Polyvinylpyrrolidone-Coordinated Single-Site Platinum Catalyst Exhibits High Activity for Hydrogen Evolution Reaction.

The essence of developing a Pt-based single-atom catalyst (SAC) for hydrogen evolution reaction (HER) is the preparation of well-defined and stable single Pt sites with desired electrocatalytic efficacy. Herein, we report a facile approach to generate uniformly dispersed Pt sites with outstanding HER performance via a photochemical reduction method using polyvinylpyrrolidone (PVP) molecules as the key additive to significantly simplify the synthesis and enhance the catalytic performance. The as-prepared catalyst displays remarkable kinetic activities (20 times higher current density than the commercially available Pt/C) with excellent stability (76.3 % of its initial activity after 5000 cycles) for HER. EXAFS measurements and DFT calculations demonstrate a synergetic effect, where the PVP ligands and the support together modulate the electronic structure of the Pt atoms, which optimize the hydrogen adsorption energy, resulting in a considerably improved HER activity.

Microbial diversity of an Antarctic subglacial community and high-resolution replicate sampling inform hydrological connectivity in a polar desert.

Antarctic subglacial environments host microbial ecosystems and are proving to be geochemically and biologically diverse. The Taylor Glacier, Antarctica, periodically expels iron-rich brine through a conduit sourced from a deep subglacial aquifer, creating a dramatic red surface feature known as Blood Falls. We used Illumina MiSeq sequencing to describe the core microbiome of this subglacial brine and identified previously undetected but abundant groups including the candidate bacterial phylum Atribacteria and archaeal phylum Pacearchaeota. Our work represents the first microbial characterization of samples collected from within a glacier using a melt probe, and the only Antarctic subglacial aquatic environment that, to date, has been sampled twice. A comparative analysis showed the brine community to be stable at the operational taxonomic unit level of 99% identity over a decade. Higher resolution sequencing enabled deconvolution of the microbiome of subglacial brine from mixtures of materials collected at the glacier surface. Diversity patterns between this brine and samples from the surrounding landscape provide insight into the hydrological connectivity of subglacial fluids to the surface polar desert environment. Understanding subice brines collected on the surfaces of thick ice covers has implications for analyses of expelled materials that may be sampled on icy extraterrestrial worlds.

Genomic and physiological characterization and description of Marinobacter gelidimuriae sp. nov., a psychrophilic, moderate halophile from Blood Falls, an antarctic subglacial brine.

Antarctic subice environments are diverse, underexplored microbial habitats. Here, we describe the ecophysiology and annotated genome of a Marinobacter strain isolated from a cold, saline, iron-rich subglacial outflow of the Taylor Glacier, Antarctica. This strain (BF04_CF4) grows fastest at neutral pH (range 6-10), is psychrophilic (range: 0°C-20°C), moderately halophilic (range: 0.8%-15% NaCl) and hosts genes encoding potential low temperature and high salt adaptations. The predicted proteome suggests it utilizes fewer charged amino acids than a mesophilic Marinobacter strain. BF04_CF4 has increased concentrations of membrane unsaturated fatty acids including palmitoleic (33%) and oleic (27.5%) acids that may help maintain cell membrane fluidity at low temperatures. The genome encodes proteins for compatible solute biosynthesis and transport, which are known to be important for growth in saline environments. Physiological verification of predicted metabolic functions demonstrate BF04_CF4 is capable of denitrification and may facilitate iron oxidation. Our data indicate that strain BF04_CF4 represents a new Marinobacter species, Marinobacter gelidimuriae sp. nov., that appears well suited for the subglacial environment it was isolated from. Marinobacter species have been isolated from other cold, saline environments in the McMurdo Dry Valleys and permanently cold environments globally suggesting that this lineage is cosmopolitan and ecologically relevant in icy brines.

Development of a Mycobacterium smegmatis transposon mutant array for characterising the mechanism of action of tuberculosis drugs: Findings with isoniazid and its structural analogues.

The development of new drugs is required to control human tuberculosis (TB). This study examined whether drug hypersensitive mutants could be used to reveal novel aspects of the mechanism of action of a TB drug. A transposon mutant collection with an estimated 1.1-fold genome coverage (7680 mutants) was constructed in Mycobacterium smegmatis and screened in high-throughput against isoniazid. Hypersensitive transposants with mutations in genes known to influence the mode of action of isoniazid were isolated. To further investigate the role of one of these genes, nudC, the corresponding mutant was tested for sensitivity towards isoniazid structural analogues. Overexpression of nudC, as well as inhA which encodes a known target of isoniazid, increased M. smegmatis resistance to isoniazid, but failed to increase resistance to three of the analogues, NSC27607, NSC33759, and NSC40350. In contrast, overexpression of katG resulted in increased sensitivity to each of the isoniazid analogues tested including NSC27607, NSC33759, and NSC40350. This provides evidence that the latter isoniazid analogues are activated by KatG in a NudC-independent manner and that InhA may not be their primary target. In summary, characterisation of drug hypersensitive mutants detected genes involved in the mode of action of isoniazid. Furthermore, it identified isoniazid analogues which are resilient to both InhA- and NudC-dependent mechanisms of resistance.

Interaction energy and the shift in OH stretch frequency on hydrogen bonding for the H2O --> H2O, CH3OH --> H2O, and H2O --> CH3OH dimers.

The ability to use calculated OH frequencies to assign experimentally observed peaks in hydrogen bonded systems hinges on the accuracy of the calculation. Here we test the ability of several commonly employed model chemistries--HF, MP2, and several density functionals paired with the 6-31+G(d) and 6-311++G(d,p) basis sets--to calculate the interaction energy (D(e)) and shift in OH stretch fundamental frequency on dimerization (delta(nu)) for the H(2)O --> H(2)O, CH(3)OH --> H(2)O, and H(2)O --> CH(3)OH dimers (where for X --> Y, X is the hydrogen bond donor and Y the acceptor). We quantify the error in D(e) and delta(nu) by comparison to experiment and high level calculation and, using a simple model, evaluate how error in D(e) propagates to delta(nu). We find that B3LYP and MPWB1K perform best of the density functional methods studied, that their accuracy in calculating delta(nu) is approximately 30-50 cm(-1) and that correcting for error in D(e) does little to heighten agreement between the calculated and experimental delta(nu). Accuracy of calculated delta(nu) is also shown to vary as a function of hydrogen bond donor: while the PBE and TPSS functionals perform best in the calculation of delta(nu) for the CH(3)OH --> H(2)O dimer their performance is relatively poor in describing H(2)O --> H(2)O and H(2)O --> CH(3)OH.