Antibacterial activity of SiO2/hydroxypropyl cellulose hybrid materials containing silver nanoparticles

Silica hybrid materials containing tetraethyl orthosilicate (TEOS) as SiO₂ precursor, hydroxypropyl cellulose (HPC) as an organic compound with incorporation of silver were prepared, and their structure and surface morphology were examined by FTIR measurements and SEM. The quantity of organic substance was 5 wt.% and the silver concentration varied from 0.5 to 2.5 wt.%. It is suggested that the main structural units build an amorphous network of synthesized hybrids from depolymerized [SiO₄] tetrahedra giving strong bands at 1050 and 790 cm^? 1. The surface morphology changed from smooth to rough with the increasing amount of silver. The possible antibacterial behavior of the hybrid materials was also studied. The results indicate pronounced antibacterial performance against Escherichia coli and Bacillus subtilis. Highest antibacterial activity was detected against B. subtilis. The increase of silver concentration up to 2.5 wt.% Ag leads to stronger antibacterial effects with both strains.     

A correlation of electrochemical and spectroelectrochemical properties of poly(o-toluidine)

A comparative discussion of the electrochemical and spectroelectrochemical properties of poly(o-toluidine) POT, a methyl substituted derivative of polyaniline, PANI, is presented. POT exists in various oxidation states and shows an insulator to conductor transition when doped by electrooxidation. The transformation of the polymer film from its non-conducting leucoemeraldine to its conducting emeraldine state and further on to its again non-conducting pernigraniline form was observed with different techniques including cyclic voltammetry, in situ conductivity measurements and in situ UV-vis and Raman spectroelectrochemical methods. Results reveal that POT shows a good correlation between its electrochemical and spectroelectrochemical properties in its different oxidation states.     

Novel meso-substituted porphyrins: Synthesis, characterization and photocatalytic activity of their TiO2-based composites

Two series of novel meso-substituted porphyrins, namely 5,10,15,20-tetra[4-(3-phenoxy)-propoxy]phenyl porphyrin, the structural analogue 5,10,15,20-tetra[2-(3-phenoxy)-propoxy]phenyl porphyrin and their Co(II) Cu(II) and Zn(II) complexes were synthesized. The compounds were characterized using various spectroscopic techniques and their molecular structure was proposed based on density functional theory calculations. The diverse properties of the porphyrin derivatives result from the different stereochemistry of the particular substituents at the meso site on the macrocycle and are controlled also by the coordinated metal. The ¹H NMR spectrum of the free-base porphyrin showed a complicated spin-splitting. The photocatalytic activities in degradation of 4-nitrophenol were investigated using polycrystalline TiO₂ impregnated with the porphyrins and metalloporphyrins. The Cu(II) porphyrin was a more effective sensitizer than other metal containing compounds (M = Co, Zn) as well as the free-base. Photocatalytic activity was also influenced by spatial positions of the substitutions on the porphyrin molecules.     

Study of initial stages of thin film growth by means of atomistic computer simulation and image analysis

Nucleation and initial stages of three-dimensional film growth were studied by a computer experiment. The experiment consisted of two parts - preparation of simulated thin-film structures and computational analysis of their images. The simulated structures were generated by a model combining the molecular dynamics and Monte Carlo approaches. The analysis of the obtained structures was based on the ’Quadrat Counts’ method, which proved to be one of the most promising algorithms of image processing. The results obtained by image analysis of simulated thin films were discussed and the most suitable algorithms were suggested for the analysis of experimentally prepared films.     

Computational completeness of complete,star-like,and linear hybrid networks of evolutionary processors with a small number of processors

A hybrid network of evolutionary processors (HNEP) is a graph where each node is associated with a special rewriting system called an evolutionary processor, an input filter, and an output filter. Each evolutionary processor is given a finite set of one type of point mutations (insertion, deletion or a substitution of a symbol) which can be applied to certain positions in a string. An HNEP rewrites the strings in the nodes and then re-distributes them according to a filter-based communication protocol; the filters are defined by certain variants of random-context conditions. HNEPs can be considered both as languages generating devices (GHNEPs) and language accepting devices (AHNEPs); most previous approaches treated the accepting and generating cases separately. For both cases, in this paper we show that five nodes are sufficient to accept (AHNEPs) or generate (GHNEPs) any recursively enumerable language by showing the more general result that any partial recursive relation can be computed by an HNEP with (at most) five nodes with the underlying graph structure for the communication between the evolutionary processors being the complete or the linear graph with five nodes, whereas with a star-like communication graph we need six nodes. If the final results are defined by only taking the terminal strings out of the designated output node, then for these extended HNEPs we can prove that only four nodes are needed in all cases—for computing any partial recursive relation as well as for generating and accepting any recursively enumerable language—and the underlying communication structure can be a complete or a linear graph, but now even a star-like graph, too.     

Revisiting the Buckling Metrology Method to Determine the Young's Modulus of 2D Materials

Measuring the mechanical properties of 2D materials is a formidable task. While regular electrical and optical probing techniques are suitable even for atomically thin materials, conventional mechanical tests cannot be directly applied. Therefore, new mechanical testing techniques need to be developed. Up to now, the most widespread approaches require micro‐fabrication to create freely suspended membranes, rendering their implementation complex and costly. Here, a simple yet powerful technique is revisited to measure the mechanical properties of thin films. The buckling metrology method, that does not require the fabrication of freely suspended structures, is used to determine the Young's modulus of several transition metal dichalcogenides (MoS₂, MoSe₂, WS₂, and WSe₂) with thicknesses ranging from 2 to 10 layers. The obtained values for the Young's modulus and their uncertainty are critically compared with previously published results, finding that this simple technique provides results which are in good agreement with those reported using other highly sophisticated testing methods. By comparing the cost, complexity, and time required for the different methods reported in the literature, the buckling metrology method presents certain advantages that make it an interesting mechanical test tool for 2D materials.     

Numerical iterative methods and repetitive processes

Implicit schemes are a popular approach to the discretization of linear partial differential equations by finite differences. They require to solve a set of linear equations in each time step. Since finite difference discretizations lead to a local coupling, these systems of equations are sparse and can be effectively solved by iterative methods. Numerical procedures of this type are known in control theory as repetitive processes. They have mostly been used to solve problems in control like processes where passes of finite length are repeated over and over. This paper shows how the implicit discretization of partial differential equations can be cast into the framework of repetitive processes. Thus it establishes a link between yet unrelated results in numerical mathematics and control theory.     

Identification of the crystalline-phases in thin pentacene layers by Raman spectroscopy

We investigated the different crystallographic phases in thin pentacene layers by the micro-Raman spectroscopy. For the first time we have determined the presence of orthorhombic, thin film and triclinic bulk phase in thin pentacene layers by the micro-Raman polarization spectroscopy, which were confirmed by XRD measurements.     

Science-based decision matrix for the identification of endocrine disruptors for regulatory purposes

Recent EU legislation for chemical substances requires a particular assessment of endocrine disrupting properties that may cause adverse effects in humans. Especially for pesticidal active substances, measures concerning specific scientific criteria for the determination of endocrine disrupting properties should have been presented by the European Commission until December 2013. But presently, no specific science-based approach for the assessment of these substances has been agreed upon. This paper is discussing common scientific principles for the evaluation and grouping of substances with endocrine disrupting properties that may cause adverse effects in humans. A matrix-based approach is proposed to be applied in various fields of scientific evaluation of chemical substances, which is based on a scientific evaluation of all available data that may contribute to ensure a high level of protection of human health. This evaluation is expected to be proportionate, consistent and predictable to support administrative decisions in regulatory toxicology. However, a scientifically based categorisation in a decision matrix as a backbone for specific and legally binding rules should be performed according to the relevant EU regulations for the aforementioned groups of substances. Considering the complexity of the matter, it appears appropriate to base possible categorisation on considerations in a decision matrix, which take into account severity, reversibility, potency and consistency of an adverse effect. Based on this decision matrix it should be possible to allocate substances falling under the WHO/IPCS definition to categorise as endocrine disruptors (EDs) or even dispense such substances from categorisation.