Improving real-time measurement of H/D exchange using a FTIR biospectroscopic probe

We describe the improvement of a novel approach to investigating hydrogen/deuterium (H/D) exchange kinetics in biomolecules using transmission infrared spectroscopy. The method makes use of a Fourier transform infrared spectrometer coupled with a microdialysis flow cell to determine exchange rates of labile hydrogens. With this cell system, the monitoring of exchange reactions has been studied here as a function of some cell characteristics such as: (a) dialysis membrane surface contacting both the H₂O and D₂O compartments; (b) molecular cutoff of dialysis membrane; and (c) distance between the cell-filling holes. The best improvement has been obtained by increasing the dialysis membrane surface followed by increase of molecular cutoff. However, not significant differences were found using various distances between filling holes. The fastest exchange rate which can be measured with the cell system used here is found to be k = 0.41 ± 0.02 min⁻¹, that is, about threefold greater than the one got in a previous work. This microdialysis flow cell has been used here for the study of H/D exchange in nucleic acids with subsequent structural analysis by 2D correlation spectroscopy.     

[Cu(H2btec)(bipy)]∞: Reusable Metal Organic Polymer Catalyst for Epoxidation Reactions

Summary: The search of new inorganic materials with better catalytic properties is an important field of research. Reusability, efficiency and atom economy correspond to the main parameters to characterize a catalyst. In this work, we inform the effectiveness of [Cu(H₂btec)(bipy)]_∞ (H₄btec = 1,2,4,5-benzenetetracarboxylic acid) as an heterogeneous coordination polymer catalyst for the oxidation of olefins. The catalyst exhibits good atom economy, high turnover numbers and good selectivity for a ratio of 4000/1 substrate/catalyst for cyclohexene and styrene oxidation. Furthermore, the catalyst was recycled and reused for seven consecutive cycles, retaining the structural integrity and effectiveness as catalyst in all the performed experiments.     

Double relaxation processes in the glass system xEu2O3·PbO·2B2O3 studied by broadband dielectric spectroscopy

In this work we study the effect of introducing europium oxide in lead borate glasses, in concentrations up to x = 0.20, using the impedance spectroscopy in a large frequency range (0.1 Hz to 9 GHz). Two relaxation processes can be identified. The low frequency process deviates considerably from the Debye type and is modelled by the Cole-Davidson expression. The high frequency relaxation is also a non-Debye type and is fitted by the Cole-Cole expression. These results imply some distribution of relaxation times, due to the interaction between the dipoles.The behaviour of the dielectric strength is similar in the low and high frequency regions, indicating a cluster formation at a critical concentration of europium oxide (x = 0.03).     

DC electrical conductivity of carbon black polymer composites at low temperatures

The understanding of the charge transport mechanism of the conducting polymers and their composites is important for the successful fabrication of semiconductor devices.In this work, the DC electrical conductivity of carbon black particles in a polystyrene matrix, in the temperature range of 80 to 250 K is examined, for concentrations below the critical percolation concentration. We show that three-dimensional variable range hopping is observed, that is, the temperature behavior of the DC conductivity can be expressed by . From the hopping parameter we obtained the mean hopping distance, the density of active centers and the energy associated with it.     

Growth morphology of gypsum in the presence of copolymers

Gypsum is the most abundant natural sulphate, and in industrial application it plays an important role in gypsum based binders. Furthermore, it plays a critical role in the hydration of Portland cement, and then gypsum is one of the most important cement additive. In this paper we investigated the role of two commercial polymeric additives in modifying the crystal habits and size of gypsum, growth in aqueous solution. These two additives belong to the categories of acrylic polymers and they are known only by their commercial names of SP1 and SP3. We found that these substances can act as shape modifiers mainly at concentration over 0.04% by weight, with a shortening in the elongation of gypsum crystal and some change in the characters of {001} form, from stepped to flat, due to a change in the growth mechanism. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of composition and temperature on the amount and type of nanoferrite particles inserted in Fe2O3–ZnO–MgO–SiO2 glass–ceramics

Glass–ceramics with the composition 2Fe₂O₃.1ZnO.1MgO.96SiO₂ [4ZnMgFe] and 2Fe₂O₃.2ZnO.3MgO.93SiO₂ [7ZnMgFe] (mol%) were prepared using the sol–gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron diffraction (ED) and Mössbauer spectroscopy (MS) were used to investigate the glass–ceramics structure. The samples contain ferrite nanoparticles embedded in a glass matrix. However, zinc ferrite nanoparticles seems to be the preferential crystalline phase formed. The amount of ferrite particles depends on treatment temperature and sample composition. The Mössbauer spectroscopy measurements show that ferrite nanoparticles can exhibit a ferrimagnetic behaviour combined with superparamagnetism.     

Are inconsistent decisions better? An experiment with pairwise comparisons

This paper tries to contribute to the well-known and lengthy discussion on whether we should allow decision makers to be inconsistent, or, to put it in another way, if intransitive decisions better represent their preferences. We will focus specifically on the multiple-criteria decision making problem, since it is one of the most usual stances where this intransitivity appears. Results from an experiment carried out with graduate students shows that, when intransitivities are removed, the preferences of decision makers are not better represented, and therefore that the effort to do so may not be justified.     

Asymptotic behaviour of a phase-field model with three coupled equations without uniqueness

We prove the existence of weak solutions for a phase-field model with three coupled equations with unknown uniqueness, and state several dynamical systems depending on the regularity of the initial data. Then, the existence of families of global attractors (level-set depending) for the corresponding multi-valued semiflows is established, applying an energy method. Finally, using the regularizing effect of the problem, we prove that these attractors are in fact the same.