Modification of interface anisotropy and its effect on microstructural evolution during ostwald ripening

We performed an experiment to study the role of anisotropy in interfacial energy during the coarsening of a complex oxide CaCu₃Ti₄O₁₂ (CCTO) material system. When we altered the interface anisotropy, we observed that evolution and sizes of spherical grains completely altered to facetted cubes. When interface became anisotropic, crystal growth appears to occur by the surface attachment/detachment, the motion of ledges, and the nucleation of new layers. Our observations showed that new layers grew by screw dislocation mechanism. This suggests that nucleation limited coarsening is occurring by the development of a transient bimodal grain size distribution consisting of large growing grains with step. In presence of PbO we always observed the development of shaped nucleus which grew larger. Sometimes very complex shaped crystals grew as a metastable shape. These shapes became uniform as the growth progressed and size of grains became larger. This process produces smaller grains that act as a source of material for the growing less defective larger grains.     

Convergent synthesis of dihydroquinolones from o-aminoarylboronates

An efficient and convergent one-step synthesis of substituted dihydroquinolin-2-ones from α,β-unsaturated esters and aminoaryl pinacolboronates under rhodium catalysis is reported. The reaction is easily applicable in parallel synthesis format and provides convenient access to this pharmaceutically-relevant motif.     

A differential scanning calorimetry study of picoline complexes of cadmium chloride

The decomposition of picoline complexes of cadmium chloride has been studied using differential scanning calorimetry. The 2:1 complexes with 3-picoline and 4-picoline decompose in three steps corresponding to the loss of one, one-third, and two-thirds of a molecule of ligand, respectively, in these steps. Sample size apparently controls the mode of decomposition of the 1:1 complex with 2-picoline. In some cases, two-thirds of a molecule of ligands is lost and in other cases one-third is lost first. Thermal parameters have been determined for the various decomposition reactions.     

Proton affinities of sulfate and bisulfate ions

The decomposition of (NH₄)₂SO₄(s) has been studied by DSC. The decomposition takes place in two steps to produce NH₃(g) and NH₄HSO₄(s) in the first and NH₃(g) and H₂SO₄(g) in the second. Enthalpies for these reactions are 195 and 169 kJ/mole, respectively. These values permit calculation of the proton affinities of SO ₄ ^2– and HSO ₄ ^– , and the values found are 1847 and 1338 kJ/mole, respectively.

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Zusammenfassung Die Zersetzung von (NH₃)₂SO₄(s) wurde mittels DSC untersucht. Sie läuft in zwei Stufen ab, wobei während der ersten NH₃(g) und NH₄HSO₄(s) und während der zweiten NH₃(g) und H₂SO₄(g) gebildet werden. Die Enthalpien für diese Reaktionen belaufen sich auf 195 bzw. 169 kJ/mol. Diese Angaben ermöglichen die Errechnung der Protonenaffinität von SO ₄ ^2– und HSO ₄ ^– , deren Werten 1847 bzw. 1338 kJ/mol betragen.

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. , — . , , 195 169 /, - , , 1847 1338 /.

     

Carbon monoxide binding by de novo heme proteins derived from designed combinatorial libraries.

Carbon monoxide binding was studied in a collection of de novo heme proteins derived from combinatorial libraries of sequences designed to fold into 4-helix bundles. The design of the de novo sequences was based on the previously reported "binary code" strategy, in which the patterning of polar and nonpolar amino acids is specified explicitly, but the exact identities of the side chains are varied extensively.(1) The combinatorial mixture of amino acids included histidine and methionine, which ligate heme iron in natural proteins. However, no attempt was made to explicitly design a heme binding site. Nonetheless, as reported previously, approximately half of the binary code proteins bind heme.(2) This collection of novel heme proteins provides a unique opportunity for an unbiased assessment of the functional potentialities of heme proteins that have not been prejudiced either by explicit design or by evolutionary selection. To assess the capabilities of the de novo heme proteins to bind diatomic ligands, we measured the affinity for CO, the kinetics of CO binding and release, and the resonance Raman spectra of the CO complexes for eight de novo heme proteins from two combinatorial libraries. The CO binding affinities for all eight proteins were similar to that of myoglobin, with dissociation constants (K(d)) in the low nanomolar range. The CO association kinetics (k(on)) revealed that the heme environment in all eight of the de novo proteins is partially buried, and the resonance Raman studies indicated that the local environment around the bound CO is devoid of hydrogen-bonding groups. Overall, the CO binding properties of the de novo heme proteins span a narrow range of values near the center of the range observed for diverse families of natural heme proteins. The measured properties of the de novo heme proteins can be considered as a "default" range for CO binding in alpha-helical proteins that have neither been designed to bind heme or CO, nor subjected to genetic selections for heme or CO binding.     

An ion grouping method for calculating the Madelung constant for the sodium chloride lattice

A method has been developed for calculating the Madelung constant for a sodium chloride lattice. In this method, a reference ion is selected and all other ions are placed in groups around the reference ion. To include ions in all locations, seven types of groups are necessary. Recursion formulas are obtained to compute the effect of each group of ions and the Madelung constant is computed from the total effect produced by all the groups. A total of 29 cubical shells of ions around the reference ion were used in the calculation. The computation produces an oscillating function which alternately goes above and below the actual Madelung constant as the computation is expanded to include each successive shell of ions. A numerical method is described to obtain the average value of the oscillating function. A value of the Madelung constant of 1.74759 results from the abbreviated calculation.