Optical studies of ZnO nanocrystals doped with Eu3+ ions

Synthetic ZnO nanocrystals have been intentionally doped with Eu³⁺ ions. Structural analysis performed on the nanocrystals showed wurtzite-ZnO as the only phase present in the samples. Photoluminescence in emission and excitation modes allows the assignment of the intra-4f⁶ transitions for the Eu³⁺ ions. From the analysis of the optical data we are able to demonstrate that multiple Eu-related optical centres are present in the studied samples. Oxygen vacancies are likely candidates to be responsible for the ion accommodation in the ZnO lattice and from the photoluminescence excitation data we tentatively assign a trap level at ∼200 meV below the conduction band to this intrinsic defect. PACS 78.66.Hf; 78.67.-n; 82.80.Yc     

A dysprosium single molecule magnet outperforming current pseudocontact shift agents

A common criterion for designing performant single molecule magnets and pseudocontact shift tags is a large magnetic anisotropy. In this article we present a dysprosium complex chemically designed to exhibit strong easy-axis type magnetic anisotropy that is preserved in dichloromethane solution at room temperature. Our detailed theoretical and experimental studies on the magnetic properties allowed explaining several features typical of highly performant SMMs. Moreover, the NMR characterization shows remarkably large chemical shifts, outperforming the current state-of-the art PCS tags.

A robust dysprosium(iii) single molecule magnet with large uniaxial magnetic anisotropy induces pseudocontact shifts at almost doubled distance compared to standard shift agents.     

Effect of Bauhinia monandra Kurz Leaf Preparations on Embryonic Stages and Adult Snails of Biomphalaria glabrata (Say, 1818), Schistosoma mansoni Cercariae and Toxicity in Artemia salina

Biomphalaria glabrata snails constitute the main vector of schistosomiasis in Brazil, and Bauhinia monandra Kurz, the leaves of which contain BmoLL lectin with biocidal action, is a plant widely found on continents in which the disease is endemic. This work describes the composition of B. monandra preparations and the effect on embryos and adult snails, their reproduction parameters and hemocytes. We also describe the results of a comet assay after B. glabrata exposure to sublethal concentrations of the preparations. Additionally, the effects of the preparations on S. mansoni cercariae and environmental monitoring with Artemia salina are described. In the chemical evaluation, cinnamic, flavonoid and saponin derivatives were detected in the two preparations assessed, namely the saline extract and the fraction. Both preparations were toxic to embryos in the blastula, gastrula, trochophore, veliger and hippo stages (LC₅₀ of 0.042 and 0.0478; 0.0417 and 0.0419; 0.0897 and 0.1582; 0.3734 and 0.0974; 0.397 and 0.0970 mg/mL, respectively) and to adult snails (LC₅₀ of 6.6 and 0.87 mg/mL, respectively), which were reproductively affected with decreased egg deposition. In blood cell analysis, characteristic cells for apoptosis, micronucleus and binucleation were detected, while for comet analysis, different degrees of nuclear damage were detected. The fraction was able to cause total mortality of the cercariae and did not present environmental toxicity. Therefore, B. monandra preparations are promising in combating schistosomiasis since they can control both the intermediate host and eliminate the infectious agent, besides being safe to the environment.     

Metal and trace element assessments of bottom sediments from medium Tietê River basin,Sao Paulo State,Brazil: part II

Journal of Radioanalytical and Nuclear Chemistry - Concentration of metals in 15 bottom sediment samples from Tietê River, a significantly polluted river, were assessed. Total and partial...     

Molecular orbital description of the polythiazyl polymer Part 1. MNDO calculations of models of (SN)x

Semiempirical MNDO calculations are performed on various models for the polythiazyl polymer with increasing chain sizes. Population analysis, geometry optimization and the evolution of the frontier orbital energies are discussed. A low-lying broken symmetry structure with (SN)₂ repeating units is detected.     

Studies on immobilizd lipase in hydrophobic sol-gel

The hydrolysis of tetraethoxysilane using the sol-gel process was used to produce silica matrices, and these were tested for the immobilization of lipase from Candida rugosa by three methods: physical adsorption, covalent binding, and gel entrapment in the presence and absence of polyethylene glycol (PEG-1450). The silica matrices and their derivatives were characterized regarding particle size distribution, specific surface area, pore size distribution (Brunauer, Emmett, and Teller [B.E.T.] method), yield of grafting (thermogravimetric analyzer [TGA]), and chemical composition (Fourier transform infrared). Immobilization yields based on recovered lipase activity varied from 3.0 to 32.0%, and the highest efficiency was attained when lipase was encapsulated in the presence of PEG.     

Mixture Design PARAFAC HPLC-DAD Metabolomic Fingerprints of Fractionated Organic and Basic Extracts from <Emphasis Type="Italic">Erythrina speciosa</Emphasis> Andrews Leaves

HPLC-DAD analysis of statistical mixture design extracts of Erythrina speciosa Andrews leaves provided chromatographic and UV–visible profiles of their basic and organic fractions that were treated with the PARAFAC multivariate method. The design extracts provided greater varieties and amounts of metabolites than could be obtained by classical extraction methods. Fractionation provided more diverse fingerprint information than obtained previously from only the crude extract. The two largest chromatographic peaks, one with a 4.8 min elution time having an intense spectral band at 235 nm and the other a 5.8 min peak with an intense 238 nm band for the basic fraction were obtained with the ternary 1:1:1 ethanol–dichloromethane–hexane mixture. These can be assigned to diene-type and lactonic alkaloids. Peaks with the same retention times are also found in the organic fraction but are extracted with different mixtures and have distinct spectral behavior in the 235 nm region, probably being aromatic alkaloids. The above strategy permits a more unambiguous assignment of metabolic groups to specific chromatographic peaks. This can be expected to provide higher quality chromatographic fingerprints for natural products’ chemistry.     

N-Vinyl- and C-vinylpyrroles from azafulvenium methides. flash vacuum pyrolysis route to 5-Oxo-5H-pyrrolizines and 1-azabenzo[f]azulenes

1-Azafulvenium methides, generated from pyrrolo[1,2-c]thiazole-2,2-dioxides' thermal extrusion of sulfur dioxide, led to the synthesis of functionalized pyrroles. The intramolecular trapping of these transient 8pi 1,7-dipoles in pericyclic reactions, namely sigmatropic [1,8]H shifts and 1,7-electrocyclization, allowed the synthesis of N-vinylpyrroles and C-vinylpyrroles which, under flash vacuum pyrolysis conditions, are converted into 5-oxo-5H-pyrrolizines or 4-oxo-1,4-dihydro-1-aza-benzo[f]azulenes, respectively. These heterocycles can also be obtained directly from FVP of pyrrolo[1,2-c]thiazole 2,2-dioxides. The synthesis and X-ray structure of a new 6-oxocyclopenta[b]pyrrole derivative is also reported.     

Modelling of Pb-(TAPS)x-(OH)y system and refinement of stability constants in the region of lead hydrolysis and lead hydroxide precipitation

The influence of [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) on solutions containing lead(II) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP). The readings were taken at fixed total TAPS to total lead(II) concentration ratios and various pH values, at 25.0 ± 0.1 °C and ionic strength 0.1 M KNO₃.Due to the basic pK_a of the ligand, which occurs in the pH range where large amount of lead polynuclear species are formed, and the occurrence of ligand adsorption, that disabled the use of high concentrations of TAPS on DCP experiments, GEP and DCP experimental conditions were put to the limit in order to provide the correct Pb-TAPS-OH model and reliable stability constants.The proposed final model is: PbL, PbL₂, PbL₂(OH) and PbL₂(OH)₂ with overall stability constants values, as log β, 3.27 ± 0.06, 6.5 ± 0.1, 12.7 ± 0.1 and 17.27 ± 0.06, respectively.A comparative analysis of the strength of complexation of TAPS and a structural related buffer, 2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid (TAPSO), with lead is also discussed.