Implementation of simultaneous ultraviolet/visible and x-ray absorption spectroscopy with microfluidics.

X-ray spectroscopies are uniquely poised to describe the geometric and electronic structure of metalloenzyme active sites under a wide variety of sample conditions. UV/Vis (ultraviolet/visible) spectroscopy is a similarly well-established technique that can identify and quantify catalytic intermediates. The work described here reports the first simultaneous collection of full in situ UV/Vis and high-energy resolution fluorescence detected x-ray absorption spectra.

No Bridge between Us: EXAFS and Computations Confirm Two Distant Iron Ions Comprise the Active Site of Alkane Monooxygenase (AlkB).

Alkane monooxygenase (AlkB) is the dominant enzyme that catalyzes the oxidation of liquid alkanes in the environment. Two recent structural models derived from cryo-electron microscopy (cryo-EM) reveal an unusual active site: a histidine-rich center that binds two iron ions without a bridging ligand. To ensure that potential photoreduction and radiation damage are not responsible for the absence of a bridging ligand in the cryo-EM structures, spectroscopic methods are needed.

Open-source electrochemical cell for in situ X-ray absorption spectroscopy in transmission and fluorescence modes.

X-ray spectroscopy is a valuable technique for the study of many materials systems. Characterizing reactions in situ and operando can reveal complex reaction kinetics, which is crucial to understanding active site composition and reaction mechanisms. In this project, the design, fabrication and testing of an open-source and easy-to-fabricate electrochemical cell for in situ electrochemistry compatible with X-ray absorption spectroscopy in both transmission and fluorescence modes are accomplished via windows with large opening angles on both the upstream and downstream sides of the cell.

Atomically Dispersed Zn/Co-N-C as ORR Electrocatalysts for Alkaline Fuel Cells.

Hydrogen fuel cells have drawn increasing attention as one of the most promising next-generation power sources for future automotive transportation. Developing efficient, durable, and low-cost electrocatalysts, to accelerate the sluggish oxygen reduction reaction (ORR) kinetics, is urgently needed to advance fuel cell technologies. Herein, we report on metal-organic frameworks-derived nonprecious dual metal single-atom catalysts (SACs) (Zn/Co-N-C), consisting of Co-N and Zn-N local structures.

High-Energy-Resolution X-ray Spectroscopy of Evolving Cu Nanoparticle Electrocatalysts for CO Reduction.

Advances in electrocatalysis research rely heavily on building a thorough mechanistic understanding of catalyst active sites under realistic operating conditions. Only recently have techniques emerged that enable sensitive spectroscopic data collection to distinguish catalytically relevant surface sites from the underlying bulk material under applied potential in the presence of an electrolyte layer. Here, we demonstrate that high-energy-resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) is a powerful spectroscopic method which offers critical surface chemistry insights in CO electroreduction with sub-electronvolt energy resolution using hard X-rays.

Fundamental mechanistic insights into the catalytic reactions of Li─S redox by Co single-atom electrocatalysts via operando methods.

Lithium-sulfur batteries represent an attractive option for energy storage applications. A deeper understanding of the multistep lithium-sulfur reactions and the electrocatalytic mechanisms are required to develop advanced, high-performance batteries. We have systematically investigated the lithium-sulfur redox processes catalyzed by a cobalt single-atom electrocatalyst (Co-SAs/NC) via operando confocal Raman microscopy and x-ray absorption spectroscopy (XAS).

Resonant Excitation Unlocks Chemical Selectivity of Platinum Lβ Valence-to-Core X-ray Emission Spectra.

Valence-to-core X-ray emission spectroscopy (VtC XES) is an emerging technique that uses hard X-rays to probe the valence electronic structure of an absorbing atom. Despite finding varied applications for light elements and first row transition metals, little work has been done on heavier elements such as second and third row transition metals. This lack of application is at least partially due to the relatively low resolution of the data at the high energies required to measure these elements, which obscures the useful chemical information that can be extracted from the lower energy, higher resolution spectra of lighter elements.

Operando studies reveal active Cu nanograins for CO electroreduction.

Carbon dioxide electroreduction facilitates the sustainable synthesis of fuels and chemicals. Although Cu enables CO-to-multicarbon product (C) conversion, the nature of the active sites under operating conditions remains elusive. Importantly, identifying active sites of high-performance Cu nanocatalysts necessitates nanoscale, time-resolved operando techniques.

Systematic assessment of DFT methods for geometry optimization of mononuclear platinum-containing complexes.

Platinum is used extensively as a catalyst for a wide variety of chemical reactions, though its scarcity and price present limitations to expansions of its use. To understand the origin of platinum's versatility-with the goals of both improving the efficiency of existing catalysts and mimicking its reactivity with more abundant metals-the mechanisms of platinum-catalyzed chemical reactions must be understood structural and spectroscopic characterization of these catalysts under conditions. Such data, typically consisting of complex mixtures of species, often prove challenging to interpret, inviting the aid of chemical theory.

Risks to different populations and age classes of gannets from impacts of offshore wind farms in the southern North Sea.

The southern North Sea holds the world's highest concentration of offshore wind farms (OWFs). Northern gannets (Morus bassanus), a species considered at high risk from OWF impacts, show a strong seasonal peak there in November, but it is unclear which populations and age classes are most at risk of collision with wind turbines. We tagged adult and juvenile gannets at the world's largest colony (Bass Rock) and reviewed two sources of survey data for different age classes to study their movements through southern North Sea waters.

X-ray Absorption Spectroscopy of PtNi-Nanowire/Vulcan XC-72R under Oxygen Reduction Reaction in Alkaline Media.

Studying the oxygen reduction reaction (ORR) in the alkaline electrolyte has proven to promote better catalytic responses and accessibility to commercialization. Ni-nanowires (NWs) were synthesized via the solvothermal method and modified with Pt using the spontaneous galvanic displacement method to obtain PtNi-NWs. Carbon Vulcan XC-72R (V) was used as the catalyst support, and they were doped with NH to obtain PtNi-NWs/V and PtNi-NWs/V-NH.

From theory to practice in pattern-oriented modelling: identifying and using empirical patterns in predictive models.

To robustly predict the effects of disturbance and ecosystem changes on species, it is necessary to produce structurally realistic models with high predictive power and flexibility. To ensure that these models reflect the natural conditions necessary for reliable prediction, models must be informed and tested using relevant empirical observations. Pattern-oriented modelling (POM) offers a systematic framework for employing empirical patterns throughout the modelling process and has been coupled with complex systems modelling, such as in agent-based models (ABMs).

Vulnerability of northern gannets to offshore wind farms; seasonal and sex-specific collision risk and demographic consequences.

There is a pressing need to quantify the risks of renewable energy developments such as offshore wind farms for protected populations. However, assessments are often based on incomplete data, or fail to consider variation in risk between sexes and at different times of year. We tracked northern gannets foraging from the world's largest colony (Bass Rock, Scotland) across five consecutive breeding seasons.

Correction: Sexual dichromatism in the neotropical genus Mannophryne (Anura: Aromobatidae).

[This corrects the article DOI: 10.1371/journal.pone.

Sexual dichromatism in the neotropical genus Mannophryne (Anura: Aromobatidae).

Recent reviews on sexual dichromatism in frogs included Mannophryne trinitatis as the only example they could find of dynamic dichromatism (males turn black when calling) within the family Aromobatidae and found no example of ontogenetic dichromatism in this group. We demonstrate ontogenetic dichromatism in M. trinitatis by rearing post-metamorphic froglets to near maturity: the throats of all individuals started as grey coloured; at around seven weeks, the throat became pale yellow in some, and more strongly yellow as development proceeded; the throats of adults are grey in males and variably bright yellow in females, backed by a dark collar.

High-resolution iron X-ray absorption spectroscopic and computational studies of non-heme diiron peroxo intermediates.

Ferritin-like carboxylate-bridged non-heme diiron enzymes activate O for a variety of difficult reactions throughout nature. These reactions often begin by abstraction of hydrogen from strong CH bonds. The enzymes activate O at their diferrous cofactors to form canonical diferric peroxo intermediates, with a range of possible coordination modes.

Evidence for Modulation of Oxygen Rebound Rate in Control of Outcome by Iron(II)- and 2-Oxoglutarate-Dependent Oxygenases.

Iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenases generate iron(IV)-oxo (ferryl) intermediates that can abstract hydrogen from aliphatic carbons (R-H). Hydroxylation proceeds by coupling of the resultant substrate radical (R•) and oxygen of the Fe(III)-OH complex ("oxygen rebound"). Nonhydroxylation outcomes result from different fates of the Fe(III)-OH/R• state; for example, halogenation results from R• coupling to a halogen ligand cis to the hydroxide.

Two-Color Valence-to-Core X-ray Emission Spectroscopy Tracks Cofactor Protonation State in a Class I Ribonucleotide Reductase.

Proton transfer reactions are of central importance to a wide variety of biochemical processes, though determining proton location and monitoring proton transfers in biological systems is often extremely challenging. Herein, we use two-color valence-to-core X-ray emission spectroscopy (VtC XES) to identify protonation events across three oxidation states of the O -activating, radical-initiating manganese-iron heterodinuclear cofactor in a class I-c ribonucleotide reductase. This is the first application of VtC XES to an enzyme intermediate and the first simultaneous measurement of two-color VtC spectra.

Structural Basis for Superoxide Activation of Flavobacterium johnsoniae Class I Ribonucleotide Reductase and for Radical Initiation by Its Dimanganese Cofactor.

A ribonucleotide reductase (RNR) from Flavobacterium johnsoniae ( Fj) differs fundamentally from known (subclass a-c) class I RNRs, warranting its assignment to a new subclass, Id. Its β subunit shares with Ib counterparts the requirements for manganese(II) and superoxide (O) for activation, but it does not require the O-supplying flavoprotein (NrdI) needed in Ib systems, instead scavenging the oxidant from solution. Although Fj β has tyrosine at the appropriate sequence position (Tyr 104), this residue is not oxidized to a radical upon activation, as occurs in the Ia/b proteins.

Vanadyl as a Stable Structural Mimic of Reactive Ferryl Intermediates in Mononuclear Nonheme-Iron Enzymes.

The iron(II)- and 2-(oxo)glutarate-dependent (Fe/2OG) oxygenases catalyze an array of challenging transformations via a common iron(IV)-oxo (ferryl) intermediate, which in most cases abstracts hydrogen (H•) from an aliphatic carbon of the substrate. Although it has been shown that the relative disposition of the Fe-O and C-H bonds can control the rate of H• abstraction and fate of the resultant substrate radical, there remains a paucity of structural information on the actual ferryl states, owing to their high reactivity. We demonstrate here that the stable vanadyl ion [(V-oxo)] binds along with 2OG or its decarboxylation product, succinate, in the active site of two different Fe/2OG enzymes to faithfully mimic their transient ferryl states.