Electrochemical behavior of electrodeposited film derived from rhein and its activity towards myoglobin reduction

The stable electroactive thin film of rhein has been investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical impedance spectroscopy of the electrodeposited film derived from rhein indicated the electrode reaction was kinetically controlled in the region of higher frequency, the charge transfer resistance was 2.6×10³ Ω cm² and capacitance value was 13.2 μF cm² . The electrodeposited film derived from rhein exhibited a good electrocatalytic activity for myoglobin (Mb) reduction. In 0.30 mol dm⁻³ H₂SO₄solution, the catalysis currents were proportional to the concentrations of Mb over the range of 1.5×10⁻⁷–1.3×10⁻⁵ mol dm⁻³. The detection limit is 1.0×10⁻⁷ mol dm⁻³ (S/N=3). The relative standard deviation is 4.8% for eight successive determinations of 5.0×10⁻⁷ mol dm⁻³ Mb.     

Hydrolysis of titanium sulphate compounds

The influence of TiOSO₄ and free sulphuric acid concentrations in the starting solution on the degree of titanyl sulphate conversion to hydrated titanium dioxide and post-hydrolytic sulphuric acid was studied. Titanyl sulphate solution, an intermediate product in the commercial preparation of titanium dioxide pigments by sulphate route, was used. It was found that the degree of hydrolysis markedly depends on the studied parameters. The lower was the content of TiOSO₄ in the starting solution, the higher conversion was achieved. The degree of hydrolysis at the final stage varied between 81 % (420 g TiOSO₄ dm⁻³, 216 g H₂SO₄ dm⁻³) and 92 % (300 g TiOSO₄ dm⁻³, 216 g H₂SO₄ dm⁻³). The same relation was obtained when changing the concentration of free H₂SO₄ in the starting solution. The degree of hydrolysis at the final stage varied between 49 % (261 g H₂SO₄ dm⁻³, 340 g TiOSO₄ dm⁻³) and 96 % (136 g H₂SO₄ dm⁻³, 340 g TiOSO₄ dm⁻³). The particle size of the obtained hydrated titanium dioxide (HTD) also depends on the initial solution composition. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Kinetics and mechanism of the reactions of hexaaqua rhodium (III) with sulphur (IV) in aqueous medium

An O-bonded sulphito complex, Rh(OH₂)₅(OSO₂H)²⁺, is reversibly formed in the stoppedflow time scale when Rh(OH₂) ₆ ³⁺ and SO₂/HSO ₃ ⁻ buffer (1 <pH< 3) are allowed to react. For Rh(OH₂)₅OH₂₊+ SO₂ □ Rh(OH₂)₅(OSO₂H)²⁺ (k₁/k_-1), k₁ = (2.2 ±0.2) × 10³ dm³ mol⁻¹ s⁻¹, k₋1 = 0.58 ±0.16 s⁻¹ (25°C,I = 0.5 mol dm⁻³). The protonated O-sulphito complex is a moderate acid (K _d = 3 × 10⁻⁴ mol dm⁻³, 25°C, I= 0.5 mol dm⁻³). This complex undergoes (O, O) chelation by the bound bisulphite withk= 1.4 × 10⁻³ s⁻¹ (31°C) to Rh(OH₂)₄(O₂SO)⁺ and the chelated sulphito complex takes up another HSO ₃ ⁻ in a fast equilibrium step to yield Rh(OH₂)₃(O₂SO)(OSO₂H) which further undergoes intramolecular ligand isomerisation to the S-bonded sulphito complex: Rh(OH₂)₃(O₂SO)(OSO₂)^- → Rh(OH₂)₃(O₂SO)(SO₃)⁻ (k _iso = 3 × 10⁻⁴ s⁻¹, 31°C). A dinuclear (μ-O, O) sulphite-bridged complex, Na₄[Rh₂(μ-OH)₂(OH)₂(μ-OS(O)O)(O₂SO)(SO₃) (OH₂)]5H₂O with (O, O) chelated and S-bonded sulphites has been isolated and characterized. This complex is sparingly soluble in water and most organic solvents and very stable to acid-catalysed decomposition     

Differential pulse polarographic study of thiamine (vitamin B1) in neutral and acidic aqueous solutions

The differential pulse (dp) polarograms of thiamine in neutral aqueous solutions exhibited six peaks at low depolarizer concentration (⋦10⁻⁴ mol dm⁻³) and only three peaks at concentrations ≥10⁻³ mol dm⁻³. Only one of these was found to correspond to the diffusion-controlled reduction of this compound at the dme and this was shown to be an irreversible two-electron process. The kinetic parameters derived from the dp polarograms were found to be in good agreement with those calculated from classical polarograms and were:E _1/2=−1·261 Vvs SCE,an _a=0·54 andD≈3·5×10⁻⁶ cm² sec⁻¹ for 10⁻³ mol dm⁻³ thiamine in 0·1 mol dm⁻³ acetate buffer (pH 6·5). The reduction product has been identified as dihydrothiamine. The effect of pH on the dpp of thiamine was studied in the pH range 0–7. In the pH region 5·5 to 7·0 only one peak attributable to the B₁ ⁺ form of thiamine is present. In the pH region 3·5–5·5 another dpp peak attributable to the protonated form (B₁H²⁺) of thiamine was also observed. At pHs less than 3 only one peak was observed which could be attributed to the doubly protonated form (B₁ H₂ ³⁺) of thiamine. Surfactants like triton-X-100 and CTABr were found to inhibit the electroreduction of thiamine due to the strong adsorption of these compounds on the dme. Thiamine itself was found to have an inhibitory effect on its own electroreduction, although to a smaller extent.     

Outer-Sphere electron-transfer and the effect of linkage isomerism in the titanium(III) reduction of nitro-pentacyanocobaltate(III) and nitro-, and nitrito-pentaamminecobalt(III) complexes in aqueous acidic media

The reductions of [Co(CN)₅NO₂]³⁻, [Co(NH₃)₅NO₂]²⁺ and [Co(NH₃)₅ONO]²⁺, by Ti^III in aqueous acidic solution have been studied spectrophotometrically. Kinetic studies were carried out using conventional techniques at an ionic strength of 1.0 mol dm⁻³ (LiCl/HCl) at 25.0 ± 0.1 °C and acid concentrations between 0.015 and 0.100 mol dm⁻³. The second-order rate constant is inverse—acid dependent and is described by the limiting rate law:- k₂ ≈ k₀ + k[H⁺]⁻¹,where k=k′K_a and K_a is the hydrolytic equilibrium constant for [Ti(H₂O)₆]³⁺. Values of k₀ obtained for [Co(CN)₅NO₂]³⁻, [Co(NH₃)₅NO₂]²⁺ and [Co(NH₃)₅ONO]²⁺ are (1.31 ± 0.05) × 10⁻² dm³ mol⁻¹ s⁻¹, (4.53 ± 0.08) × 10⁻² dm³ mol⁻¹ s⁻¹ and (1.7 ± 0.08) × 10⁻² dm³ mol⁻¹ s⁻¹ respectively, while the corresponding k′ values from reductions by TiOH²⁺ are 10.27 ± 0.45 dm³ mol⁻¹ s⁻¹, 14.99 ± 0.70 dm³ mol⁻¹ s⁻¹ and 17.93 ± 0.78 dm³ mol⁻¹ s⁻¹ respectively. Values of K _a obtained for the three complexes lie in the range (1–2) × 10⁻³ mol dm⁻³ which suggest an outer-sphere mechanism.     

Mechanism of the acid catalysed hydrolysis of the chromatopenta-amminecobalt(III) ion

The kinetics of the acid hydrolysis of chromatopenta-amminecobalt(III) ion has been studied using a stopped-flow method over the acidity range 0.01≤[H⁺]<-1.0 mol dm⁻³ and 20.0°C<-ϕ<-30.0°C at ionic strengths 0.5 and 1.0 mol dm⁻³ (LiNO₃). These studies reveal that the complex is first protonated and subsequently hydrolysed to the aquapentaammine cobalt(III) ion. The rate constants for the hydrolysis of the mono and diprotonated species at 25°C are 0.83±0.01 s⁻¹ and (1.60±0.02)×10⁴ mol⁻¹ dm⁻³ s⁻¹, respectively. TMC 2664     

Glassy carbon and boron doped glassy carbon electrodes for voltammetric determination of linuron herbicide in the selected samples

In this study the application of home-made unmodified (GC) and bulk modified boron doped glassy carbon (GCB) electrodes for the voltammetric determination of the linuron was investigated. The electrodes were synthesized with a moderate temperature treatment (1000°C). Obtained results were compared with the electrochemical determination of the linuron using a commercial glassy carbon electrode (GC-Metrohm). The peak potential (E _p ) of linuron oxidation in 0.1 mol dm⁻³ H₂SO₄ as electrolyte was similar for all applied electrodes: 1.31, 1.34 and 1.28 V for GCB, GC and GC-Metrohm electrodes, respectively. Potential of linuron oxidation and current density depend on the pH of supporting electrolyte. Applying GCB and GC-Metrohm electrodes the most intensive electrochemical response for linuron was obtained in strongly acidic solution (0.1 mol dm⁻³ H₂SO₄). Applying the boron doped glassy carbon electrode the broadest linear range (0.005–0.1 μmol cm⁻³) for the linuron determination was obtained. The results of voltammetric determination of the linuron in spiked water samples showed good correlation between added and found amounts of linuron and also are in good agreement with the results obtained by HPLC-UV method. This appears to be the first application of a boron doped glassy carbon electrode for voltammetric determination of the environmental important compounds.      

Two-Dimensional Photoluminescence Behavior of Langmuir-Blodgett Monolayers and Multilayers Composed of Decatungstoeuropate

Decatungstoeuropate/dimethyldioctadecylammonium (EuW₁₀/DODA) Langmuir-Blodgett (LB) monolayers and multilayers (7 layers) were fabricated by using aqueous solution of EuW₁₀ with different concentration (1.0–3.0 μmol dm⁻³). The results of specular X-ray reflectivity (SXR) and grazing incidence X-ray diffraction (GIXD) measurements for the EuW₁₀/DODA LB films indicated an increase in the interlayer distance and in-plane molecular ordering for the film fabricated with the concentrated EuW₁₀ solution, reflecting the dense packing of DODA and EuW₁₀ molecules. Their photoluminescence property also depended on the concentration of the EuW₁₀ solution. With an increase in the EuW₁₀ concentration in the subphase, both the relative intensity of the ⁵D₀→⁷F₁ transition and the emission lifetime increased. The lifetime of emission of the EuW₁₀ LB monolayers changed from 0.8±0.1 ms (1.0 μmol dm⁻³) to 1.0±0.1 ms (2.1 μmol dm⁻³) and 1.3±0.1 ms (3.0 μmol dm⁻³), which became closer to that (2.6 ms) of the solid, and EuW₁₀/DODA LB multilayers had the same tendency. The elongation of the emission lifetime was due to a decrease in the number of aqua molecules within the Eu³⁺-coordination sphere, which will be caused by the dense and regular packing of EuW₁₀ molecules.     

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

The reactions between Fe(Phen)₃²⁺[phen = tris-(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm⁻³ (NaCl/HCl). Plots of k₂ versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (Z_AZ_B) for the reactions of Fe(Phen)₃²⁺ with the chloro-, bromo- and iodo- complexes respectively. Z_AZ_B of ≈ −2 suggests that the charge on these Co^III complexes cannot be −3 but is −1. This suggests the possibility of protonation of these Co^III complexes. Protonation was investigated over the range [H⁺] = 0.0001 −0.06 mol dm⁻³ and the protonation constants K_a obtained are 1.22 × 10³, 7.31 × 10³ and 9.90 × 10² dm⁶ mol⁻³ for X = Cl, Br and I, respectively.     

Effect of pH and ionic strength on the interaction of humic acid with aluminium oxide

The effect of pH and neutral electrolyte on the interaction between humic acid/humate and γ-AlOOH (boehmite) was investigated. The quantitative characterization of surface charging for both partners was performed by means of potentiometric acid–base titration. The intrinsic equilibrium constants for surface charge formation were logK _a,1 ^int=6.7±0.2 and logK _a,2 ^int = 10.6±0.2 and the point of zero charge was 8.7±0.1 for aluminium oxide. The pH-dependent solubility and the speciation of dissolved aluminium was calculated (MINTEQA2). The fitted (FITEQL) pK values for dissociation of acidic groups of humic acid were pK ₁ = 3.7±0.1 and pK ₂ = 6.6±0.1 and the total acidity was 4.56 mmol g⁻¹. The pH range for the adsorption study was limited to between pH 5 and 10, where the amount of the aluminium species in the aqueous phase is negligible (less than 10⁻⁵ mol dm⁻³) and the complicating side equilibria can be neglected. Adsorption isotherms were determined at pH ∼ 5.5, ∼8.5 and ∼9.5, where the surface of adsorbent is positive, neutral and negative, respectively, and at 0.001, 0.1, 0.25 and 0.50 mol dm⁻³ NaNO₃. The isotherms are of the Langmuir type, except that measured at pH ∼ 5.5 in the presence of 0.25 and 0.5 mol dm⁻³ salt. The interaction between humic acid/humate and aluminium oxide is mainly a ligand-exchange reaction with humic macroions with changing conformation under the influence of the charged interface. With increasing ionic strength the surface complexation takes place with more and more compressed humic macroions. The contribution of Coulombic interaction of oppositely charged partners is significant at acidic pH. We suppose heterocoagulation of humic acid and aluminium oxide particles at pH ∼ 5.5 and higher salt content to explain the unusual increase in the apparent amount of humic acid adsorbed. Received: 20 July 1999 /Accepted in revised form: 20 October 1999     

Activation of methanol-tolerant carbon-supported RuSe<Subscript>x</Subscript> electrocatalytic nanoparticles towards more efficient oxygen reduction

An electrocatalytic system that utilizes tungsten oxide modified carbon-supported RuSe_x nanoparticles is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic voltammetry and rotating ring-disk voltammetry, as well as upon its introduction (as cathode) to the low-temperature hydrogen–oxygen fuel cell. After the modification of RuSe_x catalytic centers with ultra-thin films of WO₃, the potential of oxygen reduction in 0.5 mol dm⁻³ H₂SO₄ (in the absence and presence of methanol) is shifted ca. 70 mV (under rotating disk voltammetric conditions) towards more positive values, and the percent formation (at ring) of the undesirable hydrogen peroxide has decreased approximately twice when compared to the WO₃-free system. Relative to bare electrocatalyst, an increase of power density from 75 to 100 mW cm⁻² (at 300 mA cm⁻²) has been observed upon utilization of WO₃-modified RuSe_x in polymer electrolyte membrane fuel cell at 80 °C. In comparison to Vulcan-supported Pt nanoparticles, the overall electrocatalytic performance of tungsten oxide modified carbon-supported RuSe_x nanoparticles is lower, but the latter system is practically insensitive to the presence of methanol even at 0.5 mol dm⁻³ level. Dedicated to Professor Dr. Algirdas Vaskelis on the occassion of his 70th birthday.     

Sorption and desorption of 125I-, 137Cs+, 85Sr2+ and 152,154Eu3+ on disturbed soils under dynamic flow and static batch conditions

Sorption of radionuclides on homogenized soils (under 2.5 mm grain size) from synthetic groundwater of 8·10⁻³M ionic strength and pH 8.5 has been studied under dynamic (flow) and static (batch) conditions. The corresponding water-soluble compounds, as carriers in the 10⁻⁶ mol/dm³ concentration, were added into the SGW prior to the experiments. Soil samples were taken from several locations around the environment of the High Level Waste Storage Facility at Nuclear Research Institute Řež plc in 5–100 cm depth. The dynamic experiments were carried out in columns made of PP+PE injection syringes of 17.8 cm length and 2.1 cm in diameter. A multi-head peristaltic pump was used for pumping the water upward through the columns at a seepage velocity of about 0.06 cm/min in average. The radioactive nuclides were added into the water stream individually in a form of a short pulse in 0.1 cm³ of demineralized water. Dynamic desorption experiments were performed with the same experimental arrangement using a mixture of 10⁻²N H₂SO₄ and 10⁻²N HNO₃ in a volume ratio of 2: 1. Retardation, distribution and hydrodynamic dispersion coefficients during transport of radionuclides were determined by the evaluation of the integral form of a simple advection-dispersion equation, used for fitting experimental data and modeling the theoretical sorption breakthrough and desorption displacement curves. The static experiments were realized in 100 cm³ plastic bottles stirring 5 g of soil samples with SGW occasionally in a soil to SGW ratio of 1: 10 (m/V). Kinetic parameters including equilibrium sorption activity, activity transfer rate constants and sorption half-times were also determined. The results of dynamic experiments were compared with static sorption experiments.     

Mechanistic study of iodide catalysed oxidation of l-glutamic acid by cerium(IV) in aqueous sulphuric acid medium

A minute quantity (10⁻⁶ mol dm⁻³) of iodide catalysed oxidation of l-glutamic acid by Ce^IV has been studied in H₂SO₄ and SO ₄ ²⁻ media. The reaction was first order each in [Ce^IV] and [I⁻]. The order with respect to [l-glutamic acid] was less than unity (0.71). Increase in [H₂SO₄] decreased the reaction rate. The added HSO ₄ ⁻ and SO ₄ ²⁻ decreased the rate of reaction. The added product, succinic acid, had no effect on the reaction rate, whereas added Ce^III retarded the reaction. The ionic strength and dielectric constant did not have any significant effect on the rate of reaction. The active species of oxidant was Ce(SO₄)₂. A suitable mechanism was proposed. The activation parameters were determined with respect to the slow step of the mechanism. The thermodynamic quantities were also determined and discussed.     

Determination of total and extractable hydrogen peroxide in organic and aqueous solutions of uranyl nitrate

The development of a spectrophotometric method for the determination of hydrogen peroxide in uranyl nitrate solutions is reported. The method involves the measurement of the absorbance at 520 nm of a vanadyl peroxide species. This species was formed by the addition of a reagent consisting of vanadium (V) (50 mmol·dm⁻³) in dilute sulphuric acid (2 mol·dm⁻³ H₂SO₄). This reagent, after dilution, was also used as an extractant for organic phase samples. The method is simple and robust and tolerant of nitric acid and U(VI). Specificity and accuracy were improved by the application of solid phase extraction techniques to remove entrained organic solvents and Pu(IV). Reverse phase solid phase extraction was used to clean-up aqueous samples or extracts which were contaminated with entrained solvent. A solid phase extraction system based upon an extraction chromatography system was used to remove Pu(IV). Detection limits of 26 μmol·dm⁻³ (0.88 μg·cm⁻³) or 7 μmol·dm⁻³ (0.24 μg·cm⁻³) for, respectively, a 1 and 4 cm path length cell were obtained. Precisions of RSD=1.4% and 19.5% were obtained at the extremes of the calibration curve (5 mmol·dm⁻³ and 50 μmol·dm⁻³ H₂O₂, 1 cm cell). The introduction of the extraction and clean-up stages had a negligible effect upon the precision of the determination. The stability of an organic phase sample was tested and no loss of analyte could be discerned over a period of at least 5 days. The presence of trace levels of reductants interfered with the determination, e.g., hydrazine (<2 mmol·dm⁻³), but this effect was ameliorated by increasing the concentration of the colormetric reagent.     

Determination of bioavailable iron in noncontaminated Slovak soils by flame atomic absorption spectrometry

A method for the extraction of bioavailable iron from soils from various parts of Slovakia using a buffered diethylenetriaminepentaacetic acid (DTPA) solution was utilized. The extractant consists of 0.005 mol dm⁻³ DTPA, 0.1 mol dm⁻³ CaCl₂, and 0.1 mol dm⁻³ triethanolamine with pH of 7.3. DTPA was selected as the chelating agent because it can effectively extract micronutrient metal, iron. Distribution of iron in the horizons of various types of soils with respect to bioavailable iron was evaluated. The bioavailable iron in the extracts was determined by flame atomic absorption spectrometry. The calibration standards were prepared in the same surroundings as the extracts. Comparing to the average of 2.7–3.7 % total iron contents in Slovak soils, the available amounts of iron represent in average only very small amounts, approximately 0.3 % in comparison to total amounts.     

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

The kinetics of the reactions between Fe(phen) ₃ ²⁺ [phen = tris–(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm⁻³ (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H⁺] = 0.01 mol dm⁻³) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm³ mol⁻¹ s⁻¹. Ion-pair constants K _ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 10⁴, 3.00 × 10² and 4.02 × 10⁴ mol⁻¹ dm⁻³ for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K⁻¹ mol⁻¹) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K⁻¹) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E _a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm³ mol⁻¹ s⁻¹) = (7.079 ± 0.035) × 10¹⁶, (1.413 ± 0.011) × 10¹⁷, and (9.772 ± 0.027) × 10²⁰ for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions.     

Stability constants of oxalate complexes of copper (II) and nickel (II) by paper electrophoresis

Summary Stability constants of copper (II) and nickel (II) oxalates have been determined by paper electrophoresis. Oxalic acid (0.005 mol dm⁻³) was added to the background electrolyte: 0.1 mol dm⁻³ HClO₄. The proportions of HC₂O ₄ ⁻ and C₂O ₄ ²⁻ were varied by changing the pH of the electrolyte, these anions yielding the complex ions MHC₂O ₄ ⁺ and M(C₂O₄) ₂ ²⁻ , average values of the stability constants for which are 10^2.4 and 10^7.6 respectively for Cu(II), and 10^2.3 and 10^6.5 for Ni(II) (μ=0.1,30°).     

Temperature influence on the malonic acid decomposition in the Belousov-Zhabotinsky reaction

The kinetic investigations of the malonic acid decomposition (8.00 × 10⁻³ mol dm⁻³ ≤ [CH₂(COOH)₂]₀ ≤ 4.30 × 10⁻² mol dm⁻³) in the Belousov-Zhabotinsky (BZ) system in the presence of bromate, bromide, sulfuric acid and cerium sulfate, were performed in the isothermal closed well stirred reactor at different temperatures (25.0°C ≤ T ≤ 45.0°C). The formal kinetics of the overall BZ reaction, and particularly kinetics in characteristic periods of BZ reaction, based on the analyses of the bromide oscillograms, was accomplished. The evolution as well as the rate constants and the apparent activation energies of the reactions, which exist in the preoscillatory and oscillatory periods, are also successfully calculated by numerical simulations. Simulations are based on the model including the Br₂O species. The article is published in the original.     

Solubility and hydrolysis of lutetium at different [Lu<Superscript>3+</Superscript>]<Subscript>initial</Subscript>

Solubility product (Lu(OH)_3(s)⇆Lu³⁺+3OH⁻) and first hydrolysis (Lu³⁺+H₂O⇆Lu(OH)²⁺+H⁺) constants were determined for an initial lutetium concentration range from 3.72·10⁻⁵ mol·dm⁻³ to 2.09·10⁻³ mol·dm⁻³. Measurements were made in 2 mol·dm⁻³ NaClO₄ ionic strength, under CO₂-free conditions and temperature was controlled at 303 K. Solubility diagrams (pLu_aq vs. pC _H) were determined by means of a radiochemical method using ¹⁷⁷Lu. The pC _H for the beginning of precipitation and solubility product constant were determined from these diagrams and both the first hydrolysis and solubility product constants were calculated by fitting the diagrams to the solubility equation. The pC _H values of precipitation increases inversely to [Lu³⁺]_initial and the values for the first hydrolysis and solubility product constants were log₁₀ β* _Lu,H = −7.92±0.07 and log₁₀ K*_sp,Lu(OH)3 = −23.37±0.14. Individual solubility values for pC _H range between the beginning of precipitation and 8.5 were S _Lu3+ = 3.5·10⁻⁷ mol·dm⁻³, S _Lu(OH)2+ = 6.2·10⁻⁷ mol·dm⁻³, and then total solubility was 9.7·10⁻⁷ mol·dm⁻³.     

Mononuclear Rare Earth Metal Complexes based on 1,10-phenanthroline Derivatives as Catalysts for Hydrolysis of p-nitrophenyl Phosphate (NPP)

Two multidentate ligands: N,N′-di-(propionic acid-2′-yl-)-2,9-diaminomethyl-1,10-phenanthroline (L1) and N,N′-di-(3′-methylbutyric acid-2′-yl-)-2,9-diaminomethyl-1,10-phenanthroline (L2) were synthesized. The hydrolytic kinetics of p-nitrophenyl phosphate (NPP) catalyzed by complexes of L1 and L2 with La(III), Gd(III) have been studied. Both LnL and LnLH₋₁ have been examined as catalysis for the hydrolysis of NPP in aqueous solution at 298 K, I = 0.10 mol dm⁻³ KNO₃ at the pH range 7.4–9.1, respectively. Kinetic studies show that both LnL and LnLH₋₁ have catalytic activity, but LnLH₋₁ is more active than LnL in the hydrolysis of NPP. The second-order rate constants for the hydrolysis of NPP are k_GdL1H−1 = 0.01399 mol⁻¹ dm³ s⁻¹, k_GdL1 = 0.0000110 mol⁻¹ dm³ s⁻¹ for complexes GdL1H₋₁ and GdL1, respectively. A new mechanism was proposed for the hydrolysis of NPP catalyzed by LnL and LnLH₋₁.