186,855 research outputs found
Isomerization of m-Xylene without Side Reactions, over a Perfluorinated Polymer Sulfonic Acid. A Kinetic Study
No full textA solid superacidic catalyst was obtained from the corresponding potassium salt (Nafion-K) and employed for studying the m-xylene isomerization in a fixed bed flow reactor. Temperature ranged from 143 to 173°C. A mixture of m-xylene with toluene, trimethylbenzenes, and 1,2,4,5-tetramethylbenzene, in ratios closely approaching the overall equilibrium between polymethylbenzene fractions, was fed in a nitrogen stream. Disproportionation reactions were thus avoided, a clean isomerization of m- to o- and p-xylene observed, and its kinetics measured. Since the catalyst deactivates, checks of its decreasing activity were performed at intervals and a correction of kinetic measurements devised, in order to evaluate the rate coefficients for a fresh catalyst
Expression of CYP153A6 in acetic acid bacteria allowed the production of carboxylic acids starting from alkanes
No full textEnzymatic hydroxylation mediated by cytochrome P450 monooxygenases has been extensively studied since only molecular oxygen and reducing equivalents from NAD(P)H are requested for the reaction, which often occurs with high chemo- and regioselectivity. Even if many genetic approaches have been developed for the functional expression of CYP450 (together with cofactor regeneration systems and alkane transporter1), low biocatalytic efficiency and low enzymatic stability were frequently reported. Here we present the development of genetically modified acetic acid bacteria (AAB) as biocatalysts for the functionalization of methyl groups in the allylic position of different terpene derivatives (e.g., limonene, carveol, carvone) and non-functionalized methyl groups of aromatic substrates (e.g., toluene, xylenes, p-cymene, p-ethyl toluene).
We engineered two acetic acid bacteria (AAB) strains (Acetobacter malorum and Komagataeibacter xylinus) with a plasmid (based on the pSEVA331Bb vector backbone) encoding for a limonene monoxygenase operon from Mycobacterium spp. 1, including genes for the expression of a CYP153A6, a ferredoxin and a ferredoxin reductase for cofactor recycling.
The resulting recombinant strains were able to hydroxylate different terpenes thanks to the monooxygenase activity and to further oxidize alcohols into the corresponding aldehydes and carboxylic acids, exploiting the action of the AAB’s unspecific membrane-bound alcohols (ADH) and aldehydes (ALDH) dehydrogenases2. Their activity towards (S)- and (R)-limonene was compared with a recombinant strain of E. coli expressing the same genes2: whereas the use of the E. coli strain allowed for the preparation of perillyl alcohol, recombinant AABs gave complete oxidation of both the enantiomers of limonene to perillic acid, with transient formation of perillyl alcohol and perillaldehyde
Functions of the haspin genes in the control of budding yeast cell cycle
No full textFunctions of the haspin genes in the control of budding yeast cell cycle Haspin is a serine/threonine kinase, originally identified in mouse and human cells. Haspin-like proteins have been found in all eukaryotic organisms, including yeast the Saccharomyces cerevisiae. In budding yeast there are two haspin-like homologues encoded by the genes ALK1 and ALK2, these two ORFs are previously uncharacterized. We identified Alk1 as an interactor of the DNA damage checkpoint protein Ddc1 in a two hybrid screening, also Alk2 interacts with Ddc1 in the same system. The first part of my thesis work consisted in the biochemical characterization of the Alk1 and Alk2 proteins and their cell cycle regulation. To gain some insight in the in vivo function of Alk1 and Alk2, we decided to use two classic genetic experimental approach: overexpression and deletion of ALK1 and ALK2 genes. While ALK1 overexpression does not affect cell cycle progression, the overexpression of ALK2 leads to accumulation of cells with a 2C DNA content and undivided nuclei. We found that cohesin cleavage induced by the TEV protease, bypasses these phenotypes. It is possible that Alk2 plays a direct action on the cohesin complex or, on the separase. Our results suggest, a role for Alk2 in the establishment of chromosomal cohesion, in the control of cohesin stability and in the regulation of separase. The second approach was based on a classical genetic analysis of deletion mutants. Dalk1 and Dalk2 strains did not show any sensitivity of single and double mutants to genotoxic agents, or defects in DNA damage checkpoint activation. Later, by analysing the phenotype of ALK2 overexpression, a mitotic role for Alk2 was emerged, and we thus decided to focus our attention on the role of Alk1 and Alk2 in mitosis. On plates Dalk1Dalk2 cells show sensitivity to benomyl treatment, this result orients our study on the role of haspins toward the spindle dynamics field. We first test the role of Alk1 and Alk2 in the regulation of the spindle checkpoint but our results seem to exclude a role for Alk1 and Alk2. We tested whether Dalk1Dalk2 cells are capable to re-assemble and re-orient the mitotic spindle correctly after microtubule depolymerization, in Dalk1Dalk2 cells this process seems to takes place with normal timing
TOUGH2-SEED: A COUPLED FLUID FLOW MECHANICAL-STATISTICAL MODEL FOR THE STUDY OF INJECTION-INDUCED SEISMICITY
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An alternative way to predict knowledge hiding: The lens of transformational leadership
No full textThe present study explores one of the biggest causes of the lack of organizational knowledge creation: knowledge hiding (KH). KH can be provoked by the deviant and detached behaviours of leaders and/or the motivations of employees. In this context, leaders assume a key role in reducing the effect of KH. Through the lens of transformational leadership (TL), a sample of 758 European SMEs with a total number of 2,232 employees operating in a knowledge-intensive sector is investigated. The scope is to evaluate the correlation between the three main characteristics of transformational leadership (i.e., trust, a collaborative environment, and the involvement of employees) and the phenomenon of KH through a logistic regression analysis. It emerges that TL can influence the organizational context and redefine the behaviours related to KH. In addition, empathic leadership can provide added value for companies since a collaborative environment and common objectives reduce the level of KH
[Breech presentation: relation between asphyxia and the method of delivery observed in 3 academic years]
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