Abordagem contextual nos capítulos de estequiometria e de soluções dos livros didáticos de Química aprovados pelo PNLD (Programa Nacional do Livro Didático - Brasil) /2012

A contextualização tem sido proposta no currículo escolar com o propósito de promover mudanças de comportamentos, atitudes e valores. Nessa abordagem, entende-se que o ensino de química deve se desenvolver de forma ampla, envolvendo também aspectos sociais, políticos, econômicos,ambientais e culturais, e não somente aspectos científicos. Tendo em vista a grande importância dada ao livro didático (LD) na prática docente, buscamos analisar a abordagem contextual nos capítulos de estequiometria e soluções nos LD de química aprovados pelo PNLD/2012. Os resultados mostraram que os autores dos LD analisados reconhecem a contextualização como elemento central para a formação da cidadania, porém a abordagem é diferente em cada obra. As leituras dos LD possibilitaram a identificação de alguns "níveis" de contextualização que percorreram quatro categorias de análise

Portabilitaet und Adaption von Software der linearen Algebra fuer Distributed Memory Systeme

Available from TIB Hannover: RR 5549(238)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Origin of the Two Bands in the B800 Ring and Their Involvement in the Energy Transfer Network of <i>Allochromatium vinosum</i>

Bacterial photosynthesis features robust and adaptable energy-harvesting processes in which light-harvesting proteins play a crucial role. The peripheral light-harvesting complex of the purple bacterium <i>Allochromatium vinosum</i> is particularly distinct, featuring a double peak structure in its B800 absorption band. Two hypothesesnot necessarily mutually exclusiveconcerning the origin of this splitting have been proposed; either two distinct B800 bacteriochlorophyll site energies are involved, or an excitonic dimerization of bacteriochlorophylls within the B800 ring takes place. Through the use of two-dimensional electronic spectroscopy, we present unambiguous evidence that excitonic interaction shapes the split band. We further identify and characterize all of the energy transfer pathways within this complex by using a global kinetic fitting procedure. Our approach demonstrates how the combination of two-dimensional spectral resolution and self-consistent fitting allows for extraction of information on light-harvesting processes, which would otherwise be inaccessible due to signal congestion

Determination of Excited-State Energies and Dynamics in the B Band of the Bacterial Reaction Center with 2D Electronic Spectroscopy

Photosynthetic organisms convert photoenergy to chemical energy with near-unity quantum efficiency. This occurs through charge transfer in the reaction center, which consists of two branches of pigments. In bacteria, both branches are energy-transfer pathways, but only one is also an electron transfer pathway. One barrier to a full understanding of the asymmetry is that the two branches contain excited states close in energy that produce overlapping spectroscopic peaks. We apply polarization-dependent, 2D electronic spectroscopy to the B band of the oxidized bacterial reaction center. The spectra reveal two previously unresolved peaks, corresponding to excited states localized on each of the two branches. Furthermore, a previously unknown interaction between these two states is observed on a time scale of ∼100 fs. This may indicate an alternative pathway to electron transfer for the oxidized reaction center and thus may be a mechanism to prevent energy from becoming trapped in local minima

Conformational Complexity in the LH2 Antenna of the Purple Sulfur Bacterium <i>Allochromatium vinosum</i> Revealed by Hole-Burning Spectroscopy

This work discusses the protein conformational complexity of the B800–850 LH2 complexes from the purple sulfur bacterium <i>Allochromatium vinosum</i>, focusing on the spectral characteristics of the B850 chromophores. Low-temperature B850 absorption and the split B800 band shift blue and red, respectively, at elevated temperatures, revealing isosbestic points. The latter indicates the presence of two (unresolved) conformations of B850 bacteriochlorophylls (BChls), referred to as conformations 1 and 2, and two conformations of B800 BChls, denoted as B800_R and B800_B. The energy differences between average site energies of conformations 1 and 2, and B800_R and B800_B are similar (∼200 cm^–1), suggesting weak and strong hydrogen bonds linking two major subpopulations of BChls and the protein scaffolding. Although conformations 1 and 2 of the B850 chromophores, and B800_R and B800_B, exist in the ground state, selective excitation leads to 1 → 2 and B800_R → B800_B phototransformations. Different static inhomogeneous broadening is revealed for the lowest energy exciton states of B850 (fwhm ∼195 cm^–1) and B800_R (fwhm ∼140 cm^–1). To describe the 5 K absorption spectrum and the above-mentioned conformations, we employ an exciton model with dichotomous protein conformation disorder. We show that both experimental data and the modeling study support a two-site model with strongly and weakly hydrogen-bonded B850 and B800 BChls, which under illumination undergo conformational changes, most likely caused by proton dynamics

Energy Transfer Pathways in Light-Harvesting Complexes of Purple Bacteria as Revealed by Global Kinetic Analysis of Two-Dimensional Transient Spectra

Excited state dynamics in LH2 complexes of two purple bacterial species were studied by broad-band two-dimensional electronic spectroscopy. The optical response was measured in the 500–600 nm spectral region on the 0–400 fs time scale. Global target analysis of two-dimensional (2D) transient spectra revealed the main energy transfer pathways between carotenoid S₂, 1B_u^– and S₁ states and bacteriochlorophyll Q_<i>x</i> state. Global analysis ascertained the evolutionary and vibration-associated spectra, which also indicated the presence of a higher-lying vibrational level in the carotenoid S₁ state. The estimation of the spectral overlap between the 1B_u^– state and the Q_<i>x</i> state indicated a significant contribution of the 1B_u^– state to the overall S₂-to-Q_<i>x</i> excitation energy transfer

Hybrid Nanostructures for Enhanced Light-Harvesting: Plasmon Induced Increase in Fluorescence from Individual Photosynthetic Pigment–Protein Complexes

We studied the optical response from more than 13 000 individual photosynthetic pigment–protein complexes interacting with spherical gold nanoparticles. The nanodots were arranged in a quasi-hexagonal array by diblock copolymer micellar nanolithography. Exciting the proteins within the spectral range of the nanoparticles’ plasmon resonance yields a clear enhancement of the protein fluorescence intensity, whereas excitation far out of the plasmon resonance features no effect. This result indicates a strategy for the construction of efficient hybrid light-harvesting devices

Genomic and phylogenomic context of the <i>yhaOMKJ</i> locus.

<p>(A) Genomic context of the D-serine tolerance locus (blue) in three distinct <i>E</i>. <i>coli</i> isolates–CFT073 (UPEC), EDL933 (EHEC) and MG1655 (K-12). The system encodes DsdC (a LysR type transcriptional regulator), DsdX (a D-serine outer membrane transporter) and DsdA (a D-serine deaminase). In EDL933 the D-serine tolerance locus is truncated and replaced with the sucrose utilization locus (<i>cscRAKB</i> highlighted in green). (B) Genomic context of the second putative D-serine sensory locus (red) in CFT073, EDL933 and MG1655. The system encodes YhaJ (a putative LysR type transcriptional regulator), YhaK (a redox-sensitive bicupin), YhaM (a putative deaminase) and YhaO (a putative inner membrane D-serine transporter). (B) The <i>yhaOMKJ</i> locus is highly conserved across the <i>E</i>. <i>coli</i> phylogeny. Circularized phylogenomic tree of 1591 <i>E</i>. <i>coli</i> and <i>Shigella</i> isolates overlaid with gene carriage for the <i>dsdCXA</i> locus and the <i>yhaOMKJ</i> locus. The <i>yhaOMKJ</i> genes are indicated by red blocks and the <i>dsdCXA</i> locus by blue blocks. Ordering of the genes is numbered and corresponds to the gene in the legend labeled *. Presence of a gene is determined by > 80% identity over > 80% of the coding sequence. Pseudogenes are indicated as yellow blocks. <i>E</i>. <i>coli</i> phylogroups are subdivided by color with the branch point labeled on the tree. Phylogroup A = Blue; Phylogroup B1 = Green; Phylogroup B2 = Red; Phylogroup C = Magenta; Phylogroup D = Purple; Phylogroup E = Cyan; Phylogroup F = Brown; <i>Shigella</i> = Gold. The position of prototypical strains is indicated on the outside of the figure.</p

Identification of YhaO and YhaJ as potential virulence determinants.

<p>(A) Screening of the <i>yhaOMKJ</i> locus for a role in virulence. SDS-PAGE profile of secreted proteins from TUV93-0, <i>yhaO</i>, <i>yhaM</i>, <i>yhaK</i> and <i>yhaJ</i> cultured in MEM-HEPES. Arrows indicate the location of the major LEE-encoded secreted effectors Tir, EspD and EspA as identified by mass-spectrometry. Samples were normalized according to cellular OD⁶⁰⁰ to normalize loading into each well. Immunoblot analysis of EspD levels from secreted (Sec) and whole cell lysate (WCL) fractions confirmed the SDS-PAGE results. Anti-GroEL was used to verify equal concentrations of WCL, which corresponded to OD⁶⁰⁰ normalized culture samples, loaded into each well (B) SDS-PAGE analysis highlighting complementation of the <i>ΔyhaO</i> and <i>ΔyhaJ</i> phenotypes by plasmids p<i>yhaO</i> and p<i>yhaJ</i>. SDS PAGE and immunoblot analysis of secreted protein profiles and EspD cytoplasmic expression confirmed the results. Protein secretion experiments were performed on multiple occasions.</p

YhaJ directly regulates the LEE in EHEC.

<p>(A) Schematic representation of the LEE pathogenicity island. The master regulator <i>ler</i> upstream regulatory region is expanded to illustrate the rationale behind the design of the nested deletion series to monitor <i>LEE1</i> promoter activity as described by Islam <i>et al</i>. Promoters P1 and P2 as well as corresponding -10 and -35 elements are indicated. (B) Monitoring the impact of YhaJ on <i>LEE1</i> expression in TUV93-0. LEE10 and LEE20 plasmids were transformed into TUV93-0 (grey) and <i>ΔyhaJ</i> (orange) and LacZ activity was measured in Miller units at an OD⁶⁰⁰ of approximately 0.7 during growth in MEM-HEPES. The presence of promoters P1 and P2 in each assay is indicated above the graph. * and NS denote P ≤ 0.05 and no significance respectively and the data was calculated from three biological replicates. (C) Purified YhaJ was tested for its ability to bind the <i>LEE1</i> P1 and P2 promoter regions by EMSA. DIG-labeled LEE1 P1 and P2 specific DNA probes were incubated with increasing concentrations of YhaJ. A shift in free-DNA that corresponds to a YhaJ-DNA complex was only observed for <i>LEE1</i> P1 and this was in agreement with the data presented in panel B. Specificity of the binding reaction was tested by the addition of a 100-fold excess (+) of unlabeled P1 or P2 probe to the binding reaction to outcompete binding of the DIG-labeled probe to YhaJ. A 100-fold excess of unlabeled <i>kan</i> probe was also used as a non-specific competitor for YhaJ binding to the P1 region (<i>LEE1</i> P1 vs <i>kan</i>) to ensure specify of the band shift pattern. EMSA experiments were performed in triplicate to confirm the results.</p