Properties of a triazolopyridine system as a molecular chemosensor for metal ions, anions, and amino acids

The characteristics as a chemosensor of the compound 3-methyl-6,8-di(2-pyridyl)-[1,2,3]triazolo[5',1':6,1]pyrido[2,3-]pyrimidine (1) have been analyzed. Interaction with Cu(2+) produces a quenching of the fluorescence, while interaction with Zn(2+) leads to a quenching of the fluorescence followed by a bathochromic shift. The crystal structure of the Zn(1)(H(2)O)(3)(ClO(4))(2) x H(2)O complex shows the coordination of Zn(2+) through the terpyridine moiety. The octahedral site is completed by three water molecules. Interactions of the Zn(2+) complex with the anions sulfate, nitrate, nitrite, and dihydrogenphosphate in ethanol produce hypsochromic shifts and restoration of the fluorescence whose magnitude depends on the anion involved. The maximum interaction is observed for H(2)PO(4)(-). Interactions of the Zn(2+) complex with the amino acids l-aspartate and l-glutamate have also been explored showing a higher interaction with l-aspartate.     

<Emphasis Type=Italic>Euphorbia antisyphilitica</Emphasis> residues as a new source of ellagic acid

In this study, a new source of ellagic acid (EA) is reported. Euphorbia antisyphilitica or “candelilla” was used to extract phenolic dilactone. Cereous layers and fibrous tissue were analyzed. A completely randomized experimental design with a treatment factorial arrangement was employed. The factors considered were: plant/extracting agent ratio, extraction temperature and time. Candelilla wax does not contain EA. Temperature and the ratio plant/extracting agent were determinant during the EA extraction process. Around 20 mg of free EA per gram of fibrous tissue were found. Residues of candelilla are a good source of EA.     

1,5-Asymmetric induction in boron-mediated aldol reactions of beta-oxygenated methyl ketones

This tutorial review describes that high levels of substrate-controlled, 1,5-stereoinduction are obtained in the boron-mediated aldol reactions of beta-oxygenated methyl ketones with achiral and chiral aldehydes. Remote induction from the boron enolates gives the 1,5-anti adducts, with the enolate pi-facial selectivity critically dependent upon the nature of the beta-alkoxy protecting group. This 1,5-anti aldol methodology has been strategically employed in the total synthesis of several natural products with remarkable pharmacological activities. At present, the origin of the high level of 1,5-anti induction obtained with the boron enolates is unclear, although a model based on hydrogen bonding between the beta-alkoxy oxygen and the formyl aldehyde hydrogen has recently been proposed.     

Use of large-volume sample stacking in on-line solid-phase extraction-capillary electrophoresis for improved sensitivity

We present a new system for the sensitive analysis of cephalosporins by CE using both on-line SPE and large-volume sample stacking (LVSS). Sample volumes of 250 muL were loaded onto the SPE microcolumn which was then desorbed with 426 nL of ACN. The SPE elution plug was injected into the CE system via an in-line valve interface filling approximately 60% of the volume of the separation capillary. Subsequently, LVSS was performed by applying a voltage of -5 kV, which resulted in the simultaneous removal of the elution solvent and the preconcentration of the analytes in a narrow zone. This way the amount of analyte loaded into the capillary could be considerably increased without serious loss of CE separation efficiency. LODs for cefoperazone and ceftiofur were in the ng/L range which represents an improvement of a factor of 8450 and 11 450 when compared with direct CE injection. The cephalosporin test compounds presented a good linear response (corrected peak area) between 0.5 and 10 mug/L with correlation coefficients higher than 0.995. The final method is compared with previously reported LVSS-CE and SPE-CE systems for the analysis of cephalosporins.     

Differential properties of Aspergillus niger tannase produced under solid-state and submerged fermentations

Significant differences on structure, stability, and catalytic properties of tannase were found when this enzyme was produced under solid-state and submerged fermentations (SSF and SmF) by Aspergillus niger. The specific activity was 5.5 times higher on SSF than in SmF. Significant differences in isoelectric points of tannases were found. The pH optima for both types of enzyme was found at 6 and the pH stability of SSF and SmF tannase were at 6 and 5–8, respectively. The optimal temperature range was from 50 to 60 °C for SmF tannase and 60 °C for SSF tannase, and both enzyme types showed tolerance to high temperatures (60–70 °C). The SSF tannase showed a major specificity for methyl gallate substrate while SmF tannase for tannic acid. All metal ions tested, had an activity inhibition from 30–46% on SSF tannase. SDS-PAGE analysis as well as gel localization studies of both SSF and SmF purified tannases showed a single band with a molecular weight of 102 and 105 kDa, respectively. Different levels of glycosylation were found among SSF and SmF purified tannases. This is the first report about structural differences among tannase produced under SSF and SmF and this study provides basis for explanation of the stability and catalytic differences observed previously for this two tannase types.     

Selective linkage detection of O‐sialoglycan isomers by negative electrospray ionization ion trap tandem mass spectrometry

Sialylated O‐linked oligosaccharides are involved in many biological processes, such as cell‐cell interactions, cell‐substance adhesion, and virus‐host interactions. These activities depend on their structure, which is frequently determined by tandem mass spectrometry. However, these spectra are frequently analyzer‐dependent, which makes it difficult to develop widely applicable analytical methods. In order to deepen the origin of this behavior, two couples of isomers of sialylated O‐linked oligosaccharides, NeuAcα2‐3Galβ1‐3GalNAc‐ol/Galβ1‐3(NeuAcα2‐6)GalNAc‐ol and NeuGcα2‐3Galβ1‐3GalNAc‐ol/Galβ1‐3(NeuGcα2‐6)GalNAc‐ol, were analyzed by liquid chromatography/negative electrospray ionization ion trap tandem mass spectrometry (LC/ESI(?)‐MSⁿ) using both an ion trap and a triple quadrupole mass spectrometer. Results clearly showed that while ions obtained in the triple quadrupole instrument fitted very well with the standard fragmentation routes, in the ion trap several intense ions could not be explained by these rules, specially a fragment at m/z 597. Furthermore, this ion was observed in the mass spectrum of those isomers that sialic acid binds to GalNAc by an α2‐6 linkage. From the MS³ spectrum of this ion an unexpected structure was deduced, and it led to propose alternative fragmentation pathways. Molecular mechanics calculations suggested that the found atypical route could be promoted by a hydrogen bond located only in α2‐6‐linked oligosaccharides. It has also been demonstrated that this process follows a slow kinetic, explaining why it cannot be observed using an ion beam‐type mass analyzer. In conclusion, ion traps seem to be more appropriate than triple quadrupoles to develop a reliable analytical method to distinguish between isomeric O‐linked glycans. Copyright © 2010 John Wiley & Sons, Ltd.     

Reactivity and Selectivity of Captodative Olefins as Dienes in Hetero‐Diels–Alder Reactions

The reactivity and selectivity of the the captodative olefins 1‐acylvinyl benzoates 1a – 1f and 3a as heterodienes in hetero‐Diels–Alder reactions in the presence of electron‐rich dienophiles is described. Heterodienes 1 undergo regioselective cycloaddition with the alkyl vinyl etherdienophiles 6a , b and 9 to give the corresponding dihydro‐2H‐pyrans 7, 8 , and 10 under thermal conditions. The reactivity of these cycloadditions depends, to a large extent, on the electronic demand of the substituent in the aroyloxy group of the heterodiene. Frontier‐molecular‐orbital (FMO; ab initio) and density‐functional‐theory (DFT) calculations of the ground and transition states account for the reactivity and regioselectivity observed in these processes.     

Gas permeability and selectivity of benzophenone aromatic isophthalic copolyamides

The synthesis, thermal, and gas transport properties of poly(benzophenone isophthalamide), DBF/ISO, poly(benzophenone‐5‐tert‐butylisophthalamide), DBF/TERT, homopolymers, and their copolyamides with different DBF/TERT ratios are reported. The results indicate that the glass transition temperatures of the copolyamides increase as the concentration of DBF/TERT in the polyamide increases. The gas permeability coefficients for DBF/ISO are around 10^?2 Barrers for O₂ which situates this polymer as a barrier polymer. It was also found that permeability coefficients in all polyamides and copolyamides are independent of pressure for He or decrease slightly particularly with O₂, CO₂, and N₂. It was seen that DBF/TERT is up to 15 times more permeable than DBF/ISO, depending on the gas being considered. This behavior was assigned to the presence of the bulky lateral substituent, the tert‐butyl group, in DBF/TERT and DBF/TERT‐co‐DBF/ISO copolyamides. This bulky substituent increases fractional free volume and interchain spacing; as a consequence, the gas permeability and diffusion coefficients generally increase. The experimental results for the gas permeability coefficients and permselectivity for the copolyamides was well represented by a semilogarithmic mixing rule of the homopolyamides permeability coefficients as a function of their volume fraction. The selectivity of gas pairs, such as He/O₂ and He/CO₂, decreased slightly with the addition of DBF/TERT. The temperature dependence of permeability for homopolyamides and copolyamides can be described by an Arrhenius type equation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2083–2096, 2007     

Acid Hydrolysis of Pectin and Mucilage from Cactus (Opuntia ficus) for Identification and Quantification of Monosaccharides

Pectin and mucilage are polysaccharides from the cactus Opuntia ficus-indica, which are also known as hydrocolloids, with useful properties in industries such as food, pharmaceuticals, and construction, among others. In the present work, cactus hydrocolloids were hydrolyzed characterized using two techniques: first, thin-layer chromatography, to identify the monosaccharides present in the sample, followed by the phenol–sulfuric acid method to determine the monosaccharide content. The hydrolyzing method allowed us to reduce the processing time to 180 min and, considering the identification and quantification procedures, the proposed methodology is much simpler and more cost-effective compared to other methods, such as high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR), and mass spectrometry. The analysis of the results revealed that the maximum concentration of monosaccharides was obtained after hydrolyzing for 90 min. Under such conditions, with pectin being the main component contained in the cactus hydrocolloids analyzed here, galacturonic acid was found in the largest quantities.     

Structured ternary fluids as nanocrystal incubators for enhanced crystallization control

In crystallization from solution, a ubiquitous process in both industry and the natural world, nucleation is usually the rate-determining step, followed by faster crystal growth. Consequently, crystals typically exist in the nm-size range for such limited times that their investigation and manipulation is hindered. Here, we show that, owing to a degree of restricted diffusion, crystallization in structured ternary fluids (STFs) can proceed via higher nucleation rate and slower crystal growth pathways. This enables STFs to act as nanocrystal incubators, with the nanocrystals existing for extended times. We demonstrate that this generates enhanced crystallization control, with the three ambient pressure polymorphs of glycine, the α-, γ- and β-forms, all crystallizing from the octanol/ethanol/water STF, despite the well-known difficulty in crystallizing the slow growing γ-form and the instability of the β-form. The ability of STFs to produce notoriously hard to crystallize polymorphs should make them a versatile tool, ideal for polymorph discovery. This may enable a step change in the current, scatter-gun approach to polymorph screening. Furthermore, we show that aliquots of the nanocrystal-containing fluids can successfully seed metastable solutions. Hence, STFs may ultimately help provide a generic methodology for producing crystals and seed suspensions of any desired polymorph to supersede current targeted crystallization and seeding strategies.

Crystallization in structured ternary fluids can proceed via higher nucleation rate and slower crystal growth pathways that are impossible to access in normal unstructured solutions. Hence, structured ternary fluids can act as nanocrystal incubators.