Kinetic study of the protonations and substitutions of different cobalt(III)–nta complexes

The behaviour of the Cobalt(III)–nta (nta = nitrilotriacetate) system in an acidic medium was investigated. The acid dissociation constant, pK _a1, of [(nta)(H₂O)Co(-OH)Co(H₂O)(nta)]^– was determined as 3.09(3) and the pK _a of the cis-[Co(nta)(H₂O)₂]/[Co(nta)(H₂O)(OH)]^– equilibrium was determined as 6.71(1). cis-[Co(nta)(H₂O)₂] undergoes ring-opening upon acidification below pH = 2.0. The formation of [Co( ³-nta)(H₂O)₃]⁺ was also studied. The substitutions between cis-[Co(nta)(H₂O)₂] and NCS^– ions were investigated in the pH = 2–7 ranges. [Co(nta) (H₂O)(OH)]^– reacts ca. 70 times faster at 24.7 °C with NCS^– ions than cis-[Co(nta)(H₂O)₂], indicating a cis-labilising effect of the OH^– ligand.     

The development of a gas chromatographic–mass spectrometric analytical procedure for the determination of lipids,proteins and resins in the same paint micro-sample avoiding interferences from inorganic media

This paper presents a GC–MS analytical procedure for determining proteinaceous materials, glycerolipids, natural waxes and terpenoid resins in the same paint micro-sample. The procedure is also reliable when high amounts of interfering inorganic pigments, dryers and charges are present. The characterisation of proteinaceous binders in a paint sample can be subject to analytical interferences by inorganic materials. Such materials may form complexes with functional groups of proteins, thus preventing their efficient derivatisation, which is necessary prior to GC analysis. For this reason an analytical procedure has been developed based on two extractions and a clean-up step, in order to obtain two fractions: a lipid-resinous fraction and a proteinaceous fraction. The lipid-resinous fraction is subjected to salification/saponification assisted by microwaves, followed by acidification, extraction, derivatisation and GC–MS analysis. The proteinaceous fraction is analysed by GC–MS after hydrolysis and derivatisation of the freed amino acids. The desalting step is applied before the hydrolysis, and is based on the use of the monolithic sorbent tip technology with a C4 stationary phase. Reference paint replicas of egg, casein and animal glue were prepared with and without several metals containing pigments, and used to develop and validate the analytical procedure. The procedure proved to be efficient in desalting the proteinaceous materials both from cations and anions. Although non quantitative, it is reliable in the analysis of samples whose content of extractable proteins is <1 μg, thus showing it to be suitable for the characterisation of paint samples. An example of how the analytical procedure was used to characterise a sample from a 15th century panel painting is also discussed.     

Investigation of topology of intermolecular interactions in the benzene–acetylene co-crystal by different theoretical methods

Crystal structure of benzene–acetylene co-crystal was analysed based on calculated energies of intermolecular interactions between basic molecules located in asymmetric part of unit cell and their neighbours belonging to their first coordination sphere. It is demonstrated that the basic structural motif of the crystal is represented by infinite chains formed by the hydrogen-bonded benzene and acetylene molecules. Energy of interaction of the basic pair of molecules to neighbours within the chain is 2.2 times higher than the energy of interactions with molecules of any neighbouring chain. This ratio almost does not depend on method of calculation of interaction energy. Also, results of calculations were compared with analysis of topology of electron density distribution in crystal. The possibility to find the basic structural motif of the crystal based on properties of intermolecular bond critical points is demonstrated.     

Correlation of the extraction constants of the system Cd(II)–H3PO4/Cyanex 302–kerosene at different ionic strengths

Bromley's theory for calculating activity coefficients in order to correlate the values of cadmium extraction constant by Cyanex 302 from phosphoric acid solutions at different ionic strengths has been applied. A chemical model for the aqueous phase including the species H₃PO₄, H₂PO₄⁻, H₅P₂O₈⁻, H₆P₂O₈, CdHPO₄ and CdH₂PO₄⁺ has been considered. The increase observed for the extraction constant value when increasing the phosphoric acid concentration is probably due to the significant increase of the cadmium activity coefficient. A reaction extraction including water as a component has been proposed, and the value of the thermodynamic extraction constant of log K⁰=7.02 for the formation of CdR₂(HR) species, HR being the major component of Cyanex 302, has been obtained.     

Electrochemical study of the thermodynamic properties of matildite (β-AgBiS2) in different temperature and compositional ranges

Thermodynamic properties of matildite (β-AgBiS₂) in equilibrium with sulfur and bismuth have been studied by an EMF method, using the fast Ag⁺ ion-conducting solid electrolytes AgI and RbAg₄I₅. The ternary phases were synthesized from the pure binary compounds. Properties of the electrolytes used have been reviewed, and their usage as pure conductors of Ag⁺ ions in the temperature ranges of the electrochemical cells employed was well defined. The EMF measurements were carried out using the solid-state electrochemical cells Pt(?)|Ag|RbAg₄I₅|β‐AgBiS₂?+?AgBi₃S₅?+?S|Pt(+) and Pt(?)|Ag|AgI|β‐AgBiS₂?+?AgBi₃S₅?+?Bi|C|Pt(+), in the temperature range 325–464 K. Based on the obtained results, thermodynamic functions for the formation of matildite (β-AgBiS₂) at sulfur and bismuth saturation have been determined. The obtained experimental values have been compared with the available literature values. New experimentally determined thermodynamic properties of the bismuth-saturated matildite (β-AgBi_1?+?x S₂) and sulfur-saturated matildite (β-AgBiS_2?+?y ) were generated and analyzed in detail.     

Novel application of liquid chromatography/mass spectrometry for the characterization of drying oils in art: Elucidation on the composition of original paint materials used by Edvard Munch (1863–1944)

Modern oil paints, introduced at the beginning of the 20th century, differ from those classically used in antiquity in their chemical and compositional features. The main ingredients were still traditional drying oils, often used in mixtures with less expensive oils and added with several classes of additives. Consequently, detailed lipid profiling, together with the study of lipid degradation processes, is essential for the knowledge and the conservation of paint materials used in modern and contemporary art.     

The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Natural radioactivity in rocks of the Modane–Aussois region (SE France)

The activity concentrations of ⁴⁰K, ²³²Th, and ²³⁸U in the characteristic rocks of the Modane-Aussois region (Western Alps, France) were determined using an HPGe gamma-ray spectrometry system. The activity concentrations of ⁴⁰K varied from 18 Bqkg⁻¹ (limestone dolomite) to 392 Bqkg⁻¹ (calcschist), while those of ²³²Th varied from 0.7 Bqkg⁻¹ (limestone dolomite) to 18 Bqkg⁻¹ (calcschist). The activities associated with ²³⁸U ranged from 9 (quartzite) to 29 Bqkg⁻¹ (dolomite). In the investigated rock samples, concentrations of ²³⁸U (ppm) and ⁴⁰K (%) had a strong negative correlation.     

Determination of the stability constants of Pb–(DIPSO)x–(OH)y and Pb–(AMPSO)x–(OH)y systems

In this work, complexation between lead ion and the ligands 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) and N-(1,1-dimethyl-2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid (AMPSO), which are commercial pH buffers, is presented. Both ligands form complexes with lead in their pH buffer range (between pH 6.5 and 8.5 for DIPSO and between pH 8.0 and 9.0 for AMPSO). The final models and the overall stability constants, which are reported here, were determined by direct current polarography and glass electrode potentiometry [only for the Pb–(DIPSO)_x–(OH)_y system] at 25.0 °C and 0.1 M KNO₃ ionic strength. For the Pb–(DIPSO)_x–(OH)_y system, the proposed final model contains PbL, PbL₂, PbL₂(OH), and PbL₂(OH)₂ with stability constants, as log β, of 3.4 ± 0.1, 6.35 ± 0.15, 12.8 ± 0.2, and 18.0 ± 0.3, respectively. For the Pb–(AMPSO)_x–(OH)_y system, the species observed are PbL, PbL(OH), and PbL(OH)₂ with stability constants, as log β, of 2.9 ± 0.5, 9.4 ± 0.1, and 14.5 ± 0.2, respectively. For AMPSO, the possible adsorption of the ligand at the mercury electrode surface was evaluated by alternating current polarography through calculation of the capacitance of the double layer.     

Catalytic Properties of Bulk (1–x)Ni–xW Alloys in the Decomposition of 1,2-Dichloroethane with the Production of Carbon Nanomaterials

Kinetics and Catalysis - This work was devoted to a search for effective catalysts for the processing of chlorine-substituted hydrocarbons to obtain carbon nanomaterials. A series of porous...     

Speciation in the Vanadium(III)–Carnosine System

Speciation in the aqueous V(III)–carnosine system has been determined from potentiometric and spectroscopic (UV-Vis absorption and CD) data. Application of the Hyperquad program to the experimental potentiometric data indicates that under our experimental conditions (I=0.5 mol⋅L⁻¹ NaClO₄, pH=2 to 6.5, and L/M>5) only ML₂H₄, ML₂H₃, ML₂H₂ and ML₂H form. These potentiometric results prove that stable complexes form and, with use of the spectroscopic methods, the binding sites are identified.     

Luminescence recognition of different organophosphorus pesticides by the luminescent Eu(III)–pyridine-2,6-dicarboxylic acid probe

Luminescence quenching of a novel long lived Eu(III)–pyridine-2,6-dicarboxylic acid probe of 1:2 stoichiometric ratio has been studied in 0.10 volume fraction ethanol–water mixture at pH 7.5 (HEPES buffer) in the presence of the organophosphorus pesticides chlorfenvinphos (P1), malathion (P2), azinphos (P3), and paraxon ethyl (P4). The luminescence intensity of Eu(III)–(PDCA)₂ probe decreases as the concentration of the pesticide increases. It was observed that the quenching due to P3 and P4 proceeds via both diffusional and static quenching processes. Direct methods for the determination of the pesticides under investigation have been developed using the luminescence quenching of Eu(III)–pyridine-2,6-dicarboxylic acid probe in solution. The linear range for determination of the selected pesticides is 1.0–35.0 μM. The detection limits were 0.24–0.55 μM for P3, P4, and P1 and 2.5 μM for P2, respectively. The binding constants (K), and thermodynamic parameters of the OPs with Eu(III)–(PDCA)₂ were evaluated. Positive and negative values of entropy (ΔS) and enthalpy (ΔH) changes for Eu(III)–(PDCA)₂–P1 ternary complex were calculated. As the waters in this study do not contain the above mentioned OPs over the limit detectable by the method, a recovery study was carried out after the addition of the adequate amounts of the organophosphorus pesticides under investigation.     

Spectrophotometric study of stability constants of cimetidine–Ni(II) complex at different temperatures

Cimetidine, a histamine H₂-receptor, has a structure which enables it to act as a chelating agent. The formation of nickel(II) complex with cimetidine has been studied spectrophotometrically at an absorption maximum of 622 nm at different temperatures. The data show that nickel(II) and cimetidine combine in the molar ratio of 1:2. The stability constants of the complex were calculated to be 1.40–2.4 × 10⁸ by continuous variation method and 1.24–2.4 × 10⁸ by mole ratio method at 25 and 40 °C, respectively. The immediately formed complex shows stability with respect to time and temperature.     

QSAR for the Organophosphate-Induced Inhibition and ‚Aging‚ of the Enzyme Neuropathy Target Esterase (NTE)

Abstract

QSAR was devised for the neuropathy potency of various organophosphate (OP) compounds. The neuropathy-target-esterase (NTE) inhibition data were either obtained from the literature for a number of OP compounds or were determined experimentally for methamidophos, acephate, coumaphos and EPN. Aging Index that determined whether or not an OP would age NTE, correlated with molecular depth (MD) and the index density dipole-moment (density? Ω) (Eq. (1)). The t_1/2 values that represented the time (min) during which 50% of the OP-inhibited brain NTE undergoes ?aging‘, correlated with the topological indices Dif₃ and 1/Dif₄ (Eq. (2)). Log₁₀I₅₀ for AChE that determined the OP concentration causing 50% inhibition in AChE activity, correlated with E_bond and Charge^?1 (Eq. 3)). Log₁₀I₅₀ for NTE correlated with 1 HS² and H-Bonding (Eq. (4)). The (Log₁₀I₅₀NTE)/(Log₁₀I₅₀AChE) ratio that determined an OPs neuropathy potential relative to its cholinergic toxicity potential, correlated with log P and Log₁₀Polarity (Eq. (6)). Equation (3) accurately predicted AChE inhibition by methamidophos, coumaphos and EPN, but not by acephate. Equations (1), (2), (4)–(6), accurately predicted their respective biological indices. Therefore, it is proposed that the QSAR models developed in this study may accurately predict the neuropathy potential of OP compounds. The only exception is Eq. (3) that did not accurately predict the acephate-induced inhibition of AChE, possibly because acephate and other OPs inhibit the enzyme by distinct mechanisms.     

Effect of the Composition of Ethanol–Water Mixtures on the Properties of Oxide (Zn-Zr-Si) and Zeolitic (Ta/SiBEA) Catalysts in the Production of 1,3-Butadiene

Theoretical and Experimental Chemistry - The reasons for the deactivating effect of water on the conversion of ethanol to 1,3-butadiene in the presence of Zn-Zr(La)-Si oxide and Cu(Ag, Zn)/Ta/SiBEA...     

Kinetic Determination of Iodide Traces Based on the Manganese(III) Metaphosphate–Arsenic(III) Reaction in the Presence of Orthophosphoric Acid

The kinetics of the iodide-catalyzed Mn(III) metaphosphate–As(III) reaction was studied in the presence of orthophosphoric acid. The reaction rate was followed spectrophotometrically at 516nm. It was established that orthophosphoric acid increased the reaction rate and that the extent of the non-catalytic reaction was extremely small. A kinetic equation was postulated and the apparent rate constant calculated. The dependence of the reaction rate on temperature was investigated and the energy of activation and other kinetic parameters determined. Iodide was determined under the optimal experimental conditions in the range 0.6–2.5ng·mL^–1 with a relative standard deviation of up to 6.7% and a detection limit of 0.12ngmL^–1. The effect of foreign ions on the accuracy of the determinations was also investigated.