Gas adsorption over zeolites is at the basis of important applications of this class of microporous crystalline solids, notably as separation media and catalysts, but it may also be complex and not ...straightforward to understand. Here we report that for temperature below 323 K propane adsorption on the small-pore pure-silica zeolite ITW exhibits a clear step (pseudosaturation). This is absent in the case of propene and the other small linear alkanes. An intermediate plateau, clearly observed in the 293 K isotherm, always occurs when one molecule of propane is loaded in every other cage, i.e., at half-saturation. The simulation results show a swelling of the ITW structure upon propane adsorption. The strong dependence of available pore volume on the adsorbate loading level implies that adsorption cannot occur on the void structure while saturation can only be reached on highly loaded structures. To account for this unprecedented adsorption phenomenon, we propose the term “guest-modulated effect”.
A sol-gel methodology has been duly developed in order to perform a controlled covalent coupling of tetrapyrrole macrocycles (e.g., porphyrins, phthalocyanines, naphthalocyanines, chlorophyll, etc.) ...to the pores of metal oxide networks. The resulting absorption and emission spectra intensities in the UV-VIS-NIR range have been found to depend on the polarity existing inside the pores of the network; in turn, this polarization can be tuned through the attachment of organic substituents to the tetrapyrrrole macrocycles before bonding them to the pore network. The paper shows clear evidence of the real possibility of maximizing fluorescence emissions from metal-free bases of substituted tetraphenylporphyrins, especially when these molecules are bonded to the walls of functionalized silica surfaces via the attachment of alkyl or aryl groups arising from the addition of organo-modified alkoxides.
Heavy doping changes an intrinsic semiconductor into a metallic conductor by the introduction of impurity states. However, Ga impurities in thermoelectric skutterudite CoSb3 with lattice voids ...provides an example to the contrary. Because of dual‐site occupancy of the single Ga impurity charge‐compensated compound defects are formed. By combining first‐principle calculations and experiments, we show that Ga atoms occupy both the void and Sb sites in CoSb3 and couple with each other. The donated electrons from the void‐filling Ga (GaVF) saturate the dangling bonds from the Sb‐substitutional Ga (GaSb). The stabilization of Ga impurity as a compound defect extends the region of skutterudite phase stability toward Ga0.15Co4Sb11.95 whereas the solid–solution region in other directions of the ternary phase diagram is much smaller. A proposed ternary phase diagram for Ga‐Co‐Sb is given. This compensated defect complex leads to a nearly intrinsic semiconductor with heavy Ga doping in CoSb3 and a much reduced lattice thermal conductivity (κL) which can also be attributed to the effective scattering of both the low‐ and high‐frequency lattice phonons by the dual‐site occupant Ga impurities. Such a system maintains a low carrier concentration and therefore high thermopower, and the thermoelectric figure of merit quickly increases to 0.7 at a Ga doping content as low as 0.1 per Co4Sb12 and low carrier concentrations on the order of 1019 cm−3.
Ga occupies both the void and Sb sites in CoSb3 which is proven by combining first‐principles calculations and experiments. The stabilization of the Ga impurity as a compound defect extends the region of skutterudite phase stability toward Ga0.15Co4Sb11.95, whereas the solid–solution region becomes much smaller in other directions of the phase diagram. This compensated defect complex leads to a nearly intrinsic semiconductor with low carrier concentration, and therefore high thermopower, which possesses a much reduced lattice thermal conductivity.
For zeolites synthesized using imidazolium cations, the organic matter can be extracted at very low temperatures (100 °C) using ozone. This is possible for zeolites with 12-ring or larger pores but ...requires higher temperatures in medium-pore zeolites. The first chemical events in this process occur fast, even at room temperature, and imply the loss of aromaticity likely by the formation of an adduct between ozone and the imidazole ring through carbons C4 and C5. Subsequent rupture of the imidazole ring provides smaller and more flexible fragments that can desorb more readily. This process has been studied experimentally, mainly through infrared spectroscopy, and theoretically by density functional theory. Amazingly, fluoride anions occluded in the small double-four-ring units (d4r) during the synthesis remain inside the cage throughout the whole process when the temperature is not too high (≤150 °C). However, fluoride in larger cages in MFI ends up bonded to silicon in penta or hexacoordinated units, likely out of the cages, after ozone treatment at 150 °C. For several germanosilicate zeolites, the process allows their subsequent degermanation to yield stable high-silica zeolites. Quaternary ammonium cations require harsher conditions that eventually also extract fluoride from zeolite cages, including the d4r unit.
We present the RUPTURA code (
https://github.com/iraspa/ruptura
) as a free and open-source software package (MIT license) for (1) the simulation of gas adsorption breakthrough curves, (2) mixture ...prediction using methods like the Ideal Adsorption Solution Theory (IAST), segregated-IAST and explicit isotherm models, and (3) fitting of isotherm models on computed or measured adsorption isotherm data. The combination with the RASPA software enables computation of breakthrough curves directly from adsorption simulations in the grand-canonical ensemble. RUPTURA and RASPA have similar input styles. IAST is implemented near machine precision but we also provide several explicit mixture prediction methods that are non-iterative and potentially faster than IAST. The code supports a wide variety of isotherm models like Langmuir, Anti-Langmuir, BET, Henry, Freundlich, Sips, Langmuir-Freundlich, Redlich-Peterson, Toth, Unilan, O'Brian & Myers, Asymptotic Temkin, and Bingel & Walton. The isotherm model parameters can easily be obtained by the fitting module. Breakthrough plots and animations of the column properties are automatically generated. In addition to highlighting the code, we also review all the developed techniques from literature for mixture prediction, breakthrough simulations, and isotherm model fitting, and provide a tutorial discussing the workflows.
Since the high incidence of aflatoxin M1 (AFM1) in milk and dairy products poses a serious risk to human health, this work aimed to investigate the complex formation between bovine α-lactalbumin ...(α-La) and AFM1 using different spectroscopic methods coupled with molecular docking studies. Fluorescence spectroscopy measurements demonstrated the AFM1 addition considerably reduced the α-La fluorescence intensity through a static quenching mechanism. The results indicated on the endothermic character of the reaction, and the hydrophobic interaction played a major role in the binding between AFM1 and α-La. The binding site stoichiometric value (n = 1.32) and a binding constant of 2.12 × 103 M−1 were calculated according to the Stern-Volmer equation. The thermodynamic parameters ΔH, ΔS and ΔGb were determined at 93.58 kJ mol−1, 0.378 kJ mol−1 K−1 and -19.17 ± 0.96 kJ mol−1, respectively. In addition, far-UV circular dichroism studies revealed alterations in the α-La secondary structures when the α-La-AFM1 complex was formed. An increased content of the α-helix structures (from 35 to 40%) and the β-sheets (from 16 to 19%) were observed. Furthermore, protein-ligand docking modelling demonstrated AFM1 could bind to the hydrophobic regions of α-La protein. Overall, the gathered results confirmed the α-La-AFM1 complex formation.
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•Interaction of AFM1 and α-La was studied by in vitro and in silico methods.•The formation of a complex between AFM1 and α-La by spectroscopy methods was demonstrated.•Thermodynamics parameters demonstrated that the interaction is hydrophobic.•The interaction of AFM1 with α-La causes ordering of its secondary structures.•Two possible binding sites for AFM1 on α-La was founded by molecular docking.
The energy of sprinkler irrigation drops splashing on the soil surface or the crop canopy depends on their size and velocity. The kinetic energy of sprinkler irrigation drops is a major factor ...degrading the soil surface. The effect of a growing maize canopy on sprinkler drop energy dissipation and water partitioning was analyzed. A field experiment was performed on a solid-set sprinkler irrigated plot cropped with maize. Measurements were performed at different locations and heights into the sprinkler layout. Tests were performed at five maize heights. At each maize height, drop population characteristics and pluviometry were measured above and below the maize canopy. Drop population was measured with an optical disdrometer. Catch-can devices were used to measure pluviometry. Solid-set sprinkler irrigation distributes water quite homogeneously, but drop characteristics largely differ between layout locations. The effect of the crop on drop characteristics intensified as the canopy height increased. The canopy cover reduced drop diameter more than it reduced drop velocity. As the canopy grew, its capacity to intercept and derive irrigation water to stemflow increased. The largest part of energy dissipation by the maize canopy took place in the top 1.5 m. A fully developed maize canopy reduced the drop kinetic energy reaching the soil to 13.6% of that reaching bare soil. As a management practice, in sensitive soils or in sprinkler systems applying water with high specific kinetic power, irrigation of bare soils should be avoided.
Here we develop a measure of functional connectivity describing the degree of covariability between a brain region and the rest of the brain. This measure is based on previous formulas for the mutual ...information (MI) between clusters of regions in the frequency domain. Under the current scenario, the MI can be given as a simple monotonous function of the multiple coherence and it leads to an easy visual representation of connectivity patterns. Computationally efficient formulas, adequate for short time series, are presented and applied to functional magnetic resonance imaging (fMRI) data measured in subjects (
N
=
34) performing a working memory task or being at rest. While resting state coherence in high (0.17–0.25 Hz) and middle (0.08–0.17 Hz) frequency intervals is bilaterally salient in several limbic and temporal areas including the insula, the amygdala, and the primary auditory cortex, low frequencies (<
0.08 Hz) have greatest connectivity in frontal structures. Results from the comparison between resting and N-back conditions show enhanced low frequency coherence in many of the areas previously reported in standard fMRI activation studies of working memory, but task related reductions in high frequency connectivity are also found in regions of the default mode network. Finally, potentially confounding effects of head movement and regional volume on MI are identified and addressed.
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