ESR investigation of structure and dynamics of paramagnetic centres in lime mortars from Budinjak,Croatia

This study presents the preliminary results of investigation of the types and dynamics of paramagnetic centres in lime mortars from Sveta Petka church in Budinjak, Croatia, using Electron Spin Resonance (ESR) spectroscopy. The excavation in Budinjak discovered a very unique four lobed plan object Sveta Petka, with no additional finds or reliable historical records about the time of its construction. The lime mortars from the church were chosen for analysis in order to characterize the building material and to verify the site chronology by dating them. Lime mortar is valuable but problematic material for luminescence and radiocarbon dating. This type of material has not been dated before using ESR; therefore, careful studies are required to identify the useful paramagnetic centres. The ESR approach suggested in this work concentrates on a calcium carbonate signal. All samples were γ-irradiated in ⁶⁰C bomb with the doses of 1, 10, 20, 50, 80 and 100 kGy. In all spectra signals from Fe³⁺ and Mn²⁺ ions have been observed. Paramagnetic centres which give the ESR signals may be interpreted as CO₂^?, CO₃^?, CO₃^3?, HCO₃^2?, SO₂^?, SO₃^?, PO₂^? and PO₃^2? species. However, all spectra are complex and signals are interfering; therefore, computer resolution enhancement method will be needed in further research. The changes in ESR signals amplitude measured at magnetic field range about 3440–3450 G were analysed versus the dose of irradiation, using Mn²⁺ signals as a reference. Exponential growth of the curve and saturation for doses above 20 kGy were observed; therefore, irradiation with smaller doses is required. These preliminary studies will be helpful in future attempts of dating lime mortars by ESR method.     

Compositional control of electrical transport properties in the new series of defect thiospinels, Ga1−xGexV4S8−δ (0≤x≤1)

A new series of non-stoichiometric sulfides Ga_1−xGe_xV₄S_8−δ (0≤x≤1; δ≤0.23) has been synthesized at high temperatures by heating stoichiometric mixtures of the elements in sealed quartz tubes. The samples have been characterized by powder X-ray diffraction, SQUID magnetometry and electrical transport-property measurements. Structural analysis reveals that a solid solution is formed throughout this composition range, whilst thermogravimetric data reveal sulfur deficiency of up to 2.9% in the quaternary phases. Magnetic measurements suggest that the ferromagnetic behavior of the end-member phase GaV₄S₈ is retained at x≤0.7; samples in this composition range showing a marked increase in magnetization at low temperatures. By contrast Ga_0.25Ge_0.75V₄S_8−δ appears to undergo antiferromagnetic ordering at ca. 15 K. All materials with x≠1 are n-type semiconductors whose resistivity falls by almost six orders of magnitude with decreasing Ga content, whilst the end-member phase GeV₄S_8−δ is a p-type semiconductor. The results demonstrate that the physical properties are determined principally by the degree of electron filling of narrow-band states arising from intracluster V-V interactions.     

Textile with silver silica spheres: its antimicrobial activity against <Emphasis Type="Italic">Escherichia coli and Staphylococcus aureus</Emphasis>

The aim of this study was to investigate antimicrobial activity of textiles doped with silver in different forms. Three types of textiles were prepared and examined: textiles doped with commercially available Ag nanoparticles, textiles doped with commercial colloidal silver and textiles doped with silver silica SiO₂/Ag spheres. The specimens of silica submicron spheres were synthesized by the sol–gel method as a matrix for biological active silver. The results of microbiological tests revealed that among three kinds of Ag doped textiles only these doped with SiO₂/Ag spheres are bacteriostatically active. During the experiments minimal inhibiting bacteria growth concentration of active SiO₂/Ag spheres added to textiles was determined.     

Enhancement of Activity and Development of Low Pt Content Electrocatalysts for Oxygen Reduction Reaction in Acid Media

Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, then O₂-reduction often proceeds at a less positive potential, and produces higher amounts of undesirable H₂O₂-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO₂, WO₃, Ta₂O₅, Nb₂O₅, and ZrO₂), stabilize Pt and carbon nanostructures and diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction in oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. Alternatively, the Pt-based bi- and multi-metallic catalysts, including PtM alloys or M-core/Pt-shell nanostructures, where M stands for certain transition metals (e.g., Au, Co, Cu, Ni, and Fe), can be considered. The catalytic efficiency depends on geometric (decrease in Pt–Pt bond distances) and electronic (increase in d-electron vacancy in Pt) factors, in addition to possible metal–support interactions and interfacial structural changes affecting adsorption and activation of O₂-molecules. Despite the stabilization of carbons, doping with heteroatoms, such as sulfur, nitrogen, phosphorus, and boron results in the formation of catalytically active centers. Thus, the useful catalysts are likely to be multi-component and multi-functional.     

1/f Noise modeling of InAs/GaSb superlattice mid-wavelength infrared detectors

The empirical 1/f noise model for p\(^{+}\)-p-n infrared detector made of type-II InAs/GaSb superlattice material is presented. It is shown that 1/f noise magnitude can be accurately estimated if dark current contributions are determined and noise coefficients are known. It is found that the shunt, the bulk generation–recombination, and the trap-assisted tunneling currents contribute to the total 1/f noise. No 1/f noise connected with the diffusion and the band-to-band tunneling currents is observed.     

The symmetric amino-wagging band of hydrazine: Assignment and analysis

For the first time a weak fundamental symmetric amino-wagging band, ν₆, was assigned in the high-resolution Fourier-transform infrared spectrum of hydrazine. The analysis of the Fermi-type resonance between the ν₆ and the third excited torsional state, 3ν₇, is presented. A global fitting was carried out taking into account 3392 lines of the ν₆ band (for K′ from 0 to 10 and for all symmetry species) and 428 lines of the 3ν₇ band (for K′ from 3 to 9 and only for the symmetry species in resonance). For all 3820 rovibrational transitions the overall standard deviation of the fit of 0.019 cm⁻¹ was obtained. The band centers of the symmetric wagging state and the third torsional were determined at 795.137 and 860.138 cm⁻¹, respectively. Individual fits were also carried out for K′ from 3 to 8 for all symmetry species with much improved standard deviations. The effective group-theoretical Hamiltonian for the coupling between inversion and torsion states was used.     

New Hybrid Polyurea-Polyurethane Elastomers with Antistatic Properties and an Influence of Various Additives on Their Physicochemical Properties

Polyurea is a synthetic high-strength elastomeric material that can be sprayed as a coating over existing structures in order to protect against weathering effects. It is ideal for anti-corrosion protection and is characterized by excellent mechanical properties and adhesion to various surfaces. Further development of this technology may allow obtaining new coatings with improved antistatic properties, which would be an excellent alternative compared to used antistatic epoxy paints. This paper will examine the influence of tetraalkylammonium salt (1), potassium hexafluorophosphate solution (2) and imidazolium-based ionic liquid (3) on the improvement of antistatic properties of the polyurea-polyurethane coatings. In addition, the modified samples were also verified in terms of changes in mechanical properties and the appearance of functional groups other than in the reference sample, as well as surface defects that may arise due to incompatibility of the antistatic additive with the polymer matrix. In order to obtain information about the properties mentioned above, the electrical resistance was determined, the tensile strength and elongation were measured, FT-IR spectra were made, and images were taken with the use of scanning electron microscopy. The conducted research showed that the antistatic properties of the tested hybrid coatings could be improved, but their use may be associated with certain limitations that should be taken into account when designing such materials.     

Targeting DNA Topoisomerase II in Antifungal Chemotherapy

Topoisomerase inhibitors have been in use clinically for the treatment of several diseases for decades. Although those enzymes are significant molecular targets in antibacterial and anticancer chemotherapy very little is known about the possibilities to target fungal topoisomerase II (topo II). Raising concern for the fungal infections, lack of effective drugs and a phenomenon of multidrug resistance underlie a strong need to expand the range of therapeutic options. In this review paper, we discussed the usefulness of fungal topo II as a molecular target for new drug discovery. On the basis of previously published data, we described structural and biochemical differences between fungal and human enzymes as well as a molecular basis of differential sensitivity to known anticancer drugs targeting the latter. This review focuses especially on highlighting the differences that may underlie the selectivity of action of new inhibitors. Distinct sites within fungal topo II in comparison with human counterparts are observed and should be further studied to understand the significance of those sites and their possible usage in design of new drugs.     

Zinc–Cobalt Oxide Thin Films: High Curie Temperature Studied by Electron Magnetic Resonance

The material with a high Curie temperature of cobalt-doped zinc oxide embedded with silver-nanoparticle thin films was studied by electron magnetic resonance. The nanoparticles were synthesized by the homogeneous nucleation technique. Thin films were produced with the pulsed laser deposition method. The main aim of this work was to investigate the effect of Ag nanoparticles on the magnetic properties of the films. Simultaneously, the coexisting Ag⁰ and Ag²⁺ centers in zinc oxide structures are shown. A discussion of the signal seen in the low field was conducted. To analyze the temperature dependence of the line parameters, the theory described by Becker was used. The implementation of silver nanoparticles causes a significant shift of the line, and the ferromagnetic properties occur in a wide temperature range with an estimated Curie temperature above 500 K.