Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

The effect of polyamidoamine dendrimers on human erythrocyte membrane acetylcholinesterase activity

Polyamidoamine (PAMAM) dendrimers impact on activity of acetylcholinesterase was studied. It has been shown that dendrimers induce a biphasic effect: depending on their concentrations they increase or decrease enzyme activity. It may be due to two types of interactions: direct--between dendrimers and the enzyme; indirect--via a modification of the physical state of membrane phospholipids affecting the acetylcholinesterase.     

Thermosensitivity of red blood cells from Down's syndrome individuals

Biochemical disturbances of the reactive oxygen species metabolism revealed in subjects with Down's syndrome (DS), and the findings indicating that heat-induced cell alterations have been, at least, partly mediated by reactive oxygen species, made the elucidation of the response of trisomic cells to elevated temperatures of special interest. Kinetic analysis of cell-survival curves, accompanied by the flow cytometry and the scanning electron microscopy (SEM) examinations, and their relationship with the cell membrane fluidity, were undertaken. At each temperature (48-54 degrees C), Dq parameters, representing the ability to accumulate sublethal damages, were similar for both cell groups. D0 parameters (inverse leakage rates; D0 = 1/k) were greater for DS cells at each temperature below 54 degrees C. The haemolysis sensitivity ratio (HSR) showed that DS erythrocytes were, in average, 1.60 times more resistant to heat injury than those from normal subjects. Activation energies of haemolysis, calculated according to the Arrhenius equation, were similar both for normal (290.8 +/- 6.5 [kJ/mol]) and DS erythrocytes (288.0 +/- 5.5 [kJ/mol]). Flow cytometry studies showed that the scattering properties of intact DS erythrocytes (reflecting size, volume, shape and cell membrane surface morphology) were different than those of normal cells. Scanning electron micrographs and scattering diagrams obtained for cells submitted to heat stress (51 degrees C) confirmed that DS erythrocytes were more resistant, to a certain extent, to heat-induced disruption than normal cells. The steady-state fluorescence anisotropy of TMA-DPH (1-(4-trimethyl-ammoniumphenyl)-6-phenyl-1,3,5-hexatriene) showed that untreated DS erythrocytes had substantially lower fluidity (r = 0.356 +/- 0.008) of the outer monolayer of cell membranes as compared to normal cells (r = 0.324 +/- 0.011). The increase of the cell membrane fluidity during exposure to heat was observed. The greatest elevation of cell membrane fluidity occurred during the preleakage period, immediately upon the heat treatment and was considered as a rate-limiting step of heat-induced haemolysis.     

Interactions between PAMAM dendrimers and gallic acid molecules studied by spectrofluorimetric methods

Interactions between gallic acid molecules and different types of polyamidoamine (PAMAM) dendrimers with modified surfaces were studied by spectrofluorimetric methods. Changes in fluorescence intensity of gallic acid and in a position of spectrum were monitored. It was found that the extent of gallic acid incorporation into dendrimers depends on a type of a dendrimer.     

Water-soluble carbosilane dendrimers protect phosphorothioate oligonucleotides from binding to serum proteins

Treatment of dendriplexes formed between water-soluble carbosilane dendrimers and phosphorothioate oligodeoxynucleotides (ODN) with the anionic detergent sodium dodecyl sulfate disrupted the complexes indicating that the nature of the union in such dendriplexes is merely electrostatic. However, dendriplexes were not dissociated by serum proteins like bovine or human serum albumins, as assessed by gel electrophoresis and fluorescence experiments. This would imply a dendrimer-mediated protective effect able to prevent ODN interactions with serum proteins and additionally could translate into a reduction of the ODN doses needed to achieve the biological effects. The employment of carbosilane dendrimers as carriers may solve the problem of ODN kidnapping by plasmatic proteins as a key drawback for therapeutics involving ODNs. As examples, transfection processes on normal primary peripheral blood cells and diagnosis of HIV infection in the presence of serum have been assayed.     

A dynamic study of earthworm feeding ecology -using stable isotopes

Changes in the specific diet of earthworms with time in relation to landuse changes and two different climates were studied by analysing (13)C and (15)N natural abundance in soils and animals. Soil samples from three depths (0-10, 10-20 and 20-30 cm) and earthworms were collected from two sites: Santiago (Northwest Spain) and North Wyke (Southwest England) both consisting of replicated long-term grasslands and recently converted to maize plots. Earthworms were hand-sorted in the field at the peak of the maize growth and after harvesting at both sites. In the Spanish plots, nine and eight earthworm species, all belonging to the three ecological categories (epigeic, anecic and endogeic), were found under maize and permanent pasture, whereas at the English site five and seven different species were, respectively, identified. At both sites (13)C isotopic values of the earthworm tissues reflected changes in diet from C(3) to C(4) with epigeic and epi/anecic worms in the maize plots showing one delta unit difference in relation to the ones found in the grassland plots. Anecic worms seemed to be less responsive to landuse changes. The higher (13)C values of the Spanish soils were also reflected in the earthworm tissues when compared with the English samples. (15)N values showed no clear relationship with the cropping treatments but were clearly related to the ecological grouping, with endogeic worms reaching the highest values whereas for the epigeic and epi/anecic species the lowest values were obtained. This finding was also previously recorded by other authors1 and suggests that, in the future, stable isotope techniques could also be a useful tool in taxonomic studies. Copyright 1999 John Wiley & Sons, Ltd.