Complexation study of europium(III) and curium(III) with urea in aqueous solution investigated by time-resolved laser-induced fluorescence spectroscopy

The complex formation of europium(III) and curium(III) with urea in aqueous solution has been studied at I = 0.1 M (NaClO₄), room temperature and trace metal concentrations in the pH-range of 1-8 at various ligand concentrations using time-resolved laser-fluorescence spectroscopy. While for curium(III) the luminescence maximum is red shifted upon complexation, in case of europium(III) emission wavelengths remain unaltered but a significant change in peak splitting occurs. Both heavy metals form weak complexes of the formulae ML³⁺ and MLOH²⁺ with urea. Stability constants were determined to be log β₁₁₀ = −0.12 ± 0.05 and log β_11-1 = −6.86 ± 0.15 for europium(III) and log β₁₁₀ = −0.28 ± 0.12 and log β_11-1 = −7.01 ± 0.15 for curium(III).     

Spectrophotometric determination of formation constants for the Cu-ethylenediamine-halogen (chloride and bromide) system and their catalytic effect on the oxidative coupling of 2,6-di-tert-butyl-phenol

In order to explain the mechanism of the dimerization of 2,6-di-tert-butyl-phenol when catalyzed by the copper-ethylenediamine complexes, a spectrophotometric study of the speciation of copper(II) complexes in methanol of Cu(II), ethylendiamine and Cl⁻ or Br⁻ was carried out at 303 K. The formation constants obtained for the copper chloride system are: log β₁₀₁ = 2.90 ± 0.03, log β₁₀₂ = 6.39 ± 0.03 and log β₁₀₃ = 8.62 ± 0.04, for the copper bromide system are log β₁₀₁ = 3.01 ± 0.10, log β₁₀₂ = 5.50 ± 0.08, for the copper-ethylendiamine complexes are log β₁₁₀ = 6.13 ± 0.05 and log β₁₂₀ = 10.54 ± 0.08, and for the ternary copper-ethylenediamine chloride or bromide systems are log β₁₁₁ = 10.21 ± 0.03 and log β₁₁₁ = 10.07 ± 0.03, respectively. Knowing the speciation of the copper-ethylenediamine-halide systems, the kinetic studies can be correlated with the species in solution. Comparative studies of the oxidation reaction of 2,6-di-tert-butyl-phenol using different copper(II) complexes with chloride or bromide and ethylenediamine as catalyst are reported. Their catalytic activity in the oxidation of 2,6-di-tert-butyl-phenol was monitored in methanol solution, following the corresponding quinone formation, at 418 nm (ε = 3.95 × 10⁴ mol⁻¹ L cm⁻¹ at 303 K). The results indicate that the most active species are [Cu(en)X]⁺, where X is bromide or chloride, Both complexes have similar activity.     

The aluminium(III)-sialic acid interaction: A potential role in aluminium-induced cellular membrane degeneration

The coordination between Al(III) and sialic acid (N-acetylneuraminic acid, HL, pK_a = 2.58 ± 0.01) was studied by potentiometric titrations at 25 °C in aqueous 0.2 M KCl, by ¹H NMR, and by electrospray ionization mass spectrometry (ESI-MS). The potentiometric measurements gave the following aluminium complex stoichiometries and stability constants: , log β(AlLH₋₂) = −6.34 ± 0.02, and log β(AlL₂H₋₁) = −1.14 ± 0.04. The ¹H NMR spectra yielded structural information on species . The ESI-MS data confirmed the metal-ligand stoichiometry of the complexes.The metal-ligand speciation at micromolar Al(III) concentrations (i.e., under in vivo conditions) at physiological pH values reveals that considerable amount of Al(III) is complexed. This suggests that the toxic effect of Al(III) towards cellular membranes might be due to its coordination by protein-bound sialic acid.     

(E)-2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione: Tautomery and coordination to copper(II)

(E)-2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione (H₂L) was synthesized by azocoupling of diazonium salt of 2-hydroxyaniline with 1-phenylbutane-1,3-dione and characterized by IR, ¹H and ¹³C NMR spectroscopies and X-ray diffraction analysis. In solution, H₂L exists as a mixture of the enol-azo and hydrazone tautomeric forms and a decrease of temperature and of solvent polarity shifts the tautomeric balance to the hydrazone form. In the solid state, H₂L crystallizes from ethanol-water in the monohydrate hydrazone form, as shown by X-ray analysis. The dissociation constants of H₂L (pK₁ = 5.98 ± 0.04, pK₂ = 9.72 ± 0.03) and the stability constants of its copper(II) complex (log β₁ = 11.01 ± 0.07, log β₂ = 20.19 ± 0.08) were determined by the potentiometric method in aqueous-ethanol solution. The copper(II) complex [Cu₂(μ-L)₂]_n was isolated in the solid state and found by X-rays to be a coordination polymer of a binuclear core with a distorted square pyramidal metal coordination geometry.     

Rare earth complexation with 1,3,5-trideoxy-1,3,5-tris(2-hydroxybenzyl)amino-cis-inositol

The protonation constants of 1,3,5-trideoxy-1,3,5-tris(2-hydroxyl-benzyl)amino-cis-inositol (thci) in I = 1 M (NaClO₄) were determined to be: pK_a1 5.96 ± 0.03, pK_a2 7.21 ± 0.01, pK_a3 8.32 ± 0.07, pK_a4 8.95 ± 0.06. The solvent extraction studies were consistent with the formation of the Ln(thci)³⁺ and complexes. The log of the stability constants (log β₁ and log β₂) at 25 °C in 1 M (NaClO₄) at pH 4 for formation of these complexes are reported. Laser luminescence measurements of the ⁷F₀-⁵D₀ transition of Eu(III) complexed by thci indicated two species. The shifts in the peaks relative to that of Eu(aq)³⁺ were comparable to the values reported for other complexes of Eu(III) with organic ligands, but the intensities were greater. Luminescence lifetime measurements of the fluorescence spectra indicated that the complex has 5 inner sphere water molecules bound to the Eu(III) cation at pH 6.71-8.52. This was consistent with bidentate chelation of Eu(III) with each thci molecule. gaussian view energy calculations indicated bonding for M(III) to the amino and hydroxyl groups of the cyclohexanetriol and (2-hydroxybenzyl)amino moieties in the Ln(thci)³⁺ complex.     

Complexation of curium(III) by adenosine 5′-triphosphate (ATP): A time-resolved laser-induced fluorescence spectroscopy (TRLFS) study

The complex formation of curium(III) with adenosine 5′-triphosphate (ATP) was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS). The interaction between soluble species of curium(III) with ATP was studied at trace Cm(III) concentrations (3 × 10⁻⁷ M). The concentrations of ATP were varied between 6.0 × 10⁻⁷ and 1.5 × 10⁻⁴ M in the pH range of 1.5-7.0 using 0.154 M NaCl as background electrolyte.Three Cm-ATP species, M_pH_qL_r, could be identified from the fluorescence emission spectra: (i) CmH₂ATP⁺ with a peak maximum at 598.6 nm, (ii) CmHATP with a peak maximum at 600.3 nm, and (iii) CmATP⁻ with a peak maximum at 601.0 nm. The formation constants of these complexes were calculated from TRLFS measurements to be log β₁₂₁ = 16.86 ± 0.09, log β₁₁₁ = 13.23 ± 0.10, and log β₁₀₁ = 8.19 ± 0.16. The hydrated Cm-ATP species showed fluorescence lifetimes between 88 and 96 μs; whereas the CmATP⁻ complex has a significantly longer fluorescence lifetime of 187 ± 7 μs.     

Polymerization study of o-Si(OH)4 and complexation with Am(III), Eu(III) and Cm(III)

The stability constants of Am⁺³, Cm³⁺ and Eu³⁺ with ortho silicate, were measured at pH 3.50 and in ionic strengths of 0.20-1.00 M (NaClO₄) by the solvent extraction method. The Am⁺³, Cm³⁺ and Eu³⁺ forms 1:1 complex with ortho silicate ion at pH 3.60 with the stability constant (log β₁) value of 8.02 ± 0.10, 7.78 ± 0.08 and 7.81 ± 0.11, respectively. The stability of these metal ions decrease with increased ionic strength from 0.20 to 1.00 M (NaClO₄) for silicic acid concentrations of 0.002-0.020 M. Increasing silicic acid concentration above 0.02 M increased the amount of M³⁺ extracted into the organic phase, contrary to the trend usually observed for increased ligand concentration in solvent extraction. This reversed trend is likely due to the extraction of cationic species of silicic acid by HDEHP. Aging time (60-300 min) had no effect on the stability constant of these metal ions for 0.002-0.020 M silicic acid at pH 3.50 and I = 0.20 M (NaClO₄).The fraction of polymeric silicic acid present in solutions of 0.20-4.50 M NaClO₄ solutions at pH 3.0-10.0, T = 0-60 °C and aging time = 5-300 min was measured for determination of the silicomolybdate reaction to ascertain the proper conditions to study metal-silicate complexation.     

Complexes of the highly preorganized ligand PDALC (2,9-bis(hydroxymethyl)-1,10-phenanthroline) with trivalent lanthanides. A thermodynamic and crystallographic study

Metal ion complexing properties of the highly preorganized tetradentate ligand PDALC (2,9-bis(hydroxymethyl)-1,10-phenanthroline) are presented. The structure of [Gd(PDALC)(NO₃)₃]·H₂O (1) is reported: triclinic, , a = 7.545(12), b = 10.811(17), c = 11.909(18) Å, α = 97.71(2)°, β = 91.56(2)°, γ = 109.06(2)°, V = 907(2) Å³, Z = 2, R = 0.0354. The Gd is 10-coordinate, with the coordination sphere comprising the four donor atoms of the PDALC plus the six O-donors of three chelated nitrates. Comparison with structures in the literature suggests that the Gd-L (L = ligand) bond lengths, particularly those to the alcoholic O-donors of PDALC, are a little short. It was suggested that the short Gd-L bond lengths in 1 were due to the efficiency of packing of the nitrates around the Gd, with the short ‘bite’ distances of the nitrate ligand. Formation constants (log K₁) were measured spectroscopically in 0.1 M NaClO₄ at 25 °C by monitoring the variation of the π-π∗ transitions of 2 × 10⁻⁵ M PDALC in the range 200-350 nm as a function of pH, in the presence of 1:1 concentrations of the lanthanide(III) (Ln(III)) metal ion. The measured log K₁ values varied from 5.34 (La(III)) to 6.40 (Lu(III), which is an unusually small variation across the series of Ln(III) ions. Values of log K₁ with PDALC were also measured for Y(III) (5.85) and Sc(III) (6.02). The small amount of variation in log K₁ for PDALC across the series of Ln(III) ions was rationalised in terms of the effect of neutral oxygen donors on complex stability, which promotes selectivity for larger metal ions such as La(III). It was discussed how the small amount of variation in log K₁ across the Ln(III) series might lead to optimal selectivity for the Am(III) ion relative to the Ln(III) ions as a group.     

Thermodynamics and laser luminescence spectroscopy of binary and ternary complexation of Am, Cm and Eu with citric acid, and citric acid + EDTA at high ionic strength

The binary complexation of Am³⁺, Cm³⁺and Eu³⁺ with citrate has been studied at I = 6.60 m (NaClO₄), pcH 3.60 and in the temperatures range of 0-60 °C employing a solvent extraction technique with di-(2-ethylhexyl)phosphoric acid/heptane. Two complexes, MCit and , were formed at all temperatures. For the three metal ions, the log β₁₀₁ was between 5.9 and 6.2 and log β₁₀₂ between 10.2 and 10.6 at 25 °C. The thermodynamic parameters for the Am-Cit system have been calculated from the temperature dependence of the β₁₀₁ and β₁₀₂ values. Positive enthalpy and entropy values for the formation of both complexes are interpreted as due to the contributions from the dehydration of the metal ions exceeding the exothermic cation-anion pairing. The formation of the ternary complex M(EDTA)(Cit)⁴⁻ (M = Cm and Eu) was measured to have large stability constants (log β₁₁₁ between 20.9 and 24.4) at 25 and 60 °C. Time resolved laser luminescence spectroscopy and lifetime measurement data validated the nature of the complexes of Eu(III) formed in the presence of Cit and EDTA + Cit in 6.60 m (NaClO₄) solution.     

Determination of formation constants for complexes of very high stability: log β4 for the [Pd(CN)4] ion

The formation constant, log β₄ = 62.3 for [Pd(CN)₄]²⁻ is reported at 25 °C in 0.1 M NaClO₄. This value of log β₄ was determined using a competition reaction, monitored using UV-Vis spectroscopy and ¹H NMR. The competition reaction used was with the tetraamine ligand 2,3,2-tet(1,4,8,11-tetraazaundecane), for which log K₁ = 47.8 at 25 °C in 0.1 M NaClO₄ was determined by competition with thiocyanate, as described by earlier workers (Q.Y. Yan, G. Anderegg, Inorg. Chim. Acta 105 (1985) 121.). Also reported is a value of log β₄ for the [Pd(SCN)₄]²⁻ ion of 27.2 in 0.1 M NaClO₄, determined by competition with 2,2,2-tet. Measurement of log K₁ for cyclam with Pd(II) was attempted using a competition reaction with cyanide, combined with the very high value of log β₄ for [Pd(CN)₄]²⁻ measured here. It appeared that the equilibrium being followed was actually [Pd(cyclam)]²⁺ + 2CN⁻ ? [Pd(cyclam)(CN)₂], for which a constant of log K = 5.2 was obtained. ¹H NMR and IR studies suggested that the complex [Pd(cyclam)(CN)₂] was prone to oxidation to Pd(IV), followed by disproportionation to [Pd(cyclam)]²⁺ and, presumably, (CN)₂. The very high value of log β₄ for [Pd(CN)₄]²⁻ found here appears to be the highest formation constant known for any metal ion.     

A fluorescent ligand rationally designed to be selective for zinc(II) over larger metal ions. The structures of the zinc(II) and cadmium(II) complexes of N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine

The metal ion coordinating properties of the ligands N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine (DQPEA) and N,N-bis(2-methylquinoline)-2-(2-aminomethyl)pyridine (DQPMA) are presented. DQPEA and DQPMA differ only in that DQPEA forms six-membered chelate rings that involve the pyridyl group, whereas DQPMA forms analogous five-membered chelate rings.These two ligands illustrate the application of a ligand design principle, which states that increase of chelate ring size in a ligand will result in increase in selectivity for smaller relative to larger metal ions. The formation constants (log K₁) of DQPEA and DQPMA with Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) are reported. As expected from the applied ligand design principle, small metal ions such as Ni(II) and Zn(II) show increases in log K₁ with DQPEA (six-membered chelate ring) relative to DQPMA (five-membered chelate ring), while large metal ions such as Cd(II) and Pb(II) show decreases in log K₁ when the chelate ring increases in size. In order to further understand the steric origin of the destabilization of complexes of metal ions of differing sizes by the six-membered chelate ring of DQPEA, the structures of [Zn(DQPEA)H₂O](ClO₄)₂ (1) [triclinic, , a = 9.2906(10), b = 10.3943(10), c = 17.3880(18) Å, α = 82.748(7)°, β = 88.519(7)°, γ = 66.957(6)°, Z = 4, R = 0.073] and [Cd(DQPEA)(NO₃)₂] (2) [monoclinic, C2/c, a = 22.160(3), b = 15.9444(18), c = 16.6962(18) Å, β = 119.780(3)°, Z = 8, R = 0.0425] are reported. The Zn in (1) is five-coordinate, with a water molecule completing the coordination sphere. The Cd(II) in (2) is six-coordinate, with two unidentate nitrates coordinated to the Cd. It is found that the bonds to the quinaldine nitrogens in the DQPEA complexes are considerably stretched as compared to those of analogous TPyA (tri(pyridylmethyl)amine) complexes, which effect is attributed to the greater steric crowding in the DQPEA complexes. The structures are analyzed for indications of the origins of the destabilization of the complex of the large Cd(II) ion relative to the smaller Zn(II) ion. A possible cause is the greater distortion of the six-membered chelate ring in (2) than in (1), as evidenced by torsion angles that are further away from the ideal values in (2) than in (1). Fluorescence properties of the DQPMA and DQPEA complexes of Zn(II) and Cd(II) are reported. It is found that the DQPEA complex of Zn(II) has increased fluorescence intensity compared to the DQPMA complex, while for the Cd(II) complex the opposite is found. This is related to the greater strain in the six-membered chelate ring of the Cd(II) DQPEA complex as compared to the Zn(II) complex, with resulting poorer overlap in the Cd-N bond, and hence greater ability to quench the fluorescence in the Cd(II) complex.     

Comparison of the SOD-like activity of hexacoordinate Mn(II), Fe(II) and Ni(II) complexes having isoindoline-based ligands

Recently, a series of Fe(II) complexes have been published by our group with 3 N-donor 1,3-bis(2′-Ar-imino)isoindoline ligands containing various Ar-groups (pyridyl, 4-methylpyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl). The superoxide scavenging activity of the compounds showed correlation with the Fe(III)/Fe(II) redox potentials. Analogous, electroneutral chelate complexes with Mn(II) and Ni(II) in 2:1 ligand:metal composition are reported here. Each Mn(II) complex exhibits one reversible redox wave that is assigned as the Mn(III)/Mn(II) redox transition. The E_1/2 spans a 180 mV range from − 98 (Ar = 3-methylpyridyl) to 82 mV (Ar = thiazolyl) vs. the Fc⁺/Fc depending on the Ar-sidearm. The SOD-like (SOD=superoxide dismutase)activity of all complexes was determined according to the McCord-Fridovich method. The Mn(II) isoindolinates have IC₅₀ values - determined with 50 μM cytochrome c Fe(III) - that range from (3.22 ± 0.39) × 10^− 6 (Ar = benzimidazolyl) to (10.80 ± 0.54) × 10^− 6 M (Ar = N-methylbenzimidazolyl). In contrast with the Fe(II) complexes, the IC₅₀ concentrations show no significant dependence on the E_1/2 values in this narrow potential range emphasizing that the redox potential is not the governing factor in the Mn(II)-containing scavengers. The analogous Ni(II) compounds show no redox transitions in the thermodynamically relevant potential range (− 0.40 to 0.65 V vs. SCE) and accordingly, their superoxide scavenging activity (if any) is below the detection level.     

Syntheses and characterization of novel binuclear chromium (III) complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam)

The syntheses and characterization of novel binuclear chromium (III) complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) are described. The complex [(cyclam)Cr(OH)]₂Cl₄ · 7H₂O (1) crystallizes in the monoclinic space group C2/c with four binuclear formula units in a cell of dimensions a = 17.403 (2), b = 16.803 (3), c = 12.708 (2) Å, and β = 100.83 (1)°. The cation in 1 consists of di-μ-hydroxodichromium (III) units. The bridging OH groups lie on a twofold axis, which relates one end of the dimer to the other and gives rise to a rigorously planar Cr₂O₂ bridging unit. The Cr?Cr separation is 3.122 (1) Å and the average bridging Cr-O-Cr angle is 104.6 (4)°. The complex [(cyclam)Cr(SO₄)]₂ (ClO₄) · H₂O (5) crystallizes in the monoclinic space group P2₁/c with two binuclear formula units in a cell of dimensions a = 9.516 (2), b = 13.263 (3), c = 14.870 (3) Å, and β = 104.08 (3)°. This cation consists of bis-μ-sulfato-di-chromium (III) units, in which the two chromium centers are bridged by two bridging sulfate groups leading to an eight-membered {Cr-O-S-O}₂ bridging framework. Both dimers exhibit antiferromagnetic interactions, with J = 27.7 cm⁻¹ for complex 1 and J = 4.7 cm⁻¹ for complex 5. The EPR spectrum of the complex 1 has been simulated, demonstrating that the spectrum almost entirely originates from the quintet state, while a few lines can be attributed as triplet and septet transitions.     

Kinetic study of dissociation of Eu(III) complex with H8dotp (H8dotp = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylphosphonic acid))

The dissociation kinetics of the europium(III) complex with H₈dotp ligand was studied by means of molecular absorption spectroscopy in UV region at ionic strength 3.0 mol dm⁻³ (Na,H)ClO₄ and in temperature region 25-60 °C. Time-resolved laser-induced fluorescence spectroscopy (TRLIFS) was employed in order to determine the number of water molecules in the first coordination sphere of the europium(III) reaction intermediates and the final products. This technique was also utilized to deduce the composition of reaction intermediates in course of dissociation reaction simultaneously with calculation of rate constants and it demonstrates the elucidation of intimate reaction mechanism. The thermodynamic parameters for the formation of kinetic intermediate (ΔH⁰ = 11 ± 3 kJ mol⁻¹, ΔS⁰ = 41 ± 11 J K⁻¹ mol⁻¹) and the activation parameters (E_a = 69 ± 8 kJ mol⁻¹, ΔH^≠ = 67 ± 8 kJ mol⁻¹, ΔS^≠ = −83 ± 24 J K⁻¹ mol⁻¹) for the rate-determining step describing the complex dissociation were determined. The mechanism of proton-assisted reaction was proposed on the basis of the experimental data.     

Platinum (II) and palladium (II) 1,3,5-triaza-7-phosphaadamantane (PTA) complexes as intramolecular hydroamination catalysts in aqueous and organic media

Complexes of the general formula cis-[MX₂(PTA)₂] (M = Pd, Pt; X = Cl, Br, I; PTA = 1,3,5-triaza-7-phosphaadamantane) were used to study the catalytic intramolecular hydroamination/cyclization of 4-pentyn-1-amine into 2-methyl-pyrroline in water, methanol, and dimethyl sulfoxide (DMSO). Kinetic data were measured via ¹H NMR under homogeneous conditions at 50 °C and showed the following trends in rate: (i) Fastest rates were observed in D₂O. (ii) The Pd complexes of this study produced faster rates than the Pt complexes. (iii) The identity of the halide had no effect on the catalytic rate. Cyclization by the catalytic precursor cis-[PdCl₂(PTA)₂] (4) in D₂O was zero-order in substrate and first-order in metal complex with ΔH^‡ = 20.0 ± 2.1 kcal/mol, ΔS^‡ = −7.4 ± 6.3 cal/mol K, and E_a = 20.6 ± 2.1 kcal/mol. The acetylide complex, trans-[Pt(CC(CH₂)₃NH₂)₂(PTA)₂] (6) precipitated from a catalytic mixture involving cis-[PtBr₂(PTA)₂] (2). Spectroscopic and kinetic studies indicated that 6 and its cis analog, 7, were the predominant species in solution and that they were both active catalysts for the cyclization reaction. These data, in conjunction with the rate trends, indicated that the mechanism of the Pd(II) and Pt(II) catalyzed hydroamination of terminal alkynylamines in aqueous solution followed a unique mechanism with cyclization of an acetylenic-amine ligand being rate determining.     

Complex formation between protactinium(V) and sulfate ions at 10 and 60 °C

Protactinium complexation with sulfate ions was studied with the element at tracer scale (C_Pa ∼ 10⁻¹² M) by solvent extraction method. The involved aqueous system was Pa(V)/H₂O/HClO₄/Na₂SO₄/NaClO₄ at 10 and 60 °C. The extraction experiments were conducted using the chelating agent thenoyltrifluoroacetone (TTA) in toluene. For both values of temperature, a systematic study was performed in order to determine the formation constants (β₁, β₂ and β₃) of sulfate complexes of Pa(V) at different ionic strength. For each temperature, the extrapolation of these constants to zero ionic strength was performed using the Specific Interaction Theory, leading to values of 2.8 ± 0.5, 6.5 ± 0.5, 7.8 ± 0.5 at 10 °C and 4.3 ± 0.3, 8.4 ± 1.3, 9.6 ± 0.4 at 60 °C. Interaction coefficients involving the sulfate complexes of protactinium(V) were also derived.     

Formation of the nanostructure on a silica surface as mercury(II) ions adsorption sites

The present work investigates the adsorptive interactions of Hg(II) ions with hydroxylated silica, aminopropylsilica and silica chemically modified by β-cyclodextrin in aqueous medium. Batch adsorption studies were carried out with various agitation time and mercury(II) concentration. The maximum adsorption was observed within 15-30 min of agitation. The kinetics of the interactions, tested with model of Lagergren for pseudo-first and pseudo-second order equations, showed better agreement with first order kinetics (k₁ = 3.4 ± 0.2 to 5.9 ± 0.3 min⁻¹). The adsorption data gave good fits with Langmuir isotherms. The results have shown that β-cyclodextrin-containing adsorbent has the largest adsorption specificity to Hg(II) : K_L = 14 400 ± 700 L/mg. “β-Cyclodextrin-” inclusion complexes with ratio 1:1 and super molecules with composition С₄₂H₇₀O₃₅ · 3Hg(NO₃)₂ are formed on the surface of β-cyclodextrin-containing silica.     

Praseodymium (III) complexes with 1,10-phenanthroline and cyanamide derivatives as N-donor ligands

The molecular structure of praseodymium (III) complex with 1,10-phenanthroline (phen), [Pr(phen)₂Cl₃·OH₂] (1) was determined by single-crystal X-ray diffraction. Crystal data: crystal system, triclinic, space group P and Z = 2, a = 7.1110(7) ?, b = 10.1716(10) ?, c = 17.2367(18) ?, α = 80.922(5)°, β = 78.759(5)°, γ = 70.151(5)°, R₁ = 0.036; wR₂ = 0.076 for all data. Treatment of aqueous solution of [Pr(phen)₂Cl₃·OH₂] (1) with thallium phenylcyanamide salts yield [Pr(phen)₂(L)₃] (L = pcyd (2), 2-Clpcyd (3), 2,3,5-Cl₃pcyd (4), 2,3,4,5-Cl₄pcyd (5)). Four new praseodymium (III) complexes have been characterized by IR, UV-Vis and ¹H NMR spectroscopy as well as elemental analysis. The ¹H NMR spectra of these complexes show broadening of ligand protons attributed to coordination of paramagnetic center.     

An in vivo microdialysis coupled with liquid chromatography/tandem mass spectrometry study of cortisol metabolism in monkey adipose tissue

It is postulated that elevated tissue concentrations of cortisol may be associated with the development of metabolic syndrome, obesity, and type 2 diabetes. The 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) enzyme regenerates cortisol from inactive cortisone in tissues such as liver and adipose. To better understand the pivotal role of 11β-HSD1 in disease development, an in vivo microdialysis assay coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis using stable isotope-labeled (SIL) cortisone as a substrate was developed. This assay overcomes the limitations of existing methodologies that suffer from radioactivity exposure and analytical assay sensitivity and specificity concerns. Analyte extraction efficiencies (E_d) were evaluated by retrodialysis. The conversion of SIL-cortisone to SIL-cortisol in rhesus monkey adipose tissue was studied. Solutions containing 100, 500, and 1000 ng/mL SIL-cortisone were locally delivered through an implanted 30-mm microdialysis probe in adipose tissue. At the delivery rate of 1.0 and 0.5 μL/min, E_d values for SIL-cortisone were between 58.7 ± 5.6% (n = 4) and 72.7 ± 1.3% (n = 4), whereas at 0.3 μL/min E_d reached nearly 100%. The presence of 11β-HSD1 activities in adipose tissue was demonstrated by production of SIL-cortisol during SIL-cortisone infusion. This methodology could be applied to cortisol metabolism studies in tissues of other mammalian species.