Critical flocculation density of dilute water-in-CO2 emulsions stabilized with block copolymers

The critical flocculation density (CFD), that is, the CO(2) density below which flocculation occurs, was studied for dilute water-in-CO(2) (W/C) miniemulsions stabilized with poly(1,1-dihydroperfluorooctyl methacrylate)-b-poly(ethylene oxide) (PFOMA-b-PEO) surfactants. The CFD, which was measured by turbidimetry, decreased as the PFOMA molecular weight was increased, the average droplet size was decreased, the surfactant loading was increased, and the temperature was increased. A simple model, which addressed both the van der Waals attraction between droplets and osmotic solvent-tail interactions, was in good qualitative agreement with the experimentally observed trends for the CFD and predicted a decrease in emulsion stability as the CO(2) density was lowered toward the theta density for PFOMA in bulk CO(2).     

Highly fluorescent, water-soluble, size-tunable gold quantum dots

Highly fluorescent, water-soluble, few-atom Au quantum dots have been created that behave as multielectron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near IR. Correlation of nanodot sizes with emission energies fits the simple relation, EFermi/N1/3, predicted by the jellium model. Providing the "missing link" between atomic and nanoparticle behavior in noble metals, these emissive, water-soluble Au nanoclusters open new opportunities for biological labels, energy transfer pairs, and light emitting sources in nanoscale optoelectronics.     

Access to Indoles via Diels–Alder Reactions of 5‐Methylthio‐2‐vinylpyrroles with Maleimides

Diels–Alder reactions of 5‐methylthio‐2‐vinyl‐1H‐pyrroles with maleimides followed by isomerization gave tetrahydroindoles in moderate to good yield. Aromatization using activated MnO₂ in refluxing toluene gave the corresponding 2‐methylthioindoles in good yields, and demethylthioation using Raney nickel gave the 2‐H indoles in excellent yields. The protection of the adducts produced aromatization in improved yield, demonstrating the effectiveness of the methylthio group as a protecting group for pyrroles; however, 5‐methylthio‐2‐vinylpyrrole was shown to perform with slightly less efficiency than 2‐vinylpyrrole in Diels–Alder reactions, indicating the protective group was more deactivating than desired. This route toward indoles offers high convergency and conveniently available starting materials that are easily purified. Bis‐methylthioated vinylpyrroles were shown to have potential as highly activated Diels–Alder dienes.     

Some magnetic properties of the cores of various ferritins

⁵⁷Fe Mössbauer spectra of the mineral cores of various ferritins show both paramagnetic and superparamagnetic relaxation effects and in some cases a combination of both. Correlations have been observed between data on the crystallinity, phosphate content and percentage iron in the cores and their magnetic ordering and mean blocking temperatures derived from the Mössbauer spectra.     

Applied field Mössbauer studies of the iron storage proteins ferritin and haemosiderin

Applied field Mössbauer spectra obtained from ferritin and haemosiderin have been fitted using a spin-Hamiltonian model, to determine the effect of the applied field on the direction of the iron magnetic moments. The results of these fits indicate that the ordering of magnetic moments within the ferrihydrite core of these proteins is antiferromagnetic. The values of the anisotropy field obtained from these fits correspond to much higher values of the superparamagnetic blocking temperatures than those actually observed. This anomaly has implications for our understanding of the superparamagnetic relaxation processes in these materials.     

On Voronoi reduction of positive definite quadratic forms

There are two methods of reduction of positive definite quadratic forms due to Voronoi. One of these methods is based on the perfect forms and the other on the type of Voronoi polyhedra associated with the form. It was conjectured by Voronoi that these two methods are strongly connected.     

Iron Chelation in Local Infection

Iron is an essential element in multiple biochemical pathways in humans and pathogens. As part of the innate immune response in local infection, iron availability is restricted locally in order to reduce overproduction of reactive oxygen species by the host and to attenuate bacterial growth. This physiological regulation represents the rationale for the therapeutic use of iron chelators to support induced iron deprivation and to treat infections. In this review paper we discuss the importance of iron regulation through examples of local infection and the potential of iron chelation in treating infection.     

Antiplasmodial Securinega alkaloids from Phyllanthus fraternus: Discovery of natural (+)-allonorsecurinine

The chemical investigation of the antimalarial plant Phyllanthus fraternus G. L. Webster (Phyllanthaceae) resulted in the discovery of the Securinega alkaloid (+)-allonorsecurinine (1), previously reported as a synthetic compound, together with the known ent-norsecurinine (2), nirurine (3), bubbialine (4), epibubbialine (5) and the lignan phyllanthin (6). The structure and absolute configuration of the new compound were elucidated on the basis of extensive spectroscopic analysis, optical rotation, and GIAO NMR shift calculation followed by CP3 analysis. The antiplasmodial activity of these compounds was evaluated against chloroquine-resistant (W2) and -sensitive (3D7) strains of Plasmodium falciparum. Among them, ent-norsecurinine (2) and (+)-allonorsecurinine (1) showed the strongest activity (IC₅₀: 1.14 ± 0.32 and 2.57 ± 0.53 µM) respectively, against W2 but one of the weakest against 3D7.     

Nonequilibrium molecular dynamics simulation for studying the effect of pressure difference and periodic boundary conditions on water transport through a CNT membrane

A NEMD simulation system is constructed to simulate at two-dimensional (2D) periodic boundary conditions (PBCs) and to create two different pressures on two sides of the carbon nanotube (CNT) membrane. The simulation results show that water permeation through the same CNT membrane driven by different pressure differences exhibit similar transport phenomenon including unusually fast water permeation and a periodic (non-parabolic) radial velocity distribution unlike the parabolic form characteristic of continuum flow in the CNT membrane. A three-dimensional (3D) PBC system is also constructed to simulate water permeation through the same CNT membrane at the same pressure differences, to show the effect of PBC and simulation methodologies on transport phenomenon. The two systems both show that the forward/backward water flux increases/decreases with increasing the pressure difference from 1.0 MPa to 8.0 MPa. However, the net flux is higher for the 3D PBC system, especially at higher pressure difference is high. In general, the NEMD simulation method using the 2D PBC system is shown to be a feasible and valuable tool for studying pressure-driven permeation processes such as nanofiltration through these studies with model CNT membrane.