Spectrophotometric determination of iron (II) with quinisatin oxime

A sensitive spectrophotometric determination of iron is based on the blue color (absorption maximum at 660 mμ) formed by reaction of iron (II) with quinisatin oxime in buffered solution containing ethyl alcohol and a small amount of dimethylformamide. The color develops rapidly and is stable for a few h. The absorbance is well reproducible, and conforms to Beer's law. The optimum concentration range at 1 cm optical path is about 0.5 to 2.5 p.p.m. of iron. Small amounts of iron(III) are reduced by the reagent and cause no difficulty. Cobalt and nickel interfere. Iron(II) and quinisatin oxime react in a 1:3 mole ratio; some possible modes of complex formation are suggested.     

Alternating current electrophoretic deposition (EPD) of TiO2 nanoparticles in aqueous suspensions

TiO(2)-nanostructured coatings from aqueous suspensions have been successfully prepared by the application of alternating current (AC) instead of direct current (DC) during electrophoretic deposition (EPD). No organic additives in suspension were required for successful EPD. The quality of the AC-EPD TiO(2) coatings in terms of homogeneity and extent of microcracking, upon drying, observed by SEM, was superior to that of DC-EPD coatings made from the same type of suspensions. The main difference between AC- and DC-EPD was the suppression of bubble formation. The absence of water electrolysis at the electrodes can be explained by the particular distribution of the electric field during AC mode, which prevents the nucleation of bubbles. The preparation of TiO(2) coatings from aqueous suspension and without the aid of organic stabilizers opens the possibility for co-deposition of sensitive materials such as biomolecules and even cells for biomedical applications, given the high biocompatibility of TiO(2). The deposition of TiO(2) coatings from aqueous suspensions is also attractive from environmental and economical points of view.     

Investigation of radionuclide 60Co(II) binding to TiO2 by batch technique, surface complexation model and DFT calculations

The interaction between radionuclides and solid/water interfaces is important to understand the physicochemical processes of radionuclides in the natural environment.Herein,the interaction of 60Co(Ⅱ) with TiO 2 in aqueous solution as a function of pH and ionic strength was studied by using batch technique combined with surface complexation model and density functional theory(DFT) calculations.The batch experimental results showed that the adsorption of 60Co(Ⅱ) was dependent on pH and independent of ionic strength,indicating the formation of inner-sphere surface complexes on TiO 2 surfaces.The results of surface complexation models and DFT calculations indicated that the surface species of 60Co(Ⅱ) adsorbed on TiO 2 followed the trend:B structure(i.e.,60Co(Ⅱ) was linked to one bridge oxygen site) was the dominant surface species at low pH,and TT structure(i.e.,60Co(Ⅱ) was linked to two terminal oxygen sites) became the important surface complex at neutral and alkaline pH values.These results demonstrated that a multi-technique approach could lead to definitive information on the structures of adsorbed 60Co(Ⅱ) at the molecular level at the TiO 2 /water interfaces,as well as realistic models to rationalize and accurately evaluate the macroscopic manifestations of radionuclide adsorption phenomena.     

Mixed-ligand complexation of iron(III) ethylenediaminetetraacetate with iminodiacetate and ethylenediamine in aqueous solution

The formation of the heteroleptic complexes FeEdtaIda³⁻ and FeEdtaEn⁻(Ida²⁻ is the iminodiacetate anion and En is ethylenediamine) was examined by direct calorimetry, pH potentiometry, and spectrophotometry at 298.15 K and the ionic strength I = 0.5 (KNO₃). A possible way of coordination of the ligands in the heteroleptic complexes was discussed.     

The kinetics of complexation of nickel(II) and cobalt(II) with cinchomeronate in aqueous solution

The pressure-jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are k_f = 2.27 × 10⁶ M^?1 s^?1 and k_r = 3.81 × 10¹ s^?1 for the nickel(II) complex and k_f = 1.23 × 10⁷ M^?1 s^?1 and k_r = 2.66 × 10² s^?1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.     

The kinetics of cobalt(II) complexation with o-phthalate in aqueous solution

The rate constants for the formation and dissociation of cobalt(II) complexes with o-phthalate in aqueous solution have been determined by a pressure-jump technique. The forward and reverse rate constants obtained are k_f = 1.1 x 10⁶ M⁻¹ s⁻¹ and k_r = 1.6 x 1O³ s⁻ at 25°C, respectively. The activation parameters of the reaction were also obtained from the temperature variation study. The results indicate that chelate ring closure and rupture are affected by the rigidity of the benzene ring of the ligand, and thus the rate determining step of the reaction is the chelate ring closure process.     

Experimental study and computer modeling of Ni(II) and Cu(II) complexation with ceftazidime

The protonation constants of the anion of the cephalosporin antibiotic ceftazidime Ctzd^– and formation constants of its complexes with Ni²⁺ and Cu²⁺ have been determined by pH metric titration at 25°С and ionic strength 0.1 (KNO₃): logβ(HCtzd) = 4.82 ± 0.04, logβ(H₂Ctzd⁺) = 7.62 ± 0.06, logβ(H₃Ctzd²⁺) = 9.23 ± 0.09, logβ(NiCtzd⁺) = 4.04 ± 0.03, logβ(Ni(Ctzd)₂) = 6.41 ± 0.06, and logβ(CuCtzd⁺) = 5.03 ± 0.06. The potentiometric method has failed to reveal the complexation of Ctzd^– with Co²⁺, Zn²⁺, and Cd²⁺. The composition of the [Ni(Ctzd)₂] and [CuCtzd]⁺ complexes has been confirmed by spectrophotometry. The computer models of the [NiCtzd]⁺ and [CuCtzd]⁺ complexes have been calculated by the DFT method with the use of the B3LYP hybrid functional and the LACV3P**++ basis set.     

Nitrilotriacetic acid transformation photo-induced by complexation with iron(III) in aqueous solution

Summary The phototransformation of iron(III) nitrilotriacetate, Fe(NTA), was studied at 20 °C under monochromatic excitation at different pHs. The conjugation of excitation wavelength and pH gives rise to different photochemical behaviour. In acidic medium, it always results in a redox process giving rise to Fe^II, HCHO and CO₂ but the stoichiometry of the photoproducts depends on the excitation wavelength. At long wavelength (365 nm), the Fe^II/HCHO ratio of unity implies a redox reaction between Fe^III and the carboxylic group whereas at short wavelength (254 nm) the Fe/HCHO ratio is equal to 2 and implies a redox process between Fe^III and a water ligand. In neutral solution and at 365 nm, a photosolvation is observed with NTA release; at 254 nm a subsequent redox process between OH and the hydrous ferric oxide is involved. In terms of the fate of Fe(NTA) in the environment at pH 5–6 and under sunlight, all of the above photochemical reactions can occur.     

Cd(II) complexation in aqueous solution with dipyridine- and phenanthroline-containing polyamine macrocycles

The coordination features toward Cd(II) of four phenanthroline-containing and three dipyridine-containing macrocyclic polyamines have been studied by means of potentiometric and spectrophotometric UV–Vis measurements in aqueous solutions. All ligands form stable 1:1 metal complexes. The stability constants of the Cd(II) are generally lower than those reported for Cd(II) complexes with aliphatic macrocyclic polyamines containing the same number of nitrogen donors. This effect is mainly related to the stiffening of the ligands, due to the insertion of a large and rigid heteroaromatic moiety within the aliphatic polyamine framework. This structural feature does not allow the nitrogen donor to achieve an optimal arrangement around the metal ion. The decreased stability is often accompanied by facile protonation of the complexes, suggesting that some amine groups are not involved in metal binding.     

Thermodynamics of complexation of lead(II) and cobalt(II) with N-(carboxymethyl)aspartic acid in aqueous solutions

The enthalpies of complexation of lead(II) and cobalt(II) with N-(carboxymethyl)aspartic acid (H₃Y) were determined calorimetrically at 298.15 K within a wide ionic strength range (KNO₃). The thermodynamic characteristics of formation of the CoY₂- and PbY_2? complexes were calculated at non-zero and zero ionic strengthes. The explanation of the obtained values is given.     

The chemistry of adsorbed Cu(II) and Mn(II) in aqueous titanium dioxide suspensions

We studied the adsorption behavior of Cu(II) and Mn(II) on the surface of titanium dioxide over the pH range from 2.0 to 11.5. The titanium dioxide we used in these experiments was prepared by hydrolyzing TiCl₄ and had a surface area of 113.7 m² g⁻¹. All suspensions, which were 9.04 × 10⁻³ M in NaClO₄, contained 20 m² liter⁻¹ of oxide surface and divalent metal ion concentrations sufficient (at full adsorption from solution) to cover the available surface with one-half, one, and four layers of close-packed, hydrated ions. Both divalent ions began adsorption below titanium dioxide's isoelectric point (pH = 6.2). Cu²⁺ adsorption was accompanied by net OH⁻ uptake from solution and it was inferred that the titania surface also provided OH⁻ for Cu²⁺ adsorption. ESR spectra demonstrate the coexistence of two distinct forms adopted by these metal ions on the surface. A portion of the adsorbed metal ions occupies sites magnetically isolated one from another, as evidenced by the paramagnetic behavior of this form. The majority of the metal ions, however, exist in hydrous-metal-ion clusters in which spin-exchange coupling of the electron dipoles determines the magnetic behavior. Electrophoretic mobility measurements indicate that ions adsorbed at isolated sites exert a stronger influence on the electrophoretically measured charge of the suspension particles than ions in clusters. Even though these experiments were performed in the absence of oxygen, we observed the oxidation of a limited amount of the Mn(II) on the surface as low as pH = 5. Presumably this occurs as a result of electron transfer between photo-induced electron holes and Mn(II) on the surface.     

Identification of photocatalytic degradation products of bezafibrate in TiO(2) aqueous suspensions by liquid and gas chromatography

In the present study the photocatalytic degradation of bezafibrate (BZF), a lipid regulator agent, has been investigated using TiO(2) suspensions and simulated solar light. The study focus on the identification of degradation products (DPs) using powerful analytical techniques such as liquid chromatography time of flight mass spectrometry (LC-TOF-MS), gas chromatography mass spectrometry (GC-MS), and high-performance liquid chromatography with diode-array detection (HPLC-DAD). Each technique provided complementary information that enabled the identification of 21 DPs. Accurate mass measurements obtained by LC-TOF-MS provided the elucidation of 17 DPs. Mass errors lower than 2mDa, allowed the assignment of empirical formula for the mayor DPs to be determined confidently. Three DPs were identified by GC-MS through the structural information provided by full scan mass spectra obtained by electron impact (EI) ionization and two more by HPLC-DAD by comparing the retention times (t(R)) and the UV spectra of the unknown DPs with those of commercial standards. Based on this by-product identification a possible multi-step degradation scheme was proposed. The pathways include single or multiple hydroxylation of BZF with subsequent phenoxy ring opening and the cleavage of the amide and ether bonds.     

Kinetics of complexation of nickel (II) and copper (II) with some azophenol derivatives in aqueous nonionic surfactant solution

The kinetics of formation of 11 complexes of nickel(II) and copper(II) ions with some azophenol derivatives in aqueous and micellar solution of a nonionic surfactant, Triton X-100, have been studied by a stopped-flow spectrophotometric method. Second order rate constants for the reactions were determined at 298 K and ionic strength 0.1 (NaClO₄) in aqueous solution. In the surfactant solution, the pseudo-first-order rate constants for the complexation reactions,k_obs, decreased with increasing the concentration of Triton X-100. This observation was explained by the assumption that the chelating reagents distribute between the micelle of the surfactant and bulk aqueous phase and rate-controlling reactions occur only in the bulk aqueous phase. On the basis of the relation betweenk_obs and the concentration of the surfactant, the partition constants of the reagents between micellar and aqueous phases were determined.     

On the complexation of copper (II) ion with 2-hydroxybenzamide

The complexation of the Cu2+ ion with 2-Hydroxybenzamide (salicylamide, HL) has been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in NaCIO4 media for ionic strength ranging from 0.5 to 3 mol/dm3. The data are consistent with the formation of the complexes CuH(-1)(HL)+, CuH(-2)(HL)2, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL). The minor species, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL), amount to at least 20% of the total copper. Elaboration of the data according to the Specific Interaction Theory yields the constants valid in the infinite dilution reference state: [formulas: see text] and the interaction coefficients (kg/mol) of complex species with medium ions: b(L-,Na+) = 0.11 +/- 0.03; b(CuH(-1)(HL)+,NaClO4) = 0.17 +/- 0.05; b(CuH(-2)(HL)2,NaClO4) = 0.11 +/- 0.05; b(Cu2H(-2)(HL)2(2+),NaClO4) = 0.2(7) +/- 0.1; b(CuH(-2)(HL),NaClO4) = -0.0(3) +/- 0.1.     

Thermodynamics of mixed-ligand complexation of mercury(II) ethylenediaminetetraacetate with histidine and lysine in aqueous solution

The formation of mixed-ligand complexes HgEdtaIm²⁻, HgEdtaL³⁻, HgEdtaHL²⁻, and (HgEdta)₂L⁵⁻ (L is histidine, lysine; Im is imidazole) was studied by calorimetry, pH-metry, and NMR spectroscopy. The thermodynamic parameters (logK, ΔrG ⁰, ΔrH, Δr _S) for the reactions of complex formation at 298.15 K and ion strength of 0.5 (KNO₃) were determined. The most likely coordination mode for the complexone and amino acid in the mixed complexes was identified.     

Simultaneous determination of iron(II) and iron(III) in aqueous solution by kinetic spectrophotometry with tiron

A kinetic spectrophotometric method that requires no prior measurement of rate constants is developed for the simultaneous determination of iron(II) and iron(III). The method is based on the aerial oxidation of iron(II) in the presence of tiron and acetate ions. The iron(III) formed is subsequently complexed with tiron and the absorbance/time relation is evaluated. The concentrations of iron(III) and iron(II) are obtained from the absorbance values at the start and at equilibrium, respectively, calculated by non-linear least-squares fitting. A linear calibration graph is obtained up to 12 μg ml^?1 iron(II)/iron(III). The method is applied to iron-rich ground water.