15275-07-7Relevant academic research and scientific papers
Coordination Chemistry of Microbial Iron Transport Compounds. 21. Kinetics and Mechanism of Iron Exchange in Hydroxamate Siderophore Complexes
Tufano, Thomas P.,Raymond, Kenneth N.
, p. 6617 - 6624 (1981)
The kinetics of iron exchange and iron removal from two siderophore complexes have been examined, using 55Fe labeling techniques and UV-vis spectrophotometric methods, respectively.Iron exchange between the ferric complexes of ferrioxamine B (FeHDFO+) and ferrichrome A (FeDFC3-), two trihydroxamate siderophores from microbial cultures, is extremely slow; under conditions where there is a 5percent excess of H4DFO+ per FeHDFO+, the half-time for exchange for equimolar concentrations (4.0 mM) of the two complexes at 25 deg C and pH 7.4 is approximately 220 h.The kinetic reveal an apparent first-order dependence of the rate on each of the competing metal complexes, with the exchange proceeding through a chain reaction involving free ligand.Furthermore, pH dependence studies demonstrate that the exchange rate is accelerated as a function of increasing hydrogen ion concentration.Kinetics of iron removal from ferrioxamine B with use of ethylenediaminetetraacetic acid (EDTA) show first-order dependence on the concentrations of the iron complex and hydrogen ion at 25 deg C, with a pseudo-first-order rate constant of 4.8*10-5 s-1 at pH 5.4.Variation of the initial rate with EDTA concentration shows saturation kinetics at high ligand concentrations.The results are interpreted in terms of a two-step mechanism involving: (1) protonation of the ferrioxamine B complex and (2) subsequent bimolecular reaction with EDTA.Results of kinetic studies of the reverse process are consistent with the known equilibrium constants and microscopic reversibility.The reaction is first-order in the FeEDTA complex and desferrioxamine B.Although essentially no pH dependence is observed for this reverse process between pH 4 and 6, the reaction rate varies inversely with hydrogen ion concentration above pH 6.This is explained by consideration of the acid-base equilibria associated with the reactants, which give rise to multiple pathway for product formation.Specifically, the deprotonated form of the ferric-EDTA complex, Fe(OH)EDTA2-, displays faster reaction kinetics with desferrioxamine B than does its conjugate acid form.A comparison of observed rate constants for the forward and reverse processes with known equilibrium constants shows good agreement.The postulated mechanisms for siderophore mediated microbial iron transport are evaluared in terms of the rates of iron exchange observed in these experiments.
Synthesis, solution behavior, thermal stability, and biological activity of an Fe(III) complex of an artificial siderophore with intramolecular hydrogen bonding networks
Matsumoto, Kenji,Ozawa, Tomohiro,Jitsukawa, Koichiro,Masuda, Hideki
, p. 8538 - 8546 (2004)
Previously, an artificial siderophore complex, the iron(III) complex with tris[2-{(N-acetyl-N-hydroxy)glycylamino}-ethyl]amine (TAGE), was constructed in order to understand the effect of intramolecular hydrogen bonding interaction on the siderophore function, and its structural characterization in the solid state was reported (Inorg. Chem. 2001, 40, 190). In this paper, the solution behavior of the M(III)-TAGE (M = Fe, Ga) system has been investigated using 1H NMR, UV-vis, and FAB mass spectroscopies in efforts to characterize the biological implication of hydrogen bonding networks between the amide hydrogens and coordinating aminohydroxy oxygens of the complex. The temperature dependence of 1H NMR spectra for Ga(III) complex of TAGE indicates that hydrogen bonding networks are maintained in polar solvents such as DMSO-d6 and D2O. The UV-vis spectra of the Fe(III)-TAGE system under various pH conditions have shown that TAGE forms a tris(hydroxamato)iron(III) complex in an aqueous solution in the pH range 4-8. By contrast, tris[2-{(N-acetyl-N-hydroxy)propylamido}ethyl]amine (TAPE; TAGE analogue that is difficult to form intramolecular hydrogen bonding networks), which has been synthesized as a comparison of TAGE, forms both of bis- and tris(hydroxamato)iron(III) complexes in the same pH range. Both the stability constants (log βFeTAGE = 28.6; βFeTAGE = [FeIIITAGE]/([Fe3+][TAGE3-])) and pM (-log[Fe3+]) value for FeIIITAGE (pM 25) are comparable to those of a natural siderophore ferrichrome (log β = 29.1 and pM 25.2). The kinetic study of the TAGE-Fe(III) system has given the following rate constants: the rate of the ligand exchange reaction between FeIIITAGE and EDTA is 6.7 × 10-4 s-1, and the removal rates of iron from diferric bovine plasma transferrin by TAGE are 2.8 × 10 -2 and 6.0 × 10-3 min-1. These values are also comparable to those of a natural siderophore desferrioxamine B under the same conditions. In a biological activity experiment, TAGE has promoted the growth of the siderophore-auxotroph Gram-positive bacterium Microbacterium flavescens, suggesting that TAGE mimics the activity of ferrichrome. These results indicate that the artificial siderophore with intramolecular hydrogen bonding networks, TAGE, is a good structural and functional model for a natural ferrichrome.
Synthesis and iron sequestration equilibria of novel exocyclic 3-hydroxy-2-pyridinone donor group siderophore mimics
Harrington, James M.,Chittamuru, Sumathi,Dhungana, Suraj,Jacobs, Hollie K.,Gopalan, Aravamudan S.,Crumbliss, Alvin L.
, p. 8208 - 8221 (2010/12/19)
The synthesis of a novel class of exocyclic bis- and tris-3,2- hydroxypyridinone (HOPO) chelators built on N2 and N3 aza-macrocyclic scaffolds and the thermodynamic solution characterization of their complexes with Fe(III) are described. The chelators for this study were prepared by reaction of either piperazine or N,N′,N′′-1,4,7- triazacyclononane with a novel electrophilic HOPO iminium salt in good yields. Subsequent removal of the benzyl protecting groups using HBr/acetic acid gave bis-HOPO chelators N2(etLH)2 and N2(prLH) 2, and tris-HOPO chelator N3(etLH)3 in excellent yields. Solution thermodynamic characterization of their complexes with Fe(III) was accomplished using spectrophotometric, potentiometric, and electrospray ionization-mass spectrometry (ESI-MS) methods. The pKa's of N2(etLH)2, N2(prLH)2, and N 3(etLH)3, were determined spectrophotometrically and potentiometrically. The Fe(III) complex stability constants for the tetradentate N2(etLH)2 and N2(prLH)2, and hexadentate N3(etLH)3, were measured by spectrophotometric and potentiometric titration, and by competition with ethylenediaminetetraacetic acid (EDTA). N3(etLH)3 forms a 1:1 complex with Fe(III) with log β110 = 27.34 ± 0.04. N2(prLH)2 forms a 3:2 L:Fe complex with Fe(III) where log β230 = 60.46 ± 0.04 and log β110 = 20.39 ± 0.02. While N2(etLH)2 also forms a 3:2 L:Fe complex with Fe(III), solubility problems precluded determining log β230; log β110 was found to be 20.45 ± 0.04. The pFe values of 26.5 for N3(etLH)3 and 24.78 for N2(prLH)2 are comparable to other siderophore molecules used in the treatment of iron overload, suggesting that these hydroxypyridinone ligands may be useful in the development of new chelation therapy agents.
Influence of the polyamino carboxylate chelating ligand (L) on the kinetics and mechanism of the formation of FeII(L)NO in the system FeII(L)/NO/HONO/NO2- in aqueous solution
Zang,Van Eldik
, p. 4462 - 4468 (2008/10/08)
FeII(L) reacts with NO, HONO, and NO2- to produce FeII(L)NO for L = diethylenetriaminepentaacetate, ethylenediaminetetraacetate, N-(hydroxyethyl)ethylenediaminetriacetate, nitrilotriacetate, ethylenediaminediacetate, and water. The reaction with HONO and NO2- occurs in two parallel paths of different order with respect to the reaction components. The systematic variation of the nature of L enables an investigation of the role of labile coordination sites on the Fe(II) center during such reactions. The parallel reactions are characterized by the rate law -d[FeII(L)]/dt = kA[HONO]2 + kB[FeII(L)][HONO], and the contribution of each path depends on the nature of L, pH, and total nitrite concentration. The kinetic data support the formation of a reactive intermediate, most probably N2O3 (kA path), and the reduction of HONO by FeII(L) to NO (kB path). The observed reactions and reactivity patterns strongly depend on the availability of labile coordinated solvent molecules on FeII(L), as governed by the nature of the ligand L. The results of this study are discussed in reference to the available literture data and in comparison to the kinetics of oxidation of these complexes by molecular oxygen.
Kinetics and mechanism of the autoxidation of iron(II) induced through chelation by ethylenediaminetetraacetate and related ligands
Zang,Van Eldik
, p. 1705 - 1711 (2008/10/08)
The oxidation of FeII(L) complexes by molecular oxygen is significantly enhanced by the presence of a chelating ligand L. The kinetics of this reaction was studied for L = ethylenediaminetetraacetate, N-(hydroxyethyl)ethylenediaminetriacetate, and diethylenetriaminepentaacetate as a function of [FeII(L)], [O2], pH, temperature, and pressure. All the observed kinetic relationships can be accounted for in terms of a mechanism in which O2 rapidly reacts with FeII(L) to produce FeII(L)O2, followed by three parallel reaction steps. These include spontaneous and acid-catalyzed electron transfer, as well as a reaction with FeII(L) to produce (L)FeIII-O22--FeIII(L). The results are discussed in reference to the available literature data for these and related oxidation processes.
Interaction of the iron (III) complex of N-[2-((o-hydroxyphenyl)glycino)ethyl]salicylideneamine with catechol and cyanide: A model for the binding site in the dioxygenase enzymes
Spartalian,Carrano, Carl J.
, p. 19 - 24 (2008/10/08)
The interaction of N-[2-((o-hydroxyphenyl)glycino)ethyl]salicylideneamine, Fe(EHGS), with catechol and cyanide in aqueous solution has been investigated. Catechol appears to bind the iron center of Fe(EHGS) in a bidentate mode with a binding constant of log K = 10.6 (2) for the reaction Fe(EHGS) + cat2- ? Fe(EHGS)cat. The reaction of Fe(EHGS) with cyanide initially produces a violet high-spin monocyano complex via displacement of H2O/OH in the sixth coordinating position. Further reaction yields a green low-spin tricyano species, which ultimately decays to ferricyanide. The kinetics of these reactions are consistent with this model. Analysis of the spectral properties of the cyano complexes of several phenolate-containing model compounds and non-heme iron proteins suggests that an anisotropic g ≈ 2.0 EPR signal and a strong absorption band (εM ≈ 900-1500) in the 620-720-nm range may characterize low-spin Fe(III) tyrosinate proteins. It is proposed that the nitrile hydratases (J. Am. Chem. Soc. 1987, 109, 5848) may belong to this new group.
Coordination compounds of titanium(IV) with furoylphenylhydroxylamine and 1,8-dihydroxynaphthalene
Pilipenko,Eremenko,Falendysh
, p. 1 - 5 (2008/10/08)
Complex compounds of titanium(IV) with furoylphenylhydroxylamine and 1,8-dihydroxynaphthalene, isolated preparatively from solutions with pH 5-6, 3-1, and also 1 and 11 M HCI were studied by the IR spectroscopic method. Their composition was established, and the probable structure of the coordination compounds was suggested.
Water-soluble Hexadentate Schiff-base Ligands as Sequestrating Agents for Iron(III) and Gallium(III)
Evans, Dennis F.,Jakubovic, David A.
, p. 2927 - 2934 (2007/10/02)
Complexes of FeIII and GaIII with hexadentate Schiff-base ligands have been characterised in aqueous solution.They were prepared by the condensation of salicylaldehydes, containing a sulphonate or trimethylammonium group, with polyamines in the presence of the metal ions.These complexes have stabilities, at physiological pH, similar to those of the hydroxamic acid siderophore complexes.The kinetics of the displacement of FeIII from III(edta)>(1-) (edta = ethylenediamine-N,N,N',N'-tetra-acetate) by two of these ligands has been studied.
