New aspects of the photodegradation of iron(III) citrate: spectroscopic studies and plant-related factors

Revealing the nuclearity of iron citrate complexes at biologically relevant conditions

Citric acid plays an ubiquitous role in the complexation of essential metals like iron and thus it has a key function making them biologically available. For this, iron(III) citrate complexes are considered among the most significant coordinated forms of ferric iron that take place in biochemical processes of all living organisms. Although these systems hold great biological relevance, their coordination chemistry has not been fully elucidated yet. The current study aimed to investigate the speciation of iron(III) citrate using Mössbauer and electron paramagnetic resonance spectroscopies. Our aim was to gain insights into the structure and nuclearity of the complexes depending on the pH and iron to citrate ratio. By applying the frozen solution technique, the results obtained directly reflect the iron speciation present in the aqueous solution. At 1:1 iron:citrate molar ratio, polynuclear species prevailed forming most probably a trinuclear structure. In the case of citrate excess, the coexistence of several monoiron species with different coordination environments was confirmed. The stability of the polynuclear complexes was checked in the presence of organic solvents.

Hexakis(urea-O)iron Complex Salts as a Versatile Material Family: Overview of Their Properties and Applications

Due to their Fe- and N-containing reactive urea ligand content, the hexakis(urea-O)iron(II) and hexakis(urea-O)iron(III) complexes were found to be versatile materials in various application fields of industry and environmental protection. In our present work, we have comprehensively reviewed the synthesis, structural and spectroscopic details, and thermal properties of hexakis(urea-O)iron(II) and hexakis(urea-O)iron(III) salts with different anions (NO3-, Cl-, Br- I-, I3-, ClO4-, MnO4-, SO42-, Cr2O72-, and S2O82-). We compared and evaluated the structural, spectroscopic (IR, Raman, UV-vis, Mössbauer, EPR, and X-ray), and thermogravimetric data. Based on the thermal behavior of these complexes, we evaluated the solid-phase quasi-intramolecular redox reactions of anions and urea ligands in these complexes and summarized the available information on the properties of the resulting simple and mixed iron-containing oxides. Furthermore, we give a complete overview of the application of these complexes as catalysts, reagents, absorbers, or agricultural raw materials.

Analysis of the iron states in iron-containing pharmaceutical products using Mössbauer spectroscopy

Iron-containing pharmaceuticals, namely: (i) PreNatal with ferrous fumarate, (ii) Tardyferon® with ferrous sulfate, (iii) Fenules with water free ferrous sulfate, (iv) Iron Complex with iron glycinate, citrate, (v) Gentle Iron, (vi) Hema-Plex® and (vii) Iron Bisglycinate with iron (ferrous) bisglycinate chelate (iron compounds are given as declared by the manufactures) were studied by 57Fe Mössbauer spectroscopy with X-ray diffraction and magnetization measurements for analysis of the iron state. The obtained results demonstrate that the iron compound announced by the manufacturer in each pharmaceutical is not homogeneous and exists as some modifications of this compound or results of its transformation/oxidation probably due to its instability. The presence of ferrous and ferric compounds is observed, and the relative ferric iron fractions are roughly determined for each pharmaceutical product. This analysis clearly shows the differences between the iron compounds proclaimed by the manufacturers and those obtained by Mössbauer spectroscopy. That justifies as to why this technique should be used for the control and analysis of the iron-containing pharmaceuticals.

Iron uptake of etioplasts is independent from photosynthesis but applies the reduction-based strategy

Introduction

Iron (Fe) is one of themost important cofactors in the photosynthetic apparatus, and its uptake by chloroplasts has also been associated with the operation of the photosynthetic electron transport chain during reduction-based plastidial Fe uptake. Therefore, plastidial Fe uptake was considered not to be operational in the absence of the photosynthetic activity. Nevertheless, Fe is also required for enzymatic functions unrelated to photosynthesis, highlighting the importance of Fe acquisition by non-photosynthetic plastids. Yet, it remains unclear how these plastids acquire Fe in the absence of photosynthetic function. Furthermore, plastids of etiolated tissues should already possess the ability to acquire Fe, since the biosynthesis of thylakoid membrane complexes requires a massive amount of readily available Fe. Thus, we aimed to investigate whether the reduction-based plastidial Fe uptake solely relies on the functioning photosynthetic apparatus.

Methods

In our combined structure, iron content and transcript amount analysis studies, we used Savoy cabbage plant as a model, which develops natural etiolation in the inner leaves of the heads due to the shading of the outer leaf layers.

Results

Foliar and plastidial Fe content of Savoy cabbage leaves decreased towards the inner leaf layers. The leaves of the innermost leaf layers proved to be etiolated, containing etioplasts that lacked the photosynthetic machinery and thus were photosynthetically inactive. However, we discovered that these etioplasts contained, and were able to take up, Fe. Although the relative transcript abundance of genes associated with plastidial Fe uptake and homeostasis decreased towards the inner leaf layers, both ferric chelate reductase FRO7 transcripts and activity were detected in the innermost leaf layer. Additionally, a significant NADP(H) pool and NAD(P)H dehydrogenase activity was detected in the etioplasts of the innermost leaf layer, indicating the presence of the reducing capacity that likely supports the reduction-based Fe uptake of etioplasts.

Discussion

Based on these findings, the reduction-based plastidial Fe acquisition should not be considered exclusively dependent on the photosynthetic functions.

Beyond iron-storage pool: functions of plant apoplastic iron during stress

Iron (Fe) is an essential micronutrient for plants, and its storage in the apoplast represents an important Fe pool. Plants have developed various strategies to reutilize this apoplastic Fe pool to adapt to Fe deficiency. In addition, growing evidence indicates that the dynamic changes in apoplastic Fe are critical for plant adaptation to other stresses, including ammonium stress, phosphate deficiency, and pathogen attack. In this review, we discuss and scrutinize the relevance of apoplastic Fe for plant behavior changes in response to stress cues. We mainly focus on the relevant components that modulate the actions and downstream events of apoplastic Fe in stress signaling networks.

Alginate/xanthan gum hydrogels as forensic blood substitutes for bloodstain formation and analysis

Understanding the behaviour of human blood outside of the body has important implications in forensic research, especially related to bloodstain pattern analysis (BPA). The design of forensic blood substitutes (FBSs) can provide many advantages, including the incorporation of multiple physiological components for use as safe and reliable materials for forensic applications. In this work, we present the design of synthetic alginate and xanthan gum-based hydrogels that contain electrosprayed microparticles (MPs) with and without crosslinked DNA. In addition to the MPs, the alginate/xanthan gum FBS materials include fillers to alter the physical appearance and fluid properties of the material. The optimized FBS consisted of alginate (1% w/v) and xanthan gum (5.0 × 10^-3% w/v), 2 mM CaCl₂, ferric citrate (0.5% w/v), magnesium silicate (0.25% w/v), Allura Red dye (2% w/v), 0.025% v/v Tween 20 and 9.5% v/v MPs. The FBS was tested in passive dripping experiments relevant to BPA scenarios at various impact angles. The spreading ratio (D_s/D₀) was determined for 90° stains made on a paper surface and compared to bovine blood where the FBS was shown to simulate accurate and predictable spreading behaviour. In addition, we simulated other common BPA scenarios (e.g., impact patterns) and evidence processing potential. The FBS could be swabbed, and the DNA could be extracted, amplified, and genotyped analogous to human blood evidence. A stability test was also conducted which revealed a shelf-life of over 4 weeks where the material remains relevant to human blood at physiological temperature.

Mechanism of Reduction of Aqueous U(V)-dpaea and Solid-Phase U(VI)-dpaea Complexes: The Role of Multiheme c-Type Cytochromes

The biological reduction of soluble U(VI) complexes to form immobile U(IV) species has been proposed to remediate contaminated sites. It is well established that multiheme c-type cytochromes (MHCs) are key mediators of electron transfer to aqueous phase U(VI) complexes for bacteria such as Shewanella oneidensis MR-1. Recent studies have confirmed that the reduction proceeds via a first electron transfer forming pentavalent U(V) species that readily disproportionate. However, in the presence of the stabilizing aminocarboxylate ligand, dpaea^2- (dpaeaH₂═bis(pyridyl-6-methyl-2-carboxylate)-ethylamine), biologically produced U(V) persisted in aqueous solution at pH 7. We aim to pinpoint the role of MHC in the reduction of U(V)-dpaea and to establish the mechanism of solid-phase U(VI)-dpaea reduction. To that end, we investigated U-dpaea reduction by two deletion mutants of S. oneidensis MR-1-one lacking outer membrane MHCs and the other lacking all outer membrane MHCs and a transmembrane MHC-and by the purified outer membrane MHC, MtrC. Our results suggest that solid-phase U(VI)-dpaea is reduced primarily by outer membrane MHCs. Additionally, MtrC can directly transfer electrons to U(V)-dpaea to form U(IV) species but is not strictly necessary, underscoring the primary involvement of outer membrane MHCs in the reduction of this pentavalent U species but not excluding that of periplasmic MHCs.

MCO1 and MCO3, two putative ascorbate oxidases with ferroxidase activity, new candidates for the regulation of apoplastic iron excess in Arabidopsis

Iron (Fe) is an essential metal ion that plays a major role as a cofactor in many biological processes. The balance between the Fe2+ and Fe3+ forms is central for cellular Fe homeostasis because it regulates its transport, utilization, and storage. Contrary to Fe3+ reduction that is crucial for Fe uptake by roots in deficiency conditions, ferroxidation has been much less studied. In this work, we have focused on the molecular characterization of two members of the MultiCopper Oxidase family (MCO1 and MCO3) that share high identity with the Saccharomyces cerevisiae ferroxidase Fet3. The heterologous expression of MCO1 and MCO3 restored the growth of the yeast fet3fet4 mutant, impaired in high and low affinity Fe uptake and otherwise unable to grow in Fe deficient media, suggesting that MCO1 and MCO3 were functional ferroxidases. The ferroxidase enzymatic activity of MCO3 was further confirmed by the measurement of Fe2+-dependent oxygen consumption, because ferroxidases use oxygen as electron acceptor to generate water molecules. In planta, the expression of MCO1 and MCO3 was induced by increasing Fe concentrations in the medium. Promoter-GUS reporter lines showed that MCO1 and MCO3 were mostly expressed in shoots and histochemical analyses further showed that both promoters were highly active in mesophyll cells. Transient expression of MCO1-RFP and MCO3-RFP in tobacco leaves revealed that both proteins were localized in the apoplast. Moreover, cell plasmolysis experiments showed that MCO1 remained closely associated to the plasma membrane whereas MCO3 filled the entire apoplast compartment. Although the four knock out mutant lines isolated (mco1-1, mco1-2, mco3-1, and mco3-2) did not display any macroscopic phenotype, histochemical staining of Fe with the Perls/DAB procedure revealed that mesophyll cells of all four mutants overaccumulated Fe inside the cells in Fe-rich structures in the chloroplasts, compared with wild-type. These results suggested that the regulation of Fe transport in mesophyll cells had been disturbed in the mutants, in both standard condition and Fe excess. Taken together, our findings strongly suggest that MCO1 and MCO3 participate in the control of Fe transport in the mesophyll cells, most likely by displacing the Fe2+/Fe3+ balance toward Fe3+ in the apoplast and therefore limiting the accumulation of Fe2+, which is more mobile and prone to be transported across the plasma membrane.

The Impact of the Functional Layer Composition of Glucose Test-Strips on the Stability of Electrochemical Response

Herein, the impact of the chemical stability of RedOx mediator ferricyanide, K3[Fe(CN)6] (FC), a type of buffer solution used for bioreceptor preparation, gel composition (carboxymethylcellulose, CMC, Aerosile, AS, and alginate, ALG) on the long term stability of glucose test-strips and their analytical performance was examined. By simple addition of ALG to the functional gel aiming to improve its viscosity, we managed to enhance the sensitivity of conventional CMC-containing amperometric glucose test-strips from 3.3 µA/mM to 3.9 µA/mM and extend their shelf life from 8 months to 1.7 years. Moreover, during the course of investigations, it was revealed that the activity of enzyme in dependence with the used buffer did not linearly correlate with its activity in a dried functional layer, and the entire long-term electrochemical signal of glucose test-strips was determined by RedOx mediator FC chemical stability. The most stable and sensitive test-strips were obtained by the screen-printing approach from a gel containing 24 mg/mL GOx prepared in citrate buffer with pH 6, 200 mg/mL of FC and 10 mg/mL of CMC supplemented with 25 mg/mL of ALG.