Insights into Mechanistic Aspect of Organic Materials for Aluminum-Ion Batteries.

Rechargeable aluminum-ion batteries (AIBs) with organic electrode materials have garnered significant attention due to their excellent safety profile, cost-effectiveness, and eco-friendly nature. This review delves into the intrinsic attributes of organic compounds and their impact on battery performance, mainly focusing on the alteration of ion interactions and charge storage mechanisms at the active sites. The ultimate aim is to propose innovative design approaches for AIBs that overcome the constraints associated with various types of organic materials. The review also discusses the application of advanced analytical tools, providing insights to better understand the electrochemical process of AIBs.

Dynamically Stabilizing Oxygen Atoms in Silver Catalyst for Highly Selective and Durable CO2 Reduction Reaction.

Oxide derived catalyst displays outstanding catalytic activity and selectivity in electrochemical carbon dioxide reduction reaction (CO2RR), in which, it is found that residue oxygen atoms play a pivotal role in regulating the catalyst's electronic structure and thus the CO2RR process. Unfortunately, the intrinsic thermodynamic instability of oxygen atoms in oxide derived catalyst under cathodic CO2RR potentials makes it unstable during continuous electrolysis, greatly hindering its practical industrial applications. In this work, we develop a pulsed-bias technique that is able to dynamically stabilize the residue oxygen atoms in oxide derived catalyst during electrochemical CO2RR. As a result, the oxide derived catalyst under pulsed bias exhibits super catalytic stability in catalyzing electrochemical CO2RR, while keeping excellent catalytic activity and selectivity.

Theoretical study on the luminescent and reaction mechanism of dansyl-based fluorescence probe for detecting hydrogen sulfide.

The photophysical and photochemical properties of the sulfonyl azide-based fluorescent probe DNS-Az and its reduction product DNS by hydrogen sulfide (H2S) have been investigated theoretically. The calculated results indicated the first excited states of DNS-Az was dark state (oscillator strength less than 0.03) and DNS was bright state (oscillator strength more than 0.1), which determined the predicted radiative rate kr of DNS-Az was much smaller than that of DNS, meanwhile, due to more larger reorganization energy of DNS-Az, its predicted internal conversion rate kic was four times larger than that of DNS; moreover, owing to the effect of heavy atom from sulfur atom in DNS-Az, its predicted intersystem crossing rate kisc was seven times larger than that of DNS, thus the calculated fluorescence quantum yield of DNS-Az was only 2.16% and that of DNS was more than 77.2%, the above factors is the basis for DNS-Az molecule to function as a fluorescent probe. Regarding both DNS-Az and DNS molecules, their maximum Huang-Rhys factors, which are less than unity, signify the reliability of 0-0 transitions between their S0 and S1 electronic states. In addition, for DNS, our simulated emission peak of the 0-0 transition is 515 nm, a value that exhibits enhanced accuracy and coherence when compared to the experimental datum of 528 nm. The reaction mechanism of DNS-Az generating DNS by H2S has been investigated too, according to the potential energy profile, we found that the fluorescent probe firstly protonated, then this organic ion broke down into DNS with the aid of a proton.

Investigation of Neighboring Group Participation in 3,4-Diacetylated Glycosyl Donors in the Gas Phase.

A key challenge in oligosaccharide synthesis is the stereoselective installation of glycosidic bonds. Each glycosidic linkage has one of two possible stereo-chemical geometries, α/ß or 1,2-cis/trans. An established approach to install 1,2-trans glycosidic bonds is neighboring group participation (NGP), mediated by a 2-O-acyl group. Extension of this intramolecular stabilization to nucleophilic groups located at more remote positions has also been suggested, but remains poorly understood. Previously, we employed infrared ion spectroscopy to characterize the molecular ions of monoacetylated sugar donors and showed how the strength of the stabilizing effect depends on the position of the participating ester group on the glycosyl donor ring as well as on its relative stereochemistry. In this work, we investigated glycosyl donors carrying two acyl groups. Using isotope labelling and isomer population analysis we were able to resolving spectra of isomeric mixtures and establish the relative contribution of individual species. We conclude that 3,4-diacetyl mannosyl donors exclusively form a dioxanium ion as a result of C-3 acyl stabilization. In contrast, the glucosyl and galactosyl cations form mixtures of C-3 and C-4 acyl participation products. Hence, the combination of isotope labeling and population analysis allows for the study of increasingly complex glycosyl cations.

Secondary Sphere Lewis Acid Activated Heme Superoxo Adducts Mimic Crucial Non-Covalent Interactions in IDO/TDO Heme Dioxygenases.

Heme enzymes play a central role in a medley of reactivities within a wide variety of crucial biological systems. Their active sites are highly decorated with pivotal evolutionarily optimized non-covalent interactions that precisely choreograph their biological functionalities with specific regio-, stereo-, and chemo-selectivities. Gaining a clear comprehension of how such weak interactions within the active sites control reactivity offers powerful information to be implemented into the design of future therapeutic agents that target these heme enzymes. To shed light on such critical details pertaining to tryptophan dioxygenating heme enzymes, this study investigates the indole dioxygenation reactivities of Lewis acid-activated heme superoxo model systems, wherein an unprecedented kinetic behavior is revealed. In that, the activated heme superoxo adduct is observed to undergo indole dioxygenation with the intermediacy of a non-covalently organized precursor complex, which forms prior to the rate-limiting step of the overall reaction landscape. Spectroscopic and theoretical characterization of this precursor complex draws close parallels to the ternary complex of heme dioxygenases, which has been postulated to be of crucial importance for successful 2,3-dioxygenative cleavage of indole moieties.

Structure-Activity Relationships in Oxygen Electrocatalysis.

Oxygen electrocatalysis, as the pivotal circle of many green energy technologies, sets off a worldwide research boom in full swing, while its large kinetic obstacles require remarkable catalysts to break through. Here, based on summarizing reaction mechanisms and in situ characterizations, the structure-activity relationships of oxygen electrocatalysts are emphatically overviewed, including the influence of geometric morphology and chemical structures on the electrocatalytic performances. Subsequently, experimental/theoretical research is combined with device applications to comprehensively summarize the cutting-edge oxygen electrocatalysts according to various material categories. Finally, future challenges are forecasted from the perspective of catalyst development and device applications, favoring researchers to promote the industrialization of oxygen electrocatalysis at an early date.

Enantioconvergent and Site-Selective Etherification of Carbohydrate Polyols through Chiral Copper Radical Catalysis.

Going beyond currently reported two electron transformations that formed the core backdrop of asymmetric catalytic site-selective carbohydrate polyol functionalizations, we herein report a seminal demonstration of an enantioconvergent copper catalyzed site-selective etherification of minimally protected saccharides through a single-electron radical pathway. Further, this strategy paves a rare strategy, through which a carboxamide scaffold that is present in some glycomimetics of pharmacological relevance, can be selectively introduced. In light of the burgeoning interest in chiral radical catalysis, and the virtual absence of such stereocontrol broadly in carbohydrate synthesis, our strategy showcased the unknown capability of chiral radical copper catalysis as a contemporary tool to address the formidable site-selectivity challenge on a remarkable palette of naturally occurring saccharides. When reducing sugars were employed, a further dynamic kinetic resolution type glycosylation can be activated by the catalytic system to selectively generate the challenging ß-O-glycosides.

The Dialuminene AriPr8AlAlAriPr8 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2).

Careful analysis of the crystals formed in the reduction of AriPr8AlI2 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2) with sodium on sodium chloride showed them to contain the long sought-after dialuminene AriPr8AlAlAriPr8 (1) that forms alongside the previously characterized alanediyl:AlAriPr8. The single crystal X-ray structure of 1 revealed a nearly planar, trans-bent C(ipso)AlAlC(ipso) core with an Al-Al distance of 2.648(2) Å. The molecular and electronic structure of 1 are consistent with a Al-Al double dative interaction augmented with diradical character and stabilized by dispersion interactions. Density functional theory calculations showed that the reactivity of:AlAriPr8 with dihydrogen involves 1, not:AlAriPr8, as the reactive species. In contrast, the reaction of:AlAriPr8 with ethylene gave two products, the 1,4-dialuminacyclohexane AriPr8Al(C2H4)2AlAriPr8 (2) and the aluminacyclopentane AriPr8Al(C4H8) (3), that can both form from the aluminacyclopropane intermediate AriPr8Al(C2H4). Although the [2+2+2] cycloaddition of 1 with two equivalents of ethylene was also calculated to be exergonic, it is likely to be kinetically blocked by the numerous isopropyl substituents surrounding the Al-Al bond. Attempts to fine-tune the steric bulk of the terphenyl ligand to allow stronger Al-Al bonding were unsuccessful, leading to the isolation of the sodium salt of a cyclotrialuminene, Na2[AlAriPr6]3 (4), instead of AriPr6AlAlAriPr6.

Theoretical analysis of naproxen reaction with sulfate and hydroxyl radicals in the aqueous phase: Investigating reactive sites and reaction kinetics.

In this study, we have utilized theoretical calculations to predict the reaction active sites of naproxen when reacting with radicals and to further study the thermodynamics and kinetics of the reactions with ·OH and SO4-·. The evidence, derived from the average local ionization energy and electrostatic potential, points to the naphthalene ring as the preferred site of attack, especially for the C2, C6, C9, and C10 sites. The changes in Gibbs free energy and enthalpy of the reactions initiated by ·OH and SO4-· ranged between -19.6 kcal/mol - 26.3 kcal/mol and -22.3 kcal/mol -18.5 kcal/mol, respectively. More in-depth investigation revealed that RA2 pathway for ·OH exhibited the lowest free energy of activation, suggesting this reaction is more inclined to proceed. The second-order rate constant results indicate the ·OH attacking reaction is faster than reactions initiated by SO4·-, yet controlled by diffusion. The consistency between theoretical findings and experimental data underscores the validity of this computational method for our study.

In Situ Characterization Techniques for Electrochemical Nitrogen Reduction Reaction.

The electrochemical reduction of nitrogen to produce ammonia is pivotal in modern society due to its environmental friendliness and the substantial influence that ammonia has on food, chemicals, and energy. However, the current electrochemical nitrogen reduction reaction (NRR) mechanism is still imperfect, which seriously impedes the development of NRR. In situ characterization techniques offer insight into the alterations taking place at the electrode/electrolyte interface throughout the NRR process, thereby helping us to explore the NRR mechanism in-depth and ultimately promote the development of efficient catalytic systems for NRR. Herein, we introduce the popular theories and mechanisms of the electrochemical NRR and provide an extensive overview on the application of various in situ characterization approaches for on-site detection of reaction intermediates and catalyst transformations during electrocatalytic NRR processes, including different optical techniques, X-ray-based techniques, electron microscopy, and scanning probe microscopy. Finally, some major challenges and future directions of these in situ techniques are proposed.

Efficient degradation of benzalkonium chloride (BAC) by zero-valent iron activated persulfate: Kinetics, reaction mechanisms, theoretical calculations and toxicity evolution.

The present study systematically investigated the elimination of benzalkonium chloride (BAC) in the zero valent iron activated persulfate (Fe0/PS) system. The influence of operational parameters, including PS concentration, Fe0 dosage and pH, were investigated through a series of kinetic experiments. When the Fe0 dosage was 5.0 mM, the initial ratio of [PS]: [BAC] was 10:1, the degradation efficiency could achieve 91.7% at pH 7.0 within 60 min. Common inorganic anions and humic acid did not significantly affect BAC degradation, implying that Fe0/PS system had a potential application prospect in the actual wastewater remediation. Based on the electron paramagnetic resonance test and quenching experiments, the BAC degradation was found to be contributed by •OH, SO4•- and Fe(IV). A total of 23 intermediates were identified by the liquid chromatography-mass spectrometry, and the degradation pathways were proposed accordingly, including dealkylation and demethylation, hydroxylation, sulfate substitution and benzyl C-N cleavage reactions. Density functional theory based calculations were conducted to realize the rationality of the proposed reaction mechanisms. The toxicity of transformation products was predicted by ECOSAR program. This work demonstrated the possibility of BAC removal in hospital and municipal wastewater by Fe0/PS treatment, and also provides a safe choice for deep treatment of quaternary ammonium salt wastewater.

Mechanism of the Oxidative Ring-Closure Reaction during Gliotoxin Biosynthesis by Cytochrome P450 GliF.

During gliotoxin biosynthesis in fungi, the cytochrome P450 GliF enzyme catalyzes an unusual C-N ring-closure step while also an aromatic ring is hydroxylated in the same reaction cycle, which may have relevance to drug synthesis reactions in biotechnology. However, as the details of the reaction mechanism are still controversial, no applications have been developed yet. To resolve the mechanism of gliotoxin biosynthesis and gain insight into the steps leading to ring-closure, we ran a combination of molecular dynamics and density functional theory calculations on the structure and reactivity of P450 GliF and tested a range of possible reaction mechanisms, pathways and models. The calculations show that, rather than hydrogen atom transfer from the substrate to Compound I, an initial proton transfer transition state is followed by a fast electron transfer en route to the radical intermediate, and hence a non-synchronous hydrogen atom abstraction takes place. The radical intermediate then reacts by OH rebound to the aromatic ring to form a biradical in the substrate that, through ring-closure between the radical centers, gives gliotoxin products. Interestingly, the structure and energetics of the reaction mechanisms appear little affected by the addition of polar groups to the model and hence we predict that the reaction can be catalyzed by other P450 isozymes that also bind the same substrate. Alternative pathways, such as a pathway starting with an electrophilic attack on the arene to form an epoxide, are high in energy and are ruled out.

Quantum Mechanical Cluster Models for Calculations on Enzymatic Reaction Mechanisms: Set-Up and Accuracy.

Enzymes turnover substrates into products with amazing efficiency and selectivity and as such have great potential for use in biotechnology and pharmaceutical applications. However, details of their catalytic cycles and the origins surrounding the regio- and chemoselectivity of enzymatic reaction processes remain unknown, which makes the engineering of enzymes and their use in biotechnology challenging. Computational modelling can assist experimental work in the field and establish the factors that influence the reaction rates and the product distributions. A popular approach in modelling is the use of quantum mechanical cluster models of enzymes that take the first- and second coordination sphere of the enzyme active site into consideration. These QM cluster models are widely applied but often the results are dependent on model choice and selection. Herein, we show that QM cluster models can produce highly accurate results that reproduce experimental product distributions and free energies of activation, regarded that large cluster models with >300 atoms are used. In this tutorial review, we give general guidelines on the set-up and applications of the QM cluster method and discuss its accuracy and reproducibility. Finally, several representative QM cluster model examples on metal-containing enzymes are presented, which highlight the strength of the approach.

Gold(I)-Catalyzed Desymmetrization of Homopropargylic Alcohols via Cycloisomerization: Enantioselective Synthesis of Cyclopentenes Featuring a Quaternary Chiral Center.

Cyclopentene rings possessing a chiral quaternary center are important structural motifs found in various natural products. In this work, we disclose expedient and efficient access to this class of synthetically valuable structures via highly enantioselective desymmetrization of prochiral propargylic alcohols. The efficient chirality induction in this asymmetric gold catalysis is achieved via two-point bindings between a gold catalyst featuring a bifunctional phosphine ligand and the substrate homopropargylic alcohol moiety - an H-bonding interaction between the HO group and a ligand phosphine oxide moiety and the gold-alkyne complexation. The propargylic alcohol substrates can be prepared readily via propargylation of ketone precursors, and spirocyclic and bicyclic cyclopentenes are formed with additional neighboring chiral centers of flexible stereochemistry in addition to the quaternary center. This work represents rare gold-catalyzed highly enantioselective cycloisomerization of 1,5-enynes. Density functional theory (DFT) calculations support the chirality induction model and suggest that the rate acceleration enabled by the bifunctional ligand can be attributed to a facilitated protodeauration step at the end of the catalysis.

Reaction Mechanisms of High-Rate Copper Electrochemical Machining in Nitrate Electrolytes.

The high-rate electrochemical dissolution of copper in nitrate electrolytes is investigated primarily via polarization curves, while varying parameters such as the electrolyte flow velocity, the electrolyte resistance, the anode geometry, and the temperature. This study focuses on the re-rise in current at high voltages after the limiting current plateau. As a result of the studies, a change in the complexation mechanism from hydration to "solvo-nitration" is proposed, which requires an additional potential drop within the electrochemical double layer.

What is the Origin of the Regioselective C3-Hydroxylation of L-Arg by the Nonheme Iron Enzyme Capreomycin C?

The nonheme iron dioxygenase capreomycin C (CmnC) hydroxylates a free L-arginine amino acid regio- and stereospe-cifically at the C3-position as part of the capreomycin antibiotics biosynthesis. Little is known on its structure, catalytic cycle and substrate specificity and, therefore, a comprehensive computational study was performed. A large QM cluster model of CmnC was created of 297 atoms and the mechanisms for C3-H, C4-H and C5-H hydroxylation and C3-C4 desaturation were investigated. All low-energy pathways correspond to radical reaction mechanisms with an initial hydrogen atom abstraction followed by OH rebound to form alcohol product complexes. The work is compared to alternative L-Arg hydroxylating nonheme iron dioxygenases and the differences in active site polarity are compared. We show that a tight hydrogen bonding network in the substrate binding pocket positions the substrate in an ideal orientation for C3-H activation, whereby the polar groups in the substrate binding pocket induce an electric field effect that guides the selectivity.

Impacts of chloride ions on the electrochemical decomplexation and degradation of Cr(III)-EDTA: Reaction mechanisms of HO• and RCS.

The removal of Cr(III)-organic complexes, encompassing both decomplexation and ligand degradation, presents significant challenges in industrial wastewater treatment. As one of the most common anions in wastewater, Cl- significantly improves the efficiency of electrochemically removing Cr(III)-organic complexes through generated reactive chlorine species (RCS). In the electrochemical chlorine (EC/Cl2) process, extensive experimentation revealed that ClO• plays a dominant role in the degradation of Cr(III)-EDTA, surpassing the effects of free chlorine, direct electrooxidation, HO•, and other RCS. Density functional theory calculations indicated that RCS, primarily Cl• and ClO•, preferentially oxidize the ligand in Cr(III)-EDTA via H-abstraction, whereas HO• trends to attack the Cr atom through electron transfer. The influential factors on the degradation efficiency of Cr(III)-EDTA, Cr(VI) yield, and total organic carbon removal in EC/Cl2 were also assessed, including Cl- concentration, current density, and pH. Real industrial wastewater was employed as a reaction matrix to evaluate the application of the EC/Cl2 process for treating Cr(III)-EDTA, accompanied by energy efficiency calculations. Additionally, a two-chamber reactor was established to simultaneously oxidize Cr(III)-EDTA at the anode and reduce Cr(VI) at the cathode. This study provided insight into developing RCS-dominated AOPs to effectively decomplex and decompose organic Cr(III)-complexes in Cl--containing industrial wastewater.

Photochemical Initiation and Reactions of Thiyl Radicals Studied with SH2' Radical Traps.

A radical trapping method based on an SH2' homolytic substitution reaction was applied to study the mechanism of a photochemical spirocyclisation of indole-ynones in the presence of thiols. Starting material, products and a range of trapped radical intermediates were simultaneously detected in reaction mixtures by mass spectrometry (MS). The trapped intermediates included both initiating and main chain propagating radicals. These data made it possible to propose a self-initiation mechanism consistent with the originally postulated photoexcitation of an intramolecular electron donor-acceptor complex of the substrate. The effect of thiol structure on the MS peak intensity of the reaction components was rationalised in terms of the relative stability of the radical intermediates. The results were compared to a simpler related reaction, a photochemical thiol-ene addition where reagents, products and trapped intermediate radicals were also detected by MS. Relative MS peak intensities were again explained by a combination of electronic and steric effects on the stability of intermediate radicals. Overall, SH2' radical trapping was demonstrated to be a powerful experimental technique for providing mechanistic evidence on photochemical and other organic radical reactions.

Dissociative Electron Attachment Dynamics of a Promising Cancer Drug Indicates Its Radiosensitizing Potential.

2-Bromo-1-(3,3-dinitroazetidin-1-yl)ethan-1-one (RRx-001) is a hypoxic cell chemotherapeutics with already demonstrated synergism in combined chemo-radiation therapy. The interaction of the compound with secondary low-energy electrons formed in large amounts during the physico-chemical phase of the irradiation may lead to these synergistic effects. The present study focuses on the first step of RRx-001 interaction with low-energy electrons in which a transient anion is formed and fragmented. Combination of two experiments allows us to disentangle the decay of the RRx-001 anion on different timescales. Sole presence of the electron initiates rapid dissociation of NO2 and HNO2 neutrals while NO2 - and Br- anions are produced both directly and via intermediate complexes. Based on our quantum chemical calculations, we propose that bidirectional state switching between π*(NO2) and σ*(C-Br) states explains the experimental spectra. The fast dynamics monitored will impact the condensed phase chemistry of the anion as well.

Sulfur-based fluorescent probes for biological analysis: A review.

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.