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Abstract
Iron(III) complexes of D-saccharose and D-glucose were prepared. The compositions of the complexes were determined by standard analytical methods. The Mssbauer spectra reflected the presence of high-spin iron(III) in the polynuclear species. EPR spectroscopy demonstrated antiferromagnetically coupled iron(III) centers within the solid complexes. The13C NMR spectra indicated the presence of a mixture of coordination isomers of iron(III) complexes containing the sugar ligand in differently bound forms.
... Dans ce présent chapitre, le D-glucose est utilisé comme seule source de carbone. Le glucose est é galement connu comme excellent agent ché latant pour l'ancrage du cation mé tallique (ici les ions Fe 3+ ) dans la solution de pré curseur [19,20]. Plus important encore, le rendement de carbonisation du glucose, qui est plus é levé que celui de l'acide citrique, permet de produire des catalyseurs à plus grande é chelle en vue des transferts technologiques futurs. ...
... In this work, D-glucose, a non-toxic and earth abundance component, is used as only carbon source. In addition, glucose is also known to serve as an excellent chelating agent for the anchorage of the metal cation (Fe 3+ ions here) in the precursor solution [19,20]. More importantly, the higher carbonization yield of glucose respect to that of citric acid enables more practicality and the large-scaled production. ...
... The O2 dissociating energy barrier on carbon materials surface is relatively high, as reported by some DFT studies[49], thus not favorable for four-electron transfer pathway. As a result, the experimental measured electron transfer numbers for most carbon materials reported to date are much less than 4. On the contrary, the dissociating19 energy barrier on metal surface is much lower than that occurred on carbon materials especially for noble metal Pt. For example, the O2 dissociating energy barrier on the surface of Pt (111) is calculated to be less than 0.3 eV (or ca. ...
Fe-N-C electrocatalyst is becoming a challenging research topic with great expectations for the next-generation energy devices due to its high intrinsic ORR activity comparable to platinum group metals (PGM) electrocatalyst. However, a high effective preparation strategy with improved catalytic performance and high robustness, employing noncritical components is of great importance for the development of Fe-N-C electrocatalyst, and the identification nature of active site for pyrolytic Fe-N-C material is still a topic of heated debate due to potential presence of multiple active sites.In this work we developed catalysts with N-decorated single atom Fe catalysts in porous carbon by high temperature pyrolysis using cost-effective, non-toxic raw components. Systematic variation of composition of N, and C precursors and various structuring agents, as well as conditions of different steps allowed us to determine the optimal parameters for a multi-step synthesis. Various characteristic technologies, including TGA/TPD-MS, Raman, BET, XRD, XPS, HAADF-STEM and XAS have been applied to study the composition and structure of synthesized Fe-N-C catalysts. The electrocatalytic performance of the catalysts were studied by (R)RDE measurements and accelerated durability tests. This study allowed us to demonstrate that Fe-N-C electrocatalysts with optimized structure and composition provide stable 4e- oxygen electroreduction performance in 0.1 M KOH electrolyte with activity outperforming benchmark 20% Pt/C catalysts. Most importantly, the nature of active sites and structure-performance correlation of as-obtained electrocatalysts are systematically investigated. The work aims to provide fundamental understanding of Fe-N-C catalyst from both material design and natura of active sites which is believed to favor the development of next generation electrocatalyst for fuel cell technology.
... Consequently, the glucose molecules chelate the metal ions and anchor them on the surface of g-C 3 N 4 , thereby preventing the metal atoms from aggregation (Supplementary Figs. [23][24][25] 25,26 . On the other hand, samples prepared with only g-C 3 N 4 and glucose show perfect graphene features as confirmed by TEM images and Raman spectra (Supplementary Figs. 26 and 27). ...
Single-atom catalysts with maximum metal utilization efficiency show great potential for sustainable catalytic applications and fundamental mechanistic studies. We here provide a convenient molecular tailoring strategy based on graphitic carbon nitride as support for the rational design of single-site and dual-site single-atom catalysts. Catalysts with single Fe sites exhibit impressive oxygen reduction reaction activity with a half-wave potential of 0.89 V vs. RHE. We find that the single Ni sites are favorable to promote the key structural reconstruction into bridging Ni-O-Fe bonds in dual-site NiFe SAC. Meanwhile, the newly formed Ni-O-Fe bonds create spin channels for electron transfer, resulting in a significant improvement of the oxygen evolution reaction activity with an overpotential of 270 mV at 10 mA cm ⁻² . We further reveal that the water oxidation reaction follows a dual-site pathway through the deprotonation of *OH at both Ni and Fe sites, leading to the formation of bridging O 2 atop the Ni-O-Fe sites.
... These features make such carbon substrate perfect for anchoring glucose-chelated Fe complex. The chelation of α-D-glucose and Fe(III) ions to form α-D-glucose-Fe(III) complex has been reported in the literatures 47,48 and supported by our density functional theory (DFT) calculations ( Supplementary Fig. 4 XRD and TEM results suggest that Fe may exist in a form of single atom. For clearly revealing the state of Fe, the high-angle annular dark-filed scanning TEM (HAADF-STEM) was used to acquire the evidence of Fe distribution at atomic resolution. ...
Although single-atomically dispersed metal-Nx on carbon support (M-NC) has great potential in heterogeneous catalysis, the scalable synthesis of such single-atom catalysts (SACs) with high-loading metal-Nx is greatly challenging since the loading and single-atomic dispersion have to be balanced at high temperature for forming metal-Nx. Herein, we develop a general cascade anchoring strategy for the mass production of a series of M-NC SACs with a metal loading up to 12.1 wt%. Systematic investigation reveals that the chelation of metal ions, physical isolation of chelate complex upon high loading, and the binding with N-species at elevated temperature are essential to achieving high-loading M-NC SACs. As a demonstration, high-loading Fe-NC SAC shows superior electrocatalytic performance for O2 reduction and Ni-NC SAC exhibits high electrocatalytic activity for CO2 reduction. The strategy paves a universal way to produce stable M-NC SAC with high-density metal-Nx sites for diverse high-performance applications.
... Ceric ammonium sulfate was standardized against As 2 O 3 by potentiometric titration. ISC and SFGC were prepared and purified according to known procedures [9,10]. ...
A robust voltammetric method has been developed and validated for the determination of Fe(II) and Fe(III) in pharmaceutical iron polysaccharidic complexes. Undesirable low molecular weight iron complexes, at concentration about 3% in the pharmaceutical formulation, can be easily determined with good accuracy and precision. This methodology can be proposed as a viable, environmentally sustainable substitute for the conventional Normal Pulse Polarographic method in US Pharmacopeia, with better analytical figures of merit, and reduced Hg consumption. A deeper insight in Fe(II) and Fe(III) composition can be gained by the combined use of a new potentiometric technique after chemical decomposition of the complex.
Part of the performance of single-atom catalysts (SACs) is greatly influenced by the microenvironment around a single metal site, of which the oxygen reduction reaction (ORR) is counted as one of them. However, an in-depth understanding of the catalytic activity regulation by the coordination environment is still lacking. In this study, a single Fe active center with axial fifth hydroxyl (OH) and asymmetric N,S coordination embedded in a hierarchically porous carbon material (Fe-SNC) are prepared. Compared to Pt/C and most of the reported SACs, as-prepared Fe-SNC has certain advantages in terms of ORR activity and maintains sufficient stability. Furthermore, the assembled rechargeable Zn-air battery exhibits impressive performance. The combination of multiple findings revealed that the introduction of S atoms not only facilitates the formation of porous structures but also facilitates the desorption and adsorption of oxygen intermediates. On the other hand, with the introduction of axial OH groups, the bonding strength of the ORR intermediate is reduced, and even the central position of the Fe d-band is optimized. The developed catalyst is expected to lead to further research on the multiscale design of the electrocatalyst microenvironment.
A new iron-catalyzed reaction for the coupling of perfluoroalkyl iodides (R F I) with aromatic substrates is described. The perfluoroalkylated arene products are obtained in good to excellent yields in the presence of a [(bpy)Fe(II)] catalyst(10%) electrochemically regenerated or generated from [(bpy)Fe(III)] at room temperature. The development, scope, and preliminary mechanistic studies of these transformations are 10 reported.
Simple sugars and their derivatives — with oxygen, nitrogen, sulphur or phosphorous anchoring donor groups — form metal ion complexes of various composition and stability. The emergence of new experimental methods allowed the assignment of the metal binding sites in the different isomeric complexes of these multidentate ligands, and also the determination of the most effective chelating isomers of the ligands — being present as a mixture of different conformational and/or configurational isomers in solution. We review the literature on the metal ion complexes of carbohydrate type ligands with the emphasis on the past 20 years, discussing the equilibria and structure in aqueous solution together with the structures determined for the solid state complexes. Stability and structural data are collected for comparison.
To study the effect of the conformation of sugar hydroxy groups on metal complexation processes, complex formation of eight saccharides (D-fructose, L-sorbose, L-arabinose, D-arabinose, D-glucose, D-sorbitol, 2-deoxy-D-glucose and D-saccharose) with dimethyltin(IV)2+ cations was investigated in aqueous solution by potentiometric equilibrium measurements, 13C NMR, polarimetric and Mössbauer spectroscopic methods. The experimental results proved that deprotonation of D-fructose and L-sorbose is caused by the coordination of dimethyltin(IV)2+ in the unusual low pH interval 4-6 in contrast to the other saccharides deprotonated in analogous way at pH > 8. Increasing the pH of the solution resulted in the formation of further complexes. Stability and composition of the species was determined by potentiometric studies. 13C NMR measurements led to the assignment of the sugar OH groups participating in the processes. Mössbauer investigations in the quick-frozen solutions permitted the determination of the stereochemistry of tin(IV) in the complexes.
Phosphate binders that contain aluminum or calcium are frequently prescribed to treat hyperphosphatemia in patients with end-stage renal disease (ESRD), but an accumulation of aluminum can lead to encephalopathy, aluminum-related bone disease (ARBD) such as osteomalacia, anaemia, and resistance to erythropoietin, and calcium accumulation can lead to hypercalcaemia. High phosphate concentrations are reduced in vitro and in vivo by a phosphate adsorption pill, which is synthesized by hydrolyzing ferrous sulfate in the presence of saccharides, to form an iron (III)-saccharide complex that is acid resistant and binds phosphate greater than iron (III) hydroxide alone. Under in vitro conditions, containing 3.26 mg P/dL, the iron (III)-sucrose complex showed the highest phosphate adsorption capacity at pH 2 with artificial gastric juice, 58.9 mg P/g binder. For the 7 day in vivo study, 0% (Group 1), 1% (Group 2), 4% (Group 3), and 8% (Group 4) iron (III)-sucrose complex was admixed into the rodent chow by weight and fed to 15 male Wistar rats. The weight and volume of the feces and urine, and the calcium, iron, and phosphorus excretions in the feces and urine samples were monitored for any signs of irregularity. Total urine outflow was collected during a 24-h period to determine the amount of phosphate recovered, which indicates the ability of the phosphate binder to reduce gastrointestinal phosphate absorption. The fecal iron excretion was significantly effected by the amount of binder ingested throughout the study for Group 2 (p < 0.001), Group 3 (p < 0.01), and Group 4 (p < 0.001). The urinary calcium excretion (mg/rat/24-h) significantly increased by the 7th day for Group 2 (p < 0.05) and Group 4 (p < 0.01) in comparison to the control. Finally, after 7 days, there was a significant drop in the urinary phosphorus levels (mg P/rat/24-h) in a dose dependent manner for Group 2: from 7.82 +/- 1.46 to 1.98 +/- 0.10 mg P/rat/24-h (102 mg P/dL/24-h; p < 0.05); Group 3: from 6.70 +/- 1.14 to 0.16 +/- 0.09 mg P/rat/24-h (6.0 mg P/dL/24-h; p < 0.01); and Group 4: from 8.25 +/- 0.67 to 0.04 +/- 0.01 mg P/rat/24-h (0.9 mg P/dL/24-h; p < 0.01). The results show that this new adsorbent might provide an alternative to conventional aluminum and calcium containing phosphate-binding agents for combating hyperphosphataemia.
NMR investigation and molecular weight determinations of the stannatranes, types I and II, have shown unequivocally the pentacoordination of tin and different stabilities of the SnN bonds.Mössbauer studies of the compounds show that this method is not suitable for the unequivocal determination of the coordination number in tin complexes.ZusammenfassungIn den Stannatranen des Typs I und II wurden durch Molmassebestimmungen und NMR-Untersuchungen eindeutig Pentakoordination und eine unterschiedliche Stabilität der SnN-Bindung nachgewiesen Aus mössbauerspektroskopischen Untersuchungen geht hervor, dass diese Methode zur eindeutigen Bestimmung der Koordinationszahl in Zinnkomplexen nicht geeignet ist.
A novel, water soluble, electrically neutral polynuclear iron(III) mixed ligand complex has been prepared for use in parenteral iron therapy. The composition of the new compound has been determined by preparative and analytical methods. Osmomotic pressure measurements have shown its polymeric nature. The complex molecule has a composition of Fe8L2D2AcO(OH)19 where L denotes the lactiobionate ion, D stands for one glucopyranose unit of dextrane and Ac is the acetate ion. Iron(III) acetate is the starting material in the preparation of the complex. The acetate neutralises the protons liberated in the interaction of iron(III) and the ligands and the acetic acid formed in this reaction is removed by steam distillation. An aqueous solution of 1.8 mol dm−3 iron concentration was prepared which has an osmotic pressure below 300 mosmol.
The synthesis of new Fe(III)sorbitol, Fe(III)glucuronic acid and Fe(III)glucosamine complexes has been performed. The complexes were characterized by physico-chemical measurements and chemical analysis. Molecular weight determination and Mössbauer spectroscopic measurements showed that the complexes are polymeric in the solid state and also in aqueous solutions.
Low molecular weight complexes of Fe(III) with selected diols, glycerol and sorbitol and their hydrolysis products in alkaline aqueous media have been prepared and characterized. The three types of ligands interfered distinctly different with hydrolysis. According to solubility measurements of Fe in the presence of the two monomethylethers of glycerol, deprotonated 1,2-diolato entities are bound to Fe(III) in strongly alkaline aqueous solutions. The magnetic susceptibility measurements and Vis spectra indicate the formation of a mononuclear glycerol complex at high base and ligand concentration (⩾ 1M). At pH 12–13, the growth of polynuclear complexes was investigated by laser light scattering and by kinetic measurements of the rate of degradation in 2 M HCl. A monotonic increase of the hydrodynamic radius (11–40 Å) and half life (0.5–10 s) over a period of four weeks was observed. Polynuclear Fe(III)-sorbitol complexes have a pH-dependent molecular weight, hydrodynamic radius and half life of degradation, with a small low molecular weight complex (pH ⩾ 10.5) and a gel (pH ⩾ 7) as the extremes of the series. The polymerization of these Fe(III)-sorbitol complexes is completely reversible.
Three kinds of iron(III) complexes formed with sugar-type ligands, ketose, polyalcohol and sugar acid, were prepared. The Fe K-edge absorption spectra of the complexes were measured both in aqueous solution and in the solid stare to reveal the structure from the analysis of their EXAFS and XANES. It was concluded that the iron(III) sugar complexes have a distorted octahedral structure with a mean FeO distance of 195 pm irrespective of the sugar type ligands both in aqueous solution and in the solid state. In the case of iron(III) fructose complex the dimerization of the complex was evidenced and the most likely structure was proposed.
Abragam and Pound's method for the calculation of the longitudinal relaxation time T1 has been extended to the transverse relaxation time T2. Explicit calculations have been carried out for a pure dipole-dipole interaction, showing that for an interacting pair of like spins, or for nuclei in paramagnetic solution, T1 is exactly equal to T2 in the extreme narrow case. For a pair of interacting unlike spins, it is shown that the longitudinal components of the magnetic moments do not have simple exponential decays. This gives rise to a steady and transient Overhauser effect. The transverse components, however, have in all cases, simple exponential decay defined by a single relaxation time T2. A set of modified Bloch's equations is found, giving the correct equation of motion of the macroscopic magnetic moments of such a system of pairs of unlike spins. The equality of T1 and T2 has been verified in paramagnetic solutions, and a nuclear Overhauser effect has been observed in anhydrous hydrofluoric acid. If one assumes that the extreme narrow case corresponds to the actual motion, the experimental results are not consistent with the picture of a pure dipole-dipole interaction between the hydrogen and fluorine nuclei of a molecule without taking into account the effect of the other molecules.
The interaction between iron(III) and glycerol or related polyols was studied in some detail over a pH range of 1 to 13 mainly by spectrophotometric and NMR measurements. At acidic pH, there appeared a new absorption band at 350 nm in the difference spectra of iron(III) before and after the addition of glycerol, showing that iron(III) and glycerol form a 1 : 1 complex. Although the 13C NMR relaxation rates for all of the carbon atoms of glycerol and 1,3-propanediol were markedly affected by the addition of iron(III), the rate for C-2 of 1,4-butanediol remained unchanged. These facts indicate that either 1,2- or 1,3-diol, as didentate ligand, coordinates to a hydrolyzed iron(III) ion at acidic pH. In all of the present systems of iron(III) and polyols, iron(III) hydroxide-like precipitates resulted at around neutral pH. The polyols were removed in some quantities from solutions by adsorption on the precipitates; the removability depended on their molecular structures. In these polyols, only glycerol, which has three neighboring OH groups, formed soluble complexes at pH > 9 if R > 20. Accordingly, three neighboring OH groups seemed to be essential in the formation of soluble complexes at alkaline pH. In conclusion, the interaction between iron(III) and polyols are severely dependent upon the molecular structures of the polyols.
Plots of the effective magnetic moment (mu(eff)) of the iron(III) ion against pH for aqueous iron(III) ion solutions of 1,2-ethanediol, 1,3-propanediol, glycerol, D-glucitol, D-fructose, two oligo-sugars, poly(vinyl alcohol) (PVA), and methyl cellulose at various concentration ratios of polyols or sugars to the iron(III) ion ([iron(III) ion]=10.0 mM) at room temperature were obtained by the Gouy method. At low concentraion ratios, precipitation resulted at around neutral pH, where the concentration of polymers is expressed in terms of the monomeric residues. The pH range for precipitation became narrower as the ratio increased. However, the precipitates, once formed for the case of the former two diols, remained unchanged at any alkaline pH. During the course of the change in pH from 1 to 13, the mu(eff) value in units of B.M. was initially ca. 6, but steeply decreased at around pH 2, and then leveled off at a constant value of ca. 3.6 in the pH range 3 to 10. It gradually rose to a value of 5-6 beyond pH 10 for the cases of glycerol, D-glucitol, and sugars. This fact, together with the ESR data obtained here, indicates that iron(III) ions exist as usual hydrated ions at pH 1-2, as some cluster like Fe(OH)3 at pH 3-10, and mostly as mononuclear ions coordinated to the alcoholic OH groups at a stronger base pH.