A method for stabilizing the cis prolyl peptide bond: influence of an unusual n→π interaction in 1,3-oxazine and 1,3-thiazine containing peptidomimetics

The cis/trans isomer ratios of the Xaa-Pyr (Pyr = pyrrolidine) 3° amide bonds are significantly high (∼90% cis) in the novel peptidomimetics where Pyr contains 1,3-oxazine (Oxa) or 1,3-thiazine (Thi) at its 2 position. We find that an unusual n→π_i−1^∗ interaction, selectively stabilizes the cis conformer and the n)(n repulsion destabilizes the trans conformer of these molecules. Both these electronic effects oppose the steric effects in the 3° amide bond. The structural requirements for manifestation of these electronic effects are determined.     

Influence of terminal substitution on structural, DNA, protein binding, anticancer and antibacterial activities of palladium(II) complexes containing 3-methoxy salicylaldehyde-4(N) substituted thiosemicarbazones

The variable chelating behavior of 3-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazones was observed in equimolar reactions with [PdCl(2)(PPh(3))(2)]. The new complexes were characterized by various analytical, spectroscopic techniques (mass, (1)H-NMR, absorption, IR). All the new complexes were structurally characterized by single crystal X-ray diffraction. Crystallographic results showed that the ligands H(2)L(1) and H(2)L(4) are coordinated as binegative tridentate ONS donor ligands in the complexes 1 and 4 by forming six and five member rings. However, the ligands H(2)L(2) and H(2)L(3) bound to palladium in 2 and 3 as uninegative bidentate NS donors by forming a five member chelate ring. From this study, it was found that the substitution on terminal 4(N)-nitrogen may have an influence on the chelating ability of thiosemicarbazone. The presence of hydrogen bonding in 2 and 3 might be responsible for preventing the coordination of phenolic oxygen to the metal ion. The interaction of the complexes with calf-thymus DNA (CT-DNA) has been explored by absorption and emission titration methods. Based on the observations, an electrostatic binding mode of DNA has been proposed. The protein binding studies were monitored by quenching of tryptophan and tyrosine residues in the presence of complexes using Lysozyme as model protein. Antibacterial activity studies of the complexes have been screened against pathogenic bacteria such as Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa. MIC50 values of the complexes showed that they exhibited significant activity against the pathogens and among them, 3 exhibited higher activity. Further, anticancer activity of the complexes on the lung cancer cell line A549 has also been studied.     

Dielectric studies of alkyl acrylates with primary alcohols using time domain reflectometry

Binary polar–polar liquid mixtures of alkyl acrylates (methyl acrylate, ethyl acrylate and butyl acrylate) with primary alcohols (propan-1-ol, butan-1-ol and hexan-1-ol) were subjected to dielectric studies at 303?K for different concentrations using time domain reflectometry (TDR) over the frequency range from 10?MHz to 10?GHz. Static permittivity (ε₀) dielectric constant at high frequency (ε_∞) and relaxation time (τ) were found through dielectric measurements for different concentrations of each system. The Bruggeman dielectric factor, Kirkwood correlation factor and the excess inverse relaxation time were determined and discussed to yield information on the molecular interactions of the systems. Deviations from the linearity of various models suggest molecular association through hydrogen bonding between the ?OH group of alcohols and C=O group of esters. The results also show a dependence of dielectric parameters on the alkyl chain length of both the alcohols and esters.     

Femtosecond dynamics of the collinear-to-spiral antiferromagnetic phase transition in CuO

We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase. These results indicate that the ultimate speed for this antiferromagnetic reorientation transition in CuO is limited by the long-wavelength magnetic excitation connecting the two phases.     

Structural studies on Na0.75CoO2 thermoelectric material at high pressures

The crystal structure of Na_0.75CoO₂ was studied at ambient and low temperatures down to 10 K at pressures up to 40 GPa using synchrotron x-rays and a diamond cell in angle dispersion geometry. A reduction in the c/a ratio was observed at both conditions with the application of pressure. An increase in Co–O bond lengths and a decrease in Na–O bond lengths were observed above 10 GPa. The results of the density functional calculations performed agree well with the pressure induced bond length changes. The anomalous change in the c/a ratio and bond lengths indicate a pressure induced isostructural phase transition above 10 GPa. Bulk modulus calculations show this compound is less compressible than its hydrated analogues.     

Phosphonated mesoporous silica based composite membranes for high temperature proton exchange membrane fuel cells

Journal of Solid State Electrochemistry - Mesoporous Santa Barbara Amorphous (SBA-15) was synthesized, and it was grafted with phosphonate functionality using a simple two-step process involving...     

Investigation of a Spin Transition in a LaCoO<Subscript>3</Subscript> Single Crystal by the Method of X-Ray Magnetic Circular Dichroism at the Cobalt <Emphasis Type="Italic">K</Emphasis>- and <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript>-Edges

Spin transitions of cobalt ions in LaCoO₃ single crystals have been studied by the method of X-ray magnetic circular dichroism (XMCD) at the K- and L_2,3-edges of Co³⁺ ions. The orbital momentum of cobalt ions obtained for the K-edge at the 3d level in the region of the spin transition in the temperature range from 25 to 120 K increases by a factor of approximately 1.6, whereas the slope of the magnetization curve value in the same temperature range and magnetic field increases by a factor of more than 10. XMCD experiments at the cobalt L_2,3-edges demonstrate gradual growth of the ratio of the orbital momentum to the spin one L/S from 0.48 to 0.53 in the temperature range from 60 K to 120 K.     

Dynamic response of composite plates with cut-outs,part I: Simply-supported plates

The effect of square cut-outs on the natural frequencies of square, simply-supported composite plates is investigated. The forced and free dynamic response of plates with cut-outs is formulated. Laminations are assumed to be symmetric about the mid-plane and the plates are considered analytically as homogeneous anisotropic plates. In the method of solution it is assumed that the effect of the cut-out is equivalent to an external loading on the plate. For free vibration, the method leads to an infinite system of frequency equations. Depending upon the accuracy required, a suitable size of the system of frequency equations is selected. Results are given for square, simply-supported composite plates with centrally located square cut-outs for different modulus ratios. A comparison of results obtained from this method for isotropic plates with cut-outs with available literature is made and excellent agreement is obtained.     

APPLICATION OF STRAIN GAGES TO MEASURE ADHESIVE STRAINS THROUGH THE THICKNESS OF AN ADHESIVELY -BONDED STIFFENED STRIP

Small strain gages were used to measure the through-the-thickness extensional strain distribution in an adhesively-bonded stiffened strip subjected to four-point bending. A comparison between experiment and analysis was conducted. The results show good correlation of the experimental and analytical trends of the through-the-thickness extensional strain distribution in the adhesive layer.