An Amine‐Catalyzed Enantioselective [3+2] Cycloaddition of Azomethine Ylides and α,β‐Unsaturated Aldehydes: Applications and Mechanistic Implications

The catalytic enantioselective [3+2] cycloaddition between azomethine ylides and α,β‐unsaturated aldehydes catalyzed by α,α‐diphenylprolinol has been studied in detail. In particular, the reaction has been extended to the use of 2‐alkenylidene aminomalonates generated in situ as azomethine ylide precursors. These reactions lead to the formation of pyrrolidines containing a 5‐alkenyl side chain with potential for chemical manipulation. Moreover, a detailed and concise computational study has been carried out to understand the exact nature of the mechanism of this reaction and especially the consequences derived from the incorporation of the chiral secondary amine catalyst on the reaction pathway.     

Optimization and validation of organochlorine compounds in adipose tissue by SPE‐gas chromatography

Scientific evidence has shown an association between organochlorine compounds (OCC) exposure and human health hazards. Concerning this, OCC detection in human adipose samples has to be considered a public health priority. This study evaluated the efficacy of various solid‐phase extraction (SPE) and cleanup methods for OCC determination in human adipose tissue. Octadecylsilyl endcapped (C₁₈‐E), benzenesulfonic acid modified silica cation exchanger (SA), poly(styrene‐divinylbenzene (EN) and EN/RP₁₈ SPE sorbents were evaluated. The relative sample cleanup provided by these SPE columns was evaluated using gas chromatography with electron capture detection (GC–ECD). The C₁₈‐E columns with strong homogenization were found to provide the most effective cleanup, removing the greatest amount of interfering substance, and simultaneously ensuring good analyte recoveries higher than 70%. Recoveries > 70% with standard deviations (SD) < 15% were obtained for all compounds under the selected conditions. Method detection limits were in the 0.003–0.009 mg/kg range. The positive samples were confirmed by gas chromatography coupled with tandem mass spectrometry (GC‐MS/MS). The highest percentage found of the OCC in real samples corresponded to HCB, o,p′‐DDT and methoxychlor, which were detected in 80 and 95% of samples analyzed respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and structure of the cluster ion pair [Ru3(CO)9[mu-P(NPri2)2]3][Ru6(CO)15(mu 6-C)[mu-P(NPri2)2]]. A theoretical overview of M3(mu-PR2)3 frameworks

The compound [Ru3(CO)9[mu-P(NPri2)2]3][Ru6(CO)15(mu 6-C)[mu-P(NPri2)2]] (1), obtained via the addition of PCl(NPri2)2 to K2[Ru4(CO)13], crystallizes in the monoclinic space group P2l/c with a = 15.537(8) A, b = 36.151(16) A, c = 19.407(5) A, beta = 91.14(2) degrees, Z = 4, and R = 0.069 for 8006 observed reflections. The unit cell is unusual in that it contains both a typical octahedral Ru6 cluster anion (1a), featuring an encapsulated carbide, and a symmetrical phosphido bridge, in addition to a 50-electron trinuclear cluster cation [Ru3(CO)9[mu-P(NPri2)2]3]+ (1c). The latter, with approximate D3h symmetry, exhibits long Ru-Ru distances (> or = 3.15 A). Among the family of clusters with M3(mu-PR2)3 cores and different numbers of both electrons (TEC) and terminal ligands (LxLyLz), 1c is unique in that it is a 333 stereotype with 50 valence electrons. MO calculations permit us to predict the existence of redox congeners of 1c clusters and related 48e Re3 clusters. This work also presents a summary of the relationships between the electronic and the geometric structures for all known M3LxLyLz(mu-PR2)3 species. The basic stereochemical features are influenced by the total-electron count and, hence, by the degree of M-M bonding, as well as the remarkable flexibility of the phosphido bridging ligands. The mu-PR2 ligands need not necessarily lie in the M3 plane, and a wide range of M-P-M angles (as small as 72 degrees or as large as 133 degrees) have been observed.     

Effects of Alkylamines on the Percolation Phenomena in Water/AOT/Isooctane Microemulsions

We carried out an investigation on the influence of several alkylamines, frequently present in reactions carried out in microemulsions, on the properties of the water/AOT/isooctane system. The presence of alkylamines has an important effect on the electrical percolation phenomena. This effect of amines on the electrical percolation of microemulsions of AOT/isooctane/water can be explained by taking into account the ability of these substrates to associate with the AOT film in the microemulsion, the basicity of the amine, and the different solubility of the amine in the three pseudophases of the system. Copyright 2000 Academic Press.     

Non-coherent visible and infrared radiation increase survival to UV (254 nm) in Escherichia coli K12

Interactions between visible or infrared (IR) and ultraviolet (UV, 254 nm) radiation have been studied in E. coli. Pre-illumination with non-coherent monochromatic 446, 466, 570 and 685 nm radiation, as well as with polychromatic red and IR radiation at room temperature, leads to increased cell survival after a subsequent irradiation with UV light. In the thermic range of the spectrum (red and IR), IR but not red light pre-treatment is able to increase cell survival to a subsequent lethal heat (51 degrees C) challenge, suggesting that increased UV survival may be due to IR-induced heat-shock response. On the other hand, visible-light-induced resistance may be due to a different mechanism, possibly involved with unknown bacterial light receptors.     

Catalytic effect of copper(II) oxide on oxidation of cellulosic biomass

The reuse and recycling of biomass materials can minimize the environmental impact of society, and can help create a sustainable community. Although cellulosic biomass from demolished buildings is a promising resource for recycling, contaminants, such as wood preservatives that likely contain metal oxides, are found in recycled wood dust. These oxides could act as catalysts for the oxidation of organic materials, resulting in spontaneous ignition of large piles of recycled wood dust. Copper(II) oxide (CuO) is major component in wood preservative and plays a catalytic role in the oxidation of cellulose, which could cause spontaneous ignition. The present study focused on the influence of CuO on oxidation of cellulose. The exothermal behavior and mass loss of cellulose/CuO mixtures were investigated. Changes in exothermal behavior and mass loss with an increasing amount of CuO were measured by differential scanning calorimetry and thermogravimetry. In addition, kinetics and spectroanalysis were conducted to determine the catalytic effect of CuO on oxidation of cellulose and help determine the oxidation model of cellulose upon addition of CuO. Results revealed a change in exothermal behavior and increase in mass loss with increasing amounts of CuO. In addition, CuO had a catalytic effect on the oxidation of cellulose, which helped determine the oxidation model of cellulose upon addition of CuO.     

Identification of isomeric spin adducts of Leu-Tyr and Tyr-Leu free radicals using liquid chromatography-tandem mass spectrometry

Free radical species are generally short-lived due to their high reactivity and thus direct measurement and identification are often impossible. In this study we used a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), to trap radical intermediates formed during the oxidation of isomeric dipeptides tyrosine-leucine (Tyr-Leu) and leucine-tyrosine (Leu-Tyr), induced by the hydroxyl radical. To investigate the influence of the amino acid position in the peptide chain on the oxidation and free radical generation, the spin adducts were characterized using LC-MS and MS(n) . We detected carbon and oxygen DMPO adducts and adducts bearing two DMPO, which were analyzed by MS(n) . Both alkoxyl and peroxyl radicals were identified. Radical intermediates were localized in Tyr during oxidation of Tyr-Leu, while radicals were identified in Leu and Tyr during oxidation of Leu-Tyr. DMPO adducts of acyl radical species formed from cleavage of the peptide backbone, promoted by the alkoxyl radical in α carbon of the N-terminal amino acid were observed. The results show that the amino acid position has an influence in the oxidation process, at least on small peptides, and that the α carbon of the N-terminal amino acid is more vulnerable to the attack of the electrophilic hydroxyl radical.     

Interpretation of the Metabolic Enthalpy Change, ΔHmet,Calculated for Microbial Growth Reactions in Soils

The microcalorimetric method was used to calculate the metabolic enthalpy change per mol of glucose degraded by soil microorganisms, ΔH _met. This parameter has been calculated by microcalorimetry for many organic, inorganic and biochemical reactions, but there is only some information about its quantification for microbial growth reactions in soils. Values of ΔH _met were calculated for different soil samples collected in Galicia (Spain) and Campinas (Săo Paolo, Brazil). Exponential microbial growth was stimulated in all soil samples by the addition of glucose and power-time curves were recorded. Results showed changes in the values of ΔH _met calculated for all the soil samples, suggesting a dependence of this value with the microbial growth rate constant, with the percentage of growth, with the initial number of microorganisms of soil samples, with the quantity of glucose added and with the strain of bacteria growing in soil. The interpretation of variations of ΔH _met provides important qualitative and quantitative information. It reports data that allow to interpret from a qualitative point of view, the increase in biomass as a consequence of the degradation of the organic matter in soil, to understand changes in the percentages of soil organic matter and to know if the microbial population growing in differential soil samples is homogeneous. Therefore, to report that value would be very important in ecological studies, but beforehand, it is necessary to solve some problems that can appear in the experiments done to make the quantification . This revised version was published online in August 2006 with corrections to the Cover Date.