Stability studies of an electrochemically formed [C60]fullerene-palladium two-component film

The stability of C₆₀ and palladium two-component films, C₆₀/Pd, has been investigated. The effect of different polymerization conditions on the electrochemical stability of the film upon prolonged potential cycling has been studied. Stable voltammetric behavior was observed for polymers formed at potentials less negative than the potential of third C₆₀ reduction step. The incorporation of palladium particles into the structure of C₆₀/Pd polymers increases the polymer stability. The C₆₀/Pd films are doped with supporting electrolyte cations during reduction. The size of these cations is a crucial factor in determining the stability of the film. A strong solvent effect on the potential stability of the film was also observed. The wildest range of stable voltammetric properties was found for acetonitrile and N,N-dimethylformamide. No effect of the temperature on the film stability was observed. The results reported in this work allow for the determination of the optimal conditions for the formation of stable C₆₀/Pd films.     

Ferrocene-mannose conjugates as electrochemical molecular sensors for concanavalin A lectin

The binding affinity of a series of electroactive glycoconjugates, based on a ferrocene core bearing alpha-mannose units on one or both of its cyclopentadienyl rings, to lectin Con A was studied by isothermal titration calorimetry (ITC) and voltammetry. Voltammetric measurements were performed by differential pulse adsorptive stripping voltammetry (DPAdSV). Upon complexation of ferrocene-mannose conjugates with Con A, voltammograms showed a decrease of the peak current. Both the monomannosylated ferrocene and the bis(mannosylated) ferrocene derivatives form more stable complexes with Con A than methyl alpha-D-mannopyranoside. Bis(mannosylated) ferrocene conjugates were found to bind to Con A with enhanced affinity due to the multivalent effect. A comparison of the thermodynamic data obtained by ITC and voltammetry is presented.     

Hydration of ionic species studied by the reference interaction site model with a repulsive bridge correction

We have tested the reference interaction site model (RISM) for the case of the hypernetted chain (HNC) and the partially linearized hypernetted chain (PLHNC) closures improved by a repulsive bridge correction (RBC) for ionic hydrated species. We have analyzed the efficiency of the RISM/HNC+RBC and RISM/PLHNC+RBC techniques for decomposition of the electrostatic and the nonpolar hydration energies on the energetic and the enthalpic parts for polyatomic ions when the repulsive bridge correction is treated as a thermodynamic perturbation, and investigate the repulsive bridge effect on the electrostatic potential induced by solvent on solute atoms. For a number of univalent and bivalent atomic ions, molecular cations, and anions, the method provides hydration energies deviating only by several percents from the experimental data. In most cases, the enthalpic contributions to the free energies are also close to the experimental results. The above models are able to satisfactory predict the hydration energies as well as the electrostatic potential around the ionic species. For univalent atomic ions, they also provide qualitative estimates of the Samoilov activation energies.     

Surfactant dependent morphology of polymeric capsules of perfluorooctyl bromide: influence of polymer adsorption at the dichloromethane-water interface

In a strategy to develop more stable ultrasound contrast agents (UCAs), we have designed a process to obtain nano/microcapsules with a single core of liquid perfluorocarbon within a biodegradable polymeric shell of homogeneous thickness. During the optimization of perfluorooctyl bromide (PFOB) encapsulation by solvent emulsion-evaporation, a marked influence of surfactants has been observed. While sodium cholate leads to spherical capsules of homogeneous thickness, sodium taurocholate induces to the formation of “acorn”-particles with one hemisphere of PFOB and another one of PLGA, and polyvinyl alcohol is responsible for the coexistence of both morphologies. Whereas the theoretical model proposed by Torza and Mason [J. Colloid Interface Sci. 33 (1970) 67] fails to predict the observed morphologies, microscopic observations of the evaporation and interfacial tension measurements provide an insight into the mechanism of formation of these structures. Most probably, there is a competition between PLGA and the surfactant stabilizing the emulsion at the dichloromethane–water interface. If PLGA is able to adsorb at the interface, the core–shell morphology is obtained, otherwise the acorn morphology is preferentially formed. When the surfactant rearrangement at the interface is long (>30 min), a coexistence of morphologies can be obtained.     

Anion effect on the construction of copper(II) coordination polymers with the twisted ligand bis(4-pyridylthio)methane

The reaction of CuSO₄ · H₂O with 4-bpytm [4-bpytm = bis(4-pyridylthio)methane] in EtOH afforded the complex [Cu(SO₄)(4-bpytm)(H₂O)₃] · H₂O (1 · H₂O) while the reaction of 4-bpytm with Cu(NO₃)₂ · 3H₂O in EtOH afforded the complex [Cu(NO₃)₂(4-bpytm)₂] · H₂O (2 · H₂O). The reaction of 4-bpytm with Cu(NO₃)₂ · 3H₂O in EtOH/dmf under microwave irradiation afforded the pseudo-polymorph [Cu(NO₃)₂(4-bpytm)₂] · Solv (2 · Solv). Compound 1 · H₂O forms helical chains while compounds 2 · H₂O and 2 · Solv are 2D coordination polymers with a (4,4) topology based on rhombic grids in 2 · H₂O and on a parquet motif in 2 · Solv. The 3D supramolecular organization through hydrogen bonding is analyzed for the three compounds and their thermal behaviour was also investigated.     

Validation of the Tessier scheme for speciation of metals in soil using the Bland and Altman test

The Tessier extraction method was used for speciation of Cu, Pb, Zn, As, Fe and Mn in a large concentration range in contaminated soil with various mineralogical compositions. The results were compared by X-ray fluorescence spectrometry (XRF) as a reference method using the Bland and Altman test. A sum of five fractions (exchangeable, bound to carbonates, Fe-Mn oxides, organic matter and residual forms) was compared with the total content determined on solid matrix by the reference method. A good agreement between the methods in the whole concentration range was found for Cu, Zn, As, and Fe. For Mn and Pb, XRF was found suitable to verify the sequential extraction only for concentrations above 250 mg kg⁻¹. This was a consequence of a poorer reproducibility of Pb extraction using the Tessier scheme due to a great difference in the mineralogical composition and the diversity of the Pb species identified in soil. The poorer result of Mn was attributed to the spectral interference of Fe in XRF. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Surface-structured molecular sensor for the optical detection of acidity

In this letter, we report on the development of a surface molecular sensor for the detection of acidity. Lithographically controlled wetting deposition has been applied to form the nanostructure of a new fluorescent compound with three protonation states featuring different optical properties on a glass substrate. Atomic force microscopy demonstrates the functionalization of the surface with ordered arrays of the sensor molecules. The fluorescence properties of the resulting nanopattern at different pH values have been investigated by confocal fluorescene microsopy, thus revealing the fast, sensitive, reversible response of the prepared nanosensor to gas flows of varying acidity.     

Versatile scorpionates and new developments in the denticity changes of NNCp hybrid scorpionate/cyclopentadienyl ligands in Sc and Y compounds: from kappa1-Neta5-Cp to kappa2-NNeta5-Cp

Reaction of hybrid scorpionate/cyclopentadienyl ligands in the form of the lithium derivatives [Li(bpzcp)(THF)] [bpzcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl], [Li(bpztcp)(THF)] [bpztcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl], and the in situ-generated "Li(bpzpcp)" [bpzpcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-phenylethylcyclopentadienyl] with MCl3(THF)3 afforded the group 3 halide compounds [MCl2(bpzcp)(THF)] (M=Sc, 1; Y, 2), [MCl2(bpztcp)(THF)] (M=Sc, 3; Y, 4), and [MCl2(bpzpcp)(THF)] (M=Sc, 5; Y, 6). The H2O adduct of 4, [YCl2(bpztcp)(H2O)] (7), was formed when a solution of 4 was allowed to stand at room temperature in the presence of moisture. Complexes 1-7 adopt a pseudo-octahedral structure with heteroscorpionate ligands kappa2-NNeta5-Cp coordinated to the metal through the cyclopentadienyl group and two imino nitrogens of pyrazole rings. The alkyl heteroscorpionate scandium and yttrium complexes recently reported by our group, [M(CH2SiMe3)2(bpzcp)], react with 2,6-dimethylphenol and 3,5-dimethylphenol to give the bis(aryloxide) derivatives [M(OAr)2(bpzcp)] (M=Sc, OAr=2,6-dimethylphenoxide, 8; M=Y, OAr=2,6-dimethylphenoxide, 9; M=Y, OAr=3,5-dimethylphenoxide, 10). Complex 9 underwent an interesting hydrolysis process to give the tetranuclear complex [{Y(bpzcp)}(micro-OH)2(micro3-OH){Y(OAr)2}]2 (11). Variable-temperature 1H NMR experiments on 9 and 10 revealed a rapid fluxional exchange between coordinated and noncoordinated pyrazolyl rings, producing interconversion between the two enantiomers in which the scorpionate ligand can be coordinated in a kappa1-Neta5-Cp form. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 2, 7, and 11 were also established. Complexes 1 and 2 are active olefin polymerization catalysts after activation with methylaluminoxane. These compounds gave atactic polystyrenes with narrow molecular weight distribution (Mn/Mw 1.26-1.91) and with low molecular weights.     

How many electrons form chemical bonds in the NgBeS (Ng = Ar,Kr, Xe) molecules? Topological study using the electron localisation function (ELF) and electron localisability indicator (ELI-D)

Nature of bonding in the NgBeS (Ng = Ar, Kr, Xe) molecules has been studied using topological analysis of ELF, ELI-D functions with the wave function approximated at the DFT (M062X, B3LYP + ZORA), MP2, CCSD and CASSCF level of calculations. Both Xe–Be and Be=S bonds display topological features typical for the covalent-dative bonding. The V₂(Xe) attractor characterising electron density, involved in interaction with the beryllium atom, is closer to the C(Be) core than to C(Xe). The population of the respective basin ranges between 1.59e (B3LYP + ZORA) and 1.83e (CCSD). The beryllium–sulphur bond is described by the bonding disynaptic basin V(Be,S) with the population between 3.22e (CASSCF) and 3.48e (M062X). The approximate weights for the Be–S and Be=S resonance forms are 0.3 and 0.7, respectively, in all molecules. Both the NgBe and BeS bonds are highly polarised with the values of the p _SBe and p _NgBe polarity indices (CCSD) of 0.8 and 0.9–1.0 for all studied molecules.