Synthesis of Polyethylene Glycol–Chitosan–Nano Ag Composites and their Antibacterial Properties

Journal of Applied Spectroscopy - This study showed the synthesis of polyethylene glycol–chitosan–nano Ag (PEG–Chi–Ag) composites to improve the homogeneous distribution of...     

The Interplay of Cholesterol and Ligand Binding in hTSPO from Classical Molecular Dynamics Simulations

The translocator protein (TSPO) is a 18kDa transmembrane protein, ubiquitously present in human mitochondria. It is overexpressed in tumor cells and at the sites of neuroinflammation, thus representing an important biomarker, as well as a promising drug target. In mammalian TSPO, there are cholesterol–binding motifs, as well as a binding cavity able to accommodate different chemical compounds. Given the lack of structural information for the human protein, we built a model of human (h) TSPO in the apo state and in complex with PK11195, a molecule routinely used in positron emission tomography (PET) for imaging of neuroinflammatory sites. To better understand the interactions of PK11195 and cholesterol with this pharmacologically relevant protein, we ran molecular dynamics simulations of the apo and holo proteins embedded in a model membrane. We found that: (i) PK11195 stabilizes hTSPO structural fold; (ii) PK11195 might enter in the binding site through transmembrane helices I and II of hTSPO; (iii) PK11195 reduces the frequency of cholesterol binding to the lower, N–terminal part of hTSPO in the inner membrane leaflet, while this impact is less pronounced for the upper, C–terminal part in the outer membrane leaflet, where the ligand binding site is located; (iv) very interestingly, cholesterol most frequently binds simultaneously to the so-called CRAC and CARC regions in TM V in the free form (residues L150–X–Y152–X(3)–R156 and R135–X(2)–Y138–X(2)–L141, respectively). However, when the protein is in complex with PK11195, cholesterol binds equally frequently to the CRAC–resembling motif that we observed in TM I (residues L17–X(2)–F20–X(3)–R24) and to CRAC in TM V. We expect that the CRAC–like motif in TM I will be of interest in future experimental investigations. Thus, our MD simulations provide insight into the structural features of hTSPO and the previously unknown interplay between PK11195 and cholesterol interactions with this pharmacologically relevant protein.     

Optical Properties of Doxorubicin Hydrochloride Load and Release on Silica Nanoparticle Platform

Silica nanoparticles (SiO₂ NPs) synthesized by the Stober method were used as drug delivery vehicles. Doxorubicin hydrochloride (DOX·HCl) is a chemo-drug absorbed onto the SiO₂ NPs surfaces. The DOX·HCl loading onto and release from the SiO₂ NPs was monitored via UV-VIS and fluorescence spectra. Alternatively, the zeta potential was also used to monitor and evaluate the DOX·HCl loading process. The results showed that nearly 98% of DOX·HCl was effectively loaded onto the SiO₂ NPs’ surfaces by electrostatic interaction. The pH-dependence of the process wherein DOX·HCl release out of DOX·HCl-SiO₂ NPs was investigated as well. For comparison, both the free DOX·HCl molecules and DOX·HCl-SiO₂ NPs were used as the labels for cultured cancer cells. Confocal laser scanning microscopy images showed that the DOX·HCl-SiO₂ NPs were better delivered to cancer cells which are more acidic than healthy cells. We propose that engineered DOX·HCl-SiO₂ systems are good candidates for drug delivery and clinical applications.     

A three-dimensional radiative transfer model to interpret ranging scatterometer measurements from a pine forest

This paper addresses the propagation of microwaves in forested media. It interprets the vertical distribution of backscatter acquired by a ranging scatterometer in a pine forest at X band (9.5 GHz) and vertical incidence by means of modelling. A plane parallel radiative transfer model for the forest canopy exhibits a large discrepancy between the measured and estimated distribution. This is attributed to failure to represent the horizontal heterogeneity in the forest. Taking into account the height variability of the trees significantly improves the estimated distribution at the top of the canopy but the backscatter from the lower layers and the ground is still underestimated. To deal with this, a fully three-dimensional (3D) radiative transfer model is developed. By modelling precisely the propagation of the wave through the medium, the 3D approach allows accurate estimation of the ground backscatter and slightly improves the estimated backscatter from the lower layers. It is demonstrated that 3D modelling is required to estimate accurately the vertical distribution of backscatter, total backscatter and the height of the centre of backscatter in the experimental data. These results have implications for the interpretation of more general measurements scenarios, especially as regards forest height measurement by radar interferometry.     

Enhancing the photoluminescence intensity of conjugated polycationic polymers by using quantum dots as antiaggregation reagents

The aggregation in conjugated polyelectrolytes (CPs) can be effectively reduced by the formation of CP/nanoparticle assemblies. The photophysical properties of various nanoassemblies were studied by means of UV-visible and fluorescence spectroscopy in solution and as thin films. The dissociation of the polymer chains is caused by favorable electrostatic interactions between the cationic substituents of the CPs and the anionic charges present on the surface of the nanoparticles. Such an efficient displacement of pi-stacking by competitive positive interactions constitutes the first example of positive aggregation modulation.     

Some Remarks on a Class of Nonuniformly Elliptic Equations of p-Laplacian Type

This paper deals with the existence of weak solutions in W ₀¹(Ω) to a class of elliptic problems of the form

Reentrant behavior of divalent-counterion-mediated DNA-DNA electrostatic interaction

The problem of DNA-DNA interaction mediated by divalent counterions is studied using computer simulation. Although divalent counterions cannot condense free DNA molecules in solution, we show that if DNA configurational entropy is restricted, divalent counterions can cause DNA reentrant condensation similar to that caused by tri- or tetravalent counterions. DNA-DNA interaction is strongly repulsive at small or large counterion concentration and is negligible or slightly attractive for a concentration in between. Implications of our results to experiments of DNA ejection from bacteriophages are discussed. The quantitative result serves to understand electrostatic effects in other experiments involving DNA and divalent counterions.