NMR studies of inclusion complexation of the pyrrolizidine alkaloid retronecine and p-sulfonic acid calix[6]arene

Accidental or intentional drug toxicity in humans and animals is a major concern and the search for detoxificant agents is a challenge. Pyrrolizidine-producing forages are a threat not only to livestock, but also to humans as a consequence of food contamination. Supramolecular systems are promising as detoxificant agents by decreasing the bioavailability of toxic compounds in biological environment. Cyclodextrin and calix[n]arenes are well known hosts for a variety of molecules and/or ions. Surprisingly, only few studies describe the potential of calix[n]arenes as host for toxic molecules. This study focused on the use of NMR techniques as tools for the investigation of the interactions between p-sulfonic acid calix[6]arene and retronecine, a toxic pyrrolizidine alkaloid.     

Concentration of Whey Proteins by Using Temperature-Sensitive Polymer Gel Poly(N-isopropylacrylamide)

Summary: In this work, the use of a temperature-sensitive polymer gel, poly(N-isopropylacrylamide), for the concentration of whey proteins was studied. The studied variables were: gel mass/solution volume ratio and concentration temperature. The concentration percentage and the selectivity were determined. The gel 20 × 5 (20% w/w total monomer/solution and 5% w/w crosslinking agent/total monomer), contacted with whey proteins solutions, at 5 °C and at 20 °C, was capable of concentrating the solution, in protein, from 10 to 33%, depending on the gel mass/solution volume ratio. The separation efficiencies, for the different studied systems, varied from around 40 to 80%. The results were discussed in the context of gels thermodynamics and through correlations between synthesis parameters and structure of the obtained gels. The obtained results for the concentration of whey proteins solutions, by using temperature-sensitive polymer gel, poly(N-isopropylacrylamide), showed that the Gel Process can indeed be used as an advantageous alternative for such separation, either from an economic or from an environmental view point.     

Effect of the Inducers Veratryl Alcohol, Xylidine, and Ligninosulphonates on Activity and Thermal Stability and Inactivation Kinetics of Laccase from Trametes versicolor

Laccase production from Trametes versicolor was improved in the presence of the inducers ligninosulphonates, veratryl alcohol, and xylidine respectively two-, four-, and eightfold. The thermal inactivation of the produced laccase, after partial purification with ammonium sulfate was kinetically investigated at various temperatures (60?C70?°C) and pH values (3.5, 4.5, and 5.5). The inactivation process followed first-order kinetics for all conditions tested, except for veratryl alcohol, for which a constant activity level was observed at the end of the inactivation, also after first-order decay. Enzyme thermostability was affected by the type of inducer used in the culture medium for the production of laccase and also by the pH of incubation mixture. Generally, laccase stability increased with pH increment, being more stable at pH?5.5, except with xylidine. At pHs?4.5 and 5.5, the three inducers significantly increased laccase thermal stability, with the higher effect being observed for pH?5.5 and ligninosulphonates, where increment of half-life times ranged from 3- to 20-fold, depending on the temperature.     

On the information-based complexity of stochastic programming

Existing complexity results in stochastic linear programming using the Turing model depend only on problem dimensionality. We apply techniques from the information-based complexity literature to show that the smoothness of the recourse function is just as important. We derive approximation error bounds for the recourse function of two-stage stochastic linear programs and show that their worst case is exponential and depends on the solution tolerance, the dimensionality of the uncertain parameters and the smoothness of the recourse function.     

Spectroscopic evidence for and characterization of a trinuclear ferroxidase center in bacterial ferritin from Desulfovibrio vulgaris Hildenborough

Ferritins are ubiquitous and can be found in practically all organisms that utilize Fe. They are composed of 24 subunits forming a hollow sphere with an inner cavity of ~80 ? in diameter. The main function of ferritin is to oxidize the cytotoxic Fe(2+) ions and store the oxidized Fe in the inner cavity. It has been established that the initial step of rapid oxidation of Fe(2+) (ferroxidation) by H-type ferritins, found in vertebrates, occurs at a diiron binding center, termed the ferroxidase center. In bacterial ferritins, however, X-ray crystallographic evidence and amino acid sequence analysis revealed a trinuclear Fe binding center comprising a binuclear Fe binding center (sites A and B), homologous to the ferroxidase center of H-type ferritin, and an adjacent mononuclear Fe binding site (site C). In an effort to obtain further evidence supporting the presence of a trinuclear Fe binding center in bacterial ferritins and to gain information on the states of the iron bound to the trinuclear center, bacterial ferritin from Desulfovibrio vulgaris (DvFtn) and its E130A variant was loaded with substoichiometric amounts of Fe(2+), and the products were characterized by M?ssbauer and EPR spectroscopy. Four distinct Fe species were identified: a paramagnetic diferrous species, a diamagnetic diferrous species, a mixed valence Fe(2+)Fe(3+) species, and a mononuclear Fe(2+) species. The latter three species were detected in the wild-type DvFtn, while the paramagnetic diferrous species was detected in the E130A variant. These observations can be rationally explained by the presence of a trinuclear Fe binding center, and the four Fe species can be properly assigned to the three Fe binding sites. Further, our spectroscopic data suggest that (1) the fully occupied trinuclear center supports an all ferrous state, (2) sites B and C are bridged by a μ-OH group forming a diiron subcenter within the trinuclear center, and (3) this subcenter can afford both a mixed valence Fe(2+)Fe(3+) state and a diferrous state. Mechanistic insights provided by these new findings are discussed and a minimal mechanistic scheme involving O-O bond cleavage is proposed.     

Photoluminescence and Optical Absorption of Cs2NaScF6:Cr3+

The main objective of this paper is the characterization of the spectroscopic properties of new materials that are prospective laser media. This approach allows for the comparison of the properties of the Cr³⁺ in different environments. Here, we have studied the photoluminescence and optical absorption of Cs₂NaScF₆:Cr³⁺ single crystals. On the basis of near-infrared luminescence measurements at 2, 77, and 300 K the observed lines originated from the Cr³⁺-centres were associated with the transition and the lifetimes were obtained. In spite of the quenching observed as a function of temperature at least 10% of the 2 K emission intensity for Cs₂NaScF₆ doped with 1% of Cr³⁺ remains at room temperature. Besides, the 2 K emission broad band could be well described in terms of normal modes of the octahedral complex [CrF₆]³⁻, and the Racah and crystal-field parameters calculated.     

Implications of exposure to dextran-coated and uncoated iron oxide nanoparticles to developmental toxicity in zebrafish

Iron oxide nanoparticles (IONPS) have been widely investigated as a platform for a new class of multifunctional theranostic agents. They are considered biocompatible, and some formulations are already available in the market for clinical use. However, contradictory results regarding toxicity of IONPs raise a concern about the potential harm of these nanoparticles. Changes in the nanoparticle (NP) physicochemical properties or exposure media can significantly alter their behavior and, as a consequence, their toxic effects. Here, behavior and two-step RT-qPCR were employed to access the potential toxicological effects of dextran-coated IONPs (CLIO-NH2) and uncoated IONPs (UCIO) in zebrafish larvae. Animals were exposed for 7 days to NP solutions ranging from 0.1–100 μg/mL directly mixed to the system water. UCIO showed high decantation and instability in solution, altering zebrafish mortality but showing no alterations in behavior and molecular expression analysis. CLIO-NH2 exposure did not cause significant mortality or changes in hatching rate of zebrafish larvae; however, behavior and expression profiles of the group exposed to lower concentration (1 μg/mL) presented a tendency to decrease the locomotor activity and apoptotic pathway activation.     

The effect of chemical distribution on the magnetocaloric effect: A case study in second-order phase transition manganites

Ferromagnetic manganites of general formula ${\text{ABMnO}}_3$ (where A is a trivalent rare-earth ion and B is a divalent dopant) are candidates for magnetic cooling applications, since they can present either second- or first-order magnetic phase transitions, and the perovskite structure allows for substantial chemical substitution and tuning of the magnetocaloric properties. The consequent chemical distribution from substitution affects the magnetic and magnetocaloric properties of the compound. The change of relative cooling power with chemical disorder is discussed by the use of the molecular mean-field model. We present experimental results of the ferromagnetic, second-order phase transition ${\text{La}}_{0.70-x}(\text{Er,}\text{Eu}{)}_x{\text{Sr}}_{0.30}{\text{MnO}}_3$ system.