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.     

Complex formation equilibria in iron(III)-L-alanine system

Summary Complex formation in iron(III)-L-alanine solutions was studied by emf glass electrode and spectrophotometric measurements, in 0.5 mol dm ^–3 (Na)NO₃ medium, at 25 ° C. In the concentration range 0.5 [Fe]₀ 20.0, 5.0 [Ala]₀ 1000.0 (mmol dm^–3) and 1.0 -log [H⁺] 3.5; {[Ala]/[Fe] = 10:1-100:1| the equilibria in the title system were explained by the model including the species FeHL, FeL, Fe(OH)L, Fe₂(OH)₂L₂ (where HL denotes L-alanine) and several hydrolytic products. The stability constants of complexes are given. The mechanism of formation and structure of complexes in solution is proposed.Abbreviations Ala alaninate ion - HAla alanine (zwitterion) - AlaH alanine (neutral) - H₂Ala⁺ alanine cation     

Study of equilibria and kinetics of the acid catalysed interaction of iron(III) with salicylaldehyde ando-hydroxyacetophenone

The equilibria and kinetics of the reaction of Fe^III with salicylaldehyde ando-hydroxyacetophenone, leading to 1∶1 chelate formation, have been studied at different temperatures (25–35°C) and ionic strength, I = 1.0 mol dm⁻³ (NaClO₄+HClO₄). A dual path mechanism involving both Fe _aq ³⁺ and Fe(OH) _aq ²⁺ species and undissociated free ligand (LH) is consistent with the experimental observations where [H⁺]≫[Fe]_T≫[L]_T (where [Fe]_T and [L]_T stand for total concentrations of iron and ligand respectively). The results conform to k_obs/B = k₁[H⁺]+k₂K_h where B = [Fe]_T/(K_h+[H⁺])+1/Q; K_h = hydrolysis constant of Fe _aq ³⁺ ; k₁, k₂ are the forward second order rate constants of Fe _aq ³⁺ and Fe(OH) _aq ²⁺ , respectively, and Q is the equilibrium constant of the reaction, Fe³⁺+LH⇋FeL²⁺+H⁺. Thermodynamic parameters for each of the steps have been determined. Fe(OH) _aq ²⁺ appears to react in a dissociative fashion (Eigen-Tamm mechanism), whilst Fe _aq ³⁺ appears to react through the associative inter-change (I_a) mechanism. The equilibrium constants (Q) obtained spectrophotometrically are compared with those obtained from kinetic studies. TMC 2638     

On the complex formation equilibria between iron (III) and sulfate ions

The equilibria have been investigated at 25 degrees C in 3 M NaClO4 using potentiometry, glass and redox Fe3+/Fe2+ half-cells, and UV optical absorptiometry. The concentration of the reagents was chosen in the intervals: 10(-4) < or = [Fe(III)] < or = 5.10(-3) M, 0.01 < or = [SO4(2-)]tot < or = 0.65 M. The value of [H+] was kept at 0.1 M or more to reduce the hydrolysis of the Fe3+ ion to less than 1%. Auxiliary constants, corresponding to the formation of Fe(II)-sulfate complexes and to the association of H+ with SO4(2-) ions, were taken from previous determinations. The experimental data could be explained with the equilibria [formula: see text] Equilibrium constants at infinite dilution, log beta 101 degrees = 3.82 +/- 0.17, log beta 102 degrees = 5.75 +/- 0.17 and log beta 111 degrees = 3.68 +/- 0.35, have been evaluated by applying the specific interaction theory.     

Compleximetric titrations of iron(III) and iron(II) with triethylenetetraminehexaacetic acid

The stability constants of the iron(II) complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from measured pH and redox potentials. The values of the cumulative constants obtained were: log β_FeL= 15.37, log β_FeHL = 23.83, log β_FeH2L = 28.0, log β_Fe2L = 24.73. On the basis of these values and the previously determined constants ofiron(III) complexes, the possibilities of titrating iron(III) and iron(II) with TTHA were investigated. Depending on the experimental conditions, either FeL or Fe₂L formed. Actual titrations were in agreement with the developed theory. The influence of aluminium and titanium on titrations of iron(III) solutions was elucidated.     

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 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.     

Isobaric (vapour+liquid) equilibria data for the binary systems (toluene+acetic acid) and (toluene+methyl ethyl ketone) at atmospheric pressure

Isobaric vapour–liquid equilibrium data have been measured for the binary systems toluene (1) + acetic acid (2) and toluene (1) + methyl ethyl ketone (2) at atmospheric pressure. An all-glass Fischer–Labodest-type apparatus, capable of handling pressures from 0.25 to 400 kPa and temperatures up to 523.15 K was used. The data were correlated by means of the NRTL, UNIQUAC, WILSON models and the applied UNIFAC model with satisfactory results; the relevant parameters are given and results were tested with regard to thermodynamic consistency using the methods of a modified Redlich–Kister and Herington equations.     

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.     

Quadrupole hyperfine interaction in iron(III) dicarboxylic acid complexes

Mössbauer and infrared spectroscopic studies of a series of iron(III) complexes of dicarboxylic acids, maleic, malonic, succinic, glutaric, adipic, pimelic, suberic, azealic and sebacic have been carried out at room temperature. All complexes exhibit a quadrupole doublet with isomer shift () values in the range of 0.62 –0.72 mm·s^–1 (with respect to SNP) and quadrupole splitting, E_Q=0.53–0.74 mm· s^–1. It is observed that tris complexes are formed up to pimelic acid, while bis complexes are formed those for the other three acids. Isomer shift () values do not vary significantly but E_Q values show a somewhat regular trend. Magnetic moment data indicate high spin Fe(III) in octahedral geometry.     

Synthesis of (S)-3-hydroxytetrahydropyran from l-glutamic acid

A concise synthesis of (S)-3-hydroxytetrahydropyran from natural l-glutamic acid has been developed. The intramolecular etherification starting from 1,5-diol was promoted by trifluoromethanesulfonic anhydride. The clinnamates of the alcohols were prepared for accurately determining the optical purity by HPLC method.     

Spectrophotometric studies on ion-pair extraction equilibria of the iron(ii) and iron(III) complexes with 4-(2-pyridylazo)resorcinol

The ion-pair extraction equilibria of the iron(II) and iron(III) chelates of 4-(2-pyridylazo)resorcinol (PAR, H(2)L) are described. The anionic chelates were extracted into chloroform with benzyldimethyltetradecylammonium chloride (QC1) as counter-ion. The extraction constants were estimated to be K(ex1)(Fe(II)) = [Q{Fe(II)(HL)L}](0)/[Q(+)][{Fe(II)(HL)L}(-)] = 10(8.59 +/- 0.11), K(ex2)(Fe(II)) = [Q(2){Fe(II)L(2)}](o)/ [Q(+)](2)[{Fe(II)L(2)}(2-)] = 10(12.17 +/- 0.10) and K(ex1)(Fe(III)) = [Q{Fe((III))L(2)}](o)/(Q(+)][{Fe(III)L(2)}(-)] = 10(6.78 +/- 0.15) at I = 0.10 and 20 degrees , where [ ](o) is concentration in the chloroform phase. Aggregation of Q{Fe(III)L(2)} in chloroform was observed and the dimerization constant (K(d) = [Q(2){Fe(III)L(2)}(2)](o)/[Q{Fe(III)L(2)}](o)(2)) was evaluated as log K(d) = 4.3 +/- 0.3 at 20 degrees . The neutral chelates of {Fe(II)(HL)(2)} and {Fe(III)(HL)L}, and the ion-pair of the cationic chelate, {Fe(III)(HL)(2)}ClO(4), were also extracted into chloroform or nitrobenzene. The relationship between the forms and extraction properties of the iron(II) and iron(III) PAR chelates are discussed in connection with those of the nickel(II) and cobalt(III) complexes. Correlation between the extraction equilibrium data and the elution behaviour of some PAR chelates in ion-pair reversed-phase partition chromatography is also discussed.     

Photochemistry of organic iron(III) complexing ligands in oceanic systems

Iron is a limiting nutrient for primary production in marine systems, and photochemical processes play a significant role in the upper ocean biogeochemical cycling of this key element. In recent years, progress has been made toward understanding the role of biologically produced organic ligands in controlling the speciation and photochemical redox cycling of iron in ocean surface waters. Most (>99%) of the dissolved iron in seawater is now known to be associated with strong organic ligands. New data concerning the structure and photochemical reactivity of strong Fe(III) binding ligands (siderophores) produced by pelagic marine bacteria suggest that direct photolysis via ligand-to-metal charge transfer reactions may be an important mechanism for the production of reduced, biologically available iron (Fe[II]) in surface waters. Questions remain, however, about the importance of these processes relative to secondary photochemical reactions with photochemically produced radical species, such as superoxide (O2-). The mechanism of superoxide-mediated reduction of Fe(III) in the presence of strong Fe(III) organic ligands is also open to debate. This review highlights recent findings, including both model ligand studies and experimentallobservational studies of the natural seawater ligand pool.     

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.