Kinetic and thermodynamic study of the substituent effect on the amino-Claisen rearrangement of para-substituted N-allyl-N-arylamine: a Hammett study via DFT

In order to find the susceptibility of the amino-Claisen rearrangement and the next proton shift reaction of N-allyl-N-arylamine to the substituent effects in the para position, the kinetic and thermodynamic parameters were calculated at the B3LYP level using the 6-31G^** basis set. The calculated activation energies for the rearrangements and proton shift reactions are close to 44.4 and 49.5 kcal mol^? 1, respectively. The transition states of the rearrangement with electron-donor substituents are more stable than those with electron-withdrawing substituent groups, but for the proton shift reaction, this situation is reversed (with the exception of fluorine atom for the rearrangement and fluorine and chlorine atoms for the proton shift reaction). Negative values for the activation entropy confirm the concerted mechanism for the amino-Claisen rearrangement and proton shift reaction. The Hammett ρ values of ? 2.4172 and ? 1.7791 are obtained for σ_p and σ^?  (enhanced sigma) in the amino-Claisen rearrangement, respectively. The correlation between log(k _X/k _H) and σ_p is weaker than that with σ^?  (enhanced sigma). A negative Hammett ρ value indicates that the electron-donating groups slightly increase the rate of amino-Claisen rearrangement. A positive Hammett ρ value (2.4921) for the proton shift reaction indicates that electron-withdrawing groups increase the rate of reaction.     

Characterizing gene movements between chromosomes in Drosophila

Drosophila have a variety of innate immune strategies for defending itself from infection, including humoral and cell mediated responses to invading microorganisms. At the front lines of these responses, are a diverse group of pattern recognition receptors that recognize pathogen associated molecular patterns. These patterns include bacterial lipopolysaccharides, peptidoglycans, and fungal β?1,3 glucans. Some of the receptors catalytically modify the pathogenic determinant, but all are responsible for directly facilitating a signaling event that results in an immune response. Some of these events require multiple pattern recognition receptors acting sequentially to activate a pathway. In some cases, a signaling pathway may be activated by a variety of different pathogens, through parallel receptors detecting different pathogenic determinants. In this chapter, we review what is known about pattern recognition receptors in Drosophila, and how those lessons may be applied towards a broader understanding of immunity.     

A reverse genetics and genomics approach to gene paralog function and disease: Myokymia and the juxtaparanode

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A divergent approach to the preparation of cysteine and serine analogs

Malonate diesters containing a prochiral quaternary carbon have been successfully transformed into analogs of cysteine and serine. The chiral half‐esters are obtained in good yield, and enantioselectivity by selective hydrolysis using Pig‐Liver Esterase (PLE) as the catalyst. The resulting half‐ester intermediates are transformed into α^{2, 2}‐, β^{2, 2}‐, and β^{3, 3}‐analogs of cysteine and serine. The methodology described here allows for the preparation of both enantiomers of the amino‐acid analogs by selective manipulation of the ester and acid functionalities. This divergent strategy allows a common synthetic strategy to be used to prepare a variety of unnatural amino‐acid classes from a common intermediate which should prove useful in the design of novel peptide libraries. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.     

Genetic battle between Helicobacter pylori and humans. The mechanism underlying homologous recombination in bacteria,which can infect human cells

Helicobacter pylori is a gram-negative pathogenic bacterium that colonises the human stomach. The chronic infection it causes results in peptic ulcers and gastric cancers. H. pylori can easily establish a chronic infection even if the immune system attacks this pathogen with oxidative stress agents and immunoglobulins. This is attributed to bacterial defence mechanisms against these stresses. As a defence mechanism against oxidative stresses, in bacterial genomes, homologous recombination can act as a repair pathway of DNA's double-strand breaks (DSBs). Moreover, homologous recombination is also involved in the antigenic variation in H. pylori. Gene conversion alters genomic structures of babA and babB (encoding outer membrane proteins), resulting in escape from immunoglobulin attacks. Thus, homologous recombination in bacteria plays an important role in the maintenance of a chronic infection. In addition, H. pylori infection causes DSBs in human cells. Homologous recombination is also involved in the repair of DSBs in human cells. In this review, we describe the roles of homologous recombination with an emphasis on the maintenance of a chronic infection.     

Probing TGF-β1-induced cytoskeletal rearrangement by fluorescent-labeled silica nanoparticle uptake assay

Cytoskeletal proteins are essential in maintaining cell morphology, proliferation, and viability as well as internalizing molecules in phagocytic and non-phagocytic cells. Orderly aligned cytoskeletons are disturbed by a range of biological processes, such as the epithelial–mesenchymal transition, which is observed in cancer metastasis. Although many biological methods have been developed to detect cytoskeletal rearrangement, simple and quantitative in vitro approaches are still in great demand. Herein, we applied a flow cytometry-based nanoparticle uptake assay to measure the degree of cytoskeletal rearrangement induced by transforming growth factor β1 (TGF-β1). For the assay, silica nanoparticles, selected for their high biocompatibility, were fluorescent-labeled to facilitate quantification with flow cytometry. Human keratinocyte HaCaT cells were treated with different concentrations of TGF-β1 and then exposed to FITC-labeled silica nanoparticles. Increasing concentrations of TGF-β1 induced gradual changes in cytoskeletal rearrangement, as confirmed by conventional assays. The level of nanoparticle uptake increased by TGF-β1 treatment in a dose-dependent manner, indicating that our nanoparticle uptake assay can be used as a quick and non-destructive approach to measure cytoskeletal rearrangement.     

Genomic rearrangement in long-term shoot competent cell cultures of hexaploid wheat

Summary By use of a method for regenerating wheat plants (Triticum aestivum L.) from cells from long-term suspension culture, the chromosome complement and stability of cultured cells of cv. Mustang were examined. Massive chromosome restructuring and genomic rearrangements were detected by HCl−KOH-Giemsa banding techniques. Chromosome structural variations involved mainly heterochromatin and centromeric regions. These included B genome chromosome elimination; heterochromatin amplification; megachromosomes and extrachromosomal DNA particles; translocations and deletions; telocentric, dicentric, and multicentric chromosomes; and somatic pairing and crossing over. At least 65 break-fusion sites were identified. Most of the sites were located in the B genome chromosomes (42 sites, 64.6%); 36.9% (20 sites) were located in the A genome chromosomes; and the fewest (3 sites, 4.6%) were detected in the D genome. Most of the chromosome break-fusion is in the heterochromatin and centromeric regions. The B genome chromosomes appeared to be eliminated nonrandomly, and the stability of the genome may vary among the genotypes and depend on culture duration. We also checked chromosome number of 1-year-old shoot-competent cells. Only 20% of the cells still had 2n=42 chromosomes. Most of the cells (60%) were hyperploid. These observed variations describe the types of tissue-culture-induced variations and suggest the unsuitability of using wheat cells from long-term cultures for genetic transformation experiments.     

Significant differences between the chloroplast genomes of two Acetabularia mediterranea strains

Summary The chloroplast DNAs of Acetabularia mediterranea strains 5 and 17 differ significantly in their restriction patterns. Southern blotting analysis using gene probes derived from the coding regions of spinach genes showed that psbB and petB each map to unique restriction fragments which are shared in strains 5 and 17. On the other hand psaA, psbA and rbcL map to different restriction fragments in strains 5 and 17 probably as a result of restriction fragment length polymorphism. In addition to restriction fragment polymorphism there is evidence for much larger differences in the organization of the plastome. The most striking difference is the absence in strain 5 of a 10 kb repeated sequence which has previously been demonstrated in strain 17. However, both strains apparently share at least 8 kb of the 10 kb repeated sequence. Restriction analysis of independent clones of the 10 kb sequence revealed a family of non-identical repeats.This paper is dedicated to the memory of Prof. H.G. Schweiger, Director of the Max-Planck-Institut fur Zellbiologie, who died in November 1986Deceased     

Effect of the fungicide Prochloraz-Mn on the cell wall structure of <Emphasis Type="Italic">Verticillium fungicola</Emphasis>

The chemical structure of the cell wall of two isolates of Verticillium fungicola collected from diseased fruit bodies of the commercial mushroom Agaricus bisporus treated with the fungicide Prochloraz-Mn was analyzed. The isolates were obtained during different periods of time and grown in the absence and presence of the LD₅₀ values of the fungicide for V. fungicola. In addition, another V. fungicola isolate collected previous to the routine utilization of Prochloraz-Mn but grown under the same conditions was also analyzed. The overall chemical composition of the cell wall from the three isolates showed detectable differences in their basic components, with a significant decrease in the protein content in fungicide-treated cells. This inhibitory effect was partially compensated by an increase in neutral and/or aminated carbohydrates and was accompanied by appreciable modifications of polysaccharide structure, as deduced after methylation analysis and gas-liquid chromatography-mass spectrometry (GLC-MS). Moreover, differences in hyphal morphology caused by the fungicide were observed by transmission electron microscopy (TEM). Accepted 2 May 2002 Electronic Publication     

In vivo genetic systems in lactic acid bacteria

Abstract A review of in vivo genetic systems covers the key features of transduction and conjugation but emphasises the intramolecular and intermolecular DNA interactions that are often associated with these processes. As well as the transfer of many lactose plasmids, conjugal transfer of nisin genes and the use of conjugation to construct bacteriophage-resistant dairy starter cultures are discussed. The discovery and characterization of insertion sequences in Lactobacillus and Lactococcus and the exploitation of heterologous conjugation and transposition systems in the lactic acid bacteria are described.