Iron(III)-siderophore coordination chemistry: Reactivity of marine siderophores

Two remarkable features of many siderophores produced by oceanic bacteria are the prevalence of an α-hydroxy-carboxylic acid functionality either in the form of the amino acid β-hydroxy aspartic acid or in the form of citric acid, as well as the predominance of amphiphilic siderophores. This review will provide an overview of the photoreactivity that takes place when siderophores containing β-hydroxy aspartic acid and citric acid are coordinated to iron(III). This photoreactivity raises questions about the role of this photochemistry in microbial iron acquisition as well as upper-ocean iron cycling. The self-assembly of amphiphilic siderophores and the coordination-induced phase-change of the micelle-to-vesicle transformation will also be reviewed. The distinctive photosensitive and self-assembly properties of marine siderophores hint at possibly new microbial iron acquisition mechanisms.     

Quantum chemical investigation of hyperfine coupling constants on first coordination sphere water molecule of gadolinium(III) aqua complexes

Hyperfine interactions (HFI) on the nuclei of the first coordination sphere water molecules in a model [Gd(H(2)O)(8)](3+) aqua complex and in the magnetic resonance imaging contrast agent [Gd(DOTA)(H(2)O)](-) were studied theoretically. Density functional theory (DFT) calculations combined with classical molecular dynamics (MD) simulations have been used in order to take into account dynamic effects in aqueous solution. DFT relativistic calculations show a strong spin-polarization of the first coordination sphere water molecules. This spin-polarization leads to a positive (17)O isotropic hyperfine coupling constant (A(iso)((17)O) = 0.58 +/- 0.11 MHz) and to a significant increase of the effective distance (r(eff)(Gd-O) = 2.72 +/- 0.06 A) of dipolar interaction compared to the mean internuclear distance (r(Gd-O) = 2.56 +/- 0.06 A) obtained from the MD trajectory of [Gd(DOTA)(H(2)O)](-) in aqueous solution. The point-dipole model for anisotropic hyperfine interaction overestimates therefore the longitudinal relaxation rate of the (17)O nucleus by approximately 45%. The (1)H isotropic hyperfine coupling constant of the bound water molecule is predicted to be very small (A(iso)((1)H) = 0.03 +/- 0.02 MHz), and the point-dipole approximation for first coordination sphere water protons holds. The calculated hyperfine parameters are in good agreement with available experimental data.     

Magnetic anisotropy in Ni(II)-Y(III) binuclear complexes: on the importance of both the first coordination sphere of the Ni(II) ion and the Y(III) ion belonging to the second coordination sphere

The synthesis of a new Ni(II)-Y(III) binuclear complex with a marked elongation axis in the first coordination sphere of the Ni(II) ion is presented. Its zero-field splitting (ZFS) is studied by means of magnetic data and state-of-the-art ab initio calculations. A good agreement between the experimental and theoretical ZFS parameter values is encountered, validating the whole approach. The magnetic anisotropy axes are extracted from the ab initio calculations, showing that the elongation axis around the Ni(II) ion corresponds to the hard axis of magnetization and that the sign of the axial D parameter is imposed by this axis. The Ni-Y axis is found to be an easy axis of magnetization, which is, however, not significant according to the sign of D. The already reported [(H(2)O)Ni(ovan)(2)(μ-NO(3))Y(ovan)(NO(3))]·H(2)O (ovan = o-vanillin) complex is then revisited. In this case, the elongation axis in the Ni(II) coordination sphere is less marked and the ZFS is dominated by the effect of the Y(III) ion belonging to the second coordination sphere. As a consequence, the D parameter is negative and the low-temperature behavior is dominated by the Ni-Y easy axis of magnetization. A competition between the first coordination sphere of the Ni(II) ion and the electrostatic effect of the Y(III) ion belonging to the second coordination sphere is then evidenced in both complexes, and the positive and negative D parameters are then linked to the relative importance of both effects in each complex.     

Photoreactivity of iron(III)-aerobactin: photoproduct structure and iron(III) coordination

UV photolysis of the ferric aerobactin complex results in decarboxylation of the alpha-hydroxy carboxylic acid group of the central citrate moiety of aerobactin. The structure determination of the photooxidized ligand shows that decarboxylation occurs at the citrate moiety forming a 3-ketoglutarate moiety. Proton and carbon-13 NMR establish the presence of keto and enol tautomers of the apo-photoproduct, with the enol form prevailing in water. The photoproduct retains the ability to coordinate iron(III). The values of the ligand protonation constants, the pKa of the Fe(III)-ligand complex, and the Fe(III) stability constant of the photoproduct of aerobactin are all close to those of aerobactin. CD spectroscopy suggests that the chirality of the ferric complexes of aerobactin and its photoproduct are similar. Like aerobactin, the photoproduct promotes iron acquisition by the source bacterium, Vibrio sp. DS40M5.     

Carrier-facilitated liquid membrane extraction of penicillin G from aqueous streams

Kinetics and mechanism for the carrier-facilitated transport of penicillin G from aqueous solutions through a supported liquid membrane containing Amberlite LA-2 were investigated. The strip phase was either phosphate buffer or sodium carbonate solution. Experiments were performed as a function of the pH, the concentrations of penicillin G in the feed phase and of amine in the membrane phase. A transport model was proposed considering aqueous film diffusion, interfacial chemical reaction, and membrane diffusion. The calculated rates were found to agree with the measured ones (average standard error, 12%). Under the conditions investigated (feed pH 5.02–7.83, penicillin G concentration 10–500 mol/m³, amine concentration 50–1000 mol/m³), the present transport process was shown to be governed by combined interfacial chemical reaction and membrane diffusion.     

Design and coordination behavior of the first selective recognition ligand of 147Pm(III)

A new amide tripodal ligand, 6-[2-(2-diethylamino-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-diazatetradecanamide (4) has been designed and synthesized for the recognition of rare earth ions. Three representative complexes of trivalent lighter (La), middle (Gd), and heavier (Er) rare earth ions with 4 were synthesized and characterized by X-ray crystallography. In the complex, the heptadentate forms a cup-like coordination cavity encapsulating the central ion. Different supramolecular complex dimers are constructed by pi-pi interaction and van der Waals forces in accordance with the lanthanide contraction. The differences of the cavity and dimer structures were investigated further by assessing the separation efficiency of in multitrace solvent extraction of rare earth ions from picrate acid solution and the ligand has the best separation factor for 147Pm(III).     

Extraction and transport of chromium(VI) through a bulk liquid membrane containing triphenylphosphine

The solvent extraction of chromium(VI) in chloroform, dichloromethane, dichloroethane and its transport through a chloroformic bulk liquid membrane from sulphuric acid solutions with the neutral extractant triphenylphosphine (TPP) were studied. It was highlighted that the TPP extractant is an interesting complexing and efficient carrier for transport of chromium(VI) as [(HTPP)HCr2O7] complex from a 2M sulphuric acid solutions. It has a high ability to concentrate the chromium(VI) in the receiving phase according to the Donnan equilibrium. The co-extraction and the co-transport of sulphuric acid is very low and has no effect on the transport efficiency. The transport rate depends mainly on the initial concentration of the extractant.     

Tris(2,2,2-trichloroethoxy)iron(III) complexes

Summary The preparation, magnetic moments, i.r., reflectance and⁵⁷Fe Mössbauer spectra of adducts of tris(2,2,2-trichloroethoxy)iron (III) complexes are reported. An alkoxybridged structure is supported by i.r. spectra.⁵⁷Fe Mössbauer spectra are explained in terms of two inequivalent sites in highspin iron(III) octahedral symmetry.Abbreviations Pic-O -picolineN-oxide - Ur urea - DMU N,N-dimethylurea - Suc succinimide - Diox dioxan - Bipy 2,2-bipyridine - Phen 1,10-phenanthroline     

Spin transition in iron(III) and iron(II) complexes

The main stages of the studies on the spin transitions in iron(III) and iron(II) complexes are considered. The types of the spin transitions and the factors responsible for the latter are reported. The problems arising during experiments in this field are discussed.     

Application of europium(III) extraction with organophosphinic acid to liquid membrane transport

The extraction behavior of Eu(III) has been studied using di(2,4,4-trimethylpentyl)phosphinic acid (DTMPPA, HA) in kerosene. Europium was extracted as Eu(HA₂)₃ with the extraction constant of 2.0·10^–3. This extraction system was applied to the transport of Eu(III) across a DTMPPA liquid membrane supported on porous polytetrafluoroethylene. Europium was quantitatively moved through the liquid membrane containing 0.1M (HA)₂ as a mobile carrier from the feed solution of pH above 3 into the product solution of 0.1M HNO₃, yielding a concentration factor of ten. The transport rate increased with increasing pH and DTMPPA concentration.     

Simultaneous flow injection speciation of iron(II) and iron(III) cyano complexes utilizing electrochemical and atomic absorption detectors in series

Summary A method is described for the simultaneous speciation of Fe(CN) ₆ ^4– and Fe(CN) ₆ ^3– in a flow injection (FIA) system comprising electrochemical (EC) and flame atomic absorption spectrometry (AAS) detectors in series. One of these species is detected amperometrically at a Pt-electrode by applying the required potential and measuring the resulting reduction or oxidation current of the appropriate iron cyanide complex. Total iron in both species is determined by an AAS detector. The EC detector is inherently more sensitive, with a detection limit of 0.5 g Fe l^–1 and a relative standard deviation of 1.0% for a 0.040 g Fe ml^–1 sample. The limit of detection for the AAS detector is 0.5 g Fe ml^–1, and the relative standard deviation for a 5.70 g Fe ml^–1 sample is 0.40%. The method enables up to 60 analyses (120 speciations) per hour and obviates the problem of easy oxidation of Fe(CN) ₆ ^4– .

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Simultane Speziation von Eisen(II)- und Eisen(III)-Cyanokomplexen durch Flie\injektionsanalyse mit Hilfe von hintereinander geschalteten elektrochemischen und AAS-Detektoren

     

Solid complexes of iron(II) and iron(III) with rutin

Solid complex compounds of Fe(II) and Fe(III) ions with rutin were obtained. On the basis of the elementary analysis and thermogravimetric investigation, the following composition of the compounds was determined: (1) FeOH(C₂₇H₂₉O₁₆)·5H₂O, (2) Fe₂OH(C₂₇H₂₇O₁₆)·9H₂O, (3) Fe(OH)₂(C₂₇H₂₉O₁₆)·8H₂O, (4) [Fe₆(OH)₂(4H₂O)(C₁₅H₇O₁₂)SO₄]·10H₂O. The coordination site in a rutin molecule was established on the basis of spectroscopic data (UV–Vis and IR). It was supposed that rutin was bound to the iron ions via 4C=O and 5C—oxygen in the case of (1) and (3). Groups 5C–OH and 4C=O as well as 3′C–OH and 4′C–OH of the ligand participate in binding metals ions in the case of (2). At an excess of iron(III) ions with regard to rutin under the synthesis conditions of (4), a side reaction of ligand oxidation occurs. In this compound, the ligands’ role plays a quinone which arose after rutin oxidation and the substitution of Fe(II) and Fe(III) ions takes place in 4C=O, 5C–OH as well as 4′C–OH, 3′C–OH ligands groups. The magnetic measurements indicated that (1) and (3) are high-spin complexes.     

Facilitated transport of 5-aminosalicylic acid through bulk liquid membrane

This paper describes the experimental results obtained at the transport of 5-aminosalicylic acid (5ASA) through agitated bulk liquid membrane, using Aliquat 336, as carrier, dissolved in a chloroform membrane. The influence of 5-aminosalicylic acid concentration in the feed source, HCl concentration in the stripping phase and carrier (Aliquat 336) concentration in the membrane were investigated. The optimal pH condition of feed source was established based on the speciation diagram of 5-aminosalicylic acid. The assessment of the transport process was performed by determining the kinetic parameters—mass transfer coefficient and entrance and exist flow in and out of the chloroform membrane.     

Six-coordinate nitrato complexes of iron(III) porphyrins

The interaction of tetrahydrofuran (THF) with thin films of the nitrato complexes Fe(III)(Por)(eta(2)-O(2)NO) [Por = meso-tetraphenylporphyrinato (TPP) and meso-tetratolylporphyrinato (TTP) dianion] at low temperature leads to the formation of the six-coordinate nitrato complex Fe(Por)(THF)(NO(3)), which was characterized by IR and UV-visible spectroscopies. Formation of the THF adduct was accompanied by nitrate linkage isomerization from bidentate to monodentate coordination. The iron(III) center remains in a high spin state in contrast with the previously observed low-spin nitratonitrosyl complex Fe(TPP)(NO)(eta(10-ONO(2)). Upon warming, THF dissociates to restore the initial five-coordinate bidentate nitrato complex.     

Stability constants of iron(III) borate complexes

The ultraviolet absorbance data from experiments conducted at constant pH and total iron concentration but variable B(OH)₃ concentration were used to determined the stability constants of FeB(OH) ₄ ²⁺ and Fe[B(OH)_{4 2} ⁺ at 25°C and an ionic strength of 0.68. The estimates obtained were *₁ = 1.0 ± 0.2 × 10^–2 and *₂ = 2 ± 1 × 10^–5, respectively (uncertainties are two times the standard error of the estimates). A calculation of the extent of iron(III) borate formation in ocean water at pH 8.2 shows that iron(III) borates are not a significantly large component of iron(III) speciation in seawater.     

Separation of yttrium(III) from iron(III) through liquid membrane impregnated with di(2-ethylhexyl)phosphoric acid

The selective transport of yttrium(III) in the presence of iron(III) through a supported liquid membrane (SLM) has been investigated by using di(2-ethylhexyl)phosphoric acid (DEHPA) as a mobile carrier. Yttrium(III) with fast kinetics was preferentially transported from the feed solution of dilute acid into the product solution of 1M H₂SO₄, while most of iron(III) with slow kinetics remained in the feed solution. The effective separation of yttrium(III) from a large amount of iron(III) was accomplished by the selective transport of yttrium(III) through the SLM.     

Gaseous iron(II) and iron(III) complexes with BINOLate ligands

Electrospray ionization (ESI) of dilute solutions of 1,1'-bi-2-naphthol (BINOL) and iron(II) or iron(III) sulfate in methanol/water allows the generation of monocationic complexes of iron and deprotonated BINOL ligands with additional methanol molecules in the coordination sphere, and the types of complexes formed can be controlled by the valence of the iron precursors used in ESI. Thus, iron(II) sulfate leads to [(BINOLate)Fe(CH3OH)n]+ complexes (n=0-3), whereas usage of iron(III) sulfate allows the generation of [(BINOLdiate)-Fe(CH3OH)n]+ cations (n=0-2); here, BINOLate and BINOLdiate stand for singly and doubly deprotonated BINOL, respectively. Upon collision-induced dissociation, the mass-selected ions with n>0 first lose the methanol ligands and then undergo characteristic fragmentations. Bare [(BINOLdiate)Fe]+, a formal iron(III) species, undergoes decarbonylation, which is known as a typical fragmentation of ionized phenols and phenolates either as free species or as the corresponding metal complexes. The bare [(BINOLate)Fe]+ cation, on the other hand, preferentially loses neutral FeOH to afford an organic C20H12O+* cation radical, which most likely corresponds to ionized 1,1'-dinaphthofurane.     

Selective transport of zirconium (IV) and niobium (V) from hydrochloric media through a bulk liquid membrane

The selective transport of zirconium/niobium from hydrochloric medium has been investigated through a bulk liquid membrane (BLM) using tri-n-butyl-phosphate (TBP), tri-n-octylamine and dibenzo-18-crown-6 (DBC-6) as the extractants (carriers). The Optimization studies have been carried out by scrutinizing the effect of variables such as the hydrochloric acid concentration in the feed solution, membrane type and hydrochloric acid concentration in the strip solution using the Taguchi approach. The Quantitative transport of zirconium/niobium has been observed by 30% (v/v) TBP in 1200 min from the feed composed of a 9.0 M hydrochloric acid solution of Zr(IV), Nb(V) and lanthanide cations, while the transport of other cations, which have been presented along with Zr/Nb are less than 3% during the same time. Moreover, the possible mechanism of Zr(IV)/Nb(V) ion transport through the BLM has also been discussed and the results show a consecutive, irreversible second-order reaction at the interfaces. Transfer kinetics studies show that niobium transfer process exhibits slightly faster kinetics than zirconium.