Iterative Bragg peak removal on X-ray absorption spectra with automatic intensity correction.

This study introduces a novel iterative Bragg peak removal with automatic intensity correction (IBR-AIC) methodology for X-ray absorption spectroscopy (XAS), specifically addressing the challenge of Bragg peak interference in the analysis of crystalline materials. The approach integrates experimental adjustments and sophisticated post-processing, including an iterative algorithm for robust calculation of the scaling factor of the absorption coefficients and efficient elimination of the Bragg peaks, a common obstacle in accurately interpreting XAS data, particularly in crystalline samples. The method was thoroughly evaluated on dilute catalysts and thin films, with fluorescence mode and large-angle rotation. The results underscore the technique's effectiveness, adaptability and substantial potential in improving the precision of XAS data analysis. While demonstrating significant promise, the method does have limitations related to signal-to-noise ratio sensitivity and the necessity for meticulous angle selection during experimentation. Overall, IBR-AIC represents a significant advancement in XAS, offering a pragmatic solution to Bragg peak contamination challenges, thereby expanding the applications of XAS in understanding complex materials under diverse experimental conditions.

Predicting a Sharp Decline in Selectivity for Catalytic Esterification of Alcohols from van der Waals Interactions.

Controlling the selectivity of catalytic reactions is a critical aspect of improving energy efficiency in the chemical industry; thus, predictive models are of key importance. Herein the performance of a heterogeneous, nanoporous Au catalyst is predicted for the complex catalytic self-coupling of the series of C2 -C4 alkyl alcohols, based solely on the known kinetics of the elementary steps of the catalytic cycle for methanol coupling, using scaling methods augmented by density functional theory. Notably, a sharp decrease in selectivity for ester formation with increasing molecular weight to favor the aldehyde due to van der Waals interactions of reaction intermediates with the surface was predicted and subsequently verified quantitatively by experiment. Further, the agreement between theory and experiment clearly demonstrates the efficacy of this approach for building a predictive model of catalytic behavior for a homologous set of reactants using a small set of experimental information.

New Architectures for Designed Catalysts: Selective Oxidation using AgAu Nanoparticles on Colloid-Templated Silica.

A highly modular synthesis of designed catalysts with controlled bimetallic nanoparticle size and composition and a well-defined structural hierarchy is demonstrated. Exemplary catalysts-bimetallic dilute Ag-in-Au nanoparticles partially embedded in a porous SiO2 matrix (SiO2 -Agx Auy )-were synthesized by the decoration of polymeric colloids with the bimetallic nanoparticles followed by assembly into a colloidal crystal backfilled with the matrix precursor and subsequent removal of the polymeric template. This work reports that these new catalyst architectures are significantly better than nanoporous dilute AgAu alloy catalysts (nanoporous Ag3 Au97 ) while retaining a clear predictive relationship between their surface reactivity with that of single-crystal Au surfaces. This paves the way for broadening the range of new catalyst architectures required for translating the designed principles developed under controlled conditions to designed catalysts under operating conditions for highly selective coupling of alcohols to form esters. Excellent catalytic performance of the porous SiO2 -Agx Auy structure for selective oxidation of both methanol and ethanol to produce esters with high conversion efficiency, selectivity, and stability was demonstrated, illustrating the ability to translate design principles developed for support-free materials to the colloid-templated structures. The synthetic methodology reported is customizable for the design of a wide range of robust catalytic systems inspired by design principles derived from model studies. Fine control over the composition, morphology, size, distribution, and availability of the supported nanoparticles was demonstrated.

Modelling analysis of the structure and porosity of covalent triazine-based frameworks.

Varying degrees of order have been found experimentally for a series of covalent triazine-based frameworks (CTFs) when synthesised under different reaction conditions. Here, we use molecular modelling to discuss the potential origins of this structural order by analysis of the node and strut building blocks. We use a combination of small model structures based on DFT optimised monomer units and more extended simulations using automated structure growth and molecular dynamics to discuss the influence of the strut structure on the local crystallinity of these materials.

Interrogating site dependent kinetics over SiO2-supported Pt nanoparticles.

A detailed knowledge of reaction kinetics is key to the development of new more efficient heterogeneous catalytic processes. However, the ability to resolve site dependent kinetics has been largely limited to surface science experiments on model systems. Herein, we can bypass the pressure, materials, and temperature gaps, resolving and quantifying two distinct pathways for CO oxidation over SiO2-supported 2 nm Pt nanoparticles using transient pressure pulse experiments. We find that the pathway distribution directly correlates with the distribution of well-coordinated (e.g., terrace) and under-coordinated (e.g., edge, vertex) CO adsorption sites on the 2 nm Pt nanoparticles as measured by in situ DRIFTS. We conclude that well-coordinated sites follow classic Langmuir-Hinshelwood kinetics, but under-coordinated sites follow non-standard kinetics with CO oxidation being barrierless but conversely also slow. This fundamental method of kinetic site deconvolution is broadly applicable to other catalytic systems, affording bridging of the complexity gap in heterogeneous catalysis.

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis.

Nanoparticle (NP) size and proximity are two physical descriptors applicable to practically all NP-supported catalysts. However, with conventional catalyst design, independent variation of these descriptors to investigate their individual effects on thermocatalysis remains challenging. Using a raspberry-colloid-templating approach, we synthesized a well-defined catalyst series comprising Pd12Au88 alloy NPs of three distinct sizes and at two different interparticle distances. We show that NP size and interparticle distance independently control activity and selectivity, respectively, in the hydrogenation of benzaldehyde to benzyl alcohol and toluene. Surface-sensitive spectroscopic analysis indicates that the surfaces of smaller NPs expose a greater fraction of reactive Pd dimers, compared to inactive Pd single atoms, thereby increasing intrinsic catalytic activity. Computational simulations reveal how a larger interparticle distance improves catalytic selectivity by diminishing the local benzyl alcohol concentration profile between NPs, thus suppressing its readsorption and consequently, undesired formation of toluene. Accordingly, benzyl alcohol yield is maximized using catalysts with smaller NPs separated by larger interparticle distances, overcoming activity-selectivity trade-offs. This work exemplifies the high suitability of the modular raspberry-colloid-templating method as a model catalyst platform to isolate individual descriptors and establish clear structure-property relationships, thereby bridging the materials gap between surface science and technical catalysts.

A transient flow reactor for rapid gas switching at atmospheric pressure.

Herein, we present a design for a transient flow reactor system with high detection sensitivity and minimal dead volume, such that it is capable of sub-second switching of the gas stream flowing through a catalytic bed. We demonstrate the reactor's capabilities for step transient, pulse, and stream oscillation experiments using the model system of CO oxidation over Pd catalysts, and we find that we are able to precisely model step transients for CO oxidation using a pseudo-homogenous-packed bed reactor model. The design principles leading to minimal gas hold-up time and increased sensitivity that are described in this paper can be implemented into existing flow reactor designs with minimal cost, providing a readily accessible alternative to the existing transient instrumentation.

Gas phase stabiliser-free production of hydrogen peroxide using supported gold-palladium catalysts.

Hydrogen peroxide synthesis from hydrogen and oxygen in the gas phase is postulated to be a key reaction step in the gas phase epoxidation of propene using gold-titanium silicate catalysts. During this process H2O2 is consumed in a secondary step to oxidise an organic molecule so is typically not observed as a reaction product. We demonstrate that using AuPd nanoparticles, which are known to have high H2O2 synthesis rates in the liquid phase, it is possible to not only oxidise organic molecules in the gas phase but to detect H2O2 for the first time as a reaction product in both a fixed bed reactor and a pulsed Temporal Analysis of Products (TAP) reactor without stabilisers present in the gas feed. This observation opens up possibility of synthesising H2O2 directly using a gas phase reaction.

Induction of the early-late Ddc gene during Drosophila metamorphosis by the ecdysone receptor.

During Drosophila metamorphosis, the 'early-late' genes constitute a unique class regulated by the steroid hormone 20-hydroxyecdysone. Their induction is comprised of both a primary and a secondary response to ecdysone. Previous work has suggested that the epidermal expression of the dopa decarboxylase gene (Ddc) is likely that of a typical early-late gene. Accumulation of the Ddc transcript is rapidly initiated in the absence of protein synthesis, which implies that the ecdysone receptor plays a direct role in induction. However, full Ddc expression requires the participation of one of the transcription factors encoded by the Broad-Complex. In this paper, we characterize an ecdysone response element (EcRE) that contributes to the primary response. Using gel mobility shift assays and transgenic assays, we identified a single functional EcRE, located at position -97 to -83 bp relative to the transcription initiation site. This is the first report of an EcRE associated with an early-late gene in Drosophila. Competition experiments indicated that the affinity of the Ddc EcRE for the ecdysone receptor complex was at least four-fold less than that of the canonical EcRE of the hsp27 gene. Using in vitro mutagenesis, we determined that the reduced affinity of the EcRE resided at two positions where the nucleotides differed from those found in the canonical sequence. The ecdysone receptor, acting through this EcRE, releases Ddc from a silencing mechanism, whose cis-acting domain we have mapped to the 5'-upstream region between -2067 and -1427 bp. Deletion of this repressive element resulted in precocious expression of Ddc in both epidermis and imaginal discs. Thus, epidermal Ddc induction at pupariation is under the control of an extended genomic region that contains both positive and negative regulatory elements.

Expression of tumor necrosis factor alpha and its mRNA in the spinal cord following a weight-drop injury.

The effect of traumatic spinal cord injury (SCI) on the expression of tumor necrosis factor (TNFalpha) and its mRNA was examined. Quantitative reverse transcription polymerase chain reaction assay showed TNFalpha mRNA level increased > 20-fold at the lesion site by 1 h after the injury compared to that in uninjured controls. The TNFalpha mRNA level was still significantly higher than in the controls 72 h after the injury. TNFalpha mRNA in the samples collected immediately caudal to the lesion site was also increased. Levels of TNFalpha protein, determined by a cytotoxic bioassay, were also significantly increased at the lesion site. The TNFalpha protein level was maximal 1 and 8 h after the injury and still significantly higher than in the controls 24 h post-injury. The present results demonstrate that TNFalpha is rapidly induced in the spinal cord after the injury, and it may play a significant role in secondary events in SCI.

Apolipoprotein E epsilon4 and catechol-O-methyltransferase alleles in autopsy-proven Parkinson's disease: relationship to dementia and hallucinations.

We determined whether apolipoprotein E epsilon4 (ApoE4) or catechol-O-methyltransferase (COMT) genotypes were associated with dementia, hallucinations, Alzheimer's disease pathological findings (AP), or cortical Lewy bodies (CLBs) in autopsy-confirmed cases of Parkinson's disease (PD). Outcomes were obtained from medical records. Pathology reports identified AP and CLBs. Brain tissue was genotyped. A total of 47 subjects (33 men, 14 women) had PD onset at 62.4 +/- 8.7 years of age and died at 77.8 +/- 5.6 years of age. Demented and hallucinating patients did not differ in age at onset (AO) of PD or age at death, or the proportion ApoE4+, AP+, or CLB+ compared to nondemented patients or non-hallucinating patients. ApoE4 and COMT (low metabolizer [LH], intermediate metabolizer [HL], or high metabolizer [HH]) did not influence AO, death, or dementia- or hallucination-free survival, based on age or duration of treatment. All seven subjects with AP were demented and had hallucinations. CLBs were associated with dementia but not hallucinations. In Cox regression models adjusting for AO and duration of treatment, increased risk of dementia was associated with male sex but not significantly with ApoE4; inclusion of AP in the model did not affect the results; COMT was not a risk factor for dementia. Psychosis risk was not associated with ApoE4, COMT, or sex. The observation that males have increased dementia risk and the trend for ApoE4 requires confirmation in larger prospective autopsy studies.