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.     

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.     

Reactions of 1,3-bis(ω-bromoalkyl)-6-methyluracils with 2-(dialkylamino)ethylphosphonates and 2-(dialkylamino)ethyl phosphates

1,3-Bis(4-bromobutyl)-6-methyluracil reacts with diethyl 2-(dimethylamino)ethylphosphonate to form a bisquaternary ammonium salt, whereas the reaction of 1,3-bis-(6-bromohexyl)-6-methyluracil with diethyl 2-(diethylamino)ethyl phosphate gives 1,3-bis-[(6-diethoxyphosphoryloxy)hexyl]-6-methyluracil and 1,1,4,4-tetraethylpiperazinium dibromide. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1130–1132, June, 2000.     

Açaí (Euterpe oleracea Mart.) Seed Extracts from Different Varieties: A Source of Proanthocyanidins and Eco-Friendly Corrosion Inhibition Activity

Euterpe oleracea Mart. (Arecaceae) is an endogenous palm tree from the Amazon region. Its seeds correspond to 85% of the fruit’s weight, a primary solid residue generated from pulp production, the accumulation of which represents a potential source of pollution and environmental problems. As such, this work aimed to quantify and determine the phytochemical composition of E. oleracea Mart. seeds from purple, white, and BRS-Pará açaí varieties using established analytical methods and also to evaluate it as an eco-friendly corrosion inhibitor. The proanthocyanidin quantification (n-butanol/hydrochloric acid assay) between varieties was 6.4–22.4 (w/w)/dry matter. Extract characterization showed that all varieties are composed of B-type procyanidin with a high mean degree of polymerization (mDP ≥ 10) by different analytical methodologies to ensure the results. The purple açaí extract, which presented 22.4% (w/w) proanthocyanidins/dry matter, was tested against corrosion of carbon steel AISI 1020 in neutral pH. The crude extract (1.0 g/L) was effective in controlling corrosion on the metal surface for 24 h. Our results demonstrated that the extracts rich in polymeric procyanidins obtained from industrial açaí waste could be used to inhibit carbon steel AISI 1020 in neutral pH as an abundant, inexpensive, and green source of corrosion inhibitor.     

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.

     

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.     

Reaction of 6-methyluracyl derivatives with acetylacetone and ethyl acetoacetate

Reaction of acetylacetone and ethyl acetoacetate with 1-(ω-bromoalkyl)-3,6-dimethyluracyls and 1,3-bis(ω-bromoalkyl)-6-methyluracyls lead to the formation of uracyl derivatives containing the ketone and ketoester fragments. Conditions leading to the highest yields of the compounds synthesized were found.     

Phosphorylation of Pyrimidinophane in the Reversed Micellar Solutions of Cationic and Nonionogenic Surfactants

Reactions of a macrocycle containing three pyrimidine fragments and N,N′-bis(2-methylthio-6-methylpyrimidin-4-yl)-hexamethylenediamine with p-nitrophenyl bis(chloromethyl)phosphinate in the micellar solutions of cetyltrimethylammonium bromide, polyethyleneglycol-600 laurate and their mixture in chloroform was investigated spectrophotometrically. Catalytic activity of micelles depends on their structure, concentration of surfactants, molar fraction of the latter in solution, and structure of the nucleophilic reagent.