Understanding three-dimensional effects in polarized observations with the ground-based ADMIRARI radiometer during the CHUVA campaign

Measurements of down-welling microwave radiation from raining clouds performed with the Advanced Microwave Radiometer for Rain Identification (ADMIRARI) radiometer at 10.7-21-36.5 GHz during the Global Precipitation Measurement Ground Validation ""Cloud processes of the main precipitation systems in Brazil: A contribution to cloud resolving modeling and to the Global Precipitation Measurement"" (CHUVA) campaign held in Brazil in March 2010 represent a unique test bed for understanding three-dimensional (3D) effects in microwave radiative transfer processes. While the necessity of accounting for geometric effects is trivial given the slant observation geometry (ADMIRARI was pointing at a fixed 30 elevation angle), the polarization signal (i.e., the difference between the vertical and horizontal brightness temperatures) shows ubiquitousness of positive values both at 21.0 and 36.5 GHz in coincidence with high brightness temperatures. This signature is a genuine and unique microwave signature of radiation side leakage which cannot be explained in a 1D radiative transfer frame but necessitates the inclusion of three-dimensional scattering effects. We demonstrate these effects and interdependencies by analyzing two campaign case studies and by exploiting a sophisticated 3D radiative transfer suited for dichroic media like precipitating clouds.

Selectivity in the mechanism of action of antimicrobial mastoparan peptide Polybia-MP1

Many potent antimicrobial peptides also present hemolytic activity, an undesired collateral effect for the therapeutic application. Unlike other mastoparan peptides, Polybia-MP1 (IDWKKLLDAAKQIL), obtained from the venom of the social wasp Polybia paulista, is highly selective of bacterial cells. The study of its mechanism of action demonstrated that it permeates vesicles at a greater rate of leakage on the anionic over the zwitterionic, impaired by the presence of cholesterol or cardiolipin; its lytic activity is characterized by a threshold peptide to lipid molar ratio that depends on the phospholipid composition of the vesicles. At these particular threshold concentrations, the apparent average pore number is distinctive between anionic and zwitterionic vesicles, suggesting that pores are similarly formed depending on the ionic character of the bilayer. To prospect the molecular reasons for the strengthened selectivity in Polybia-MP1 and its absence in Mastoparan-X, MD simulations were carried out. Both peptides presented amphipathic alpha-helical structures, as previously observed in Circular Dichroism spectra, with important differences in the extension and stability of the helix; their backbone solvation analysis also indicate a different profile, suggesting that the selectivity of Polybia-MP1 is a consequence of the distribution of the charged and polar residues along the peptide helix, and on how the solvent molecules orient themselves according to these electrostatic interactions. We suggest that the lack of hemolytic activity of Polybia-MP1 is due to the presence and position of Asp residues that enable the equilibrium of electrostatic interactions and favor the preference for the more hydrophilic environment.

Interactions of mast cell degranulating peptides with model membranes: A comparative biophysical study

In the last decade, there has been renewed interest in biologically active peptides in fields like allergy, autoimmume diseases and antibiotic therapy. Mast cell degranulating peptides mimic G-protein receptors, showing different activity levels even among homologous peptides. Another important feature is their ability to interact directly with membrane phospholipids, in a fast and concentration-dependent way. The mechanism of action of peptide HR1 on model membranes was investigated comparatively to other mast cell degranulating peptides (Mastoparan, Eumenitin and Anoplin) to evidence the features that modulate their selectivity. Using vesicle leakage, single-channel recordings and zeta-potential measurements, we demonstrated that HR1 preferentially binds to anionic bilayers, accumulates, folds, and at very low concentrations, is able to insert and create membrane spanning ion-selective pores. We discuss the ion selectivity character of the pores based on the neutralization or screening of the peptides charges by the bilayer head group charges or dipoles. (C) 2009 Elsevier Inc. All rights reserved.

Low-Frequency Noise in Field-Effect Devices Functionalized With Dendrimer/Carbon-Nanotube Multilayers

Low-frequency noise in an electrolyte-insulator- semiconductor (EIS) structure functionalized with multilayers of polyamidoamine (PAMAM) dendrimer and single-walled carbon nanotubes (SWNT) is studied. The noise spectral density exhibits 1/f(gamma) dependence with the power factor of gamma approximate to 0.8 and gamma = 0.8-1.8 for the bare and functionalized EIS sensor, respectively. The gate-voltage noise spectral density is practically independent of the pH value of the solution and increases with increasing gate voltage or gate-leakage current. It has been revealed that functionalization of an EIS structure with a PAMAM/SWNTs multilayer leads to an essential reduction of the 1/f noise. To interpret the noise behavior in bare and functionalized EIS devices, a gate-current noise model for capacitive EIS structures based on an equivalent flatband-voltage fluctuation concept has been developed.

Osmotin from Calotropis procera latex: New insights into structure and antifungal properties

This study aimed at investigating the structural properties and mechanisms of the antifungal action of CpOsm, a purified osmotin from Calotropis procera latex. Fluorescence and CD assays revealed that the CpOsm structure is highly stable, regardless of pH levels. Accordingly, CpOsm inhibited the spore germination of Fusarium solani in all pH ranges tested. The content of the secondary structure of CpOsm was estimated as follows: alpha-helix (20%), beta-sheet (33%), turned (19%) and unordered (28%). RMSD 1%. CpOsm was stable at up to 75 degrees C, and thermal denaturation (T(m)) was calculated to be 77.8 degrees C. This osmotin interacted with the negatively charged large unilamellar vesicles (LUVs) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-1-glycerol (POPG), inducing vesicle permeabilization by the leakage of calcein. CpOsm induced the membrane permeabilization of spores and hyphae from Fusarium solani, allowing for propidium iodide uptake. These results show that CpOsm is a stable protein, and its antifungal activity involves membrane permeabilization, as property reported earlier for other osmotins and thaumatin-like proteins. (C) 2011 Elsevier B.V. All rights reserved.

Effect of cholesterol on the interaction of the amphibian antimicrobial peptide DD K with liposomes

DD K is an antimicrobial peptide previously isolated from the skin of the amphibian Phyllomedusa distincta. The effect of cholesterol on synthetic DD K binding to egg lecithin liposomes was investigated by intrinsic fluorescence of tryptophan residue, measurements of kinetics of 5(6)-carboxyfluorescein (CF) leakage, dynamic light scattering and isothermal titration microcalorimetry. An 8 nm blue shift of tryptophan maximum emission fluorescence was observed when DD K was in the presence of lecithin liposomes compared to the value observed for liposomes containing 43 mol% cholesterol. The rate and the extent of CF release were also significantly reduced by the presence of cholesterol. Dynamic light scattering showed that lecithin liposome size increase from 115 to 140 nm when titrated with DD K but addition of cholesterol reduces the liposome size increments. Isothermal titration microcalorimetry studies showed that DD K binding both to liposomes containing cholesterol as to liposomes devoid of it is more entropically than enthalpically favored. Nevertheless, the peptide concentration necessary to furnish an adjustable titration curve is much higher for liposomes containing cholesterol at 43 mol% (2 mmol L-1) than in its absence (93 mu mol L-1). Apparent binding constant values were 2160 and 10,000 L mol(-1), respectively. The whole data indicate that DD K binding to phosphatidylcholine liposomes is significantly affected by cholesterol, which contributes to explain the low hemolytic activity of the peptide. (C) 2007 Elsevier Inc. All rights reserved.

Flexural properties, microleakage, and degree of conversion of a resin polymerized with conventional light and argon laser

Objective: To evaluate the flexural strength, microleakage, and degree of conversion of a microhybrid resin polymerized with argon laser and halogen lamp. Method and Materials: For both flexural test and degree of conversion analysis, 5 bar samples of composite resin were prepared and polymerized according to ISO 4049. The halogen light-curing unit was used with 500 MW/cm(2) for 20 seconds and the argon laser with 250 mW for 10 and 20 seconds. Samples were stored in distilled water in a dark environment at 37 degrees C for 24 hours. The flexural property was quantified by a 3-point loading test. For the microleakage evaluation, 60 bovine incisors were used to prepare standardized Class 5 cavities, which were restored and polished. Specimens were stored in distilled water for 24 hours at 37 degrees C and thermocycled 500 times (6 degrees C to 60 degrees C). Specimens were then immersed in art aqueous solution of basic fuchsin for 24 hours. Longitudinal sections of each restoration were obtained and examined with a stereomicroscope for qualitative evaluation of microleakage. Fourier transform (FT)-Raman RFS 100/S spectrometer (Bruker) was used to analyze the degree of conversion. Results: ANOVA showed no statistically significant differences of flexural strength between the photoactivation types evaluated in the flexural study. Microleakage data were statistically analyzed by Mann-Whitney and Kruskal-Wallis tests. Enamel margins resulted in a statistically lower degree of leakage than dentin margins. No statistically significant difference was found among the 3 types of photocuring studied. ANOVA also showed no statistically significant difference in the degree of conversion among the studied groups. Conclusion: According to the methodology used in this research, the argon laser is a possible alternative for photocuring, providing the same quality of polymerization as the halogen lamp. None of the photocured units tested in this study completely eliminated microleakage.