Coordination Features of a Polyaza-Bipyridine-Macrocyclic Ligand toward Co(II) and Cd(II) in Water and Dimethylsulfoxide

The coordination features of a polyaza macrocycle, containing the diverse bipyridine unit 4,4′-(2,5,6,11,14-pentaaza[15]-[15](2,2′)-bipyridylophane (L3), with Co(II) and Cd(II) have been studied in aqueous solution and in the aprotic solvent dimethylsulfoxide (DMSO). The study was carried out at 298 K by means of potentiometric, spectrophotometric and calorimetric techniques. The formation of the dinuclear species M₂ L3 is observed for Co(II) both in water and in DMSO, whereas Cd(II) is able to form this type of dinuclear complex only in DMSO. The FT-IR spectra of the mononuclear species ML3, formed in both solvents, provide evidence that the rigid structure of the polyaminic chain prevents metal ions from being coordinated by all of the nitrogens of the macrocyclic cavity, in good agreement with the behavior suggested by the thermodynamic parameters. The results are compared with those for the complexation of Co(II) and Cd(II) with similar polyazamacrocycles containing a bipyridine unit directly inside the cavity. Semi-empirical calculations were also performed to obtain structural information.     

Spectral and Mechanistic Investigation of the Osmium(VIII) Catalyzed Oxidation of Diclofenac Sodium by the Copper(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of the osmium(VIII) (Os(VIII)) catalyzed oxidation of diclofenac sodium (DFS) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium has been studied spectrophotometrically at a constant ionic strength of 1.0 mol⋅dm⁻³. The reaction showed first order kinetics in [Os(VIII)] and [DPC] and less than unit order with respect to [DFS] and [alkali]. The rate decreased with increase in [periodate]. The reaction between DFS and DPC in alkaline medium exhibits 1:2 [DFS]:[DPC] stoichiometry. However, the order in [DFS] and [OH⁻] changes from first order to zero order as their concentration increases. Changes in the ionic strength and dielectric constant did not affect the rate of reaction. The oxidation products were identified by LC-ESI-MS, NMR, and IR spectroscopic studies. A possible mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The catalytic constant (K _C) was also calculated for Os(VIII) catalysis at the studied temperatures. From plots of log ₁₀ K _C versus 1/T, values of activation parameters have been evaluated with respect to the catalytic reaction. The activation parameters with respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined. The active osmium(VIII) and copper(III) periodate species have been identified.     

Kinetic Investigation of the Electrochemical Oxidation of Bis(benzene)chromium(0) in Diethyl ketone/N,N-Dimethylformamide

The cyclic voltametric technique utilizing a platinum working electrode was applied for the investigation of the electrochemical oxidation of bis(benzene)chromium(0), (C₆H₆)₂Cr to bis(benzene)chromium(I), (C₆H₆)₂Cr⁺ in diethyl ketone (DEK), N,N-dimethylformamide (DMF), and DEK/DMF binary mixtures containing n-tetrabutylammonium hexafluorophosphate (TBAPF₆) as the supporting electrolyte at T=298.15 K. The half-wave potentials (E _1/2) of the (C₆H₆)₂Cr^+/0 redox couple in DEK, DMF and DEK/DMF binary mixtures, were determined. The variation of E _1/2 with the solvent composition was found to be almost linear. The E _1/2 results were analyzed in terms of the electron-donating power of the solvent medium. The diffusion coefficients, D, were calculated using the Randles-Sevcik equation. The kinetics of the electrode reaction were investigated through the determination of the heterogeneous electron-transfer rate constants, k _s, according to the electrochemical rate equation proposed by Nicholson. Furthermore, the activation Gibbs energies for the electron-transfer process (ΔG ^≠) were also calculated. The results indicate that the redox couple (C₆H₆)₂Cr^+/0 exhibits an electrochemically reversible and diffusion-controlled process in all the investigated solvent media.     

Fluorescence Quenching of Tris(2,2′-bipyridine)Ruthenium(II) Dichloride by Certain Organic Dyes

Fluorescence quenching of [Ru(bpy)₃]²⁺ by a series of organic dyes has been investigated by using the steady state fluorescence technique in aqueous medium. The dyes used are anthraquinone dyes: uniblue, acid blue 129, alizarin, alizarin red S and the azo dyes: congo red, sunset yellow, methyl orange, tartrazine, acid orange 63, methyl red and erichrome black T. The quenching of [Ru(bpy)₃]²⁺ was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear indicating dynamic quenching. The quenching rate constants (k _q) were calculated from the fluorescence data. The mechanism of quenching was discussed on the basis of the quenching rate constants as well as the reduction potential of dyes. The electron transfer mechanism has been proved by the calculation of Gibbs energy changes (ΔG _et) by applying the Rehm-Weller equation.     

Self-assembly snapshots of a 2 × 2 copper(I) grid

Self-assembled 2 × 2 grids have been characterised as high-fidelity species produced when the correct stoichiometric ratios are met, but rarely are the individual steps leading to and from their formation characterised. Here, we present such a study using equilibrium-restricted factor analysis to model a set of UV–vis spectra starting from a bis-bidentate ligand to the assembly of a 2 × 2 grid complex upon titration with 1 equiv. of [Cu(MeCN)₄](PF₆) and to disassembly upon further titration. Intermediate species [CuL₂]⁺, [Cu₂L₃]²⁺, [Cu₃L₂]³⁺ and [Cu₂L]²⁺ are evidenced along the assembly and disassembly pathways. Complementary ¹H NMR titrations are consistent with the rich set of complexes and equilibria involved. Given the nature of the assembly process, the assembly is entropy driven and likely enthalpy driven as well. The disassembly process is both enthalpy and entropy driven according to the standard free energy values derived from the modelling of the spectrophotometric titration data.     

Complexation of Sc(III), Ga(III), In(III) and Ln(III) with Eriochrome Red B

Cyclic linear-sweep voltammetry was used to study the complexation of Sc(III), Ga(III), In(III) and Ln(III) with eriochrome red B (ERB). It was established that all metal ions investigated form complex compounds with azodye having a mole ratio, M(III):ERB = 1:2. The hydroxo forms of M(III) ions, which take part in interaction with ERB, were determined by the Nazarenko method. The stability constants for the formation of these chelates are nearly the same. It was shown that the reduction of the ligand in the complex does not only depend on the peculiarities of complexation, but the processes occurring in pre-electrode layer also influence it.     

The Interaction of Arsenazo III with Nd(III)—A Chemometric and Metrological Analysis

Interactions of Arsenazo III with Nd(III) in aqueous solutions (pH range 3 to 4) were studied using a spectrophotometric method. Some discrepancies are present in literature concerning the concentrations of the prevailing species and their composition. Threshold bootstrap computer-assisted target factor analysis (TB CAT) was applied to the evaluation of UV-VIS spectra of Arsenazo III in aqueous solutions containing varying amounts of neodymium(III) ions. The thus obtained experimental data are interpreted with consideration of the measurement uncertainties affecting this system. Within the limits of resolution of the experimental method, two complexes NdAazo and Nd(Aazo)₂ were indicated in the studied pH range. The values of formation constants for log ₁₀ β ₁₁ fall in the range 4.9 to 6.3 and for log ₁₀ β ₁₂ fall between 10.5 and 12.1.     

Thermodynamic Features of the Complexation of Neodymium(III) and Americium(III) by Lactate in Trifluoromethanesulfonate Media

The protonation of lactate has been studied in a variety of electrolyte solutions using microcalorimetry to reveal a distinct medium influence imposed on the thermochemistry of the equilibrium. The thermochemistry of lactate protonation, when studied directly in 1.0 mol⋅L⁻¹ sodium lactate, agreed well with the studies performed in trifluoromethanesulfonate (triflate). This thermodynamic agreement suggests that the physical chemistry of lactate in the solutions applicable to the TALSPEAK process—a solvent extraction method for separating trivalent actinides from trivalent lanthanides within the scope of used nuclear fuel processing efforts—may be simulated in triflate solutions. Potentiometry, spectrophotometry and microcalorimetry have been subsequently used to study the thermodynamic features of neodymium and americium complexation by lactate using triflate as a strong background electrolyte. Three successive mononuclear lactate complexes were identified for Nd(III) and Am(III). The stability constants for neodymium, β ₁₀₁=2.60±0.01, β ₁₀₂=4.66±0.02 and β ₁₀₃=5.6±0.1, and for americium, β ₁₀₁=2.60±0.06, β ₁₀₂=4.7±0.1 and β ₁₀₃=6.2±0.2, were found to closely agree with the thermodynamic studies reported in sodium perchlorate solutions. Consequently, the thermodynamic medium effect, imposed on the TALSPEAK-related solution equilibria by the presence of strong background electrolytes such as NaClO₄ and NaNO₃, does not significantly impact the speciation in solution.     

Interaction between Glyoxal-bis-(2-hydroxyanil) and Bovine Serum Albumin in Solution

The interaction between glyoxal-bis-(2-hydroxyanil) (GBH) and bovine serum albumin (BSA) was studied by spectroscopic methods including fluorescence spectroscopy, circular dichroism (CD) and UV–visible absorption spectra. The mechanism for quenching the fluorescence of BSA by GBH is discussed. The number of binding sites n and observed binding constant K _b were measured by the fluorescence quenching method. The thermodynamic parameters ΔH ^θ , ΔG ^θ , and ΔS ^θ were calculated at different temperatures and the results indicate that hydrogen bonding and van der Waals forces played major roles in the reaction. The distance r between the donor (BSA) and acceptor (GBH) molecules was obtained according to Förster’s theory of non-radiation energy transfer. Synchronous fluorescence and three-dimensional fluorescence spectra were used to investigate the structural change of BSA molecules that occur upon addition of GBH, and these results indicate that the secondary structure of BSA molecules is changed by the presence of GBH.     

Adsorption of arsenic (V) from a water solution onto a surfactant-modified zeolite

In this study a surfactant-modified zeolite (SMZ) was prepared by adsorbing the cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide on a clinoptilolite. The adsorption of the surfactant modified the surface properties of the clinoptilolite and enhanced the anionic capacity of the SMZ. The adsorption equilibrium data of As(V) from the water solution on the SMZ were obtained in a batch adsorber, and the Langmuir isotherm matched the data reasonably well. The As(V) adsorption capacity of the SMZ was 12.5 times greater than that of the clinoptilolite. The adsorption of As(V) on SMZ was mainly due to the interactions between the anionic sites of the SMZ and the As(V) anions in water solution. The adsorption capacity of the SMZ was dependent on the solution pH. The adsorption capacity was increased and decreased by augmenting the pH from 5 to 7 and from 7 to 12, respectively. This unusual behavior was due to the fact that the affinity of the As(V) for the SMZ was dependent on the As(V) species that were present in solution. The adsorption capacity of the SMZ was slightly favored by decreasing the temperature from 25 to 15 °C. The heat of adsorption was estimated to be ΔH _ads=−46.82 KJ/mol, indicating that the adsorption was exothermic and the As(V) was chemisorbed on the SMZ.     

Ruthenium(III) Catalyzed Oxidative Degradation of Amitriptyline-A Tricyclic Antidepressant Drug by Permanganate in Aqueous Acidic Medium

The oxidation of amitriptyline by potassium permanganate has been investigated spectrophotometrically in the presence of ruthenium(III) as catalyst in aqueous acidic medium at a constant ionic strength of 0.20 mol⋅dm⁻³. The stoichiometry was found to be 1:1 in terms of the mole ratio of amitriptyline and permanganate ions consumed. The order of the reaction with respect to manganese(VII) and ruthenium(III) concentration was unity while the order with respect to amitriptyline was less than unity over the concentration range studied. The rate increased with an increase in acid concentration. The reaction rates revealed that the Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction. The oxidation products were identified by spectral analysis. A tentative mechanism consistent with the kinetics has been proposed. The reaction constants involved in the different steps of the reaction mechanism were calculated. Kinetic experiments suggest that HMnO₄ is the reactive permanganate species and [Ru(H₂O)₆]³⁺ is the reactive Ru(III) species.     

Synthesis, Solution Equilibria and Antibacterial Activity of Co(II) with 2-(Aminomethyl)-Benzimidazole and Dicarboxylic Acids

Formation equilibria of cobalt(II) complexes of 2-(aminomethyl)-benzimidazole (AMBI) and the ternary complexes Co(AMBI)L (L = aliphatic or aromatic dicarboxylic acids) were investigated in aqueous solutions at 25?°C and 0.1 mol?dm^?3 ionic strength. Stoichiometry and stability constants are reported for the complexes formed. The speciation of the complexes was resolved. Values of $\log_{10}\ (K_{\mathrm{Co(AMBI)L}}^{\mathrm{Co(AMBI)}})$ and Δlog?₁₀ K are calculated and discussed. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. The effect of temperature on the dissociation constant of AMBI, CBDCA, and the formation constant of Co(AMBI) and Co(AMBI)-CBDCA complexes was studied and the thermodynamic parameters were calculated. Formation of the metal complexes has been found to be spontaneous, exothermic and entropically favorable. The solid complexes of [Co(AMBI)L] (L = oxalic acid, 1,1-cyclobutanedicarboxylic acid (CBDCAH₂) and malonic acid) have been synthesized and characterized by elemental analysis, infrared, spectra, magnetic and conductance measurements. Electronic spectra and μ _eff values suggest a tetrahedral geometry for Co(II)-complexes. The isolated metal chelates have been screened for their antibacterial activities and the complexes show a significant antibacterial activity against Pseudomonas fluorescence (Gram ?ve) and Bacillus subtilis (Gram +ve). The activity increases at higher concentration of the compounds.     

Hetero-heptanuclear (Fe–Na) complexes of salicylaldehydes: crystal and molecular structure of [Fe2(3-OCH3-salo)8 · Νa5] · 3OH · 8H2Ο

The reaction of Fe(III) with the substituted salicylaldehydes [X-saloH, where X = 3-OCH₃ (L ¹ ), 5-CH₃ (L ² ), 5-Cl (L ³ ), 5-NO₂ (L ⁴ )] led to the formation of four new iron(III) hetero-heptanuclear complexes (Fe–Na) under the general formula [Fe₂(X-salo)₈Νa₅] · 3OH · zH₂Ο. The two different coordination modes of the ligand, as well as the geometry around the metal ions were deduced by X-ray structure analysis of compound 1, [Fe₂(3-OCH₃-salo)₈Νa₅] · 3OH · 8H₂Ο. The complexes have also been characterized by physicochemical and spectroscopic (IR, UV–Vis, Mössbauer) methods.     

Distorted colloidal crystal of similar-sized aggregates (1.5 μm in diameter) of nano-sized diamond particles (4 nm in diameter)

Distorted colloidal crystal suspension of similar-sized aggregates of diamonds (1.5 μm in diameter) was obtained by the deionization of aqueous suspension of the pre-particles of diamond, 4 nm in diameter. The stability, characteristics, and the rigidity of the crystal-like suspensions were studied. The main cause for the formation of the similar-sized aggregates is deduced to be the cooperation between the van de Waals inter-particle attraction and the repulsion induced by the vigorous thermal motion of the pre-particles. The rigidity was evaluated from the microscopic observation in the sedimentation equilibrium. Fluctuation parameters of the distorted colloidal crystals estimated from the rigidities were between 0.03 and 0.06, which are quite similar to those of typical colloidal crystals and solids of hard spheres.     

Stability and Coordination Mode of Complexes of Polyphosphates and Polymetaphosphates with Copper(II) Ions in Aqueous Solution—Potentiometric,Spectral and Theoretical Studies

Complexes of copper(II) with a number of polyphosphate and polymetaphosphate anions have been studied in aqueous solutions by potentiometric, spectroscopic and theoretical methods. Stability constants of the complexes have been determined as well as their coordination modes. Results of the equilibrium studies provided evidence for the formation of ML, MHL and ML(OH) _x type complexes with the ligands studied. The length of the polyphosphate chain was found to affect the oxygen atom charge that is reflected in the stability constants of the ML type complexes. Moreover, the stability of the complex is also influenced by the spatial arrangement of the phosphate groups in phosphates and metaphosphates. The spectral parameters observed for certain complexes have permitted us to deduce the inner coordination sphere of the studied complexes.     

Aqueous Equilibrium and Solution Structural Studies of the Interaction of N,N′-bis(4-imidazolymethyl)etylenediamine with Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) Metal Ions

Divalent metal complexes of N,N′-bis(4-imidazolymethyl)etylenediamine (EMI) have been studied using potentiometric and spectroscopic techniques (UV-Vis and NMR methods) in aqueous 0.1 mol⋅L⁻¹ KCl supporting electrolyte at 25 °C. Final models and overall stability constants for the complexes of Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) have been established by potentiometry for all M(II)–EMI systems, except for Co(II)–EMI. The data revealed that EMI forms ML complexes with all M(II)–EMI systems, which is the dominant species over a wide range of pH except for the Ca(II)–EMI and Mg(II)–EMI systems. Formation of the MnHL complex was also found for Mn(II)–EMI solutions. In addition, the UV-Vis and ¹H NMR results allowed us establish the coordination modes for the metal complexes between EMI with Cd(II), Cu(II), Ni(II) and Zn(II).     

Drying dissipative structure of similar sized aggregates (1.5 μm in diameter) of nano-sized diamond particles (4 nm in diameter)

Macroscopic and microscopic drying patterns were observed on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous suspensions of similar sized aggregates of diamonds (CD1), which formed from the deionization of the pre-particles of diamond 4 nm in diameter. Two kinds of macroscopic patterns, i.e., outer and inner broad rings, and spoke lines were formed. Cooperative drying processes of the convection, sedimentation, and solidification were clarified. Microscopic drying patterns showing the formation of very large dendritic aggregates from the CD1 particles were observed only when the excess amount of sodium chloride higher than 2 mM coexisted in the initial suspensions before dryness and further initial CD1 concentration is lower than 0.17 wt%.     

Systematic trends in (0 0 1) surface ab initio calculations of ABO3 perovskites

By means of the hybrid exchange–correlation functionals, as it is implemented in the CRYSTAL computer code, ab initio calculations for main ABO₃ perovskite (0 0 1) surfaces, namely SrTiO₃, BaTiO₃, PbTiO₃, CaTiO₃, SrZrO₃, BaZrO₃, PbZrO₃ and CaZrO₃, were performed. For ABO₃ perovskite (0 0 1) surfaces, with a few exceptions, all atoms of the upper surface layer relax inward, all atoms of the second surface layer relax outward, and all third layer atoms, again, inward. The relaxation of (0 0 1) surface metal atoms for ABO₃ perovskite upper two surface layers for both AO and BO₂-terminations, in most cases, are considerably larger than that of oxygen atoms, what leads to a considerable rumpling of the outermost plane. The ABO₃ perovskite (0 0 1) surface energies always are smaller than the (0 1 1) and especially (1 1 1) surface energies. The ABO₃ perovskite AO and BO₂-terminated (0 0 1) surface band gaps always are reduced with respect to the bulk values. The B–O chemical bond population in ABO₃ perovskite bulk always are smaller than near the (0 0 1) and especially (0 1 1) surfaces.     

Buffer Standards for pH Measurement of N-(2-Hydroxyethyl)piperazine-N′-2-ethanesulfonic Acid (HEPES) for I=0.16 mol⋅kg−1 from 5 to 55 °C

The values of the second dissociation constant, pK ₂, of N-(2-hydroxyethyl) piperazine-N′-2-ethanesulfonic acid (HEPES) have been reported at twelve temperatures over the temperature range 5 to 55 °C, including 37 °C. This paper reports the results for the pa _H of eight isotonic saline buffer solutions with an I=0.16 mol⋅kg⁻¹ including compositions: (a) HEPES (0.01 mol⋅kg⁻¹) + NaHEPES (0.01 mol⋅kg⁻¹) + NaCl (0.15 mol⋅kg⁻¹); (b) HEPES (0.02 mol⋅kg⁻¹) + NaHEPES (0.02 mol⋅kg⁻¹) + NaCl (0.14 mol⋅kg⁻¹); (c) HEPES (0.03 mol⋅kg⁻¹) + NaHEPES (0.03 mol⋅kg⁻¹) + NaCl (0.13 mol⋅kg⁻¹); (d) HEPES (0.04 mol⋅kg⁻¹) + NaHEPES (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (e) HEPES (0.05 mol⋅kg⁻¹) + NaHEPES (0.05 mol⋅kg⁻¹) + NaCl (0.11 mol⋅kg⁻¹); (f) HEPES (0.06 mol⋅kg⁻¹) + NaHEPES (0.06 mol⋅kg⁻¹) + NaCl (0.10 mol⋅kg⁻¹); (g) HEPES (0.07 mol⋅kg⁻¹) + NaHEPES (0.07 mol⋅kg⁻¹) + NaCl (0.09 mol⋅kg⁻¹); and (h) HEPES (0.08 mol⋅kg⁻¹) + NaHEPES (0.08 mol⋅kg⁻¹) + NaCl (0.08 mol⋅kg⁻¹). Conventional pa _H values, for all eight buffer solutions from 5 to 55 °C, have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 °C have been determined based on the NBS/NIST standard between the physiological phosphate standard and four buffer solutions. These are recommended as pH standards for physiological fluids in the range of pH = 7.3 to 7.5 at I=0.16 mol⋅kg⁻¹.