Structural basis for the conformational protection of nitrogenase from O.

The low reduction potentials required for the reduction of dinitrogen (N) render metal-based nitrogen-fixation catalysts vulnerable to irreversible damage by dioxygen (O). Such O sensitivity represents a major conundrum for the enzyme nitrogenase, as a large fraction of nitrogen-fixing organisms are either obligate aerobes or closely associated with O-respiring organisms to support the high energy demand of catalytic N reduction. To counter O damage to nitrogenase, diazotrophs use O scavengers, exploit compartmentalization or maintain high respiration rates to minimize intracellular O concentrations.

O Activation and Enzymatic C-H Bond Activation Mediated by a Dimanganese Cofactor.

Dioxygen (O) is a potent oxidant used by aerobic organisms for energy transduction and critical biosynthetic processes. Numerous metalloenzymes harness O to mediate C-H bond hydroxylation reactions, but most commonly feature iron or copper ions in their active site cofactors. In contrast, many manganese-activated enzymes─such as glutamine synthetase and isocitrate lyase─perform redox neutral chemical transformations and very few are known to activate O or C-H bonds.

O Cleavage at a Preorganized Triiron Cluster.

In Nature, the four-electron reduction of O is catalyzed at preorganized multimetallic active sites. These complex active sites often feature low-coordinate, redox-active metal centers precisely positioned to facilitate rapid O activation processes that obviate the generation of toxic, partially reduced oxygen species. Very few biomimetic constructs simultaneously recapitulate the complexity and reactivity of these biological cofactors.

scRNA-seq identifies unique macrophage population in murine model of ozone induced asthma exacerbation.

Ozone (O ) inhalation triggers asthmatic airway hyperresponsiveness (AHR), but the mechanisms by which this occurs are unknown. Previously, we developed a murine model of dust mite, ragweed, and (DRA)-induced allergic lung inflammation followed by O exposure for mechanistic investigation. The present study used single cell RNA-sequencing for unbiased profiling of immune cells within the lungs of mice exposed to DRA, O , or DRA+O , to identify the components of the immune cell niche that contribute to AHR.

Demonstration of a 263-GHz Traveling Wave Tube for Electron Paramagnetic Resonance Spectroscopy.

In this letter, a 263 GHz traveling wave tube for electron paramagnetic resonance spectroscopy is designed, fabricated and tested. A periodic permanent magnet focused pencil beam electron optical system is adopted. A folded waveguide slow-wave structure with modified serpentine bends is optimized to provide high-power wideband performance and stable operation.

Iron homo- and heterobimetallic complexes supported by a symmetrical dinucleating ligand.

The selective synthesis of biomimetic Fe/Mn complexes able to mimic the geometry and catalytic activity of enzymes possessing this cofactor is still a challenge. Herein, we discuss the stepwise synthesis, characterization, and magnetic properties of a Fe(II)/Mn(II) species and related Fe(II)/Fe(II) complexes.

Threonine Aldolase-Catalyzed Enantioselective α-Alkylation of Amino Acids through Unconventional Photoinduced Radical Initiation.

Visible light-driven pyridoxal radical biocatalysis has emerged as a promising strategy for the stereoselective synthesis of valuable noncanonical amino acids (ncAAs). Previously, the use of well-tailored photoredox catalysts represented the key to enable efficient pyridoxal phosphate (PLP) enzyme-catalyzed radical reactions. Here, we report a PLP-dependent threonine aldolase-catalyzed asymmetric α-C-H alkylation of abundant amino acids using Katritzky pyridinium salts as alkylating agents.

The H-cluster of [FeFe] Hydrogenases: Its Enzymatic Synthesis and Parallel Inorganic Semisynthesis.

ConspectusNature's prototypical hydrogen-forming catalysts─hydrogenases─have attracted much attention because they catalyze hydrogen evolution at near zero overpotential and ambient conditions. Beyond any possible applications in the energy sphere, the hydrogenases feature complicated active sites, which implies novel biosynthetic pathways. In terms of the variety of cofactors, the [FeFe]-hydrogenase is among the most complex.

Innate immune responses are increased in children with acute asthma exacerbation.

Background: Little is known about the immune responses during acute asthma exacerbation. In this study, we examined immune responses in children following an acute asthma exacerbation.

Methods: We evaluated pro-inflammatory cytokine levels and gene expression profiles in blood samples from pediatric patients admitted for acute asthma exacerbation.

Panoply of P: An Array of Rhenium-Phosphorus Complexes Generated from a Transition Metal Anion.

We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (, BDI = -bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate) to generate several rhenium-phosphorus complexes. Complex reacts in a metathetical manner with chlorophosphines PhPCl, NHP-Cl, and OHP-Cl to generate XL-type phosphido complexes , , and , respectively (NHP-Cl = 2-chloro-1,3-dimethyl-1,3,2-diazaphospholidine; OHP-Cl = 2-chloro-1,3,2-dioxaphospholane). Crystallographic and computational investigations of phosphido triad , , and reveal that increasing the electronegativity of the phosphorus substituent (C < < O) results in a shortening and strengthening of the rhenium-phosphorus bond.

Challenges in Media Attention toward COVID-19-Preventive Behaviors: Dual Roles of Threat and Perceived Capability for Information Systems and Health Care.

Based on the extended parallel process model, this study investigated the relationship between young adults' media exposure to COVID-19 and their adoption of protective behaviors. This study surveyed 141 college students and found that increased risk perceptions led to greater intentions to engage in COVID-19-preventive behaviors and that these intentions were mediated by normative beliefs. There was no significant difference in risk perceptions between traditional media and social media.

Quantification of Free Radicals from Vaping Electronic Cigarettes Containing Nicotine Salt Solutions with Different Organic Acid Types and Concentrations.

Electronic (e-) cigarette formulations containing nicotine salts from a range of organic acid conjugates and pH values have dominated the commercial market. The acids in the nicotine salt formulations may alter the redox environment in e-cigarettes, impacting free radical formation in e-cigarette aerosol. Here, the generation of aerosol mass and free radicals from a fourth-generation e-cigarette device was evaluated at 2 wt % nicotine salts (pH 7, 30:70 mixture propylene glycol to vegetable glycerin) across eight organic acids used in e-liquids: benzoic acid (BA), salicylic acid (SLA), lactic acid (LA), levulinic acid (LVA), succinic acid (SA), malic acid (MA), tartaric acid (TA), and citric acid (CA).

Oxygen Isotopologues Resolved from Water Oxidation Electrocatalysis by Electron Paramagnetic Resonance Spectroscopy.

Electrocatalytic water oxidation is a key transformation in many strategies designed to harness solar energy and store it as chemical fuels. Understanding the mechanism(s) of the best electrocatalysts for water oxidation has been a fundamental chemical challenge for decades. Here, we quantitate evolved dioxygen isotopologue composition via gas-phase EPR spectroscopy to elucidate the mechanisms of water oxidation on metal oxide electrocatalysts with high precision.

Final Stages in the Biosynthesis of the [FeFe]-Hydrogenase Active Site.

The paper aims to elucidate the final stages in the biosynthesis of the [2Fe] active site of the [FeFe]-hydrogenases. The recently hypothesized intermediate [Fe(SCHNH)(CN)(CO)] ([1]) was prepared by a multistep route from [Fe(S)(CN)(CO)]. The following synthetic intermediates were characterized in order: [Fe(SCHNHFmoc)(CNBEt)(CO)], [Fe(SCHNHFmoc)(CN)-(CO)], and [Fe(SCHNHFmoc)(CN)(CO)], where Fmoc is fluorenylmethoxycarbonyl).

Indications for Readmission for Small Bowel Obstruction: A Comparison of Medical vs Surgical Service Admission.

Small bowel obstruction (SBO) impacts the health care system and patient quality of life. Previously, we evaluated differences between medical and surgical admissions in the management of SBO. This study investigates indications for readmission based on original admission to medical (MS) or surgical services (SS).

Type of Prior Operation Does Not Predict Surgical Intervention for Small Bowel Obstruction.

: Patients with prior abdominal surgeries are at higher risk for intra-abdominal adhesive tissue formation and subsequently higher risk for small bowel obstruction (SBO).: In this study, we investigated whether surgical intervention for SBO was more likely following specific types of abdominal surgeries.: With retrospective chart review, we pooled data from 799 patients, ages 18 to 89, admitted with SBO between 2012 and 2019.

Downregulation of protein phosphatase 2Aα in asthmatic airway smooth muscle.

Airway smooth muscle cell (ASM) is renowned for its involvement in airway hyperresponsiveness through impaired ASM relaxation and bronchoconstriction in asthma, which poses a significant challenge in the field. Recent studies have explored different targets in ASM to alleviate airway hyperresponsiveness, however, a sizeable portion of patients with asthma still experience poor control. In our study, we explored protein phosphatase 2 A (PP2A) in ASM as it has been reported to regulate cellular contractility by controlling intracellular calcium ([Ca]), ion channels, and respective regulatory proteins.

Radical SAM Enzyme PylB Generates a Lysyl Radical Intermediate in the Biosynthesis of Pyrrolysine by Using SAM as a Cofactor.

Pyrrolysine, the 22nd amino acid encoded by the natural genetic code, is essential for methanogenic archaea to catabolize methylamines into methane. The structure of pyrrolysine consists of a methylated pyrroline carboxylate that is linked to the ε-amino group of the l-lysine via an amide bond. The biosynthesis of pyrrolysine requires three enzymes: PylB, PylC, and PylD.

Bioinformatic Discovery of a Cambialistic Monooxygenase.

Dinuclear monooxygenases mediate challenging C-H bond oxidation reactions throughout nature. Many of these enzymes are presumed to exclusively utilize diiron cofactors. Herein we report the bioinformatic discovery of an orphan dinuclear monooxygenase that preferentially utilizes a heterobimetallic manganese-iron (Mn/Fe) cofactor to mediate an O-dependent C-H bond hydroxylation reaction.

Does Organizational Messaging Make a Difference? Investigating Themes and Language Style in Twitter Discourse and Engagement by Mental Health Organizations.

The present study investigated the latent topics and language styles present in mental health organizational discourse on Twitter. The researchers sought to analyze identifying the prevalence of and language used in social support messaging in tweets about mental health care, the overarching topics regarding mental health care, and predicted that tweets with higher engagement will have increased frequency of words with positively valenced emotion and cognitive processing. A GSDMM was run to uncover latent themes that emerged in a data set of 326.

Predictors of recurrent wheezing in late preterm infants.

Introduction: Premature infants have an increased risk of respiratory morbidity, including the development of recurrent wheezing. We sought to determine perinatal factors in late preterm infants associated with an increased risk of recurrent wheezing in the first 3 years of life.

Methods: A retrospective chart review of infants born between 32 and 36 weeks gestational age at a tertiary hospital from 2013 to 2016 was performed.

Reactive high-spin iron(IV)-oxo sites through dioxygen activation in a metal-organic framework.

In nature, nonheme iron enzymes use dioxygen to generate high-spin iron(IV)=O species for a variety of oxygenation reactions. Although synthetic chemists have long sought to mimic this reactivity, the enzyme-like activation of O to form high-spin iron(IV) = O species remains an unrealized goal. Here, we report a metal-organic framework featuring iron(II) sites with a local structure similar to that in α-ketoglutarate-dependent dioxygenases.