Abstract
Mucormycosis is a fungal infection caused by Mucorales, with a high mortality rate. However, only a few virulence factors have been described in these organisms. This study showed that ...deletion of
rfs
, which encodes the enzyme for the biosynthesis of rhizoferrin, a siderophore, in
Mucor lusitanicus
, led to a lower virulence in diabetic mice and nematodes. Upregulation of
rfs
correlated with the increased toxicity of the cell-free supernatants of the culture broth (SS) obtained under growing conditions that favor oxidative metabolism, such as low glucose levels or the presence of H
2
O
2
in the culture, suggesting that oxidative metabolism enhances virulence through rhizoferrin production. Meanwhile, growing
M. lusitanicus
in the presence of potassium cyanide, N-acetylcysteine, a higher concentration of glucose, or exogenous cAMP, or the deletion of the gene encoding the regulatory subunit of PKA (
pkaR1
), correlated with a decrease in the toxicity of SS, downregulation of
rfs
, and reduction in rhizoferrin production. These observations indicate the involvement of the cAMP-PKA pathway in the regulation of rhizoferrin production and virulence in
M. lusitanicus
. Moreover,
rfs
upregulation was observed upon macrophage interaction or during infection with spores in mice, suggesting a pivotal role of
rfs
in
M. lusitanicus
infection.
The abundance of pelagic
Sargassum
has increased in the Atlantic Ocean since 2011. Massive beaching of these algae causes environmental, socioeconomic, and human health problems in several countries ...in the Greater Caribbean and western Africa.
Sargassum
cleanup is expensive. Its valorization could reduce costs and impacts. The periodicity in landings, its high biomass, and the many bioactive compounds and minerals contained in these algae represent an opportunity for its use in animal feeding. A review of the existing literature regarding the chemical characteristics of
Sargassum
and the concentration of compounds to determine its potential use for animals used for human consumption is presented. The main findings are that these pelagic species have high amounts of fiber, salts, complex carbohydrates, and potentially toxic elements that limit their use in high quantities in animal nutrition. However,
Sargassum
also has minerals, trace elements, amino acids, fatty acids, and bioactive compounds that could benefit animal health if added as an ingredient at a concentration below 5%. Information gaps and recommendations for future research are presented.
Well-defined surface, such as surface of a single crystal, is being used to provide precise interpretation of catalytic processes, while the nanoparticulate model catalyst more closely represents the ...real catalysts that are used in industrial processes. Nanocrystal superlattice, which combines the chemical and physical properties of different materials in a single crystalline structure, is an ideal model catalyst, that bridge between conventional models and real catalysts. We identify the active sites for carbon monoxide (CO) oxidation on Au-FeO x catalysts by using Au-FeO x binary superlattices correlating the activity to the number density of catalytic contacts between Au and FeO x . Moreover, using nanocrystal superlattices, we propose a general strategy of keeping active metals spatially confined to enhance the stability of metal catalysts. With a great range of nanocrystal superlattice structures and compositions, we establish that nanocrystal superlattices are useful model materials through which to explore, understand, and improve catalytic processes bridging the gap between traditional single crystal and supported catalyst studies.
Well-defined surfaces of Pt have been extensively studied for various catalytic processes. However, industrial catalysts are mostly composed of fine particles (e.g., nanocrystals), due to the desire ...for a high surface to volume ratio. Therefore, it is very important to explore and understand the catalytic processes both at nanoscale and on extended surfaces. In this report, a general synthetic method is described to prepare Pt nanocrystals with various morphologies. The synthesized Pt nanocrystals are further purified by exploiting the “self-cleaning” effect which results from the “colloidal recrystallization” of Pt supercrystals. The resulting high-purity nanocrystals enable the direct comparison of the reactivity of the {111} and {100} facets for important catalytic reactions. With these high-purity Pt nanocrystals, we have made several observations: Pt octahedra show higher poisoning tolerance in the electrooxidation of formic acid than Pt cubes; the oxidation of CO on Pt nanocrystals is structure insensitive when the partial pressure ratio p O2/p CO is close to or less than 0.5, while it is structure sensitive in the O2-rich environment; Pt octahedra have a lower activation energy than Pt cubes when catalyzing the electron transfer reaction between hexacyanoferrate (III) and thiosulfate ions. Through electrocatalysis, gas-phase-catalysis of CO oxidation, and a liquid-phase-catalysis of electron transfer reaction, we demonstrate that high quality Pt nanocrystals which have {111} and {100} facets selectively expose are ideal model materials to study catalysis at nanoscale.
Magneto-plasmonic hybrid nanoparticles (HNPs) are promising for a large number for dual magneto-optical bioapplications. Gas-phase techniques offer a good alternative to chemical routes for the ...generation of tailored HNPs. Here, we present a novel method to synthesize ternary HNPs composed of multiple dumbbell-like FeAg cores encapsulated by an amorphous Si shell. The method involves a simultaneous sputtering of Fe, Ag and Si targets under controlled conditions. We demonstrate that the morphology and the size of the HNPs can be modulated by tuning experimental parameters such as the energy and the cooling rate, or the collision and coalescence processes experienced by the HNPs during their formation. We find that by increasing the residence time of the HNPs in the aggregation zone, we increase both the size of the HNPs, and the thickness of the Si shell. HNPs exhibit ferromagnetic behavior and show an enhanced, red-shifted, light absorption band due to the strong near-field coupling between the Ag cores and the Si shell. A mechanism of formation of these HNPs is suggested, combining the physico-chemical properties of the materials (Fe, Ag, Si) with the experimental conditions.
•Preparation of FeAg multicores NPs with Si shell by inert-gas-condensation method.•The size of NPs is increased by increasing their residence time in the aggregation zone.•Thicker Si shell improves protection against oxidation and inhibits NPs aggregation.•The increment of Si thickness induces an additional red-shift light absorption band.•Mechanism of formation based on the physico-chemical properties of Fe, Ag and Si.
Annealing is a valuable method for fine-tuning the ultrasmall magnetic properties of alloy nanoparticles (NPs) by controlling their sizes, modifying their surfaces, and affecting their magnetic ...interactions. Herein, we study the effect of moderate annealing (450 °C) on strongly interacting NiCr nanoparticle assemblies (0 ≤ atom % Cr ≤ 15) immediately after deposition. Concurrent temperature-dependent electron microscopy and magnetization data demonstrate the interplay of two competing factors, namely, enhanced particle aggregation and element-specific surface segregation, on the magnetic properties, with the former boosting and the latter suppressing them. Strong interparticle interactions can lead to a magnetic response different from that of superparamagnetic particles, namely, from canonical spin-glass (0 atom % Cr) to correlated spin-glass (5–15 atom % Cr) behavior below higher spin-glass transition temperatures T g (20–350 K). The observation of “high-field susceptibility” below cryogenic temperatures (≤20 K) is ascribed to the presence of inhomogeneity/defects caused by Cr segregation. This work emphasizes the necessity of taking into account the delicate balance of such competing factors to understand the magnetic properties of nanoparticulate samples.
Temperature‐dependent continuous‐excitation and time‐resolved photoluminescence are studied to probe carrier localization and recombination in nearly strain‐balanced m‐plane ...In0.09Ga0.91N/Al0.19Ga0.81N multi‐quantum wells grown by plasma‐assisted molecular‐beam epitaxy. An average localization depth of 21 meV is estimated for the undoped sample. This depth is much smaller than the reported values in polar structures and m‐plane InGaN quantum wells. As part of this study, temperature and magnetic field dependence of time‐resolved photoluminescence is performed. At 2 K, an initial fast decay time of ≈0.3 ns is measured for both undoped and doped structures. The undoped sample also exhibits a slow decay component with a time scale of 2.2 ns. The existence of two relaxation paths in the undoped structure can be attributed to different localization centers. The fast relaxation decays are relatively insensitive to external magnetic fields, while the slower relaxation time constant decreases significantly with increasing magnetic fields. The fast decay time scale in the undoped sample is likely due to indium fluctuations in the quantum well. The slow decay time may be related to carrier localization in the barriers. The addition of doping leads to a single fast decay time likely due to stronger exciton localization in the InGaN quantum wells.
Continuous‐excitation and time‐resolved photoluminescence are investigated in m‐plane InGaN/AlGaN multi‐quantum wells grown by plasma‐assisted molecular‐beam epitaxy. Dual localization centers are identified in undoped structures, while a single type of localization center is found in doped structures. Magnetic field dependence of time‐resolved photoluminescence at low temperatures reveals distinct properties of carrier localization in the wells and barriers.
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