PIXE analysis of Tillandsia usneoides for air pollution studies at an industrial zone in Central Mexico

In order to find out if there is a relation between atmospheric particulate matter composition and human health effects, metals and other elements measurement are performed. Analysis of atmospheric aerosols collected in filters is the usual method to achieve this task. Biological monitors provide an advantageous alternative way of sampling, since there is no need of special sampling devices, and accumulation time can be as long as desired. In this study, Tillandsia usneoides a reliable air pollution biological monitor that occurs naturally throughout Mexico was used to monitor air quality of Tula–Tepeji corridor at central Mexico. This area is considered critical zone because of atmosphere contaminants high concentration. Some biomonitors were transplanted from a clean environment to four sites at the Tula corridor. Plants samples were collected every two weeks from February to April 2008. PM₁₀ sampling in filters was also performed simultaneously at three locations where T. usneoides was transplanted, for a comparison. Chemical composition was determined by PIXE. Results showed that T. usneoides incorporates anthropogenic elements reaching maximal levels after 6 to 10 weeks approximately. Since results obtained with biomonitors agree with those obtained with aerosol filters, T. usneoides could be employed as a first approximation to provide insights of the atmospheric pollution level previous to a detailed study using filters.     

Elastic scattering of neutrons on natPb at forward angles

Angular distributions were measured for neutron elastically scattered by ^natPb at 2.9, 3.0, 3.1, 3.2 and 3.4MeV at very forward angles. The mono-energetic neutron flux was produced at the tandem accelerator facility of the National Institute of Nuclear Research (ININ), Mexico, using the Associated Particle Technique (APT) in the D(d, n)³He reaction. Optical model predictions with best potential systematic show a fairly good agreement with our data, and also the need for a better understanding of the neutron scattering process at very small angles from the theoretical point of view.     

Teachers’ conceptions of tangent line

In order to study the conceptions, and their evolutions, of the tangent line to a curve an updating workshop which took place in México was designed for upper secondary school teachers. This workshop was planned using the methodology of cooperative learning, scientific debate and auto reflection (ACODESA) and the conception-knowing-concept model (cK¢) developed mainly by Balacheff. In order to initiate the conceptions reorganization, an initial activity was made in the graphic frame; it seems optimal to start the debates without leading participants to failure. The mathematical core of the workshop was formed by an algebraic method to find tangents to algebraic curves which is close to Descartes’ method. The ACODESA methodology allowed some intense debates mainly concerning the local character of a tangent, generating the teachers’ cognitive unbalance which is a starting point for the refinement or transformation of their conceptions. On the other hand, the cK¢ model allows to understand the conceptions of participants and to analyze the evolution of their knowings.     

Diferrocenophosphaborin: A Planar‐Chiral,Redox‐Active and Anion‐Responsive Ambiphilic Ligand

A new class of Janus‐like ambiphilic ligands is introduced. The rigid diferrocene backbone in heterocycles 4‐SnP and 4‐BP creates an unprecedented chiral environment as demonstrated by multinuclear NMR and single‐crystal X‐ray studies. In addition, the ligands are redox‐responsive and the Lewis acidic borane moiety in 4‐BP can be exploited to further tune the properties: a clear decrease in the CO stretching frequency of a Vaska‐type Rh^I complex 5‐BP is observed upon addition of fluoride ions. Thus, the Lewis acid and Lewis base sites influence each other and their strength can be modulated by redox chemistry and anion binding.     

Copper‐Catalyzed Formation of α‐Alkoxycycloalkenones from N‐Tosylhydrazones

The combination of 20 mol % of copper iodide and lithium tert‐butoxide triggers the formation of a broad range of substituted, functionalized α‐alkoxy 2H‐naphthalenones from readily available N‐tosylhydrazones. The data suggests that this transformation occurs through cycloaddition of a copper carbenoid with an ester, followed by a Lewis acid‐catalyzed [1,2] alkyl shift of the in situ generated alkoxyepoxide intermediate.     

What Is a Fraction? Developing Fraction Understanding in Prospective Elementary Teachers

Classroom teachers need a well‐developed deep understanding of fractions and pedagogic practices so they can provide meaningful experiences for students to explore and construct ideas about fractions. This study sought to examine prospective elementary teachers' understandings of fraction by focusing specifically on their use of fractions meanings and interpretations. Results indicated that prospective elementary teachers bring with them to their final methods course a limited understanding of fractions and that experiences in methods courses resulted only in minor improvement of those limited understandings. The limited part‐whole understanding of fractions that prospective elementary teachers entered the course with was resilient. The implications of this study suggest a need for prospective elementary teachers to continue to develop their conceptual understanding of fractions and for changes to the content and instructional strategies of mathematics content courses designed for prospective elementary teachers.     

Synthesis, spectroscopic characterization, DFT studies and biological assays of a novel gold(I) complex with 2-mercaptothiazoline

A new gold(I) complex with 2-mercaptothiazoline (MTZ) with the coordination formula [AuCN(C₃H₅NS₂)] was synthesized and characterized by chemical and spectroscopic measurements, DFT studies and biological assays. Infrared (IR) and ¹H, ¹³C and ¹⁵N nuclear magnetic resonance (NMR) spectroscopic measurements indicate coordination of the ligand to gold(I) through the nitrogen atom. Studies based on DFT confirmed nitrogen coordination to gold(I) as a minimum of the potential energy surface with calculations of the hessians showing no imaginary frequencies. Thermal decomposition starts at temperatures near 160 °C, leading to the formation of Au⁰ as the final residue at 1000 °C. The gold(I) complex with 2-mercaptothiazoline (Au-MTZ) is soluble in dimethyl sulfoxide (DMSO), and is insoluble in water, methanol, ethanol, acetonitrile and hexane. The antibacterial activities of the Au-MTZ complex were evaluated by an antibiogram assay using the disc diffusion method. The compound showed an effective antibacterial activity against Staphylococcus aureus (Gram-positive) and Escherichia coli and Pseudomonas aeruginosa (Gram-negative) bacterial cells. Biological analysis for evaluation of the cytotoxic effect of the Au-MTZ complex was performed using HeLa cells derived from human cervical adenocarcinoma. The complex presented a potent cytotoxic activity, inducing 85% of cell death at a concentration of 2.0 μmol L⁻¹.     

A-type cranberry proanthocyanidins inhibit the RANKL-dependent differentiation and function of human osteoclasts

This study investigated the effect of A-type cranberry proanthocyanidins (AC-PACs) on osteoclast formation and bone resorption activity. The differentiation of human pre-osteoclastic cells was assessed by tartrate-resistant acid phosphatase (TRAP) staining, while the secretion of interleukin-8 (IL-8) and matrix metalloproteinases (MMPs) was measured by ELISA. Bone resorption activity was investigated by using a human bone plate coupled with an immunoassay that detected the release of collagen helical peptides. AC-PACs up to 100 μg/mL were atoxic for osteoclastic cells. TRAP staining evidenced a dose-dependent inhibition of osteoclastogenesis. More specifically, AC-PACs at 50 μg/mL caused a 95% inhibition of RANKL-dependent osteoclast differentiation. This concentration of AC-PACs also significantly increased the secretion of IL-8 (6-fold) and inhibited the secretion of both MMP-2 and MMP-9. Lastly, AC-PACs (10, 25, 50 and 100 μg/ml) affected bone degradation mediated by mature osteoclasts by significantly decreasing the release of collagen helical peptides. This study suggests that AC-PACs can interfere with osteoclastic cell maturation and physiology as well as prevent bone resorption. These compounds may be considered as therapeutic agents for the prevention and treatment of periodontitis.