The effect of UVB irradiation on ferritin subunit synthesis,ferritin assembly and Fe metabolism in cultured canine lens epithelial cells

Ferritin is a multimeric protein consisting of heavy and light chains assembled in different tissue-specific ratios, which can protect cells from oxidative stress by storing reactive iron (Fe). Because the lens is constantly exposed to UV irradiation, we studied its effects on ferritin synthesis and Fe metabolism in cultured lens epithelial cells with and without ascorbic acid (Asc). UVB caused a large increase in accumulation of newly synthesized ferritin chains; this increase was additive to that induced by Asc. In contrast to the Asc-induced increase in Fe storage, Fe storage in ferritin was unaltered by UVB. Although UVB increased accumulation of newly synthesized ferritin chains, total ferritin levels were unaltered. In contrast, Asc, which induced a quantitatively similar increase in accumulation of newly synthesized ferritin chains, doubled the total amount of ferritin. Because UVB did not change Fe storage in ferritin or the size of the labile Fe pool, it was hypothesized and then determined that these newly synthesized chains did not assemble into functional holoferritin. Numerous studies detail the effects of various treatments on de novo ferritin synthesis; however, this study provides a cautionary note regarding the conclusions of such studies in the absence of data indicating assembly of functional ferritin molecules.     

Encapsulation of the ferritin protein in sol-gel derived silica glasses

A significant recent development in sol-gel science has been the encapsulation of biomolecules such as proteins and enzymes in optically transparent silica glasses. This paper reports on the encapsulation of an iron (Fe) storage protein, ferritin, to develop a magnetic silica glass. Native ferritin, which has a nanometer-sized microcrystalline Fe oxide core, was encapsulated in optically transparent silica glasses using the sol-gel process. Fe could be released from ferritin but could not be reconstituted into apoferritin when the protein was trapped in the pores of the glass. Transmission electron microscopy of ferritin-doped aged silica gels indicated that crystallinity of the Fe oxide core was retained upon sol-gel encapsulation. Magnetic measurements on ferritin-doped silica gels indicated the material to be paramagnetic, but not superparamagnetic.     

A new dinuclear heme-copper complex derived from functionalized protoporphyrin IX

A new biomimetic model for the heterodinuclear heme/copper center of respiratory oxidases is described. It is derived from iron(III) protoporphyrin IX by covalent attachment of a Gly-L-His-OMe residue to one propionic acid substituent and an amino-bis(benzimidazole) residue to the other propionic acid substituent of the porphyrin ring, yielding the Fe(III) complex 1, and subsequent addition of a copper(II) or copper(I) ion, according to needs. The fully oxidized Fe(III)/Cu(II) complex, 2, binds azide more strongly than 1, and likely contains azide bound as a bridging ligand between Fe(III) and Cu(II). The two metal centers also cooperate in the reaction with hydrogen peroxide, as the peroxide adducts obtained at low temperature for 1 and 2 display different optical features. Support to this interpretation comes from the investigation of the peroxidase activity of the complexes, where the activation of hydrogen peroxide has been studied through the phenol coupling reaction of p-cresol. Here the presence of Cu(II) improves the catalytic performance of complex 2 with respect to 1 at acidic pH, where the positive charge of the Cu(II) ion is useful to promote O-O bond cleavage of the iron-bound hydroperoxide, but it depresses the activity at basic pH because it can stabilize an intramolecular hydroxo bridge between Fe(III) and Cu(II). The reactivity to dioxygen of the reduced complexes has been studied at low temperature starting from the carbonyl adducts of the Fe(II) complex, 3, and Fe(II)/Cu(I) complex, 4. Also in this case the adducts derived from the Fe(II) and Fe(II)/Cu(I) complexes, that we formulate as Fe(III)-superoxo and Fe(III)/Cu(II)-peroxo exhibit slightly different spectral properties, showing that the copper center participates in a weak interaction with the dioxygen moiety.     

Synthetic control over magnetic moment and exchange bias in all-oxide materials encapsulated within a spherical protein cage

This work focuses on the synthetic control of magnetic properties of mixed oxide magnetic nanoparticles of the general formula Fe(3-x)Co(x)O(4) (x < or = 0.33) in the protein cage ferritin. In this biomimetic approach, variations in the chemical synthesis result in the formation of single-phase Fe(3-x)Co(x)O(4) alloys or intimately mixed binary phase Fe/Co oxides, modifying the chemical structure and magnetic behavior of these particles, as characterized by static and dynamic magnetization measurements and X-ray absorption spectroscopy.     

Adsorption of Pb(II), Cu(II), Cd(II), Zn(II), Ni(II), Fe(II), and As(V) on bacterially produced metal sulfides

The adsorption of Pb(II), Cu(II), Cd(II), Zn(II), Ni(II), Fe(II) and As(V) onto bacterially produced metal sulfide (BPMS) material was investigated using a batch equilibrium method. It was found that the sulfide material had adsorptive properties comparable with those of other adsorbents with respect to the specific uptake of a range of metals and, the levels to which dissolved metal concentrations in solution can be reduced. The percentage of adsorption increased with increasing pH and adsorbent dose, but decreased with increasing initial dissolved metal concentration. The pH of the solution was the most important parameter controlling adsorption of Cd(II), Cu(II), Fe(II), Ni(II), Pb(II), Zn(II), and As(V) by BPMS. The adsorption data were successfully modeled using the Langmuir adsorption isotherm. Desorption experiments showed that the reversibility of adsorption was low, suggesting high-affinity adsorption governed by chemisorption. The mechanism of adsorption for the divalent metals was thought to be the formation of strong, inner-sphere complexes involving surface hydroxyl groups. However, the mechanism for the adsorption of As(V) by BPMS appears to be distinct from that of surface hydroxyl exchange. These results have important implications to the management of metal sulfide sludge produced by bacterial sulfate reduction.     

Evaluation of biacetyl(2-pyridyl)hydrazone thiosemicarbazone as spectrophotometric analytical reagent

Summary The synthesis and analytical properties of biacetyl(2-pyridyl)hydrazone thiosemicarbazone (BPHT) have been studied. A spectrophotometric method has been used to determine the protonation constants of the reagent and a Spectrophotometric survey of the reactions of various cations with BPHT has been made. BPHT gives coloured complexes with various cations such as Ni(II), Co(II), Fe(II), Cu(II), Pd(II), Zn(II), Cd(II), In(III). The sensitivity has been compared with that of other analogous reagents of the biacetyl type.     

Compositions and structures of copper hexacyanoferrates(II) and (III): experimental results

The preparation, composition and structure of copper hexacyanoferrates have been investigated. Three methods were used: precipitation, local growth in an aqueous solution, and growth in a gel. Four compounds were obtained, either in powdered form or as single crystals: Cu(II)(2)Fe(II)(CN)(6) . xH(2)O, Cu(II)(3)[Fe(III)(CN)(6)](2) . xH(2)O, Na(2)Cu(II)Fe(II)(CN)(6) . 10H(2)O and K(2)Cu(II)Fe(II)(CN)(6). Powders of Cu(II)(2)Fe(II)(CN)(6) . xH(2)O and Cu(II)(3)[Fe(III) (CN)(6)](2) . xH(2)O are easily prepared by precipitation and can also be obtained by local growth. They crystallise generally with cubic symmetry, in space group Fm3m, and are structurally disordered. The mixed copper hexacyanoferrates of general formulae M(1)(2)Cu(II)Fe(II)(CN)(6) or M(I)Cu(II)Fe(III)(CN)(6) (here M(I) is Na, K) were not obtained by precipitation. The appropriate method was local growth for the preparation of powders of K(2)Cu(II)Fe(II)(CN)(6). Single crystals of Na(2)Cu(II)Fe(II)(CN)(6) were obtained by growth in a gel, and their study using single crystal X-ray diffraction revealed a new monoclinic structure.     

Iron Binding in the Ferroxidase Site of Human Mitochondrial Ferritin

Ferritins are nanocage proteins that store iron ions in their central cavity as hydrated ferric oxide biominerals. In mammals, further the L (light) and H (heavy) chains constituting cytoplasmic maxi-ferritins, an additional type of ferritin has been identified, the mitochondrial ferritin (MTF). Human MTF (hMTF) is a functional homopolymeric H-like ferritin performing the ferroxidase activity in its ferroxidase site (FS), in which Fe(II) is oxidized to Fe(III) in the presence of dioxygen. To better investigate its ferroxidase properties, here we performed time-lapse X-ray crystallography analysis of hMTF, providing structural evidence of how iron ions interact with hMTF and of their binding to the FS. Transient iron binding sites, populating the pathway along the cage from the iron entry channel to the catalytic center, were also identified. Furthermore, our kinetic data at variable iron loads indicate that the catalytic iron oxidation reaction occurs via a diferric peroxo intermediate followed by the formation of ferric-oxo species, with significant differences with respect to human H-type ferritin.     

Cyanide-bridged molecular squares with ferromagnetically coupled dpi,dsigma, and ppi spin system

Cyanide-bridged molecular squares of [Fe(II)(2)Cu(II)(2)(mu-CN)(4)(dmbpy)(4)(impy)(2)](ClO(4))(4).4CH(3)OH.C(6)H(6) (1) and of [Fe(III)(2)Cu(II)(2)(mu-CN)(4)(dmbpy)(4)(impy)(2)](ClO(4))(6).4CH(3)OH.4H(2)O (2) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine; impy = 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy) were prepared. In the squares of 1 and 2, the Fe(II/III) (low spin) and Cu(II) ions are alternately bridged by the cyanide groups, in which the cyanide carbon atoms coordinated to the Fe(II) ions and Cu(II) ions are coordinated by imino nitroxide. Magnetic susceptibility measurements for 1 and 2 revealed that the Cu(II) ion and imino nitroxide are ferromagnetically coupled with a fairly strong coupling constant (J(Cu-radical) > 300 K) and act as triplet species. In 1 the Cu(II)-radical moieties are magnetically separated by the Fe(II) ions. In the square of 2, dpi (Fe(III)), dsigma (Cu(II)), and ppi (imino nitroxide) spins are alternately assembled, and this situation allowed the square to have an S = 3 spin ground state. The exchange coupling constant of Fe(III) and the Cu(II)-radical moiety in 2 was estimated to be J = 4.9 cm(-1) (H = -2JSigmaS(Fe).S(Cu-radical)).     

Hydrogen peroxide formation upon oxidation of oxalic acid in presence and absence of oxygen and of manganese(II)--III. Iron(III) and copper(II) as retarders

The formation of considerable amounts of hydrogen peroxide upon the slow addition of various oxidizing agents to oxalic acid in dilute sulphuric acid in the presence of oxygen and Mn(II) is greatly retarded in the presence of Fe(III) or Cu(II). With hydrogen peroxide as oxidizing agent and a trace of Fe(II) there is considerable decomposition of peroxide, under a nitrogen atmosphere, after a few hours at 25 degrees in light (from a tungsten lamp), and less decomposition in the dark. This decomposition is decreased by Mn(II) and also when the original mixture contains Fe(III). With oxygen as the oxidizing agent Fe(II) is about 100 times as effective an inhibitor of peroxide formation as Fe(III). With all oxidizing agents used, Cu(II) is some 6-10 times more effective as a retarder than Fe(III). The inhibition is accounted for by the reaction Fe(III) [or Cu(II)] + CO(-)(2) --> Fe(II) [or Cu(I)] + CO(2).     

Exceptional affinity of nanostructured organic-inorganic hybrid materials towards dioxygen: confinement effect of copper complexes

We report the exceptional reactivity towards dioxygen of a nanostructured organic-inorganic hybrid material due to the confinement of copper cyclam within a silica matrix. The key step is the metalation reaction of the ligand, which can occur before or after xerogel formation through the sol-gel process. The incorporation of a Cu(II) center into the material after xerogel formation leads to a bridged Cu(I)/Cu(II) mixed-valence dinuclear species. This complex exhibits a very high affinity towards dioxygen, attributable to auto-organization of the active species in the solid. The remarkable properties of these copper complexes in the silica matrix demonstrate a high cooperative effect for O(2) adsorption; this is induced by close confinement of the two copper ions leading to end-on mu-eta(1):eta(1)-peroxodicopper(II) complexes. The anisotropic packing of the tetraazamacrocycle in a lamellar structure induces an exceptional reactivity of these copper complexes. We show for the first time that the organic-inorganic environment of copper complexes in a silica matrix fully model the protecting role of protein in metalloenzymes. For the first time an oxygenated dicopper(II) complex can be isolated in a stable form at room temperature, and the reduced Cu(2) (I,I) species can be regenerated after several adsorption-desorption cycles. These data also demonstrate that the coordination scheme and reactivity of the copper cyclams within the solid are quite different from that observed in solution.     

Membrane-derived fluorinated radicals detected by electron spin resonance in UV-irradiated Nafion and Dow ionomers: effect of counterions and H2O2

Electron spin resonance (ESR) spectroscopy was used to detect and identify radicals formed by UV irradiation of Nafion and Dow perfluorinated membranes partially or fully neutralized by Cu(II), Fe(II), and Fe(III). This method allowed the monitoring of ESR signals from the paramagnetic counterions together with the appearance of membrane-derived radical species. The most surprising aspect of this study was the formation of membrane-derived radical species only in the neutralized membranes, and even in the absence of H2O2 in the case of Nafion/Cu(II) and Nafion/Fe(III). In Nafion/Cu(II), ESR spectra from radicals exhibiting hyperfine interactions with three equivalent 19F nuclei (the "quartet") and with four equivalent 19F nuclei (the "quintet") were detected. In Nafion/Fe(II) exposed to H2O2 solutions, the formation of Fe(III) was detected. Upon UV irradiation, strong signals from the chain-end radical ROCF2CF2* were detected first, followed by the appearance, upon annealing above 200 K, of the quartet signal observed in Nafion/Cu(II). In subsequent experiments with Nafion and Dow membranes neutralized by Fe(III), the ROCF2CF2* radicals were formed even in the absence of H2O2, indicating that the role of H2O2 is oxidation of Fe(II) to Fe(III); moreover, in these systems small amounts of the chain-end radicals were detected even without UV irradiation. This result validates the method used to form the radicals: the role of UV irradiation is to accelerate the formation of a signal that is produced, albeit slowly, even in the dark, and possibly during fuel cell operation. The major conclusion is that cations are involved in degradation processes; the point of attack appears to be at or near the pendant chain of the ionomer. Therefore when studying membrane stability, it is important to consider not only the formation of oxygen radicals, such as HO*, HOO*, and O2*-, that can attack the membrane but also the specific reactivity of counterions.     

Sequential separation of Cu(II)/Ni(II)/Fe(II) from strong-acidic pickling wastewater with a two-stage process based on a bi-pyridine chelating resin

A self-synthesized bi-pyridine chelating resin (PAPY) could separate Cu(II)/Ni(II)/Fe(II) sequentially from strong-acidic pickling wastewater by a two-stage pH-adjusted process, in which Cu(II), Ni(II), and Fe(II) were successively preferred by PAPY. In the first stage (pH 1.0), the separation factor of Cu(II) over Ni(II) reached 61.43 in Cu(II)-Ni(II)-Fe(II) systems. In the second stage (pH 2.0), the separation factor of Ni(II) over Fe(II) reached 92.82 in Ni(II)-Fe(II) systems. Emphasis was placed on the selective separation of Cu(II) and Ni(II) in the first-stage. The adsorption amounts of Cu(II) onto PAPY were 1.2 mmol/g in the first stage, while those of Ni(II) and Fe(II) were lower than 0.3 mmol/g. Cu(II) adsorption was hardly affected by Ni(II) with the presence of dense Fe(II), but Cu(II) inhibited Ni(II) adsorption strongly. Part of preloaded Ni(II) could be replaced by Cu(II) based on the replacement effect. Compared with the absence of Fe(II), dense Fe(II) could obviously enhance the separation of Cu(II)-Ni(II). More than 95.0% of Cu(II) could be removed in the former 240 BV (BV for bed volume of the adsorbent) in the fixed-bed adsorption column process with the flow rate of 2.5 BV/h. As proved by X-ray photoelectron spectrometry (XPS) and density functional theory (DFT) analyses, Cu(II) exerted a much stronger deprotonation and chelation ability toward PAPY than Ni(II) and Fe(II). Thus, the work shows a great potential in the separation and purification of heavy metal resources from strong-acidic pickling wastewaters.     

Electrochemical functions of metallosupramolecular nanomaterials

Self-assembly of metal ions and organic ligands results in the formation of extended or discrete metallosupramolecular structures. In case of neutral ditopic ligands such as bisterpyridines, extended metallosupramolecular coordination polyelectrolytes (MEPEs) are formed. Metal ion-induced self-assembly of 1,4-bis(2,2':6',2'-terpyridin-4'-yl)benzene with Fe(II) or Co(II) results in MEPEs with interesting electrochemical properties. These MEPEs reversibly change their color when oxidized or reduced. The heterometallic MEPE consisting of Fe(II) and Co(II) combines the properties of the individual MEPEs and therefore shows their different states: red-purple, blue, and transparent. On the other hand, complexation of cyclic phenylazomethines with metal ions results in discrete metallosupramolecular structures. We find that metal ion assembly to the organic module occurs in a stepwise fashion because of a difference in the basicity of the imine conformers, and the metal ion assembly can be controlled electrochemically. This example illustrates how metal ion binding can be controlled by the conformation of the receptor, an important step toward assembling organic ligands and metal ions in predictable ways.     

Copper(II) ion-selective microelectrochemical transistor

A device has been developed for the measurement of copper(II) ions (Cu⁺⁺) in aqueous medium. The device reported here is an electrochemical transistor that consists of two platinum electrodes separated by 100-μm spacing and bridged with an anodically grown polycarbazole film. The undoped polycarbazole film is observed to be highly selective for the Cu(II) ions. In a completed device, the conductivity of the polycarbazole film changes on addition of Cu (II)ions. This change in conductivity is attributed to the conformational changes in the polymer phase on occupation of the Cu(II) ions, without affecting electron/proton transfer. The device turns on by adding 2.5×10⁻⁶ M Cu(II) ions and reaches a saturation region above a concentration of 10⁻⁴ M Cu(II) ions. In this concentration range, the plot of I _D vs log[Cu(II)] is linear. The selectivity of the device for other metal ions such as Cu(I), Co(II), Fe(II), Fe(III), Zn(II), and Pb(II) is also studied.     

Cu单原子修饰对Fe(111)表面CO吸附性能及电子性质调变的第一性原理研究

采用密度泛函理论方法研究了Cu单原子修饰对Fe(111)表面CO吸附性能和电子性质的调变作用,其中,Cu单原子修饰研究了吸附和取代两种方式。结果表明,CO在Cu修饰的Fe(111)面吸附能力都会变弱,一是Cu原子自身提供的位点对CO的吸附较弱;二是Cu会使其附近的Fe对CO的吸附变弱。分析电子性质表明,Cu作用于Fe表面后,会导致Cu附近Fe原子部分电子向Cu原子转移,进而削弱了Fe与吸附分子间电子交互作用而改变Fe原子的吸附能力。故Cu原子改性Fe表面可以很好地调变CO的吸附、解离及后续反应催化活性,这为进一步探究Cu改性Fe表面的合成气催化反应机理提供了基础信息。     

Colloidal synthesis of wurtzite Cu2ZnSnS4 nanorods and their perpendicular assembly

The quaternary copper chalcogenide Cu(2)ZnSnS(4) is an important emerging material for the development of low-cost and sustainable solar cells. Here we report a facile solution synthesis of stoichiometric Cu(2)ZnSnS(4) in size-controlled nanorod form (11 nm × 35 nm). The monodisperse nanorods have a band gap of 1.43 eV and can be assembled into perpendicularly aligned arrays by controlled evaporation from solution.     

Metallobleomycin-mediated cleavage of DNA not involving a threading-intercalation mechanism.

The DNA cleavage properties of metallobleomycins conjugated to three solid supports were investigated using plasmid DNA, relaxed covalently closed circular DNA, and linear duplex DNA as substrates. Cleavage of pBR322 and pSP64 plasmid DNAs by Fe(II).BLM A(5)-CPG-C(2) was observed with efficiencies not dissimilar to that obtained using free Fe(II).BLM A(5). Similar results were observed following Fe(II).BLM A(5)-CPG-C(2)-mediated cleavage of a relaxed plasmid, a substrate that lacks ends or negative supercoiling capable of facilitating strand separation. BLMs covalently tethered to solid supports, including Fe(II).BLM A(5)-Sepharose 4B, Fe(II).BLM A(5)-CPG-C(6), and Fe(II).BLM A(5)-CPG-C(2), cleaved a 5'-(32)P end labeled linear DNA duplex with a sequence selectivity identical to that of free Fe(II).BLM A(5); cleavage predominated at 5'-G(82)T(83)-3' and 5'-G(84)T(85)-3'. To verify that these results could also be obtained using other metallobleomycins, supercoiled plasmid DNA and a linear DNA duplex were employed as substrates for Co(III).BLM A(5)-CPG-C(2). Free green Co(III).BLM A(5) was only about 2-fold more efficient than green Co(III).BLM A(5)-CPG-C(2) in effecting DNA cleavage. A similar result was obtained using Cu(II).BLM A(5)-CPG-C(2) + dithiothreitol. In addition, the conjugated Co.BLM A(5) and Cu.BLM A(5) cleaved the linear duplex DNA with a sequence selectivity identical to that of the respective free metalloBLMs. Interestingly, when supercoiled plasmid DNA was used as a substrate, conjugated Fe.BLM A(5) and Co.BLM A(5) were both found to produce Form III DNA in addition to Form II DNA. The formation of Form III DNA by conjugated Fe.BLM A(5) was assessed quantitatively. When corrected for differences in the intrinsic efficiencies of DNA cleavage by conjugated vs free BLMs, conjugated Fe.BLM A(5) was found to produce Form III DNA to about the same extent as the respective free Fe.BLM A(5), arguing that this conjugated BLM can also effect double-strand cleavage of DNA. Although previous evidence supporting DNA intercalation by some metallobleomycins is convincing, the present evidence indicates that threading intercalation is not a requirement for DNA cleavage by Fe(II).BLM A(5), Co(III).BLM A(5), or Cu(I).BLM A(5).     

Hydrothermal syntheses,crystal structures,and properties of two-dimensional homo- and heterometallic cyanide-bridged complexes: [Cu2(CN)2(bpym)] and [Fe(bipy)2(CN)4Cu2] (bpym = 2,2'-bipyrimidine,bipy = 2,2'-bipyridine)

The hydrothermal reaction of K(3)[Fe(CN)(6)], CuCl(2), and 2,2'-bipyridine (bipy) resulted in the formation of a 2D cyanide-bridged heterobimetallic Fe(II)-Cu(I) complex, [Fe(bipy)(2)(CN)(4)Cu(2)], 1. Working in the same conditions, but using 2,2'-bipyrimidine (bpym) instead of bipy and methanol as solvent, we obtained the homometallic Cu(I) complex [Cu(2)(CN)(2)(bpym)](2), 2. The structure of 1 consists of cyanide-bridged Fe(II)-Cu(I) layers, constructed from alternately fused 6 (Fe(2)Cu(4)) and 10 (Fe(2)Cu(8)) metal-membered centrosymmetric rings, in which copper(I) and iron(II) ions exhibit distorted trigonal planar and octahedral cooordination environments, respectively. The formation of 1 can be explained by assuming that, under high pressure and temperature, iron(III) and copper(II) ions are reduced with the simultaneous and/or subsequent substitution of four cyanide ligands by two bipy molecules in the ferricyanide anions. It is interesting to note that 1 is the first cyanide-bridged heterobimetallic complex prepared by solvothermal methods. The structure of 2 consists of neutral 2D honeycomb layers constructed from fused Cu(6)(CN)(4)(bpym)(2) rings, in which copper(I) atoms exhibit distorted tetrahedral geometry. The isolation of 1 and 2, by using K(3)[Fe(CN)(6)] as starting material, demonstrates that hydrothermal chemistry can be used not only to prepare homometallic materials but also to prepare cyanide-bridged bimetallic materials. The temperature dependence of chi(M)T and M?ssbauer measurements for 1 reveal the existence of a high spin <--> low spin equilibrium involving the Fe(II) ions.