Search

This work is aimed at exploring some pedagogical opportunities of using photographs in physics instruction. In our study, the photography has been used for eliciting and probing students' ideas regarding the physics of fluids in noninertial frames of reference and under conditions of equilibrium. The study involved a heterogeneous sample of 235 secondary school students, 41 physics students, and 48 physics teachers. They were presented with a photograph of a wine glass filled with liquid whose surface appeared inclined. The students were asked to comment on the reality of the phenomenon captured in the photograph, and the teachers were asked to predict the students' responses. The results showed that about half of the students had a complete or partially complete understanding of the physical ideas and that their practical and conceptual knowledge was not dependent on their education level or curriculum followed. Most of the respondents found the task interesting and relevant. The results indicate that the teachers' expectations regarding students' understanding of physics often significantly depart from reality. We suggest that physics teachers include some photography-based problems and discussions in their classes. This could encourage a broad participation of students with different levels of abilities. [ABSTRACT FROM AUTHOR]

Abstract: We report thermopower and resistivity measurements of an YbAl3 single crystal obtained by the “self-flux” method. Our data reveal Fermi liquid behavior up to T FL =35K. The Kondo temperature, T K ≈450K, was determined from the high temperature thermopower data. The characteristic temperature, T 0, extracted from the temperature slope of the thermopower in the Fermi liquid regime is higher than the T K. We discuss a possible explanation of the obtained energy scales of YbAl3. [Copyright &y& Elsevier]

In this article, a model is developed for the quantitative and calibration-free determination of the diameter and concentration of colloidal metal nanoparticles synthesized by laser ablation in water. The model is valid under the assumption that all the ablated material is converted into nanoparticles. This is proved by Mie theory under dipole approximation and the Beer–Lambert law using experimentally determined ablated crater volumes, size distributions and photoabsorbances. The novelty of the model is shown through the possibility of determining the diameter and concentration of nanoparticles by using only the volume (or mass) of the ablated crater and the UV–Vis photoabsorbance spectrum. It allows fast, accurate and simple quantitative analysis of colloidal metal nanoparticles without the use of electron microscopy, mass spectrometry or relevant experimental techniques. [ABSTRACT FROM AUTHOR]

Abstract Antimicrobial peptides (AMPs) are plausible candidates for the development of novel classes of antibiotics with a low tendency to elicit resistance. They often form lesions in the bacterial membrane making it hard for bacteria to develop permanent resistance. However, a potent antibacterial activity is often accompanied by excessive cytotoxicity towards host cells. Modifying known natural sequences, based on desirable biophysical properties, is expensive and time-consuming and often with limited success. 'Mutator' is a freely available web-based computational tool for suggesting residue variations that potentially increase a peptide's selectivity, based on the use of quantitative structure activity relationship (QSAR) criteria. Although proven to be successful, it has never been used to analyze multiple sequences simultaneously. Modifying the Mutator algorithm allowed screening of many sequences in the dedicated Database of Anuran Defense Peptides (DADP) and by implementing limited amino acid substitutions on appropriate candidates, propose 8 potentially selective AMPs called Dadapins. Two were chosen for testing, confirming the prediction and validating this approach. They were shown to efficiently inactivate bacteria by disrupting their membranes but to be non-toxic for host cells, as determined by flow cytometry and confirmed by atomic force microscopy (AFM). Graphical abstract Unlabelled Image Highlights • Mutator tool suggests subtle mutations on AMPs to increase selectivity index (SI). • This tool was modified for a simultaneous AMP analysis in a dedicated database. • This resulted in Dadapin peptides showing high selectivity towards bacteria. • The peptides are membrane active for bacterial cells but non-toxic to host cells. [ABSTRACT FROM AUTHOR]

Abstract Antimicrobial peptides (AMPs) are naturally produced, gene encoded molecules with a direct antimicrobial activity against pathogens, often also showing other immune-related properties. Anuran skin secretions are rich in bioactive peptides, including AMPs, and we have reported a novel targeted sequencing approach to identify novel AMPs simultaneously in different frog species, from small quantities of skin tissue. Over a hundred full-length peptides were identified from specimens belonging to five different Ranidae frog species, out of which 29 were novel sequences. Six of these were selected for synthesis and testing against a panel of Gram-negative and Gram-positive bacteria. One peptide, identified in Rana arvalis , proved to be a potent and broad-spectrum antimicrobial, active against ATCC bacterial strains and a multi-drug resistant clinical isolate. CD spectroscopy suggests it has a helical conformation, while surface plasmon resonance (SPR) that it may self-aggregate/oligomerize at the membrane surface. It was found to disrupt the bacterial membrane at sub-MIC, MIC and above-MIC concentrations, as observed by flow cytometry and/or visualized by atomic force microscopy (AFM). Only a limited toxicity was observed towards peripheral blood mononuclear cells (PBMC) with a more pronounced effect observed against the MEC-1 cell line. Graphical abstract Unlabelled Image Highlights • Targeted DNA sequencing allowed identifying 127 peptides in five Ranidae species. • Six peptides with diverse physico-chemical properties were selected for synthesis. • One peptide, from Rana arvalis , showed potent anti-staphylococcal activity. • It is membrane-active and may self-aggregate/oligomerize at the membrane surface. • Limited toxicity was observed against circulating human blood cells. [ABSTRACT FROM AUTHOR]

Abstract Quaternary ammonium compounds (QACs) are amphiphilic molecules displaying a broad-spectrum of antibacterial activity. QACs are commonly used antiseptics in industrial, home and hospital settings. Given the emergence of the QAC-resistant bacteria, there is an urgent need to design new QACs with good antimicrobial activity, able to escape the host resistance mechanism. Therefore, a series of QACs derived from quinuclidine-3-ol and an alkyl chain of variable length (QOH-C3 to -C14), was designed and synthesized. The antimicrobial potential of the new monoquaternary QACs was surveyed against seventeen strains of emerging food spoilage and pathogenic microorganisms, including clinical multidrug-resistant ESKAPE isolates. The QOH-C14 proved to have the strongest antimicrobial activity. It was highly active against all pathogens tested, particularly against the Gram-positive bacteria with minimal inhibitory concentrations (MICs) ranging from 0.06 to 3.9 μg/mL, and fungi exerting the MIC 90 between 0.12 and 3.9 μg/mL. The potency of QOH-C14, confirmed that alkyl chains are an important part of the structure with their lengths playing a critical role in bioactivity of these compounds. The atomic force microscopy images show the disruption of a cell membrane upon the treatment with QOH-C14. These results were additionally confirmed by flow cytometry and fluorescence microscopy. A relatively low toxicity toward healthy human cells underline that QOH-C14 has a potential as new QAC antimicrobial candidate. Graphical abstract Image 1 Highlights • A series of QACs based on naturally derived quinuclidine was synthesized and evaluated for antimicrobial activity. • Addition of alkyl chains longer than 10 carbon atoms dramatically affect antimicrobial potential of new compounds. • Derivative containing 14 carbon atoms in a side chain, QOH-C14 had the best antimicrobial potential. • Compound QOH-C14 is equally effective as a control, but slower acting in a first few hours of exposure. • The compound is targeting cell membrane and has lower toxicity toward healthy human cell lines than a control. [ABSTRACT FROM AUTHOR]

Increasing use of nano-enabled products provides many benefits in various industrial processes and medical applications, but it also raises concern about release of nanoparticles (NPs) into the environment and subsequent human exposure. While potential toxicity of individual NPs types has been well described in scientific literature, exposure and health-related effects of nanomixtures has been poorly described. This study aimed to evaluate the combined effect of silver (AgNP) and polystyrene NPs (PSNP) on the human macrophages. AgNP are one of the most commercialized NPs due to efficient antimicrobial activity, while PSNP are ubiquitous in terrestrial and aquatic environments due to plastic pollution and degradation of polystyrene-based products. Differentiated monocytic cell line THP-1 were used as an in vitro model of human macrophages. Multiple aspects of cellular response to AgNP-PSNP nanomixture were analyzed including cell death, induction of apoptosis, oxidative stress response, expression of pro- and anti-inflammatory cytokines, and nanomechanical properties of cells. NPs uptake was visualized by confocal microscopy and quantified using flow cytometry. Results show that nanomixture increased apoptosis and cell death, expression of IL-6, IL-8 and TNFa, oxidative stress and mitochondrial dysfunction in cells compared to AgNP and PSNP applied as single treatments, indicating mixture additive action. Anti-inflammatory cytokines IL1b, IL-4 and IL-10 were not affected by combined exposure compared to single NPs. Visualization of NPs uptake and internalization showed that AgNP and PSNP were localized mostly in cytoplasm, with small fraction of AgNP translocated into cell nuclei, which explain increased number of double-stranded DNA breaks following exposure of cells to AgNPs alone or in the mixture. Study outcomes represent clear warnings on the human co-exposure to AgNP and PSNP that needs to be implemented in risk assessment approaches towards toxic-free environment. [Display omitted] • Response of human macrophages to nanomixture was evaluated. • Nanomixture consisted of silver (AgNP) and polystyrene nanoparticles (PSNP). • Nanomixture showed increased toxicity compared to AgNP and PSNP. • Nanomixture increased oxidative stress, apoptosis and inflammatory response in macrophages. [ABSTRACT FROM AUTHOR]

Abstract: We report on the resistivity and thermopower measurements together with the microstructural investigations of two highly concentrated alloys of the U x Y1−x Ru2Si2 alloy system, for x =0.5 and x =0.67, nominally. Microstructural analysis shows the existence of two different crystalline phases at the room temperature: the solid solution U c Y1−c Ru2Si2 (c < x) phase and the phase which can be represented by chemical formula URu2Si. We show that the uranium single ions dissolved in the YRu2Si2 matrix exhibit the ordinary or single-channel Kondo effect described by the Coqblin–Schrieffer Hamiltonian. In the light of the obtained results, the URu2Si2 compound is discussed. [Copyright &y& Elsevier]

• Myticalins are proline-rich antimicrobial peptides (PrAMPs) of mussel. • Unlike other PrAMPs, myticalins kill bacteria permeabilizing their membranes. • Myticalins permeablize bacteria without adopting secondary structures. • These peptides are potent antimicrobials but display also cytotoxic effect. • Myticalins may protect the gills of the mussels from pathogens. Bivalve mollusks are continuously exposed to potentially pathogenic microorganisms living in the marine environment. Not surprisingly, these filter-feeders developed a robust innate immunity to protect themselves, which includes a broad panel of antimicrobial peptides. Among these, myticalins represent a recently discovered family of linear cationic peptides expressed in the gills of Mytilus galloprovincialis. Even though myticalins and insect and mammalian proline-rich antimicrobial peptides (PrAMPs) share a similar amino acid composition, we here show that none of the tested mussel peptides use a non-lytic mode of action relying on the bacterial transporter SbmA. On the other hand, all the tested myticalins perturbed and permeabilized the membranes of E. coli BW25113, as shown by flow-cytometry and atomic force microscopy. Circular dichroism spectra revealed that most myticalins did not adopt recognizable secondary structures in the presence of amphipathic environments, such as biological membranes. To explore possible uses of myticalins for biotech, we assessed their biocompatibility with a human cell line. Non-negligible cytotoxic effects displayed by myticalins indicate that their optimization would be required before their further use as lead compounds in the development of new antibiotics. [ABSTRACT FROM AUTHOR]

[Display omitted] • New benzylimidazole QACs with long alkyl chains were synthesized and investigated. • The BnI-14 derivative showed the most promising antimicrobial potential. • The mode of action investigation indicate that BnI-14 induces membrane damage. • BnI-14 binds to DNA suggesting that membrane might not be the only target of QACs. • The low toxicity toward human cells identifies BnI-14 as new potential QACs. Quaternary ammonium compounds (QACs) are antimicrobial agents displaying a broad spectrum of activity due to their mechanism of action targeting the bacterial membrane. The emergence of bacterial resistance to QACs, especially in times of pandemics, requires the continuous search for new and potent QACs structures. Here we report the synthesis and biological evaluation of QACs based on imidazole derivative, N -benzylimidazole. The antimicrobial activity was tested against a range of pathogenic bacteria and fungi, both ATCC and clinical isolates, showing varying activities ranging in minimal inhibitory concentrations (MICs) from as low as 7 ng/mL. The most promising compound, N -tetradecyl derivative (BnI-14), proved to be very potent against bacterial biofilms, even at sub-MIC doses, suggesting interference with the bacterial growth and/or division process. The BnI-14 treatment induces bacterial membrane disruption, as observed by fluorescence spectroscopy and atomic force microscopy and it also binds to DNA indicating that bacterial membrane might not be the only cellular target of QACs. Most importantly, BnI-14 exhibits low toxicity to healthy human cell lines, suggesting that N -benzylimidazolium-based QACs may be promising new antimicrobial agents. [ABSTRACT FROM AUTHOR]

We aim to elucidate the mode of antibacterial action of the laser-synthesized silver colloid against Escherichia coli. Membrane integrity was studied by flow cytometry, while the strain viability of the treated culture was determined by plating. The spectrofluorometry was used to obtain the time development of the reactive oxygen species (ROS) inside the nanoparticle-treated bacterial cells. An integrated atomic force and bright-field/fluorescence microscopy system enabled the study of the cell morphology, Young modulus, viability, and integrity before and during the treatment. Upon lethal treatment, not all bacterial cells were shown to be permeabilized and have mostly kept their morphology with an indication of cell lysis. Young modulus of untreated cells was shown to be distinctly bimodal, with randomly distributed softer parts, while treated cells exhibited exponential softening of the stiffer parts in time. Silver nanoparticles and bacteria have shown a masking effect on the raw fluorescence signal through absorbance and scattering. The contribution of cellular ROS in the total fluorescence signal was resolved and it was proven that the ROS level inside the lethally treated cells is not significant. It was found that the laser-synthesized silver nanoparticles mode of antibacterial action includes reduction of the cell's Young modulus in time and subsequently the cell leakage. [ABSTRACT FROM AUTHOR]