Electrochemical behavior of active surface layers in AA8xxx aluminum alloys

AA8xxx alloys employed in the HVAC&R sector (heating, ventilating, air conditioning, and refrigerating) were investigated to highlight the effect of active surface layers in heat-exchanger fins. The local behavior of the surface and the bulk of the alloy sheets was studied by means of an electrochemical microcell in combination with glow-discharge optical-emission spectrometry. Surface layers strongly enhance the electrochemical activity of the fin material. This is related to the segregation of Mg and other elements (Sn) strongly impairing the protective behavior of the oxide film generated during thermomechanical processing.     

Speciation of phytate ion in aqueous solution. Cadmium(II) interactions in aqueous NaCl at different ionic strengths

Interactions between myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate) (phytic acid) and cadmium(II) were studied by using potentiometry (at 25 °C with the ISE-H⁺ glass electrode) in different metal to ligand (Phy) ratios (1:1≤Cd²⁺:Phy≤4:1) in NaCl_aq at different ionic strengths (0.1≤I/mol L⁻¹≤1). Nine Cd_iH_jPhy^{(12−2i−j)−} species are formed with i=1 and 2 and 4≤j≤7; and trinuclear Cd₃H₄Phy²⁻. Dependence of complex formation constants on ionic strength was modeled by using Specific ion Interaction Theory (SIT) equations. Phytate and cadmium speciation are also dependent on the metal to ligand ratio. Stability of Cd_iH_jPhy^{(12−2i−j)−} species was modeled as a function of both the ligand protonation step (j) and the number of metal cations bound to phytate (i), and relationships found were used for the prediction of species other than those experimentally determined (mainly di- and tri-protonated complexes), allowing the possibility of modeling Phy and Cd(II) behavior in natural waters and biological fluids. A critical evaluation of phytate sequestering ability toward cadmium(II) has been made under several experimental conditions, and the determination of an empirical parameter has been proposed for an objective “quantification” of this ability. A thorough analysis of literature data on phytate–cadmium(II) complexes has been performed. Previous contributions to this series: [1–8]     

Defining the nucleotide binding sites of P2Y receptors using rhodopsin-based homology modeling

Ongoing efforts to model P2Y receptors for extracellular nucleotides, i.e., endogenous ADP, ATP, UDP, UTP, and UDP-glucose, were summarized and correlated for the eight known subtypes. The rhodopsin-based homology modeling of the P2Y receptors is supported by a growing body of site-directed mutagenesis data, mainly for P2Y₁ receptors. By comparing molecular models of the P2Y receptors, it was concluded that nucleotide binding could occur in the upper part of the helical bundle, with the ribose moiety accommodated between transmembrane domain (TM) 3 and TM7. The nucleobase was oriented towards TM1, TM2, and TM7, in the direction of the extracellular side of the receptor. The phosphate chain was oriented towards TM6, in the direction of the extracellular loops (ELs), and was coordinated by three critical cationic residues. In particular, in the P2Y₁, P2Y₂, P2Y₄, and P2Y₆ receptors the nucleotide ligands had very similar positions. ADP in the P2Y₁₂ receptor was located deeper inside the receptor in comparison to other subtypes, and the uridine moiety of UDP-glucose in the P2Y₁₄ receptor was located even deeper and shifted toward TM7. In general, these findings are in agreement with the proposed binding site of small molecules to other class A GPCRs.     

Hydrolysis of (CH3)3Sn+ in Various Salt Media

The hydrolysis of trimethyltin(IV) has been studied by potentiometry (H⁺ -glass electrode) and calorimetry in various salt media (NaNO₃, NaCl, KCl, Na₂SO₄, and NaNO₃—NaCl mixtures). The effect of ionic strength on the hydrolysis constants is accounted for by a simple Debye–Hückel type equation and by Pitzer equations. The results allow us to obtain H for hydrolysis and the temperature dependence of the Pitzer parameters. The resulting coefficients can be used to examine the speciation of (CH₃)₃Sn⁺ in multicomponent electrolyte solutions, such as natural waters, over a wide range of temperature and ionic strength.     

Physical and electrochemical properties of N-alkyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquids: PY13FSI and PY14FSI

Two ionic liquids based upon N-alkyl-N-methylpyrrolidinium cations (PY(1R)(+)) (R=3 for propyl or 4 for butyl) and the bis(fluorosulfonyl)imide (FSI(-)), N(SO2F)2(-), anion have been extensively characterized. The ionic conductivity and viscosity of these materials are found to be among the highest and lowest, respectively, reported for aprotic ionic liquids. Both ionic liquids crystallize readily on cooling and undergo several solid-solid phase transitions on heating prior to melting. PY13FSI and PY14FSI are found to melt at -9 and -18 degrees C, respectively. The thermal stability of PY13FSI and PY14FSI is notably lower than for the analogous salts with the bis(trifluoromethanesulfonyl)imide (TFSI(-)), N(SO2CF3)2(-), anion. Both ionic liquids have a relatively wide electrochemical stability window of approximately 5 V.     

A full multiple scattering model for the analysis of time-resolved X-ray difference absorption spectra

A full multiple theoretical model (MXAN) is applied to fit picosecond difference X-ray absorption spectra at the ruthenium L(3) edge upon photoexcitation of aqueous [RuII(bpy)3]2+. We show that fitting difference spectra allows an increase in sensitivity, such that slight structural changes can be retrieved, which are not detected in fitting full spectra. The Ru-N bond distances of the excited complex in the (3)MLCT state are in good agreement with recently published values. The implementation of the present approach to L-edge spectra and its high sensitivity opens opportunities for its extension to a large class of experiments where difference X-ray absorption spectra are recorded.     

Single Drop Dynamics under Shearing Flow in Systems with a Viscoelastic Phase

In this article, we discuss the dynamics of a single drop immersed in an immiscible liquid, under an imposed shear flow. The two situations of a viscoelastic matrix with a Newtonian drop and of a viscoelastic drop in a Newtonian matrix are considered, both systems being characterized by a viscosity ratio equal to one, and by the same elasticity parameter. Experimental data are taken with a rheo-optical computer-assisted shearing device, allowing for drop observation from the vorticity direction of the shear flow. Data favourably compare with predictions of the recently proposed Maffettone-Greco model, where the drop is described as a deforming ellipsoid.     

Azido‐Substituted BODIPY Dyes for the Production of Fluorescent Carbon Nanotubes

A series of azido‐dyes were synthesized through Knoevenagel reactions of an azido‐BODIPY with aromatic aldehydes. The nature of the substituents allowed the fine tuning of their spectroscopic properties. The dyes were used to decorate oxidized multiwalled carbon nanotubes (ox‐MWCNTs), bearing terminal triple bond groups, by CuAAC reactions, affording fluorescent materials. This decoration allowed the efficient determination of the internalization of the ox‐MWCNT derivatives by different model cancer cells, such as MCF7.     

σ‐Alkylpalladium Intermediates in Intramolecular Heck Reactions:Isolation and Catalytic Activity

The isolation of σ‐alkylpalladium Heck intermediates, possible when β‐hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N‐allyl‐2‐halobenzylamines in the presence of [Pd(PPh₃)₄], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X‐ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five‐membered palladacycle with the metal center bearing a PPh₃ ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ‐alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β‐hydride elimination. Subsequently, the thus obtained bridged five‐membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross‐coupling processes such as Suzuki and Stille reactions.     

Lactococcus lactis catalyses electricity generation at microbial fuel cell anodes via excretion of a soluble quinone

Lactococcus lactis is a gram-positive, normally homolactic fermenter that is known to produce several kinds of membrane associated quinones, which are able to mediate electron transfer to extracellular electron acceptors such as Fe³⁺, Cu²⁺ and hexacyanoferrate. Here we show that this bacterium is also capable of performing extracellular electron transfer to anodes by utilizing at least two soluble redox mediators, as suggested by the two-step catalytic current developed. One of these two mediators was herein suggested to be 2-amino-3-dicarboxy-1,4-naphthoquinone (ACNQ), via evaluation of standard redox potential, ability of the bacterium to exploit the quinone when exogenously provided, as well as by high performance liquid chromatography coupled with UV spectrum analysis. During electricity generation, L. lactis slightly deviated from its normal homolactic metabolism by excreting acetate and pyruvate in stoichiometric amounts with respect to the electrical current. In this metabolism, the anode takes on the role of electron sink for acetogenic fermentation. The finding that L. lactis self-catalyses anodic electron transfer by excretion of redox mediators is remarkable as the mechanisms of extracellular electron transfer by pure cultures of gram-positive bacteria had previously never been elucidated.