Measurement of Microscopic Bridging Stresses in an Alumina/Molybdenum Composite by In Situ Fluorescence Spectroscopy

The R -curve behavior of an Al₂O₃ ceramic with 25 vol% of molybdenum-metal particles added was studied by using fracture-mechanics experiments and in situ piezospectroscopic measurements of microscopic bridging tractions. Cracks were propagated by using a crack stabilizer, which allowed stable crack growth in a bending geometry. Microscopic bridging stresses were measured in situ during fracture propagation by detecting the shift of the Cr³⁺ fluorescence lines of Al₂O₃. Laser spots ∼1 µm in diameter and ∼10 µm deep were focused at the ceramic/metal interface of the bridging sites, and the closure stresses that acted on the crack faces were recorded as a function of external load. The maximum stress that was experienced by the stretched metal particles prior to final failure was ∼0.4 GPa. The maximum stress magnitude was not markedly different in relatively small (i.e., <5 µm) metal particles, failing with large ductility, as compared with larger particles which, instead, fractured in semibrittle fashion. A map of bridging tractions along the crack wake was constructed under a constant stress intensity factor, almost equal to that which is critical for crack propagation. Using this map to theoretically predict the rising R -curve behavior of the composite led to results that were consistent with the fracture-mechanics experiments, thus enabling us to explain the observed toughening, primarily in terms of a crack-bridging mechanism.     

Grain-Boundary Viscosity of Polycrystalline Silicon Carbides

Internal friction experiments were conducted on three SiC polycrystalline materials with different microstructural characteristics. Characterizations of grain-boundary structures were performed by high-resolution electron microscopy (HREM). Observations revealed a common glass-film structure at grain boundaries of two SiC materials, which contained different amounts of SiO₂ glass. Additional segregation of residual graphite and SiO₂ glass was found at triple pockets, whose size was strongly dependent on the amount of SiO₂ in the material. The grain boundaries of a third material, processed with B and C addition, were typically directly bonded without any residual glass phase. Internal friction data of the three SiC materials were collected up to similar/congruent2200°C. The damping curves as a function of temperature of the SiO₂-bonded materials revealed the presence of a relaxation peak, arising from grain-boundary sliding, superimposed on an exponential-like background. In the directly bonded SiC material, only the exponential background could be detected. The absence of a relaxation peak was related to the glass-free grain-boundary structure of this polycrystal, which inhibited sliding. Frequency-shift analysis of the internal friction peak in the SiO₂-containing materials enabled the determination of the intergranular film viscosity as a function of temperature.     

Exosomal MicroRNAs as Potential Biomarkers of Hepatic Injury and Kidney Disease in Glycogen Storage Disease Type Ia Patients

Glycogen storage disease type Ia (GSDIa) is an inherited metabolic disorder caused by mutations in the enzyme glucose-6-phosphatase-α (G6Pase-α). Affected individuals develop renal and liver complications, including the development of hepatocellular adenoma/carcinoma and kidney failure. The purpose of this study was to identify potential biomarkers of the evolution of the disease in GSDIa patients. To this end, we analyzed the expression of exosomal microRNAs (Exo-miRs) in the plasma exosomes of 45 patients aged 6 to 63 years. Plasma from age-matched normal individuals were used as controls. We found that the altered expression of several Exo-miRs correlates with the pathologic state of the patients and might help to monitor the progression of the disease and the development of late GSDIa-associated complications.     

High-Light versus Low-Light: Effects on Paired Photosystem II Supercomplex Structural Rearrangement in Pea Plants

In plant grana thylakoid membranes Photosystem II (PSII) associates with a variable number of antenna proteins (LHCII) to form different types of supercomplexes (PSII-LHCII), whose organization is dynamically adjusted in response to light cues, with the C₂S₂ more abundant in high-light and the C₂S₂M₂ in low-light. Paired PSII-LHCII supercomplexes interacting at their stromal surface from adjacent thylakoid membranes were previously suggested to mediate grana stacking. Here, we present the cryo-electron microscopy maps of paired C₂S₂ and C₂S₂M₂ supercomplexes isolated from pea plants grown in high-light and low-light, respectively. These maps show a different rotational offset between the two supercomplexes in the pair, responsible for modifying their reciprocal interaction and energetic connectivity. This evidence reveals a different way by which paired PSII-LHCII supercomplexes can mediate grana stacking at diverse irradiances. Electrostatic stromal interactions between LHCII trimers almost completely overlapping in the paired C₂S₂ can be the main determinant by which PSII-LHCII supercomplexes mediate grana stacking in plants grown in high-light, whereas the mutual interaction of stromal N-terminal loops of two facing Lhcb4 subunits in the paired C₂S₂M₂ can fulfil this task in plants grown in low-light. The high-light induced accumulation of the Lhcb4.3 protein in PSII-LHCII supercomplexes has been previously reported. Our cryo-electron microscopy map at 3.8 Å resolution of the C₂S₂ supercomplex isolated from plants grown in high-light suggests the presence of the Lhcb4.3 protein revealing peculiar structural features of this high-light-specific antenna important for photoprotection.     

Raisins and Currants as Conventional Nutraceuticals in Italian Market: Natural Occurrence of Ochratoxin A

The healthy consumers make a strong pressure to natural products that can prevent the chronic diseases and improve the general health status, and therefore an important aspect that have to be considered is the safe level of the nutraceuticals. This study reports the occurrence of Ochratoxin A (OTA) and associated fungal contamination in 35 samples of dried vine fruits imported in the European community potentially used for the development of new nutraceutical supplements. High pressure liquid chromatography analysis identified 18 samples as contaminated by OTA with an average level of 2.6 μg/kg. OTA was measured in 4 samples of currants (mean value of 6.6 μg/kg) and 13 samples of raisins (mean value of 1.4 μg/kg). In one sample of currants and one of raisins from Turkey OTA exceeded the limits set by European Commission of 10 μg/kg, being contaminated with 12.61 and 15.99 μg/kg, respectively. All the positive samples were confirmed by Orbitrap Q Exactive through their molecular weight and the corresponding fragmentation. The worldwide consumption of dried vine fruits contributed to OTA exposure in several group of consumers. In particular, considering the potential nutraceutical approach, this consumption may be represent a severe risk for healthy consumers that consider these products like healthy and salutistic for their contents in antioxidants, flavonoids, and polyphenols. Data reported in this study confirmed the need to regularly monitor mycotoxin levels in these food products and optimize the process of fruits drying in order to reduce the development of toxigenic molds.     

Obesity and sleep disturbance: the chicken or the egg?

Epidemiological studies suggested an association between obesity and sleep disturbances. Obstructive sleep apnea is the most prevalent type of obesity-related sleep disorder that lead to an increased risk for numerous chronic health conditions. In addition the increased visceral adipose tissue might be responsible for the secretion of inflammatory cytokines that could contribute to alter the sleep-wake rhythm. Unhealthy food characterized by high consumption of fat and carbohydrate seems to negatively influence the quality of sleep while diet rich of fiber is associated to more restorative and deeper sleep. Although obesity could cause through several pathogenetic mechanisms an alteration of sleep, it has been reported that subjects suffering from sleep disorders are more prone to develop obesity. Experimental laboratory studies have demonstrated that decreasing either the amount or quality of sleep increase the risk of developing obesity. Experimental sleep restriction also causes physiological, hormonal and food behavioral changes that promote a positive energy balance and a compensatory disproportionate increase in food intake, decrease in physical activity, and weight gain. Thus, the aim of this review is to provide observational evidence on the association of obesity with sleep disturbances and viceversa with emphasis on possible pathophysiological mechanisms (hormonal and metabolic) that link these two pathological conditions.     

Synthesis,SAR, and Biological Evaluation of α‐Sulfonylphosphonic Acids as Selective Matrix Metalloproteinase Inhibitors

Selective MMP inhibitors : Eleven α‐sulfonylphosphonates were synthesized and tested as MMP inhibitors. The IC₅₀ values for most of them are in the nanomolar range against MMP‐2, ‐8, ‐13, and ‐14, with an interesting selectivity profile versus MMP‐9.