One of the most interesting periods in the history of the Roman cavalry were the Punic wars. Many historians believe that during these conflicts the ill fame of the Roman cavalry was founded but, as ...it can be observed it was not the determination that lacked. The main issue is the presence of the political factor who decided in the main battles of this conflict. The present paper has as aim to outline a few aspects of how the Roman mid-republican cavalry met these odds and how they tried to incline the balance in their favor.
The physicochemical properties of rare-earth zirconates can be tuned by the rational modification of their structures and phase compositions. In the present work, La3+-, Nd3+-, Gd3+-, and ...Dy3+-zirconate nanostructured materials were prepared by different synthetic protocols, leading to powders, xerogels, and, for the first time, monolithic aerogels. Powders were synthesized by the co-precipitation method, while xerogels and aerogels were synthesized by the sol–gel technique, followed by ambient and supercritical drying, respectively. Their microstructures, thermogravimetric profiles, textural properties, and crystallographic structures are reported. The co-precipitation method led to dense powders (S BET < 1 m2 g–1), while the sol–gel technique resulted in large surface area xerogels (S BET = 144 m2 g–1) and aerogels (S BET = 168 m2 g–1). In addition, the incorporation of lanthanide ions into the zirconia lattice altered the crystal structures of the powders, xerogels, and aerogels. Single-phase pyrochlores were obtained for La2Zr2O7 and Nd2Zr2O7 powders and xerogels, while defect fluorite structures formed in the case of Gd2Zr2O7 and Dy2Zr2O7. All aerogels contain a mixture of cubic and tetragonal ZrO2 phases. Thus, a direct effect is shown between the drying conditions and the resulting crystalline phases of the nanostructured rare-earth zirconates.
N-oxides of N-heteroaromatic compounds find widespread applications in various fields of chemistry. Although the strictly planar aromatic structure of 1,10-phenanthroline (phen) is expected to induce ...unique features of the corresponding N-oxides, so far the potential of these compounds has not been explored. In fact, appropriate procedure has not been reported for synthesizing these derivatives of phen. Now, we provide a straightforward method for the synthesis of a series of mono-N-oxides of 1,10-phenanthrolines. The parent compounds were oxidized by a green oxidant, peroxomonosulfate ion in acidic aqueous solution. The products were obtained in high quality and at good to excellent yields. A systematic study reveals a clear-cut correlation between the basicity of the compounds and the electronic effects of the substituents on the aromatic ring. The UV spectra of these compounds were predicted by DFT calculations at the TD-DFT/TPSSh/def2-TZVP level of theory.
The imaging of non-conducting materials by scanning electron microscopy (SEM) is most often performed after depositing few nanometers thick conductive layers on the samples. It is shown in this work, ...that even a 5 nm thick sputtered gold layer can dramatically alter the morphology and the surface structure of many different types of aerogels. Silica, polyimide, polyamide, calcium-alginate and cellulose aerogels were imaged in their pristine forms and after gold sputtering utilizing low voltage scanning electron microscopy (LVSEM) in order to reduce charging effects. The morphological features seen in the SEM images of the pristine samples are in excellent agreement with the structural parameters of the aerogels measured by nitrogen adsorption-desorption porosimetry. In contrast, the morphologies of the sputter coated samples are significantly distorted and feature nanostructured gold. These findings point out that extra care should be taken in order to ensure that gold sputtering does not cause morphological artifacts. Otherwise, the application of low voltage scanning electron microscopy even yields high resolution images of pristine non-conducting aerogels.
Mesoporous aerogel microparticles are promising drug delivery systems. However, their in vivo biodistribution pathways and health effects are unknown. Suspensions of fluorescein-labeled ...silica–gelatin hybrid aerogel microparticles were injected into the peritoneum (abdominal cavity) of healthy mice in concentrations of 52 and 104 mg kg−1 in a 3-week-long acute toxicity experiment. No physiological dysfunctions were detected, and all mice were healthy. An autopsy revealed that the aerogel microparticles were not present at the site of injection in the abdominal cavity at the end of the experiment. The histological study of the liver, spleen, kidneys, thymus and lymphatic tissues showed no signs of toxicity. The localization of the aerogel microparticles in the organs was studied by fluorescence microscopy. Aerogel microparticles were not detected in any of the abdominal organs, but they were clearly visible in the cortical part of the parathymic lymph nodes, where they accumulated. The accumulation of aerogel microparticles in parathymic lymph nodes in combination with their absence in the reticuloendothelial system organs, such as the liver or spleen, suggests that the microparticles entered the lymphatic circulation. This biodistribution pathway could be exploited to design passive targeting drug delivery systems for flooding metastatic pathways of abdominal cancers that spread via the lymphatic circulation.
In present study the effect of iron (Fe) and manganese (Mn) contamination was assessed by modeling a freshwater food web of water, zooplankton (
Daphnia pulex
), and zebrafish (
Danio rerio
) under ...laboratory conditions. Metals were added to the rearing media of
D. pulex
, and enriched zooplankton was fed to zebrafish in a feeding trial. The elemental analysis of rearing water, zooplankton, and fish revealed significant difference in the treatments compared to the control. In
D. pulex
the Mn level increased almost in parallel with the dose of supplementation, as well as the Fe level differed statistically. A negative influence of the supplementation on the fish growth was observed: specific growth rate (SGR%) and weight gain (WG) decreased in Fe and Mn containing treatments. The redundancy analysis (RDA) of concentration data showed strong correlation between the rearing water and
D. pulex
, as well as the prey organism of Fe- and Mn-enriched
D. pulex
and the predator organism of
D. rerio
. The bioconcentration factors (BCF) calculated for water to zooplankton further proved the relationship between the Fe and Mn dosage applied in the treatments and measured in
D. pulex
. Trophic transfer factor (TTF) results also indicate that significant retention of the metals occurred in
D. rerio
individuals, however, in a much lower extent than in the water to zooplankton stage. Our study suggests that Fe and Mn significantly accumulate in the lower part of the trophic chain and retention is effective through the digestive track of zebrafish, yet no biomagnification occurs.
Graphical abstract
Fenton reactions with metal complexes of substituted porphyrins and hydrogen peroxide are useful tools for the mineralization of environmentally dangerous substances. In the homogeneous phase, ...autooxidation of the prophyrin ring may also occur. Covalent binding of porphyrins to a solid support may increase the lifetime of the catalysts and might change its activity. In this study, highly water-insoluble copper and iron complexes of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin were synthesized and bonded covalently to a very hydrophilic silica aerogel matrix prepared by co-gelation of the propyl triethoxysilyl-functionalized porphyrin complex precursors with tetramethoxysilane, followed by a supercritical carbon dioxide drying. In contrast to the insoluble nature of the porphyrin complexes, the as-prepared aerogel catalysts were highly compatible with the aqueous phase. Their catalytic activities were tested in the mineralization reaction of phenol, 3-chlorophenol, and 2,4-dichlorophenol with hydrogen peroxide. The results show that both aerogels catalyzed the oxidation of phenol and chlorophenols to harmless short-chained carboxylic acids under neutral conditions. In batch experiments, and also in a miniature continuous-flow tubular reactor, the aerogel catalysts gradually reduced their activity, due to the slow oxidation of the porphyrin ring. However, the rate and extent of the degradation was moderate and did not exclude the possibility that the as-prepared catalysts, as well as their more stable derivatives, might find practical applications in environment protection.
The mesoporous polyamide (PA) aerogel similar in chemical structure to DuPont's Kevlar is an advanced thermal insulation material tested in airspace applications. Unfortunately, the monolithic ...aerogel readily absorbs humidity (from moist air), which dramatically alters its mechanical properties. The compressive strength of the PA aerogel first increases when its water content increases, but subsequently decreases following additional hydration. To provide a coherent explanation for this non‐monotonic change, the aerogel is hydrated stepwise and its hydration mechanism is elucidated by multiscale experimental characterization. The molecular structure is investigated by solid‐state and liquid‐state nuclear magnetic resonance (NMR) spectroscopy, and the morphology by small angle neutron scattering (SANS) at each equilibrium hydration state. The physico‐chemical changes in the molecular level and in the nanoscale architecture are reconstructed. The first water molecules bind into the vacancies of the intermolecular H‐bonding network of the PA macromolecules, which strengthens this network and causes concerted morphological changes, leading to the macroscopic stiffening of the monolith. Additional water disrupts the original H‐bonding network of the macromolecules, which causes their increased segmental motion, marking the start of the partial dissolution of the nanosized fibers of the aerogel backbone. This eventually plasticizes the monolith.
Polyamide aerogel readily absorbs humidity from moist air, which dramatically alters its mechanical properties in a non‐monotonic manner. Young's modulus first increases with increasing water content, and subsequently decreases. The unique hydration mechanism of the aerogel accounts for this phenomenon. The presented results highlight the importance of understanding the hydration of advanced materials as a key factor altering their performance.
β-Tricalcium phosphate was combined with silica aerogel in composites prepared using the sol-gel technique and supercritical drying. The materials were used in this study to check their biological ...activity and bone regeneration potential with MG63 cell experiments. The composites were sintered in 100 °C steps in the range of 500-1000 °C. Their mechanical properties, porosities, and solubility were determined as a function of sintering temperature. Dissolution studies revealed that the released Ca-/P molar ratios appeared to be in the optimal range to support bone tissue induction. Cell viability, ALP activity, and type I collagen gene expression results all suggested that the sintering of the compound at approximately 700-800 °C as a scaffold could be more powerful in vivo to facilitate bone formation within a bone defect, compared to that documented previously by our research team. We did not observe any detrimental effect on cell viability. Both the alkaline phosphatase enzyme activity and the type I collagen gene expression were significantly higher compared with the control and the other aerogels heat-treated at different temperatures. The mesoporous silica-based aerogel composites containing β-tricalcium phosphate particles treated at temperatures lower than 1000 °C produced a positive effect on the osteoblastic activity of MG63 cells. An in vivo 6 month-long follow-up study of the mechanically strongest 1000 °C sample in rat calvaria experiments provided proof of a complete remodeling of the bone.
PDF
