Vortex fluctuations in underdoped Bi(2)Sr(2)CaCu(2)O(8+delta) crystals

Vortex thermal fluctuations in heavily underdoped Bi(2)Sr(2)CaCu(2)O(8+delta) (T(c)=69.4 K) are studied using Josephson plasma resonance. From the zero-field data, we obtain the c-axis penetration depth lambda(L,c)(0)=230+/-10 micrometer and the anisotropy ratio gamma(T). The low plasma frequency allows us to study phase correlations over the whole vortex solid state and to extract a wandering length r(w) of vortex pancakes. The temperature dependence of r(w) as well as its increase with dc magnetic field is explained by the renormalization of the vortex line tension by the fluctuations, suggesting that this softening is responsible for the dissociation of the vortices at the first order transition.     

The Computer-Aided Design,Synthesis, and Activity Prediction of New Leucine Aminopeptidase Inhibitors

The design, stereo-, and enantioselective synthesis and activity prediction of aminophosphonic acids as new leucine aminopeptidase inhibitors will be discussed.     

Facile Synthesis of bis‐α‐Aminoalkylphosphinates

Herein we report a facile synthesis of esters of bis‐α‐aminoalkylphosphinic acids obtained by an addition of Cbz‐protected phosphinic analogues of amino acid methyl esters to an appropriate imine in refluxing benzene. Complete deprotection of the esters could be achieved in one step by the action of 30% HBr in acetic acid.     

One-Pot Synthesis and Applications of N-Heteroaryl Iodonium Salts

An efficient one-pot synthesis of N-heteroaryl iodonium triflates from the corresponding N-heteroaryl iodide and arene has been developed. The reaction conditions resemble our previous one-pot syntheses, with suitable modifications to allow N-heteroaryl groups. The reaction time is only 30 min, and no anion exchange is required. The obtained iodonium salts were isolated in a protonated form, these salts can either be employed directly in applications or be deprotonated prior to use. The aryl groups were chosen to induce chemoselective transfer of the heteroaryl moiety to various nucleophiles. The reactivity and chemoselectivity of these iodonium salts were demonstrated by selectively introducing a pyridyl moiety onto both oxygen and carbon nucleophiles in good yields.     

Barrier Dispersion-Based Coatings Containing Natural and Paraffin Waxes

Petroleum, synthetic, and natural waxes have been used as hydrophobic bases for dispersions intended for use as barrier coatings for packaging paper. Oil-in-water dispersions with alkaline pH were prepared by a two-step homogenization procedure containing paraffin wax, with various characteristics, the Fischer–Tropsch synthesis product or beeswax. The size of the dispersed particles determined by dynamic light scattering depended on the type of hydrophobic base used and was in the range of 350–440 nm. The ability of dispersion particles in aggregation driven by electrostatic attraction, evaluated by Zeta potential analysis by electrophoretic light scattering, was from −26 to −50 mV. Static multiply light scattering was used for 30 days of stability assessment and helped to select the dispersion with a Sarawax SX70 wax base as the most stable. Dispersions were further used for coating the backing of kraft paper by the Meyer rod method. Coated paper with an applied coating of 6 g/m² had very good hydrophobic properties (Cobb60 < 4 g/m²), sufficient strength properties, and air permeation, which enabled its application as a packaging material. The dispersions based on Sarawax SX70 wax were evaluated as the best coating for Mondi ProVantage Kraftliner 125 g/m² backing paper. Good hydrophobic properties and strength properties indicate the possibility of using the SX70-based wax dispersion coating as a replacement for PFAS coatings in some applications.     

Selected local stability problems of channel section flanges made of aluminium alloys

The paper addresses the issue of local buckling of compressed flanges of cold-formed thin-walled channel columns and beams with nonstandard flanges composed of aluminium alloys. The material behaviour follows the Ramberg–Osgood law. It should be noted that the proposed solution may be also applied for other materials, for example: stainless steel, carbon steel. The paper is motivated by an increasing interest in nonstandard cold-formed section shaping in local buckling analysis problems. Furthermore, attention is paid to the impact of material characteristics on buckling stresses in a nonlinear domain. The objective of the paper is to propose a finite element method (FEM) model and a relevant numerical procedure in ABAQUS, complemented by an analytical one. It should be noted that the proposed FEM energetic technique makes it possible to compute accurately the critical buckling stresses. The suggested numerical method is intended to accurately follow the entire structural equilibrium path under an active load in elastic and inelastic ranges. The paper is also focused on correct modelling of interactions between sheets of cross section of a possible contact during buckling analysis. Furthermore, the FEM results are compared with the analytical solution. Numerical examples confirm the validity of the proposed FEM procedures and the closed-form analytical solutions. Finally, a brief research summary is presented and the results are discussed further on.     

The carbenium ion - oxonium ion exchange processes related to vinyl and ring-opening polymerization

It has previously been proposed (Ref. 1) that in the cationic vinyl polymerizations, proceeding with termination due to the collapse of ion pairs, addition of bases increases “livingness”, because of the fast convertion of the otherwise dead (within the time of polymerization) covalent species into the onium ions; these, in turn, fast convert into carbenium ions, the actually propagating species. Equilibria between carbenium ions (CH₃OCH₂⁺A⁻ has been used as a model) and their onium counterparts ((CH₃)₂O taken as a model base) as well as between covalent species (CH₃OCH₂OSO₂CF₃) and the corresponding oxonium ion (with a (CH₃)₂O ligand) have been studied by dynamic ¹H and ¹⁹F NMR. Total ionization of methoxymethyl triflate (CH₃OCH₂OSO₂CF₃) has been shown to increase indeed from 10⁴ (-10°C) to 10⁶ (-70°C) times when 1,0 mol·L⁻¹ of (CH₃)₂O is added. Although this model system better describes polymerization of cyclic acetals than that of vinyl ethers, it shows at least qualitatively the importance of bases in ionization of covalent species, which may be responsible for reinitiation in the cationic polymerization of vinyl ethers.     

Polymerization of phosphorus containing cyclic monomers: Synthesis of polymers related to biopolymers

The mechanism of polymerization is discussed, in which cyclic esters of phosphoric acid, and related compounds are converted into linear macromolecules, modelling nucleic and teichoic acid backbones. Structures like deoxyribose polyphosphate and glycerol polyphosphate were prepared from the corresponding cyclic compounds. These polymerizations involve heterolytic breaking of the P-O bond in the cyclic monomer and proceed by ionic mechanism. Both 5- and 6-membered monomers have been polymerized. The thermodynamic parameters of the ring-chain interconversion were determined; the 5-membered rings polymerization is driven by the exothermicity of the ring-opening, whereas polymerization of several 6-membered rings is endothermic and allowed because of the positive change of entropy. Anionic polymerization, and particularly the pseudo(coordinate)anionic polymerization provides, in contrast to the cationic process, high-molecular-weight polymers with more uniform structure. Anionic polymerization proceeds mostly (at the applied conditions) on the macroion – -pairs. The elementary reactions consist of the nucleophilic attack of the paired macroanions on the phosphorus atom in the cyclic monomer molecule. Rate constants of the elementary reactions for the model monomers will be presented. Stereochemistry of the propagation steps is shown to be governed by the statistical ring-opening, leading to the three kinds of polymer units (head-to-tail and two symmetrical units). Apart from the ring-opening, the polyaddition of diepoxides to phosphorous and phosphoric acids is described. Finally, a few examples of preparation of models of biopolymers are given, namely poly(deoxyribose phosphate) and poly(glycerol phosphate).