Alternative spiroketalization methods toward purpuromycin: a diketone approach to prevent benzofuran formation

The central portion of purpuromycin has been assembled via a classical spiroketalization reaction. Key to promoting this reaction mode versus benzofuran formation was the oxidation state of the spiroketal core. With a higher oxidation state, even the electron-deficient isocoumarin found in purpuromycin could be employed directly in the spiroketalization. The two halves of the spiroketalization precursor were joined via a nitrile oxide/styrene 1,3-dipolar cycloaddition. A very mild selenium dioxide oxidation was used to introduce the required oxidation state of the spiroketal core.     

Dephosphorylation reactions with deferoxamine, a potential chemical nuclease

We report a detailed kinetic and mechanistic study of the reaction of a widely used therapeutic agent, deferoxamine (DFO), which contains three nucleophilic hydroxamate groups, with the model phosphate diester bis-2,4-dinitrophenylphosphate BDNPP. We clarify the mechanism by detecting important phosphorylated intermediates in the model reaction and show that the mechanism can be extended to the reaction with DNA. The effectiveness of DFO in cleaving DNA was examined over a range of pH in the absence and presence of a biologically available metal (Zn(2+)). The results inform and complement ongoing studies involving DFO, which can act as a powerful nucleophile toward DNA and other targets susceptible to nucleophilic attack.     

Phosphorylimidazole derivatives: potentially biosignaling molecules

The phosphorylation of imidazole by two activated phosphate diesters and a triester gives phosphorylimidazole derivatives that are stable enough in aqueous solution to be observed and identified by ESI-MS/MS and NMR. Half-lives ranging from hours to days (in the case of the monoethyl ester) show that it is possible to design molecules with variable half-lives with potential to be used for biological intervention experiments as possible inhibitors of biosignaling processes or as haptens for the generation of antibodies.     

Determination of the Biodiesel Content in Diesel/Biodiesel Blends: A Method Based on Fluorescence Spectroscopy

Blends of biodiesel and diesel are being used increasingly worldwide because of environmental, economic, and social considerations. Several countries use biodiesel blends with different blending limits. Therefore, it is necessary to develop or improve methods to quantify the biodiesel level in a diesel/biodiesel blend, to ensure compliance with legislation. The optical technique based on the absorption of light in the mid-infrared has been successful for this application. However, this method presents some challenges that must be overcome. In this paper, we propose a novel method, based on fluorescence spectroscopy, to determine the biodiesel content in the diesel/biodiesel blend, which allows in loco measurements by using portable systems. The results showed that this method is both practical and more sensitive than the standard optical method.     

Plasma Response to Resonant Perturbations at Tokamak Edge

In certain circumstances, plasma response suppresses magnetic islands expected at perturbed resonant magnetic surfaces. We investigate the plasma response to the resonant magnetic perturbations in a large aspect ratio tokamak perturbed by external resonant helical windings, considering polar toroidal coordinates for which analytical toroidal equilibrium solutions and perturbing fields are available. We apply an empirical approach to mimic the plasma screening effects by introducing presumed plasma current sheets on the resonance surfaces to cancel the RMP effects. Numerical examples show the effect of plasma response reducing magnetic islands at the plasma edge and also regularizing field lines around the resonant surface. The distribution of connection lengths along the plasma cross section indicates that the plasma response increases the connection lengths since more toroidal turns are performed until a field line reaches the tokamak wall.     

Pectinases Secretion by Saccharomyces cerevisiae: Optimization in Solid-State Fermentation and Identification by a Shotgun Proteomics Approach

A sequential design strategy was applied to optimize the secretion of pectinases by a Saccharomyces cerevisiae strain, from Brazilian sugarcane liquor vat, on passion fruit residue flour (PFRF), through solid-state fermentation (SSF). A factorial design was performed to determine the influence variables and two rotational central composite designs were executed. The validated experimental result was of 7.1 U mL⁻¹ using 50% PFRF (w/w), pH 5, 30 °C for 24 h, under static SSF. Polygalacturonase, pectin methyl esterase, pectin–lyase and pectate–lyase activities were 3.5; 0.08; 3.1 and 0.8 U mL⁻¹, respectively. Shotgun proteomics analysis of the crude extract enabled the identification of two pectin–lyases, one pectate–lyase and a glucosidase. The crude enzymatic extract maintained at least 80% of its original activity at pH values and temperatures ranging from 2 to 8 and 30 to 80 °C, respectively, over 60 min incubation. Results revealed that PFRF might be a cost-effective and eco-friendly substrate to produce pectinases. Statistical optimization led to fermentation conditions wherein pectin active proteins predominated. To the extent of our knowledge, this is the first study reporting the synthesis of pectate lyase by S. cerevisiae.     

Modelling the Vapor–Liquid Equilibrium of Polymer Solutions Using a Cubic Equation of State

This work presents the vapor–liquid equilibrium calculations in an isothermal flash, applied to polymer solutions, using the Peng–Robinson cubic equation of state modified by Stryjek–Vera, and the mixing rule introduced by Wong–Sandler. This rule allows combining the rigid lattice thermodynamic model of Flory–Huggins to the Peng–Robinson–Stryjek–Vera equation of state. As the Gibbs free energy must be minimum in the equilibrium state, a stochastic optimization method, the simulated annealing algorithm, was used to find out the extreme of this thermodynamic potential.     

Design of smart nanodevices based on N-vinyl caprolactam nanogels for photosensitizers

Smart PVCL-based nanogels for photosensitizers were prepared following the thermo precipitation methodology. PVCL-based imprinted and non-imprinted NGs are reported with different percentages of N,N′-methylenebisacrylamide (BIS) as crosslinker agent. Zn(II)phthalocyanine (ZnPc) is employed as a model photosensitizer and incorporated as a template molecule for imprinted NGs or it loads post-synthesis for non-imprinted NGs. In order to analyze the chemical structure, NGs were characterized using infrared microscopy. Hydrodynamic diameter was determined by dynamic light scattering. The phase transition temperature was measured by UV–vis spectroscopy. The phase transition temperature and D_h values were regulated by the percentage of crosslinker and the presence of the photosensitizer as a template or post-synthesis load. In all cases, the yields were acceptable and the smart nanodevices were stable.