Affinity For Fe3 Research Articles

Substitution of carbonate by non-physiological synergistic anion modulates the stability and iron release kinetics of serum transferrin

Serum transferrin (sTf) is a bi-lobal protein. Each lobe of sTf binds one Fe3+ ion in the presence of a synergistic anion. Physiologically, carbonate is the main synergistic anion but other anions such as oxalate, malonate, glycolate, maleate, glycine, etc. can substitute for carbonate in vitro. The present work provides the possible pathways by which the substitution of carbonate with oxalate affects the structural, kinetic, thermodynamic, and functional properties of blood plasma sTf. Analysis of equilibrium experiments measuring iron release and structural unfolding of carbonate and oxalate bound diferric-sTf (Fe2sTf) as a function of pH, urea concentration, and temperature reveal that the structural and iron-centers stability of Fe2sTf increase by substitution of carbonate with oxalate. Analysis of isothermal titration calorimetry (ITC) scans showed that the affinity of Fe3+ with apo-sTf is enhanced by substituting carbonate with oxalate. Analysis of kinetic and thermodynamic parameters measured for the iron release from the carbonate and oxalate bound monoferric-N-lobe of sTf (FeNsTf) and Fe2sTf at pH 7.4 and pH 5.6 reveals that the substitution of carbonate with oxalate inhibits/retards the iron release via increasing the enthalpic barriers.

Ultrasensitive fluorescence detection of Fe3+ ions using fluorescein isothiocyanate functionalized Ag/SiO2/SiO2 core–shell nanocomposites

Fluorescein isothiocyanate (FITC) functionalized Ag/SiO2/SiO2 core–shell (CS) nanoparticles (NPs) and nanorods (NRs) are synthesized by chemical method to perform the fluorescence detection of Fe3+ in aqueous medium. The Fe3+ ion sensing is performed on the basis of metal-enhanced fluorescence and subsequent fluorescence quenching of fluorophore (fluorescein isothiocyanate) in aqueous medium. The intensity of fluorescence of FITC is found to get enhanced with increasing the silica shell thickness. The fluorescence intensity of FITC of spherical Ag/SiO2/SiO2 (FITC) CS NPs (AgSiF50) is amplified up to 2.25-folds whereas, in case of Ag/SiO2/SiO2 (FITC) CS NRs (AgSiFNR), the fluorescence intensity of FITC is amplified up to 3.63-folds compared to that of pure FITC. Owing to the amplified fluorescence of FITC, AgSiF50 and AgSiFNR samples are evaluated for detection of Fe3+ in an aqueous medium and the proposed nanoprobes exhibit good sensitivity towards Fe3+ detection because of strong binding affinity of Fe3+ with isothiocyanate group of FITC. The limit of detections for AgSiF50 and AgSiFNR are found to be 19.4 nM and 0.8 nM, respectively. The BET surface areas of AgSiF50 and AgSiFNR are calculated to be 157.64 m2 g−1 and 193.42 m2 g−1, respectively. The higher sensitivity of AgSiFNR compared to AgSiF50 for Fe3+ ion sensing is accredited to the higher adsorption capacity and higher fluorescence of FITC. This Ag/SiO2/SiO2 (FITC) CS NRs probe is a very simple and efficient sensor for Fe3+ ion detection and thus, using this sample, a very simple Arduino based electronic device is fabricated which can give real-time application of the idea.

Metal-Ligand Interactions and Salt Bridges as Sacrificial Bonds in Mussel Byssus-Derived Materials.

The byssus that anchors mussels to solid surfaces is a protein-based material combining strength and toughness as well as a self-healing ability. These exceptional mechanical properties are explained in part by the presence of metal ions forming sacrificial bonds with amino acids. In this study, we show that the properties of hydrogel films prepared from a byssus protein hydrolyzate (BPH) can also be improved following the biomimetic formation of sacrificial bonds. Strengthening and toughening of the materials are both observed when treating films with multivalent ions (Ca2+ or Fe3+) or at the BPH isoelectric point (pI) as a result of the formation of metal-ligand bonds and salt bridges, respectively. These treatments also provide a self-healing behavior to the films during recovery time following a deformation. While pI and Ca2+ treatments have a similar but limited pH-dependent effect, the modulus, strength, and toughness of the films increase largely with Fe3+ concentration and reach much higher values. The affinity of Fe3+ with multiple amino acid ligands, as shown by vibrational spectroscopy, and the more covalent nature of this interaction can explain these observations. Thus, a judicious choice of treatments on polyampholyte protein-based materials enables control of their mechanical performance and self-healing behavior through the strategic exploitation of reversible sacrificial bonds.

π-Plasmon absorption of carbon nanotubes for the selective and sensitive detection of Fe3+ ions.

Inspired by the remarkable electronic and optical properties of single walled carbon nanotubes (SWNTs), various molecular sensing devices with sensitivity down to the single molecule level have been developed. However, most sensing approaches such as field effect transistors or near infrared (NIR) fluorescence require the rigorous debundling and separation of metallic tubes and semiconducting tubes in order to reach the desired high sensitivity. Interestingly, all carbon nanomaterials including carbon nanotubes, graphite, graphene, and even amorphous carbon exhibit extremely strong π-plasmon absorption in the ultraviolet region. This strong absorption has been studied as an undesired optical background for applications based on visible and NIR absorptions. For the first time, we found that the strong π-plasmon absorption of SWNTs in the ultraviolet region is extremely sensitive to ion binding. It is even much more sensitive than the absorption in the visible and NIR regions. Herein, we present our first exploration into using the extremely strong plasmon absorption of SWNTs to develop a new sensing platform for the detection of metallic ions. The detection selectivity is realized by modifying the surface of SWNTs with molecular ligands that have a high specificity for metal ions. As a demonstration, the new method is applied to selectively detect iron ions (Fe3+) by modifying the surface of the SWNTs with deferoxamine (DFO), a natural bacterial siderophore, which has a high specificity and affinity for Fe3+. The selective detection of Fe3+ in both aqueous solution and complex rain water is achieved with a pM level of sensitivity and detection limit. In situ resonant Raman spectroscopy demonstrated that the sensitive detection possibly involves electron transfer between the formed Fe-DFO complexes and the SWNTs. We envisage that it can be used to detect other metal ions when a specific binding chelator is attached to the carbon nanotube surface.

The behaviour of inositol 1,3,4,5,6-pentakisphosphate in the presence of the major biological metal cations

The inositol phosphates are ubiquitous metabolites in eukaryotes, of which the most abundant are inositol hexakisphosphate (InsP6) and inositol 1,3,4,5,6-pentakisphosphate [Ins(1,3,4,5,6)P5)]. These two compounds, poorly understood functionally, have complicated complexation and solid formation behaviours with multivalent cations. For InsP6, we have previously described this chemistry and its biological implications (Veiga et al. in J Inorg Biochem 100:1800, 2006; Torres et al. in J Inorg Biochem 99:828, 2005). We now cover similar ground for Ins(1,3,4,5,6)P5, describing its interactions in solution with Na+, K+, Mg2+, Ca2+, Cu2+, Fe2+ and Fe3+, and its solid-formation equilibria with Ca2+ and Mg2+. Ins(1,3,4,5,6)P5 forms soluble complexes of 1:1 stoichiometry with all multivalent cations studied. The affinity for Fe3+ is similar to that of InsP6 and inositol 1,2,3-trisphosphate, indicating that the 1,2,3-trisphosphate motif, which Ins(1,3,4,5,6)P5 lacks, is not absolutely necessary for high-affinity Fe3+ complexation by inositol phosphates, even if it is necessary for their prevention of the Fenton reaction. With excess Ca2+ and Mg2+, Ins(1,3,4,5,6)P5 also forms the polymetallic complexes [M4(H2L)] [where L is fully deprotonated Ins(1,3,4,5,6)P5]. However, unlike InsP6, Ins(1,3,4,5,6)P5 is predicted not to be fully associated with Mg2+ under simulated cytosolic/nuclear conditions. The neutral Mg2+ and Ca2+ complexes have significant windows of solubility, but they precipitate as [Mg4(H2L)]·23H2O or [Ca4(H2L)]·16H2O whenever they exceed 135 and 56 μM in concentration, respectively. Nonetheless, the low stability of the [M4(H2L)] complexes means that the 1:1 species contribute to the overall solubility of Ins(1,3,4,5,6)P5 even under significant Mg2+ or Ca2+ excesses. We summarize the solubility behaviour of Ins(1,3,4,5,6)P5 in straightforward plots.Electronic supplementary materialThe online version of this article (doi:10.1007/s00775-009-0510-z) contains supplementary material, which is available to authorized users.

Siderophore activity of myo-inositol hexakisphosphate in Pseudomonas aeruginosa

myo-Inositol hexakisphosphate (InsP6), which is found in soil and most, if not all, plant and animal cells, has been estimated to have an affinity for Fe3+ in the range of 10(25) to 10(30) M-1. In this report, we demonstrate that the Fe-InsP6 complex has siderophore activity and is able to reverse the iron-restricted growth inhibition of Pseudomonas aeruginosa by ethylene diamine di(o-hydroxyphenyl)acetic acid. With 55Fe-InsP6 in transport studies, iron uptake is strongly iron regulated, being repressed after growth in iron-replete conditions and inhibited by treatment with potassium cyanide and carbonyl cyanide m-chlorophenylhydrazone. The kinetics of iron transport revealed a Km of 100 nM. Self-displacement of binding of [3H]InsP6 to isolated membranes by InsP6 revealed a single class of binding sites (Kd = 143 +/- 6 nM; Hill coefficient, 1.1 +/- 0.1). The binding of [3H]InsP6 to membranes was not dependent on whether cells had been grown under conditions of high or low iron concentrations. We believe that this is the first report of inositol polyphosphate activity in prokaryotic cells.

Energy-independent binding of iron complexed to small organic chelants by Neisseria meningitidis.

Fe3+-dicitrate binding and iron uptake from citrate have been characterized in three carrier and three case isolates of Neisseria meningitidis. Culture in Fe3+-dicitrate rich medium did not induce subsequent Fe3+-dicitrate binding as it does for Escherichia coli and other bacteria. Growth in iron-restricted conditions slightly stimulated the Fe3+-dicitrate binding system in all the strains studied. Total binding of citrate as Fe3+-dicitrate was 2.5 times that of citrate in the absence of iron. Affinity for Fe3+-dicitrate ranged from 6.3×104 to 2.6×105l/mol, and the number of receptors per cell ranged from 8, 500 to 64, 800. The binding system was highly specific for Fe3+-dicitrate (it did not bind other iron complexes with isocitrate, lactate, pyruvate or EDDA). Fe uptake efficiency was significatively higher in the case strains but, due to the higher number of receptors per cell in the carrier strains, the resulting iron uptake rate is similar in both groups.