Antimicrobial Activity of MgB2 Powders Produced via Reactive Liquid Infiltration Method

We report for the first time on the antimicrobial activity of MgB₂ powders produced via the Reactive Liquid Infiltration (RLI) process. Samples with MgB₂ wt.% ranging from 2% to 99% were obtained and characterized, observing different levels of grain aggregation and of impurity phases. Their antimicrobial activity was tested against Staphylococcus aureus ATCC BAA 1026, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 10231. A general correlation is observed between the antibacterial activity and the MgB₂ wt.%, but the sample microstructure also appears to be very important. RLI-MgB₂ powders show better performances compared to commercial powders against microbial strains in the planktonic form, and their activity against biofilms is also very similar.     

Ensemble Dependence of Fluctuations: Canonical Microcanonical Equivalence of Ensembles

We study the equivalence of microcanonical and canonical ensembles in continuous systems, in the sense of the convergence of the corresponding Gibbs measures and the first order corrections. We are particularly interested in extensive observables, like the total kinetic energy. This result is obtained by proving an Edgeworth expansion for the local central limit theorem for the energy in the canonical measure, and a corresponding local large deviations expansion. As an application we prove a formula due to Lebowitz–Percus–Verlet that express the asymptotic microcanonical variance of the kinetic energy in terms of the heat capacity.     

How Phospholipid-Cholesterol Interactions Modulate Lipid Lateral Diffusion, as Revealed by Fluorescence Correlation Spectroscopy

Cholesterol is a key player in regulating physico-chemical properties of cellular membranes and, thereby, ensuring cell viability. In particular, lipid-cholesterol interactions may provide important information on the spatio-temporal organization of membrane components. Here, we apply confocal imaging and Fluorescence Correlation Spectroscopy (FCS) to Giant Unilamellar Vesicles (GUVs) composed of binary mixtures of lipids and cholesterol.The effect of cholesterol on lipid dynamics and molecular packing order of unsaturated, monounsaturated, fully saturated (with both low and high phase transition temperatures, T_m) glycero-phospholipids and sphingomyelin has been investigated. We show that, for unsaturated glycerophospholipids, the decrease of the lipid diffusion coefficient as a result of the interaction with cholesterol does not depend on the fatty acid chain length. However, the values of the diffusion coefficient change as a function of chain length. The monounsaturated phospholipid palmitoyl-oleoyl-phosphatidylcholine (POPC) exhibits a dynamic behavior very similar to the unsaturated dioleoyl-phosphatidylcholine (DOPC). By contrast, for saturated (low T_m) glycero-phospholipids, cholesterol causes a decrease of lipid mobility in a chain length-dependent manner.FCS can be employed as a valuable tool to study lipid-sterol interactions and their effect on lipid dynamics, molecular packing and degree of conformational order.     

Polymer Membranes Dispersed Liquid Crystal (PMDLC): a new electro-optical device

Polymer Dispersed Liquid Crystals (PDLCs) are liquid crystal dispersions in a polymer matrix, which look like opaque in their OFF state, when no electric field is applied, and transparent in their ON state. They are generally obtained by a phase separation process, such as Thermal, Solvent- and Polymerization-Induced Phase Separation (TIPS, SIPS and PIPS, respectively), between two transparent conductive glass substrates. In this paper, a new electro-optical device, formed by a porous polymer membrane imbibed with liquid crystal by capillary suction, is presented (Polymer Membranes Dispersed Liquid Crystals, PMDLC). Polymer membrane surfaces were made conductive before liquid crystal loading by magnetron sputtering of a thin layer of conductive indium tin oxide. The morphology and the electro-optical response of these devices were investigated and the observed transmittances and relaxation times were found to be similar to those of conventional PDLCs. In addition, PMDLCs showed interesting flexibility as no solid conductive substrate is required and economic convenience as there is no loss of liquid crystal in the polymer matrix.     

On a multistep method approximating a linear sectorial evolution equation

This paper concerns the linear multistep approximation of anabstract dissipative linear sectorial evolution equation ona Banach space X. We study how well the semigroup generatedby a sectorial operator A is approximated by the numerical semigroupgenerated by a q-step, strictly A ()-stable multistep method.An optimal order error bound is obtained.     

Hydrophilic Films Based on Blends of Poly(acrylic acid) and Poly(2‐hydroxyethyl vinyl ether): Thermal,Mechanical, and Morphological Characterization

Hydrophilic films based on blends of poly(acrylic acid) and poly(2‐hydroxyethyl vinyl ether) were prepared by casting. The characterization of the films was performed by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM). It was shown that an increase of poly(2‐hydroxyethyl vinyl ether) content in the blends considerably decreases the glass transition temperature of the samples. The films containing 10 and 20 mol‐% of poly(2‐hydroxyethyl vinyl ether) show behavior of polymers in the glassy state, but a further increase of nonionic polymer content in the blend (30–50 mol‐%) provides the mechanical properties typical of a rubbery state. The content of water traces in the films has a significant effect on the mechanical properties of the materials.

Normalized DSC thermograms of PAA:PHEVE films. [PAA]:[PHEVE] = 90:10 (1), 80:20 (2), 70:30 (3), 60:40 (4), 50:50 mol‐% (5).     

Raft domain reorganization driven by short- and long-chain ceramide: a combined AFM and FCS study

Naturally occurring long-chain ceramides (Cer) are known to alter the lateral organization of biological membranes. In particular, they produce alterations of microdomains that are involved in several cellular processes, ranging from apoptosis to immune response. In order to induce similar biological effects, short-chain Cer are extensively used in in vivo experiments to replace their long-chain analogues. In this work, we used the combined approach of atomic force microscopy (AFM) and fluorescence correlation spectroscopy (FCS) to investigate the effect of Cer chain length in lipid bilayers composed of sphingomyelin, dioleoyl-phosphatidylcholine, and cholesterol. Our results show that only long-chain Cer, like C18 and C16, are able to segregate from the liquid-ordered phase, forming separate Cer-enriched domains. Conversely, short-chain Cer do not form a separate phase but alter the physical properties of the liquid-ordered domains, decreasing their stability and viscosity and perturbing the lipid packing. These differences may contribute to the explanation of the different physiological effects that are often observed for the long- and short-chain Cer.     

Inhibitory Effects by Soy Antioxidants on the Oscillations of the Briggs‐Rauscher Reaction

Inhibitory effects by addition of aqueous extracts of soy flour to an active Briggs‐Rauscher mixture are reported. The effect consists of an immediate cessation of oscillations, but, after some time, the oscillatory behavior is regenerated with amplitude and frequency different from those observed in a reference mixture. The inhibition time depends linearly on the concentration of substances contained in the extract in a wide range of concentration. The inhibitory effects are due to the high free‐radical scavenging activity of substances contained in the soy flour. Two preponderant products contained in the soy flour extract were identified and characterized as malonyldaidzin and malonylgenistin. The antioxidant activity of these isoflavones contained in the extracts was determined on the basis of the inhibition time. A qualitative mechanistic explanation of the inhibitory effects is given. Our findings are decisive indirect evidence of involvement and important role played by HOO^. radicals in establishing oscillations in the Briggs‐Rauscher (BR) system. The linear relationship between the inhibition time and the whole‐mass concentration of antioxidant contained in soy extracts added to a BR mixture is an indication of the possibility to develop and implement an analytical procedure for monitoring the activity of antioxidant scavengers of free radicals based on the oscillating Briggs‐Rauscher reaction.     

Ethene/propene copolymerisations with rac-EBTHIZrR2/alumoxane: σ-ligands effect

We report here about the role played by the σ-ligands of a metallocene in ethene/propene (E/P) copolymerisations promoted by rac-[ethylenebis(4,5,6,7-tetrahydro-1-indenyl)]zirconium dichloride 1, and its corresponding dimethyl derivative rac-EBTHIZrMe₂ 2 and binaphtholate rac-EBTHIZr(BNP) 3 derivative, in the presence of several alumoxanes.

Alumoxanes alternative to the traditional polymethylalumoxane (MAO) were synthesised and characterised. They are based on Al(2,4,4-trimethylpentyl)₃ (TIOA) 4 and were prepared by reaction of 4 with water to give either tetraisooctylalumoxane (TIOAO) 5 or polyisooctylalumoxane (TAO) 6 depending on the stoichiometry of the reaction. ¹H NMR spectra of these products are characterised by the presence of broad bands and of resolved multiplets. Their relative amount in the region between 1.9 and 2.5 ppm was identified as the “fingerprint” of the polymerisation activity. A comparison of the results obtained in polymerisation with metallocenes having different σ-ligands allowed us to shed more light on the role played by those species.

In conclusion, the nature of the σ-ligands of a metallocene affects its catalytic activity in polymerisation, as a function of the alumoxane employed and of the relative ratio with the metallocene, and this effect is enhanced in “critical conditions,” i.e. with a weakly activating cocatalyst or at a low Al/Zr ratio.