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The reaction chemistry and degradation mechanism of MnO2‐based cathodes remain controversial, which hinder their applications in energy storage. Herein, a conversion reaction between Zn4SO4·(OH)6·nH2O (ZSH) and ZnxMnO(OH)2 (ZMO) is proposed in ZnSO4‐based electrolytes. The conversion reaction is an important component of the reaction chemistry as well as the Zn2+/H+ intercalation/deintercalation reaction, which not only provides electrochemical capacity but also dominates the degradation of MnO2 cathodes. The massive accumulation of inactive ZMO seriously destroying the dynamic performance of MnO2 cathodes is deemed to be a principal trigger of the degradation mechanism. Intriguingly, the conversion reaction is sensitive to voltage, which can be activated by voltage modulation. Active ZMO generated in the activated conversion reaction is endowed with higher reversibility and electrooxidation, avoiding the accumulation of inactive ZMO and the decline of kinetic performance, which are evidenced by MnO2 and ZSH cathodes. Accordingly, superior cycling stability with a capacity retention of 89.1% after 2000 cycles is achieved at 2 A g−1 for the MnO2 cathode equipped with the activated conversion reaction. Impressively, the conversion reaction activated by voltage modulation is applicable to various crystal forms of MnO2 (α‐, β‐, γ‐, δ‐), which is significant for the ZIBs with a long lifespan. [ABSTRACT FROM AUTHOR]

The enzymatic biosynthesis of fragrance molecules from lignin fragments is an important reaction in biotechnology for the sustainable production of fine chemicals. In this work we investigated the biosynthesis of vanillin from lignostilbene by a nonheme iron dioxygenase using QM/MM and tested several suggested proposals via either an epoxide or dioxetane intermediate. Binding of dioxygen to the active site of the protein results in the formation of an iron(II)−superoxo species with lignostilbene cation radical. The dioxygenase mechanism starts with electrophilic attack of the terminal oxygen atom of the superoxo group on the central C=C bond of lignostilbene, and the second‐coordination sphere effects in the substrate binding pocket guide the reaction towards dioxetane formation. The computed mechanism is rationalized with thermochemical cycles and valence bond schemes that explain the electron transfer processes during the reaction mechanism. Particularly, the polarity of the protein and the local electric field and dipole moments enable a facile electron transfer and an exergonic dioxetane formation pathway. [ABSTRACT FROM AUTHOR]

The nonheme iron dioxygenase deoxypodophyllotoxin synthase performs an oxidative ring-closure reaction as part of natural product synthesis in plants. How the enzyme enables the oxidative ring-closure reaction of (-)-yatein and avoids substrate hydroxylation remains unknown. To gain insight into the reaction mechanism and understand the details of the pathways leading to products and by-products we performed a comprehensive computational study. The work shows that substrate is bound tightly into the substrate binding pocket with the C7'-H bond closest to the iron(IV)-oxo species. The reaction proceeds through a radical mechanism starting with hydrogen atom abstraction from the C7'-H position followed by ring-closure and a final hydrogen transfer to form iron(II)-water and deoxypodophyllotoxin. Alternative mechanisms including substrate hydroxylation and an electron transfer pathway were explored but found to be higher in energy. The mechanism is guided by electrostatic perturbations of charged residues in the second-coordination sphere that prevent alternative pathways. [ABSTRACT FROM AUTHOR]

Obtaining a rapid deflagration-to-detonation transition (DDT) within a short smooth tube is a challenging task. Here, an unconventional means of flame acceleration propagating upstream in subsonic and supersonic mixtures within a smooth tube was introduced to acquire a speedy DDT. The Navier–Stokes equations with an adaptive mesh refinement technique and a detailed hydrogen–air chemistry reaction mechanism of 11 species and 27 steps were utilized to resolve the entire DDT characteristics. The effect of the initial Mach number on flame acceleration and DDT mechanism was revealed comprehensively. The results demonstrated that a prompt oblique shock wave (SW) occurs when the flame propagates upstream along the boundary walls due to the boundary layer influence. An intense coupling between the SW and the leading flame front is enhanced by increasing the initial Mach number of the mixture. The speedy generation of the oblique SW is formed at the incipient stage, mainly produced by the boundary layer influence and the coalescences of the compression waves. Consequently, the run-up time to detonation is shortened accordingly through a fierce reflected SW due to the intense leading SW after it reflects from the confined wall. Furthermore, three kinds of DDT evolution are revealed from the obtained results: (1) localized ignition in the upper boundary wall after the reflected and transverse shock waves propagate in the upper wall regions; (2) autoignition is formed in the confined wall corner after the reflected SW; and (3) direct detonation transition occurs at the end wall behind a strongly reflected SW in the supersonic case. [ABSTRACT FROM AUTHOR]

As high-energy cathode materials, conversion-type metal fluorides provide a prospective pathway for developing next-generation lithium-ion batteries. However, they suffer from severe performance decay owing to continuous structural destruction and active material dissolution upon cycling, which worsen at elevated temperatures. Here, we design a novel FeF2 cathode with in situ polymerized solid-state electrolyte systems to enhance the cycling ability of metal fluorides at 60 °C. Novel FeF2 with a mesoporous structure (meso-FeF2) improves Li+ diffusion and relieves the volume change that typically occurs during the alternating conversion reactions. The structural stability of the meso-FeF2 cathode is strengthened by an in situ polymerized solid-state electrolyte, which prevents the pulverization and ion dissolution that are inevitable for conventional liquid electrolytes. Under the double action of this in situ polymerized solid-state electrolyte and the meso-FeF2's mesoporous structure, the active material maintains an intact SEI layer and part of the mesoporous structure after long charge-discharge cycling, showing excellent cycling stability at high temperatures. [ABSTRACT FROM AUTHOR]

The presented Review is focused on the latest research in the field of inorganic chemistry performed by the van Eldik group and his collaborators. The first part of the manuscript concentrates on the interaction of nitric oxide and its derivatives with biologically important compounds. We summarized mechanistic information on the interaction between model porphyrin systems (microperoxidase) and NO as well as the recent studies on the formation of nitrosylcobalamin (CblNO). The following sections cover the characterization of the Ru(II)/Ru(III) mixed‐valence ion‐pair complexes, including Ru(II)/Ru(III)(edta) complexes. The last part concerns the latest mechanistic information on the DFT techniques applications. Each section presents the most important results with the mechanistic interpretations. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide is a versatile reductant that under the right conditions can react to form dioxygen in an electrochemical reaction. This reaction has a low carbon footprint and applications are being sought for batteries. In this work a computational study is presented on a recently reported nonheme iron(II) complex where we study mechanistic pathways leading to dioxygen formation from H2O2. The work shows that upon reduction of the iron(III)‐hydroperoxo species it rapidly leads through heterolytic cleavage of the dioxygen bond to form iron(IV)‐oxo(hydroxo). The dimerization reaction of two iron(IV)‐oxo(hydroxo) complexes then leads to formation of the dioxygen bond rapidly with small barriers. Dissociation of the dimer expels dioxygen in an exothermic reaction. An alternative mechanism through the formation of a μ‐1,2‐peroxo‐μ‐1,1‐hydroperoxodiiron(II) intermediate was also tested but found to be highly endergonic. These studies highlight the electrochemical feasibilities of nonheme iron(III)‐hydroperoxo complexes. [ABSTRACT FROM AUTHOR]

Highlights: Detailed discussion and summary of aqueous electrolyte chemistry, parasitic reactions chemistry, and storage energy chemistry and their relationship in aqueous zinc ions batteries are conducted. The recent development of strategies for enhancing the inherent stability of electrolyte and zinc anode to restrain parasitic reactions is reviewed from a thermodynamic perspective. The regulation strategies of electrolyte/electrode interfaces to block parasitic reactions by adsorbents and solid electrolyte interphase are reviewed from a kinetic perspective. Based on the attributes of nonflammability, environmental benignity, and cost-effectiveness of aqueous electrolytes, as well as the favorable compatibility of zinc metal with them, aqueous zinc ions batteries (AZIBs) become the leading energy storage candidate to meet the requirements of safety and low cost. Yet, aqueous electrolytes, acting as a double-edged sword, also play a negative role by directly or indirectly causing various parasitic reactions at the zinc anode side. These reactions include hydrogen evolution reaction, passivation, and dendrites, resulting in poor Coulombic efficiency and short lifespan of AZIBs. A comprehensive review of aqueous electrolytes chemistry, zinc chemistry, mechanism and chemistry of parasitic reactions, and their relationship is lacking. Moreover, the understanding of strategies for suppressing parasitic reactions from an electrochemical perspective is not profound enough. In this review, firstly, the chemistry of electrolytes, zinc anodes, and parasitic reactions and their relationship in AZIBs are deeply disclosed. Subsequently, the strategies for suppressing parasitic reactions from the perspective of enhancing the inherent thermodynamic stability of electrolytes and anodes, and lowering the dynamics of parasitic reactions at Zn/electrolyte interfaces are reviewed. Lastly, the perspectives on the future development direction of aqueous electrolytes, zinc anodes, and Zn/electrolyte interfaces are presented. [ABSTRACT FROM AUTHOR]

CO2 utilization is an important process in the chemical industry with great environmental power. In this work we show how CO2 and H2 can be reacted to form methanol on an iron(II) center and highlight the bottlenecks for the reaction and what structural features of the catalyst are essential for efficient turnover. The calculations predict the reactions to proceed through three successive reaction cycles that start with heterolytic cleavage of H2 followed by sequential hydride and proton transfer processes. The H2 splitting process is an endergonic process and hence high pressures will be needed to overcome this step and trigger the hydrogenation reaction. Moreover, H2 cleavage into a hydride and proton requires a metal to bind hydride and a nearby source to bind the proton, such as an amide or pyrazolyl group, which the scorpionate ligand used here facilitates. As such the computations highlight the non‐innocence of the ligand scaffold through proton shuttle from H2 to substrate as an important step in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Aromaticity, in general, can promote a given reaction by stabilizing a transition state or a product via a mobility of π electrons in a cyclic structure. Similarly, such a promotion could be also achieved by destabilizing an antiaromatic reactant. However, both aromaticity and transition states cannot be directly measured in experiment. Thus, computational chemistry has been becoming a key tool to understand the aromaticity-driven reaction mechanisms. In this review, we will analyze the relationship between aromaticity and reaction mechanism to highlight the importance of density functional theory calculations and present it according to an approach via either aromatizing a transition state/product or destabilizing a reactant by antiaromaticity. Specifically, we will start with a particularly challenging example of dinitrogen activation followed by other small-molecule activation, C–F bond activation, rearrangement, as well as metathesis reactions. In addition, antiaromaticity-promoted dihydrogen activation, CO2 capture, and oxygen reduction reactions will be also briefly discussed. Finally, caution must be cast as the magnitude of the aromaticity in the transition states is not particularly high in most cases. Thus, a proof of an adequate electron delocalization rather than a complete ring current is recommended to support the relatively weak aromaticity in these transition states. [ABSTRACT FROM AUTHOR]

High‐valent metal‐oxo species play critical roles in enzymatic catalysis yet their properties are still poorly understood. In this work we report a combined experimental and computational study into biomimetic iron(IV)‐oxo and iron(III)‐oxo complexes with tight second‐coordination sphere environments that restrict substrate access. The work shows that the second‐coordination sphere slows the hydrogen atom abstraction step from toluene dramatically and the kinetics is zeroth order in substrate. However, the iron(II)‐hydroxo that is formed has a low reduction potential and hence cannot do OH rebound favorably. The tolyl radical in solution then reacts further with alternative reaction partners. By contrast, the iron(IV)‐oxo species reacts predominantly through OH rebound to form alcohol products. Our studies show that the oxidation state of the metal influences reactivities and selectivities with substrate dramatically and that enzymes will likely need an iron(IV) center to catalyze C−H hydroxylation reactions. [ABSTRACT FROM AUTHOR]

High‐valent iron(IV)‐oxo intermediates are versatile oxidants in the biotransformation of various substrates by metalloenzymes and catalyze essential reactions for human health as well as in the biodegradation of toxic organic pollutants in the environment. Herein, we report a biomimetic system that efficiently reacts with halophenols through defluorination reactions and characterize various short‐lived intermediates along the reaction mechanism. We study the reactivity pattern of a nonheme iron(IV)‐oxo species with a series of trihalophenols (X=F, Cl, Br). A combined experimental and computational study reveals that the oxidative dehalogenation of 2,4,6‐trifluorophenol is initiated with an H‐atom abstraction from the phenolic group by the iron(IV)‐oxo species resulting in the formation of a phenolate radical and an iron(III)‐hydroxo species. This iron(III)‐hydroxo species forms an adduct with the oxidized substrate with λmax at 558 nm which subsequently decays to give quinones as products. [ABSTRACT FROM AUTHOR]

The microscopic properties of nonequilibrium arc plasma have great significance for researching the breaking capacity of SF6 circuit breakers and constructing arc plasma simulation models. The polytetrafluoroethylene (PTFE) vapor generated by the ablation of the nozzle material significantly affects the SF6 arc plasma particles and thus affects the microscopic properties of the nonequilibrium arc plasma. At present, the calculation of the microscopic properties of nonequilibrium SF6–PTFE arc plasma has not been reported, mainly because the basic data for the chemical reaction mechanism and chemical reaction rate in the plasma cannot be obtained effectively. In this paper, quantum chemistry was used to theoretically research the reaction mechanisms and rates between CF3, CF2, and CF radicals and SF6, SF5, SF4, SF3, SF3, SF2, and SF in SF6–PTFE arc plasma at 298–10 000 K. A total of 18 chemical reactions are included. Structural optimizations, vibrational frequency calculations, and zero-point energy calculations for the reactants, products, and transition states were performed at the B3LYP/6-311++G(d,p) level of theory. The single-point energies of all species were obtained at the CCSD(T)/aug-cc-PVTZ level. The reaction rates of all reactions between 298 and 10 000 K were obtained by using transition state theory. The reaction rates were successfully fitted using the Arrhenius equation and the three-parameter Arrhenius equation. It has found that reactions between CF2 and fluoro sulfides have higher potential energies. Reactions R13, R7, R14, and R8 exhibit higher reaction rates at 298–10 000 K, whereas R3, R4, R5, and R6 have lower reaction rates. This work can provide theoretical guidance for research on nonequilibrium SF6–PTFE and SF6–CF4 arc plasma microscopic properties. [ABSTRACT FROM AUTHOR]

Bioorthogonal chemistry involves selective biocompatible reactions between functional groups that are not normally present in biology. It has been used to probe biomolecules in living systems, and has advanced biomedical strategies such as diagnostics and therapeutics. In this review, the challenges and opportunities encountered when translating in vitro bioorthogonal approaches to in vivo settings are presented, with a focus on methods to deliver the bioorthogonal reaction components. These methods include metabolic bioengineering, active targeting, passive targeting, and simultaneously used strategies. The suitability of bioorthogonal ligation reactions and bond cleavage reactions for in vivo applications is critically appraised, and practical considerations such as the optimum scheduling regimen in pretargeting approaches are discussed. Finally, we present our own perspectives for this area and identify what, in our view, are the key challenges that must be overcome to maximise the impact of these approaches. [ABSTRACT FROM AUTHOR]

Context: The Maillard reaction is a high-temperature reaction of amino acids and carbohydrates to produce macromolecular substances such as melanoidins and intermediate reducing ketones, aldehydes, and volatile compounds. At present, only very limited researches involved the reaction mechanisms of Maillard reaction, which causes a lot of confusion in understanding numerous food processes. The detailed calculations of Maillard reaction are urgently needed. Methods: The density functional theory (DFT) method (M06-2X/6-311G*) was used to deeply explore the specific mechanism of the primary and intermediate stages of Maillard reaction for a selected model system. Results: The results show that the basic reaction processes in primary stage are the formation of Schiff-base by the condensation of amino and carbonyl groups, and then, Schiff-base tautomerization twice through proton transfer to generate Amadori rearrangement products. In the intermediate stage, two main reaction paths, 1-2 and 2-3 enolization, were comprehensively investigated. The first route finally generates 5-hydroxymethylfurfural through isomerization, dehydration, hydrolysis, elimination, and condensation, and the second route products dicarbonyl compounds through isomerization and elimination and then Strecker degradation forms aldehydes through condensation, decarboxylation, hydrolysis, and elimination. The results show that both paths are involved in complex reactions, some are lower barrier reactions, and some higher barrier reactions. An important aspect is that water catalysis is critical in all of these reactions; it is present in most processes. Our study deepens the understanding of the Maillard reaction from molecular level and facilitate the regulation of some harmful products. [ABSTRACT FROM AUTHOR]

Computational investigation of interfacial failure in composite materials is challenging because it is inherently multi-scale: the bond-breaking processes that occur at the covalently bonded interface and initiate failure involve quantum mechanical phenomena, yet the mechanisms by which external stresses are transferred through the matrix occur on length and time scales far in excess of anything that can be simulated quantum mechanically. In this work, we demonstrate and validate an adaptive quantum mechanics (QM)/molecular mechanics simulation method that can be used to address these issues and apply it to study critical failure at a covalently bonded carbon nanotube (CNT)-polymer interface. In this hybrid approach, the majority of the system is simulated with a classical forcefield, while areas of particular interest are identified on-the-fly and atomic forces in those regions are updated based on QM calculations. We demonstrate that the hybrid method results are in excellent agreement with fully QM benchmark simulations and offers qualitative insights missing from classical simulations. We use the hybrid approach to show how the chemical structure at the CNT-polymer interface determines its strength, and we propose candidate chemistries to guide further experimental work in this area. [ABSTRACT FROM AUTHOR]

The role of vibrational excitation of reactants in driving reactions involving polyatomic species has been often studied by means of classical or quasi-classical trajectory simulations. We propose a different approach based on investigation of vibrational features of the Cl−⋯CH3Cl pre-reaction complex for the Cl− + CH3Cl SN2 reaction. We present vibrational power spectra and frequency estimates for the title pre-reaction complex calculated at the level of classical, semiclassical, and second-order vibrational perturbation theory on a pre-existing analytical potential energy surface. The main goals of the paper are the study of anharmonic effects and understanding of vibrational couplings that permit energy transfer between the collisional kinetic energy and the internal vibrations of the reactants. We provide both classical and quantum pictures of intermode couplings and show that the SN2 mechanism is favored by the coupling of a C–Cl bend involving the Cl− projectile with the CH3 rocking motion of the target molecule. We also illustrate how the routines needed for semiclassical vibrational spectroscopy simulations can be interfaced in a user-friendly way to pre-existing molecular dynamics software. In particular, we present an implementation of semiclassical spectroscopy into the VENUS suite of codes, thus providing a useful computational tool for users who are not experts of semiclassical dynamics. [ABSTRACT FROM AUTHOR]

• After adding 5 ppm oxygen, the activity is increased to 2.38×106 g·(mol Cr·h)−1. • The amount of polyethylene is significantly reduced after introducing oxygen. • Possible reaction mechanisms of oxygen with TMA and MMAO are proposed through NMR. • Oxygen can react with TMA and MMAO to form lager oligomers and oxidized oligomers. • The oxidation MMAO affected the catalytic species of catalyst system. We have investigated the effect of oxygen on ethylene oligomerization activity and selectivity toward 1-hexene (1-C 6) and 1-octene (1-C 8) using Cr(III) diphosphine catalyst system. The addition of a small amount of oxygen (5 ppm) can improve the activity from 1.75×106 g·(mol Cr·h)−1 to as much as 2.38×106 g·(mol Cr·h)−1, greatly reducing the amount of polyethylene from 1.88 wt% to 0.59 wt%, and maintaining the overall selectivity of 1-C 6 and 1-C 8. The variation trend of the system performance with temperature and n (Al)/ n (Cr) was basically the same before and after. The maximum activity of oxygen modified MMAO activated system reached 2.14×106 g·(mol Cr·h)−1. Through the analysis of NMR and UV–vis DRS results, oxygen mainly reacts with MMAO or residual TMA to produce larger steric bulk oligomers and oxidized oligomers. The larger oligomers resulting in more steric hindrance around the active Cr species, disfavor the attack of impurity small molecules and long chain molecules on the active center, thereby inhibiting the reaction inactivation and the PE formation. The modification MMAO affected the catalyst species, which may also affect the catalyst performance, especially at high O 2 concentration. [Display omitted] [ABSTRACT FROM AUTHOR]

• A theoretical study of the structure, electronic, and reaction mechanism of CO 2 to methanol on In 3 Ru(212) surfaces with different surface In/Ru ratio. • In 3 Ru could achieve high methanol selectivity by adding a H 2 O into each elementary step because it benefits the O H formation process. Designing high-performance catalyst is vital in the field of CO 2 methanolization. In this study, two In 3 Ru surfaces (In 3 Ru_i and In 3 Ru_r) were employed as computational models and the density functional theory was applied to study the influence of surface In/Ru ratio on their surface morphologies, reaction mechanisms and catalysis performance for methanol synthesis. Surface characterization reveals that In 3 Ru_i is higher in surface In/Ru ratio than In 3 Ru_r, and such difference facilitates CO 2 adsorption on In 3 Ru_r. Being different in surface In/Ru ratio, two surfaces exhibit distinct variations in the reaction mechanism of methanol formation. For In 3 Ru_i, the "Formate" pathway dominates the first CO 2 activation step which leads to methanol production. On the other hand, In 3 Ru_r prefers the "reverse water-gas shift" pathway (RWGS) in the initial step of CO 2 activation, but this mechanism is unable to generate CH 3 OH due to the kinetic limitation of CO* hydrogenation. Based on the microkinetic modeling, In 3 Ru_i is superior in both CO 2 production rate and CH 3 OH selectivity than the other one, suggesting higher surface In/Ru ratio benefits methanol formation, which complies well with the experiment. Overall, our study offers a new perspective with respect to how surface morphology of the bimetallic catalyst influences the reaction mechanisms of CO 2 hydrogenation. [Display omitted] [ABSTRACT FROM AUTHOR]

Several recent mass spectrometry experiments reveal a marked enhancement of the reaction rate of organic reactions in microdroplets. This enhancement has been tentatively attributed to the accumulation of excess charge on a surface, which in turn can give rise to a lowering of activation energy of the reaction. Here we model the reactions in droplets as a three-step process: (i) diffusion of a reactant from the core of the droplet to the surface, (ii) search by diffusion of the reactant on the surface to find a reactive partner, and finally (iii) the intrinsic reaction leading to bond breaking and product formation. We obtain analytic expressions for the mean search time (MST) to find a target located on the surface by a reactant in both two- and three-dimensional droplets. Analytical results show quantitative agreement with Brownian dynamics simulations. We find, as also reported earlier, that the MST varies as R2/D, where R is the radius of the droplet and D is the diffusion constant of the molecules in the droplet medium. We also find that a hydronium ion in the vicinity can substantially weaken the bond and hence lowers the activation barrier. We observe a similar facilitation of bond breaking in the presence of a static dipolar electric field along any of the three Cartesian axes. If the intrinsic reaction is faster compared to the mean search time involved, it becomes primarily a diffusion-controlled process; otherwise the reaction cannot be accelerated in the droplet medium. The air-droplet interface provides a different environment compared to the interior of the droplet. Hence, we might also expect a completely different mechanism and products in the case of droplet reactions. [ABSTRACT FROM AUTHOR]

A kinetic study is reported for reactions of 2,4-dinitrophenyl X-substituted-benzenesulfonates (1a–1f) and Y-substituted-phenyl benzenesulfonates (2a–2f) with Z-substituted-pyridines. The reactions proceed through S–O and C–O bond scissions competitively. The Yukawa–Tsuno plot for the reactions of 1a–1f with 4-oxypyridine (S–O bond fission) exhibits an excellent linearity. The Brønsted-type plot for the reactions of 2,4-dinitrophenyl benzenesulfonate (1d) with pyridines (S–O bond fission) is also linear with βnuc = 0.62. The Brønsted-type plot for the reactions of 2a–2f with 4-oxypyridines (S–O bond fission) is linear with βlg = –1.17. Thus, the reactions have been concluded to proceed through a concerted mechanism, in which leaving-group expulsion is significantly more advanced than bond formation between the electrophilic center and nucleophile at the transition state. The Hammett plot for the reactions of 1a–1f with 4-oxypyridine (C–O bond fission) exhibits scattered points with ρX = 0.98. The Brønsted-type plot for the reactions of 1d with Z-substituted-pyridines (C–O bond fission) results in an excellent linear correlation with βnuc = 0.38. Thus, the reactions (C–O bond fission) have been concluded to proceed through a stepwise mechanism with a Meisenheimer complex, in which expulsion of the leaving group occurs after the rate-determining step. Factors governing regioselectivity and reaction mechanism are discussed. [ABSTRACT FROM AUTHOR]

This work presents a new CFD model developed to investigate the SiC film growth over a fuel combustion nozzle in the commercial hot-wall CVD reactor. A detailed 3D model consisting of the compressive transport models and the reaction mechanism to account for the chemistry of the gas-phase and surface reactions are developed. The velocity, temperature, and concentration profiles inside the reactor are predicted numerically. The multispecies transport and its interplay with the gas and surface reactions are understood to operate the reactor effectively. The natural convection and hydrodynamics stability of the flow is investigated using various dimensionless groups (Re, Pr. Pe, and Gr/Re2). It has been observed that the buoyancy-driven flow is dominant at a large Reynolds number (Re) and Gr/Re2 ratio. This results in flow recirculation, which ultimately deteriorates the film uniformity. A sensitivity analysis is performed to identify how critical parameters affect the deposition process. Besides, the optimisation of the CVD reactor is also served by combining the support vector machine, a versatile supervised machine learning method, and the Nelder-Mead algorithm to improve the film quality. Our results demonstrate that the present methodology effectively obtains optimal process conditions, significantly enhancing the film performance. [ABSTRACT FROM AUTHOR]

The chelator-mediated Fenton (CMF) chemistry is one of the main biological non-enzymatic systems for oxygen-centered radical generation. A perhydroxyl radical (HO2˙) is a secondary radical specie in CMF systems, however, despite being reported as an iron reducer, its production and role in the CMF redox chemistry are not yet well understood. We assessed the production profiles of HO2˙ and HO˙ generated in situ in CMF systems by EPR, iron-reducing capacity with and without HO2˙, and ligand concentration using CMF systems with p-substituted catecholates between pH values 3.0 and 7.0. The results showed that HO2˙ was generated as a secondary radical in all CMF systems but it also showed evidence of a HO2˙-independent pathway that contributes to the reduction of Fe3+. Along with the current knowledge of the reaction mechanism of the CMF chemistry, the SQ˙ of the ED ligand is proposed to contribute to the generation of HO2˙. [ABSTRACT FROM AUTHOR]

Organic chemistry (OC) appears to be an unstructured and confusing subject to many learners. Reaction mechanisms often seem to be an additional challenge rather than a helpful guideline. Comparable problems were also found for OC as a science at the beginning of the 20th century. One turning point was the systematic application of physical principles on organic reactions through Ingold and coworkers. Kinetic measurements implied for example that in nucleophilic substitution reactions the elimination of the leaving group and the attack of the nucleophile could either occur at the same time or stepwise. In this work the historic insights are made accessible for school lessons by easy experiments suitable for school students. A fictional audio diary of Hilda Ingold is proposed as a history lift to make learners realize that in principle different reaction pathways are possible for one reaction type. [ABSTRACT FROM AUTHOR]

Taurine/α‐ketoglutarate dioxygenase is an important enzyme that takes part in the cysteine catabolism process in the human body and selectively hydroxylates taurine at the C1‐position. Recent computational studies showed that in the gas‐phase the C2−H bond of taurine is substantially weaker than the C1−H bond, yet no evidence exists of 2‐hydroxytaurine products. To this end, a detailed computational study on the selectivity patterns in TauD was performed. The calculations show that the second‐coordination sphere and the protonation states of residues play a major role in guiding the enzyme to the right selectivity. Specifically, a single proton on an active site histidine residue can change the regioselectivity of the reaction through its electrostatic perturbations in the active site and effectively changes the C1−H and C2−H bond strengths of taurine. This is further emphasized by many polar and hydrogen bonding interactions of the protein cage in TauD with the substrate and the oxidant that weaken the pro‐R C1−H bond and triggers a chemoselective reaction process. The large cluster models reproduce the experimental free energy of activation excellently. [ABSTRACT FROM AUTHOR]

Aryloxyalkanoate dioxygenases are unique herbicide biodegrading nonheme iron enzymes found in plants and hence, from environmental and agricultural point of view they are important and valuable. However, they often are substrate specific and little is known on the details of the mechanism and the substrate scope. To this end, we created enzyme models and calculate the mechanism for 2,4‐dichlorophenoxyacetic acid biodegradation and 2‐methyl substituted analogues by density functional theory. The work shows that the substrate binding is tight and positions the aliphatic group close to the metal center to enable a chemoselective reaction mechanism to form the C2‐hydroxy products, whereas the aromatic hydroxylation barriers are well higher in energy. Subsequently, we investigated the metabolism of R‐ and S‐methyl substituted inhibitors and show that these do not react as efficiently as 2,4‐dichlorophenoxyacetic acid substrate due to stereochemical clashes in the active site and particularly for the R‐isomer give high rebound barriers. [ABSTRACT FROM AUTHOR]

This rosarium article relates the adventure started 50 years ago of a computational chemist who was interested in molecules; what are they, what are their shape and how do they react. The story describes results, still valid today, obtained with highly simplified models of chemical reality and elementary computational methods and the gain resulting from the use of better models and more elaborate computational methods. It was necessary to select examples. In this presentation, focus is on hydride and dihydrogen complexes as well as on nucleophiles. Nucleophiles were considered as free hydrides in gas phase at the start of the rosarium while the Grignard reaction is treated with ab initio molecular mechanisms at the end of it. [ABSTRACT FROM AUTHOR]

This paper reports the results of modelling of the current-voltage characteristics (I-V) of a planar mid-wave Mercury Cadmium Telluride photodiode in a gate controlled diode experiment. It is reported that the diode exhibits nearly ideal I-V characteristics under the optimum surface potential leading to the minimal surface leakage current. Deviations from the optimum surface potential lead to non ideal I-V characteristics, indicating a strong relationship between the ideality factor of the diode with its surface leakage current. Diode's I-V characteristics have been modelled over a range of gate voltages from -9V to -2V. This range of gate voltages includes accumulation, flat band, and depletion and inversion conditions below the gate structure of the diode. It is shown that the I-V characteristics of the diode can be very well described by (i) thermal diffusion current, (ii) ohmic shunt current, (iii) photo-current due to background illumination, and (iv) excess current that grows by the process of avalanche multiplication in the gate voltage range from -3V to -5V that corresponds to the optimum surface potential. Outside the optimum gate voltage range, the origin of the excess current of the diode is associated with its high surface leakage currents. It is reported that the ohmic shunt current model applies to small surface leakage currents. The higher surface leakage currents exhibit a nonlinear shunt behaviour. It is also shown that the observed zero-bias dynamic resistance of the diode over the entire gate voltage range is the sum of ohmic shunt resistance and estimated zero-bias dynamic resistance of the diode from its thermal saturation current. [ABSTRACT FROM AUTHOR]

Catalyst-free and catalyst-assisted nanowire (NW) syntheses are increasingly carried out by mechanism(s) other than the well-known VLS (vapor-liquid-solid) mechanism. Yet these growths are not fully understood. An in-depth investigation has been carried out to understand the mechanism of the catalyst-free and catalyst-mediated non-VLS NW growths. Various chemical and physical processes involved in these growths have been studied to formulate general principles. Phase transitions, synthesis routes, and the fundamentals underlying these routes have been explored. Nanoparticle surfaces conducive to NW syntheses have been examined. The role of surface treatment, such as oxidation, oxygenation, doping, acid treatment, plasma treatment, etc., in creating such surfaces has been elucidated. Surface treatment and phase transition under appropriate growth conditions (temperature, pressure, ambient, and the presence of contaminants) have been found to be important. They play a crucial role in creating diffusion paths for the diffusion of the growth species for NW growths. Interdiffusion of the catalyst and the growth species on the nanoparticle surface has been found also to add a new dimension to the growth kinetics. When integrated together, they create a unified platform versatile enough to explain essentially all catalyst-free and catalyst-mediated non-eutectic NW growths. The platform uncovers numerous growth-related problems never understood before. Available experiments extensively support this platform. These experiments suggest that it is based on solid foundation and has broad and probably universal appeal. It pertains to the vapor-quasiliquid-solid, vapor-quasi-solid-solid mechanism proposed some six years ago. [ABSTRACT FROM AUTHOR]

• Carbamate and urea derivatives as representative linker units of polyurethanes. • Mn(I) effective catalyst for hydrogenation of carbamate or carbamide derivatives. • The different hydrogenation steps follow diverse mechanisms. • In most cases the H-transfer from the metal to carbonyl c atom is the slowest step. • Computations confirm a major resistance of carbamide derivatives to be hydrogenated. A comprehensive computational study is reported here on the mechanism of the reaction through which a Mn(I) pincer catalyst is able to assist the hydrogenation process of carbamate and urea derivatives, chosen as representative linker units of polyurethanes. Four substrate models, carbamate and urea derivatives, have been examined in order to evaluate their influence on the hydrogenation mechanism of polyurethanes to generate useful alcohols and amines organic building blocks. The outcomes of the computational exploration highlight a different behavior of the catalyst in assisting hydrogenation of carbamate or carbamide derivatives in the different steps of the whole reaction mechanism. Indeed, for the first hydrogenation step, the viability of a ligand-assisted mechanism has been found only for carbamide derivatives and involves a reversible structural change of the pincer ligand that can partially detach from the metal to favor the coordination of the molecule to be processed. The carbamate derivatives, instead, go through the formation of an intermediate in which the substrate interacts with the complex without binding. The mechanism of second hydrogenation is common to all the examined cases and requires the exploitation of the hemilabile nature of the PNN ligand. From the calculated energies put into play it clearly appears the great ability of the Mn(I) complex in catalyzing the hydrogenation of both carbamate and carbamide derivatives. [Display omitted] [ABSTRACT FROM AUTHOR]

Thiol dioxygenases are important enzymes for human health; they are involved in the detoxification and catabolism of toxic thiol‐containing natural products such as cysteine. As such, these enzymes have relevance to the development of Alzheimer's and Parkinson's diseases in the brain. Recent crystal structure coordinates of cysteine and 3‐mercaptopropionate dioxygenase (CDO and MDO) showed major differences in the second‐coordination spheres of the two enzymes. To understand the difference in activity between these two analogous enzymes, we created large, active‐site cluster models. We show that CDO and MDO have different iron(III)‐superoxo‐bound structures due to differences in ligand coordination. Furthermore, our studies show that the differences in the second‐coordination sphere and particularly the position of a positively charged Arg residue results in changes in substrate positioning, mobility and enzymatic turnover. Furthermore, the substrate scope of MDO is explored with cysteinate and 2‐mercaptosuccinic acid and their reactivity is predicted. [ABSTRACT FROM AUTHOR]

Reaction monitoring by electrospray ionization mass spectrometry (ESI‐MS) is a popular method for investigation of reaction mechanisms. Here, we present a new approach based on a coupling between a modular capillary flow reactor and ESI‐MS. The flow reactor allows a sequential adding of the reactants. We demonstrate the approach for oxidation of Ph2S by ArIO catalyzed by [(TPA)Fe(TfO)2] (ArIO=2‐(tBuSO2)C6H4IO, TPA=tris(2‐pyridylmethyl)amine, TfO−=triflate). In steps, we could follow the formation of the reactive iron(IV)oxo complexes, then the oxygen transfer reaction from the iron(IV)oxo to the sulfide, and finally the reoxidation of the iron complexes. The flow reactor also allows kinetic experiments by changing relative concentrations of the reactants. We could analyze in detail the formation of various [(TPA)FeIVO(X)]2+/+ complexes (X=MeCN, ArI, ArIO, TfO−) and compare their relative reactivity with Ph2S. The [(TPA)FeIVO(MeCN)]2+ complex is the most reactive complex for the oxygen atom transfer reaction whilst [(TPA)FeIVO(ArIO)]2+ prevails in solution under catalytic conditions. [ABSTRACT FROM AUTHOR]

The quantum calculation gives the insight of reaction mechanism in chemistry. In this work, we predict hydrogen evolution reaction (HER) mechanism in Ni(abt)2 (abt = 2‐aminobenzenethiolate) catalyst. Using density functional theory (DFT) and coupled‐cluster singles, doubles and perturbative triples (CCSD(T)) methods, we demonstrate the potential energy surface (PES) for the HER reaction result with two intermediate states (IM) and transition states (TS). Our result shows that the hydrogen atoms are migrated to Ni atom one by one from each of two amino groups. It indicates that the HER reaction in Ni(abt)2 occurs following the ligand‐assisted metal‐centered H2 production. Finally, two hydrogen atoms are merged in Ni atom site which generates hydrogen molecule. This would be meaningful prediction to understand the role of metal catalyst in HER reaction pathway. [ABSTRACT FROM AUTHOR]

The cytochrome P450 enzymes are important enzymes in the liver that trigger drug metabolism reactions. In biotechnology and biomimetic chemistry, synthetic models of the active species of P450 have been developed and designed and often react differently. Here, we investigate a biomimetic P450 model complex with phthalocyanine equatorial ligand rather than heme or porphyrin and with and without four tert-butyl substituents to the periphery of the ligand. Density functional theory studies on the electronic properties of the active species of the system, namely the iron(IV)-oxo with equatorial ligand cation radical species and its reactivity in oxygen atom transfer were studied. The work shows that a phthalocyanine equatorial ligand rather than porphyrin leads to a dramatic effect on the orbital energy levels of the iron(IV)-oxo species and creates a species with close-lying doublet and quartet spin states with two unpaired electrons in π*xz and π*yz for the Fe−O interaction coupled to a ligand radical in an a1u-type orbital. The latter contrasts P450 Compound I that has the a1u orbital doubly occupied and a singly occupied a2u orbital instead, As a consequence, our biomimetic model gives a reduced redox potential as compared to a system with a porphyrin-based radical and makes it a weaker oxidant. Nevertheless, the iron(IV)-oxo cation radical species with phthalocyanine ligand is shown to react with para-X-substituted thioanisole (X = CH3, Cl, CN, H, NO2, OCH3) substrates with small oxygen atom transfer barriers that align with the σ-Hammett parameter. The reactions are concerted with a single barrier leading to sulfoxide products. Synopsis: A series of density functional theory studies are presented on the electronic properties of a phthalocyanine ligated iron(IV)-oxo cation radical species and its reactivity with para-substituted thioanisole substrates. The studies show that despite the fact the reactant is electronically different from cytochrome P450 Compound I, it should react with sulfides in a concerted synchronous manner efficiently. [ABSTRACT FROM AUTHOR]

Reaction coordinates are of central importance for correct understanding of reaction dynamics in complex systems, but their counter-intuitive nature made it a daunting challenge to identify them. Starting from an energetic view of a reaction process as stochastic energy flows biased towards preferred channels, which we deemed the reaction coordinates, we developed a rigorous scheme for decomposing energy changes of a system, both potential and kinetic, into pairwise components. The pairwise energy flows between different coordinates provide a concrete statistical mechanical language for depicting reaction mechanisms. Application of this scheme to the C7eq → C7ax transition of the alanine dipeptide in vacuum revealed novel and intriguing mechanisms that eluded previous investigations of this well studied prototype system for biomolecular conformational dynamics. Using a cost function developed from the energy decomposition components by proper averaging over the transition path ensemble, we were able to identify signatures of the reaction coordinates of this system without requiring any input from human intuition. [ABSTRACT FROM AUTHOR]

An effective way to accelerate rare events in molecular dynamics simulations is to apply a bias potential which destabilizes minima without biasing the transitions between stable states. This approach, called hyperdynamics, is limited by our ability to construct general bias potentials without having to understand the reaction mechanisms available to the system, a priori. Current bias potentials are typically constructed in terms of a metric which quantifies the distance that a trajectory deviates from the reactant state minimum. Such metrics include detection of negative curvatures of the potential, an energy increase, or deviations in bond lengths from the minimum. When one of these properties exceeds a critical value, the bias potentials are constructed to approach zero. A problem common to each of these schemes is that their effectiveness decreases rapidly with system size. We attribute this problem to a diminishing volume defined by the metrics around a reactant minimum as compared to the total volume of the reactant state basin. In this work, we mitigate the dimensionality scaling problem by constructing bias potentials that are based upon the distance to the boundary of the reactant basin. This distance is quantified in two ways: (i) by following the minimum mode direction to the reactant boundary and (ii) by training a machine learning algorithm to give an analytic expression for the boundary to which the distance can be calculated. Both of these ridge-based bias potentials are demonstrated to scale qualitatively better with dimensionality than the existing methods. We attribute this improvement to a greater filling fraction of the reactant state using the ridge-based bias potentials as compared to the standard potentials. [ABSTRACT FROM AUTHOR]

In order to identify two-step chemical mechanisms, we propose a method based on a small temperature modulation and on the analysis of the concentration oscillations of a single tagged species involved in the first step. The thermokinetic parameters of the first reaction step are first determined. Then, we build test functions that are constant only if the chemical system actually possesses some assumed two-step mechanism. Next, if the test functions plotted using experimental data are actually even, the mechanism is attributed and the obtained constant values provide the rate constants and enthalpy of reaction of the second step. The advantage of the protocol is to use the first step as a probe reaction to reveal the dynamics of the second step, which can hence be relieved of any tagging. The protocol is anticipated to apply to many mechanisms of biological relevance. As far as ligand binding is considered, our approach can address receptor conformational changes or dimerization as well as competition with or modulation by a second partner. The method can also be used to screen libraries of untagged compounds, relying on a tracer whose concentration can be spectroscopically monitored. [ABSTRACT FROM AUTHOR]

The need for enhanced education in catalysis is common to many countries. Dramatic progress in catalysis fundamental science and technology occurred in the last two decades enables teaching and learning of catalysis based on a unified approach in which catalysis including all its subdisciplines is taught in a logically consistent way using the organic chemistry reaction mechanism, namely the main chemistry conceptual methodology with its unique usefulness as predictive and creative tool. Selected lessons from the past are taken into account along with new insight on the role of catalysis and green chemistry in chemistry education based on systems thinking. [ABSTRACT FROM AUTHOR]

• The catalytic rules of the non-halogen anion and cation for the cycloaddition reaction were revealed. • the reaction mechanism was deeply explored by DFT calculations and in-situ IR spectroscopy. • Six new non-halogen ionic liquids were synthesized and used as efficient catalysts for cycloaddition reaction. Non-halogen ionic liquids are considered efficient catalyst for CO 2 conversion into cyclic carbonates. In this work, six carboxylic acid ionic liquids with different types and sizes of cations are designed and synthesized to systematically investigate the catalytic contribution of the non-halogen cation and anion for CO 2 conversion into cyclic carbonate. The result shows that the anion could improve the catalytic activity by improve the basicity of ionic liquids, and the cation that has a weak interaction with anion is more conducive for the reactivity. Further, the reaction mechanism is deeply studied by using the optimized [P 4444 ][IsoNic]: two reaction intermediates are captured by In-situ infrared, combined with DFT calculation, the anion directly inducing ring-opening mechanism is proposed. This work provides an in-depth understanding of catalytic contribution of non-halogen ionic liquids used in cycloaddition reaction. Graphical Abstract [Display omitted] [ABSTRACT FROM AUTHOR]

CFD simulations are presented for an in-depth study on different formulations (including implementation details) of the Eddy Dissipation Concept (EDC) turbulent combustion model, with infinitely fast chemistry as well as finite-rate chemistry with different reaction mechanisms. A turbulent line burner and a gaseous pool fire are chosen as first step in an extensive validation campaign for large eddy simulations of this kind, performed with OpenFOAM v1912. Artificial flame anchoring is necessary to establish a burning flame with finite-rate chemistry. Differences in mean temperatures, and the resulting flow fields, as obtained with the different formulations of the EDC combustion model, are explained by the impact of the reaction rates. CO is discussed as the most important of minor species as well. It is demonstrated that both the formulation of EDC and the choice of the chemistry mechanism can have a significant impact when the CFD mesh is not sufficiently fine, even though the flames studied are unsuppressed. This can lead to significant deviations from experimental data. This is a point of attention for future work, focusing on extinction and re-ignition phenomena. • CFD simulations with EDC and infinitely fast/finite-rate chemistry are presented. • The EDC formulation can significantly affect the mean flame temperatures. • The finite-rate chemistry reaction mechanism affects the local reaction rates. • Flame anchoring is needed to obtain a sustained flame with finite-rate chemistry. [ABSTRACT FROM AUTHOR]

This article, titled "Mechanism of CO2 Reduction to Methanol with H2 on an Iron(II)-scorpionate Catalyst," explores the reaction mechanism of a homogeneous catalyst that binds H2 and CO2 on an iron(II)-scorpionate complex. Through calculations, it is determined that the iron complex can cleave H2 into a hydride and proton, which then bind to different sites on the complex. CO2 is subsequently reduced through a series of hydride and proton transfer steps, ultimately resulting in the formation of methanol products. The full research article provides more detailed information on this topic. [Extracted from the article]

Selective oxidation is one of the most important and challenging transformations in both academic research and chemical industry. Recently, a highly selective and efficient way to synthesize biologically active γ-hydroxy-α,β-unsaturated molecules from Cu-catalyzed vinylogous aerobic oxidation of α,β- and β,γ-unsaturated compounds has been developed. However, the detailed reaction mechanism remains elusive. Herein, we report a density functional theory study on this Cu-catalyzed vinylogous aerobic oxidation of γ,γ-disubstituted α,β- and β,γ-unsaturated isomers. Our computational study unveils detailed mechanism for each elementary step, i.e. deprotonation, O2 activation, and reduction. Besides, the origin of regioselectivity, divergent reactivities of substrates as well as reducing agents, and the byproduct generation have also been investigated. Notably, the copper catalyst retains the + 2 oxidation state through the whole catalytic cycle and plays essential roles in multiple steps. These findings would provide hints on mechanistic studies and future development of transition metal-catalyzed aerobic oxidation reactions. [ABSTRACT FROM AUTHOR]

The peroxidase–oxidase (PO) reaction involves the oxidation of reduced nicotinamide adenine dinucleotide by molecular oxygen. When both reactants are supplied continuously to a reaction mixture containing the enzyme and a phenolic compound, the reaction will exhibit oscillatory behavior. In fact, the reaction exhibits a zoo of dynamical behaviors ranging from simple periodic oscillations to period-doubled and mixed mode oscillations to quasiperiodicity and chaos. The routes to chaos involve period-doubling, period-adding, and torus bifurcations. The dynamic behaviors in the experimental system can be simulated by detailed semiquantitative models. Previous models of the reaction have omitted the phenolic compound from the reaction scheme. In the current paper, we present new experimental results with the oscillating PO reaction that add to our understanding of its rich dynamics, and we describe a new variant of a previous model, which includes the chemistry of the phenol in the reaction mechanism. This new model can simulate most of the experimental behaviors of the experimental system including the new observations presented here. For example, the model reproduces the two main routes to chaos observed in experiments: (i) a period-doubling scenario, which takes place at low pH, and a period-adding scenario involving mixed mode oscillations (MMOs), which occurs at high pH. Our simulations suggest alternative explanations for the pH-sensitivity of the dynamics. We show that the MMO domains are separated by narrow parameter regions of chaotic behavior or quasiperiodicity. These regions start as tongues of secondary quasiperiodicity and develop into strange attractors through torus breakdown. [ABSTRACT FROM AUTHOR]

Model chemistry G3(MP2,CC)//B3LYP/6‐311G(d,p) calculations of the potential energy surface for the reaction of phenyl radical (C6H5) with phenylacetylene (C8H6) have been carried out and combined with Rice‐Ramsperger‐Kassel‐Marcus/Master Equation calculations of temperature‐ and pressure‐dependent rate constants. The results showed that the reaction can serve as a viable source for the formation of phenanthrene via an indirect route involving a primary reaction of phenyl addition to the ortho carbon in the ring of phenylacetylene and H elimination producing 2‐ethynylbiphenyl followed by secondary H‐assisted isomerization of 2‐ethynylbiphenyl to phenanthrene. In the secondary reaction, the H atom adds to the α carbon of the ethynyl side chain, then a six‐member ring closure takes place followed by aromatization via an H loss. The channel of H addition to the side chain of 2‐ethynylbiphenyl appears to be much faster than H addition to the ortho carbon in the ethynyl‐substituted ring leading back to the initial C6H5 + C8H6 reactants. Rate constants for the primary C6H5 + C8H6←→2‐ethynylbiphenyl (p1) + H and secondary p1 + H←→phenanthrene (p2) + H reactions have been computed in the temperature range of 500‐2500 K at pressures of 30 Torr, 1, 10, and 100 atm and fitted to modified Arrhenius expressions. The suggested kinetic scheme and rate constants are proposed as a prototype for the modeling of the growth of polycyclic aromatic hydrocarbons via the phenyl addition‐dehydrocyclization (PAC) mechanism involving an addition of a PAH radical to an ethynyl‐substituted PAH molecule. [ABSTRACT FROM AUTHOR]

• Reductive inks were used to assess the photocatalytic activity. • Oxidative fluorescence probe was used to assess the photocatalytic activity. • Emulsions coatings and cement-based materials were evaluated. • Limitations of the Resazurin-ink test for some materials were demonstrated. • Oxidative and reductive reaction rates were correlated with nitrogen oxide removal. The photocatalytic activity of a wide variety of photocatalytic construction materials with different intrinsic properties, mainly microstructure and TiO 2 crystallographic phases, were obtained using alternative methods (Rz and NBT-reductive inks and TA-oxidative fluorescence probe) and the NOx removal standard ISO 22197-1:2007. The Rz-ink test was shown to be unsuitable for some of the materials due to spontaneous colour change in the dye upon contact with these (here denominated, reactive samples), in the absence of radiation. No such shortcomings were observed for either NBT-ink or TA-probe. Comparison of the three set of results showed a reasonably high correlation among the activities determined by the different methods, despite the wide variation in the characteristics of the photocatalytic materials tested, underlying reaction mechanisms and the physics and chemistry of the inter-phase contact (ink/probe/contaminant-substrate). The findings attest to the possible relationship between the rates of oxidative and reductive reactions in semiconductor photocatalysis. These alternative methods may be regarded as a new 'cheap and simple' approach to photocatalytic activity measurements. [ABSTRACT FROM AUTHOR]