On the probability of the outcomes in buckling of an elastic beam

A nonlinear time-varying one-degree-of-freedom system, which is used for the modelling of the buckling of a loaded beam in Euler??s problem, is considered. For a slowly changing load, the deterministic approach in this problem fails if the trajectories pass through the separatrix. An expression for the probability of possible outcomes of the evolution of the oscillations is obtained. The analytical and numerical results are compared.     

Pyrrolidine-thioxotetrahydropyrimidinone as an efficient organocatalyst for the enantioselective Michael addition of cyclic ketones to nitrodienes

Among the various Michael additions, the enantioselective reaction between cyclic ketones and nitrodienes has received little attention in comparison to the corresponding reaction with nitroolefins. A bifunctional organocatalyst consisting of the pyrrolidine moiety and a thioxotetrahydropyrimidinone ring successfully catalyzed this asymmetric transformation. The products of the reaction between various ketones and nitrodienes were obtained in high yields (up to 96%) with excellent diastereo- (up to >98:2 dr) and enantioselectivities (up to 99:1% er).     

Percolation Thresholds in Ternary Polymer Melt Blends with Separate Dispersions of the Inner Phases: Mathematical Model

A mathematical model based on a straightforward geometrical background is developed which enables predictions of a transition of one dispersed phase to a cocontinuous one (i.e., the percolation threshold) on addition of another dispersed phase during melt mixing in ternary polymer blends. The present work concerns only ternary blends with two separate dispersions of the inner phases in which no encapsulation takes place. In addition, in order to simplify the model, one of the inner phases was represented by hard, nondeformable microspheres The expression developed describes well an experimental relationship between the percolation threshold, the concentration above which the former dispersed phase transforms to a continuous one, and concentrations of both inner phases. The results agree well with the experimental data obtained in a previous work.     

Fine Tuning of Heme Reactivity: Hydrogen-Bonding and Dipole Interactions Affecting Ligand Binding to Hemoproteins

Heme reactivity in hemoproteins is governed by the microenvironment near the ligand binding site. In order to quantify polarity effects on heme ligand binding, the kinetics of O₂ and CO binding have been measured for a series of synthetic heme models equipped with a range of groups of varying dipole moments positioned near the heme coordination site. For hemes with polar aprotic groups, both O₂ on (k′) and off rates (k) are found to be dependent on the dipole moment. For model systems containing protic groups, the O₂ off rate is substantially reduced due to hydrogen bonding with the coordinated O₂. The hydrogen-bonding stabilization is estimated to be 0.7 and 1.6 kcal/mol for an alcohol and a secondary amide, respectively. CO binding displays little correlation with a polarity effect; instead it seems to depend upon the size and position of the polar group.     

Wetting behavior of pulmonary surfactant aqueous solutions

The wetting properties of pulmonary surfactant aqueous solutions with respect to solid surfaces with different degree of hydrophobicity have been studied. The contact angles θ of drops from a pulmonary surfactant solution onto SiO₂-glass surfaces have been measured as a function of their degree of hydrophobicity θ _w. The completely hydrophilic SiO₂-glass surface is essentially hydrophobized by the animal-derived pulmonary surfactant Curosurf. The hydrophobization depends on the surfactant concentration—the contact angles increase with increasing the Curosurf concentration C _s in the low concentration range, but they remain almost constant in a wide range of C _s >90 μg/ml. Additions like NaCl and bovine serum albumin influence the θ-values. The contact angles θ naturally increase with increasing θ _w but this dependence is not linear—the curve steepens at larger θ _w values. The thickness h of the wetting thin liquid films from Curosurf aqueous solutions depends on the hydrophobicity θ _w of the solid surface and the h(θ _w) curves always pass a minimum. The h-values, as well as the h(θ _w) curve, are mainly determined by the steric and hydrophobic disjoining pressures, which depend on the orientations and conformations of the molecules adsorbed on the solid surface from the very complicated multi-component aqueous solutions.     

Photolysis of 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins—Effective Fluorescence Decay

Photophysical characteristics of new 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins have been measured. These coumarin derivatives are found to be effective fluorophores and show high values of quantum yields of fluorescence both in nonpolar and in polar solvents. The 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins turned to be photosensitive compounds and undergo photolysis under irradiation in the range of 310–465 nm. Photolysis is suggested to include retro-cyclization and retro-condensation steps. The process is accompanied by a sharp drop of fluorescence that can be of interest for the creation of new media in optical recording of information.     

One-pot five-component high diastereoselective synthesis of polysubstituted 2-piperidinones from aromatic aldehydes,nitriles, dialkyl malonates and ammonium acetate

Molecular Diversity - A novel five-component diastereoselective synthesis of polysubstituted 2-piperidinones is reported. The Knoevenagel condensation–Michael addition–Mannich cascade...