Mechanism and kinetics of thermal decomposition of precipitates of the zinc oxide-aluminium oxide system from non-isothermal tg curves

Kinetics of decomposition of the precipitates of the ZnO&2sbndAl₂O₃ system, prepared by coprecipitation and mechanical mixing of the individual precipitates, have been studied. The decomposition of zinc basic carbonate is a first order rate process with an activation energy of 34.5 kcal/mole (Coats and Redfern equation). The decomposition of aluminium hydroxide is also best described as a first order rate process with one break in the Coats and Redfern plot corresponding to activation energies of 29.4 and 8.3 kcal/mole respectively. The entire course of decomposition of coprecipitated as well as mechanically mixed samples cannot be described by any one of the many rate equations available. Consequently, the Coats and Redfern equation has been employed. The plots indicate one or two breaks and thus two to three values of activation energy are reported. From the results it is to be concluded that decomposition of these precipitates is a heterogeneous process. The first step is definitely the decomposition of zinc basic carbonate followed by decomposition of aluminium hydroxide and/or interaction of the two precipitates resulting in the formation of “precursor” to spinel. The results of our earlier investigation on the same system (especially the formation of precursors) are well supported by the results reported in this investigation. p]A new equation (a modified form of the Elovich equation) has been proposed for such heterogeneous decomposition processes. The proposed equation also appears to be the general form of the equations where diffusion is the rate controlling process.     

Protein crystal nucleation: is the pair interaction potential the primary determinant of kinetics?

Fundamental understanding of protein crystal nucleation facilitates crystallization of biological macromolecules for structure determination and control of crystal size distribution. In the studies presented here, nucleation kinetics of hen egg-white lysozyme crystals were measured at solution conditions that exhibited equal solubility by adjusting pH, temperature, or sodium chloride concentration. It was observed that solution conditions that lead to equal solubility resulted in equal nucleation rates and hence kinetic parameters. Since the solubility of globular proteins correlates with the osmotic second virial coefficient, B(22), an integral measure of the protein pair interaction potential, this observation indicates that the protein pair interaction plays a key role in determining nucleation kinetic parameters.     

A variational coupled cluster theory for closed shells using a propagator modification procedure

A general partial summation method for including arbitrary classes of diagrams to all orders in the coupled cluster based size consistent energy functional for closed shell states is developed. Since the various reduced density matrices which appear in the energy functional are essentially the time-independent analogues of the corresponding many body Green functions, it is possible to derive Dyson-like equations for these quantities. By expanding the associated proper self energy parts in terms of the T-amplitudes, one can carry out partial summations in the reduced density matrices and thus in energy. At a higher level, higher order terms in a proper self energy can also be generated by renormalizing the internal propagators in it, and considering only the irreducible self-energy terms.     

Solvent water tapes in two hydrates of μ‐oxo‐bis­[bis­(2,2′‐bipyridine‐κ2N,N′)(sulfato‐κO)iron(III)]

The title compound, [Fe₂O(SO₄)₂(C₁₀H₈N₂)₄], crystallizes as two different hydrates, viz. 11H₂O, (I), and 15H₂O, (II). The complex is binuclear, in which the two Fe^III atoms are coordinated in an octa­hedral geometry to four N atoms from the two bipyridine ligands, to one O atom from the sulfate ion and to an oxide ion on a twofold axis, which acts as a bridge between the symmetry‐related units. The Fe⋯Fe separation is 3.556 (4) Å and the Fe—O—Fe angle is 161.6 (2)° in (I); the corresponding values are 3.544 (1) Å and 165.8 (2)° in (II). In (II), one of the O atoms of the sulfate ion is disordered over two positions. In both compounds, the solvent water mol­ecules form slightly different one‐dimensional hydrogen‐bonded networks which pass along the c axis of the unit cell. In (I), three solvent water mol­ecules and, in (II), one solvent water mol­ecule, are situated on the twofold axis. In both (I) and (II), the central O atom of the metal complex lies on a twofold axis.     

Electrochemical and chemical polymerization of acrylamide

The electrochemical and chemical polymerization of acrylamide (AA) has been studied. The electrolysis of the monomer in N,N-dimethylformamide (DMF) containing (C₄H₉)₄NClO₄ as the supporting electrolyte leads to polymer formation in both anode and cathode compartments. The cathodic polymer dissolves in the reaction mixture and the anodic polymer precipitates during the course of polymerization. A plausible mechanism for the anodic and cathodic initiation reaction has been given. The chemical polymerization of acrylamide that has been initiated by HClO₄ is analogous to its anodic polymerization. The polymer yield increases with an increase in concentration of the monomer and HClO₄. Raising the reaction temperature also enhances the polymerization rate. The overall apparent activation energy of the polymerization was determined to be ca. 19 kcal/mole. The copolymerization of acrylamide was carried out with methyl methacrylate (MMA) in a solution of HClO₄ in DMF. The reactivity ratios are r₁ (AA) = 0.25 and r₂ = 2.50. The polymerization with HClO₄ appears to be by a free radical mechanism. When the polymerization of acrylamide is carried out with HClO₄ in H₂O, a crosslinked water-insoluble gel formation takes place.     

Synthesis and characterization of supramolecular optically active bisamides derived from amino acids

The synthesis and phase transitional behaviour of three pairs of enantiomeric supramolecular hexacatenar liquid crystals (LCs) derived from natural α-amino acids such as l/d-alanine, l/d-leucine and l/d-valine are described. Their preparation with high enantiomeric purity was accomplished by condensing optically active (amino acid residue containing) trialkoxy amines with a 3,4,5-trialkoxy cinnamic acid core using a peptide coupling reagent namely, 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyl-uronium hexafluorophosphate (HBTU). The mesomorphic behaviour of these self-complementing mesogens was ascertained by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. The compounds exhibit columnar (Col) phase over a wide thermal range. Particularly, a pair of enantiomers derived from l/d-leucine residues notably stabilize hexagonal Col (Col_h) phase over a wide temperature range of ?5 °C to 180 °C. Circular dichroism (CD) and FTIR studies suggest the chiral (helical) organization of mesogens within the columns through intermolecular hydrogen bonding; thus, these enantiomers represent one of the rarely reported examples of LCs exhibiting supramolecular Col_h phase at room temperature. The gelation studies reveal the ability of these bisamides to form stable supramolecular gels in ethanol caused through H-bonding interactions.     

Molecular ordering of a cyano compound at a displacive transition temperature: a statistical analysis based on quantum mechanics and computer simulations

A statistical analysis has been carried out to determine the configurational preference of a pair of 4-cyanophenyl 4-n-pentylbenzoate (CPPB) molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. Configurational energy has been computed using the Rayleigh—Schodinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at the phase transition temperature using the Maxwell—Boltzmann formula. An attempt has been made to identify the most probable configuration at the phase transition temperature. Further, the flexibility of various configurations has been studied in terms of variation of probability due to small departures from the most probable configuration. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of the molecular pair have been considered. The results are discussed in the light of experimental as well as theoretical observations. The nature of the mesophase has been correlated with the parameter introduced in this paper.     

The effect of decrease in supercooling on the growth rates: n-Pentadecanoic acid

The Growth rates of crystals fluctuate randomly. In view of such fluctuations, it is more appropriate if a statistical approach is adopted to describe the growth rates of crystals.     

Anti-Obesity Potential of Ponciri Fructus: Effects of Extracts,Fractions and Compounds on Adipogenesis in 3T3-L1 Preadipocytes

Background: Ponciri Fructus, a crude drug consisting of the dried immature fruits of Poncirus trifoliata (L.) Raf., is a popular folk medicine used for the treatment of allergy and gastrointestinal disorders in Korea and China. In this study, the anti-adipogenic activity of extracts and isolated compounds were evaluated using 3T3-L1 preadipocytes. Methods: Dried immature fruits were extracted and fractionated into n-hexane, ethyl acetate (EtOAc), n-butanol and water-soluble fractions. The ethanol extract and fractions were tested for anti-adipogenic activity in the 3T3-L1 cell line. The active fractions (n-hexane and EtOAc fractions) were further subjected to chromatographic techniques to isolate and identify active compounds. Furthermore, the isolated compounds were evaluated for their anti-adipogenic activity. Results: Altogether, seven compounds, including two flavonoids, one phytosteroid and four coumarin derivatives, were isolated. Ethanol extract, n-hexane fraction, EtOAc fraction and three isolated compounds (phellopterin, oxypeucedanin and poncirin) showed significant anti-adipogenic activity as observed by reduced lipid deposition in differentiated 3T3-L1 cells. Further, oxypeucedanin downregulated the key adipogenic markers, such as peroxisome proliferator-activated receptors proteins γ (PPAR-γ), sterol response element binding proteins-1 (SREBP-1), CCAAT/enhancer binding proteins-α (C/EBP-α), adipocyte-specific lipid binding proteins (FABP-4), adipocyte fatty acid binding proteins (aP2), lipoprotein lipase (LPL) and leptin. Conclusion: This study indicated that the ethanol extract, hexane fraction and ethyl acetate fraction of P. trifoliata fruits possess strong anti-adipogenic activity, containing the active compounds such as phellopterin, oxypeucedanin and poncirin. Further research is recommended to explore their efficacy and safety in animal and clinical models.     

(110) Twins of n-C28H58 crystals: Habit changes and lattice net studies

The (110) twins of normal octacosane crystals with hexagonal shape are observed. Various factors that may lead to a shape change are considered. Effect of growth rate anisotropy on the reentrent faces is studied with the help of growth patterns which are derived from a lattice net.