Iron-organic Complexes Research Articles

An extended siderophore suite from Synechococcus sp. PCC 7002 revealed by LC-ICPMS-ESIMS.

Siderophores are thought to play an important role in iron cycling in the ocean, but relatively few marine siderophores have been identified. Sensitive, high throughput methods hold promise for expediting the discovery and characterization of new siderophores produced by marine microbes. We developed a methodology for siderophore characterization that combines liquid chromatography (LC) inductively coupled plasma mass spectrometry (ICPMS) with high resolution electrospray ionization mass spectrometry (ESIMS). To demonstrate this approach, we investigated siderophore production by the marine cyanobacteria Synechococcus sp. PCC 7002. Three hydroxamate siderophores, synechobactin A-C, have been previously isolated and characterized from this strain. These compounds consist of an iron binding head group attached to a fatty acid side chain of variable length (C12, C10, and C8 respectively). In this study, we detected six iron-containing compounds in Synechococcus sp. PCC 7002 media by LC-ICPMS. To identify the molecular ions of these siderophores, we aligned the chromatographic retention times of peaks from the LC-ICPMS chromatogram with features detected from LC-ESIMS spectra using an algorithm designed to recognize metal isotope patterns. Three of these compounds corresponded to synechobactins A (614 m/z), B (586 m/z), and C (558 m/z). The MS2 spectra of these compounds revealed diagnostic synechobactin fragmentation patterns which were used to confirm the identity of the three unknown compounds (600, 628, and 642 m/z) as new members of the synechobactin suite with side chain lengths of 11, 13, and 14 carbons. These results demonstrate the potential of combined LCMS techniques for the identification of novel iron-organic complexes.

Nanocomposites of Graphene with Ferrocene or Hemin: Preparation and Application in Electrochemical Sensing

Graphene has sparked tremendous interests across many fields such as biosensors, electrochemical energy storage, and electronics due to its extraordinary physicochemical and structural properties. The redox mediator‐functionalized graphene composites may obtain highly electroactive materials with better conductivity, dispersion, and compatibility. Ferrocene and hemin, two iron‐organic complexes, are the well‐known mediators in view of their various properties, including reversibility, regeneration at low potential, and generation of stable redox states. Recently, it has been demonstrated that the use of ferrocene or hemin coupled with graphene can further improve the electrochemical performances of the developed sensors. In this contribution, we, for the first time, reviewed the preparation and applications of ferrocene/graphene and hemin/graphene nanocomposites in electrochemical sensing.

Iron stable isotopes track pelagic iron cycling during a subtropical phytoplankton bloom

The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼ 40% of the global ocean. The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailability in the marine realm, although the mechanisms facilitating exchange between iron species (inorganic and organic) and phases are poorly constrained. Here we use the isotope fingerprint of dissolved and particulate iron to reveal distinct isotopic signatures for biological uptake of iron during a GEOTRACES process study focused on a temperate spring phytoplankton bloom in subtropical waters. At the onset of the bloom, dissolved iron within the mixed layer was isotopically light relative to particulate iron. The isotopically light dissolved iron pool likely results from the reduction of particulate iron via photochemical and (to a lesser extent) biologically mediated reduction processes. As the bloom develops, dissolved iron within the surface mixed layer becomes isotopically heavy, reflecting the dominance of biological processing of iron as it is removed from solution, while scavenging appears to play a minor role. As stable isotopes have shown for major elements like nitrogen, iron isotopes offer a new window into our understanding of the biogeochemical cycling of iron, thereby allowing us to disentangle a suite of concurrent biotic and abiotic transformations of this key biolimiting element.

Investigation on the iron-uptake by natural biofilms

Biofilms are natural communities of microorganisms living in aquatic ecosystems which play an important role in the biogeochemistry of many inorganic elements, including iron. The present work aimed to study the uptake of iron by natural river biofilms (produced in the laboratory) and to examine the relationships between biofilms and iron in water. For that, biofilms were formed from natural water samples collected at different times of the year. Total content and global localization of iron were determined by a combination of chemical analyses and microscopy, which indicated that iron was systematically distributed throughout the biofilm matrix. Depending on the level of iron uptake, iron was diffuse or present as hot spots, was primarily localized to the fraction ascribed to OM compounds (45–60%) or the residual fraction (∼14–40%). Additional experiments were conducted using iron–organic complexes with different affinities (log K) to study iron uptake according to the speciation. These experiments suggested the association between iron and organic ligands (i.e. depending on the affinity constant) influenced the uptake of iron, but did not control the biofilm affinity for iron, which appeared to be controlled by chemical-kinetic laws.

Influence of organic iron complex on sow reproductive performance and iron status of nursing pigs

This experiment was conducted to evaluate the effects of organic iron complex on sow reproductive performance and iron status of nursing pigs. At day 84 of gestation, a total of 58 PIC sows at five-parity were randomly assigned to two groups receiving diets containing organic iron complex (n=33) and ferrous sulfate (n=25). According to a 2×2 factorial design of treatments, nursing pigs (2.09±0.34kg) within a given litter were divided into two groups and given either an injection with or without iron (0 vs. 200mg/pig) on day three of lactation. The feeding trial lasted for 51 days, including 30 days of gestation and 21 days of lactation. The results showed that organic iron complex did not improve the reproductive performance of sows or the growth performance of piglets. In particular, nursing pigs injected with iron had greater individual body weight at day 21 of lactation compared to pigs that were not treated with iron (P<0.05). Compared with ferrous sulfate, organic iron complex significantly increased the Cu content in mature milk (P<0.01), and the serum iron concentration at day one of lactation (P<0.05), as well as ceruloplasmin activity at day 21 of lactation (P<0.01). Piglets from sows fed organic iron complex tended to have a greater total iron binding capacity (P=0.08) and ceruloplasmin activity (P=0.05) at day 10 of lactation, and tended to have a higher concentration of hemoglobin (P=0.08), total iron binding capacity (P<0.01) and serum iron (P<0.01) at day 21 of lactation compared with piglets from sows fed ferrous sulfate. Piglets injected with iron had a greater red blood cell count (P<0.01), hemoglobin (P<0.01), serum iron (P<0.01) and total iron binding capacity (P<0.05) at day 10 and 21 of lactation compared to piglets that were not treated with iron. In conclusion, organic iron complex had minor positive effects on the iron status of sows and nursing pigs, but did not significantly improve the performance of sows and their offspring. Therefore, attempts to replace the commonly used Fe injection with a maternal organic iron complex dietary supplement failed to prevent iron-deficiency anemia of nursing pigs.

The organic complexation of iron and copper: an intercomparison of competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) techniques

Characterization of the speciation of iron and copper is an important objective of the GEOTRACES Science Plan. To incorporate speciation measurements into such a multinational program, standard practices must be adopted that allow data from multiple labs to be synthesized. Competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) is the primary technique employed for measuring metal‐binding ligands and determining metal speciation in seawater. The determination of concentrations and conditional stability constants of metal‐binding ligands is particularly challenging, as results can be influenced both by experimental conditions and interpretation of titration data. Here, we report an investigation between four laboratories to study the speciation of iron and copper using CLE‐ACSV. Samples were collected on the GEOTRACES II intercomparison cruise in the North Pacific Ocean in May 2009 at 30° N, 140° W. This intercomparison was carried out shipboard and included an assessment of the viability of sample preservation by freezing. Results showed that consensus values could be obtained between different labs, but that some existing practices were problematic and require further attention in future work. A series of recommendations emerged from this study that will be useful in implementing multi‐investigator programs like GEOTRACES.

A novel and simple approach for the synthesis of Fe3O4-graphene composite

High crystalline Fe3O4-graphene composite has been successfully synthesized via one-step thermolysis reaction. The results demonstrated that the attachment of iron-organic complex with graphene oxide sheets can facilely lead to magnetic graphene composites with a time-dependent calcination process. The composite was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The high efficient removal of methylene blue determined that Fe3O4-graphene is a promising sorbent material for wastewater treatment.

Key role of organic complexation of iron in sustaining phytoplankton blooms in the Pine Island and Amundsen Polynyas (Southern Ocean)

Primary productivity in the Amundsen Sea (Southern Ocean) is among the highest in Antarctica. The summer phytoplankton bloom in 2009 lasted for >70 days in both the Pine Island and Amundsen Polynyas. Such productive blooms require a large supply of nutrients, including the trace metal iron (Fe). The organic complexation of dissolved Fe was investigated in the Amundsen Sea during the spring of 2009 to better understand the potential role of ligands in enhancing the local stock of dissolved Fe. The main sources of Fe and ligands to the Amundsen Sea are thought to be melting sea-ice and the Circumpolar Deep Water (CDW), which is modified (MCDW) on the continental shelf and upwells beneath the coastal glaciers and ice-shelves. Upwelling of relatively warm MCDW is also responsible for the rapid melting of the Pine Island Glacier (PIG) and surrounding ice-shelves, resulting in additional release of Fe into surface waters. At upwelling stations near ice shelves, organic ligands were nearly saturated with Fe, thus enhancing the stock of Fe and its availability to the phytoplankton community. However, ligands had little capacity to buffer additional Fe input from glacial melt. In these coastal upwelling regions, much of the glacial Fe supply is lost due to vertical export of Fe via scavenging and precipitation. Conversely, within the phytoplankton bloom in the nearby coastal polynyas, the uptake of Fe combined with the production of organic matter enhanced the abundance of relatively unsaturated organic ligands capable of stabilizing additional Fe supplied from glacial melt. These unsaturated dissolved organic ligands, combined with the continuous input of Fe (dissolved and particulate) from glacial melt, appear to favor the solubilization of Fe, thus increasing the stock of bioavailable Fe and fueling the phytoplankton bloom.

The organic complexation of iron in the marine environment: a review

Iron (Fe) is an essential micronutrient for marine organisms, and it is now well established that low Fe availability controls phytoplankton productivity, community structure, and ecosystem functioning in vast regions of the global ocean. The biogeochemical cycle of Fe involves complex interactions between lithogenic inputs (atmospheric, continental, or hydrothermal), dissolution, precipitation, scavenging, biological uptake, remineralization, and sedimentation processes. Each of these aspects of Fe biogeochemical cycling is likely influenced by organic Fe-binding ligands, which complex more than 99% of dissolved Fe. In this review we consider recent advances in our knowledge of Fe complexation in the marine environment and their implications for the biogeochemistry of Fe in the ocean. We also highlight the importance of constraining the dissolved Fe concentration value used in interpreting voltammetric titration data for the determination of Fe speciation. Within the published Fe speciation data, there appear to be important temporal and spatial variations in Fe-binding ligand concentrations and their conditional stability constants in the marine environment. Excess ligand concentrations, particularly in the truly soluble size fraction, seem to be consistently higher in the upper water column, and especially in Fe-limited, but productive, waters. Evidence is accumulating for an association of Fe with both small, well-defined ligands, such as siderophores, as well as with larger, macromolecular complexes like humic substances, exopolymeric substances, and transparent exopolymers. The diverse size spectrum and chemical nature of Fe ligand complexes corresponds to a change in kinetic inertness which will have a consequent impact on biological availability. However, much work is still to be done in coupling voltammetry, mass spectrometry techniques, and process studies to better characterize the nature and cycling of Fe-binding ligands in the marine environment.

Iron redox cycling in hydroxyl radical generation during the photo-Fenton oxidative degradation: Dynamic change of hydroxyl radical concentration

Effects of Fenton reagents, iron and hydrogen peroxide, on the generation of hydroxyl radicals (OH) during photo-Fenton degradation of acetaldehyde dissolved in water were examined. The dynamic change in OH radical concentration during the acetaldehyde degradation by the photo-Fenton process was measured using a coumarin fluorescence probing technique. The OH radical concentrations increased with increasing initial Fe concentrations within the Fe dosage range examined in this study. With increasing acetaldehyde loading the OH radical concentration decreased. The OH radical concentration changed rather complicatedly as the acetaldehyde degradation by the photo-Fenton oxidation process proceeded. The dynamic change in OH radical concentration could be divided into four phases: the OH radical concentration instantaneously and significantly increased just after the start of photo-Fenton oxidation process (Phase I), subsequently decreased (Phase II), increased again after reaching its minimum value (Phase III), and gradually decreased after the OH radical concentration reached a maximum point (Phase IV). This complicated change in OH radical concentration during photo-Fenton degradation of acetaldehyde could be rationally described by the Fe-redox cycle via the Fe–organic complex formation and its oxidation by dissolved oxygen besides the Fenton and photo-Fenton reactions. It was found that the oxidation of iron–organic complexes formed by ferric iron with acetaldehyde and its degradation products accelerated the rate of Fe-redox cycle. On the other hand, the formation of Fe–organic complexes led the decrease in Fe ions available for the Fenton and photo-Fenton reactions.

Role of dust alkalinity in acid mobilization of iron

Abstract. Atmospheric processing of mineral aerosols by acid gases (e.g., SO2, HNO3, N2O5, and HCl) may play a key role in the transformation of insoluble iron (Fe in the oxidized or ferric (III) form) to soluble forms (e.g., Fe(II), inorganic soluble species of Fe(III), and organic complexes of iron). On the other hand, mineral dust particles have a potential of neutralizing the acidic species due to the alkaline buffer ability of carbonate minerals (e.g., CaCO3 and MgCO3). Here we demonstrate the impact of dust alkalinity on the acid mobilization of iron in a three-dimensional aerosol chemistry transport model that includes a mineral dissolution scheme. In our model simulations, most of the alkaline dust minerals cannot be entirely consumed by inorganic acids during the transport across the North Pacific Ocean. As a result, the inclusion of alkaline compounds in aqueous chemistry substantially limits the iron dissolution during the long-range transport to the North Pacific Ocean: only a small fraction of iron (&lt;0.2%) dissolves from hematite in the coarse-mode dust aerosols with 0.45% soluble iron initially. On the other hand, a significant fraction of iron (1–2%) dissolves in the fine-mode dust aerosols due to the acid mobilization of the iron-containing minerals externally mixed with carbonate minerals. Consequently, the model quantitatively reproduces higher iron solubility in smaller particles as suggested by measurements over the Pacific Ocean. It implies that the buffering effect of alkaline content in dust aerosols might help to explain the inverse relationship between aerosol iron solubility and particle size. We also demonstrate that the iron solubility is sensitive to the chemical specification of iron-containing minerals in dust. Compared with the dust sources, soluble iron from combustion sources contributes to a relatively marginal effect for deposition of soluble iron over the North Pacific Ocean during springtime. Our results suggest that more comprehensive data for chemical specificity of iron-rich dust is needed to improve the predictive capability for size-segregated soluble iron particles.

An evaluation of iron bioavailability and speciation in western Lake Superior with the use of combined physical, chemical, and biological assessment

An iron‐dependent cyanobacterial bioreporter (Synechococcus strain KAS101) was used in unison with size‐fractionated iron content (&gt;0.45, &lt;0.45, &lt;0.02 µm), and chemical characterization of iron complexation (C18 resin column) to elucidate the bioavailable forms of iron present in Lake Superior during periods of inverse thermal stratification (May) and strong thermal stratification (September) of the water column. The results provide evidence of organic complexation of iron in Lake Superior waters. Iron in most sampled water was complexed by organic compounds that behaved like fulvic acids, whereas some samples showed evidence for the presence of siderophore‐like compounds. The presence of dissolved organic matter suppressed the cellular luminescence of the bioreporter, indicating an increased iron bioavailability. This effect could result either from the presence of siderophores forming iron complexes that are bioavailable to the bioreporter, or from more indirect effects because of the presence of other organic compounds, such as fulvic acids or polysaccharides. Model ligand additions, iron bioaccumulation, and photo‐oxidation of dissolved organic matter were used to assess the bioavailability of organically complexed iron to the bioreporter. A significant fraction of the iron (40‐100%) was bioavailable to the bioreporter. Iron bioavailability was high enough for the bioreporter not to be iron limited in the water collected from Lake Superior. This measure of bioavailability to picocyanobacteria is relevant because picoplankton accounted for the majority of chlorophyll a in Lake Superior during this study.

Organic complexation and translocation of ferric iron in podzols of the Negro River watershed. Separation of secondary Fe species from Al species

The development of podzols in lateritic landscapes of the upper Amazon basin contributes to the exportation of organic carbon and associated metals in the black waters of the Negro River watershed. We have investigated the distribution of Fe III in the clay-size fraction of eight organic-rich horizons of waterlogged plateau podzols, to unravel the weathering conditions and mechanisms that control its transfer to the rivers. The speciation and amount of Fe III stored in residual mineral phases of laterites, or bound to organic compounds of weakly and well-expressed podzols, were determined by electron paramagnetic resonance spectroscopy combined with chemical analyses. Reducing conditions restrict the production of organo-Fe complexes in the subsoil B-horizons of waterlogged podzols and most of the Fe 2+ released from the dissolution of Fe-oxides is exported to the rivers via the perched groundwater. However, significant amounts of diluted Fe III bound to organic ligands (Fe III OM) and nano Fe-oxides are produced at the margin of the depression in the topsoil A horizons of weakly expressed podzols due to shorter periods of anoxia. The downward translocation of organically bound metals from topsoil A to subsoil B-horizons of podzols occurs in shorter distances for Fe than it does for Al. This separation of secondary Fe species from Al species is attributed to the physical fractionation of their organic carriers in texture contrasted B-horizons of podzols, as well as to the effect of pH on metal speciation in soil solutions and metal binding onto soil organic ligands (mostly for Al). This leads us to consider the topsoil A horizons of weakly expressed podzols, as well as the subsoil Bh horizon of better-expressed ones, as the main sources for the transfer of Fe III OM to the rivers. The concentration of Fe III OM rises from soil sources to river colloids, suggesting drastic biogeochemical changes in more oxygenated black waters of the Negro River watershed. The contribution of soil organic matter to the transfer of Fe to rivers is likely at the origin of the peculiar Fe isotope pattern recently recognized in podzolic environments.

Soils on hard rocks in the northwest of Russia: Chemical and mineralogical properties, genesis, and classification problems

Soil formation on hard rocks—nepheline syenite, amphibolite, metamorphized gabbro diabase, and their derivatives—was studied in the mountainous tundra and in the northern and middle taiga zones of the Kola Peninsula and Karelia (in the Kivach Reserve). It was found that the soils developing from these rocks could be classified into three groups: (1) petrozems with the O-M profile (the most common variant), (2) podzols and podzolized podburs on the substrates with an admixture of morainic derivatives of acid rocks, and (3) shallow (<5–10 cm) pebbly soils on the substrates without an admixture of allochthonous material (the rarest variant). In soils of the third group, the pedogenic alteration of the mineral matrix does not result in the appearance of phyllosilicates in the fine fractions if these phyllosilicates are initially absent in the rock. In these soils, the protion of the organic matter, and binding of iron released from the weathered silicate minerals into iron-organic complexes) are virtually undifferentiated by the separate soil horizons because of the very low thickness of the soil profiles. These soils have the Oao-BHFao-M profile; it is suggested that they can be classified as leptic podburs. An admixture of morainic material containing phyllosilicate minerals favors a more pronounced differentiation of the modern pedogenic processes by separate soil horizons even in the case of shallow soil profiles; the intense transformation of phyllosilicates takes place in the soils.

Which is the Best Oxidant for Complexed Iron Removal from Groundwater: The Kogalym Case

A short overview of the significance of a preoxidation stage groundwater treatment is presented. As an example the case of complexed iron removal from Kogalym groundwater (Tjumen, Siberia, Russian Federation) using different preoxidants (ozone, oxygen, chlorine, hydrogen peroxide, and potassium permanganate) is discussed. The key problem is stable di-and trivalent iron-organic complexes in groundwater which after aeration tend to pass through the hydroanthracite-sand gravity filters. The total organic carbon (TOC) content in raw groundwater is in the range of 3.2–6.4 mg/L, total iron content 2.7–6.0 mg/L and divalent iron content 2.4–4.0 mg/L. Separation from Kogalym groundwater by XAD-16 adsorbent humic matter fraction was homogeneous, with only 1 peak on the chromatogram with maximum Rt = 10.75 min and corresponding molecular mass 1911 (<2000). The final developed treatment technology is based on the water oxidation/reduction potential (ORP) optimization according to the iron system pE-pH diagram and consists of intensive aeration of raw water in the Gas-Degas Treatment (GDT) unit with the following sequence: filtration through the hydroanthracite and special anthracite Everzit, with intermediate enrichment of water with pure oxygen between the filtration stages.

The research on the possibility of ultrasound field application in iron removal of water

The paper describes the preliminary researches on the influence of the ultrasounds of diversified intensity (22 and 24 kHz) on the content iron compounds in water. For the researches, variable operational parameters were used, such as: the vibration amplitude and the exposure time (1–5 min). The substrate was: distilled water and natural river water of intensive colour, prepared by iron Fe(II) compounds (iron ammonium-sulphate). The effect of ultrasounds was researched as a result of the influence of sonochemical oxidation processes and ultrasound coagulation on iron in the ionized form (of ions Fe 2+) and on iron–organic complexes in the lowionized or colloidal form. The share of sonochemical and coagulation processes depends on the parameters determining the ultrasounds intensity. The effects of the iron removal were researched at the low and high intensity determining the strain of cavitation processes. As a result, the changes of iron content (Fe 2+, Fe 3+, Fe og) and the colour of water exposed to ultrasound field of variable parameters were presented. The effectiveness of the researched processes was analysed from the point of view of the possibility of determinate intensity ultrasound usage as an unconventional method of the removal of iron from water.

Superoxide-mediated reduction of organically complexed iron(III): Impact of pH and competing cations (Ca 2+)

The mechanism and kinetics of superoxide-mediated reduction of a variety of organic iron(III) complexes has been investigated over the pH range 7–9. Our experimental results show that the rate of iron(II) formation is a function of pH, ligand type and ligand concentration with the measured rate varying between 0.44 ± 0.07 and 39.25 ± 1.77 pM s −1 in the systems investigated. Additionally, our results show that the presence of competing cations such as Ca 2+ have a significant impact on iron(II) formation if the organic ligand is strongly complexed by Ca 2+. Formation of iron(II) occurs by either (or, in some instances, both) reaction of superoxide with inorganic iron(III) after its dissociation from the complex (dissociative reduction) or by direct reaction of superoxide with the complex (non-dissociative reduction). In the presence of weak ligands, dissociative reduction (DR) dominates; however non-dissociative reduction (NDR) becomes important in the presence of either strongly binding ligands or high concentrations of weakly binding ligands. The major factors contributing to the pH dependence of the iron(II) formation rate are the complexation kinetics of inorganic iron(III) (which controls the DR contribution) and the reduction kinetics of the iron(III) complex (which controls the NDR contribution). The relative NDR contribution increases with increasing superoxide and ligand concentration and decreasing pH for all ligands examined. Since iron(II) formation occurring via NDR results in a significantly larger increase in the proportion of iron in free aquated form than does DR, this non-dissociative pathway of superoxide-mediated iron(III) reduction is particularly effective in increasing the lability of iron in aquatic systems.

In vitro activity of ferroquine (SSR 97193) against Plasmodium falciparum isolates from the Thai-Burmese border.

BackgroundOn the borders of Thailand, Plasmodium falciparum has become resistant to nearly all available drugs, and there is an urgent need to find new antimalarial drugs or drug combinations. Ferroquine (SSR97193) is a new 4-aminoquinoline antimalarial active against chloroquine resistant and sensitive P. falciparum strains in vivo and in vitro. This antimalarial organic iron complex (a ferrocenyl group has been associated with chloroquine) is meant to use the affinity of Plasmodium for iron to increase the probability for encountering the anti-malarial molecule.The aim of the present study was to investigate the activity of ferroquine against P. falciparum isolates from an area with a known high multi-drug resistance rate.MethodsParasite isolates were obtained from patients with acute falciparum malaria attending the clinics of SMRU. In vitro cultures of these isolates were set-up in the SMRU-laboratory on pre-dosed drug plates, and grown in culture for 42 hours. Parasite growth was assessed by the double-site enzyme-linked pLDH immunodetection (DELI) assay.ResultsSixty-five P. falciparum isolates were successfully grown in culture. The ferroquine mean IC50 (95% CI) was 9.3 nM (95% C.I.: 8.7 – 10.0). The mean IC50 value for the principal metabolite of ferroquin, SR97213A, was 37.0 nM (95% C.I.: 34.3 – 39.9), which is four times less active than ferroquine. The isolates in this study were highly multi-drug resistant but ferroquine was more active than chloroquine, quinine, mefloquine and piperaquine. Only artesunate was more active than ferroquine. Weak but significant correlations were found between ferroquine and its principal metabolite (r2 = 0.4288), chloroquine (r2 = 0.1107) and lumefantrine (r2 = 0.2364).ConclusionThe results presented in this study demonstrate that the new ferroquine compound SSR97193 has high anti-malarial activity in vitro against multi-drug resistant P. falciparum.

Dissolved iron and its speciation in a shallow eutrophic lake and its inflowing rivers

It has been suggested that iron is a limiting factor on bloom-forming cyanobacteria in lake water. Although the availability of iron for phytoplankton depends significantly on its speciation, little is known about iron speciation in natural lake water. We investigated the horizontal distribution and temporal variation of dissolved iron and its chemical speciation in Lake Kasumigaura and its two inflowing rivers. Concentrations of dissolved iron and its organic ligands, determined by cathodic stripping voltammetry, clearly decreased as lake water flowed from the river entry points toward the center of the lake, indicating their riverine origin. The fraction of iron occurring in organic complexes tended to increase with the water flow. These results suggest that most of the dissolved iron in river water forms unstable soluble species, such as inorganic iron; thus, these unstable iron species may be scavenged in the mouths of rivers, and stable organic complexes of iron may flow to the center of the lake. Furthermore, most of the dissolved iron (88.2–99.9%) was present as organic complexes, and the inorganic iron level in Lake Kasumigaura (pFe′ value=7.8–13.6) was similar to that observed in the open ocean. This result suggests that iron is an important factor determining the structure of the phytoplankton community in Lake Kasumigaura.

Impact of iron-complex (Fe(iii)–NTA) on photoinduced degradation of 4-chlorophenol in aqueous solution

In this research work, the photochemical impact of Fe(III)-nitrilotriacetic acid complex (FeNTA) on the fate of an organic pollutant (4-chlorophenol (4-CP)) was investigated in natural waters. The quantum yields of the photodecomposition of the FeNTA complex and of Fe(II) formation, by an intra-molecular photoredox process (the first stage of the reaction) are high. This photoredox reaction represents the first step of the process leading to 4-CP disappearance. Whereas oxygen does not affect FeNTA photodegradation, 4-CP depletion requires the presence of oxygen. The radical species HO and CO3*- responsible of the degradation were identified by ESR spectroscopy under irradiation. Two different wavelength-dependent mechanisms of 4-chlorophenol degradation are proposed. It clearly appears that under solar irradiation, iron organic complexes like FeNTA can play a significant role on the fate of the organic compounds present in natural waters.