Enantioselective conjugate addition of nitro compounds to α,β-unsaturated ketones: an experimental and computational study

A series of chiral thioureas derived from easily available diamines, prepared from α-amino acids, have been tested as catalysts in the enantioselective Michael additions of nitroalkanes to α,β-unsaturated ketones. The best results are obtained with the bifunctional catalyst prepared from L-valine. This thiourea promotes the reaction with high enantioselectivities and chemical yields for aryl/vinyl ketones, but the enantiomeric ratio for alkyl/vinyl derivatives is very modest. The addition of substituted nitromethanes led to the corresponding adducts with excellent enantioselectivity but very poor diastereoselectivity. Evidence for the isomerization of the addition products has been obtained from the reaction of chalcone with [D(3)]nitromethane, which shows that the final addition products epimerize under the reaction conditions. The epimerization explains the low diastereoselectivity observed in the formation of adducts with two adjacent tertiary stereocenters. Density functional studies of the transition structures corresponding to two alternative activation modes of the nitroalkanes and α,β-unsaturated ketones by the bifunctional organocatalyst have been carried out at the B3LYP/3-21G* level. The computations are consistent with a reaction model involving the Michael addition of the thiourea-activated nitronate to the ketone activated by the protonated amine of the organocatalyst. The enantioselectivities predicted by the computations are consistent with the experimental values obtained for aryl- and alkyl-substituted α,β-unsaturated ketones.     

Study of the effects of operational parameters on multiresidue pesticide analysis by LC-MS/MS

In this paper, the influence of several operational parameters on a well established multiresidue LC-MS/MS method has been studied in relation to the analysis of 150 pesticides commonly present in vegetable samples. The operational parameters investigated are: (i) the influence of different modifiers (0.1% formic acid; 5 mM ammonium formiate; 5 mM ammonium acetate in aqueous phase) - both on the retention time and on the analytical response of the studied compounds; (ii) the effect of the analytical column's temperature on the retention time and on the analytical response of the pesticides investigated; (iii) the effects of co-elution in mixture containing 150 pesticides and, additionally, (iv) the carrying out of a study about the common transitions obtained by LC-MS/MS. Various common transitions were found among the 150 pesticides, but there were only two problematic cases, the pairs diuron-fluometuron and prometryn-terbutryn, which have common scanned transitions and have very close retention times. The use of ammonium salts as modifier instead of formic acid reports enhancement or suppression of the response depending on the pesticides. No great influence on the retention time or on the response of the pesticides and commodities studied was observed with relation to the column temperature. Two different columns: an HPLC (5 μm particle size) and an UHPLC analytical column (1.8 μm particle size) have been used. As was expected, shorter run times and lower peak width was achieved with the UHPLC column.In this paper, the effect of the compounds on each other in the MS analysis when the number of co-eluting compounds is quite high is also described. Mainly small suppression or enhancement co-elution effect was observed, but some particular pesticides presented high sensitivity (>±60% effect) when they elute together with others. This is an important factor and it has to be taken into account when performing multiresidue pesticide analysis.     

Solution SERS of an insoluble synthetic organic pigment-quinacridone quinone-employing calixarenes as dispersive cavitands

A possibility of getting SERS spectra of insoluble aromatic compounds in colloidal silver solutions is described. The method tested for the organic pigment quinacridone quinone consists of dispersing it in calix[n]arenes. The potentials of such cavitands, both as dispersing and as silver functionalization agents, is reported as a function of the substitution in their lower rim and their cavity size.     

Study of the capillary electrophoresis profile of intact α-1-acid glycoprotein isoforms as a biomarker of atherothrombosis

α-1-Acid glycoprotein (AGP) is a serum glycoprotein that presents several isoforms. Changes in the isoforms of AGP have been related to different pathological states including cardiovascular diseases (CVDs) such as acute myocardial infarction. However, to our knowledge, the role of variations of AGP isoforms as a potential biomarker of atherothrombosis has not been addressed. In this work, a preliminary study about differences in the capillary zone electrophoresis (CZE) profile of intact (non-hydrolyzed) AGP isoforms between healthy individuals and patients with atherothrombosis, specifically abdominal aortic aneurysm (AAA) and carotid atherosclerosis (CTA), has been performed. Biological samples (plasmas and sera) were analyzed by CZE after immunoaffinity chromatography purification. Up to 13 peaks corresponding to groups of isoforms of intact AGP from plasma samples were detected by CZE-UV. Electrophoretic profiles were aligned, peaks assigned, and linear discriminant analysis (LDA) of percentage of the corrected areas of AGP peaks was employed to discriminate and classify the CZE profiles of AGP samples. LDA enabled to accomplish 92.9% of correct classification of the AGP samples when the three groups of samples were considered. Besides, the LDA model showed high predictive power in the groups healthy vs. sick, healthy vs. AAA, and healthy vs. CTA. The described method was a successful approach to study the potential of AGP isoforms profile as a biomarker of atherothrombosis. To the best of our knowledge this has been the first time that a possible role of the CZE profile of intact AGP isoforms as a biomarker of vascular diseases has been demonstrated.     

Antitrypanasomal activity of novel benzaldehyde-thiosemicarbazone derivatives from kaurenoic acid

A series of new thiosemicarbazones derived from natural diterpene kaurenoic acid were synthesized and tested against the epimastigote forms of Trypanosoma cruzi to evaluate their antitrypanosomal potential. Seven of the synthesized thiosemicarbazones were more active than kaurenoic acid with IC?? values between 2-24.0 mM. The o-nitro-benzaldehyde-thiosemicarbazone derivative was the most active compound with IC?? of 2.0 mM. The results show that the structural modifications accomplished enhanced the antitrypanosomal activity of these compounds. Besides, the thiocyanate, thiosemicarbazide and the p- methyl, p-methoxy, p-dimethylamine, m-nitro and o-chlorobenzaldehyde-thiosemicarbazone derivatives displayed lower toxicity for LLMCK? cells than kaurenoic acid, exhibing an IC?? of 59.5 mM.     

Excited electron-bubble states in superfluid 4He: a time-dependent density functional approach

We present a systematic study on the excited electron-bubble states in superfluid (4)He using a time-dependent density functional approach. For the evolution of the 1P bubble state, two different functionals accompanied with two different time-development schemes are used, namely an accurate finite-range functional for helium with an adiabatic approximation for electron versus an efficient zero-range functional for helium with a real-time evolution for electron. We make a detailed comparison between the quantitative results obtained from the two methods, which allow us to employ with confidence the optimal method for suitable problems. Based on this knowledge, we use the finite-range functional to calculate the time-resolved absorption spectrum of the 1P bubble, which in principle can be experimentally determined, and we use the zero-range functional to real-time evolve the 2P bubble for several hundreds of picoseconds, which is theoretically interesting due to the break down of adiabaticity for this state. Our results discard the physical realization of relaxed, metastable configurations above the 1P state.     

Calculation of viscosity–temperature curves for glass obtained from four wastewater treatment plants in Egypt

This article establishes the relationship between the chemical composition, temperature and viscosity of glasses obtained from the four sludge treatment plants of urban and industrial wastewater from the Nile Delta in Egypt. In order to determine the working conditions of these glasses and their growth temperature, different techniques have been used: differential thermal analysis, hot stage microscopy and dilatometry. We used a prototype of hot stage microscopy, with the help of an image analysis programme developed in the present study. The chemical composition of major oxides sludge ranging from: SiO₂ (36–48 wt%), Al₂O₃ (9–16 wt%), CaO (5–25 wt%), P₂O₅ (1.5–11 wt%), and Fe₂O₃ (~9 wt%), this composition is close to a basalt rock, being necessary to incorporate some raw materials to adjust it to the basalt rock that has a good viscosity-temperature curve. The glass transition temperatures of the four glasses obtained vary between 650 and 725 °C and the growth occurs between 938 and 1,033 °C. We also obtained the viscosity–temperature curves with the aid of the hot stage microscopy that has allowed us to determine the working temperatures of the four glasses, ranging from 926 to 1,419 °C, depending on the type of forming process used.     

Synthesis, structure, and reactivity of new tetranuclear Ru-Hbpp-based water-oxidation catalysts

The preparation of three new octadentate tetranucleating ligands made out of two Ru-Hbpp-based units [where Hbpp is 3,5(bispyridyl)pyrazole], linked by a xylyl group attached at the pyrazolate moiety, of general formula (Hbpp)(2)-u-xyl (u = p, m, or o) is reported, together with its dinucleating counterpart substituted at the same position with a benzyl group, Hbpp-bz. All of these ligands have been characterized with the usual analytical and spectroscopic techniques. The corresponding tetranuclear ruthenium complexes of general formula {[Ru(2)(trpy)(2)(L)](2)(μ-(bpp)(2)-u-xyl)}(n+) [L = Cl or OAc, n = 4; L = (H(2)O)(2), n = 6] and their dinuclear homologues {[Ru(2)(trpy)(2)(L)](μ-bpp-bz)}(n+) [L = Cl or OAc, n = 2; L = (H(2)O)(2), n = 3] have also been prepared and thoroughly characterized both in solution and in the solid state. In solution, all of the complexes have been characterized spectroscopically by UV-vis and NMR and their redox properties investigated by means of cyclic voltammetry techniques. In the solid state, monocrystal X-ray diffraction analysis has been carried out for two dinuclear complexes {[Ru(2)(trpy)(2)(L)](μ-bpp-bz)}(2+) (L = Cl and OAc) and for the tetranuclear complex {[Ru(2)(trpy)(2)(μ-OAc)](2)(μ-(bpp)(2)-m-xyl)}(4+). The capacity of the tetranuclear aqua complexes {[Ru(2)(trpy)(2)(H(2)O)(2)](2)(μ-(bpp)(2)-u-xyl)}(6+) and the dinuclear homologue {[Ru(2)(trpy)(2)(H(2)O)(2)](μ-bpp-bz)}(3+) to act as water-oxidation catalysts has been evaluated using cerium(IV) as the chemical oxidant in pH = 1.0 triflic acid solutions. It is found that these complexes, besides generating significant amounts of dioxygen, also generate carbon dioxide. The relative ratio of [O(2)]/[CO(2)] is dependent not only on para, meta, or ortho substitution of the xylylic group but also on the concentration of the starting materials. With regard to the tetranuclear complexes, the one that contains the more sterically constrained ortho-substituted ligand generates the highest [O(2)]/[CO(2)] ratio.     

Spin crossover active iron(II) complexes of selected pyrazole-pyridine/pyrazine ligands

This review begins with a brief introduction to pyrazole and to spin crossover. The focus then moves to a detailed consideration of the synthesis and magnetic properties of structurally characterized iron(II) spin crossover (SCO) active complexes of pyrazole- and pyrazolate-based ligands that also contain at least one pyridine or pyrazine unit within the ligand motif. The syntheses and crystallization methods reported in the original publications are emphasized in this review. The reason for this is that these factors often affect the exact nature of the final product, including the amount and nature of the crystallization solvent molecules present and/or what polymorph is obtained, and hence they can impact strongly on the SCO properties of the resulting materials, as can be seen in this review.