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Under operating conditions, the dynamics of water and ions confined within protonic aluminosilicate zeolite micropores are responsible for many of their properties, including hydrothermal stability, acidity and catalytic activity. However, due to high computational cost, operando studies of acidic zeolites are currently rare and limited to specific cases and simplified models. In this work, we have developed a reactive neural network potential (NNP) attempting to cover the entire class of acidic zeolites, including the full range of experimentally relevant water concentrations and Si/Al ratios. This NNP has the potential to dramatically improve sampling, retaining the (meta)GGA DFT level accuracy, with the capacity for discovery of new chemistry, such as collective defect formation mechanisms at the zeolite surface. Furthermore, we exemplify how the NNP can be used as a basis for further extensions/improvements which include data-efficient adoption of higher-level (hybrid) references via Δ-learning and the acceleration of rare event sampling via automatic construction of collective variables. These developments represent a significant step towards accurate simulations of realistic catalysts under operando conditions.

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The migration of atoms and small clusters is an important process in sub-nanometre scale heterogeneous catalysis, affecting activity, accessibility and deactivation through sintering. Control of migration can be partially achieved via encapsulation of sub-nanometre metal particles into porous media such as zeolites. However, a general understanding of the migration mechanisms and their sensitivity to particle size and framework environment is lacking. Here, we extend the time-scale and sampling of atomistic simulations of platinum cluster diffusion in siliceous zeolite frameworks, by introducing a reactive neural network potential of density functional quality. We observe that Pt atoms migrate in a qualitatively different manner from clusters, occupying the dense region of the framework and avoiding the free pore space. We also find that for cage-like zeolite CHA there exists a maximum in self diffusivity for the Pt dimer beyond which, confinement effects hinder intercage migration. By extending the quality of sampling, NNP-based methods allow for the discovery of novel dynamical processes at the atomistic scale, bringing modelling closer to operando experimental characterization of catalytic materials.

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[This corrects the article DOI: 10.1039/D3SC02492J.].

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Solid state (ss-) 27Al NMR is one of the most valuable tools for the experimental characterization of zeolites, owing to its high sensitivity and the detailed structural information which can be extracted from the spectra. Unfortunately, the interpretation of ss-NMR is complex and the determination of aluminum distributions remains generally unfeasible. As a result, computational modelling of 27Al ss-NMR spectra has grown increasingly popular as a means to support experimental characterization. However, a number of simplifying assumptions are commonly made in NMR modelling, several of which are not fully justified. In this work, we systematically evaluate the effects of various common models on the prediction of 27Al NMR chemical shifts in zeolites CHA and MOR. We demonstrate the necessity of operando modelling; in particular, taking into account the effects of water loading, temperature and the character of the charge-compensating cation. We observe that conclusions drawn from simple, high symmetry model systems such as CHA do not transfer well to more complex zeolites and can lead to qualitatively wrong interpretations of peak positions, Al assignment and even the number of signals. We use machine learning regression to develop a simple yet robust relationship between chemical shift and local structural parameters in Al-zeolites. This work highlights the need for sophisticated models and high-quality sampling in the field of NMR modelling and provides correlations which allow for the accurate prediction of chemical shifts from dynamical simulations.

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While the structures of Brønsted acid sites (BAS) in zeolites are well understood, those of Lewis acid sites (LAS) remain an active area of investigation. Under hydrated conditions, the reversible formation of framework-associated octahedral aluminum has been observed in zeolites in the acidic form. However, the structure and formation mechanisms are currently unknown. In this work, combined experimental 27 Al NMR spectroscopy and computational data reveal for the first time the details of the zeolite framework-associated octahedral aluminium. The octahedral LAS site becomes kinetically allowed and thermodynamically stable under wet conditions in the presence of multiple nearby BAS sites. The critical condition for the existence of such octahedral LAS appears to be the availability of three protons: at lower proton concentration, either by increasing the Si/Al or by ion-exchange to non-acidic form, the tetrahedral BAS becomes thermodynamically more stable. This work resolves the question about the nature and reversibility of framework-associated octahedral aluminium in zeolites.

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Professor RNDr. Petr Nachtigall, PhD passed away on 28 December 2022. He was an internationally recognized expert in computational materials science; working at Charles University in the Department of Physical and Macromolecular Chemistry. We honor his memory.

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Background: Measurement of salivary caffeine (1,3,7-trimethylpurine-2,6-dione or 1,3,7-trimethylxanthine) clearance can, in principle, be used to assess hepatic function, diagnose chronic hepatic disease and conduct investigations of substrates of hepatic cytochrome P450 (CYP) isozymes in children, without recourse to venepuncture. However, little is known about childhood sexual dimorphism of hepatic CYP isoforms. Furthermore, the association, if any, between salivary caffeine clearance and age in children has not hitherto been established. The aims of this study were to assess whether salivary caffeine clearance differs between boys and girls and whether it varies with age during childhood. Methods: Following at least 24 h' abstinence from dietary caffeine, nine boys (mean (standard error) age 9.6 (1.1) y) and eight girls (mean age 11.0 (1.2) y), none of whom was a smoker or suffered from chronic hepatic disease, ingested an oral caffeine dose titrated by body mass, namely 3 mg kg-1. Salivary samples collected two and 14 h later underwent spectrophotometric caffeine analysis. Results: The boys and the girls were age matched. The mean caffeine clearance in the boys was 2.47 (0.33) mL min-1 kg-1, while that in the girls was 2.20 (0.31) mL min-1 kg-1 (p = 0.56). The salivary caffeine clearance was negatively correlated with age (r = -0.59, p = 0.01). Conclusion: Stratification by sex appears to be unnecessary when considering childhood salivary caffeine clearance or when conducting investigations in children of CYP1A2 and xanthine oxidase substrates. Furthermore, childhood salivary caffeine clearance is negatively correlated with age.

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Supported metal nanoparticles are used as heterogeneous catalysts but often deactivated due to sintering at high temperatures. Confining metal species into a porous matrix reduces sintering, yet supports rarely provide additional stabilization. Here, we used the silanol-rich layered zeolite IPC-1P to stabilize ultra-small Rh nanoparticles. By adjusting the IPC-1P interlayer space through swelling, we prepared various architectures, including microporous and disordered mesoporous. In situ scanning transmission electron microscopy confirmed that Rh nanoparticles are resistant to sintering at high temperature (750 °C, 6 hrs). Rh clusters strongly bind to surface silanol quadruplets at IPC-1P layers by hydrogen transfer to clusters, while high silanol density hinders their migration based on density functional theory calculations. Ultimately, combining swelling with long-chain surfactant and utilizing metal-silanol interactions resulted in a novel, catalytically active material-Rh@IPC_C22.

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This paper explores the economic incentives for medical procedure innovation. Using a proprietary dataset on billing code applications for emerging medical procedures, we highlight two mechanisms that could hinder innovation. First, the administrative hurdle of securing permanent, reimbursable billing codes substantially delays innovation diffusion. We find that Medicare utilization of innovative procedures increases nearly nine-fold after the billing codes are promoted to permanent (reimbursable) from provisional (non-reimbursable). However, only 29 percent of the provisional codes are promoted within the five-year probation period. Second, medical procedures lack intellectual property rights, especially those without patented devices. When appropriability is limited, specialty medical societies lead the applications for billing codes. We indicate that the ad hoc process for securing billing codes for procedure innovations creates uncertainty about both the development process and the allocation and enforceability of property rights. This stands in stark contrast to the more deliberate regulatory oversight for pharmaceutical innovations.

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Ultrathin layers of oxides deposited on atomically flat metal surfaces have been shown to significantly influence the electronic structure of the underlying metal, which in turn alters the catalytic performance. Upscaling of the specifically designed architectures as required for technical utilization of the effect has yet not been achieved. Here, we apply liquid crystalline phases of fluorohectorite nanosheets to fabricate such architectures in bulk. Synthetic sodium fluorohectorite, a layered silicate, when immersed into water spontaneously and repulsively swells to produce nematic suspensions of individual negatively charged nanosheets separated to more than 60 nm, while retaining parallel orientation. Into these galleries oppositely charged palladium nanoparticles were intercalated whereupon the galleries collapse. Individual and separated Pd nanoparticles were thus captured and sandwiched between nanosheets. As suggested by the model systems, the resulting catalyst performed better in the oxidation of carbon monoxide than the same Pd nanoparticles supported on external surfaces of hectorite or on a conventional Al2 O3 support. XPS confirmed a shift of Pd 3d electrons to higher energies upon coverage of Pd nanoparticles with nanosheets to which we attribute the improved catalytic performance. DFT calculations showed increasing positive charge on Pd weakened CO adsorption and this way damped CO poisoning.

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Zeolites are among the most environmentally friendly materials produced industrially at the Megaton scale. They find numerous commercial applications, particularly in catalysis, adsorption, and separation. Under ambient conditions aluminosilicate zeolites are stable when exposed to water or water vapor. However, at extreme conditions as high temperature, high water vapor pressure or increased acidity/basicity, their crystalline framework can be destroyed. The stability of the zeolite framework under aqueous conditions also depends on the concentration and character of heteroatoms (other than Al) and the topology of the zeolite. The factors critical for zeolite (in)stability in the presence of water under various conditions are reviewed from the experimental as well as computational sides. Nonreactive and reactive interactions of water with zeolites are addressed. The goal of this review is to provide a comparative overview of all-silica zeolites, aluminosilicates and zeolites with other heteroatoms (Ti, Sn, and Ge) when contacted with water. Due attention is also devoted to the situation when partial zeolite hydrolysis is used beneficially, such as the formation of hierarchical zeolites, synthesis of new zeolites or fine-tuning catalytic or adsorption characteristics of zeolites.

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BACKGROUND: The salivary caffeine clearance is a non-invasive, safe, saliva-based method for assessing hepatic function and diagnosing chronic liver disease. The elimination of caffeine from the body follows first-order kinetics and principally involves catabolism by hepatic CYP1A2, with a half-life usually between three and 7 h. It is known that this process is affected by age and smoking tobacco. It has been suggested that sex might also be important, but there is scant evidence for this. The aim of this study was to assess whether there is a sex difference in salivary caffeine clearance in adults. METHODS: A cohort of 213 adults was studied. They were all non-smokers and none suffered from chronic liver disease. They consisted of 67 men (mean age 40.0 years) and 146 women (mean age 44.7 years). Following a period of dietary caffeine abstinence lasting at least 24 h, each subject ingested a single oral dose in the morning of caffeine, at a dose of 3 mg per kg body mass. Salivary samples were collected at 2 h and 14 h post-caffeine ingestion and were spectrophotometrically assayed for their caffeine concentrations. RESULTS: The two groups were matched for age. The mean (standard error) salivary caffeine clearance in the male subjects was 1.51 (0.10) mL min-1 kg-1, while that in the female subjects was 1.60 (0.07) mL min-1 kg-1 (p = 0.495). CONCLUSION: This relatively large study provides no evidence of a sex difference in salivary caffeine clearance.

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Aluminosilicate zeolites are traditionally used in high-temperature applications at low water vapour pressures where the zeolite framework is generally considered to be stable and static. Increasingly, zeolites are being considered for applications under milder aqueous conditions. However, it has not yet been established how neutral liquid water at mild conditions affects the stability of the zeolite framework. Here, we show that covalent bonds in the zeolite chabazite (CHA) are labile when in contact with neutral liquid water, which leads to partial but fully reversible hydrolysis without framework degradation. We present ab initio calculations that predict novel, energetically viable reaction mechanisms by which Al-O and Si-O bonds rapidly and reversibly break at 300 K. By means of solid-state NMR, we confirm this prediction, demonstrating that isotopic substitution of 17O in the zeolitic framework occurs at room temperature in less than one hour of contact with enriched water.

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The introduction of dopant atoms into metal nanoparticles is an effective way to control the interaction with adsorbate molecules and is important in many catalytic processes. In this work, experimental and theoretical evidence of the influence of Pd doping on the bonding between small cationic AuN+ clusters and CO is presented. The CO adsorption is studied by combining low-pressure collision cell reactivity and infrared multiple photon dissociation spectroscopy experiments with density functional theory calculations. Measured dissociation rates of cluster-CO complexes (N ≤ 21) allow the estimation of cluster-CO binding energies, showing that Pd doping increases the CO adsorption energy to an extent that is size-dependent. These trends are reproduced by theoretical calculations up to N = 13. In agreement with theory, measurements of the C-O vibrational frequency suggest that for the doped PdAuN-1+ (N = 3-5, 11) clusters, CO adsorbs on an Au atom, while for N = 6-10 and N = 12-14, CO interacts directly with the Pd dopant. A pronounced red-shifting of the C-O vibrational frequency is observed when CO interacts directly with the Pd dopant, indicating a significant back-donation of electron charge from Pd to CO. In contrast, the blue-shifted frequencies, observed when CO interacts with an Au atom, indicate that σ-donation dominates the Au-CO interaction. Studying such systems at the sub-nanometre scale enables a fundamental comprehension of the interactions between adsorbates, dopants and the host (Au) species at the atomic level.

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The common understanding of zeolite acidity is based on Löwenstein's rule, which states that Al-O-Al aluminium pairs are forbidden in zeolites. This rule is generally accepted to be inviolate in zeolites. However, recent computational research using a 0 K DFT model has suggested that the rule is violated for the acid form of several zeolites under anhydrous conditions [Fletcher et al., Chem. Sci., 8, (2017), 7483]. The effect of water loading on the preferred aluminium distribution in zeolites, however, has so far not been taken into account. In this article, we show by way of ab initio molecular dynamics simulations that Löwenstein's rule is obeyed under high water solvation for acid chabazite (H-CHA) but disobeyed under anhydrous conditions. We find that varying the water loading in the pores leads to dramatic effects on the structure of the active sites and the dynamics of solvation. The solvation of Brønsted protons in the surrounding water was found to be the energetic driving force for the preferred Löwenstein Al distribution and this driving force is absent in non-Löwenstein (Al-O(H)-Al) moieties. The preference for solvated protons further implies that the catalytically active species in zeolites is a protonated water cluster, rather than a framework Brønsted site. Hence, an accurate treatment of the solvation conditions is crucial to capture the behaviour of zeolites and to properly connect simulations to experiments. This work should lead to a change in modelling paradigm for zeolites, from single molecules towards high solvation models where appropriate.

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BACKGROUND: This study aimed to determine if intranasal dexmedetomidine is a superior pre-medication to oral midazolam in older, difficult children. METHODS: This was conducted as a prospective, single-blind randomized control trial in a tertiary care center. Seventy-five children, age >5 years and weight >20 kg, who needed general anesthesia for dental procedures were randomly assigned to be pre-medicated with either oral midazolam at a dose of 0.5 mg/kg (max 15 mg) or intranasal dexmedetomidine at a dose of 2 mcg/kg (max 100 mcg). The primary outcome studied was the patients' level of sedation when separated from their parents, which was assessed using a 5-point University of Michigan Sedation Scale. Secondary outcome studied was the level of anxiolysis assessed by the acceptance of mask induction using a 4-point scale. All assessments were made by one research person blinded to the study drug. RESULTS: The two groups were similar in age, sex, weight, pre-anesthetic behavior, time from pre-medication to anesthesia induction, and surgical time. A significantly higher proportion of patients who received dexmedetomidine had satisfactory sedation at separation from parents (69.4% vs 40.5%, P = .03) compared to those who received midazolam. There were no significant differences in the rate of acceptance of mask induction (80.6% vs 78.4%, P = 1.00). Intranasal dexmedetomidine was tolerated well when administered using a mucosal atomizer and without any clinically significant effect on heart rate or systolic blood pressure. CONCLUSIONS: Intranasal dexmedetomidine provides higher success rate in sedation and parental separation compared to oral midazolam, in older, difficult children.

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2D oxide nanomaterials constitute a broad range of materials, with a wide array of current and potential applications, particularly in the fields of energy storage and catalysis for sustainable energy production. Despite the many similarities in structure, composition, and synthetic methods and uses, the current literature on layered oxides is diverse and disconnected. A number of reviews can be found in the literature, but they are mostly focused on one of the particular subclasses of 2D oxides. This review attempts to bridge the knowledge gap between individual layered oxide types by summarizing recent developments in all important 2D oxide systems including supported ultrathin oxide films, layered clays and double hydroxides, layered perovskites, and novel 2D-zeolite-based materials. Particular attention is paid to the underlying similarities and differences between the various materials, and the subsequent challenges faced by each research community. The potential of layered oxides toward future applications is critically evaluated, especially in the areas of electrocatalysis and photocatalysis, biomass conversion, and fine chemical synthesis. Attention is also paid to corresponding novel 3D materials that can be obtained via sophisticated engineering of 2D oxides.

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An increased synergy between experimental and theoretical investigations in heterogeneous catalysis has become apparent during the last decade. Experimental work has extended from ultra-high vacuum and low temperature towards operando conditions. These developments have motivated the computational community to move from standard descriptive computational models, based on inspection of the potential energy surface at 0 K and low reactant concentrations (0 K/UHV model), to more realistic conditions. The transition from 0 K/UHV to operando models has been backed by significant developments in computer hardware and software over the past few decades. New methodological developments, designed to overcome part of the gap between 0 K/UHV and operando conditions, include (i) global optimization techniques, (ii) ab initio constrained thermodynamics, (iii) biased molecular dynamics, (iv) microkinetic models of reaction networks and (v) machine learning approaches. The importance of the transition is highlighted by discussing how the molecular level picture of catalytic sites and the associated reaction mechanisms changes when the chemical environment, pressure and temperature effects are correctly accounted for in molecular simulations. It is the purpose of this review to discuss each method on an equal footing, and to draw connections between methods, particularly where they may be applied in combination.

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BACKGROUND: Sedation regimes during oral procedures frequently associated with airway obstruction. The aim of this study was to define the association of Bispectral Index (BIS) to the depth of sedation and airway obstruction events. METHODS: Forty-seven patients between 14-21 years old, who were candidates for 3rd molar teeth extraction, were enrolled in this study. Patients received a total of 4 mg midazolam, 100 microgram fentanyl followed by titrated incremental propofol in 10 mg. The Richmond Agitation Sedation Score (RASS) was used to assess the depth of sedation. Each patient was attached to BIS monitor, while clinicians were not involved in the data collection process. Apnea, airway obstruction, O2 saturation, timing and interventions for controlling the situation were recorded. All data was synchronized with BIS data monitoring. RESULTS: The results show that 97.5% of cases were ASA 1 and 2, with average age of 17.3 years (±1.4) and a median BMI of 26.1. By using linear regression, for every unit decrease of median RASS (less than zero), there was 1.78 decrease in mean BIS Score (P=0.045, 95% CI: 0.08-3.47). The mean BIS Index (over 1 minute) with airway obstruction was 64 (±10.2), which was significantly lower than the BIS during non-airway obstruction (77±11.6), (P<0.001). By using logistic regression analysis, for every on unit increase in BIS Index, there is 24% decrease in odds in having airway obstruction (P=0.0009, 95% CI: 0.65-8.94). CONCLUSIONS: This study demonstrates that the BIS could potentially be a valid continuous monitoring method to avoid airway obstruction during sedation for patients undergoing dental surgery.

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