Addition of allyltrichlorostannanes to aldehydes: application in the synthesis of 4-N-Boc-amino-3-hydroxy ketones

We wish to describe here the diastereoselective reaction between chiral N-Boc-α-amino aldehydes and achiral allyltrichlorostannanes leading to 1,2-syn-N-Boc-α-amino alcohols, which are treated with catalytic amounts of OsO₄ in the presence of NaIO₄ to provide the corresponding 4-N-Boc-amino-3-hydroxy ketones.     

Analysis of Renal Cell Carcinoma Cell Response to the Enhancement of 5-aminolevulinic Acid-mediated Protoporphyrin IX Fluorescence by Iron Chelator Deferoxamine†

As a tumor photodiagnostic agent, 5-aminolevulinic acid (ALA) is metabolized in the heme biosynthesis pathway to produce protoporphyrin IX (PpIX) with fluorescence. ALA-PpIX fluorescence was evaluated in human renal cell carcinoma (RCC) cell lines and non-tumor HK-2 cell lines. We found that extracellular PpIX level was correlated with ABCG2 activity, illustrating its importance as a PpIX efflux transporter. Extracellular PpIX was also related to the K_m of ferrochelatase (FECH) that chelates PpIX with ferrous iron to form heme. The V_max of FECH was higher in all RCC cell lines tested than in the HK-2 cell line. TCGA dataset analysis indicates a positive correlation between FECH expression and RCC patient survival. These findings suggest FECH as an important biomarker in RCC. Effects of iron chelator deferoxamine (DFO) on the enhancement of PpIX fluorescence were assessed. DFO increased intracellular PpIX in both tumor and non-tumor cells, resulting in no gain in tumor/non-tumor fluorescence ratios. DFO appeared to increase ALA-PpIX more at 1-h than at 4-h treatment. There was an inverse correlation between ALA-PpIX fluorescence and the enhancement effect of DFO. These results suggest that enhancement of ALA-PpIX by DFO may be limited by the availability of ferrous iron in mitochondria following ALA administration.     

The role of residue Thr122 of methylamine dehydrogenase on the proton transfer from the iminoquinone intermediate to residue Asp76

We present the results of combined molecular dynamics and full-quantum calculations aimed at elucidating the role of residue Thr122 of the enzyme methylamine dehydrogenase. Calculations were performed on the native structure and the T122A mutant. We found that the presence of Thr122 has a deleterious effect on the proton transfer step that is proposed to determine the rate of the reaction. Besides, at the PM3 level, the substitution of Thr122 by Ala does not significantly modify the preference of the proton by atom OD2 of Asp76. Transmission coefficients obtained form MP2/6-31G(d,p)//PBE/DZP minimum energy paths show that proton tunneling is significant.     

Poly(ethylene-co-vinyl alcohol) and poly(methyl methacrylate) blends: Phase behavior and morphology

In this work blends of poly(ethylene-co-vinyl alcohol) (EVOH) with different ethylene contents (27, 32, 38 and 44 mol%) and poly(methyl methacrylate) (PMMA) were prepared by mechanical mixing in the melted state. The miscibility and melting behavior as a function of blend composition and the ethylene content in EVOH copolymers were investigated by means of differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The morphology of the cryofractured surfaces was examined by scanning electron microscopy (SEM). DSC and DMTA data show that EVOH/PMMA blends are immiscible, independent of EVOH and blend composition. The SEM analysis in agreement with DMTA analysis indicates that the morphology of phases depends on the blend composition, with phase inversion occurring as the concentration of one or other polymer component increases. However, the copolymer composition apparently does not affect the domain size distribution for blends containing 20 wt% of EVOH or 20 wt% of PMMA. A better phase adhesion is observed mainly for blends with 50 wt% of each polymer component.     

Propagation of Scalar Fields in a Plane Symmetric Spacetime

The present article deals with solutions for a minimally coupled scalar field propagating in a static plane symmetric spacetime. The considered metric describes the curvature outside a massive infinity plate and exhibits an intrinsic naked singularity (a singular plane) that makes the accessible universe finite in extension. This solution can be interpreted as describing the spacetime of static domain walls. In this context, a first solution is given in terms of zero order Bessel functions of the first and second kind and presents a stationary pattern which is interpreted as a result of the reflection of the scalar waves at the singular plane. This is an evidence, at least for the massless scalar field, of an old interpretation given by Amundsen and Grøn regarding the behaviour of test particles near the singularity. A second solution is obtained in the limit of a weak gravitational field which is valid only far from the singularity. In this limit, it was possible to find out an analytic solution for the scalar field in terms of the Kummer and Tricomi confluent hypergeometric functions.     

Controls over spatial and seasonal variations on isotopic composition of the precipitation along the central and eastern portion of Brazil

Based on Global Network Isotopes in Precipitation (GNIP) isotopic data set, a review of the spatial and temporal variability of δ¹⁸O and δ²H in precipitation was conducted throughout central and eastern Brazil, indicating that dynamic interactions between Intertropical and South Atlantic Convergence Zones, Amazon rainforest, and Atlantic Ocean determine the variations on the isotopic composition of precipitation over this area. Despite the seasonality and latitude effects observed, a fair correlation with precipitation amount was found. In addition, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) air mass back trajectories were used to quantify the factors controlling daily variability in stable isotopes in precipitation. Through a linear multiple regression analysis, it was observed that temporal variations were consistent with the meteorological parameters derived from HYSPLIT, particularly precipitation amount along the trajectory and mix depth, but are not dependent on vapour residence time in the atmosphere. These findings also indicate the importance of convective systems to control the isotopic composition of precipitation in tropical and subtropical regions.     

Separation and Immobilization of Lipase from Penicillium simplicissimum by Selective Adsorption on Hydrophobic Supports

Lipases are an enzyme class of a great importance as biocatalysts applied to organic chemistry. However, it is still necessary to search for new enzymes with special characteristics such as good stability towards high temperatures, organic solvents, and high stereoselectivity presence. The present work’s aim was to immobilize the lipases pool produced by Penicillium simplissicimum, a filamentous fungi strain isolated from Brazilian babassu cake residue. P. simplissicimum lipases were separated into three different fractions using selective adsorption method on different hydrophobic supports (butyl-, phenyl-, and octyl-agarose) at low ionic strength. After immobilization, it was observed that these fractions’ hyperactivation is in the range of 131% to 1133%. This phenomenon probably occurs due to enzyme open form stabilization when immobilized onto hydrophobic supports. Those fractions showed different thermal stability, specificity, and enantioselectivity towards some substrates. Enantiomeric ratio for the hydrolysis of (R,S) 2-O-butyryl-2-phenylacetic acid ranged from 1 to 7.9 for different immobilized P. simplissicimum lipase fractions. Asymmetry factor for diethyl 2-phenylmalonate hydrolysis ranged from 11.8 to 16.4 according to the immobilized P. simplissicimum lipase fractions. Those results showed that sequential adsorption methodology was an efficient strategy to obtain new biocatalysts with different enantioselectivity degrees, thermostability, and specificity prepared with a crude extract produced by a simple and low-cost technology.     

Time-course expression of DNA repair-related genes in hepatocytes of zebrafish (Danio rerio) after UV-B exposure

The objective of this study was to evaluate the time-course effects of UV-B exposure on expression of genes involved in the DNA repair system of zebrafish ( Danio rerio ) hepatocytes, a highly competent species in terms of damage repair induced by UV radiation. For gene expression analysis (RT-PCR), cells were exposed to 23.3 mJ cm⁻² UV-B, which was the dose that affected viable cell number (reduction of 30% when compared with the control group) and produced no visual alteration on cell morphology. The early response observed (6 h) showed induction in the expression of the CDKI gene (cyclin-dependent kinase inhibitor) and genes related to DNA damage repair (mainly XPC and DDB2 ), while the late response observed (24 h) was more related to up-regulation of p53 and genes involved in cell cycle arrest ( gadd45a , cyclinG1 ). In all times analyzed, the anti-apoptotic gene Bcl-2 was down-regulated. Another interesting result observed was the up-regulation of the Apex- 1 gene after UV-B exposure, which could indicate the induction of oxidative lesions in the DNA molecule. In conclusion, these results demonstrate an activation of the DNA repair system in hepatocytes of zebrafish exposed to UV-B radiation, mainly involving the participation of p53.     

Regiospecific synthesis of 4-alkoxy and 4-amino substituted 2-trifluoromethyl pyrroles

A simple and regiospecific synthesis of 4-alkoxy(amino)-2-trifluoromethyl pyrroles from 5-azido-4-alkoxy(amino)-1,1,1-trifluoro-pent-3-en-2-ones by an aza-Wittig cyclization of aminophosphoranes is described. The structures of the pyrroles and their synthetic intermediates were supported by NMR and HRMS analysis.     

Analytic Model for DBF Under Multiple Particle Retention Mechanisms

Discrepancies between classical model (CM) predictions and experimental data for deep bed filtration (DBF) have been reported by various authors. In order to understand these discrepancies, an analytic continuum model for DBF is proposed. In this model, a filter coefficient is attributed to each distinct retention mechanism (straining, diffusion, gravity interception, etc.). It was shown that these coefficients generally cannot be merged into an effective filter coefficient, as considered in the CM. Furthermore, the derived analytic solutions for the proposed model (PM) were applied for fitting experimental data, and a very good agreement between experimental data and PM predictions were obtained. Comparison of the obtained results with empirical correlations allowed identifying the dominant retention mechanisms. In addition, it was shown that the larger the ratio of particle to pore sizes, the more intensive the straining mechanism and the larger the discrepancies between experimental data and CM predictions. Finally, the CM and PM were compared via statistical analysis. The obtained $p$ values allow concluding that the PM should be preferred especially when straining plays an important role.