Micelle and Vesicle Formation of Amphiphilic Nanoparticles

Nanoparticle brushes : Complex nanostructures can be formed by self assembly of amphiphilic CdSe/CdS core–shell nanoparticles that bear a brushlike layer of poly(ethylene oxide) chains. This route is based on controlling the volume fractions of hydrophilic and hydrophobic moieties within the particles and allows the formation of micellar, cylindrical, or vesicular nanoobjects (see picture).

     

Analysis of the influence of interdetector volume on local calibration in size exclusion chromatography with dual multiangle-light-scattering/concentration detection

A comparison of the s- and w-detections of molecular weight, a necessary condition for precise determination of interdetector volume in size exclusion chromatography of polymers with the dual light scattering--concentration detection, is examined. From the theoretical analysis for a polymer with the log-normal molecular weight distribution it follows that the error in determination of the local calibration, i.e., of a logarithmic dependence of molecular weight on elution volume obtained by the s-detection, from the known dependence of radius of gyration on elution volume and of molecular weight on the radius of gyration, remains linear and is slightly shifted with respect to that obtained by the w-detection (dual detection giving the weight-average molecular weight) towards higher molecular weights, the difference being below the experimental error. It also follows that the error in the slope of local calibration found by the w-detection is given by the ratio of the error in interdetector volume and the variance of the elution curve. This is demonstrated on several polymer samples with symmetric elution curves of polymer samples differing in polydispersity indices. The range of this rule depends on the broadness and symmetry of elution curves. The precision of the interdetector volume determination depends therefore strongly on the Mw/Mn ratio of the sample.     

Statistical properties of the band-broadening function

Statistical properties of the band-broadening function calculated from the equilibrium and kinetic theories of Giddings and Eyring are compared with real liquid-chromatography elution curves of low-molecular-weight substances and with light-scattering elution curves of a high-molecular-weight polystyrene standard injected at several concentrations. The curves obtained by liquid chromatography agree in a large span of elution times with the theoretical ones and can be described by one value of the plate-height. The size exclusion chromatography (SEC) elution curves seem to approach the predicted statistical properties with decreasing concentration of injected polymer but, in general, a reliable prediction of band-broadening (BB) functions in SEC of polymers, especially of non-symmetric BB functions near the exclusion limit, seems not possible at this point. The relation of the theory with the characteristic-function approach developed by Dondi is also discussed.     

Annual variation in photo acclimation and photoprotection of the photobiont in the foliose lichen Xanthoria parietina

Seasonal variation in maximal photochemical quantum yield (F(V)/F(M)) of photosystem II (PS II), light adapted quantum yield (Phi(II)) of PS II, non-photochemical quenching (NPQ), contents of chlorophylls, and xanthophyll cycle pigments (VAZ) was studied in Xanthoria parietina repeatedly sampled in one location in S Norway during one year. The seasonal course in the susceptibility to photoinhibition was evaluated as high light-induced changes (1,800 micromol photons m(-2) s(-1) for 24h) in F(V)/F(M), Phi(II), and NPQ, measured as the ability to recover after 2 and 20 h at low light in control thalli with a natural cortical parietin screen, and in thalli from which parietin had been removed prior to high light exposures. F(V)/F(M), Phi(II), chlorophyll content, and the conversion state of VAZ (DEPS) reached minimum in spring. At the same time, yearly maxima of VAZ content and NPQ were recorded. Thereafter, F(V)/F(M), Phi(II), and chlorophyll content increased gradually, reaching maximum values in late autumn. DEPS peaked already in summer. Similarly, VAZ and NPQ decreased from early summer until winter. All data show that the X. parietina photobiont acclimates to seasonal changes in solar radiation, consistent with the lichen's preference for well-lit habitats. However, a comparison with a study of seasonal acclimation in the X. parietina mycobiont shows that in order to understand the seasonal photobiont acclimation, one has to consider the seasonal variation in internal screening caused by the fungal regulation of the PAR-absorbing parietin. A joint effort of both bionts seems to be required to avoid serious photoinhibition.     

Screening for acetylcholinesterase inhibition and antioxidant activity of selected plants from Croatia

The methanol, ethyl acetate and chloroform extracts of selected Croatian plants were tested for their acetylcholinesterase (AChE) inhibition and antioxidant activity. Assessment of AChE inhibition was carried out using microplate reader at 1?mg?mL?1. Antioxidant capacities were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging test and ferric reducing/antioxidant power assay (FRAP). Total phenol content (TPC) of extracts were determined using Folin-Ciocalteu colorimetric method. Out of 48 extracts, only methanolic extract of the Salix alba L. cortex exerted modest activity towards AChE, reaching 50.80% inhibition at concentration of 1?mg?mL?1. All the other samples tested had activity below 20%. The same extract performed the best antioxidative activity using DPPH and FRAP method, too. In essence, among all extracts used in the screening, methanolic extracts showed the best antioxidative activity as well as highest TPC.     

Turing patterns in the chlorine dioxide-iodine-malonic acid reaction with square spatial periodic forcing

We use the photosensitive chlorine dioxide-iodine-malonic acid reaction-diffusion system to study wavenumber locking of Turing patterns to two-dimensional "square" spatial forcing, implemented as orthogonal sets of bright bands projected onto the reaction medium. Various resonant structures emerge in a broad range of forcing wavelengths and amplitudes, including square lattices and superlattices, one-dimensional stripe patterns and oblique rectangular patterns. Numerical simulations using a model that incorporates additive two-dimensional spatially periodic forcing reproduce well the experimental observations.     

Synthesis of erythro- and threo-α-bromo-α′-fluorosuccinic acids

$\text{erythro}$- and $\text{threo}$-α-Bromo-α′-fluorosuccinic acids have been prepared from their corresponding dimethyl esters. Because of the extreme readiness of elimination of hydrogen fluoride in basic medium, a special method of acid hydrolysis had to be applied. Hydrogen and fluorine NMR spectra are reported.     

Kinetic-photometric determination of iodide based on its inhibitory effect on the bromate oxidation of Victoria Blue 4-R.

A new sensitive kinetic method has been developed for the determination of trace amounts of I- over the range of 50-300 ng cm(-3). The method was based on the inhibitory effect of iodide on the oxidation of Victoria Blue 4-R by KBrO3. The reaction is monitored spectrophotometrically at 596.3 nm. Method development includes optimization of reagent concentration and temperature. The kinetic parameters of the reaction were reported and a rate equation was suggested. The effects of certain foreign ions upon the reaction rate were determined for the assessment of the selectivity of the method. The proposed method was successfully applied to the determination of iodide in real samples. The new developed method was found to have fairly good selectivity, sensitivity, simplicity and rapidity.