Thermogravimetric and calorimetric study of cellulose paper at low doses of gamma irradiation

The study of the behaviour of cellulose materials at low doses of ionizing radiation regained the interest because of the recent results showing that physical properties of the paper have less or no changes for absorbed doses below 10 kGy, despite the high decrease of the degree of polymerization. The understanding of the relationship among molecular, microscopic and macroscopic changes in cellulose materials may change the current opinion that irradiation of paper is not the best choice for conservation of cultural heritage. The aim of this study is to reveal the changes in gamma-irradiated pure cellulose paper by simultaneous TG/DSC analysis. For cellulose fibres, the thermal decomposition parameters depend on the cellulose degree of polymerization. For high irradiation doses, there is established a relationship between the absorbed dose and the degree of polymerization. However, a direct relationship between absorbed dose and the parameters of cellulose thermal decomposition for low irradiation doses was not established either in the literature or in our study. By using a peak separation technique, we studied the changes in the region of water loss (70–150 °C) and physical ageing (160–300 °C) for Whatman paper with low initial water content (<1 %), previously gamma irradiated at doses between 0 and 30 kGy. We concluded that strength of the hydrogen bond structure is increasing up to a point when the stress produces fractures in the fibrilar structure. This may explain the results reported for mechanical tests at low dose irradiation and it is in agreement with scanning electron microscopy pictures showing changes in fibril structure at high irradiation doses. Cellulose irradiated at low doses maintains its original hydrogen bond structure despite the decrease of the degree of polymerization.     

Application of the site blocking method to the investigation of the kinetics of carbon monoxide electrooxidation on nanostructured Pt

In this work, we apply a recently developed selective site blocking with gold adatoms (Kuznetsov et al. Electrocatal 3:211–220, 2012) for studying the electrooxidation of adsorbed carbon monoxide on electrodeposited Pt. The reaction is studied using chronoamperometry, and the obtained current transients are fitted with a nucleation-and-growth model in order to determine the characteristic kinetic parameters on defect and terrace (facet) sites. We conclude that Au selectively blocks defect sites up to very high coverages of 0.42 MLs, strongly slowing down the reaction kinetics. Blocking of defect sites with Au adatoms also results in an increase of the packing density of CO on terrace sites. The rate constant of CO oxidation on defects is higher than that on terraces and exhibits higher Tafel slope.     

Theoretical and experimental study of 15N NMR protonation shifts

A combined theoretical and experimental study revealed that the nature of the upfield (shielding) protonation effect in ¹⁵N NMR originates in the change of the contribution of the sp²‐hybridized nitrogen lone pair on protonation resulting in a marked shielding of nitrogen of about 100 ppm. On the contrary, for amine‐type nitrogen, protonation of the nitrogen lone pair results in the deshielding protonation effect of about 25 ppm, so that the total deshielding protonation effect of about 10 ppm is due to the interplay of the contributions of adjacent natural bond orbitals. A versatile computational scheme for the calculation of ¹⁵N NMR chemical shifts of protonated nitrogen species and their neutral precursors is proposed at the density functional theory level taking into account solvent effects within the supermolecule solvation model. Copyright © 2015 John Wiley & Sons, Ltd.     

Water soluble sulconazole-β-cyclodextrin complex: physico-chemical characterization and preliminary pharmacological studies

Sulconazole-β-cyclodextrin water soluble inclusion complex was prepared by freeze drying method in distilled water. The formation of inclusion complex between β-cyclodextrin and sulconazole has been studied in a previous work. Preliminary pharmacological studies concerning the antifungal activity showed that the minimal inhibitory concentrations for 90% of the tested strains decreased. Also, the acute toxicity of the sulconazole-β-cyclodextrin complex is smaller comparing with the pure drug, analyzed alone. These results recommend the described conjugates as future promising therapeutic agents.     

Oscillating Poiseuille flow in photo-aligned liquid crystal cells

We present an experimental study of thin liquid crystal (LC) layers under the action of a harmonically varied pressure gradient. Optical measurements were performed to register the linear oscillations of a nematic director related to homeotropic and homeoplanar (hybrid) initial states. In the latter case one of the inner surfaces of the rectangular channels was treated by ultraviolet light to provide a relatively weak planar anchoring. The optical response of hybrid and homeotropic LC cells under an oscillating pressure gradient was investigated in relation to on the amplitude and frequency of the pressure gradient. A hydrodynamic model is developed taking into account the LC polar anchoring strength and the surface viscosity responsible for a fast LC surface dynamics. Our estimates show that the thickness of the boundary layer corresponding to the surface viscosity does not exceed 10^-6 m, and further experiments are needed with thinner LC cells and higher frequency oscillations to achieve a more precise value. An oscillating Poiseuille flow in the hybrid cell was found to be useful for characterizing elastic and viscous properties of a weakly anchoring LC surface layer in a fast surface dynamic process.     

Tautomerism of 3‐nitro‐1,2,4‐triazole‐5‐one radical anions

The non‐degenerate tautomers of 3‐nitro‐1,2,4‐triazole‐5‐one (NTO) radical anions were investigated for the first time by an ESR method during electrochemical reduction of NTO in an aprotic medium. Copyright © 2009 John Wiley & Sons, Ltd.     

Selections and totally disconnected spaces

We demonstrate that for every n<ω there exists a separable completely metrizable space Xn which has a continuous selection for its Vietoris hyperspace of nonempty compact subsets, but dim(Xn)=n. Related results and open problems are discussed.