Thermodynamic activities in the Pb(Zr1-XTiX)O-3 solid solution at 1373 K

Although Pb(Zr1-XTiX)O-3 solid solution is the cornerstone of the piezoelectric ceramics, there is no information in the literature on thermodynamic activities of the component phases in the solid solution. Using inter-crystalline ion exchange equilibria between Pb(Zr1-XTiX)O-3 solid solution with cubic perovskite structure and (Zr1-YTiY)O-2 solid solutions with monoclinic and tetragonal structures, activities of PbTiO3 and PbZrO3 in the perovskite solid solution have been derived at 1373 K using the modified Gibbs-Duhem integration technique of Jacob and Jeffes. Tie-lines from the cubic solid solution are skewed towards the ZrO2 corner. Activities in the zirconia-rich (Zr1-YTiY)02 solid solutions are taken from a recent emf study. The results for the perovskite solid solution at 1373 K can be represented by a sub-regular solution model: Delta G(E.M) (J mol(-1)) = X-PbTiO3 X-PbZrO3(5280X(PbTiO3) - 1980X(PbZrO3)) where Delta G(E.M) is the excess Gibbs energy of mixing of the cubic solid solution and Xi represents the mole fraction of component i. There is a significant positive deviation from ideality for PbTiO3-rich compositions and mild negative deviation near the PbZrO3 corner. The cubic solid solution is intrinsically stable against composition fluctuations at temperatures down to 840 K. The results contrast sharply with the recent calorimetric data on enthalpy of mixing which signal instability of the cubic perovskite solid solution. (C) 2007 Elsevier B.V. All rights reserved.

Conformation of di-n-propylglycine residues (Dpg) in peptides: crystal structures of a type I 'beta-turn forming tetrapeptide and an alpha-helical tetradecapeptide

The crystal structures of two oligopeptides containing di-n-propylglycine (Dpg) residues, Boc-Gly-Dpg-Gly-Leu-OMe (1) and Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (2) are presented. Peptide 1 adopts a type I' beta-turn conformation with Dpg(2)-Gly(3) at the corner positions. The 14-residue peptide 2 crystallizes with two molecules in the asymmetric unit, both of which adopt alpha-helical conformations stabilized by 11 successive 5 -> 1 hydrogen bonds. In addition, a single 4 -> 1 hydrogen bond is also observed at the N-terminus. All live Dpg residues adopt backbone torsion angles (phi, psi) in the helical region of conformational space. Evaluation of the available structural data on Dpg peptides confirm the correlation between backbone bond angle N-C-alpha-C' (tau) and the observed backbone phi,psi values. For tau > 106 degrees, helices are observed, while fully extended structures are characterized by tau < 106 degrees. The mean r values for extended and folded conformations for the Dpg residue are 103.6 degrees +/- 1.7 degrees and 109.9 degrees +/- 2.6 degrees, respectively. Copyright (C) 2007 European Peptide Society and John Wiley & Sons, Ltd.

The syntheses, characterizations, X-ray crystal structures and properties of Cu(I) complexes of a bis-bidentate schiff base ligand

Bis-bidentate Schiff base ligand L and its two mononuclear complexes [CuL(CH3CN)(2)]ClO4 (1)and [CuL(PPh3)(2)]ClO4 (2)have been prepared and thoroughly characterized by elemental analyses, IR, UV-Vis, NMR spectroscopy and X-ray diffraction analysis. In both the complexes the metal ion auxiliaries adopt tetrahedral coordination environment. Their reactivity, electrochemical and photophysical behavior have been studied. Complex 1 shows reversible Cu-II/I couple with potential 0.74 V versus Ag/AgCl in CH2Cl2. At room temperature L is weakly fluorescent in CH2Cl2, however in Cu(I)complexes 1 and 2 the emission in quenched. (C) 2009 Elsevier B. V. All rights reserved.

Studies of the polarographic and coulometric behaviour of aromatic nitro-compounds: I. Nitrobenzene in ethanol

A detailed polarographic (a.c. and d.c.) and coulometric investigation of nitrobenzene has been made at various pH values in the presence of different concentrations of ethanol. Below pH 4.7, two waves are apparent but above this pH, the second wave does not appear. Coulometric evidence indicates that the first and second waves correspond to the four-and two-electron processes, respectively. The coulometric method was not applicable in sodium hydroxide and sodium acetate solutions. When the diffusion coefficients (from the diaphragm cell) are used in the Ilkovic equation, no reliable conclusions can be reached for the number of electrons involved in the reduction process in alkaline solutions. The a.c. polarographic method gives evidence for the formation of species such as: C6H5NO2H22+, C6H5NO2− and C6H5NO22−. Analysis of d.c. polarographic data by Delahay's treatment of irreversible waves, indicates that the number of electrons involved in the rate-determining step is 2. In sodium hydroxide solutions, however, the first main wave is split indicating more than one rate-determining step. The results presented in this paper indicate that the first wave in the reduction of nitrobenzene is a four-electron process at all pH values. The second wave, which appears below pH 4.7, corresponds to a two-electron process irrespective of wave heights. The difference in the a.c. polarographic behaviour in acid and alkaline solutions has given evidence for the formation of species like C6H5NO2H2, C6H5NO2−, and C6H5NO22.

Metabolism of Plasmodium berghei. I. Krebs cycle

The free parasites of Plasmodium berghei, obtained from infected cells of rats using an antiserum method, were investigated to study the operation of Krebs cycle. P. berghei was found to respire only with succinate; pyruvate, and other substrates of the Krebs cycle were not oxidized. The presence of a succinate dehydrogenase and a functioning cytochrome oxidase system was demonstrated. Cell-free extracts of free parasites showed the presence of enzymes for the utilization of C4 dicarboxylic acids; other enzymes of the Krebs cycle could not be detected. P. berghei differs from other species of Plasmodium in this respect.

Interrelations of soil micro-orgamisms and mulberry I.Phytohormone production by soil and rhizosphere bacteria and their effect on plant growth

Bacteria isolated from the rhizosphere of mulberry (Morus indica) as well as from control soil were tested for their effects on the growth of mulberry seedlings and for phytohormone production. About 12.8 per cent of the rhizosphere and 9.7 per cent of the soil isolates produced phytohormones in cultures. Rhizosphere isolates were more active in hormone synthesis than their soil counterparts. Soaking mulberry stem cuttings in culture filtrates of phytohormone synthesisers hastened their rooting. Culture filtrates of many isolates — hormone producers or not — stimulated or inhibited the growth of shoot and/or root of plants. Many cultures could also inhibit the germination of mulberry seeds.