Functionally Substituted Isocyanurates with Heteroatoms (O,S) in the N-Alkyl Chain

Alkylation of disodium benzyl and disodium methyl isocyanurates with ,'-dichlorodiethyl and ,'-dibromodiethyl ethers was used to prepare 1-benzyl and 1-methyl 3,5-bis[2-(2-haloethoxy)ethyl] isocyanurates whose reaction with thiourea followed by hydrolysis gave the corresponding 1-alkyl 3,5-bis[2-(2-mercaptoethoxy)ethyl] isocyanurates. 1-Benzyl and 1-methyl 3,5-bis[2-(2-chloroethyl)ethyl] isocyanurates were reacted with NaSCH₂CH₂OH to obtain the corresponding 1-alkyl 3,5-bis[2-(2-hydroxyethylthio)ethyl] isocyanurates. Treatment of the latter two esters with thionyl chloride gave 1-benzyl and 1-methyl 3,5-bis-[2-(2-chloroethylthio)ethyl] isocyanurates, respectively.     

Magnetic field and pressure dependence of small angle neutron scattering in MnSi

We report small angle neutron scattering of spontaneous and magnetic field aligned components of the helical spin polarization in MnSi for temperatures T down to 0.35 K, at pressures p up to 21 kbar, and magnetic field B up to 0.7 T. The parameter range of our study spans the first order transition between helical order and partial magnetic order at p{c}=14.6 kbar, which coincides with the onset of an extended regime of non-Fermi liquid resistivity. Our study suggests that MnSi above p{c} is not dominated by the remnants of the first order transition at p{c}, but that an unidentified mechanism favors stabilization of a new ground state other than helical order.     

Chemistry and kinetics of chemical vapor deposition of pyrolytic carbon from ethanol

Synthesis of pyrolytic carbon as a matrix for carbon fiber reinforced carbon composites by chemical vapor infiltration (CVI) is studied experimentally and numerically using the oxygen-containing precursor ethanol. The effects of residence time on microstructure and deposition rate of pyrolytic carbon are investigated. A short residence time is found to favor the formation of high-textured pyrolytic carbon. The evolutions of microstructure and deposition rate of pyrolytic carbon are compared with those of carbon deposited from methane. Compared to methane, ethanol exhibits a much higher deposition rate of pyrolytic carbon with similar microstructures. Pyrolysis of ethanol is modeled using a two-dimensional flow model coupled with a detailed gas-phase reaction mechanism involving 261 species taking part in 1177 reversible reactions. Reaction rate analysis reveals that C₃-hydrocarbons are the most important intermediate species contributing to the maturation of gas-phase composition. A comparison of the kinetic predictions with equilibrium calculations demonstrates that the CVD reactor applied is operated far away from equilibrium.     

Confinement and lattice quantum-electrodynamic electric flux tubes simulated with ultracold atoms

We propose a method for simulating (2+1)D compact lattice quantum-electrodynamics, using ultracold atoms in optical lattices. In our model local Bose-Einstein condensates' (BECs) phases correspond to the electromagnetic vector potential, and the local number operators represent the conjugate electric field. The well-known gauge-invariant Kogut-Susskind Hamiltonian is obtained as an effective low-energy theory. The field is then coupled to external static charges. We show that in the strong coupling limit this gives rise to "electric flux tubes" and to confinement. This can be observed by measuring the local density deviations of the BECs, and is expected to hold even, to some extent, outside the perturbative calculable regime.     

Phosphorylation of Dialkylaminomethylated Calix[4]-Resorcinarenes with Some P(III) and P(IV) Derivatives

Abstract

The phosphorylation of dialkylaminomethylated calix[4]resorcinarenes with P(m)-amides and P(TV)chlorides under various conditions results in the formation of different structures with phosphorus containing fragments fixed on the cavity rim. Hydrophosphoryl compounds based on dialkylaminomethylated calix[4]resorcinarenes have been synthesized and some of their properties investigated.     

Macrocyclic 5-bromouracil derivatives: synthesis and transformation of a uracil ring

Cyclization of 1,3-bis(ω-bromoalkyl)-5-bromouracil with p-methoxybenzylamine or sodium sulfide led to a series of pyrimidinophanes containing heteroatoms in bridges. An unusual behaviour of the 5-bromouracil ring, namely its contraction into hydantoin units during the cyclization reactions with p-methoxybenzylamine was observed. Sodium sulfide does not affect the 5-bromouracil ring, and no transformation products were observed in the synthesis of pyrimidinophanes with sulfur bridges. A possible reaction mechanism is given.     

Single ion diffusive transport within a Poly(styrene sulfonate) polymer brush matrix probed by fluorescence correlation spectroscopy

Diffusive transport within complex environments is a critical piece of the chemistry occurring in such diverse membrane systems as proton exchange and bilayer lipid membranes. In the present study, fluorescence correlation spectroscopy was used to evaluate diffusive charge transport within a strong polyelectrolyte polymer brush. The fluorescent cation rhodamine-6G was used as a counterion probe molecule, and the strong polyelectrolyte poly(styrene sulfonate) was the polymer brush. Such strong polyelectrolyte brushes show promise for charge storage applications, and thus it is important to understand and tune their transport efficiencies. The polymer brush demonstrated preferential solvation of the probe counterion as compared to solvation by the aqueous solvent phase. Additionally, diffusion within the polymer brush was strongly inhibited, as evidenced by a decrease in diffusion constant of 4 orders of magnitude. It also proved possible to tune the transport characteristics by controlling the solvent pH, and thus the ionic strength of the solvent. The diffusion characteristics within the charged brush system depend on the brush density as well as the effective interaction potential between the probe ions and the brush. In response to changes in ionic strength of the solution, it was found that these two properties act in opposition to each other within this strong polyelectrolyte polymer brush environment. A stochastic random walk model was developed to simulate interaction of a diffusing charged particle with a periodic potential, to show the response of characteristic diffusion times to electrostatic field strengths. The combined results of the experiments and simulations demonstrate that responsive diffusion characteristics in this brush system are dominated by changes in Coulombic interactions rather than changes in brush density. More generally, these results support the use of FCS to evaluate local charge transport properties within polyelectrolyte brush systems, and demonstrate that the technique shows promise in the development of novel polyelectrolyte films for charge storage/transport materials.     

Regulation of Stem Cell Differentiation by Control of Retinoic Acid Gradients in Hydrospun 3D Scaffold

Morphogen gradients have been associated with differential gene expression and are implicated in the triggering and regulation of developmental biological processes. This study focused on creating morphogenic gradients through the thickness of hydrospun scaffolds. Specifically, electrospun poly(ε‐caprolactone) fibers were loaded with all‐trans‐retinoic acid (ATRA), and designed to release ATRA at a predetermined rate. Multilayered scaffolds designed to present varied initial ATRA concentrations were then exposed to flow conditions in a bioreactor. Gradient formation was verified by a simple convection‐diffusion mathematical model approving establishment of a continuous solute gradient across the scaffold. The biological value of the designed gradients in scaffolds was evaluated by monitoring the fate of murine embryonal carcinoma cells embedded within the scaffolds. Cell differentiation within the different layers matched the predictions set forth by the theoretical model, in accordance with the ATRA gradient formed across the scaffold. This tool bears powerful potential in establishing in vitro simulation models for better understanding the inner workings of the embryo.

     

The motion of a cylindrical body in a stratified fluid under the action of a radiation force

The free motion of a thin cylindrical body is investigated based on a previously derived expression for the radiation force acting on moving point sources in a stratified fluid. The fundamental equations of motion are derived, the limits of applicability of the approximation used are indicated and the results of calculations of typical trajectories of a body which begins to move with a specified velocity from a position of neutral buoyancy at an angle to the horizon are presented. Calculations of the trajectory of motion of a thin cylindrical body in a stratified fluid when the total radiation force is taken into account show that the effect of the lateral component of this force is considerable and leads not only to quantitative corrections but also to qualitative effects (for example, to an increase in the oscillations of the body and a change in its direction of motion). The results obtained pertain both to the motion of solids in fluids and to the translational motion of vortex dipoles in weakly stratified media.