Stereoselective Synthesis of β-Hydroxy- and β-Ethoxy-δ-lactones: Model Structures for Compounds Isolated from Otoba parvifolia

Abstract: In this paper we describe a very short stereoselective synthesis of the β-ethoxylactone 13, a model structure for compounds isolated from Otoba parvifolia. The method, which also produces β-hydroxy-esters and β-hydroxy-lactones, is based on a chemo- and stereoselective Reformatsky reaction.     

Significance of data treatment and experimental setup on the determination of copper complexing parameters by anodic stripping voltammetry

Different procedures of voltammetric peak intensities determination, as well as various experimental setups were systematically tested on simulated and real experimental data in order to identify critical points in the determination of copper complexation parameters (ligand concentration and conditional stability constant) by anodic stripping voltammetry (ASV). Varieties of titration data sets (Cu_measuredvs. Cu_total) were fitted by models encompassing discrete sites distribution of one-class and two-class of binding ligands (by PROSECE software). Examination of different procedures for peak intensities determination applied on voltammograms with known preset values revealed that tangent fit (TF) routine should be avoided, as for both simulated and experimental titration data it produced an additional class of strong ligand (actually not present). Peak intensities determination by fitting of the whole voltammogram was found to be the most appropriate, as it provided most reliable complexation parameters.Tests performed on real seawater samples under different experimental conditions revealed that in addition to importance of proper peak intensities determination, an accumulation time (control of the sensitivity) and an equilibration time needed for complete complexation of added copper during titration (control of complexation kinetics) are the keypoints to obtain reliable results free of artefacts.The consequence of overestimation and underestimation of complexing parameters is supported and illustrated by the example of free copper concentrations (the most bioavailable/toxic specie) calculated for all studied cases. Errors up to 80% of underestimation of free copper concentration and almost two orders of magnitude overestimation of conditional stability constant were registered for the simulated case with two ligands.     

Translational and rotational pupil tracking by use of wavefront aberration data and image registration techniques

We present a methodology with which to evaluate translations and rotations of wavefront aberration measurements of systems in which the exit pupil suffers displacements and rotations with respect to the reference frame of the measuring device. We propose to use image registration techniques to account for rotations, translations, and scale changes of the pupil. We present a proof of principle, using an artificial eye in addition to computer simulations. The method is software based and requires no additional hardware.     

The production and properties of polylactide composites filled with expanded graphite

Composites have been produced by melt-blending biodegradable polylactide (PLA) with commercially available expanded graphite (EG). Using different techniques of addition, the manifold effects of EG on PLA molecular, thermo-mechanical and fire-retardant properties were evaluated. The EG nanofiller provides PLA composites with competitive functional properties. They have a high rigidity, with Young's modulus and storage modulus increasing with EG content. They also have excellent thermal stability while preserving the glass transition and melting temperature of the original PLA matrix. Purification and pre-dispersion of EG nanofiller proved beneficial for preserving PLA molecular weights and led to improved mechanical performance. The presence of dispersed graphene nanolayers in PLA significantly accelerated the polyester crystallization process. The flame retardant properties also displayed improvements with a large decrease in the maximum rate of heat release as recorded by cone calorimetry, whereas the horizontal burning test (UL94 HB) was successfully passed revealing non-dripping and char formation.     

Structural analysis of an unusual bioactive N-acylated lipo-oligosaccharide LOS-IV in Mycobacterium marinum

Although lipo-oligosaccharides (LOSs) are recognized as major parietal components in many mycobacterial species, their involvement in the host-pathogen interactions have been scarcely documented. In particular, the biological implications arising from the high degree of structural species-specificity of these glycolipids remain largely unknown. Growing recognition of the Mycobacterium marinum-Danio rerio as a specific host-pathogen model devoted to the study of the physiopathology of mycobacterial infections prompted us to elucidate the structure-to-function relationships of the elusive end-product, LOS-IV, of the LOS biosynthetic pathway in M. marinum. Combination of physicochemical and molecular modeling methods established that LOS-IV resulted from the differential transfer on the caryophyllose-containing LOS-III of a family of very unusual N-acylated monosaccharides, naturally present as different diastereoisomers. In agreement with the partial loss of pathogenecity previously reported in a LOS-IV-deficient M. marinum mutant, we demonstrated that this terminal monosaccharide conferred to LOS-IV important biological functions, including macrophage activating properties.     

Conformal measures and Hausdorff dimension for infinitely renormalizable quadratic polynomials

We show in this paper that iff is a quadratic infinitely many times renormalizable polynomial of sufficient high combinatorial type, then: HD (J(f))= inf{: -conformal measure for f} We use Lyubich's construction of the principal nest ([Lyu97]) in order to prove this result.Partially supported by CNP q-Brazil grant # 300534/96-5     

Magnetic Resonance Imaging of Gases: A Single-Point Ramped Imaging with T1 Enhancement (SPRITE) Study

A pure phase-encoding MRI technique, single-point ramped imaging withT₁enhancement, SPRITE, is introduced for the purpose of gas phase imaging. The technique utilizes broadband RF pulses and stepped phase encode gradients to produce images, substantially free of artifacts, which are sensitive to the gasT₁andT^*:₂relaxation times. Images may be acquired from gas phase species with transverse relaxation times substantially less than 1 ms. Methane gas images,¹H, were acquired in a phantom study. Sulfur hexafluoride,¹⁹F, images were acquired from a gas-filled porous coral sample. High porosity regions of the coral are observed in both the MRI image and an X-ray image. Sensitivity and resolution effects due to signal modulation during the time-efficient acquisition are discussed. A method to increase the image sensitivity is discussed, and the predicted improvement is shown through 1D images of the methane gas phantom.     

Epidermal lignin deposition in quinoa cotyledons in response to UV-B radiations

UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodium quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands.