The Isoperimetric Problem in Spherical Cylinders

The classical isoperimetric problem for volumes is solved in × ⁿ (1). Minimizers are shown to be invariant under the group O(n) acting standardly on ⁿ , via a symmetrization argument, and are then classified. Solutions are found among two (one-parameter) families: balls and sections of the form [a, b] × ⁿ . It is shown that the minimizers may be of both types. For n= 2, it is shown that the transition between the two families occurs exactly once. Some results for general n are also presented.     

Antitrypanosomal activity of Brazilian propolis from Apis mellifera

Extracts from different samples of Brazilian propolis were obtained by Soxhlet extraction or maceration at room temperature using ethanol, water, and accombination of both solvents. Analysis of their composition using HPLC revealed that no major differences were seen when a propolis sample was subject to different extraction methods. The activity of the 15 extracts was assayed against bloodstream trypomastigotes of Trypanosoma cruzi, the etiologic agent of Chagas' disease. Multivariate analysis was applied to evaluate the efficiency of the different extracts and the trypanocidal activity. The extracts could be divided into two groups. In the first, in which, extracts were obtained by reflux in Soxhlet using 100% ethanol, there was a lower content of bioactive compounds and consequently lower trypanocidal activity. Extract 136-Et100 stands out in this group, since it had the highest levels of bioactive compounds together with highest activity against the parasite when compared with all other extracts. The second group comprises extracts with intermediate levels of bioactive compounds and higher activity against T. cruzi.     

Temperature- and time-dependent stereochemical control in thermally induced keto-ene cyclizations

Reaction conditions determine the stereoselection in the intramolecular keto-ene reaction. The thermolysis of chiral 2-acyl-3-allyl-substituted 1,3-perhydrobenzoxazines derived from (-)-8-aminomenthol gives a mixture of only two cis-3-hydroxy-3,4-disubstituted pyrrolidine nuclei. The stereochemistry of the major diastereoisomer depends on both the temperature and the reaction time.     

Thermogravimetry applied to characterization of SBA-15 nanostructured material

Nanoporous silica with narrow pore size distribution has attracted increasing attention as a novel material for separations and reactions involving large molecules. SBA-15 has been synthesized in an acidic medium using a triblock copolymer as template. In this work, the SBA-15 was synthesized by the hydrothermal treatment at 373 K for 48 h, of a gel with the following overall molar composition: 1.0TEOS:0.017P123:5.7HCl:193H₂O, where TEOS is tetraethyl orthosilicate and P123 is poly(ethylene oxide, propylene oxide and 1,4-dioxane). The obtained material was characterized by thermogravimetry, X-ray diffraction, infrared spectroscopy and BET surface area. A kinetic study using the model free model was accomplished in the stage of decomposition of the template (P123). The obtained value of the apparent activation energy was ca. 131 kJ mol^–1.     

Chiral template mediated diastereoselective intramolecular Diels-Alder reaction using furan as a diene. Toward the synthesis of enantiopure trisubstituted tetrahydroepoxyisoindolones

[reaction: see text] Chiral precursors to the intramolecular Diels-Alder reaction using furan as a diene (IMDAF) have been prepared by diastereoselective addition of furyllithium to imines attached to perhydro-1,3-benzoxazines derived from (-)-8-aminomenthol. The acylation of the furylamines with alpha,beta-unsaturated acyl chlorides and subsequent IMDAF reaction under thermal conditions provided the corresponding cycloadducts as single diastereoisomers. The hydrolytic elimination of the chiral template yielded enantiopure perhydroepoxyisoindolones with up to five stereocenters.     

Tungsten(VI) and mixed tungsten,molybdenum(VI) complexes of tartaric acid

A number of studies of species formed in the tungsten(VI) oxide-R,R-(+)-tartaric acid-water system have been carried out(^1–3). While various species have been proposed, it is generally accepted that three main ones predominate. Two have tungsten: (+)-tartaric acid [(+)-tartH₄] ratios of 11 and the third has the same ratio of 12. This latter species cannot be that proposed by Avaloset al. ⁽³⁾ since both ligands in their structure would have to be present as unidentates.Recently we have shown⁽⁴⁾ that high resolution¹H and¹³C n.m.r. studies were particularly useful in delineating the complexes formed in aqueous solution in the analogous molybdenum(VI) system. Thus, we turned our attention to the corresponding tungsten(VI) complexes, especially in view of the controversy surrounding the nature of the species formed in aqueous solution with (+)-tartH₄. The results of our studies, presented below, indicate that only a few species are formed, and that these are quite analogous, as might be expected, to the previously described molybdenum(VI) species⁽⁴⁾. In addition we have observed the formation of a mixed dimeric species [MoWO⁴{(+)-tart}₂]^4–, whose structure is akin to the mono-metallic complexes, as well as the well-characterized antimony(III) and arsenic(III) dimers of (+)-tartH₄ ⁽⁵⁾.     

Application of over-run thin-layer and gas-liquid chromatography in the separation of closely related C19O2 steroids.

An improved method for the separation of epimeric C19O2 steroids and their related allylic alcohols is described. In this method, the steroids are first separated by over-run thin-layer chromatography, and the unresolved groups are further analysed as free or as trimethylsilyl ether derivatives by gas-liquid chromatography. The behaviour of twenty-one C19O2 steroids was investigated by thin-layer chromatography in four systems and by gas-liquid chromatography in four liquid phases. All steroid pairs of similar polarity were resolved by the combination of these two fractionation procedures.     

Biocompatibility of a Self‐Assembled Crosslinkable Hyaluronic Acid Nanogel

Hyaluronic acid nanogel (HyA‐AT) is a redox sensitive crosslinkable nanogel, obtained through the conjugation of a thiolated hydrophobic molecule to the hyaluronic acid chain. Engineered nanogel was studied for its biocompatibility, including immunocompatibility and hemocompatability. The nanogel did not compromise the metabolic activity or cellular membrane integrity of 3T3, microvascular endothelial cells, and RAW 264.7 cell lines, as determined by the 3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyl tetrazolium bromide and lactate dehydrogenase release assays. Also, we didn't observe any apoptotic effect on these cell lines through the Annexin V‐FITC test. Furthermore, the nanogel cell internalization was analyzed using murine bone marrow derived macrophages, and the in vivo and ex vivo biodistribution of the Cy5.5 labeled nanogel was monitored using a non‐invasive near‐infrared fluorescence imaging system. The HyA‐AT nanogel exhibits fairly a long half‐live in the blood stream, thus showing potential for drug delivery applications.