Search results for "Concentration."
showing 9 items of 1849 documents
Characteristics of acute toxicity dynamics of selected toxicants on aquatic crustaceans
2019
Determining the value of a half-effective or half-life concentration or dose of toxicant is the main purpose of acute toxicity studies, and this is also the most commonly used value in the toxicity characteristics of substances. By conducting tests that meet the criteria and requirements for the determination of acute toxicity, due to the use of appropriate mathematical tools and concentrations resulting in complete lethal effects in the studied groups, considerably more important values can be achieved, which give a possibility for the analysis of the entire process's dynamics, as well as determining the threshold values of the effect time and toxicant concentration. This was the purpose o…
Double copies of blaKPC-3::Tn4401a on an IncX3 plasmid in Klebsiella pneumoniae successful clone ST512 from Italy
2015
ABSTRACT A carbapenem-resistant sequence type 512 (ST512) Klebsiella pneumoniae carbapenemase 3 (KPC-3)-producing K. pneumoniae strain showing a novel variant plasmid content was isolated in Palermo, Italy, in 2014. ST512 is a worldwide successful clone associated with the spread of bla KPC genes located on the IncFIIk pKpQIL plasmid. In our ST512 strain, the bla KPC-3 gene was unusually located on an IncX3 plasmid, whose complete sequence was determined. Two copies of bla KPC-3 ::Tn 4401a caused by intramolecular transposition events were detected in the plasmid.
Acid–base properties of functionalised tripodal polyamines and their interaction with nucleotides and nucleic acids
2010
Novel, highly positively charged tripodal polyamines with appended heterocyclic moieties revealed an intriguing panel of protonation species within the biologically relevant range. Studied compounds bind nucleotide monophosphates by mostly electrostatic interactions but only the imidazole analogue showed selectivity toward UMP in respect to other nucleotides. Strong binding of all the studied compounds to both ds-DNA and ds-RNA is to some extent selective toward the latter, showing rather rare RNA over DNA preference.
Dipeptidyl Enoates As Potent Rhodesain Inhibitors That Display a Dual Mode of Action
2015
Dipeptidyl enoates were prepared through a high-yielding two-step synthetic route. They have a dipeptidic structure with a 4-oxoenoate moiety as a warhead with multiple reactive sites. Dipeptidyl enoates were screened against rhodesain and human cathepsins B and L, and were found to be potent and selective inhibitors of rhodesain. Among them (S,E)-ethyl 5-((S)-2-{[(benzyloxy)carbonyl]amino}-3-phenylpropanamido)-7-methyl-4-oxooct-2-enoate (6) was the most potent, with an IC50 value of 16.4 nm and kinact/Ki=1.6×106 m−1 s−1 against rhodesain. These dipeptidyl enoates display a reversible mode of inhibition at very low concentrations and an irreversible mode at higher concentrations. Inhibition…
Regulation of hdc expression and HDC activity by enological factors in lactic acid bacteria.
2008
Aims: The aim of this work was to study the influence of enological factors on the histidine decarboxylase gene (hdc) expression and on histidine decarboxylase enzyme (HDC) activity in Lactobacillus hilgardii, Pediococcus parvulus and Oenococcus oeni. Methods and Results: Cell extracts and whole cells were used. Glucose, fructose, malic acid and citric acid diminished the hdc expression. Ethanol did not increase hdc expression or activity in cells, but increased HDC activity. Temperature and pH had effect on the activity of HDC but not on hdc expression. Tartaric acid and l-lactic acid, and sulphur dioxide (SO2) had no effect on enzyme synthesis and activity. Bacterial species differ in t…
Antibacterial activity and cytotoxicity of selected Egyptian medicinal plants.
2011
Medicinal plants have been used as a source of remedies since ancient times in Egypt. The present study was designed to investigate the antibacterial activity and the cytotoxicity of the organic extracts from 16 selected medicinal plants of Egypt. The study was also extended to the isolation of the antiproliferative compound jaeschkeanadiol p-hydroxybenzoate (FH-25) from Ferula hermonis. The microbroth dilution was used to determine the minimal inhibitory concentration (MIC) of the samples against twelve bacterial strains belonging to four species, Providencia stuartii, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli, while a resazurin assay was used to assess the cytoto…
Structure and dynamics in liquid bismuth and Bin clusters: A density functional study
2014
Density functional/molecular dynamics simulations with more than 500 atoms have been performed on liquid bismuth at 573, 773, 923, and 1023 K and on neutral Bi clusters with up to 14 atoms. There are similar structural patterns (coordination numbers, bond angles, and ring patterns) in the liquid and the clusters, with significant differences from the rhombohedral crystalline form. We study the details of the structure (structure factor, pair, and cavity distribution functions) and dynamical properties (vibration frequencies, diffusion constants, power spectra), and compare with experimental results where available. While the three short covalent bonds typical to pnictogens are characteristi…
Short-term responses of Rana arvalis tadpoles to pH and predator stress: adaptive divergence in behavioural and physiological plasticity?
2022
Environmental stress is a major driver of ecological and evolutionary processes in nature. To cope with stress, organisms can adjust through phenotypic plasticity and/or adapt through genetic change. Here, we compared short-term behavioural (activity) and physiological (corticosterone levels, CORT) responses of Rana arvalis tadpoles from two divergent populations (acid origin, AOP, versus neutral origin, NOP) to acid and predator stress. Tadpoles were initially reared in benign conditions at pH 7 and then exposed to a combination of two pH (acid versus neutral) and two predator cue (predator cue versus no predator cue) treatments. We assessed behavioural activity within the first 15 min, an…
α-Conotoxins EpI and AuIB switch subtype selectivity and activity in native versus recombinant nicotinic acetylcholine receptors
2003
The Xenopus laevis oocyte expression system was used to determine the activities of alpha-conotoxins EpI and the ribbon isomer of AuIB, on defined nicotinic acetylcholine receptors (nAChRs). In contrast to previous findings on intracardiac ganglion neurones, alpha-EpI showed no significant activity on oocyte-expressed alpha3beta4 and alpha3beta2 nAChRs but blocked the alpha7 nAChR with an IC50 value of 30 nM. A similar IC50 value (103 nM) was obtained on the alpha7/5HT3 chimeric receptor stably expressed in mammalian cells. Ribbon AuIB maintained its selectivity on oocyte-expressed alpha3beta4 receptors but unlike in native cells, where it was 10-fold more potent than native alpha-AuIB, had…