrent of pseudorotaxane based solar cell II) Synthesis and characterization of new Fe(0) cyclopentadienone complexes

Next to conventional solar panels that harvest direct sunlight, p-type dye-sensitized solar cells (DSSCs) have been developed, which are able to harvest diffuse sunlight. Due to unwanted charge recombination events p-type DSSCs exhibit low power conversion efficiencies (PCEs). Previous research has shown that dye-redox mediator (RM) interactions can prevent these recombination events, resulting in higher PCEs. It is unknown how the nature of dye-RM interactions affects the PCEs of pseudorotaxane-based solar cells. In this research this correlation is investigated by comparing one macrocycle, the 3-NDI, in combination with the three dyes that contains a recognition sites. 2D-DOSY-NMR experiments have been conducted to evaluate the diffusion constants (LogD) of the three couple. The research project has been stopped due to the coronavirus pandemic. The continuation of this thesis would have been to synthesize a dye on the basis of the data obtained from the diffusion tests and attempt the construction of a solar cell to then evaluate its effectiveness. During my training period I synthetized new Fe(0) cyclopentadienone compounds bearing a N-Heterocyclic Carbene ligand. The aim of the thesis was to achieve water solubility by modifications of the cyclopentadienone ligand. These new complexes have been modified using a sulfonation reaction, replacing an hydroxyl with a sulfate group, on the alkyl backbone of the cyclopentadienone ligand. All the complexes were characterized with IR, ESI-MS and NMR spectroscopy, and a new Fe(0) cyclopentadienone complex, involved as an intermediate, was obtained as a single crystal and was characterized also with X-Ray spectroscopy.

Communication: Transient Anion States Of Phenol…(h₂o)n (n = 1, 2) Complexes: Search For Microsolvation Signatures.

We report on the shape resonance spectra of phenol-water clusters, as obtained from elastic electron scattering calculations. Our results, along with virtual orbital analysis, indicate that the well-known indirect mechanism for hydrogen elimination in the gas phase is significantly impacted on by microsolvation, due to the competition between vibronic couplings on the solute and solvent molecules. This fact suggests how relevant the solvation effects could be for the electron-driven damage of biomolecules and the biomass delignification [E. M. de Oliveira et al., Phys. Rev. A 86, 020701(R) (2012)]. We also discuss microsolvation signatures in the differential cross sections that could help to identify the solvated complexes and access the composition of gaseous admixtures of these species.

Evaluation Of Red Cell And Reticulocyte Parameters As Indicative Of Iron Deficiency In Patients With Anemia Of Chronic Disease.

The purpose of this study was to evaluate the effectiveness of mature red cell and reticulocyte parameters under three conditions: iron deficiency anemia, anemia of chronic disease, and anemia of chronic disease associated with absolute iron deficiency. Peripheral blood cells from 117 adult patients with anemia were classified according to iron status, and inflammatory activity, and the results of a hemoglobinopathy investigation as: iron deficiency anemia (n=42), anemia of chronic disease (n=28), anemia of chronic disease associated with iron deficiency anemia (n=22), and heterozygous β thalassemia (n=25). The percentage of microcytic red cells, hypochromic red cells, and levels of hemoglobin content in both reticulocytes and mature red cells were determined. Receiver operating characteristic analysis was used to evaluate the accuracy of the parameters in differentiating between the different types of anemia. There was no significant difference between the iron deficient group and anemia of chronic disease associated with absolute iron deficiency in respect to any parameter. The percentage of hypochromic red cells was the best parameter to discriminate anemia of chronic disease with and without absolute iron deficiency (area under curve=0.785; 95% confidence interval: 0.661-0.909, with sensitivity of 72.7%, and specificity of 70.4%; cut-off value 1.8%). The formula microcytic red cells minus hypochromic red cells was very accurate in differentiating iron deficiency anemia and heterozygous β thalassemia (area under curve=0.977; 95% confidence interval: 0.950-1.005; with sensitivity of 96.2%, and specificity of 92.7%; cut-off value 13.8). The indices related to red cells and reticulocytes have a moderate performance in identifying absolute iron deficiency in patients with anemia of chronic disease.

Reduction Of Oxidative Damage And Inflammatory Response In The Diaphragm Muscle Of Mdx Mice Using Iron Chelator Deferoxamine.

Oxidative stress and inflammatory processes strongly contribute to pathogenesis in Duchenne muscular dystrophy (DMD). Based on evidence that excess iron may increase oxidative stress and contribute to the inflammatory response, we investigated whether deferoxamine (DFX), a potent iron chelating agent, reduces oxidative stress and inflammation in the diaphragm (DIA) muscle of mdx mice (an experimental model of DMD). Fourteen-day-old mdx mice received daily intraperitoneal injections of DFX at a dose of 150 mg/kg body weight, diluted in saline, for 14 days. C57BL/10 and control mdx mice received daily intraperitoneal injections of saline only, for 14 days. Grip strength was evaluated as a functional measure, and blood samples were collected for biochemical assessment of muscle fiber degeneration. In addition, the DIA muscle was removed and processed for histopathology and Western blotting analysis. In mdx mice, DFX reduced muscle damage and loss of muscle strength. DFX treatment also resulted in a significant reduction of dystrophic inflammatory processes, as indicated by decreases in the inflammatory area and in NF-κB levels. DFX significantly decreased oxidative damage, as shown by lower levels of 4-hydroxynonenal and a reduction in dihydroethidium staining in the DIA muscle of mdx mice. The results of the present study suggest that DFX may be useful in therapeutic strategies to ameliorate dystrophic muscle pathology, possibly via mechanisms involving oxidative and inflammatory pathways.

Myoglobins: the link between discoloration and lipid oxidation in muscle and meat

Aerobic metabolism changes rapidly to glycolysis post-mortem resulting in a pH-decrease during the transformation of muscle in to meat affecting ligand binding and redox potential of the heme iron in myoglobin, the meat pigment. The inorganic chemistry of meat involves (i) redox-cycling between iron(II), iron(III), and iron(IV)/protein radicals; (ii) ligand exchange processes; and (iii) spin-equilibra with a change in coordination number for the heme iron. In addition to the function of myoglobin for oxygen storage, new physiological roles of myoglobin are currently being discovered, which notably find close parallels in the processes in fresh meat and nitrite-cured meat products. Myoglobin may be characterized as a bioreactor for small molecules like O2, NO, CO, CO2, H2O, and HNO with importance in bio-regulation and in protection against oxidative stress in vivo otherwise affecting lipids in membranes. Many of these processes may be recognised as colour changes in fresh meat and cured meat products under different atmospheric conditions, and could also be instructive for teaching purposes.