Iron chlorosis is a very common nutritional disorder in plants that can be treated using iron fertilizers. Synthetic chelates have been used to correct this problem, but nowadays environmental ...concerns have enforced the search for new, more environmentally friendly ligands, such as lignosulfonates. In this paper, Fe coordination environment and speciation in lignosulfonate (LS) complexes prepared under different experimental conditions were studied by (57)Fe Mössbauer spectroscopy in relation to the Fe-complexing capacities, chemical characteristics of the different products, and efficiency to provide iron in agronomic conditions. It has been observed that the complex formation between iron and lignosulfonates involves different coordination sites. When Fe(2+) is used to prepare the iron-LS product, complexes form weak adducts and are sensitive to oxidation, especially at neutral or alkaline pH. However, when Fe(3+) is used to form the complexes, both Fe(2+) and Fe(3+) are found. Reductive sugars, normally present in lignosulfonates, favor a relatively high content of Fe(2+) even in those complexes prepared using Fe(3+). The formation of amorphous ferrihydrite is also possible. With respect to the agronomical relevance of the Fe(2+)/Fe(3+) speciation provided by the Mössbauer spectra, it seems that the strong Fe(3+)-LS complexes are preferred when they are applied to the leaf, whereas root uptake in hydroponics could be more related with the presence of weak bonding sites.
Mononuclear iron(iii) flavonolate was synthesized as synthetic enzyme-substrate complex, and its direct and carboxylate-enhanced dioxygenation as biomimetic functional models with relevance to ...flavonol 2,4-dioxygenase are briefly described.
Poly(3-octyl-thiophene) (POT) and polypyrrole (PPy) iron oxalate composites were synthesized through a post-polymerization oxidative treatment. The composite of the latter has been prepared also by ...electrochemical polymerization. The samples have been characterized by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscope (SEM) combined with energy dispersive X-ray (EDX) spectroscopy, Mössbauer spectroscopy, cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). In case of PPy, two peaks in the XRD spectra show the presence of iron containing composite, while with POT only the layered structure originating from the octyl side-chain interactions was modified by the composite formation. The assumption of the weakening of short- and long-range interactions was proven by the decrease in conductivity of the composite. The successful electrochemical synthesis resulted a composite of ∼5% iron content, determined by EDX. Mössbauer spectroscopy measurements evidenced a composite containing mixed valence iron oxalate doping ions, which supports the indirect EQCM data.
Chrysotile asbestos from different geographic regions was characterized by
57Fe Mössbauer and FT-IR spectroscopies, and FE-SEM coupled with EDS. Mössbauer spectra showed incorporation of Fe(II) and ...Fe(III) into the crystal structure of chrysotile. The Fe(II)/Fe(III) ratios were calculated. The Fe(II) occupied the octahedral Mg(II) positions. Broadening of Mössbauer lines corresponding to the Fe(III) doublet indicated a possible presence of Fe(III) in tetrahedral and octahedral positions. In all samples magnetite (Fe
3−
x
O
4) was found as associated mineral. Changes in the FT-IR spectra of chrysotiles were assigned to structural incorporation of metal ions, such as iron or aluminium ions. The morphology of chrysotile asbestos was inspected by FE-SEM.
Chloroplasts contain 80–90% of iron taken up by plant cells. Though some iron transport-related envelope proteins were identified recently, the mechanism of iron uptake into chloroplasts remained ...unresolved. To shed more light on the process of chloroplast iron uptake, trials were performed with isolated intact chloroplasts of sugar beet (Beta vulgaris). Iron uptake was followed by measuring the iron content of chloroplasts in the form of ferrous-bathophenantroline–disulphonate complex after solubilising the chloroplasts in reducing environment. Ferric citrate was preferred to ferrous citrate as substrate for chloroplasts. Strong dependency of ferric citrate uptake on photosynthetic electron transport activity suggests that ferric chelate reductase uses NADPH, and is localised in the inner envelope membrane. The Km for iron uptake from ferric-citrate pool was 14.65 ± 3.13 μM Fe(III)-citrate. The relatively fast incorporation of 57Fe isotope into Fe-S clusters/heme, detected by Mössbauer spectroscopy, showed the efficiency of the biosynthetic machinery of these cofactors in isolated chloroplasts. The negative correlation between the chloroplast iron concentration and the rate of iron uptake refers to a strong feedback regulation of the uptake.
► Chloroplast iron acquisition prefers ferric to ferrous iron complexes. ► The release of free ferrous iron ions by reduction is obligatory for uptake. ► Km value of iron uptake from ferric iron pool is 14.65 ± 3.13 μM Fe(III)-citrate. ► Iron is preferentially incorporating into Fe-S and/or heme cofactors.
Transport and magnetic properties of LaCoO3-based compounds, doped with 20% Sr and 2.5, 5, 10, 15, 20 and 30% Fe, were investigated by means of magnetization, resistivity and magnetoresistance ...measurements as well as by 57Fe Mossbauer spectroscopy. While the temperature dependence of the dc and ac magnetic susceptibilities reveals the presence of magnetic phase separation accompanied by spin-glass and cluster-glass behavior, the electrical resistivity and magnetoresistance characteristics indicate that the mesoscopic structure of the present compounds is rather well described as consisting of ferromagnetic, metallic grains embedded in an insulating matrix. The effect of the partial Co - > Fe substitution on the bulk magnetic and transport properties, as well as on the local state of Co and Fe ions is discussed.
A sediment core containing a yellowish-green clay bed was recovered from an area of extensive hydrothermal deposition at the SE slope of the Eolo Seamount, Tyrrhenian Sea. The clay bed is composed of ...pure nontronite (described for the first time in the Tyrrhenian Sea), which appears to be the most aluminous nontronite ever found among the seafloor hydrothermal deposits. The high Al content suggests precipitation from Al-containing hydrothermal solutions. The REE distribution of the Eolo nontronite has a V-shape pattern. The heavy REE enrichment is in part due to their preferential partitioning in the nontronite structure. This enrichment was possibly further enhanced by the HREE preferential sorption on bacterial cell walls. The light REE enrichment is the result of scavenging uptake by one of the nontronite precursors, i.e., poorly-ordered Fe-oxyhydroxides, from the hydrothermal fluids. Oxygen isotopic composition of the nontronite yields a formation temperature of 30 °C, consistent with a low-temperature hydrothermal origin. The relatively radiogenic Nd isotopic signature of the nontronite compared to the present-day Mediterranean seawater indicates that approximately half of Nd, and presumably the rest of the LREE, are derived from local volcanic sources. On the other hand,
87Sr/
86Sr is dominated by present-day seawater Sr.
Scanning electron microscopy investigation revealed that the nontronite is composed of aggregates of lepispheres and tube-like filaments, which are indicative of bacteria assisted precipitation. Bacteria inhabiting this hydrothermal site likely acted as reactive geochemical surfaces on which poorly-ordered hydrothermal Fe-oxyhydroxides and silica precipitated. Upon aging, the interactions of these primary hydrothermal precipitates coating bacterial filaments and cell walls likely led to the formation of nontronite. Finally, the well-balanced interlayer and layer charges of the crystal lattice of seafloor hydrothermal nontronite decrease its sorption capacity to zero. Thus the ubiquitous nontronite precipitation along the active plate boundaries and around the hot spots has no significant impact on oceanic trace element chemistry.
A sediment core taken from the south–east slope of the Eolo Seamount is composed of alternating red-brown and light-brown to bluish-grey layers with signs of re-deposition in the middle-upper ...section. The red-brown layers are Fe-rich metalliferous sediments formed as a result of low-temperature (∼
77 °C) hydrothermal discharge, whereas the bluish-grey layers most probably originated from background sedimentation of Al-rich detrital material. The metalliferous layers are composed mainly of Si-rich goethite containing some Al. Co-precipitation of hydrothermally released SiO
4
4− and Fe
2+ as amorphous or poorly crystalline Fe–Si-oxyhydroxides explains the high Si concentration in goethite. The elevated Al content of the goethite is fairly unusual, but reflects the extremely high background Al content of the Tyrrhenian seawater due to the high eolian terrigenous flux from the Sahara desert. The Sr and Nd isotope data suggest that the Eolo metalliferous sediments are the product of a 3-component mixture: hydrothermal fluid, seawater, and detrital material (Saharan dust and Aeolian Arc material). The enrichment in Fe, P, As, Mo, Cd, Be, Sb, W, Y, V, depletion in REE and transition elements (Cu, Co, Ni, Zn) and the REE distribution patterns support the low-temperature hydrothermal deposition of the metalliferous layers. The hydrothermal field is located in a seawater layer of relative O
2 depletion, which led to a significant fractionation of the hydrothermally emitted Fe and Mn. Fe-oxyhydroxides precipitated immediately around the vents whereas Mn stayed in solution longer and the Mn-oxides precipitated higher up on the seamount slope in seawater with relatively higher O
2 levels. High seismic activity led to sediment re-deposition and slumping of the Mn-rich layers down slope and mixing with the Fe-rich layers.
Incorporation of fluoride ions into the structure of jarosite, a common precipitate in bioleaching, was studied. Crystalline jarosite was synthesized in the presence of various concentrations of ...fluoride ions and characterized by spectroscopic- and chemical analysis.
The results showed that substantial amounts of fluoride were sorbed to jarosite, increasing with pH and fluoride concentration. FTIR, XRD and Mössbauer analysis supported a structural incorporation of the fluoride. Due to the size similarity between fluoride and hydroxide ions, a probable mechanism is an exchange of hydroxide ions and fluoride ions within the jarosite, giving the composition KFe
3(SO
4)
2(OH)
6
−
x
F
x
(s). For the maximum concentration of fluoride used during synthesis, 200 mM, about 25% of the hydroxide ions were exchanged for fluoride ions. The mass of jarosite precipitated shown to be highly dependent on the fluoride concentration, with approximately half the yield using 200 mM potassium fluoride compared to in the absence of fluoride ions.
To test the influence on toxicity of the incorporation of fluoride in jarosite, a bioleaching study was performed at 65 °C. A suspension of pyrite concentrate with 4% solid content (w/v) in the modified 9 K medium was bioleached under additions of potassium fluoride. The results indicated a higher tolerance for fluoride ions, as compared to earlier reported studies on fluoride toxicity during bioleaching.
The uptake and accumulation of iron in cucumber roots exposed to cadmium were investigated with Fe sufficient and deficient cucumber plants using Mössbauer spectroscopy, Inductively Coupled Plasma ...Mass Spectrometry (ICP-MS) and ferric chelate reductase activity measurements. Both Fe sufficient and Fe deficient plants were applied. In the case of Fe sufficient cucumber roots grown in nutrient solution with 10 μM Cd no changes were found in the occurrence of Fe species (mostly hydrous ferric oxides and ferric-carboxylate complexes) compared to the control where no Cd was added. In the Fe deficient roots pretreated with 0, 0.1, 1, 10 and 100 μM Cd for 3 h then supplied also with 0.5 mM ⁵⁷Fe-citrate for 30 min, FeII was identified in a hexaaqua complex form. The relative amount of FeII was decreasing simultaneously with increasing Cd concentration, while the relative occurrence of FeIII species and total Fe concentration were increasing. The results support the inhibitory effect of Cd on Fe-chelate reduction. Although the reductase activity at 10 and 100 μM Cd treatment was lower than in the iron sufficient control plants, FeII could be identified by Mössbauer spectroscopy whereas in the Fe sufficient control, this form was below detection limit. These data demonstrate that the influx and the reoxidation of FeII was decreased by Cd, consequently, they refer to the competition of Cd²⁺ and Fe²⁺ during the membrane transport and the inhibition of the reoxidation process.
