Structure-activity relationships of antibacterial acyl-lysine oligomers

We describe structure-activity relationships that emerged from biophysical data obtained with a library of antimicrobial peptide mimetics composed of 103 oligoacyllysines (OAKs) designed to pin down the importance of hydrophobicity (H) and charge (Q). Based on results obtained with OAKs displaying minimal inhibitory concentration < or = 3 microM, the data indicate that potent inhibitory activity of the gram-negative Escherichia coli and the gram-positive Staphylococcus aureus required a relatively narrow yet distinct window of HQ values where the acyl length played multiple and critical roles, both in molecular organization and in selective activity. Thus, incorporation of long-but not short-acyl chains within a peptide backbone is shown to lead to rigid supramolecular organization responsible for poor antibacterial activity and enhanced hemolytic activity. However, sequence manipulations, including introduction of a tandem lysine motif into the oligomer backbone, enabled disassembly of aggregated OAKs and subsequently revealed tiny, nonhemolytic, yet potent antibacterial derivatives.     

Schmidt’s game on fractals

We construct (α, β) and α-winning sets in the sense of Schmidt’s game, played on the support of certain measures (absolutely friendly) and show how to compute the Hausdorff dimension for some. In particular, we prove that if K is the attractor of an irreducible finite family of contracting similarity maps of ℝ ^N satisfying the open set condition, (the Cantor’s ternary set, Koch’s curve and Sierpinski’s gasket to name a few known examples), then for any countable collection of non-singular affine transformations, Δ _i : ℝ ^N → ℝ ^N ,

Reductive Bergman-type cyclizations of cross-conjugated enediynes to fulvene and fulvalene anions: the role of the substituent

Various cross-conjugated enediynes undergo "Bergman-type" cycloaromatizations upon reduction with potassium metal, generating anions of fulvenes and fulvalene derivatives. This new anionic cyclization is considerably more facile than the classic Bergman cyclization with linear enediynes, creating highly reactive diradicals at -78 degrees C. Not all cross-conjugated enediynes yield cyclized dianions upon reduction; some give uncyclized, Y-shaped, cross-conjugated dianions, while others apparently yield radical-anions that either dimerize or persist as monomers. One system yields both a cyclized and an uncyclized dianion. The substituents are thus shown to be a critical factor in determining the outcome of the reduction. Cyclization occurs within a specific "window of opportunity" that is governed by the substituents.     

Low-concentration series in general dimension

We discuss recent work on the development and analysis of low-concentration series. For many models, the recent breakthrough in the extremely efficient no- free-end method of series generation facilitates the derivation of 15th-order series for multiple moments in general dimension. The 15th-order series have been obtained for lattice animals, percolation, and the Edwards-Anderson Ising spin glass. In the latter cases multiple moments have been found. From complete graph tables through to 13th order, general dimension 13th-order series have been derived for the resistive susceptibility, the moments of the logarithms of the distribution of currents in resistor networks, and the average transmission coefficient in the quantum percolation problem, 11th-order series have been found for several other systems, including the crossover from animals to percolation, the full resistance distribution, nonlinear resistive susceptibility and current distribution in dilute resistor networks, diffusion on percolation clusters, the dilute Ising model, dilute antiferromagnet in a field, and random field Ising model and self-avoiding walks on percolation clusters. Series for the dilute spin-1/2 quantum Heisenberg ferromagnet are in the process of development. Analysis of these series gives estimates for critical thresholds, amplitude ratios, and critical exponents for all dimensions. Where comparisons are possible, our series results are in good agreement with both-expansion results near the upper critical dimension and with exact results (when available) in low dimensions, and are competitive with other numerical approaches in intermediate realistic dimensions.     

Growing ZnO crystals on magnetite nanoparticles

We report herein on the oriented growth of ZnO crystals on magnetite nanoparticles. The ZnO crystals were grown by hydrolyzing a supersaturated aqueous solution of zinc nitrate. The seeds for the growth were magnetite nanoparticles with a diameter of 5.7 nm and a narrow size distribution. Hollowed ZnO hexagons of 0.15 microm width and 0.5 microm length filled with Fe(3)O(4) particles were obtained. HR-TEM (high-resolution transmission electron microscopy) and selected-area EDS (energy-dispersive spectroscopy) show that the nanoparticles are homogenously spread in the ZnO tubes. Zeta potential measurements were employed to understand the relationship between the nanoparticles and the oriented growth of the ZnO crystals. The results show that the surfactants induced the directional growth of the ZnO crystals.     

Adhesion in elastic-plastic spherical microcontact

An elastic-plastic adhesion model for a metallic deformable sphere pressed by a rigid flat is presented. Analytical dimensionless expressions for the local separation outside the contact area and for the adhesion force are provided covering a large range of interference values from a point contact to a fully plastic contact. Two main dimensionless parameters of the problem are identified and their effect on the adhesion is investigated. The significance of the adhesion in the elastic-plastic contact force balance is discussed and the regimes where adhesion is important or negligible are pointed out. A comparison of the present results with a previously published approximate elastic-plastic model shows substantial differences in the local separation and in the adhesion force.     

Assessing and measuring the active site density of PGM-free ORR catalysts

Journal of Solid State Electrochemistry - Fuel cells are already employed in commercial transportation even though their price is still too high to enable widespread production. A viable and...