84 research outputs found

    Silver doped magnesium ferrite nanoparticles: Physico-chemical characterization and antibacterial activity

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    Spinel phases, with unique and outstanding physical properties, are attracting a great deal of interest in many fields. In particular, MgFe2O4, a partially inverted spinel phase, could find applications in medicine thanks to the remarkable antibacterial properties attributed to the generation of reactive oxygen species. In this paper, undoped and Ag-doped MgFe2-xAgxO4 (x = 0.1 and 0.3) nanoparticles were prepared using microwave-assisted combustion and sol–gel methods. X-ray powder diffraction, with Rietveld structural refinements combined with micro-Raman spectroscopy, allowed to determine sample purity and the inversion degree of the spinel, passing from about 0.4 to 0.7 when Ag was introduced as dopant. The results are discussed in view of the antibacterial activity towards Escherichia coli and Staphylococcus aureus, representative strains of Gram-negative and Gram-positive bacteria. The sol–gel particles were more efficient towards the chosen bacteria, possibly thanks to the nanometric sizes of metallic silver, which were well distributed in the powders and in the spinel phase, with respect to microwave ones, that, however, acquired antibacterial activity after thermal treatment, probably due to the nucleation of hematite, itself displaying wellknown antibacterial properties and which could synergistically act with silver and spinel

    Neutron capture measurement at the n TOF facility of the 204Tl and 205Tl s-process branching points

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    Neutron capture cross sections are one of the fundamental nuclear data in the study of the s (slow) process of nucleosynthesis. More interestingly, the competition between the capture and the decay rates in some unstable nuclei determines the local isotopic abundance pattern. Since decay rates are often sensible to temperature and electron density, the study of the nuclear properties of these nuclei can provide valuable constraints to the physical magnitudes of the nucleosynthesis stellar environment. Here we report on the capture cross section measurement of two thallium isotopes, 204Tl and 205Tl performed by the time-of-flight technique at the n TOF facility at CERN. At some particular stellar s-process environments, the decay of both nuclei is strongly enhanced, and determines decisively the abundance of two s-only isotopes of lead, 204Pb and 205Pb. The latter, as a long-lived radioactive nucleus, has potential use as a chronometer of the last s-process events that contributed to final solar isotopic abundances

    80Se(n,?) cross-section measurement at CERN n TOF

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    Radiative neutron capture cross section measurements are of fundamental importance for the study of the slow neutron capture (s-) process of nucleosynthesis. This mechanism is responsible for the formation of most elements heavier than iron in the Universe. Particularly relevant are branching nuclei along the s-process path, which are sensitive to the physical conditions of the stellar environment. One such example is the branching at 79^{79}Se (3.27 × 105^{5} y), which shows a thermally dependent ÎČ-decay rate. However, an astrophysically consistent interpretation requires also the knowledge of the closest neighbour isotopes involved. In particular, the 80^{80}Se(n,Îł) cross section directly affects the stellar yield of the "cold" branch leading to the formation of the s-only 82^{82}Kr. Experimentally, there exists only one previous measurement on 80^{80}Se using the time of flight (TOF) technique. However, the latter suffers from some limitations that are described in this presentation. These drawbacks have been significantly improved in a recent measurement at CERN n TOF. This contribution presents a summary of the latter measurement and the status of the data analysis

    Neutron capture measurement at the n TOF facility of the 204Tl and 205Tl s-process branching points

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    Neutron capture cross sections are one of the fundamental nuclear data in the study of the s (slow) process of nucleosynthesis. More interestingly, the competition between the capture and the decay rates in some unstable nuclei determines the local isotopic abundance pattern. Since decay rates are often sensible to temperature and electron density, the study of the nuclear properties of these nuclei can provide valuable constraints to the physical magnitudes of the nucleosynthesis stellar environment. Here we report on the capture cross section measurement of two thallium isotopes, 204^{204}Tl and 205^{205}Tl performed by the time-of-flight technique at the n TOF facility at CERN. At some particular stellar s-process environments, the decay of both nuclei is strongly enhanced, and determines decisively the abundance of two s-only isotopes of lead, 204^{204}Pb and 205^{205}Pb. The latter, as a long-lived radioactive nucleus, has potential use as a chronometer of the last s-process events that contributed to final solar isotopic abundances

    Effect of the inserted active-site-covering lid loop on the catalytic activity of a mutant B. subtilis γ-glutamyltransferase (GGT)

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    \u3b3-Glutamylpeptides are compds. derived from the acylation of an amino acid or a short peptide by the \u3b3-carboxyl carbon of the side chain of glutamic acid. Due to their altered chemico-phys. and organoleptic properties, they may be interesting substitutes or precursors of parent compds. used in pharmaceutical, dietetic and cosmetic formulations. Some of them are naturally occurring flavor enhancers or are endowed with biol. activities. Enzymic approaches to the synthesis of \u3b3-glutamyl derivs. based on the use of \u3b3-glutamyltransferases (GGTs, EC 2.3.2.2) have been proposed, which should be able to alleviate the problems connected with the troublesome and low-yielding extn. from natural sources or the non-economical chem. synthesis, which requires protection/deprotection steps. With the aim of overcoming the current limitations in the use of GGTs as biocatalysts, a mutant GGT was investigated. The mutant GGT was obtained by inserting the active-site-covering lid loop of the E. coli GGT onto the structure of B. subtilis GGT. With respect to the wild-type enzyme, the mutant showed a more demanding substrate specificity and a low hydrolase activity. These results represent an attempt to correlate the structural features of a GGT to its different activities. However, the ability of the mutant enzyme to catalyze the subsequent addn. of several \u3b3-glutamyl units, inherited by the parent B. subtilis GGT, still represents a limitation to its full application as a biocatalyst for preparative purposes. [on SciFinder(R)

    The structure of PghL hydrolase bound to its substrate poly-γ-glutamate

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    The identification of new strategies to fight bacterial infections in view of the spread of multiple resistance to antibiotics has become mandatory. It has been demonstrated that several bacteria develop poly-?-glutamic acid (?-PGA) capsules as a protection from external insults and/or host defence systems. Among the pathogens that shield themselves in these capsules are Bacillus\ua0anthracis, Francisella\ua0tularensis and several Staphylococcus strains. These are important pathogens with a profound influence on human health. The recently characterised ?-PGA hydrolases, which can dismantle the ?-PGA-capsules, are an attractive new direction that can offer real hope for the development of alternatives to antibiotics, particularly in cases of multidrug resistant bacteria. We have characterised in detail the cleaving mechanism and stereospecificity of the enzyme PghL (previously named YndL) from Bacillus\ua0subtilis encoded by a gene of phagic origin and dramatically efficient in degrading the long polymeric chains of ?-PGA. We used X-ray crystallography to solve the three-dimensional structures of the enzyme in its zinc-free, zinc-bound and complexed forms. The protein crystallised with a ?-PGA hexapeptide substrate and thus reveals details of the interaction which could explain the stereospecificity observed and give hints on the catalytic mechanism of this class of hydrolytic enzymes

    A mutant γ-glutamyltransferase with improved transpeptidase activity

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    Despite their potential applicative interest as biologically active compounds and as flavor enhancers, \u3b3-glutamyl derivatives are commercially underexploited compounds. This is mainly due to the difficulties connected with their supply at a reasonable cost. As a consequence, enzymatic approaches to their preparation, based on the use of \u3b3-glutamyltransferases (GGTs), have been proposed1 to circumvent both the low-yielding extractive procedures from natural sources and the troublesome chemical synthesis, rendered uneconomical by the need of protection and deprotection steps. GGTs catalyze the transfer of a \u3b3-glutamyl moiety from a donor substrate (e.g. glutathione or glutamine) to the primary amino group of an acceptor compound in a so-called transpeptidation reaction through the formation of a \u3b3-glutamyl-enzyme intermediate. However, also the use of GGTs as biocatalysts is not free from drawbacks. In addition to the transpeptidase activity, GGTs show a non-negligible hydrolase activity towards both the donor substrate and the newly formed transpeptidation product, affording irreversibly glutamic acid.2 In our ongoing studies on bacterial GGTs, we found that the presence of the lid loop \u2013 a short amino acids sequence covering the active site in most of the known GGTs \u2013 not only affects substrate selection, but also modulates hydrolase/transpeptidase activities.3 Within the TailGluTran Project,4 aimed at the development of mutant GGTs with improved transpeptidase activity, is currently under investigation a mutant enzyme obtained by inserting the sequence of the lid loop on the structure of a GGT naturally lacking it. The mutant enzyme shows promising high transpeptidase activity with respect to wild type counterparts and represents a starting point for further modifications in the search of a suitable biocatalyst intended for preparative purposes

    Data for the synthesis of oligo-gamma-glutamylglutamines as model compounds for gamma-glutamyltransferases (GGTs) and for normalization of activities of different GGTs

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    gamma-Glutamyltransferases (GGTs) are widespread, conserved enzymes that catalyze the transfer of the gamma-glutamyl moiety from a donor substrate to water (hydrolysis) or to an acceptor amino acid (transpeptidation) through the formation of a gamma-glutamyl enzyme intermediate. Although the vast majority of the known GGTs has a short sequence called lid-loop covering the glutamate binding site, B. subtilis GGT and some other enzymes from Bacillus spp. lack the lid loop. In order to assess the possible role of the lid loop of GGTs in substrate selection, synthetic oligo-gamma-glutamylglutamines containing up to three gamma-glutamyl residues were used as model substrates. The activities of the enzymes under investigation were standardized with respect to a common reaction to ensure comparable results. The activity of an engineered mutant enzyme containing the amino acid sequence of the lid loop from E. coli GGT inserted into the backbone of B. subtilis GGT was compared to that of the lid loop-deficient B. subtilis GGT and the lid loop-carrier E. coli GGT (Calvio, Romagnuolo, Vulcano, Speranza, Morelli Enz. Micr. Technol. 2018 [1]). Here we report the experimental procedures for the synthesis of model substrates gamma-glutamylglutamines through the method of the N-phtaloyl-L-glutamic acid anhydride and the spectral data of the synthetized compounds. The data obtained in the normalization procedure of the activities of the three enzymes are also reported
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