Divalent transition metal ion mixed ligand complexes with aliphatic dicarboxylic acids and imidazoles

Summary Mixed ligand metal complexes of Co^II, Ni^II and Cu^II with dicarboxylic aliphatic acids, H₂L (succinic, malic and tartaric) as primary ligands and with imidazoles, L (imidazole and 2-methylimidazole) as secondary ligands were prepared and characterized. MLL₂ and ML₄ molecular formulae were suggested for these complexes were Formation constants of the different complexes were determined pH-metrically at T = 25 ± 0.1°C and = 0.1 mol dm^–3 (NaClO₄). The stability of the mixed ligand complexes increased as the effective basicity of the dicarboxylic aliphatic acid anion increased, namely, tartarate < malate < succinate acid.     

Voltammetric determination of mercury levels in tuna fish

Summary A reliable and rapid procedure for the determination of Hg in fish by differential pulse anodic-stripping voltammetry (DPASV) at the gold electrode has been developed for use in food control and marine ecotoxicology. Potentialities and performance are demonstrated by the investigation of tuna fish. Samples of 0.5–2.5 g are subjected to pressurized digestion with HNO₃/HClO₄ (71). The resulting analyte solution is irradiated in closed flasks with ultraviolet light in presence of H₂O₂ to decompose dissolved organic substances. This is followed by DPASV with two standard additions. The relative standard deviation for the lower g/g range is below 5%. Comparative determination by gas chromatography confirmed that in fish-muscle mercury exists almost completely in the form of toxic organomercurials, i. e. methyl- and dimethylmercury.

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Voltammetrische Bestimmung von Quecksilber in Thunfischen

Zusammenfassung Für die Lebensmittelkontrolle und marine Ökotoxikologie wurde eine neue spurenanalytische Alternative zur raschen und zuverlässigen Bestimmung des Quecksilbergehaltes in Fisch unter Einsatz der differentiellen Pulsinversvoltammetrie (DPIV) und Verwendung einer Goldscheibenelektrode entwickelt.Möglichkeiten und Leistungsfähigkeit der Methode werden durch die Untersuchung von Thunfisch demonstriert. Proben von 0,5 bis 2,5 g Frischgewicht werden zunächst einem Druckaufschluß mit HNO₃/HClO₄ (71) unterworfen. Die resultierende Analytlösung wird zum Abbau gelöster organischer Substanzen im geschlossenen Gefäß einer UV-Bestrahlung (70° C, 150 W Quecksilberlampe, 4 h) unter oxydierenden Bedingungen (H₂O₂) unterzogen. Anschließend erfolgt die voltammetrische Bestimmung mit DPIV unter Vornahme von zwei Eichzusätzen. Die relative Standardabweichung liegt im unteren mg/kg-Bereich unter 5%. Die Richtigkeit wurde durch Vergleichsbestimmung mit der Gaschromatographie getestet. Die Übereinstimmung der ermittelten Quecksilbergehalte bestätigt, daß im Muskelfleisch von Fisch das Quecksilber nahezu vollständig in toxischen organischen

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Taken in part from the Ph. D. Thesis of R. Ahmed. Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Complex series [Ru(tpy)(dpk)(X)]n+ (tpy = 2,2':6',2''-terpyridine; dpk = 2,2'-dipyridyl ketone; X = Cl-, CH3CN, NO2(-), NO+, NO*, NO-): substitution and electron transfer, structure, and spectroscopy

The complex framework [Ru(tpy)(dpk)]2+ has been used to study the generation and reactivity of the nitrosyl complex [Ru(tpy)(dpk)(NO)]3+ ([4]3+). Stepwise conversion of the chloro complex [Ru(tpy)(dpk)(Cl)]+ ([1]+) via [Ru(tpy)(dpk)(CH3CN)]2+ ([2]2+) and the nitro compound [Ru(tpy)(dpk)(NO2)]+ ([3]+) yielded [4]3+; all four complexes were structurally characterized as perchlorates. Electrochemical oxidation and reduction was investigated as a function of the monodentate ligand as was the IR and UV-vis spectroscopic response (absorption/emission). The kinetics of the conversion [4]3+/[3]+ in aqueous environment were also studied. Two-step reduction of [4]3+ was monitored via EPR, UV-vis, and IR (nu(NO), nu(CO)) spectroelectrochemistry to confirm the {RuNO}7 configuration of [4]2+ and to exhibit a relatively intense band at 505 nm for [4]+, attributed to a ligand-to-ligand transition originating from bound NO-.     

Anti-HIV Active Naphthyl Analogues of HEPT and DABO

Summary.  5-Isopropyl-6-naphthyl uracil and 5-isopropyl-6-naphthyl-2-thiouracil were alkylated to give N-1-(ethoxymethyl and methylthiomethyl) uracil and S²-cyclohexyl-thiouracil, respectively. 5-Ethyl-6-naphthyl uracil and 5-ethyl-6-naphthyl-2-thiouracil afforded N-1-(ethoxymethyl, methoxy-methyl, methylthiomethyl, acetoxyethoxy methyl and hydroxyethoxy methyl) uracil and S²-((2,2- diethoxyethyl), methoxycarbonylmethyl, ethoxycarbonylpropyl, methylthiomethyl, ethoxymethyl, methyl and cyclohexyl)-thiouracil upon alkylation. Received September 25, 2001. Accepted (revised) December 3, 2001     

Solvent extraction of trivalent lanthanide Pr(III), Ho(III) and Er(III) with N-benzoyl-N-phenylhydroxylamine

Extraction of Pr(III), Ho(III) and Er(III) has been studied in the pH range of 1–10 with N-benzoyl-N-phenylhydroxylamine (BPHA) in benzene. The separation was found to be quantitative in borate media from pH 7 to 10, at an ionic strength of 0.1M (H⁺, BO₃ ^3–). The stoichiometric composition of the complexes under the optimal conditions of shaking time, pH and reagent concentration was formulated using slope analysis and found to be M(BPHA)₃, where M=Pr(III), Ho(III) and Er(III). The effect of various masking agents shows that citrate, ascorbate, EDTA, oxalate, fluoride and phosphate form stable complexes with these rare earths as compared to BPHA. The decontamination factors for different cations with respect to these rare earths under the optimum conditions have been evaluated.     

Trioxatriangulenium (TOTA+) as a robust carbon-based Lewis acid in frustrated Lewis pair chemistry

We report the reactivity between the water stable Lewis acidic trioxatriangulenium ion (TOTA⁺) and a series of Lewis bases such as phosphines and N-heterocyclic carbene (NHC). The nature of the Lewis acid–base interaction was analyzed via variable temperature (VT) NMR spectroscopy, single-crystal X-ray diffraction, UV-visible spectroscopy, and DFT calculations. While small and strongly nucleophilic phosphines, such as PMe₃, led to the formation of a Lewis acid–base adduct, frustrated Lewis pairs (FLPs) were observed for sterically hindered bases such as P(^tBu)₃. The TOTA⁺–P(^tBu)₃ FLP was characterized as an encounter complex, and found to promote the heterolytic cleavage of disulfide bonds, formaldehyde fixation, dehydrogenation of 1,4-cyclohexadiene, heterolytic cleavage of the C–Br bonds, and interception of Staudinger reaction intermediates. Moreover, TOTA⁺ and NHC were found to first undergo single-electron transfer (SET) to form [TOTA]·[NHC]˙⁺, which was confirmed via electron paramagnetic resonance (EPR) spectroscopy, and subsequently form a [TOTA–NHC]⁺ adduct or a mixture of products depending the reaction conditions used.

Frustration at carbon! Herein, we present a frustrated Lewis pair system derived from a water stable carbon-based Lewis acid, trioxatriangulene (TOTA⁺), and a variety of Lewis bases, which successfully promotes bond cleavage and molecule fixation.     

Ruthenium(II) dendrimers containing carbazole-based chromophores as branches

Three new luminescent and redox-active Ru(II) complexes containing novel dendritic polypyridine ligands have been synthesized, and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox behavior have been investigated. The dendritic ligands are made of 1,10-phenanthroline coordinating subunits and of carbazole groups as branching sites. The first and second generation species of this novel class of dendritic ligands (L1 and L2, respectively; see Figure 1 for their structural formulas) have been prepared and employed. The metal dendrimers investigated are [Ru(bpy)(2)(L1)](2+) (1; bpy = 2,2'-bipyridine), [Ru(bpy)(2)(L2)](2+) (2), and [Ru(L1)(3)](2+) (3; see Figure 2). For the sake of completeness and comparison purposes, also the absorption spectra, redox behavior, and luminescence properties of L1 and L2 have been studied, together with the properties of 3,6-di(tert-butyl)carbazole (L0) and [Ru(bpy)(2)(phen)](2+) (4, phen = 1,10-phenanthroline). The absorption spectra of the free dendritic ligands show features which can be assigned to the various subunits (i.e., carbazole and phenanthroline groups) and additional bands at lower energies (at lambda > 300 nm) which are assigned to carbazole-to-phenanthroline charge-transfer (CT) transitions. These latter bands are significantly red-shifted upon acid and/or zinc acetate addition. Both L1 and L2 exhibit relatively intense luminescence at room temperature in fluid solution (lifetimes in the nanosecond time scale, quantum yields of the order of 10(-2)-10(-1)) and at 77 K in rigid matrix (lifetimes in the millisecond time scale). Such a luminescence is assigned to CT states at room temperature and to phenanthroline-centered pi-pi triplet levels at 77 K. The room-temperature luminescence of L1 and L2 is totally quenched by acid or zinc acetate. The metal dendrimers exhibit the typical absorption and luminescence properties of Ru(II) polypyridine complexes. In particular, metal-to-ligand charge-transfer (MLCT) bands dominate the visible absorption spectra, and formally triplet MLCT levels govern the excited-state properties. Excitation spectroscopy evidences that all the light absorbed by the dendritic branches is transferred with unitary efficiency to the luminescent MLCT states in 1-3, showing that the new metal dendrimers can be regarded as efficient light-harvesting antenna systems. All the free ligands and metal dendrimers exhibit a rich redox behavior (except L2 and 3, whose redox behavior was not investigated because of solubility reasons), with clearly attributable reversible carbazole- and metal-centered oxidation and polypyridine-centered reduction processes. The electronic interaction between the carbazole redox-active sites of the dendritic ligands is affected by Ru(II) coordination.     

Unveiling Carbon Dioxide and Ethanol Diffusion in Carbonated Water-Ethanol Mixtures by Molecular Dynamics Simulations

The diffusion of carbon dioxide (CO2) and ethanol (EtOH) is a fundamental transport process behind the formation and growth of CO2 bubbles in sparkling beverages and the release of organoleptic compounds at the liquid free surface. In the present study, CO2 and EtOH diffusion coefficients are computed from molecular dynamics (MD) simulations and compared with experimental values derived from the Stokes-Einstein (SE) relation on the basis of viscometry experiments and hydrodynamic radii deduced from former nuclear magnetic resonance (NMR) measurements. These diffusion coefficients steadily increase with temperature and decrease as the concentration of ethanol rises. The agreement between theory and experiment is suitable for CO2. Theoretical EtOH diffusion coefficients tend to overestimate slightly experimental values, although the agreement can be improved by changing the hydrodynamic radius used to evaluate experimental diffusion coefficients. This apparent disagreement should not rely on limitations of the MD simulations nor on the approximations made to evaluate theoretical diffusion coefficients. Improvement of the molecular models, as well as additional NMR measurements on sparkling beverages at several temperatures and ethanol concentrations, would help solve this issue.     

Kinetic simulation of living carbocationic polymerizations. II. Simulation of living isobutylene polymerization using a mechanistic model

This paper discusses the kinetic simulation of TiCl₄--coinitiated living carbocationic isobutylene (IB) polymerizations governed by dormant-active equilibria, using a mechanistic model. Two kinetic models were constructed from the same underlying mechanism: one using a commercial simulation software package (Predici^®), and the other using the method of moments. Parameter estimation from experimental batch reactor data with Predici yielded a rate constant of propagation k_p = 4.64 × 10⁸ ± 2.75 × 10⁸ L/mol s, with no constraints imposed. This agrees with k_p data measured with diffusion clock and competition methods, but disagrees with kinetically obtained k_p values. Estimation of rate constants with Predici^® and the GREG parameter estimation software packages revealed that it was difficult to estimate the complete set of kinetic parameters, due to correlated effects of the parameters on model predictions. Estimability analysis confirmed that some of the strongly correlating parameters could not be estimated simultaneously using the available experimental data. Using k_p = 6 × 10⁸ ± 2.75  × 10⁸ L/mol s measured by Mayr, and using starting estimates of other rate constants defined by experimentally observed correlations, yielded the set of rate constants required for the simulations. Both kinetic models yielded good agreement with experimental data, with the exception of M_w values that slightly diverged from the theoretically predicted ‘M_w−M_n = constant’ relationship. This may indicate the occurrence of a minor side reaction. However, the k_p/k₋₁ = 17.5 L/mol average run length calculated from measured and simulated MWD data agrees well with earlier literature values.