Hetarylpyrazoles. II. Reactions of pyrazol-l'-ylpyridines

Pyrazol-l'-ylpyridines undergo electrophilic substitution reactions (bromination, chlorination, and nitration) preferentially in the pyrazole ring. There is some evidence of the mutual influence of the pyrazole and the pyridine ring on the reactivity of the system. Some modifications of the substituents were also carried out. A dihydro derivative of a new ring system, pyrazolo[1′,2′-a]pyrido[2,1-c][l,2,4]triazine was also obtained.     

Automatic sequential determination of the hydrogen peroxide scavenging activity and evaluation of the antioxidant potential by the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation assay in wines by sequential injection analysis

An automatic system that performs two analytical procedures, allowing the evaluation of the relative antioxidant capacity of wine samples, was developed. Automation was carried out using a sequential injection analysis (SIA) system that allowed, thanks to its versatility, the development of two methodologies. One is based on the decolorization assay of the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical, using a spectrophotometric detector. A second methodology allowed the evaluation of the hydrogen peroxide scavenging activity by measuring the oxidation of homovanylic acid (HVA) to its fluorescent dimer, using a fluorescent detector.The developed automatic methodologies were evaluated using trolox as standard and subsequently using other antioxidant substances as gallic acid, caffeic acid, ascorbic acid, catechin and taxifolin which are abundant in wine and whose antioxidant activities were compared to that shown by trolox. The spectrophotometric and fluorimetric assays showed linearity intervals between 0.001 and 0.01 mM, and 0.001 and 0.008 mM of trolox, respectively.The evaluation of the antioxidant power of 20 white and red wine samples, from different Portuguese wine producing regions, was carried out sequentially, in the automatic system. The results were expressed in trolox equivalent antioxidant capacity (TEAC) and presented, for the ABTS and hydrogen peroxide scavenging activity methodologies, detection limits of 8.4 × 10⁻⁷ and 1.4 × 10⁻⁴ mM and relative standard deviation (R.S.D. (%)) in the range 0.6-2.4 and 1-1.8, respectively.     

Immobilization of Distinctly Capped CdTe Quantum Dots onto Porous Aminated Solid Supports

Immobilization of quantum dots (QDs) onto solid supports could improve their applicability in the development of sensing platforms and solid‐phase reactors by allowing the implementation of reusable surfaces and the execution of repetitive procedures. As the reactivity of QDs relies mostly on their surface chemistry, immobilization could also limit the disruption of solution stability that could prevent stable measurements. Herein, distinct strategies to immobilize QDs onto porous aminated supports, such as physical adsorption and the establishment of chemical linking, were evaluated. This work explores the influence of QD capping and size, concentration, pH, and contact time between the support and the QDs. Maximum QD retention was obtained for physical adsorption assays. Freundlich and Langmuir isotherms were used to analyze the equilibrium data. Gibbs free energy, enthalpy, and entropy were calculated and the stability of immobilized QDs was confirmed.     

Electrical and Thermoelectrical Behavior of Binary Composites of Phosphate Glass Loaded with Zinc Fillers: Promising Materials for Photovoltaic’s

Homogeneous xPbO?(1?x) P₂O₅ glasses where 0 % :σ x<100 % have been successfully synthesized using a melt‐quenching method. The short range structures of the prepared samples were examined by Fourier transform infrared spectroscopy, x‐powder diffraction and scanning electron microscopy. The most stable vitreous phase is of composition 45 mol%PbO‐55 mol%P₂O₅; it was loaded with zinc volume fraction. We carried out experimental and simulative investigations of the electrical characteristics of p? n junction; the obtained results indicated that conductivity of the composites increases by increasing dopent concentration. It was also observed that the current voltage characteristics of the composite were found to be ohmic in nature, wherein drastic drop of the electrical conduction was observed at an accurate temperature of 405 K. Electrical behavior of the composites as function of filler concentration and versus temperature were explained respectively by percolation theory and positive temperature coefficient effect.     

Natural abundance 13C - 13C coupling constants observed via double quantum coherence. Structural elucidation by the one- and the two-dimensional NMR experiements of velloziolone,a new seco-diterpene.

With the help of Natural Abundance ¹³C - ¹³C Coupling Constants, observed via double quantum coherence, the structural determination of VELLOZIOLONE (1), a new diterpene, has been carried out.     

Investigation of the mechanism of protein adsorption on ordered mesoporous silica using flow microcalorimetry

The adsorption of bovine serum albumin (BSA) and lysozyme (LYS) on siliceous SBA-15 with 24 nm pores was studied using flow microcalorimetry; this is the first attempt to understand the thermodynamics of protein adsorption on SBA-15 using flow microcalorimetry. The adsorption mechanism is a strong function of protein structure. Exothermic events were observed when protein–surface interactions were attractive. Entropy-driven endothermic events were also observed in some cases, resulting from lateral protein–protein interactions and conformational changes in the adsorbed protein. The magnitudes of the enthalpies of adsorption for primary protein–surface interactions decrease with increased surface coverage, indicating the possibility of increased repulsion between adsorbed protein molecules. Secondary exothermic events were observed for BSA adsorption, presumably due to secondary adsorption made possible by conformational changes in the soft BSA protein. These secondary adsorption events were not observed for lysozyme, which is structurally robust. The results of this study emphasize the influence of solution conditions and protein structure on conformational changes of the adsorbed protein and the value of calorimetry in understanding protein–surface interactions.     

6-Deoxyerythronolide B synthase thioesterase-catalyzed macrocyclization is highly stereoselective

Macrocyclic polyketide natural products are an indispensable source of therapeutic agents. The final stage of their biosynthesis, macrocyclization, is catalyzed regio- and stereoselectively by a thioesterase. A panel of substrates were synthesized to test their specificity for macrocyclization by the erythromycin polyketide synthase TE (DEBS TE) in vitro. It was shown that DEBS TE is highly stereospecific, successfully macrocyclizing a 14-member ring substrate with an R configured O-nucleophile, and highly regioselective, generating exclusively the 14-member lactone over the 12-member lactone.     

New chain-extended analogues of salacinol and blintol and their glycosidase inhibitory activities. Mapping the active-site requirements of human maltase glucoamylase

The synthesis of new chain-extended sulfonium and selenonium salts of 1,4-anhydro-4-thio-(or 4-seleno)-d-arabinitol, analogues of the naturally occurring glycosidase inhibitor salacinol, is described. Nucleophilic attack at the least hindered carbon atom of 4,6-O-benzylidene-2,5-di-O-p-methoxybenzyl-d-mannitol-1,3-cyclic sulfate by 2,3,5-tri-O-p-methoxybenzyl-1,4-anhydro-4-thio-(or 4-seleno)-d-arabinitol gave the sulfonium and selenonium sulfates, respectively. Subsequent deprotection with trifluoroacetic acid yielded the target compounds. In these analogues, an extended polyhydroxylated aliphatic side chain has been incorporated while maintaining the stereochemistry of C-2' and C-3' of salacinol or blintol. These compounds were designed to probe the premise that they would bind with higher affinity to glucosidases than salacinol because the extra hydroxyl groups in the acyclic chain would make favorable polar contacts within the active site. Both target compounds inhibited recombinant human maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine, with Ki values in the low micromolar range. Comparison of these values to those of related compounds synthesized in previous studies has provided a better understanding of structure-activity relationships and the optimal stereochemistry at the different stereogenic centers required of an inhibitor of this enzyme. With respect to chain extension, the configurations at C-2' and C-4' are critical for activity, the configuration at C-3', bearing the sulfate moiety, being unimportant. The desired configuration at C-5' is also specified. However, comparison of the activities of the chain-extended analogues with those of salacinol and blintol indicates that there is no particular advantage of the chain-extension relative to salacinol or blintol. These results are similar to those reported earlier for kotalanol, a 7-carbon-extended derivative, versus salacinol against rat intestinal maltase, sucrase, and isomaltase.     

Thermal characterization of the solid state and raw material fluconazole by thermal analysis and pyrolysis coupled to GC/MS

This article had studied the thermal characterization of the raw material and different fluconazole crystals, obtained through recrystallization with different solvents using thermoanalytical techniques (TG, DTA, DSC-50, DSC Photovisual, DSC-60) and Pyr-GC/MS. The results confirmed that the fluconazole volatilizes without decomposition until 250 °C. Pyr-GC/MS showed hexachlorobenzene like impurities in fluconazole raw material.     

Adsorption rate of Reactive Black 5 on chitosan based materials: geometry and swelling effects

The overall adsorption rate of Reactive Black 5 dye (RB5) on chitosan based materials was elucidated using diffusional models. Fundamental aspects, such as, geometry of the adsorbents and swelling effects were considered. Chitosan based materials (powder and film) were prepared from shrimp wastes and characterized regarding to the fundamental features for adsorption. Experimental decay curves were obtained under different conditions of stirring rate and initial dye concentration. The data were modeled according to the external mass transfer and diffusional models. The k_L (external mass transfer coefficient), D_ep (effective pore diffusion coefficient) and D_s (surface diffusion coefficient) values were estimated. For both adsorbents, it was found that the surface diffusion was the intraparticle diffusion mechanism governing the adsorption rate of RB5, since its contribution was higher than 92 % regardless the position and time. The D_s values ranged from 2.85 × 10^?11 to 5.78 × 10^?11 for chitosan powder and from 4.15 × 10^?11 to 12.12 × 10^?11 cm² s^?1 for chitosan films. The RB5 adsorption was faster when chitosan powder was used, mainly at higher stirring rates and initial dye concentrations. The swelling effect was most pronounced for the chitosan films, where, provided an increase of about 65 times in the D_s value.