Understanding the adsorption behavior of base probes in aluminosilicates and its relationship to the intrinsic acidity of Brønsted acid sites (BAS) is essential for the catalytic applications of ...these materials. In this study, we investigated the adsorption properties of base probe molecules with varying proton affinities (acetonitrile, acetone, formamide, and ammonia) within six different aluminosilicate frameworks (FAU, CHA, IFR, MOR, FER, and TON). An important objective was to propose a robust criterion for evaluating the intrinsic BAS acidity (i.e., state of BAS deprotonation). Based on the bond order conservation principle, the changes in the covalent bond between the aluminum and oxygen carrying the proton provide a good description of the BAS deprotonation state. The ammonia and formamide adsorption cause BAS deprotonation and cannot be used to assess intrinsic BAS acidity. The transition from ion-pair formation, specifically conjugated acid/base interaction, in formamide to strong hydrogen bonding in acetone occurs within a narrow range of base proton affinities (812-822 kJ mol
). The adsorption of acetonitrile results in the formation of hydrogen-bonded complexes, which exhibit a deprotonation state that follows a similar trend to the deprotonation induced by acetone. This allows for a semi-quantitative comparison of the acidity strengths of BAS within and between the different aluminosilicate frameworks.
Individuals with osteoporosis are predisposed to hip fracture during trips, stumbles or falls, but half of all hip fractures occur in those without generalised osteoporosis. By analysing ordinary ...clinical CT scans using a novel cortical thickness mapping technique, we discovered patches of markedly thinner bone at fracture-prone regions in the femurs of women with acute hip fracture compared with controls.
We analysed CT scans from 75 female volunteers with acute fracture and 75 age- and sex-matched controls. We classified the fracture location as femoral neck or trochanteric before creating bone thickness maps of the outer 'cortical' shell of the intact contra-lateral hip. After registration of each bone to an average femur shape and statistical parametric mapping, we were able to visualise and quantify statistically significant foci of thinner cortical bone associated with each fracture type, assuming good symmetry of bone structure between the intact and fractured hip. The technique allowed us to pinpoint systematic differences and display the results on a 3D average femur shape model.
The cortex was generally thinner in femoral neck fracture cases than controls. More striking were several discrete patches of statistically significant thinner bone of up to 30%, which coincided with common sites of fracture initiation (femoral neck or trochanteric).
Femoral neck fracture patients had a thumbnail-sized patch of focal osteoporosis at the upper head-neck junction. This region coincided with a weak part of the femur, prone to both spontaneous 'tensile' fractures of the femoral neck, and as a site of crack initiation when falling sideways. Current hip fracture prevention strategies are based on case finding: they involve clinical risk factor estimation to determine the need for single-plane bone density measurement within a standard region of interest (ROI) of the femoral neck. The precise sites of focal osteoporosis that we have identified are overlooked by current 2D bone densitometry methods.
The strength of Brønsted acid sites (BAS) affects the properties of 2D and hierarchical zeolites, but the relative contribution of internal and external BAS remains unknown. Accordingly, this study ...aims to assess the acidity of external and internal BAS in nanosponge-like MFI zeolites by comparatively analyzing hydrogen–deuterium exchange kinetics between zeolitic deuteroxyl groups and C2H6 molecules monitored by in-situ FTIR spectroscopy. For this purpose, (i) a sample pre-treatment procedure was specifically developed to deuterate only internal or only external acid sites using 2,6-di-tert-butylpyridine (DTBP) as a masking agent and (ii) DFT modeling of surface BAS was performed. Theoretical models of the thin MFI layer revealed that the external surface of MFI crystals contains three types of BAS: (i) BAS positioned in 5-membered rings, either shielded by silanol nests, rendering the site inaccessible for DTBP or yielding a very low adsorption energy for ethane, (ii) BAS pointing into the pores, due to the presence of aluminol, which hinders DTBP accessibility, or the BAS undergoes transformation to a three-coordinate aluminium site, and (iii) BAS accessible to both DTBP and ethane. The results from our kinetics measurements showed that H/D exchange at external BAS of nanosponge MFI zeolites is faster than at internal BAS (rate constants at 425 °C: 3.8 10−3 vs. 2.4 10−3 s−1 for external and internal BAS, respectively), but this cannot be attributed to the effect of diffusion. Therefore, the differences in exchange kinetics between external and internal BAS are given by mutual interplay of subtle differences in the corresponding activation barriers (113 vs. 117 kJ/mol for external and internal BAS, respectively) and pre-exponential terms (1.09 106 vs. 1.45 106 s−1 for external and internal BAS, respectively).
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•Treatment procedure to discriminate internal and external Brønsted acid sites proposed.•Three types of external Brønsted acid sites was described based on DFT modeling.•Strength of internal and external Brønsted acid sites is the same.
Purpose
Affinisol HPMC HME is a new popular form of hypromellose specifically designed for the hot melt extrusion and 3D printing of pharmaceutical products. However, reports of its thermal stability ...include only data obtained under inert N
2
atmosphere, which is not consistent with the common pharmaceutical practice. Therefore, detailed investigation of its real-life thermal stability in air is paramount for identification of potential risks and limitations during its high-temperature processing.
Methods
In this work, the Affinisol HPMC HME 15LV powder as well as extruded filaments will be investigated by means of thermogravimetry, differential scanning calorimetry and infrared spectroscopy with respect to its thermal stability.
Results
The decomposition in N
2
was proceeded in accordance with the literature data and manufacturer’s specifications: onset at ~260°C at 0.5°C·min
−1
, single-step mass loss of 90–95%. However, in laboratory or industrial practice, high-temperature processing is performed in the air, where oxidation-induced degradation drastically changes. The thermogravimetric mass loss in air proceeded in three stages: ~ 5% mass loss with onset at 150°C, ~ 70% mass loss at 200°C, and ~ 15% mass loss at 380°C. Diffusion of O
2
into the Affinisol material was identified as the rate-determining step.
Conclusion
For extrusion temperatures ≥170°C, Affinisol exhibits a significant degree of degradation within the 5 min extruder retention time. Hot melt extrusion of pure Affinisol can be comfortably performed below this temperature. Utilization of plasticizers may be necessary for safe 3D printing.
The zeolite activity in processes driven by Brønsted acid sites is determined by the distribution of the protons in the zeolite and strength of their interaction with the framework. This study aims ...to assess how much the transformation from three-dimensional (3D) bulk zeolite to its corresponding two-dimensional (2D) layered form changes the proton distribution and strength of the proton-framework interaction and thus how much it affects the zeolite Brønsted acid strength. Zeolites with three distinct topologies, MWW, PCR, and MFI, which form also layered analogues with considerably different thickness and silanol density were considered. To probe the Brønsted acidity of both 3D and 2D forms, an array of typical acidity descriptors (i.e., O-H stretching frequency, shift of O-H frequencies upon adsorption of CO probe molecule, C-O stretching frequencies and adsorption enthalpies of the CO adsorption complex) have been evaluated, employing both dispersion-corrected density functional theory and Fourier-transform infrared spectroscopy. Using these descriptors, the Brønsted acidity of 2D form is, on average, the same or just slightly lower than that of the 3D form. Transformation to layered form does affect the proton distribution and values of acidity descriptors for individual T sites, however, if all T sites are considered, the aggregate effect is almost negligible. Hence, these results suggest that a larger effect of the 3D -> 2D transformation can be expected for frameworks with fewer distinct T sites.
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•The Brønsted acidity of layered and bulk zeolites (MWW, MFI, PCR) is similar.•Proton distribution in layered and bulk zeolites is markedly different.•Brønsted acidity changes a lot for a particular T site but averages out for zeolite.•Concentration of bridging hydroxyls is high and changes from layered to bulk zeolite.
Uninterruptible power supplies (UPS), represented by lead-acid batteries, play an important role in various kinds of industries. They protect industrial technologies from being damaged by dangerous ...interruptions of an electric power supply. Advanced UPS monitoring performed by a complex battery management system (BMS) prevents the UPS from sustaining more serious damage due to its timely and accurate battery-fault detection based on voltage metering. This technique is very advanced and precise but also very expensive on a long-term basis. This article describes an experiment applying infrared thermographic measurements during a long term monitoring and fault detection in UPS. The assumption that the battery overheat implies its damaged state is the leading factor of our experiments. They are based on real measured data on various UPS battery sets and several statistical examinations confirming the high relevancy of the thermal features with mostly over 90% detection accuracy. Such a model can be used as a supplement for lead-acid battery based UPS monitoring to ensure their higher reliability under significantly lower maintenance costs.
Patients with hemophilia (PWH) develop hemophilic arthropathy of the major joints due to recurrent hemarthrosis. This study retrospectively estimated the age at which PWH may expect to develop ...hemophilic arthropathy and undergo joint replacement surgery.
Using retrospective data from PWH at a Czech orthopedic center, Kaplan Meier analyses were used to estimate the cumulative proportions of patients with hemophilic arthropathy and undergoing joint replacement surgery as a function of age.
Based on 1028 joint examinations in 167 PWH, hemophilic arthropathy of the knees, elbows, ankles and hips was estimated to develop by a median age of 48, 51, 52 and 61 years, respectively, with ≈80% of patients having such damage by ≈70 years of age. Hemophilic arthropathy of the shoulder occurred much later (median >80 years). In patients undergoing knee or hip replacement surgery, hemophilic arthropathy of the knee and hip occurred at a median age of ≈50 and ≈60 years, respectively, with replacement surgery occurring at a median of ≈70 and >75 years.
In PWH, the risk of developing hemophilic arthropathy accumulates continuously over the patient's lifetime, allowing predictions about the ages at which such damage and joint replacement surgery may occur.
The analysis of the BAS OH band in zeolites Rubeš, Miroslav; Trachta, Michal; Vaculík, Jan ...
Microporous and mesoporous materials,
August 2022, 2022-08-00, Letnik:
341
Journal Article
Recenzirano
The zeolite frameworks (FER, TON, CHA, and IFR) with a large diversity of the IR band shapes in the OH stretching region were investigated by combined use of FT-IR spectroscopy and DFT calculations. ...The analysis of various isolated Brønsted acid sites was performed with a model based on Boltzmann weighted relative energies and OH frequencies obtained by the ω/r correlation method. This approach has recently been used to reveal the non-statistical incorporation of aluminum into the H-MOR framework. The model correctly predicts the band shapes of H-FER and H-TON zeolites in the free OH region of the FT-IR spectra. For H-CHA and H-IFR, however, the mutual BAS interactions cannot be ignored even for high Si/Al ratios, which renders the concept of isolated BAS inadequate. Thus, the periodic calculations of adsorption and catalytic properties of zeotype frameworks should always be carried out with extended models mimicking real heteroatom distribution in these materials.
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•FER, TON, CHA, and IFR high-silica zeolites with a large diversity of the OH band shapes were investigated.•A combined use of FT-IR spectroscopy and periodic DFT calculations provided rationalization of observed spectral features.•Analysis of 44 different BAS in zeolites was carried out with the ω/r correlation method.•The statistical model of the BAS OH band in high-silica H-CHA was proposed based on empirical FF simulations.•Two mechanisms for the formation of free OH BAS in IFR were identified by analysis of 20 Al pairs at the DFT level.
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•Isotopic exchange reaction between deuterated hydroxyls and ethane was applied to scaling strength of Brønsted acid sites.•Temperature dependences of rate constants demonstrated a ...higher acid strength of Brønsted sites in MFI zeolite than in MWW.•D/H isotopic exchange could be proper approach for scaling the strength of acid sites, especially if acidity of zeolites is considered for hydrocarbons activation/conversion.
Acid site strength in MWW and MFI zeolites was investigated by isotopic exchange reaction between deuterated hydroxyl groups of zeolites and ethane molecules. The course of the reaction was monitored by FT-IR spectroscopy through time changes of integral intensities of the Si(OD)Al Brønsted acid sites represented by absorption bands at 2644, 2655, and 2657 cm−1 for MFI, MWW and MCM-36 zeolite, respectively. The rate of the reaction was described by pseudo first order kinetics and acid site strength was compared using rate constants characteristic of individual zeolites at constant temperature. The exchange reaction is significantly faster over MFI zeolite compared with MWW zeolites, suggesting a higher acid strength of Brønsted sites in MFI zeolite than in MWW. In our previous study (Arean et al. Phys. Chem. Chem. Phys. 16 (2014) 10,129), we found notable discrepancy in the relation between OH group frequency shift induced by adsorption of weak base molecules like CO and N2 and the change of adsorption enthalpy of these probe molecules for MWW zeolites, which calls into question the use of frequency shifts as a measure of acidity. Our reported results based on isotopic exchange reaction rate measurement correlate with the change of the probe molecules adsorption enthalpy involved in hydrogen bonding. Therefore, we believe that enthalpy change or H/D exchange activity measurement is more reliable method for assessment of acid strength than OH frequency shift probed by a weak base adsorbed at a low temperature.
The catalytic activity of zeolites is often related to their acid–base properties. In this work, the relationship between the value of apparent activation energy of ethanol dehydration, measured in a ...fixed bed reactor and by means of a temperature-programmed surface reaction (TPSR) depending on the amount of ethanol in the zeolite lattice and the value of activation energy of H/D exchange as a measure of acid–base properties of MFI and CHA zeolites, was studied. Tests in a fixed bed reactor were unable to provide reliable reaction kinetics data due to internal diffusion limitations and rapid catalyst deactivation. Only the TPSR method was able to provide activation energy values comparable to the activation energy values obtained from the H/D exchange rate measurements. In addition, for CHA zeolite, it has been shown that the values of ethanol dehydration activation energies depend on the amount of ethanol in the CHA framework, and this effect can be attributed to the substrate clustering effects supporting the deprotonation of zeolite Brønsted centers.
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