Complexation of iron(III) by pimelyldihydroxamic acid

Pimelyldihydroxamic acid forms strong complexes with iron(III) in aqueous solution at pH 2–9. Plots of n? and proton liberation against pH show plateaux regions at values of 1.5 and 3.0, respectively, over the pH range 4.0–8.0 supporting a formulation of Fe₂L₃ (logβ = 41.06). The orage-red complex exhibits maximum absorbance at 420 nm, and a well-defined peak at 0.6 V vs. SCE in differential pulse polarography.     

Complexation between iron(III) and nicotinamide in aqueous dimethyl sulfoxide

The stability constants of iron(III) complexes with nicotinamide in water-DMSO mixtures (X _DMSO = 0–0.75) were determined by potentiometric titration at 25.0 ± 0.1°C and an ionic strength of 0.25 (NaClO₄). The contributions from the solvation of the reagents to the Gibbs energy of complexation transfer were analyzed. The stabilities of iron(III), copper(II), and silver(I) complexes with nicotinamide were compared. The observed decrease in the stability constants was attributed to the stabilization of iron(III) solvate complexes as the DMSO content increases.     

Extraction of gallium(III) and aluminium(III) with O,O-dialkyldithiophosphoric acids

The extraction of Ga³⁺ and Al³⁺ with the liquid cation-exchangers di-n-butyldithiophosphoric acid (DBTPA) and di-(2-ethylhexyl)dithiophosphoric acid (DETPA) in kerosene, in the presence and absence of alcohols and tri-n-butyl phosphate (TBP) has been studied. Both Ga³⁺ and Al³⁺ can be extracted in the form of a neutral complex, MA₃, but the distribution coefficient of Ga³⁺ is the higher by about two orders of magnitude, which can be the basis of the solvent extraction separation of gallium and aluminium. The differences can be explained by the interaction between the sulphur donor atoms of the extractants and the d¹⁰ electronic shell of Ga³⁺ as well as by the lower steric hindrance of ligands co-ordinated to Ga³⁺.     

Kojic acid derivatives as powerful chelators for iron(III) and aluminium(III)

Proceeding from a ligand constituted by two units of kojic acid linked by a methylene group, which proved a very promising chelator for excess iron(III) and aluminium(III) pathologies, two new ligands have been designed and synthesized: one by adding a vanillin molecule in the linker and the second by adding an o-vanillin molecule. Both these ligands, on the basis of complex formation studies presented here, show significant potential as therapeutic agents for iron and aluminium overload. Protonation constants of the pure ligands have been determined by potentiometry, and standard reaction heats by calorimetry. Hydrogen bonding plays an important role in the protonation reactions. The crystal structures of both ligands have furthermore been resolved. Complex formation equilibria for the iron complexes have been studied by combined potentiometry-spectrophotometry and those of aluminium by potentiometry alone. All complexes were found to contain two metal ions. NMR diffusion measurements hardly applied to complex formation equilibria and the results of density functional theory (DFT) calculations were powerful tools in confirming the proposed reaction model and in evaluating the relative stabilities of the products. Further support was given by NMR chemical shift measurements and electrospray mass spectrometry.     

Complexation equilibria and spectrophotometric determination of iron(III) with resorcylic acid

The complexation equilibria of Fe(III) with resorcylic acid (2,4-dihydroxybenzoic acid, DHB) were studied spectrophotometrically in ethanol-water (4 + 6, v/v) at an ionic strength of 0.1 M NaClO4. The complexation reactions were demonstrated and characterized. A simple, rapid, and sensitive method based on the formation of the Fe(III)-DHB complex at pH 2.5 (lambdamax = 520 nm, epsilon = 0.8 x 10(4) L/mol x cm) was developed for the spectrophotometric determination of Fe(III). The effect of diverse ions on the sensitivity of the proposed method was studied. The Fe-DHB complex was isolated and characterized by both elemental analysis and infrared spectroscopy. The thermal behavior of the complex in dynamic nitrogen gas was studied by thermogravimetric and differential thermogravimetric analysis. Thermal events encountered throughout the course of decomposition were monitored. A computer program was used for regression analysis and for determination of kinetic and thermodynamic parameters from experimental nonisothermal thermogravimetric data. The proposed method was tested by determinations of iron in various synthetic samples and Portland cement materials.     

Separation of chromium (III) and chromium (VI) by capillary electrophoresis using 2,6-pyridinedicarboxylic acid as a pre-column complexation agent

A simple method was developed for the simultaneous determination of Cr(III) and Cr(VI) by capillary zone electrophoresis (CZE), where Cr(III) was chelated with ligands to form anionic complexes. Nitrilotriacetic acid, N-2-hydroxyethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and 2,6-pyridinedicarboxylic acid (PDCA) were investigated as Cr(III) complexing ligands. Of all the ligands studied, 2,6-PDCA with Cr(III) gave the largest UV response and high selectivity for Cr(III). In addition, the condition for pre-column derivatization, including pH, concentration ratio [Cr(III)/2,6-PDCA] and the stability of Cr(III) complexes were also examined. The separation of anionic forms of Cr(III) and Cr(VI) was achieved using co-CZE with UV detection at 185 nm. The electrolyte contained 30 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide, 0.1 mM 2,6-PDCA and 15% (v/v) acetonitrile at pH 6.4. The detection limits were 2 microM for Cr(III) and 3 microM for Cr(VI) and linear plots were obtained in a concentration range of 5-200 microM. The utility of the method was demonstrated for the determination of Cr(III) and Cr(VI) in contaminated soils.     

In solution sensitization of Er(III) luminescence by the 4-tetrathiafulvalene-2,6-pyridinedicarboxylic acid dimethyl antenna ligand

In the [Er(hfac)(3)(L)](2) complex (1) (L = 4-tetrathiafulvalene-2,6-pyridinecarboxylic acid dimethyl ester), the Er(III) ion is bonded to the tridentate coordination site. Electrochemical and photophysical measurements in solution reveal that the tetrathiafulvalene moiety is a versatile antenna for erbium luminescence sensitization at 6540 cm(-1) upon excitation in the low-energy charge transfer transition (donor to acceptor charge transfer) at 16600 cm(-1) assigned via time-dependent density functional theory calculations.     

Solvent extraction separation of iron(III) and aluminium(III) from other elements with Cyanex 302

A rapid method was developed for the solvent extraction separation of iron(III) and aluminium(III) from other elements with Cyanex 302 in chloroform as the diluent. Iron(III) was quantitatively extracted at pH 2.0-2.5 with 5 x 10(-3) M Cyanex 302 in chloroform whereas the extraction of aluminium(III) was quantitative in the pH range 3.0-4.0 with 10 x 10(-3) M Cyanex 302 in chloroform. Iron(III) was stripped from the organic phase with 1.0 M and aluminium(III) with 2.0 M hydrochloric acid. Both metals were separated from multicomponent mixtures. The method was applied to the separation of iron and aluminium from real samples.     

Complexes of iron(III) with cyclopropanecarbo- and cyclohexyl-acetohydroxamic acids

Summary Cyclopropanecarbohydroxamic acid (CPAH) and cyclohexylacetohydroxamic acid (CHAH) were synthesized, characterized and their pK _a's determined spectro-photometrically as 9.80 and 9.85, respectively, at 25 °C and in buffers of 0.1 mol dm^–3 ionic strength (I). A spectroscopic investigation of their reactions with Fe^III in aqueous solutions revealed the sole formation of the 1:3 complexes at equilibrium. Stability constants (log ₃ at 25 °C and I = 0.1 mol dm^–3 are 34.80 and 34.22 for [Fe(CPA)₃] and [Fe(CHA)₃], respectively. Spectral and magnetic studies of the isolated complexes indicate octahedral coordination via the O atoms of the hydroxamate group.     

Complexation equilibria and spectrophotometric determination of iron(III) with 1-amino-4-hydroxyanthraquinone

The complex equilibria of iron(III) with 1-amino-4-hydroxyanthraquinone (AMHA) were studied spectrophotometrically in 40% (v/v) ethanol and an ionic strength of 0.1M (NaClO(4)). The complexation reactions were demonstrated and characterized using graphical logarithmic analysis of the absorbance-pH graphs. A simple, rapid, selective and sensitive method for the spectrophotometric determination of trace amounts of Fe(III) is developed based on the formation of Fe(AMHA) complex at pH 2.5 (lambda(max) = 640 nm, epsilon approximately = 2.1 x 10(4) L. mol(-1) . cm(-1)) in the presence of a large number of foreign ions. Interferences caused by palladium(II) was masked by the addition of cyanide ions. The method has been applied to the determination of iron in some synthetic samples and polymetallic iron ores.     

Complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine towards Al(III), Ga(III), and In(III)

Abstract  The complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine (TRENCAT, L) with group-13 metal ions, viz., Al(III), Ga(III), and In(III), were investigated by means of potentiometric titrations and spectrophotometric measurements in an aqueous medium of 0.1 M KCl at 25 ± 1 °C. The ligand shows the potential to form various monomeric complexes of the types MLH₃, MLH₂, MLH, and ML. At low pH, the ligand is coordinated through three more acidic ortho-catecholic O-atoms to give MLH₃ species. With the rise in pH, the species MLH₃ releases three protons in steps from the meta-catecholic O-atoms to form MLH₂, MLH, and ML. The order of stability Ga(III) > Al(III) > In(III) for the species MLH₃ and MLH₂ is changed into Al(III) > Ga(III) > In(III) for the species MLH and ML. The coordination modes, binding ability, selectivity, and the change in stability order were explained with the help of experimental evidence, molecular modeling calculations, and available literature. Graphical Abstract        

Ligational behaviour of two biologically active N−S donors towards cobalt(III), iron(III), iron(II) and rhodium(III)

Summary The chelating behaviour of two biologically active ligands, pyridine-2-carboxaldehyde(4-phenyl) thiosemicarbazone(L₁H) and pyridine-2-carboxaldehyde thiosemicarbazone(LH), towards Fe^III, Co^III, Fe^II and Rh^III has been investigated. The ligands act as tridentate N–N–S donors, resulting in the formation of bis-chelate complexes of the type M^III(A)₂X·nH₂O (A=L₁ or L; X=Cl, ClO₄; M=Co^III, Rh^III, Fe^III), Fe^II(L₁H)₂SO₄·2H₂O and Fe^II(L₁)₂·H₂O. Biological activity of the ligands and the metal complexes in the form ofin vitro antibacterial activities towardsE. coli has been evaluated and the possible reasons for enhancement of the activity of ligands on coordination to metal ion is discussed.     

Complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine towards Al(III), Ga(III), and In(III)

Abstract  

The complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine (TRENCAT, L) with group-13 metal ions, viz., Al(III), Ga(III), and In(III), were investigated by means of potentiometric titrations and spectrophotometric measurements in an aqueous medium of 0.1 M KCl at 25 ± 1 °C. The ligand shows the potential to form various monomeric complexes of the types MLH₃, MLH₂, MLH, and ML. At low pH, the ligand is coordinated through three more acidic ortho-catecholic O-atoms to give MLH₃ species. With the rise in pH, the species MLH₃ releases three protons in steps from the meta-catecholic O-atoms to form MLH₂, MLH, and ML. The order of stability Ga(III) > Al(III) > In(III) for the species MLH₃ and MLH₂ is changed into Al(III) > Ga(III) > In(III) for the species MLH and ML. The coordination modes, binding ability, selectivity, and the change in stability order were explained with the help of experimental evidence, molecular modeling calculations, and available literature.     

Complexation of Al(III) by aromatic amino acids in the gas phase

The coordination properties of three natural aromatic amino acids (AAAs)-phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp)-to AlIII are studied in this work, devoting special attention to the role of the aromatic side chain. A comparison with aluminum(III)-alanine complexes is also presented. The polarizability arising from the ring has been seen to be a key factor in the stability of the complexes, with the order being Trp-AlIII > Tyr-AlIII > Phe-AlIII, starting from the most stable one. Cation-pi interactions between the metal and the aromatic ring are present in the lowest energy conformers, especially for Trp, which seems to be very well suited for these kinds of interactions, occurring with both the six- and five-membered rings of the indole side chain. The most stable coordination mode for the three AAAs is found to be tricoordinated with the N and O of the backbone chain and the aromatic ring, as was found theoretically and experimentally for other metals.     

Sorption of hydrolytic products of iron(III), aluminium(III) and chromium(III) on the silica column and its analytical use

Summary The influence of pH upon the sorption of hydrolytic products of Fe³⁺, Al³⁺, and Cr³⁺ on silica was studied under kinetic conditions. The capacity of the silica column and the influence of ionic strength upon the sorption were investigated. The results obtained are utilized for the pre-concentration of trace amounts of Al³⁺, and Fe³⁺ and their separation from an excess of several other metals (e.g. Cr, Cu, Zn, Co) at pH 4.5. The separation of Al³⁺ traces from an excess of Fe³⁺ was achieved by reduction and masking of Fe with thioglycollic acid.

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Zusammenfassung Es wurde eine Untersuchung durchgeführt über die Sorption von Hydrolyseprodukten von Fe(III), Al(III) und Cr(III) an Silicasäulen und die Abhängigkeit vom pH-Wert, von der Kapazität der Säule und der Konzentration an Fremdsalzen (KCl, KNO₃) wurde geprüft. Analytische Anwendungsmöglichkeiten ergaben sich in der Anreicherung von Al³⁺- und Fe³⁺-Spuren und ihrer Trennung von anderen Elementen (z.B. Cr, Cu, Zn, Co) sowie in der Trennung von Al³⁺-Spuren von überschüssigem Fe³⁺, wobei letzteres mit Hilfe von Thioglykolsäure reduziert und maskiert wurde.

     

Copper(II) and cobalt(II) salt complexes with 2,6-dimethyl-3.5-pyridinedicarboxylic acid dihydrazide

Complexes of 2,6-dimethyl-3,5-pyridinedicarboxylic acid dihydrazide (DH) with copper(II) and cobalt(II) nitrates and sulfates have been studied by IR and UV spectroscopy, DTA, and X-ray crystallography. The complexation results in polynuclear compounds of the {[M(DH)(ROH) _n ]An _m } _z composition (M = Cu²⁺, Co²⁺; An = SO₄²⁻, NO₃⁻; R = H, i-Pr; n = 0.5–4, m = 1.2, z ≥ 4) containing bidentate DH bridges coordinated to the metal through the carbonyl oxygen atom and the amino group nitrogen atom of the hydrazide moiety.     

Complexes of Eu(III), Tb(III) and Cu(II) with proton transfer compound between 2,6-pyridinedicarboxylic acid and 2-aminobenzothiazole: characterization of the structures and physical properties

A proton transfer compound, (ABTH)⁺(PydcH)^? (1), obtained from 2-aminobenzothiazole (ABT) and 2,6-pyridinedicarboxylic acid (Pydc) as well as its Eu(III), Tb(III), and Cu(II) complexes (ABT)₃[Eu(Pydc)₃]·5H₂O (2), (ABT)₃[Tb(Pydc)₃]·5H₂O (3), and (ABT)[Cu(Pydc)(PydcH)]·3H₂O (4) were obtained under ambient conditions and structurally verified by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and magnetic measurements. Compounds 2–4 are the first known solids containing complex anions with Pydc ligands, 2-aminobenzothiazole cations (ABT), and solvate water molecules. During the synthesis of 3, a secondary phase with the formula ABTCl?H₂O was obtained and characterized by elemental analysis and single-crystal X-ray diffraction. The asymmetric unit of 5 consists of six symmetry independent ABT cations, six chlorides, and six water molecules. The two lanthanide complexes showed characteristic emissions of Eu³⁺ and Tb³⁺ ions. The good solubilities of these complexes in water and their luminescence properties make them attractive luminescent labels of biological molecules.