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.     

Syntheses and Crystal Structures of Potassium–Lanthanoid(III) Complexes with the 1,2‐Benzenedisulfonate Ligand

The complexes [K(H₂O)₂LnL₂] (Ln = La or Nd; L = 1,2‐benzenedisulfonate) and [K(H₂O)Yb(H₂O)₄L₂] were initially isolated fortuitously from attempts to prepare the corresponding Ln₂L₃ complexes from Ln₂O₃ and H₂L in water. Indeed the bulk products from these reactions have the composition Ln₂L₃. Subsequently, deliberate syntheses by reacting equimolar amounts of Ln₂L₃ with K₂L in water gave the complexes in good yield. X‐ray crystal structures of [K(H₂O)₂LnL₂] (Ln = La or Nd) showed the complexes to be isostructural with a two dimensional polymeric network structure in which LnL₂ units are linked into chains crosslinked by potassium ions. Each Ln is nine coordinate with solely sulfonate oxygen donor atoms. Between adjacent lanthanoid ions there are three different types of sulfonate bridges and two examples of each. Most noteworthy is highly unsymmetrical bridging through μ‐η²‐sulfonate oxygen atoms. Consequently, one Ln–O bond is ca. 0.5 Å longer than the other eight. Potassium is nine‐coordinate with seven sulfonate oxygen atoms and two aqua ligands, and surprisingly <K–O(sulfonate)> is much longer than <K–O(H₂O)>. Pairs of potassium ions are linked by two μ‐η²‐sulfonate oxygen atoms, which are unsymmetrically bridging. The structure of [K(H₂O)Yb(H₂O)₄L₂] comprises discrete tetranuclear units containing two independent ytterbium ions, each coordinated by four water molecules and two chelating (via seven membered rings) disulfonate ligands, and two potassium ions, each coordinated by six sulfonate oxygen atoms and a water molecule. For each potassium, four of the coordinated sulfonate oxygen atoms are from sulfonate ligands bonded to one ytterbium atom and two from sulfonate ligands attached to the other ytterbium atom. In contrast to the Nd and La complexes, <K–O(sulfonate)> is shorter than <K–O(H₂O)>.     

Information theoretical study of chirality: enantiomers with one and two asymmetric centra

In this work, the Kullback-Leibler information deficiency is probed as a chirality measure. It is argued that the information deficiency, calculated using the shape functions of the R and S enantiomers, considering one as reference for the other, gives an information theory based expression useful for quantifying chirality. The measure is evaluated for five chiral halomethanes possessing one asymmetric carbon atom with hydrogen, fluorine, chlorine, bromine, and iodine as substituents. To demonstrate the general applicability, a study of two halogen-substituted ethanes possessing two asymmetric carbon atoms has been included as well. The basic expression of the sum of the local information deficiency over all atoms can be decomposed into separate summations over coinciding and noncoinciding atoms, or into a global and a mixing entropy term, or into a local entropy contribution for each atom individually based on the Hirshfeld partitioning. Avnir's continuous chirality measure (CCM) has been computed and confronted with the information deficiency. Finally, the relationship between chirality and optical rotation is used to study the proposed measure. The results illustrate Mezey's holographic electron density theorem with an intuitively appealing division of the strength of propagation of the atomic chirality from an asymmetric carbon atom throughout the molecule. The local information deficiency of the carbon atom is proposed as a measure of chirality; more precisely, the difference in information between the R and the S enantiomer turns out to be a quantitative measure of the chirality of the system. It may be evaluated as the arithmetic mean of the different alignments, or considering only the alignment resulting in the highest similarity value, or using the QSSA alignment.     

High-Performance Thin-Layer Chromatographic Method for Analysis of Racecadotril in the Bulk Drug

JPC – Journal of Planar Chromatography – Modern TLC - A new simple, rapid, reproducible, and stability-indicatiiig highperformance thin-layer chromatographic method for analysis of...     

Synthesis of Novel C/D Ring Modified Bile Acids

Bile acid receptors have been identified as important targets for the development of new therapeutics to treat various metabolic and inflammatory diseases. The synthesis of new bile acid analogues can help elucidate structure–activity relationships and define compounds that activate these receptors selectively. Towards this, access to large quantities of a chenodeoxycholic acid derivative bearing a C-12 methyl and a C-13 to C-14 double bond provided an interesting scaffold to investigate the chemical manipulation of the C/D ring junction in bile acids. The reactivity of this alkene substrate with various zinc carbenoid species showed that those generated using the Furukawa methodology achieved selective α-cyclopropanation, whereas those generated using the Shi methodology reacted in an unexpected manner giving rise to a rearranged skeleton whereby the C ring has undergone contraction to form a novel spiro–furan ring system. Further derivatization of the cyclopropanated steroid included O-7 oxidation and epimerization to afford new bile acid derivatives for biological evaluation.     

Quantum computing based on vibrational eigenstates: pulse area theorem analysis

In a recent paper [D. Babikov, J. Chem. Phys. 121, 7577 (2004)], quantum optimal control theory was applied to analyze the accuracy of quantum gates in a quantum computer based on molecular vibrational eigenstates. The effects of the anharmonicity parameter of the molecule, the target time of the pulse, and the penalty function on the accuracy of the qubit transformations were investigated. We demonstrate that the effects of all the molecular and laser-pulse parameters can be explained utilizing the analytical pulse area theorem, which originates from the standard two-level model. Moreover, by analyzing the difference between the optimal control theory results and those obtained using the pulse area theorem, it is shown that extremely high quantum gate fidelity can be achieved for a qubit system based on vibrational eigenstates.     

Tracelessness Unmasked: A General Linker Nomenclature

Nowadays it is rare to find an issue of a major chemistry journal without at least one article on solid-phase synthesis. This is hardly surprising: the technique promises an end to arduous work-up procedures and the ability to facilitate the creation of vast libraries of compounds using combinatorial techniques. No longer is the technique only of interest to those involved in peptide synthesis: an enormous variety of product classes have now been prepared on and isolated from the solid phase. It is the "linker" which is the focus of this article. The linker's ultimate function is to release a product from the support into solution: it does this, without exception, with a chemical change to the product at the former linkage site. Some linkers, apparently, are "traceless". But what, in fact, is "tracelessness"? Twenty years ago, in a climate where cleavage of a linker resulted in formation of a polar carboxylic acid as the vestige of the support, the concept was attractive. Today the chemist is faced with a myriad of novel linkers which have the ability to release products bearing most major functionalities at the former linkage site and we will argue here that the term "traceless", although currently in widespread use, is meaningless. Instead, we propose a new categorization of linkers based on the functionality they release upon cleavage, and suggest a nomenclature to underpin this categorization. We anticipate that the article will also serve to highlight areas of linker technology in need of further research.     

Ba4KFe3O9: a novel ferrite containing discrete 6-membered rings of corner-sharing FeO4 tetrahedra

Single crystals of a new iron-containing oxide, Ba(4)KFe(3)O(9), were grown from a hydroxide melt, and the crystal structure was determined by single-crystal X-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-membered rings of corner-sharing FeO(4) tetrahedra. M?ssbauer measurements are indicative of two tetrahedral high-spin Fe(3+) coordination environments. The observed magnetic moment (~3.9 μ(B)) at 400 K is significantly lower than the calculated spin-only (~5.2 μ(B)) value, indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional theory calculations confirm the strong antiferromagnetic coupling between adjacent Fe(3+) sites within each 6-membered ring and estimate the nearest-neighbor spin-exchange integral as ~200 K; next-nearest-neighbor interactions are shown to be negligible. The lower than expected effective magnetic moment for Ba(4)KFe(3)O(9) calculated from χT data is explained as resulting from the occupation of lower-lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of a powder sample consist of a single line at g ~ 2.01 that is characteristic of Fe(3+) ions in a tetrahedral environment, thus confirming the M?ssbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe(6) magnetic species with an intensity ratio of ~1:9. Both species have Lorentzian line shapes and indistinguishable g factors but differ in their peak-to-peak line widths (δB(pp)). The line-width ratio δB(pp)(major)/δB(pp)(minor) ~ 3.6 correlates well with the ratio of the Weiss constants, θ(minor)/θ(major) ~ 4.