Ba-DOPED ZnO MATERIALS: A DFT SIMULATION TO INVESTIGATE THE DOPING EFFECT ON FERROELECTRICITY

ZnO is a semiconductor material largely employed in the development of several electronic and optical devices due to its unique electronic, optical, piezo-, ferroelectric and structural properties. This study evaluates the properties of Ba-doped wurtzite-ZnO using quantum mechanical simulations based on the Density Functional Theory (DFT) allied to hybrid functional B3LYP. The Ba-doping caused increase in lattice parameters and slight distortions at the unit cell angle in a wurtzite structure. In addition, the doping process presented decrease in the band-gap (Eg) at low percentages suggesting band-gap engineering. For low doping amounts, the wavelength characteristic was observed in the visible range; whereas, for middle and high doping amounts, the wavelength belongs to the Ultraviolet range. The Ba atoms also influence the ferroelectric property, which is improved linearly with the doping amount, except for doping at 100% or wurtzite-BaO. The ferroelectric results indicate the ZnO:Ba is an strong option to replace perovskite materials in ferroelectric and flash-type memory devices.

Increased expression and purification of soluble iron-regulatory protein 1 from Escherichia coli co-expressing chaperonins GroES and GroEL

Iron is an essential metal for all living organisms. However, iron homeostasis needs to be tightly controlled since iron can mediate the production of reactive oxygen species, which can damage cell components and compromise the integrity and/or cause DNA mutations, ultimately leading to cancer. In eukaryotes, iron-regulatory protein 1 (IRP1) plays a central role in the control of intracellular iron homeostasis. This occurs by interaction of IRP1 with iron-responsive element regions at 5' of ferritin mRNA and 3' of transferrin mRNA which, respectively, represses translation and increases mRNA stability. We have expressed IRP1 using the plasmid pT7-His-hIRP1, which codifies for human IRP1 attached to an NH2-terminal 6-His tag. IRP1 was expressed in Escherichia coli using the strategy of co-expressing chaperonins GroES and GroEL, in order to circumvent inclusion body formation and increase the yield of soluble protein. The protein co-expressed with these chaperonins was obtained mostly in the soluble form, which greatly increased the efficiency of protein purification. Metal affinity and FPLC ion exchange chromatography were used in order to obtain highly purified IRP1. Purified protein was biologically active, as assessed by electrophoretic mobility shift assay, and could be converted to the cytoplasmic aconitase form. These results corroborate previous studies, which suggest the use of folding catalysts as a powerful strategy to increase protein solubility when expressing heterologous proteins in E. coli.

Target-directed catalytic metallodrugs

Most drugs function by binding reversibly to specific biological targets, and therapeutic effects generally require saturation of these targets. One means of decreasing required drug concentrations is incorporation of reactive metal centers that elicit irreversible modification of targets. A common approach has been the design of artificial proteases/nucleases containing metal centers capable of hydrolyzing targeted proteins or nucleic acids. However, these hydrolytic catalysts typically provide relatively low rate constants for target inactivation. Recently, various catalysts were synthesized that use oxidative mechanisms to selectively cleave/inactivate therapeutic targets, including HIV RRE RNA or angiotensin converting enzyme (ACE). These oxidative mechanisms, which typically involve reactive oxygen species (ROS), provide access to comparatively high rate constants for target inactivation. Target-binding affinity, co-reactant selectivity, reduction potential, coordination unsaturation, ROS products (metal-associated vsmetal-dissociated; hydroxyl vs superoxide), and multiple-turnover redox chemistry were studied for each catalyst, and these parameters were related to the efficiency, selectivity, and mechanism(s) of inactivation/cleavage of the corresponding target for each catalyst. Important factors for future oxidative catalyst development are 1) positioning of catalyst reduction potential and redox reactivity to match the physiological environment of use, 2) maintenance of catalyst stability by use of chelates with either high denticity or other means of stabilization, such as the square planar geometric stabilization of Ni- and Cu-ATCUN complexes, 3) optimal rate of inactivation of targets relative to the rate of generation of diffusible ROS, 4) targeting and linker domains that afford better control of catalyst orientation, and 5) general bio-availability and drug delivery requirements.

Fatty acid ethyl esters production using a non-commercial lipase in pressurized propane medium

The objective of this work is to investigate the production of fatty acid ethyl esters from soybean oil in compressed propane using a non-commercial lipase from Yarrowia lipolytica and two commercial ones as catalysts, Amano PS and Amano AY30. The experiments were performed in the temperature range of 35-65 °C. at 50 bar, enzyme concentration of 5 wt%, oil to ethanol molar ratio of 1:6 and 1:9, and solvent to substrates mass ratio of 2:1 and 4:1. The results indicated that low reaction conversions were generally obtained with the use of commercial and non-commercial lipases in pressurized propane medium. On the other hand, the aspects of low solvent to substrates mass ratio and mild temperature and pressure operating conditions used to produce ethyl esters justify further investigations to improve reaction yields.

The role of organic solvent amount in the lipase-catalyzed biodiesel production

This research note addresses the role of organic solvent amount in the production of fatty acid ethyl esters from soybean oil. N-hexane was chosen as solvent and two commercial immobilized lipases as catalysts, Novozym 435 and Lipozyme IM. The reactions were conducted in 6 hours, varying the solvent to oil ratio from zero to 50 (v/wt) and adopting adopting for Novozym 435: 65 ºC, enzyme concentration (E, wt%) = 5, oil to ethanol molar ratio (R) = 1:10, water addition (H, wt%) = 0, and for Lipozyme IM: 35 ºC, E = 5 wt%, R = 1:3, H = 10 wt%. For Lipozyme IM, an increase in solvent amount is shown to lead to an enhancement of reaction conversion, while a negligible effect was found for Novozym 435. When using 30 mL of solvent the reaction conversions were 88% for Lipozyme IM and 15% for Novozym 435.