Mágneses ellenállást mutató perovszkitok és spinellek vizsgálata Mössbauer-spektroszkópiával, mágneses és röntgendiffrakciós módszerekkel = Mössbauer spectroscopic, magnetic and x-ray diffraction studies of some perovskite and spinel materials possessing magnetoresistivity

I. Kutatásunk legfontosabb eredménye, hogy összefüggést tudtunk felmutatni a vizsgált kobaltát perovszkitok lokális elektromos és mágneses szerkezete és az általuk mutatott mágneses ellenállás között. Sikerült felvázolni a La0.8Sr0.2Co1-yFeyO3 (0 < y < 0,3) perovszkitok mágneses fázisdiagramját, részletesen elemezni tudtuk a különböző fázisok természetét, valamint a lantánionok európiummal való cseréjével megállapítottuk a ritkaföldfém lokális elektromos állapotát. Egy újabb kísérletsorozat során elkészítettük, karakterizáltuk és megvizsgáltuk a La1-xSrxFe0.025Co0.975O3 (0 < x < 0,25) összetételű perovszkitokat is. Eredményeink alapján megállapítottuk, hogy a mágneses ellenállás kiváltó oka a vizsgált perovszkitokban a nanoméretű elektromos-mágneses fázisszeparáció lehet. II. A pályázat másik kutatási témájának keretén belül növények vasfelvételi mechanizmusait vizsgáltuk Mössbauer-spektroszkópia segítségével uborka és búza felhasználásával. Bizonyítottuk az ún. I. stratégiai csoportba tartozó növények redukción alapuló vasfelvételi mechanizmusát és rámutattunk a Cd vasfelvételt (és transzportot) gátló hatásaira. Emellett biomineralizációs és szintetikus folyamatokban képződő jarozitok szerkezetét tanulmányoztuk PXRD és Mössbauer-spektroszkópiai módszerekkel. UV-látható spektrofotometria és Mössbauer-spektroszkópia alkalmazásával megvizsgáltuk a növényélettani szempontból jelentős indol-3-ecetsavnak a vas(III)-mal történő reakcióinak mechanizmusát és kinetikáját. | I. Our primer finding is that we were able to correlate the observed local electronic and magnetic properties of the investigated cobaltate perovskite samples with their magnetoresistance. We presented the magnetic phase diagram of La0.8Sr0.2Co1-yFeyO3 (0 < y < 0.3) perovskites, and we analyzed the nature of the depicted magnetic phases. Moreover, by replacing the lanthanum ions with europium, using 151Eu Mössbauer spectrometry we have determined the local electronic structure of the rare-earth cation, as well. We have also prepared and characterized La1-xSrxFe0.025Co0.975O3 (0 < x < 0.25) samples and performed several experiments on them. Due to our results, we were able to determine the possible source of the magnetoresistance of the investigated family of perovskites, being the nanosize electronic-magnetic phase separation. II. In the second part of the project, the iron-uptake mechanisms of plants were investigated by Mössbauer spectroscopy, using cucumber and wheat as model plants: direct evidence for the strategy I iron-uptake mechanism was given and the inhibitory effects of Cd on the iron-uptake and transport were demonstrated. The structure of jarosites formed during biomineralization and synthetic processes were studied with the help of PXRD and Mössbauer spectroscopy. The mechanism and the kinetics of the reaction of the plant hormone indole-3-acetic acid with iron(III) was discussed in detail using UV-Vis spectrophotometry and Mössbauer spectroscopy

Revisiting the iron pools in cucumber roots: identification and localization

Iron may accumulate in various chemical forms during its uptake and assimilation in roots. The permanent and transient Fe microenvironments formed during these processes in cucumber which takes up Fe in a reduction based process (Strategy I), have been investigated. The identification of Fe microenvironments was carried out with 57Fe Mössbauer spectroscopy and immunoblotting, whereas reductive washing and high resolution microscopy was applied for the localization. In plants supplied with 57FeIII-citrate, a transient presence of Fe-carboxylates in removable forms and the accumulation of partly removable, amorphous hydrous ferric oxide/hydroxyde have been identified in the apoplast and on the root surface, respectively. The latter may at least partly be the consequence of bacterial activity at the root surface. Ferritin accumulation did not occur at optimal Fe supply. Under Fe deficiency, highly soluble ferrous hexaaqua complex is transiently formed along with the accumulation of Fe-carboxylates, likely Fe-citrate. As 57Fe-citrate is non-removable from the root samples of Fe deficient plants the major site of accumulation is suggested to be the root xylem. Reductive washing results in another ferrous microenvironment remaining in the root apoplast, the FeII-bipyridyl complex, which accounts for ~30% of the total Fe content of the root samples treated for 10 min and rinsed with CaSO4 solution. When 57FeIII-EDTA or 57FeIII-EDDHA was applied as Fe-source higher soluble ferrous Fe accumulation was accompanied by a lower total Fe content, confirming that chelates are more efficient in maintaining soluble Fe in the medium while less stable natural complexes as Fe-citrate may perform better in Fe accumulation

Quantitative real-time PCR analysis of the utilization of an iron-containing nanomaterial by a dicot model plant

Since plants represent the primary source of iron in human consumption, iron deficiency is among the most common nutritional disorders. Due to suboptimal soil conditions (alkaline pH or high carbonate content) iron can precipitate in the soil that reduces its availability for plants in many agricultural areas. The applications of iron-containing nanoparticles such as nanoferrihydrite (NH) as fertilizer ingredients could be effective to treat iron deficiency of plants. NH is thought to be effective in increasing the available iron content of soils, providing a stable but efficient iron supply even at alkaline pH, similarly to commercial chelates and complexes like Fe-EDTA and Fe-citrate, respectively. Moreover, testing the utilisation of a new substance requires a reliable system. Molecular biological methods contribute testing the utilisation of the nanoparticles in the iron uptake of plants. Quantitative real-time PCR (qRT-PCR) is found appropriate for measuring the gene expression of key components of the iron uptake system. Here we focused on the root iron uptake system in a dicot model plant, cucumber (Cucumis sativus L. cv. Joker F1). A key enzyme of this system is the ferric-chelate oxidoreductase (FRO1) – an iron deficiency inducible membrane bound enzyme that is responsible for the reduction of iron at the root surface. We identified the homolog of Arabidopsis Fro2 gene in cucumber genome. Furthermore, to investigate the bio-utilisation of iron content of NH by cucumber roots, changes in the expression of CsFro1 were monitored by qRT-PCR upon NH treatment. The results indicate that the expression of CsFro1 is enhanced by iron deficiency but upon NH treatment it started to decrease and the tendency for decrease has become apparent within thirty minutes. This proves that the utilization of the iron content of NH has been carried out in a very short time frame. Moreover, molecular methods can be successfully used in testing the effects of nanomaterials and thus the results contribute to adjusting the proper dosage of the material, which can successfully cure iron deficiency of plants

Structure and magnetism of Fe–Co alloy nanoparticles

We report the hydrothermal synthesis and structure of FexCo1−x alloy nanoparticles with considerable stability against oxidation under ambient atmosphere. Powder X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma mass spectrometry (ICP-MS), 57Fe Mössbauer spectroscopy and magnetization measurements are applied to characterize the composition, morphology, crystal structure, atomic order and magnetic properties of the nanoparticles. As-prepared samples are composed mainly of the bcc FexCo1−x alloy phase. TEM images of heat-treated samples confirm the nanoparticle nature of the original alloys. A consistent analysis of the experimental results leads to x ≈ 53% and x ≈ 62% Fe atomic ratio respectively in two analogous alloy samples, and suggests that the atomic level structure of the nanoparticles corresponds to that of a fully disordered (A2-type) alloy phase. Exploration of the effect of cobalt on the 57Fe hyperfine parameters of iron microenvironments suggests that in these alloys the electronic state of Fe atoms is perturbed equally and in an additive manner by atoms in their first two coordination spheres

Iron oxide nanoparticles for plant nutrition? A preliminary Mössbauer study

One of the most important micronutrients for plants is iron. We have prepared iron(III) oxyhydroxide and magnetite nanoparticles with the aim to use them as possible nutrition source for plants. The iron(III)-oxide/oxyhydroxide nanoparticles prepared under our experimental conditions as colloidal suspensions proved to be 6-line ferrihydritenanoparticles as verified by XRD,TEM/SAED and Mössbauer spectroscopy measurements. 57Fe Mössbauer spectra of magnetite nanoparticles prepared under different preparation conditions could be analyzed on the basis of a common model based on the superposition of four sextet components displaying Gaussian-shaped hyperfine magnetic field distributions

Iron Nanoparticles for Plant Nutrition: Synthesis, Transformation, and Utilization by the Roots of Cucumis sativus

Nanotechnology has been evolving in the past decades as an alternative to conventional fertilizers. Ferrihydrite nanoparticles that model the available Fe pool of soils are proposed to be used to recover Fe deficiency of plants. Nevertheless, ferrihydrite aqueous suspensions are known to undergo slow transformation to a mixture of goethite and hematite, which may influence its biological availability. Several nanocolloid suspensions differing in the surfactant type were prepared for plant treatment and fully characterized by transmission electron microscopy and 57Fe Mössbauer spectroscopy supported by magnetic measurements. The rate of transformation and the final mineral composition were revealed for all the applied surfactants. Nanomaterials at different stages of transformations were the subject of plant physiological experiments aiming at comparing the behavior and plant accessibility of the manufactured suspensions of nanoscale iron(III) oxide and oxide–hydroxide particles

Iron uptake from manufactured nanomaterials: obscured mechanism, controversial effect

Transition metals in nanomaterials such as iron, manganese or zinc are essential microelements for plants. When these metals are present in suboptimal concentration for the plants, deficiency syndromes develop that causes reduced crop production or poor fruit quality. Low mineral content of plant products has a major role in human malnutrition. Most stable Fe-chelates for the correction of Fe deficiency are not biodegradable and expensive so applying manufactured nanomaterials may serve as a cheap and eco-friendly alternative. Newly designed, transition metal containing nanomaterials stabilized in colloid suspension have been characterised and then applied in hydroponic cultures to cucumber model plants in a wide range of concentration. The uptake and distribution of the elements from the nanomaterials and their utilization were investigated by microXRF mapping, ICP-MS, enzyme activity tests, gene expression measurements and the changes in some basic physiological parameters were followed. Nanoferrihydrite and nano-Mn-Zn-ferrite colloid suspensions with 3-8 nm particle size applied in 0.01-0.02 mM concentration and at slightly acidic pH proved to be a good source of Fe, Mn and Zn in various experimental conditions. Mn-Zn-ferrite has also been tested at pH 7.5 and Fe deficient cucumber plants showed a significant recovery after 3 days of application in terms of chlorophyll concentration and photosynthetic efficiency but not at pH 8.5. Mn and Zn deficient plants also showed recovery upon addition of the ferrite. Ferric chelate reductase assays showed that it is not the normal reduction-based uptake pathway that plays a role in the iron utilization of these nanoparticles. Analysis of root ferric chelate reductase expression pointed out a quick utilisation of Fe content of the nanoferrihydrite particles. Elevated concentrations of the nanoferrite at the millimolar range as compared to equal concentrations of micronutrient salts proved to be significantly less toxic. However, another nanomaterial, an insoluble nano FeCo powder applied to the nutrient solution of cucumber in high concentration causes severe chlorosis due to cobalt toxicity, pointing on that the composition of the nanoparticles is highly important for their bioactivity. Keywords: nanomaterial, ferrite, ferrihydrite, fertilizer, ferric chelate reductase, toxicity This work was supported by the National Research, Development and Innovation Office, Hungary (NKFIH) K115784, 115913, 124159 and VEKOP-2.3.3-15-2016-00008. Á. Solti was also supported by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences (BO/00207/15/4)