Thermal Analysis of Pigments Based on CeO2

The synthesis of new compounds based on CeO₂ is investigated in our laboratory. The main attention is directed to the preparation of these compounds which can be used as pigments for colouring of ceramic glazes. The synthesis of these compounds is based on high-temperature calcination of starting oxides. The optimum conditions for the syntheses of compounds have been estimated and the pigments prepared have been evaluated from the standpoint of their structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Extrapolation of accelerated thermooxidative tests to lower temperatures applying non-Arrhenius temperature functions

Extrapolations of the accelerated thermooxidative tests, based on the Arrhenius and two non-Arrhenius temperature functions, have been tested for 26 data sets. The data cover a wide range of materials from polyolefins and other polymers to biodiesel, edible oils and dried milk. It has been found that the extrapolation from high-temperature data to ambient temperature based on the Arrhenius temperature function leads to the estimations of unrealistically long durability. The best estimations corresponding most with experience are obtained for the extrapolation based on the temperature function k(T)=A _kexp(DT).     

Microfriction correction factor to the Stokes–Einstein equation for small molecules determined by NMR diffusion measurements and hydrodynamic modelling

The Stokes–Einstein relationship relating the self-diffusion coefficient with the size of a diffusing particle (a hydrodynamic radius) breaks down in case of small molecules. We present a novel method extending the range of validity of the Stokes–Einstein relationship by means of introducing a molecule-specific microfriction correction factor. This factor equals to 1 in the ordinary form of the Stokes–Einstein formula for ‘stick’ boundary conditions when molecules of solvent are much smaller than the diffusing particle. We have determined the microfriction correction factors for series of small molecules (ranging in size from ethanol to 18-crown-6 ether and tetrakis(trimethylsilyl)silane) in a dilute hexane solution by a concerted use of the NMR diffusion measurements and the molecular hydrodynamic calculations. Both of the tested hydrodynamic modelling programmes, HydroNMR (García de la Torre et al., J. Magn. Reson. 2000, 147, 138–146) and DiTe (Barone et al., J. Comput. Chem. 2008, 30, 2–13) provided very similar results after initial calibration on a molecular system, which is within the validity range of the Stokes–Einstein relationship (fullerene in hexane solution in this work).     

The structure of (theta,pyramid, 1-wheel, 3-wheel)-free graphs

In this paper, we study the class of graphs defined by excluding the following structures as induced subgraphs: theta, pyramid, 1-wheel, and 3-wheel. We describe the structure of graphs in , and we give a polynomial-time recognition algorithm for this class. We also prove that -free graphs in are 4-colorable. We remark that includes the class of chordal graphs, as well as the class of line graphs of triangle-free graphs.     

Antibacterial nanocomposite supporting cell growth and spheroid formation by chemical surface treatment of polymer foil

Octenidine dihydrochloride (OCT) has a wide spectrum of antibacterial, antifungal and virucidal activity. OCT is also newly used in tissue engineering. The aim of this work was to create a new nanocomposite consisting of OCT-grafted polymer with (i) antibacterial effect and/or (ii) surface for better cell adhesion and proliferation. The polymer foils were chemically activated with Piranha solution and subsequently grafted with OCT. Changes in surface properties before and after modifications were detected by electrokinetic analysis, goniometry, atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The final nanocomposite polymer/OCT exhibits antibacterial activity against Staphylococcus epidermidis (S. epidermidis). The new nanocomposite material has also been shown to support the growth of B14 cell culture on the substrate and to form cell multilayers, which could lead to the formation of spheroids. This behaviour strongly depends on the concentration of OCT grafted onto the polymer surfaces. This new nanocomposite could be used in medicine, for bioapplications, environmental protection.     

Do Docking Sites Persist Upon Fluorination? The Diadamantyl Ether-Aromatics Challenge for Rotational Spectroscopy and Theory

Fluorinated derivatives of biological molecules have proven to be highly efficient at modifying the biological activity of a given protein through changes in the stability and the kind of docking interactions. These interactions can be hindered or facilitated based on the hydrophilic/hydrophobic character of a particular protein region. Diadamantyl ether (C₂₀H₃₀O) possesses both kinds of docking sites, serving as a good template to model these important contacts with aromatic fluorinated counterparts. In this work, an experimental study on the structures of several complexes between diadamantyl ether and benzene as well as a series of fluorinated benzenes is reported to analyze the effect of H→F substitution on the interaction and structure of the resulting molecular clusters using rotational spectroscopy. All experimentally observed complexes are largely dominated by London dispersion interactions with the hydrogen-terminated surface areas of diadamantyl ether. Already single substitution of one hydrogen atom with fluorine changes the preferred docking site of the complexes. However, the overall contributions of the different intermolecular interactions are similar for the different complexes, contrary to previous studies focusing on the difference in interactions using fluorinated and non-fluorinated molecules.     

Direct carbamation of cellulose fiber sheets

The paper is on introducing carbamate groups in sheets of cellulose fiber assemblies by pad-dry-cure treatments with aqueous solutions of polyethylene glycol, amide and salt. The effects of process variables—on carbamation levels and on mechanical properties of the substrate—are reported. Depending on treatment conditions, the nitrogen contents in substrates are in the range 0.668–2.252 wt%, corresponding to nominal degrees of carbamate group substitution of 0.08–0.28. The carbamation is initiated at 140 °C curing, and the levels rise with temperature up to 220 °C, but decrease at higher temperatures. The duration of curing also exerts an influence. There is a catalytic effect of sodium acetate on the carbamation, but the salt also induces a brown coloration in samples, which is likely a result of Maillard-type reactions. The treatments cause hydrolytic degradation in substrates, but there are options to adjust treatment conditions and minimize damage. Pad-dry-cure treatments are a common operation in the textile and paper industries, and the process may be adopted in commercial-scale operations to create derivatized paper or fabrics (woven, knitted or non-woven) for utilization in applications such as adsorbents for heavy metals from waste water, in hygiene products, in the creation of flame retardant products, or in creating all-cellulose composites by further treatment with alkali.     

Effect of hypercrosslinking conditions on pore size distribution and efficiency of monolithic stationary phases

Three dihalogenic solvents differing in the length of alkyl chain (1,2‐dichloroethane, 1,4‐dichlorobutane, and 1,6‐dichlorohexane) with three Friedel–Crafts alkylation catalysts varying in reactivity (AlCl₃, FeCl₃, and SnCl₄) have been used to prepare hypercrosslinked poly(styrene‐co‐vinylbenzyl chloride‐co‐divinylbenzene) columns. Hydrodynamic characteristics as well as column efficiency and mass transfer resistance were tuned by the combination of swelling solvent and alkylation reaction catalyst in the modification mixture. The column swelled in 1,6‐dichlorohexane and hypercrosslinked in the presence of AlCl₃ provided the highest column efficiency and enabled fast isocratic separations of small molecules in a RP mode. To uncover factors controlling the efficiency of hypercrosslinked monolithic columns, we have studied pore volume distribution of prepared columns. We found that column efficiency increases with the higher pore volume of pores smaller than 2 nm.     

Determination of essential elements (Mn,Fe, Cu and Zn) in herbal teas by TXRF,FAAS and ICP-OES

The aim of this study was the comparison of the results obtained in the determination of the content of essential elements such as Mn, Fe, Cu and Zn in vegetation samples using different analytical approaches, including suspension preparation and total reflection X-ray fluorescence ( TXRF) analysis as well as most commonly used spectroscopic methods in the field of vegetal analysis such as acid digestion in combination with atomic emission (AES) and atomic absorption spectrometry (AAS). In the case of TXRF analysis, two instruments equipped with different X-ray tubes anodes (W and Mo) were used to better evaluate the potential of TXRF for vegetal samples analysis. Analytical figures of merit for the considered methods were determined by the analysis of plant reference materials. The one-way analysis of variance (ANOVA) applied to the analysed and certified values showed that the results were not statistically different at the significance level of p-values <0.05. Therefore, suspension preparation and TXRF analysis proved to be a sustainable and fast analytical alternative to the most commonly used ones involving a previous digestion of the sample and inductively coupled plasma optical emission spectrometry (ICP-OES) or flame atomic absorption spectrometry (FAAS) analysis. Finally, the different analytical approaches were applied to the determination of Mn, Fe, Cu and Zn in a set of herbal teas used for medical purposes.