CeO2 nanostructured electrochemical sensor for the simultaneous recognition of diethylstilbestrol and 17ß-estradiol hormones.

A new highly sensitive, selective, and inexpensive electrochemical method has been developed for simultaneously detecting diethylstilbestrol (DES) and 17ß-estradiol (E2) in environmental samples (groundwater and lake water) using a graphite sensor modified by cerium oxide nanoparticles (CPE-CeO2 NPs). The developed sensor and the materials used in its preparation were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The ab initio simulation was used to evaluate the adsorption energies between both DES and E2 with the surface of the sensor. The peak current of oxidation of both hormones showed two regions of linearity. The region of greatest sensitivity was observed for the linear range of 10 nM-100 nM. The detection and quantification limits for this concentration range were 0.8/2.6 nM and 1.3/4.3 nM for DES and E2, respectively. The analytical performance of the developed method showed high sensitivity, precision, repeatability, reproducibility, and selectivity. The CPE-CeO2 NPs sensor was successfully applied to simultaneously detect DES and E2 in real samples with recovery levels above 98%.

An Analytical Evaluation of the Synergistic Effect on Biodiesel Oxidation Stability Promoted by Binary and Ternary Blends Containing Multifunctional Additives.

The antioxidant potential of a novel additive, named maleimide p-CH3, and the synergistic effect on biodiesel stabilization when combined with a traditional synthetic antioxidant (e.g., propyl gallate (PG)) as well as alternative additives (e.g., alizarin (ALZ) and citric acid (CA)) were investigated. The additives were combined in binary and/or ternary blends at low concentrations and their effectiveness against soybean biodiesel oxidation in the absence and presence of metal was tested. The effectiveness of binary and ternary blends was also evaluated by the Rancimat® method and compared with total acid number (TAN). The results showed that the combinations presented synergetic effects and were effective in stabilizing biodiesel in accordance with the minimum requirements of EN 14214 and also revealed that the mixture containing PG and p-CH3, even at low concentrations, can be successfully applied for biodiesel preservation. In summary, we report that the biodiesel stability can be obtained by using a reduced amount of additives, suggesting that biodiesel shelf life can be improved in association with a cost reduction when compared to the use of conventional antioxidants.

Molecular basis for competitive solvation of the Burkholderia cepacia lipase by sorbitol and urea.

Increasing the stability of proteins is important for their application in industrial processes. In the intracellular environment many small molecules, called osmolytes, contribute to protein stabilization under physical or chemical stress. Understanding the nature of the interactions of these osmolytes with proteins can help the design of solvents and mutations to increase protein stability in extracellular media. One of the most common stabilizing osmolyes is sorbitol and one of the most common chemical denaturants is urea. In this work, we use molecular dynamics simulations to obtain a detailed picture of the solvation of the Burkholderia cepacia lipase (BCL) in the presence of the protecting osmolyte sorbitol and of the urea denaturant. We show that both sorbitol and urea compete with water for interactions with the protein surface. Overall, sorbitol promotes the organization of water in the first solvation shell and displaces water from the second solvation shell, while urea causes opposite effects. These effects are, however, highly heterogeneous among residue types. For instance, the depletion of water from the first protein solvation shell by urea can be traced down essentially to the side chain of negatively charged residues. The organization of water in the first solvation shell promoted by sorbitol occurs at polar (but not charged) residues, where the urea effect is minor. By contrast, sorbitol depletes water from the second solvation shell of polar residues, while urea promotes water organization at the same distances. The interactions of urea with negatively charged residues are insensitive to the presence of sorbitol. This osmolyte removes water and urea particularly from the second solvation shell of polar and non-polar residues. In summary, we provide a comprehensive description of the diversity of protein-solvent interactions, which can guide further investigations on the stability of proteins in non-conventional media, and assist solvent and protein design.