Acid-base Mechanism Research Articles

Fluorine-Modulated MXene-Derived Catalysts for Multiphase Sulfur Conversion in Lithium–Sulfur Battery

HighlightsBy introducing fluorine modulation into MXene, a new MXene-derived material TiOF/Ti3C2 was successfully synthesized with a distinctive three-dimensional structure and a tailored F distribution.In situ characterizations and electrochemical analyses demonstrate that TiOF/Ti3C2 catalysts effectively coupled the multiphase sulfur species conversion processes.The investigations reveal that the theoretical basis of the fluorine catalysis in Li–S batteries originated from Lewis acid–base mechanisms and charge compensation mechanisms.

Switching the Oxygen Evolution Mechanism on Atomically Dispersed Ru for Enhanced Acidic Reaction Kinetics.

Designing stable single-atom electrocatalysts with lower energy barriers is urgent for the acidic oxygen evolution reaction. In particular, the atomic catalysts are highly dependent on the kinetically sluggish acid-base mechanism, limiting the reaction paths of intermediates. Herein, we successfully manipulate the steric localization of Ru single atoms at the Co3O4 surface to improve acidic oxygen evolution by precise control of the anchor sites. The delicate structure design can switch the reaction mechanism from the lattice oxygen mechanism (LOM) to the optimized adsorbate evolution mechanism (AEM). In particular, Ru atoms embedded into cation vacancies reveal an optimized mechanism that activates the proton donor-acceptor function (PDAM), demonstrating a new single-atom catalytic pathway to circumvent the classic scaling relationship. Steric interactions with intermediates at the anchored Ru-O-Co interface played a primary role in optimizing the intermediates' conformation and reducing the energy barrier. As a comparison, Ru atoms confined to the surface sites exhibit a lattice oxygen mechanism for the oxygen evolution process. As a result, the delicate atom control of the spatial position presents a 100-fold increase in mass activity from 36.96 A gRu(ads)-1 to 4012.11 A gRu(anc)-1 at 1.50 V. These findings offer new insights into the precise control of single-atom catalytic behavior.

Highly efficient Cd(II) removal from groundwater utilizing layered mixed metal oxides-graphitic carbon nitride composite with improved cycling stability

Graphitic carbon nitride (GCN) and its mixed metal oxide (MMO) composites are synthesized via co-precipitation followed by the pyrolysis method using various ratios of calcium aluminium (Ca:Al) with GCN, to enhance the adsorption ability towards Cd(ii) present in wastewater. Synthesized composite materials were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis, Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. Due to its higher specific surface area (218.65 m2/g), the produced GCN and CaAl mixed metal oxide composite (GCN-MMO) exhibits improved adsorption ability towards Cd(II) ions. Approximately >99 % were adsorbed with Langmuir qmax of 131.57 mg/g. An overall pseudo-second-order (PSO) model fitted the kinetics data well. The possible mechanisms were surface complexation and precipitation, outer-sphere complexation, and acid-base mechanism. Further, the groundwater application was studied, and it achieved adsorption below the maximum permissible limit of USEPA with excellent cycling stability. The findings of this study showed that GCN-MMO composite material may be useful for the adsorption of Cd(II) heavy metal from an aqueous solution.

Sex differences in renal transporters: assessment and functional consequences.

Mammalian kidneys are specialized to maintain fluid and electrolyte homeostasis. The epithelial transport processes along the renal tubule that match output to input have long been the subject of experimental and theoretical study. However, emerging data have identified a new dimension of investigation: sex. Like most tissues, the structure and function of the kidney is regulated by sex hormones and chromosomes. Available data demonstrate sex differences in the abundance of kidney solute and electrolyte transporters, establishing that renal tubular organization and operation are distinctly different in females and males. Newer studies have provided insights into the physiological consequences of these sex differences. Computational simulations predict that sex differences in transporter abundance are likely driven to optimize reproduction, enabling adaptive responses to the nutritional requirements of serial pregnancies and lactation - normal life-cycle changes that challenge the ability of renal transporters to maintain fluid and electrolyte homeostasis. Later in life, females mayalso undergo menopause, which is associated with changes in disease risk. Although numerous knowledge gaps remain, ongoing studies will provide further insights into the sex-specific mechanisms of sodium, potassium, acid-base and volume physiology throughout the life cycle, which may lead to therapeutic opportunities.

A sequential acid-base mechanism in the interstellar medium: The emergence of cis formic acid in dark molecular clouds

A sequential acid-base mechanism in the interstellar medium: The emergence of cis formic acid in dark molecular clouds

Carbohydrate esterases involved in deacetylation of food components by the human gut microbiota.

Non-carbohydrate modifications such as acetylations are widespread in food stuffs as well as they play important roles in diverse biological processes. These modifications meet the gut environment and are removed from their carbohydrate substrates by the resident microbiota. Among the most abundant modifications are O-acetylations, contributing to polysaccharides physico-chemical properties such as viscosity and gelling ability, as well as reducing accessibility for glycosyl hydrolases, and thus hindering polysaccharide degradation. Of particular note, O-acetylations increase the overall complexity of a polymer, thus requiring a more advanced degrading machinery for microbes to utilize it. This minireview describes acetylesterases from the gut microbiota that deacetylate various food polysaccharides, either as natural components of food, ingredients, stabilizers of microbial origin, or as part of microbes for food and beverage preparations. These enzymes include members belonging to at least 8 families in the CAZy database, as well as a large number of biochemically characterized esterases that have not been classified yet. Despite different structural folds, most of these acetylesterases have a common acid-base mechanism and belong to the SGNH hydrolase superfamily. We highlight examples of acetylesterases that are highly specific to one substrate and to the position of the acetyl group on the glycosyl residue of the carbohydrate, while other members that have more broad substrate specificity. Current research aimed at unveiling the functions and regioselectivity of acetylesterases will help providing fundamental mechanistic understanding on how dietary components are utilized in the human gut and will aid developing applications of these enzymes to manufacture novel industrial products.

Formation Mechanisms of Co-existence of α-Fe and Iron Oxides Nanoparticles Decorated on Carbon Nanofibers by a Simple Liquid Phase Adsorption-Thermal Oxidation

We propose formation mechanisms of co-existence of α-Fe and iron oxides nanoparticles decorated on CNFs. The α-Fe nanoparticles are produced via oxidation-reduction mechanisms, which occur in liquid phase adsorption (LPA) assisted by ultrasonic energy, while α-Fe2O3 nanoparticles are thermally formed through mechanisms of Lewis acidbase. In addition, Fe3O4 is thermally formed by reducing Fe2O3 by CNFs. Liquid phase adsorption assisted by ultrasonic energy under ambient temperature using Fe(NO3)3•9H2O as a precursor of iron oxides and α-Fe has been applied. Then, as prepared, Fe(III)@CNFs were thermally calcined at 573 K under air atmosphere in various holding times ranging from 0.5 to 2 h. XRD data confirmed that α- Fe2O3 and Fe3O4 had been successfully grown onto CNFs. Moreover, the presence of the iron oxides and iron nanoparticles was studied by the SEMEDX technique. The iron oxide nanoparticles appeared after a heating period of 0.5h. However, at a holding time of 0.5 h, we found an exciting and unexpected phenomenon where oxygen content is zero percent while Fe is 0.23 wt %. It implies that α-Fe nanoparticles were formed earlier than α-Fe2O3 and Fe3O4 as the proposed mechanisms. Formation mechanisms of iron and its oxides such as α-Fe2O3 and Fe3O4 decorated on CNFs through liquid-phase adsorption followed by thermally treatment technique in this work is expected to give significant contribution in the field of nanocomposite materials, especially for anode materials based on iron oxides.

Enzymatic Enantioselective anti‐Markovnikov Hydration of Aryl Alkenes

AbstractThe addition of water to alkenes is an important method for the synthesis of alcohols, but the regioselectivity of acid‐catalyzed hydration of terminal alkenes yields secondary alcohols according to Markovnikov's rule, making it difficult to obtain primary alcohols. Here we report a styrene monooxygenase that catalyzes the anti‐Markovnikov hydration of the terminal aryl alkenes under anaerobic conditions. This hydration provides primary alcohols in good yields (up to 100 %), excellent anti‐Markovnikov regioselectivity (>99 : 1), and good enantiomeric purity (60–83 % ee). Residues Asn46, Asp100, and Asn309 are essential for catalysis suggesting an acid–base mechanism with a carbanion‐like intermediate that could account for the anti‐Markovnikov regioselectivity. Our work reveals a new enzymatic tool with unusual regioselectivity based on the promiscuous catalytic activity of a monooxygenase.

Enzymatic Enantioselective anti-Markovnikov Hydration of Aryl Alkenes.

The addition of water to alkenes is an important method for the synthesis of alcohols, but the regioselectivity of acid-catalyzed hydration of terminal alkenes yields secondary alcohols according to Markovnikov's rule, making it difficult to obtain primary alcohols. Here we report a styrene monooxygenase that catalyzes the anti-Markovnikov hydration of the terminal aryl alkenes under anaerobic conditions. This hydration provides primary alcohols in good yields (up to 100 %), excellent anti-Markovnikov regioselectivity (>99 : 1), and good enantiomeric purity (60-83 % ee). Residues Asn46, Asp100, and Asn309 are essential for catalysis suggesting an acid-base mechanism with a carbanion-like intermediate that could account for the anti-Markovnikov regioselectivity. Our work reveals a new enzymatic tool with unusual regioselectivity based on the promiscuous catalytic activity of a monooxygenase.

Atmospheric Sulfuric Acid Dimer Formation in a Polluted Environment.

New particle formation (NPF) contributes significantly to atmospheric particle number concentrations and cloud condensation nuclei (CCN). In sulfur-rich environments, field measurements have shown that sulfuric acid dimer formation is likely the critical step in NPF. We investigated the dimer formation process based upon the measured sulfuric acid monomer and dimer concentrations, along with previously reported amine concentrations in a sulfur-rich atmosphere (Atlanta, USA). The average sulfuric acid concentration was in the range of 1.7 × 107–1.4 × 108 cm−3 and the corresponding neutral dimer concentrations were 4.1 × 105–5.0 × 106 cm−3 and 2.6 × 105–2.7 × 106 cm−3 after sub-collision and collision ion-induced clustering (IIC) corrections, respectively. Two previously proposed acid–base mechanisms (namely AA and AB) were employed to respectively estimate the evaporation rates of the dimers and the acid–amine complexes. The results show evaporation rates of 0.1–1.3 s−1 for the dimers based on the simultaneously measured average concentrations of the total amines, much higher than those (1.2–13.1 s−1) for the acid–amine complexes. This indicates that the mechanism for dimer formation is likely AA through the formation of more volatile dimers in the initial step of the cluster formation.

Elucidating the acid-base mechanisms underlying otolith overgrowth in fish exposed to ocean acidification

Over a decade ago, ocean acidification (OA) exposure was reported to induce otolith overgrowth in teleost fish. This phenomenon was subsequently confirmed in multiple species; however, the underlying physiological causes remain unknown. Here, we report that splitnose rockfish (Sebastes diploproa) exposed to ~1600 μatm pCO2(pH ~7.5) were able to fully regulated the pH of both blood and endolymph (the fluid that surrounds the otolith within the inner ear). However, while blood was regulated around pH 7.80, the endolymph was regulated around pH ~8.30. These different pH setpoints result in increased pCO2diffusion into the endolymph, which in turn leads to proportional increases in endolymph [HCO3−] and [CO32−]. Endolymph pH regulation despite the increased pCO2suggests enhanced H+removal. However, a lack of differences in inner ear bulk and cell-specific Na+/K+-ATPase and vacuolar type H+-ATPase protein abundance localization pointed out to activation of preexisting ATPases, non-bicarbonate pH buffering, or both, as the mechanism for endolymph pH-regulation. These results provide the first direct evidence showcasing the acid-base chemistry of the endolymph of OA-exposed fish favors otolith overgrowth, and suggests that this phenomenon will be more pronounced in species that count with more robust blood and endolymph pH regulatory mechanisms.

Switching the O–O bond-formation mechanism by controlling water activity

Switching the O–O bond-formation mechanism by controlling water activity

New Insights of the pH Effect on Hydrogen Evolution and Oxidation Reactions Mechanisms in Alkaline Solutions

The sluggish kinetics of the hydrogen evolution and oxidation reactions (HER/HOR) of Pt in alkaline solutions remains elusive. Elucidation of the mechanisms of the HER/HOR in alkaline can not only deepen our understandings of alkaline electrochemistry, but also help to rationalize the design of highly active catalysts for alkaline fuel cells and electrolyzers. Herein, we investigate the HER/HOR kinetics of a variety of catalysts including monometallic catalysts (Ni, Pt, Ru, Au) and bimetallic catalysts (NiMo, Pt-M) by comparing their HER/HOR performance in 0.1 M KOH and 1 M KOH. We found that the HER/HOR kinetics of these systems are not always slower in 1 M KOH (pH =14) than in 0.1 M KOH (pH = 13). These observations do not follow the general trend that the HER/HOR kinetics of a wide range of elements slows down with increasing pH1. We propose to resolve this inconsistency by pointing out that the pH is only one of the factors that affect the transport of the HER/HOR intermediates (hydroxyl for HER, Had for HOR) throughout the double layer region, among other factors such as the oxophicility of the surface sites, the cation environment, etc. These factors co-determine the HER/HOR kinetics of catalysts (such as Pt/C) that is limited by the transport of reactions throughout the double layer region. As the electrolyte changes from 0.1 M KOH to 1 M KOH, the pH shifts from 13 to 14, slowing down the HER/HOR kinetics. Meanwhile, the K+ concentration increases one order of magnitude, which promotes the transport of OHad according to the hard-soft acid-base (HSAB) mechanism we recently proposed 2, thereby improving the HER but not the HOR until the K+ saturates. The change of the HER/HOR kinetics of a catalyst as the electrolyte changes from 0.1 M KOH to 1 M KOH is a counterbalance between these two effects, and thus varies case by case. Acknowledgements.This work was supported by the Department of Energy (DOE) under award number DE-EE0008082, Office of Naval Research (ONR) under award number N000141712608 and the Graduate Thesis/Dissertation Grant of Northeastern University. This research used beamline 7-BM (QAS) and 8-ID (ISS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. References (1)Herranz, J.; Durst, J.; Fabbri, E.; Patru, A.; Cheng, X.; Permyakova, A. A.; Schmidt, T. J. Interfacial Effects on the Catalysis of the Hydrogen Evolution, Oxygen Evolution and CO2-Reduction Reactions for (Co-)Electrolyzer Development. Nano Energy 2016, 29, 4–28. https://doi.org/10.1016/j.nanoen.2016.01.027.(2)Liu, E.; Li, J.; Jiao, L.; Doan, H. T. T.; Liu, Z.; Zhao, Z.; Huang, Y.; Abraham, K. M.; Mukerjee, S.; Jia, Q. Unifying the Hydrogen Evolution and Oxidation Reactions Kinetics in Base by Identifying the Catalytic Roles of Hydroxyl-Water-Cation Adducts. J. Am. Chem. Soc. 2019, 141 (7), 3232–3239. https://doi.org/10.1021/jacs.8b13228.

Manganese Catalyzed Direct Amidation of Esters with Amines.

The transition metal catalyzed amide bond forming reaction of esters with amines has been developed as an advanced approach for overcoming the shortcomings of traditional methods. The broad scope of substrates in transition metal catalyzed amidations remains a challenge. Here, a manganese(I)-catalyzed method for the direct synthesis of amides from a various number of esters and amines is reported with unprecedented substrate scope using a low catalyst loading. A wide range of aromatic, aliphatic, and heterocyclic esters, even in fatty acid esters, reacted with a diverse range of primary aryl amines, primary alkyl amines, and secondary alkyl amines to form amides. It is noteworthy that this approach provides the first example of the transition metal catalyzed amide bond forming reaction from fatty acid esters and amines. The acid-base mechanism for the manganese(I)-catalyzed direct amidation of esters with amines was elucidated by DFT calculations.

Elucidating the Acid-Base Mechanisms Underlying Otolith Overgrowth in Fish Exposed to Ocean Acidification

Elucidating the Acid-Base Mechanisms Underlying Otolith Overgrowth in Fish Exposed to Ocean Acidification

Enhanced removal of aqueous phenol with polyimide ultrafiltration membranes embedded with deep eutectic solvent-coated nanosilica

Novel composite hydrophilic ultrafiltration (UF) membranes, comprising a polyimide (PI) matrix embedded with silica-based nanofillers are established for the enhanced vacuum-filtration removal of small polar organics such as phenol from water. Spherical silica nanoparticles are first prepared by the surfactant-templated sol–gel approach, then coated with choline chloride-ethylene glycol deep eutectic solvent (DES) by post-impregnation. Themodified silica nanofillers are introduced into the PI matrix through the casting solution, which is then used to develop the composite UF membranes by phase inversion. Thespectroscopy and high-resolution electron microscopy measurements evidence thepresence of DES on the surface of the modified silica nanofillers. Thetopographical atomic force microscopy studies, dynamic water contact angle, and zeta potential measurements conducted on the native polymer membrane and those embedded with bare-silica and DES-coated silica confirm the successful incorporation of nanofillers into the PI matrix. Anoptimum nanofiller loading of 2 wt% is found to preserve the membrane structure and give the best mechanical properties as well as for the UF performance characteristics in vacuum-filtration studies at 85 kPa. Consistently, the DES-silica modified PI UF membranes (DES@SiO2@PI) exhibit exceptional water permeate flux (300 L m−2 h−1) and removal efficiency (96%) for 30 mg L−1 aqueous phenol compared with the native polymer and SiO2-modified membranes. The DES-engineered composite membranes can be operated within a wide feed pH window (pH: 2–10) without displaying significant loss in their removal efficiency. The pH and zeta potential results suggest that the interaction of phenol with the optimized membranes is governed by cooperative adsorption/Lewis acid-base mechanisms via hydrogen bonding and assistive ion-exchange interactions with the ethaline coating.

Acute Kidney Injury Caused by Obstructive Nephropathy.

Acute kidney injury secondary to obstructive nephropathy is a frequent event that accounts for 5 to 10% of all acute kidney injury cases and has a great impact on the morbidity and mortality in those affected. The obstruction in the urinary tract has a profound impact on kidney function due to damage produced by ischemic and inflammatory factors that have been associated with intense fibrosis. This pathology is characterized by its effects on the management of fluids, electrolytes, and the acid-base mechanisms by the renal tubule; consequently, metabolic acidosis, hyperkalemia, uremia, and anuria are seen during acute kidney injury due to obstructive nephropathy, and after drainage, polyuria may occur. Acute urine retention is the typical presentation. The diagnosis consists of a complete medical history and should include changes in urinary voiding and urgency and enuresis, history of urinary tract infections, hematuria, renal lithiasis, prior urinary interventions, and constipation. Imaging studies included tomography or ultrasound in which hydronephrosis can be seen. Management includes, in addition to drainage of the obstructed urinary tract system, providing supportive treatment, correcting all the metabolic abnormalities, and initiating renal replacement therapy when required. Although its recovery is in most cases favorable, it seems to be an undervalued event in nephrology and urology. This is because it is mistakenly believed that the resolution and recovery of kidney function is complete once the urinary tract is unobstructed. It can have serious kidney sequelae. In this review, we report the epidemiology, incidence, pathophysiological mechanisms, diagnosis, and treatment of acute kidney injury due to obstructive nephropathy.

ON REACTIVITY OF PIPERAZINE AMINOGRUPS IN INTERACTION WITH ETHYLENE OXIDE

Currently, the main method for producing N-(2-hydroxyethyl) piperazine in industry is the cyclization of ethylene glycols and ethanolamines in the presence of ammonia and hydrogen. The main disadvantage of this method is the production of a wide range of products and, as a consequence, low selectivity for N-(2-hydroxyethyl) piperazine. In this work, the object of study is the piperazine hydroxyethylation reaction in the presence of an “inert” solvent under the reaction conditions, as the most selective way to obtain N-(2-hydroxyethyl) piperazine. The solvent molecule acts as a homogeneous catalyst of the acid type and is characterized by the presence of a mobile proton for opening the oxirane ring of ethylene oxide by the acid-base mechanism. There was studied the dependence of the yield of reaction products on the parameters of the process in the temperature range of 60 - 130 ° C; solvent concentration (water, methylcellosolve) 1 - 75% wt. and molar ratio of reagents (ethylene oxide / piperazine) 0.2 - 1. Analysis of the reaction mass by gas-liquid chromatography showed that the main by-product is N, N'-bis (2-hydroxyethyl) piperazine - the product of the hydroxyethylation of N-(2-hydroxyethyl ) piperazine in the second amino group. The hydroxyl group of hydroxyethylation products are formed in a negligible amount. It was found that the composition and concentration of the solvent, as well as the temperature regime of hydroxyethylation, do not significantly affect the selectivity of the process. It was shown that piperazine hydroxyethylation is described by the kinetics of series-parallel reactions. The results obtained in the study may be of interest for the development of piperazine hydroxyethylation process technology, in terms of simplifying the mathematical model of the reactor unit by excluding from the description factors that do not significantly affect the selectivity of the formation of N-(2-hydroxyethyl) piperazine.

Room-temperature X-ray crystallography reveals the oxidation and reactivity of cysteine residues in SARS-CoV-2 3CL Mpro: insights into enzyme mechanism and drug design.

The emergence of the novel coronavirus SARS-CoV-2 has resulted in a worldwide pandemic not seen in generations. Creating treatments and vaccines to battle COVID-19, the disease caused by the virus, is of paramount importance in order to stop its spread and save lives. The viral main protease, 3CL Mpro, is indispensable for the replication of SARS-CoV-2 and is therefore an important target for the design of specific protease inhibitors. Detailed knowledge of the structure and function of 3CL Mpro is crucial to guide structure-aided and computational drug-design efforts. Here, the oxidation and reactivity of the cysteine residues of the protease are reported using room-temperature X-ray crystallography, revealing that the catalytic Cys145 can be trapped in the peroxysulfenic acid oxidation state at physiological pH, while the other surface cysteines remain reduced. Only Cys145 and Cys156 react with the alkylating agent N-ethylmaleimide. It is suggested that the zwitterionic Cys145-His45 catalytic dyad is the reactive species that initiates catalysis, rather than Cys145-to-His41 proton transfer via the general acid-base mechanism upon substrate binding. The structures also provide insight into the design of improved 3CL Mpro inhibitors.

Hot-corrosion resistance and phase stability of Yb2O3–Gd2O3–Y2O3 costabilized zirconia-based thermal barrier coatings against Na2SO4 + V2O5 molten salts

The hot corrosion behavior of plasma-sprayed Yb2O3-Gd2O3-Y2O3 co-doped ZrO2 (YGYZ) coating against Na2SO4 + V2O5 molten salts was investigated and its detailed hot corrosion mechanism was suggested. The chemical reactivity order between the stabilizers was proposed based on the electronic structure and Lewis acid-base mechanism. After hot corrosion, the YGYZ coating exhibited the maintenance of tetragonality ratio and relatively lower extent of destabilization less than 40% of conventional yttria-stabilized ZrO2 coating. These great chemical and phase stabilities imply that YGYZ is promising candidate for high-temperature thermal barrier material.