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.

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.

Apoplast utilisation of nanohaematite initiates parallel suppression of RIBA1 and FRO1&3 in Cucumis sativus

Nanoscale Fe containing particles can penetrate the root apoplast. Nevertheless, cell wall size exclusion questions that for Fe mobilisation, a close contact between the membrane integrating FERRIC REDUCTASE OXIDASE (FRO) enzymes and Fe containing particles is required. Haematite nanoparticle suspension, size of 10-20 nm, characterized by ⁵⁷Fe Mössbauer spectroscopy, TEM, ICP and SAED was subjected to Fe utilisation by the flavin secreting model plant cucumber (Cucumis sativus). Alterations in the structure and distribution of the particles were revealed by ⁵⁷Fe Mössbauer spectroscopy, HRTEM and EDS element mapping. Biological utilisation of Fe resulted in a suppression of Fe deficiency responses (expression of CsFRO 1, 2 & 3 and RIBOFLAVIN A1; CsRIBA1 genes and root ferric chelate reductase activity). Haematite nanoparticles were stacked in the middle lamella of the apoplast. Fe mobilisation is evidenced by the reduction in the particle size. Fe release from nanoparticles does not require a contact with the plasma membrane. Parallel suppression in the CsFRO 1&3 and CsRIBA1 transcript amounts support that flavin biosynthesis is an inclusive Fe deficiency response involved in the reduction-based Fe utilisation of Cucumis sativus roots. CsFRO2 is suggested to play a role in the intracellular Fe homeostasis.

A simple method for comparing peripheral and central color vision by means of two smartphones

Information on peripheral color perception is far from sufficient, since it has predominantly been obtained using small stimuli, limited ranges of eccentricities, and sophisticated experimental conditions. Our goal was to consider the possibility of facilitating technical realization of the classical method of asymmetric color matching (ACM) developed by Moreland and Cruz (1959) for assessing appearance of color stimuli in the peripheral visual field (VF). We adopted the ACM method by employing two smartphones to implement matching procedure at various eccentricities. Although smartphones were successfully employed in vision studies, we are aware that some photometric parameters of smartphone displays are not sufficiently precise to ensure accurate color matching in foveal vision; moreover, certain technical characteristics of commercially available devices are variable. In the present study we provided evidence that, despite these shortages, smartphones can be applied for general and wide investigations of the peripheral vision. In our experiments, the smartphones were mounted on a mechanical perimeter to simultaneously present colored stimuli foveally and peripherally. Trying to reduce essential discomfort and fatigue experienced by most observers in peripheral vision studies, we did not apply bite bars, pupil dilatation, and Maxwellian view. The ACM measurements were performed without prior training of observers and in a wide range of eccentricities, varying between 0 and 95°. The results were presented in the HSV (hue, saturation, value) color space coordinates as a function of eccentricity and stimulus luminance. We demonstrated that our easy-to-conduct method provided a convenient means to investigate color appearance in the peripheral vision and to assess inter-individual differences.

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

Iron (Fe) is an essential cofactor for all livings. Although Fe membrane transport mechanisms often utilize Fe^II, uncoordinated or deliberated ferrous ions can initiate Fenton reactions. Fe^III citrate complexes are among the most important complexed forms of Fe^III especially in plants that, indeed, can undergo photoreduction. Since leaves as photosynthetic organs of higher plants are generally exposed to illumination in daytime, photoreaction of ferric species may have biological relevance in iron metabolism, the relevance of which is poorly understood. In present work Fe^III citrate transformation during the photodegradation in solution and after foliar application on leaves was studied by Mössbauer analysis directly. To obtain irradiation time dependence of the speciation of iron in solutions, four model solutions of different pH values (1.5, 3.3, 5.5, and 7.0) with Fe to citrate molar ratio 1:1.1 were exposed to light. Highly acidic conditions led to a complete reduction of Fe together with the formation of Fe^II citrate and hexaaqua complexes in equal concentration. At higher pH, the only product of the photodegradation was Fe^II citrate, which was later reoxidized and polymerized, resulting in the formation of polynuclear stable ferric compound. To test biological relevance, leaves of cabbage were treated with Fe^III citrate solution. X-ray fluorescence imaging indicated the accumulation of Fe in the treated leaf parts. Mössbauer analysis revealed the presence of several ferric species incorporated into the biological structure. The Fe speciation observed should be considered in biological systems where Fe^III citrate has a ubiquitous role in Fe acquisition and homeostasis.

Mössbauer, Nuclear Forward Scattering, and Raman Spectroscopic Approaches in the Investigation of Bioinduced Transformations of Mixed-Valence Antimony Oxide

Mössbauer spectroscopy, nuclear forward scattering, and Raman spectroscopy were applied to study redox transformations of the synthesized mixed-valence (III/V) antimony oxide. The transformations were induced by a culture of a hyperthermophilic archaeon of the genus Pyrobaculum. The applied methods allowed us to reveal the minor decrease of ca. 11.0 ± 1.2% of the antimony(V) content of the mixed-valence oxide with the concomitant increase of antimony(III). The method sensitivities for the quantitative assessment of the Sb(III/V) ratio have been considered.

Pores with longitudinal irregularities distinguish objects by shape

The resistive-pulse technique has been used to detect and size objects which pass through a single pore. The amplitude of the ion current change observed when a particle is in the pore is correlated with the particle volume. Up to date, however, the resistive-pulse approach has not been able to distinguish between objects of similar volume but different shapes. In this manuscript, we propose using pores with longitudinal irregularities as a sensitive tool capable of distinguishing spherical and rod-shaped particles with different lengths. The ion current modulations within resulting resistive pulses carry information on the length of passing objects. The performed experiments also indicate the rods rotate while translocating, and displace an effective volume that is larger than their geometrical volume, and which also depends on the pore diameter.

Filtering of nanoparticles with tunable semiconductor membranes

Translocation dynamics of nanoparticles permeating through the nanopore in an n-Si semiconductor membrane is studied. With the use of Brownian Dynamics to describe the motion of the charged nanoparticles in the self-consistent membrane-electrolyte electrostatic potential, we asses the possibility of using our voltage controlled membrane for the macroscopic filtering of the charged nanoparticles. The results indicate that the tunable local electric field inside the membrane can effectively control interaction of a nanoparticle with the nanopore by either blocking its passage or increasing the translocation rate. The effect is particularly strong for larger nanoparticles due to their stronger interaction with the membrane while in the nanopore. By extracting the membrane permeability from our microsopic simulations, we compute the macroscopic sieving factors and show that the size selectivity of the membrane can be tuned by the applied voltage.