Structure-Morphology-Antimicrobial and Antiviral Activity Relationship in Silver-Containing Nanocomposites Based on Polylactide

Green synthesis of silver-containing nanocomposites based on polylactide (PLA) was carried out in two ways. With the use of green tea extract, Ag⁺ ions were reduced to silver nanoparticles with their subsequent introduction into the PLA (mechanical method) and Ag⁺ ions were reduced in the polymer matrix of PLA-AgPalmitate (PLA-AgPalm) (in situ method). Structure, morphology and thermophysical properties of nanocomposites PLA-Ag were studied by FTIR spectroscopy, wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) methods. The antimicrobial, antiviral, and cytotoxic properties were studied as well. It was found that the mechanical method provides the average size of silver nanoparticles in the PLA of about 16 nm, while in the formation of samples by the in situ method their average size was 3.7 nm. The strong influence of smaller silver nanoparticles (3.7 nm) on the properties of nanocomposites was revealed, as with increasing nanosilver concentration the heat resistance and glass transition temperature of the samples decreases, while the influence of larger particles (16 nm) on these parameters was not detected. It was shown that silver-containing nanocomposites formed in situ demonstrate antimicrobial activity against gram-positive bacterium S. aureus, gram-negative bacteria E. coli, P. aeruginosa, and the fungal pathogen of C. albicans, and the activity of the samples increases with increasing nanoparticle concentration. Silver-containing nanocomposites formed by the mechanical method have not shown antimicrobial activity. The relative antiviral activity of nanocomposites obtained by two methods against influenza A virus, and adenovirus serotype 2 was also revealed. The obtained nanocomposites were not-cytotoxic, and they did not inhibit the viability of MDCK or Hep-2 cell cultures.     

Synthesis and Post-Synthesis Transformation of Germanosilicate Zeolites

Zeolites are one of the most important heterogeneous catalysts, with a high number of large-scale industrial applications. While the synthesis of new zeolites remain rather limited, introduction of germanium has substantially increased our ability to not only direct the synthesis of zeolites but also to convert them into new materials post-synthetically. The smaller Ge-O-Ge angles (vs. Si-O-Si) and lability of the Ge−O bonds in aqueous solutions account for this behaviour. This Minireview discusses critical aspects of germanosilicate synthesis and their post-synthesis transformations to porous materials.     

Spectroscopic ellipsometry of layer by layer deposited colloidal HgTe nanocrystals exhibiting quantum confinement

We have explored the optical properties of bilayers of Mercury telluride (HgTe) nanocrystals (NCs) embedded in polymer which were prepared from a colloidal solution. These NCs show strong luminescence in the near infrared at room temperature, which makes them an interesting material for the telecommunication area. The emission wavelength can efficiently be tuned by controlling the size of the NCs. We report spectroscopic ellipsometry measurements, which clearly show an energy shift of the critical points (CPs) in the dielectric function to higher energies compared to the HgTe bulk properties. This is caused by quantum confinement in the crystals. The exact peak energies of the transitions are fitted with line-shape models for CPs. Surprisingly, concepts coming from semiconductor bulk optics, as CPs, can be applied to NCs with a diameter of less than 5 unit cells.     

Adsorption of Poly(rA) on the Carbon Nanotube Surface and its Hybridization with Poly(rU)

Adsorption of poly(rA) on a single‐walled carbon nanotube surface in aqueous suspension and the subsequent hybridization of this polymer with free poly(rU) is studied. A comparison of the temperature dependence of the absorbance of free poly(rA) and poly(rA) adsorbed on the nanotube surface [poly(rA)^NT] at ν_max=38 500 cm^?1 shows that the thermostability of the adsorbed polymer is higher. Molecular dynamics simulations demonstrate that more than half of the adenines are not stacked on the tube surface and some of them undergo self‐stacking. After addition of a complementary poly(rU) to the poly(rA)^NT suspension, a double‐stranded polymer is formed as confirmed by the characteristic S‐like form of its melting curve. However, the melting temperature of this polymer is lower than that of the free poly(rA)?poly(rU) duplex. This result indicates that poly(rU) hybridization with poly(rA)^NT occurs with defects along the whole length of the polymer because of π–π stacking between nitrogen bases and the nanotube surface, which hinders the usual hybridization process. Computer modeling demonstrates different possible structures of hybridized polymers on the nanotube surface.     

K2M(III)2(M(VI)O4)(PO4)2 (M(III) = Fe, Sc; M(VI) = Mo, W), novel members of the lagbeinite-related family: synthesis, structure, and magnetic properties

The possibility of PO(4)(3-) for MoO(4)(2-) partial substitution in the langbeinite framework has been studied by exploration of the K-Fe(Sc)-Mo(W)-P-O systems using the high-temperature solution method. It was shown that 1/3PO(4)(3-) for MoO(4)(2-) substitution leads to formation of three novel compounds K(2)Fe(MoO(4))(PO(4))(2), K(2)Sc(MoO(4))(PO(4))(2), and K(2)Sc(WO(4))(PO(4))(2) with slightly increased lattice parameters and significant distortion of the anion tetrahedra without structure changes. In contrast, the antiferromagnetic structure is modified by substitution in the low-temperature region. The structural peculiarities are discussed in light of bond-valence sums calculations.     

Explicit water molecular dynamics study of the mobility of halide ions in presence of ionene oligocations

We present explicit water molecular dynamics simulations of solutions of aliphatic 3,3- and 6,6-ionene oligocations neutralized with (i) fluoride, chloride, bromide, or iodide counterions, respectively, or (ii) with a 1:1 mixture of chloride and bromide anions in presence of a low molecular weight salt at 298 K. The SPC/E model was used to describe water molecules. Results of the simulation are presented in form of the pair distribution functions between various atoms on the ionene oligoion and counterions in solution. In addition, we were interested in the dynamics of counterions around model ionenes. We showed that counterions residing in the vicinity of the oligoion exchange rapidly with those in the bulk solution, with the frequency depending on the nature of the counterion and on the charge density of the oligoion. We calculated the average residence times of the various counterion species to the oligoions and proposed the model which divides the counterions into "free" and "bound" and calculated the fraction of "free" counterions. In the second part of the study, we investigated interaction of the sodium chloride and sodium bromide, being simultaneously present in the solution, with differently charged ionenes in water. The selectivity effect was clearly observed: bromide ions tend to replace chloride ions in the immediate vicinity of the ionene oligoions. Simulation results are discussed in light of our recent measurements of thermodynamic and transport properties of aqueous ionene solutions.     

Isothermal titration calorimetry and molecular dynamics study of ion-selectivity in mixtures of hydrophobic polyelectrolytes with sodium halides in water

Aliphatic x,y-ionenes are polyelectrolytes in which x and y denote the numbers of methylene groups separating quaternary ammonium ions. They represent useful model substances for studying hydrophobic and charge effects in aqueous solutions. We used isothermal titration calorimetry to measure the enthalpies of mixing, ΔH(mix), of 3,3- and 6,6-ionene fluorides and bromides with low molecular weight salts (NaF, NaCl, NaBr, and NaI) at 298 K in water. The signs and magnitudes of the measured enthalpies depend on the hydrophobicity of the ionene and on the nature of the added salt. For example, addition of sodium fluoride to solutions of 3,3- and 6,6-ionene fluorides produced endothermic effects, while addition of sodium bromide to 3,3-ionene bromide resulted in a strong exothermic effect. Interestingly, mixing of 6,6-ionene bromide and NaBr solutions in water gave a small exothermic heat effect. Polyelectrolyte theories, based on continuum-solvent models, predict enthalpies of mixing to be positive (endothermic) for all the solutions examined in this work. The ion-specific effect is more strongly expressed in ionene solutions with higher charge density (3,3-ionene). The most important result of this work is the finding that the enthalpy of mixing of 3,3- (and of 6,6-ionene) fluorides with sodium halides can be expressed as a linear function of the enthalpy of hydration of the halide counterions. The experimental results were complemented with an explicit water molecular dynamics simulation of solutions of oligoions modelling 3,3- and 6,6-ionenes. The computer simulation results for various nitrogen-counterion pair distribution functions were in most cases consistent with the enthalpy measurements.     

Scaling the microrheology of living cells

We report a scaling law that governs both the elastic and frictional properties of a wide variety of living cell types, over a wide range of time scales and under a variety of biological interventions. This scaling identifies these cells as soft glassy materials existing close to a glass transition, and implies that cytoskeletal proteins may regulate cell mechanical properties mainly by modulating the effective noise temperature of the matrix. The practical implications are that the effective noise temperature is an easily quantified measure of the ability of the cytoskeleton to deform, flow, and reorganize.