Hydrogen spillover has emerged as a possible technique for achieving high-density hydrogen storage at near-ambient conditions in lightweight, solid-state materials. We present a brief review of our ...combined theoretical and experimental studies on hydrogen spillover mechanisms in solid-state materials where, for the first time, the complete mechanisms that dictate hydrogen spillover processes in transition metal oxides and nanostructured graphitic carbon-based materials have been revealed. The spillover process is broken into three primary steps: (1) dissociative chemisorption of gaseous H2 on a transition metal catalyst; (2) migration of H atoms from the catalyst to the substrate and (3) diffusion of H atoms on substrate surfaces and/or in the bulk materials. In our theoretical studies, the platinum catalyst is modeled with a small Pt cluster and the catalytic activity of the cluster is examined at full H atom saturation to account for the essentially constant, high H2 pressures used in experimental studies of hydrogen spillover. Subsequently, the energetic profiles associated with H atom migrations from the catalyst to the substrates and H atom diffusion in the substrates are mapped out by calculating the minimum energy pathways. It is observed that the spillover mechanisms for the transition metal oxides and graphitic carbon-based materials are very different. Hydrogen spillover in the transition metal oxides is moderated by massive, nascent hydrogen bonding networks in the crystalline lattice, while H atom diffusion on the nanostructured graphitic carbon materials is governed mostly by physisorption of H atoms. The effects of carbon material surface curvature on the hydrogen spillover as well as on hydrogen desorption dynamics are also discussed. The proposed hydrogen spillover mechanism in carbon-based materials is consistent with our experimental observations of the solid-state catalytic hydrogenation/dehydrogenation of coronene.
Late Quaternary megafauna extinctions impoverished mammalian diversity worldwide. The causes of these extinctions in Australia are most controversial but essential to resolve, because this ...continent-wide event presaged similar losses that occurred thousands of years later on other continents. Here we apply a rigorous metadata analysis and new ensemble-hindcasting approach to 659 Australian megafauna fossil ages. When coupled with analysis of several high-resolution climate records, we show that megafaunal extinctions were broadly synchronous among genera and independent of climate aridity and variability in Australia over the last 120,000 years. Our results reject climate change as the primary driver of megafauna extinctions in the world's most controversial context, and instead estimate that the megafauna disappeared Australia-wide ∼13,500 years after human arrival, with shorter periods of coexistence in some regions. This is the first comprehensive approach to incorporate uncertainty in fossil ages, extinction timing and climatology, to quantify mechanisms of prehistorical extinctions.
Drinking water assessments use a variety of microbial, physical, and chemical indicators to evaluate water treatment efficiency and product water quality. However, these indicators do not allow the ...complex biological communities, which can adversely impact the performance of drinking water distribution systems (DWDSs), to be characterized. Entire bacterial communities can be studied quickly and inexpensively using targeted metagenomic amplicon sequencing. Here, amplicon sequencing of the 16S rRNA gene region was performed alongside traditional water quality measures to assess the health, quality, and efficiency of two distinct, full-scale DWDSs: (i) a linear DWDS supplied with unfiltered water subjected to basic disinfection before distribution and (ii) a complex, branching DWDS treated by a four-stage water treatment plant (WTP) prior to disinfection and distribution. In both DWDSs bacterial communities differed significantly after disinfection, demonstrating the effectiveness of both treatment regimes. However, bacterial repopulation occurred further along in the DWDSs, and some end-user samples were more similar to the source water than to the postdisinfection water. Three sample locations appeared to be nitrified, displaying elevated nitrate levels and decreased ammonia levels, and nitrifying bacterial species, such as Nitrospira, were detected. Burkholderiales were abundant in samples containing large amounts of monochloramine, indicating resistance to disinfection. Genera known to contain pathogenic and fecal-associated species were also identified in several locations. From this study, we conclude that metagenomic amplicon sequencing is an informative method to support current compliance-based methods and can be used to reveal bacterial community interactions with the chemical and physical properties of DWDSs.
Hydrogen spillover on the MoO3 (010) surface in the presence of a platinum catalyst was modeled using periodic density functional theory (DFT). The migration of H from a saturated Pt6 cluster to the ...MoO3 (010) surface was found to undergo a transition from repulsive electrostatic to attractive proton−oxygen interactions. The hydrogen is able to move nearly freely on the surface and diffuse into the bulk lattice at ambient temperatures, leading to the formation of hydrogen molybdenum bronze. We show that the high proton mobility is largely attributed to the massive H-bonding network in the MoO3 lattice.
High-Throughput DNA Sequencing (HTS) technologies have changed the way in which we detect and assess DNA contamination in ancient DNA studies. Researchers use computational methods to mine the large ...quantity of sequencing data to detect characteristic patterns of DNA damage, and to evaluate the authenticity of the results. We argue that unless computational methods can confidently separate authentic ancient DNA sequences from contaminating DNA that displays damage patterns under independent decay processes, prevention and control of DNA contamination should remain a central and critical aspect of ancient human DNA studies. Ideally, DNA contamination can be prevented early on by following minimal guidelines during excavation, sample collection and/or subsequent handling. Contaminating DNA should also be monitored or minimised in the ancient DNA laboratory using specialised facilities and strict experimental procedures. In this paper, we update recommendations to control for DNA contamination from the field to the laboratory, in an attempt to facilitate communication between field archaeologists, anthropologists and ancient DNA researchers. We also provide updated criteria of ancient DNA authenticity for HTS-based studies. We are confident that the procedures outlined here will increase the retrieval of higher proportions of authentic genetic information from valuable archaeological human remains in the future.
Heterogeneous catalysis in the aqueous phase is paramount to the catalytic conversion of renewable biomass resources to transportation fuels and useful chemicals. To gain fundamental insights into ...how the aqueous phase affects catalytic reactions over solid catalysts, vapor- and aqueous-phase acetic acid ketonization over a monoclinic zirconia (m-ZrO2) catalyst had been comparatively investigated using ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations. The monoclinic zirconia was modeled by the most stable ZrO2(1̅11) surface structure. The aqueous phase consisted of 111 explicit water molecules with a density of 0.93 g/cm3. The AIMD simulation results reveal that the aqueous phase/ZrO2(1̅11) interface is highly dynamic. At the typical reaction temperature of 550 K, ∼67% 6-fold-coordinated Zr6c Lewis acidic sites are occupied by either water molecules or hydroxyls, while all 2-fold-coordinated O2c sites are protonated as hydroxyls. As a result, it is expected that there are limited active sites on the ZrO2(1̅11) surface for acetic acid adsorption in the aqueous phase. Acetic acid ketonization on the ZrO2(1̅11) surface in both vapor and aqueous phases is assumed to be proceeded via the β-keto acid intermediate. In the vapor phase, an alternative Langmuir–Hinshelwood mechanism in which the neighboring coadsorbed acetic acid and dianion can directly combine together and form the CH3COOHCH2COO* intermediate is identified as the more feasible pathway than the traditional C–C coupling step via the combination of acyl and dianion. In the aqueous phase, our DFT results demonstrate that water molecules actively participate in the deprotonation and protonation steps via the Grotthuss proton transfer mechanism. Furthermore, our results suggest that an Eley–Rideal mechanism pathway for the formation of the β-keto acid intermediate is feasible in the aqueous phase on the basis of the observed energetic analysis. However, the low availability of dianion is also a key factor that inhibits the ketonization reaction in the aqueous phase. The effects of dynamic aqueous phase on the key surface reaction steps are further confirmed by sampling different reaction configurations from AIMD trajectories.
Studies of Antarctic eukaryotes have been hampered by their morphological conservatism, small size and the logistical constraints of remote field work, resulting in a deficiency of baseline ...biodiversity information about Antarctic terrestrial environments. The application of high throughput sequencing (HTS) in metataxonomic approaches is a promising alternative. Here, we apply such HTS approaches to the hitherto largely unsurveyed micro-eukaryote fauna of the Prince Charles Mountains, East Antarctica. We sequenced 18S rDNA amplicons of twelve Antarctic bulk-soil DNA extracts, retrieved from three sampling regions (four bulk-soil extracts per sampling region). After isolating eukaryotic phylotypes with a stringent filtering approach and initial network visualization, we firstly used rarefied data to compare four α diversity metrics between the three regions. Weighted and unweighted inter-sample UniFrac distances were then used for β diversity comparisons among rarefied data. Furthermore, we analysed the distribution of the most abundant phylotypes and phylotype groups. Lastly, we checked the validity of species-level taxonomic assignments using different sets of reference data in conjunction with two different taxonomy assignment approaches. Phylotype numbers in un-rarefied data compared across regions were lowest for Mount Menzies (73°S; 3330 m), intermediate at Mawson Escarpment (73°S; 807 m) and highest at Lake Terrasovoje (70°S; 173 m), likely due to low biological load at the higher latitude and elevation inland sites. Analysis of rarefied data was difficult due to low sequence coverage particularly from Mount Menzies, but indicated differences in Shannon diversity between Mawson Escarpment and Lake Terrasovoje. PCoA of weighted UniFrac distances between samples from Mawson Escarpment and Lake Terrasovoje indicated changes in community composition in relation to elevation of the sampling locations. The most widespread phylotypes were fungal, followed by non-algal protists. Species-level assignments included known Antarctic taxa in all sampling regions. We show that HTS can provide a rapid survey of the micro-eukaryote fauna to provide baseline biodiversity information for remote, harsh, and hitherto largely unsurveyed environments in the Prince Charles Mountains.
•Metagenomic approach used to survey eukaryotes in the Prince Charles Mountains, Antarctica.•Eukaryotic richness and distribution increased with a decrease in latitude and altitude.•Fungi and protists are among the most widespread taxa.•Species determination was possible for Antarctic lichen, fungi, mosses and protists.
Haplogroup H dominates present-day Western European mitochondrial DNA variability (>40%), yet was less common (~19%) among Early Neolithic farmers (~5450 BC) and virtually absent in Mesolithic ...hunter-gatherers. Here we investigate this major component of the maternal population history of modern Europeans and sequence 39 complete haplogroup H mitochondrial genomes from ancient human remains. We then compare this 'real-time' genetic data with cultural changes taking place between the Early Neolithic (~5450 BC) and Bronze Age (~2200 BC) in Central Europe. Our results reveal that the current diversity and distribution of haplogroup H were largely established by the Mid Neolithic (~4000 BC), but with substantial genetic contributions from subsequent pan-European cultures such as the Bell Beakers expanding out of Iberia in the Late Neolithic (~2800 BC). Dated haplogroup H genomes allow us to reconstruct the recent evolutionary history of haplogroup H and reveal a mutation rate 45% higher than current estimates for human mitochondria.
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