Kinetics and mechanism of iron release from the bacterial ferric binding protein<Emphasis Type="Italic"> n</Emphasis>Fbp: exogenous anion influence and comparison with mammalian transferrin

Ferric binding protein, Fbp, serves an essential biological function in shuttling naked (hydrated) Fe³⁺ across the periplasmic space of many Gram-negative bacteria. In this process, iron must be released at the cytoplasmic membrane to a permease. How iron is released from Fbp has yet to be resolved. Consequently, understanding the dynamics of iron release from Fbp is of both biological and chemical interest. Fbp requires an exogenous anion, e.g. phosphate when isolated from cell lysates, for tight iron sequestration. To address the role of exogenous anion identity and lability on Fe_aq ³⁺ dissociation from Fbp, the kinetics of PO₄ ^3– exchange in Fe³⁺ nFbp(PO₄) (nFbp=recombinant Fbp from Neisseria meningitidis) were investigated by dynamic ³¹P NMR and the kinetics of Fe³⁺ dissociation from Fe³⁺ nFbp(X) (X=PO₄ ^3–, citrate anion) were investigated by stopped-flow pH-jump measurements. We justify the use of non-physiological low-pH conditions because a high [H⁺] will drive the Fe_aq ³⁺ dissociation reaction to completion without using competing chelators, whose presence may complicate or influence the dissociation mechanism. For perspective, these studies of nFbp (which has been referred to as a bacterial transferrin) are compared to new and previously published kinetic and thermodynamic data for mammalian transferrin. Significantly, we address the lability of the Fe³⁺ coordination shell in nFbp, Fe³⁺ nFbp(X) (X=PO₄ ^3–, citrate), with respect to exogenous anion (X ^n–) exchange and dissociation, and ultimately complete dissociation of the protein to yield naked (hydrated) Fe_aq ³⁺. These findings are a first step in understanding the process of iron donation to the bacterial permease for transport across the cytoplasmic membrane.Electronic Supplementary Material Supplementary material is available in the online version of this article at . Abbreviations DTPP diethylenetriaminepenta(methylenephosphonic acid) - Fbp ferric binding protein - H₃cit citric acid - hFbp Fbp from Haemophilus influenzae - H₂ox oxalic acid - hTf human serum transferrin - 3,4-LICAMS N,N,N-tris(5-sulfo-2,3-dihydroxybenzoyl)-1,5,10-triazadecane - nFbp recombinant Fbp from Neisseria meningitidis - NTA nitrilotriacetic acid - TRENSOX tris[2-aminoethyl(8-hydroxyquinoline-5-sulfonato-7-carbonyl)]amine     

Water near its Supercritical Point and at Alkaline pH for the Production of Ferric Oxides and Silicates in Anoxic Conditions. A New Hypothesis for the Synthesis of Minerals Observed in Banded Iron Formations and for the Related Geobiotropic Chemistry inside Fluid Inclusions

An alternative hypothesis for the origin of the banded iron formations and the synthesis of prebiotic molecules is presented here. I show the importance of considering water near its supercritical point and at alkaline pH. It is based on the chemical equation for the anoxic oxidation of ferrous iron into ferric iron at high-subcritical conditions of water and high pH, that I extract from E-pH diagrams drawn for corrosion purposes (Geophysical Research Abstracts Vol 15, EGU2013–22 Bassez 2013, Orig Life Evol Biosph 45(1):5-13, Bassez 2015, Procedia Earth Planet Sci 17, 492-495, Bassez 2017a, Orig Life Evol Biosph 47:453-480, Bassez 2017b). The sudden change in solubility of silica, SiO₂, at the critical point of water is also considered. It is shown that under these temperatures and pressures, ferric oxides and ferric silicates can form in anoxic terrains. No Fe^II oxidation by UV light, neither by oxygen is needed to explain the minerals of the Banded Iron Formations. The intervention of any kind of microorganisms, either sulfate-reducing, or Fe^II-oxidizing or O₂-producing, is not required. The chemical equation for the anoxic oxidation of ferrous iron is applied to the hydrolyses of fayalite, Fe₂SiO₄ and ferrosilite, FeSiO₃. It is shown that the BIF minerals of the Hamersley Group, Western Australia, and the Transvaal Supergroup, South Africa, are those of fayalite and ferrosilite hydrolyses and carbonations. The dissolution of crustal fayalite and ferrosilite during water-rock interaction needs to occur at T&P just below the critical point of water and in a rising water which is undersaturated in SiO₂. Minerals of BIFs which can then be ejected at the surface from venting arcs are ferric oxide hydroxides, hematite, Fe^III-greenalite, siderite. The greenalite dehydrated product minnesotaite forms when rising water becomes supersaturated in SiO₂, as also riebeckite and stilpnomelane. Long lengths of siderite without ferric oxides neither ferric silicates can occur since the exothermic siderite formation is not so much dependent in T&P. It is also shown that the H₂ which is released during hydrolysis/oxidation of fayalite/ferrosilite can lead to components of life, such as macromolecules of amino acids which are synthesized from mixtures of (CO, N₂, H₂O) in Sabatier-Senderens/Fischer-Tropsch & Haber-Bosch reactions or microwave or gamma-ray excitation reactions. I propose that such geobiotropic synthesis may occur inside fluid inclusions of BIFs, in the silica chert, hematite, Fe^III-greenalite or siderite. Therefore, the combination of high-subcritical conditions of water, high solubility of SiO₂ at these T&P values, formation of CO also at these T&P, high pH and anoxic water, leads to the formation of ferric minerals and prebiotic molecules in the process of geobiotropy.     

Microsensors as a tool to determine chemical microgradients and bacterial activity in wastewater biofilms and flocs

Microsensors used in microbial ecology are reviewed with emphasis on new sensor developments (NO₃ ^-, NO₂ ^-, NH₄ ⁺, CO₂, H₂, H₂S and CH₄ microsensors as well as fiberoptical microsensors for O₂, temperature and pH). Examples of microsensor applications in biofilms and activated sludge flocs are presented, where sulfate reduction and denitrification were studied.     

Degradation of massive pyrite: Physical,chemical, and bacterial effects

Massive pyrite was shown to produce soluble iron, hydrogen, and sulfate ions on exposure to air and water. The rate of this process was directly proportional to the surface area of the mineral; it was unaffected by a drop in the pH and the presence of the ferrous and sulfate ions formed. Cupic ion had no effect but ferric ion accelerated pyrite degradation until all the ferric ion was consumed, in accordance with FeS₂ + 2Fe³⁺ —>‐3Fe²⁺ + 2S°. Thiobacillus ferrooxidans increased pyrite degradation considerably; the presence of Thiobacillus thiooxidans had no influence on pyrite degradation.     

Genetic Characterization and Role in Virulence of the Ribonucleotide Reductases of Streptococcus sanguinis

Streptococcus sanguinis is a cause of infective endocarditis and has been shown to require a manganese transporter called SsaB for virulence and O₂ tolerance. Like certain other pathogens, S. sanguinis possesses aerobic class Ib (NrdEF) and anaerobic class III (NrdDG) ribonucleotide reductases (RNRs) that perform the essential function of reducing ribonucleotides to deoxyribonucleotides. The accompanying paper (Makhlynets, O., Boal, A. K., Rhodes, D. V., Kitten, T., Rosenzweig, A. C., and Stubbe, J. (2014) J. Biol. Chem. 289, 6259–6272) indicates that in the presence of O₂, the S. sanguinis class Ib RNR self-assembles an essential diferric-tyrosyl radical (Fe^III₂-Y^•) in vitro, whereas assembly of a dimanganese-tyrosyl radical (Mn^III₂-Y^•) cofactor requires NrdI, and Mn^III₂-Y^• is more active than Fe^III₂-Y^• with the endogenous reducing system of NrdH and thioredoxin reductase (TrxR1). In this study, we have shown that deletion of either nrdHEKF or nrdI completely abolishes virulence in an animal model of endocarditis, whereas nrdD mutation has no effect. The nrdHEKF, nrdI, and trxR1 mutants fail to grow aerobically, whereas anaerobic growth requires nrdD. The nrdJ gene encoding an O₂-independent adenosylcobalamin-cofactored RNR was introduced into the nrdHEKF, nrdI, and trxR1 mutants. Growth of the nrdHEKF and nrdI mutants in the presence of O₂ was partially restored. The combined results suggest that Mn^III₂-Y^•-cofactored NrdF is required for growth under aerobic conditions and in animals. This could explain in part why manganese is necessary for virulence and O₂ tolerance in many bacterial pathogens possessing a class Ib RNR and suggests NrdF and NrdI may serve as promising new antimicrobial targets.     

Dual stimuli-responsive Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> graft poly(acrylic acid)-<Emphasis Type="Italic">block</Emphasis>-poly(2-methacryloyloxyethyl ferrocenecarboxylate) copolymer micromicelles: surface RAFT synthesis,self-assembly and drug release applications

Background

Stimuli-responsive polymer materials are a new kind of intelligent materials based on the concept of bionics, which exhibits more significant changes in physicochemical properties upon triggered by tiny environment stimuli, hence providing a good carrier platform for antitumor drug delivery.

Results

Dual stimuli-responsive Fe₃O₄ graft poly(acrylic acid)-block-poly(2-methacryloyloxyethyl ferrocenecarboxylate) block copolymers (Fe₃O₄-g-PAA-b-PMAEFC) were engineered and synthesized through a two-step sequential reversible addition-fragmentation chain transfer polymerization route. The characterization was performed by FTIR, ¹H NMR, SEC, XRD and TGA techniques. The self-assembly behavior in aqueous solution upon triggered by pH, magnetic and redox stimuli was investigated via zeta potentials, vibration sample magnetometer, cyclic voltammetry, fluorescent spectrometry, dynamic light scattering, XPS, TEM and SEM measurements. The experimental results indicated that the Fe₃O₄-g-PAA-b-PMAEFC copolymer materials could spontaneously assemble into hybrid magnetic copolymer micromicelles with core–shell structure, and exhibited superparamagnetism, redox and pH stimuli-responsive features. The hybrid copolymer micromicelles were stable and nontoxic, and could entrap hydrophobic anticancer drug, which was in turn swiftly and effectively delivered from the drug-loaded micromicelles at special microenvironments such as acidic pH and high reactive oxygen species.

Conclusion

This class of stimuli-responsive copolymer materials is expected to find wide applications in medical science and biology, etc., especially in drug delivery system.

     

Significance of Oxygen Supply in Jarosite Biosynthesis Promoted by Acidithiobacillus ferrooxidans

Jarosite [(Na⁺, K⁺, NH₄ ⁺, H₃O⁺)Fe₃(SO₄)₂(OH)₆] is an efficient scavenger for trace metals in Fe- and SO₄ ^2--rich acidic water. During the biosynthesis of jarosite promoted by Acidithiobacillus ferrooxidans, the continuous supply of high oxygen levels is a common practice that results in high costs. To evaluate the function of oxygen in jarosite production by A. ferrooxidans, three groups of batch experiments with different oxygen supply levels (i.e., loading volume percentages of FeSO₄ solution of 20%, 40%, and 70% v/v in the flasks), as well as three groups of sealed flask experiments with different limiting oxygen supply conditions (i.e., the solutions were not sealed at the initial stage of the ferrous oxidation reaction by paraffin but were rather sealed at the end of the ferrous oxidation reaction at 48 h), were tested. The formed Fe-precipitates were characterized via X-ray powder diffraction and scanning electron microscope-energy dispersive spectral analysis. The results showed that the biosynthesis of jarosite by A. ferrooxidans LX5 could be achieved at a wide range of solution loading volume percentages. The rate and efficiency of the jarosite biosynthesis were poorly correlated with the concentration of dissolved oxygen in the reaction solution. Similar jarosite precipitates, expressed as KFe₃ (SO₄) ₂(OH)₆ with Fe/S molar ratios between 1.61 and 1.68, were uniformly formed in unsealed and 48 h sealed flasks. These experimental results suggested that the supply of O₂ was only essential in the period of the oxidation of ferrous iron to ferric but was not required in the period of ferric precipitation.     

Fe3O4 precipitation in magnetotactic bacteria

Using Mössbauer resonance spectroscopy of ⁵⁷Fe, we have determined the nature and distribution of major iron compounds in the magnetotactic bacterium Aquaspirillum magnetotacticum. In addition to magnetite (Fe₃O₄), cells contained a low-density hydrous ferric oxide, a high-density hydrous ferric oxide (ferrihydrite), and ferrous iron. Analysis at different temperatures of whole cells harvested early and late in growth, of mutant cells unable to synthesize magnetite, and of cell fractions enriched in ⁵⁷Fe indicated that Fe₃O₄ precipitation resulted from partial reduction of the high-density hydrous ferric oxide precursor.     

Density Functional Geometry Optimization and Energy Calculations of Calcium(II)-Triphosphate Complexes. Polyphosphates as Possible Dissolving Agents for Calcium Pyrophosphate Dihydrate Crystals in Chondrocalcinosis Disease

Abstract

Geometry optimizations and energy calculations have been carried out via molecular orbital methods at the density functional B3LYP/LANL2DZ level on the molecules PO₃ ^?, OPO₃ ^3-, HOPO₃ ^2-, CH₃OPO₃ ^2-, H(CH₃OPO₃ ^?, O(PO₃)₂ ^4-, HO(PO₃)₂ ^3-, CH₂ (PO₃)₂ ^4-, (CH₃OPO₂)O(PO₃)^3-, O(PO₃)₃ ^5-, HO(PO₃)₃ ^4-, (PO₃)₃ ^3-, (CH₃OPO₂)O(PO₃)₂ ^3-, [Mg{O(PO₃)₂}]^2-, [Ca{O(PO₃)₂}]^2-, [Ca{CH₂ (PO₃)₂}]^2-, [Ca{CH₃OPO₂)O(PO₃)}]^?, [Ca(PO₃)₃]^?, [Ca{O(PO₃)₃}]^3-, and [Ca{CH₃OPO₂)O(PO₃)₂}]^2- with the aim to find reliable and easily accessible computational methods to simulate some phosphate-containing molecules of importance for the living cells and to study the energetics for protonation and metal-complex formation reactions. The analysis is part of a general investigation on phosphate-containing molecules as potential dissolving agents for calcium pyrophosphate dihydrate (CPPD) crystals which deposit in certain articular diseases. The basis set was expanded to 6–31G** for the P atoms for all the molecules investigated and to 6–31G* for the O atoms for OPO₃ ^3-. Calculations at the semi- empirical MNDO/d level were also carried out for comparison purposes on the free ligand molecules and on [Mg{O(PO₃)₂}]^2-. The density functional analysis reproduced well the geometry found at the solid state via X-ray diffraction. The analyses of the geometrical parameters and the total electronic energy of the molecules shows that O(PO₃)₂ ^4- and other di- and tri-phosphates are versatile ligands for divalent metal ions like Ca²⁺. The computed P-O-P bond angle for free O(PO₃)₃ ^4- is 180° and the conformation of the two PO₃ ^? groupings is staggered along the P…P vector. The linear arrangement for P-O-P is assisted by P-Oπ interactions. The bending of the P-O-P angle when accompanied by a slight P-O(b) elongation requires a very small amount of energy; 4.65 kcal/mol to pass from 180 to 140°, as calculated at the DFT level. The computed Ca-O and Mg-O bond distances for [M{O(PO₃)₂}]^2- are 2.378 and 2.079Å, when the metal ions link two oxygen atoms from each PO₃ group. The computed Ca-O bond lengths for [Ca{CH₃OPO₂)O(PO₃)}]^? are 2.482 (P_αO₂) and 2.358Å (P_βO₂), showing a significant lengthening for Ca-OP_α, when compared to the pyrophosphate derivative. The Ca-O bond lengths for [Ca{O(PO₃)₃}]^3- and [Ca{CH₃OPO₂)O(PO₃)2}]^2- are 2.251Å and 2.525 (P_αO₂), 2.407 and 2.338 (P_βO₂), and 2.251 and 2.228Å (P_γO₂), showing a shortening for the Ca-OPγ bond upon methylation. The (P_β)O-P_γ bond length increases significantly (0.09 Å) upon Ca(II) coordination to (CH₃OPO₂)O(PO₃)₂ ^4- via all the three PO₃ groups. This latter result suggests that metal complexes of linear organic-triphosphates have a larger tendency to release the P_γO₃ group when compared to the free ligand molecules. The electronic contribution to the energy of the complex formation reaction for [Ca{CH₂ (PO₃)₂}]^2- is only slightly higher (some 1.8 kcal) than that for [Ca{O(PO₃)₂}]^2-; but is much higher (some 63 kcal) than that relevant to the formation of [Ca{CH₃OPO₂)O(PO₃)₂}]^2-. Therefore the linear methyltriphosphates (and reasonably nucleoside triphosphates) are predicted to form metal complexes which are less stable than diphosphonate or inorganic diphosphate ligands, at least in the case the organic moiety does not have any appreciable coordination ability toward the metal. The energy of complex formation for [Ca{O(PO₃)₃}]^3- is much higher than that for [Ca{O(PO₃)₂}]^2- and [Ca(PO₃)₃}]^? (some 116 and 345 kcal, respectively). This is in part a rationale for the high dissolving ability (DA) toward CPPD crystals, shown by solutions of pentasodium tripolyphosphate. DA values of 65.4±3.0 μg Ca/mL were detected, via atomic absorption spectroscopy, in solutions of Na₅{O(PO₃)₃} 0.06 M after digestion (1.00 h, 37°C, pH 7.4) in the presence of CPPD crystals. Efficient non-toxic dissolving agents for CPPD crystals are needed to cure chondrocal-cinosis desease. The semi-empirical computations gave correct overall optimized structures and conformations for, at least, the free not-substituted ligands and the relevant Mg(II)-com- plexes. The optimized structure for [Mg{O(PO₃)₂}]^2- has computed P-O(t) and P-O(d) bond distances of 1.503 and 1.598Å, in perfect agreement with the results from DFT calculations.     

INTERFERENCE POTENTIAL OF PLUCHEA LANCEOLATA (ASTERACEAE): GROWTH AND PHYSIOLOGICAL RESPONSES OF ASPARAGUS BEAN,VIGNA UNGUICULATA VAR. SESQUIPEDALIS

The water-soluble compounds synthesized by the weed, Pluchea lanceolata, and released by it into the soil significantly reduced seed germination, number of nodes, internode length, shoot and root lengths, nodule number and weight, and Chl a and b and Chl a/b ratio of asparagus bean plants. The pattern of accumulation of nutrients in shoot and root of asparagus bean was also affected. In contrast, the net photosynthetic rate and stomatal conductance of fully expanded leaves were higher in plants grown with treated soil. The concentrations of Mg⁺⁺, Zn⁺⁺, and PO₄^3- were higher and K⁺ was lower in shoots of plants grown with treated soil as compared to those grown with the control soil. Also, roots of plants grown with treated soil showed greater accumulation of Mg⁺⁺ and NO₃^-. Shoot/root ratio of nutrients in plants grown with control soil were higher for Zn⁺⁺, Na⁺, Ca⁺⁺, and NO₃^-, whereas plants grown with treated soil had higher ratios for PO₄^3-. These results provide evidence for allelopathic interference by P. lanceolata to the growth of asparagus bean.     

Effect of ferric sulfate on activity of moderately thermophilic acidophilic iron-oxidizing microorganisms

The effect of high ferric sulfate concentrations on the organisms predominating in biohydrometallurgical processes (bacteria of genus Sulfobaсillus and archaea of the genus Acidiplasma) was studied. Ability of the studied strains to grow and oxidize ferrous iron in the media with 125 to 500 mM ferric sulfate was determined. High concentrations of ferric sulfate significantly inhibited the oxidative activity and growth of the studied microorganisms. Bacteria of the genus Sulfobaсillus were found to be incapable of active iron oxidation in the presence of ferric iron sulfate at concentrations exceeding 250 mM. Archaea of the genus Acidiplasma oxidized ferrous iron completely in the presence of 500 mM Fe³⁺. Microbial growth was suppressed by relatively low ferric sulfate concentrations. Almost no growth occurred at ferric sulfate concentrations exceeding 199 mM, while lysis of the cells of all studied strains was observed at higher Fe³⁺ concentrations. Archaea (genus Acidiplasma, family Ferroplasmaceae) were shown to be more tolerant to high ferric sulfate concentrations than bacteria of the genus Sulfobaсillus. The results obtained may be used for improvement of biohydrometallurgical technologies and are also important for the understanding of the patterns of formation of microbial communities carrying out the technological processes.     

Active Transport of Iron in Bacillus megaterium: Role of Secondary Hydroxamic Acids

Kinetics of radioactive iron transport were examined in three strains of Bacillus megaterium. In strain ATCC 19213, which secretes the ferric-chelating secondary hydroxamic acid schizokinen, ⁵⁹Fe³⁺ uptake from ⁵⁹FeCl₃ or the ferric hydroxamate Desferal-⁵⁹Fe³⁺ was rapid and reached saturation within 3 min. In strain SK11, which does not secrete schizokinen, transport from ⁵⁹FeCl₃ was markedly reduced; the two ferric hydroxamates Desferal-⁵⁹Fe³⁺ or schizokinen-⁵⁹Fe³⁺ increased both total ⁵⁹Fe³⁺ uptake and the ⁵⁹Fe³⁺ appearing in a cellular trichloroacetic acid-insoluble fraction, although 10 min was required to reach saturation. Certain characteristics of transport from both ferric hydroxamates and FeCl₃ suggest that iron uptake was an active process. The growth-inhibitory effect of aluminum on strain SK11 was probably due to the formation of nonutilizable iron-aluminum complexes which blocked uptake from ⁵⁹FeCl₃. Desferal or schizokinen prevented this blockage. A strain (ARD-1) resistant to the ferric hydroxamate antibiotic A22765 was isolated from strain SK11. Strain ARD-1 failed to grow with Desferal-Fe³⁺ as an iron source, and it was unable to incorporate ⁵⁹Fe³⁺ from this source. Growth and iron uptake in strain ARD-1 were similar to strain SK11 with schizokinen-Fe³⁺ or the iron salt as sources. It is suggested that the ferric hydroxamates, or the iron they chelate, may be transported by a special system which might be selective for certain ferric hydroxamates. Strain ARD-1 may be unable to recognize both the antibiotic A22765 and the structurally similar chelate Desferal-Fe³⁺, while retaining its capacity to utilize schizokinen-Fe³⁺.     

2012年夏季挪威海和格陵兰海浮游植物群落结构的色素表征

对2012年中国第5次北极科学考察期间的挪威海和格陵兰海两个断面的光合色素进行了高效液相色谱（HPLC）分级分析,通过藻类色素化学分类分析软件（CHEMTAX）获得了不同浮游植物类群对叶绿素a的贡献,进而得到该海域表层和次表层（30 m）的浮游植物群落结构。结果表明：表层总叶绿素a的浓度为23.59 ng/L,低于次表层的30.38 ng/L,其中浮游植物根据粒径划分对总叶绿素a的贡献由高到低依次是微型浮游植物、小型浮游植物和微微型浮游植物。该海域同时存在葱绿叶绿素（Prasino）、墨角藻黄素（Fuco）、别藻黄素（Allo）、多甲藻素（Perid）、玉米黄素（Zea）、19-丁墨甲藻黄素（19’BF）和19-六已墨甲藻黄素（19’HF）等色素,其浓度和分布与温盐和营养盐等环境因子存在一定的相关性。不同粒径浮游植物色素组成显示,微微型浮游植物群落中以S型定鞭藻（28%）、N型定鞭藻（21%）、硅藻（18%）和青绿藻（12%）占优;微型浮游植物群落的优势类群为S型定鞭藻（53%）、N型定鞭藻（20%）和硅藻（12%）;而小型浮游植物群落主要为硅藻（63%）和甲藻（17%）。     

Shifts in the relative availability of phosphorus and nitrogen along estuarine salinity gradients

Phosphorus (P) availability in estuaries may increase with increasing salinity because sulfate from sea salt supports production of sulfide in sediments, which combines with iron (Fe) making it less available to sequester P. Increased P availability with increased salinity may promote the generally observed switch from P limitation of primary production in freshwater ecosystems to nitrogen (N) limitation in coastal marine waters. To investigate this hypothesis, we analyzed pore water from sediment cores collected along the salinity gradients of four Chesapeake Bay estuaries (the Patuxent, Potomac, Choptank, and Bush Rivers) with watersheds differing in land cover and physiography. At salinities of 1–4 in each estuary, abrupt decreases in pore water Fe²⁺ concentrations coincided with increases in sulfate depletion and PO₄ ^3? concentrations. Peaks in water column PO₄ ^3? concentrations also occur at about the same position along the salinity gradient of each estuary. Increases in pore water PO₄ ^3? concentration with increasing salinity led to distinct shifts in molar NH₄ ⁺:PO₄ ^3? ratios from >16 (the Redfield ratio characteristic of phytoplankton N:P) in the freshwater cores to <16 in the cores with salinities >1 to 4, suggesting that release of PO₄ ^3? from Fe where sediments are first deposited in sulfate-rich waters could promote the commonly observed switch from P limitation in freshwater to N limitation in mesohaline waters. Finding this pattern at similar salinities in four estuaries with such different watersheds suggests that it may be a fundamental characteristic of estuaries generally.     

Fast Kinetics of Fe2+ Oxidation in Packed-Bed Reactors

Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous sulfate to ferric sulfate. Glass beads, ion-exchange resin, and activated-carbon particles were tested as support matrix materials. Activated carbon was tested in both a packed-bed bioreactor and a fluidized-bed bioreactor; the other matrix materials were used in packed-bed reactors. Activated carbon displayed the most suitable characteristics for use as a support matrix of T. ferrooxidans fixed-film formation. The reactors were operated within a pH range of 1.35 to 1.5, which effectively reduced the amount of ferric iron precipitation and eliminated diffusion control of mass transfer due to precipitation. The activated-carbon packed-bed reactor displayed the most favorable biomass holdup and kinetic performance related to ferrous sulfate oxidation. The fastest kinetic performance achieved with the activated-carbon packed-bed bioreactor was 78 g of Fe²⁺ oxidized per liter per h (1,400 mmol of Fe²⁺ oxidized per liter per h) at a true dilution rate of 40/h, which represents a hydraulic retention time of 1.5 min.     

Atmospheric deposition, mass balances, and processes regulating streamwater solute concentrations in mixed-conifer catchments of the Sierra Nevada, California

Solute concentrations in atmospheric deposition and stream water were measuredfrom 1984 through 1993 to determine the fate and mobility of solutes in twogauged mixed-conifer catchments (Tharp's and Log creeks) located in theSierra Nevada, California. The two catchments contain mature forest standsdominated by Abies concolor (white fir), Sequoiadendron giganteum (giantsequoia), Abies magnifica (red fir) and Pinus lambertiana (sugar pine).Ammonium, Cl^-, Ca²⁺ and NO^- ₃were highest in concentration of the solutes measured in wet deposition;bulk deposition was highest in SO^{2- 4}, NH⁺ ₄,Cl^- and H⁺. Net retention ofH⁺, NO₃ ^-, NH₄ ⁺,SO₄ ^2- and Cl^- occurred in both catchments.Discharge was dominated by spring snowmelt with the largest export yieldsfor acid neutralizing capacity (ANC), SiO₂, andCa²⁺. Export yields of H⁺,NO₃ ^-, NH₄ ⁺ and PO₄ ^3-were relatively small (0.5 kg ha^-1 y^-1).Discharge-concentration relationships for ANC, SiO₂,Na⁺, K⁺, Ca²⁺ andMg²⁺ were inverse and their concentrations in stream waterwere primarily influenced by discharge and annual differences in the relativecontributions of snowmelt and groundwater. The mobility of these solutes iscontrolled by the rates of mineral weathering and ion exchange. The positiverelationship of SO₄ ^2- concentration with increasingdischarge suggests that atmospherically deposited SO₄ ^2-is temporarily stored and that its release is controlled by the extent of soilwater flushing.     

Synthesis of 2,6-difluoro-N-(3-[11C]methoxy-1H-pyrazolo[3,4-b]pyridine-5-yl)-3-(propylsulfonamidio)benzamide as a new potential PET agent for imaging of B-RafV600E in cancers

The authentic standard 2,6-difluoro-N-(3-methoxy-1H-pyrazolo[3,4-b]pyridine-5-yl)-3-(propylsulfonamidio)benzamide was synthesized from 2,6-difluorobenzoic acid and 3-amino-5-hydroxypyrazole in 9 steps with 1% overall chemical yield. Direct desmethylation of the reference standard with TMSCl/NaI gave the precursor 2,6-difluoro-N-(3-hydroxy-1H-pyrazolo[3,4-b]pyridine-5-yl)-3-(propylsulfonamidio)benzamide for radiolabeling in 70% yield. The target tracer 2,6-difluoro-N-(3-[¹¹C]methoxy-1H-pyrazolo[3,4-b]pyridine-5-yl)-3-(propylsulfonamidio)benzamide was prepared from the precursor with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–50% decay corrected radiochemical yields with 370–740 GBq/μmol specific activity at end of bombardment (EOB).     

Coupled Dynamics of Iron and Phosphorus in Sediments of an Oligotrophic Coastal Basin and the Impact of Anaerobic Oxidation of Methane

Studies of phosphorus (P) dynamics in surface sediments of lakes and coastal seas typically emphasize the role of coupled iron (Fe), sulfur (S) and P cycling for sediment P burial and release. Here, we show that anaerobic oxidation of methane (AOM) also may impact sediment P cycling in such systems. Using porewater and sediment profiles for sites in an oligotrophic coastal basin (Bothnian Sea), we provide evidence for the formation of Fe-bound P (possibly vivianite; Fe₃(PO₄)₂ ^.8H₂O) below the zone of AOM with sulfate. Here, dissolved Fe²⁺ released from oxides is no longer scavenged by sulfide and high concentrations of both dissolved Fe²⁺ (>1 mM) and PO₄ in the porewater allow supersaturation with respect to vivianite to be reached. Besides formation of Fe(II)-P, preservation of Fe-oxide bound P likely also contributes to permanent burial of P in Bothnian Sea sediments. Preliminary budget calculations suggest that the burial of Fe-bound P allows these sediments to act as a major sink for P from the adjacent eutrophic Baltic Proper.     

Electrochemistry and spectroscopy of sulfate and thiosulfate complexes of iron porphyrins

The electrochemical and spectroscopic properties of the complex formed by the addition of thiosulfate to ferric porphyrins were examined. The NMR spectrum of the thiosulfate-ferric porphyrin complex was consistent with a high-spin ferric complex, while the EPR spectrum at liquid nitrogen temperatures indicated that the complex under these conditions was low-spin. Such behavior has been previously observed for other ferric porphyrin complexes. The visible spectra were characterized by a shift in the Soret band to higher energies, with smaller changes in the longer wavelength region. The complex was reasonably stable in DMF, but slowly reduced over several hours to Fe^II(TPP) and S₄O₆ ²⁻. The voltammetric behavior of the thiosulfate complex in DMF consists of two waves, the first of which was irreversible. The ferric/ferrous reduction in the presence of thiosulfate was shifted negatively about 400 mV, compared to the Fe(TPP)(Cl) reduction. The visible, NMR and EPR spectra were most consistent with a Fe-S bonded ferric porphyrin-thiosulfate complex, Fe(P)(SSO₃)⁻. The kinetics of the reduction of ferric porphyrin by thiosulfate in DMSO indicated an autocatalytic mechanism, where the first step is the formation of the catalyst. The identity of the catalyst could not be determined because it must be present at low concentrations, but it is formed from the reaction of the ferric complex with thiosulfate. Coordination of thiosulfate to the porphyrin was not necessary for the reduction to occur, and the reduction of Fe(TPP)(Cl) by thiosulfate was accelerated by the addition of sulfate. Under these conditions, sulfate had replaced thiosulfate as the axial ligand for the ferric porphyrin. In the presence of sulfate, the reduction occurred in a single kinetic pseudo-first order step.     

Photoluminescence properties of LiTi2 − xEux(PO4)3 phosphor

A solid‐state reaction route‐based LiTi_{2 ? x}Eu_x(PO₄)₃ was phosphor synthesized for the first time to evaluate its luminescence performance by excitation, emission and lifetime (τ) measurements. The LiTi_{2 ? x}Eu_x(PO₄)₃ phosphor was excited at λ_exci. = 397 nm to give an intense orange–red (597 nm) emission attributed to the ⁵D₀ → ⁷F₁ magnetic dipole (ΔJ = ±1) transition and red (616 nm) emission (⁵D₀ → ⁷F₂), which is an electric dipole (ΔJ = ±2) transition of the Eu³⁺ ion. Beside this, excitation and emission spectra of host LiTi₂(PO₄)₃ powder were also reported. The effect of Eu³⁺ concentration on luminescence characteristics was explained from emission and lifetime profiles. Concentration quenching in the LiTi_{2 ? x}Eu_x(PO₄)₃ phosphor was studied from the Dexter's model. Dipole–quadrupole interaction is found to be responsible for energy transfer among Eu³⁺ ions in the host lattice. The LiTi_{2 ? x}Eu_x(PO₄)₃ phosphor displayed a reddish‐orange colour realized from a CIE chromaticity diagram. We therefore suggest that this new phosphor could be used as an optical material of technological importance in the field of display devices. Copyright © 2016 John Wiley & Sons, Ltd.