A Q-learning method based on coarse-to-fine potential energy surface for locating transition state and reaction pathway

Transition state (TS) on the potential energy surface (PES) plays a key role in determining the kinetics and thermodynamics of chemical reactions. Inspired by the fact that the dynamics of complex systems are always driven by rare but significant transition events, we herein propose a TS search method in accordance with the Q-learning algorithm. Appropriate reward functions are set for a given PES to optimize the reaction pathway through continuous trial and error, and then the TS can be obtained from the optimized reaction pathway. The validity of this Q-learning method with reasonable settings of Q-value table including actions, states, learning rate, greedy rate, discount rate, and so on, is exemplified in 2 two-dimensional potential functions. In the applications of the Q-learning method to two chemical reactions, it is demonstrated that the Q-learning method can predict consistent TS and reaction pathway with those by ab initio calculations. Notably, the PES must be well prepared before using the Q-learning method, and a coarse-to-fine PES scanning scheme is thus introduced to save the computational time while maintaining the accuracy of the Q-learning prediction. This work offers a simple and reliable Q-learning method to search for all possible TS and reaction pathway of a chemical reaction, which may be a new option for effectively exploring the PES in an extensive search manner.

Combined Experimental and Density Functional Theory Study on the Mechanism of the Selective Catalytic Reduction of NO with NH3 over Metal-Free Carbon-Based Catalysts

Metal-free carbon-based catalysts are attracting much attention in the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR). However, the mechanism of the NH3-SCR reaction on carbon-based catalysts is still controversial, which severely limits the development of carbon-based SCR catalysts. Herein, we successfully reconstructed carbon-based catalysts through oxidation treatment with nitric acid, thereby enhancing their low-temperature activity in NH3-SCR. Combining experimental results and density functional theory (DFT) calculations, we proposed a previously unreported NH3-SCR reaction mechanism over carbon-based catalysts. We demonstrated that C-OH and C-O-C groups not only effectively activate NH3 but also remarkedly promote the decomposition of intermediate NH2NO. This study enhances the understanding of the NH3-SCR mechanism on carbon-based catalysts and paves the way to develop low-temperature metal-free SCR catalysts.

Synthesis, Structures and Photophysical Properties of Asymmetric Fulvene-[b]-fused BODIPYs

Herein, we developed a one-pot procedure to synthesize novel fulvene-[b]-fused BODIPYs from α-(2-alkynylphenyl)-pyrrole and acylpyrrole, using 5-exo cyclization as the key transformation. Compared to benzene-[b]-fused BODIPYs, although they have similar chemical compositions, their structures and properties significantly differ from each other, which can be attributed to the less aromaticity of the fulvene linker than benzene. Notably, fulvene-[b]-fused BODIPY 1 b exhibits helical-twisted core skeleton, intensified red-shifted absorption, and peak fluorescence. In addition, the pathway of this one-pot reaction and the mechanism of POCl3 mediated 5-exo cyclization have been proposed by a combining experimental and computational study.

Surface-Enhanced Raman Spectroscopy for Boosting Electrochemical CO2 Reduction on Amorphous-Surfaced Tin Oxide Supported by MXene

Amorphous materials disrupt the intrinsic linear scalar dependence seen in their crystalline counterparts, typically exhibiting enhanced catalytic characteristics. Nevertheless, substantial obstacles remain in terms of boosting their stability, enhancing their conductivity, and elucidating distinct catalytic mechanisms. Herein, a core-shell catalyst, comprising a crystalline SnO2 core and an amorphous SnOx shell supported on MXene (denoted as SnO2@SnOx/MXene), was prepared utilizing hydrothermal and solution reduction methods. The SnO2@SnOx/MXene catalyst excels in the electrocatalytic conversion of CO2 to formate, yielding a Faradaic efficiency (FE) as high as 93% for formate production at -1.17 V vs RHE and demonstrating exceptional durability. Both density functional theory (DFT) calculations and experimental results indicate that the SnOx shell bolsters formate formation by fine-tuning the adsorption energy of the *OCHO intermediate. In SnO2@SnOx/MXene, MXene plays a vital role in enhancing the conductivity and stability of the amorphous shell and especially amplifying Raman signals of catalyst components. The ex/in situ surface-enhanced Raman scattering (SERS) application further confirms the formation of amorphous SnOx and further enables the direct detection of the formation of the intermediate species. This work provides the basis for the application of amorphous materials in practical electrocatalytic reduction of CO2 reduction.

Reaction pathways, proton transfer, and proton pumping in ba3 class cytochrome c oxidase: perspectives from DFT quantum chemistry and molecular dynamics

After drawing comparisons between the reaction pathways of cytochrome c oxidase (CcO, Complex 4) and the preceding complex cytochrome bc1 (Complex 3), both being proton pumping complexes along the electron transport chain, we provide an analysis of the reaction pathways in bacterial ba3 class CcO, comparing spectroscopic results and kinetics observations with results from DFT calculations. For an important arc of the catalytic cycle in CcO, we can trace the energy pathways for the chemical protons and show how these pathways drive proton pumping of the vectorial protons. We then explore the proton loading network above the Fe heme a3-CuB catalytic center, showing how protons are loaded in and then released by combining DFT-based reaction energies with molecular dynamics simulations over states of that cycle. We also propose some additional reaction pathways for the chemical and vector protons based on our recent work with spectroscopic support.

Organic Molecule Bifunctionalized Polymeric Carbon Nitride for Enhanced Photocatalytic Hydrogen Peroxide Production

Modifying the polymeric carbon nitride (CN) with organic molecules is a promising strategy to enhance the photocatalytic activity. However, most previously reported works show that interchain embedding and edge grafting of the organic molecule can hardly be achieved simultaneously. Herein, we successfully synthesized organic molecule bifunctionalized CN (MBCN) through copolymerization of melon and sulfanilamide at a purposely elevated temperature of 550 °C. In MBCN, the edge grafted and interchain embedded benzene rings act as the electron-donating group and charge-transfer channel, respectively, rendering efficient photocatalytic H2 O2 production. The optimal MBCN exhibits a significantly improved non-sacrificial photocatalytic H2 O2 generation rate (54.0 μmol g-1  h-1 ) from pure water, which is 10.4 times that of pristine CN. Experimental and density functional theory (DFT) calculation results reveal that the enhanced H2 O2 production activity of MBCN is mainly attributed to the improved photogenerated charge separation/transfer and decreased formation energy barrier (▵G) from O2- to the intermediate 1,4-endoperoxide (⋅OOH). This work suggests that simultaneous formation of electron donating group and charge transfer channel via organic molecule bifunctionalization is a feasible strategy for boosting the photocatalytic activity of CN.

Controlling Phase Conversion of Cu-Sb-Se Nanoparticles through the Use of an Amide Base

The family of copper antimony selenides is important for renewable energy applications. Several phases are accessible within narrow energy and compositional ranges, and tunability between phases is not well-established. Thus, this system provides a rich landscape to understand the phase transformations that occur in hot-injection nanoparticle syntheses. Rietveld refinements on X-ray diffraction patterns model anisotropic morphologies to obtain phase percentages. Reactions targeting the stoichiometry of CuSbSe₂ formed Cu₃SbSe₃ before decomposing to thermodynamically stable CuSbSe₂ over time. An amide base was added to balance cation reactivity and directly form CuSbSe₂. Interestingly, Cu₃SbSe₃ remained present but converted to CuSbSe₂ more rapidly. We propose that initial Cu₃SbSe₃ formation may be due to the selenium species not being reactive enough to balance the high reactivity of the copper complex. The unexpected effect of a base on cation reactivity in this system provides insight into the advantages and limitations for its use in other multivalent systems.

Distinguishing homogeneous advanced oxidation processes in bulk water from heterogeneous surface reactions in organic oxidation

Clarifying the reaction pathways at the solid-water interface and in bulk water solution is of great significance for the design of heterogeneous catalysts for selective oxidation of organic pollutants. However, achieving this goal is daunting because of the intricate interfacial reactions at the catalyst surface. Herein, we unravel the origin of the organic oxidation reactions with metal oxide catalysts, revealing that the radical-based advanced oxidation processes (AOPs) prevail in bulk water but not on the solid catalyst surfaces. We show that such differing reaction pathways widely exist in various chemical oxidation (e.g., high-valent Mn³⁺ and MnO_X) and Fenton and Fenton-like catalytic oxidation (e.g., Fe²⁺ and FeOCl catalyzing H₂O₂, Co²⁺ and Co₃O₄ catalyzing persulfate) systems. Compared with the radical-based degradation and polymerization pathways of one-electron indirect AOP in homogeneous reactions, the heterogeneous catalysts provide unique surface properties to trigger surface-dependent coupling and polymerization pathways of a two-electron direct oxidative transfer process. These findings provide a fundamental understanding of catalytic organic oxidation processes at the solid-water interface, which could guide the design of heterogeneous nanocatalysts.

First-Principles Study of Nitrogen Adsorption and Dissociation on ZrMnFe(110) Surface

The adsorption, dissociation and penetration processes of N₂ on the surface of ZrMnFe(110) were investigated using the first-principles calculation method in this paper. The results indicate that the vacancy Hollow 1 composed of 4Zr1Fe on the surface of ZrMnFe(110) is the best adsorption site for the N₂ molecule and N atom, and the adsorption energies are 10.215 eV and 6.057 eV, respectively. Electron structure analysis indicates that the N₂ molecule and N atoms adsorbed mainly interact with Zr atoms on the surface. The transition state calculation shows that the maximum energy barriers to be overcome for the N₂ molecule and N atom on the ZrMnFe(110) surface were 1.129 eV and 0.766 eV, respectively. This study provides fundamental insight into the nitriding mechanism of nitrogen molecules in ZrMnFe.

Active Site Engineering on Plasmonic Nanostructures for Efficient Photocatalysis

Plasmonic nanostructures have shown immense potential in photocatalysis because of their distinct photochemical properties associated with tunable photoresponses and strong light-matter interactions. The introduction of highly active sites is essential to fully exploit the potential of plasmonic nanostructures in photocatalysis, considering the inferior intrinsic activities of typical plasmonic metals. This review focuses on active site-engineered plasmonic nanostructures with enhanced photocatalytic performance, wherein the active sites are classified into four types (i.e., metallic sites, defect sites, ligand-grafted sites, and interface sites). The synergy between active sites and plasmonic nanostructures in photocatalysis is discussed in detail after briefly introducing the material synthesis and characterization methods. Active sites can promote the coupling of solar energy harvested by plasmonic metal to catalytic reactions in the form of local electromagnetic fields, hot carriers, and photothermal heating. Moreover, efficient energy coupling potentially regulates the reaction pathway by facilitating the excited state formation of reactants, changing the status of active sites, and creating additional active sites using photoexcited plasmonic metals. Afterward, the application of active site-engineered plasmonic nanostructures in emerging photocatalytic reactions is summarized. Finally, a summary and perspective of the existing challenges and future opportunities are presented. This review aims to deliver some insights into plasmonic photocatalysis from the perspective of active sites, expediting the discovery of high-performance plasmonic photocatalysts.

A Spectroscopic Study on Nitrogen Electrooxidation to Nitrate

As a potential substitute technique for conventional nitrate production, electrocatalytic nitrogen oxidation reaction (NOR) is gaining more and more attention. But, the pathway of this reaction is still unknown owing to the lack of understanding on key reaction intermediates. Herein, electrochemical in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotope-labeled online differential electrochemical mass spectrometry (DEMS) are employed to study the NOR mechanism over a Rh catalyst. Based on the detected asymmetric NO2- bending, NO3- vibration, N=O stretching, and N-N stretching as well as isotope-labeled mass signals of N2O and NO, it can be deduced that the NOR undergoes an associative mechanism (distal approach) and the strong N≡N bond in N2 prefers to break concurrently with the hydroxyl addition in distal N.

DFT Simulation-Based Design of 1T-MoS(2) Cathode Hosts for Li-S Batteries and Experimental Evaluation

The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides (LiPSs) caused by the rapid LiPSs migration to the anode and the slow reaction kinetics in the chain of LiPSs conversion. In this study, we explore 1T-MoS₂ as a cathode host for Li-S batteries by examining the affinity of 1T-MoS₂ substrates (pristine 1T-MoS₂, defected 1T-MoS₂ with one and two S vacancies) toward LiPSs and their electrocatalytic effects. Density functional theory (DFT) simulations are used to determine the adsorption energy of LiPSs to these substrates, the Gibbs free energy profiles for the reaction chain, and the preferred pathways and activation energies for the slow reaction stage from Li₂S₄ to Li₂S. The obtained information highlights the potential benefit of a combination of 1T-MoS₂ regions, without or with one and two sulphur vacancies, for an improved Li-S battery performance. The recommendation is implemented in a Li-S battery with areas of pristine 1T-MoS₂ and some proportion of one and two S vacancies, exhibiting a capacity of 1190 mAh/g at 0.1C, with 97% capacity retention after 60 cycles in a schedule of different C-rates from 0.1C to 2C and back to 0.1C.

Oxide-Derived Core-Shell Cu@Zn Nanowires for Urea Electrosynthesis from Carbon Dioxide and Nitrate in Water

Urea electrosynthesis provides an intriguing strategy to improve upon the conventional urea manufacturing technique, which is associated with high energy requirements and environmental pollution. However, the electrochemical coupling of NO₃^- and CO₂ in H₂O to prepare urea under ambient conditions is still a major challenge. Herein, self-supported core-shell Cu@Zn nanowires are constructed through an electroreduction method and exhibit superior performance toward urea electrosynthesis via CO₂ and NO₃^- contaminants as feedstocks. Both ¹H NMR spectra and liquid chromatography identify urea production. The optimized urea yield rate and Faradaic efficiency over Cu@Zn can reach 7.29 μmol cm^-2 h^-1 and 9.28% at -1.02 V vs RHE, respectively. The reaction pathway is revealed based on the intermediates detected through in situ attenuated total reflection Fourier transform infrared spectroscopy and online differential electrochemical mass spectrometry. The combined results of theoretical calculations and experiments prove that the electron transfer from the Zn shell to the Cu core can not only facilitate the formation of *CO and *NH₂ intermediates but also promote the coupling of these intermediates to form C-N bonds, leading to a high faradaic efficiency and yield of the urea product.

Performance, Reaction Pathway and Kinetics of the Enhanced Dechlorination Degradation of 2,4-Dichlorophenol by Fe/Ni Nanoparticles Supported on Attapulgite Disaggregated by a Ball Milling-Freezing Process

Attapulgite (ATP) disaggregated by a ball milling–freezing process was used to support Fe/Ni bimetallic nanoparticles (nFe/Ni) to obtain a composite material of D-ATP-nFe/Ni for the dechlorination degradation of 2,4-dichlorophenol (2,4-DCP), thus improving the problem of agglomeration and oxidation passivation of nanoscale zero-valent iron (nFe) in the dechlorination degradation of chlorinated organic compounds. The results show that Fe/Ni nanoparticle clusters were dispersed into single spherical particles by the ball milling–freezing-disaggregated attapulgite, in which the average particle size decreased from 423.94 nm to 54.51 nm, and the specific surface area of D-ATP-nFe /Ni (97.10 m²/g) was 6.9 times greater than that of nFe/Ni (14.15 m²/g). Therefore, the degradation rate of 2,4-DCP increased from 81.9% during ATP-nFe/Ni application to 96.8% during D-ATP-nFe/Ni application within 120 min, and the yield of phenol increased from 57.2% to 86.1%. Meanwhile, the reaction rate K_obs of the degradation of 2,4-DCP by D-ATP-nFe/Ni was 0.0277 min⁻¹, which was higher than that of ATP-nFe/Ni (0.0135 min⁻¹). In the dechlorination process of 2,4-DCP by D-ATP-nFe/Ni, the reaction rate for the direct dechlorination of 2,4-DCP of phenol (k₅ = 0.0156 min⁻¹) was much higher than that of 4-chlorophenol (4-CP, k₂ = 0.0052 min⁻¹) and 2-chlorophenol (2-CP, k₁ = 0.0070 min⁻¹), which suggests that the main dechlorination degradation pathway for the removal of 2,4-DCP by D-ATP-nFe/Ni was directly reduced to phenol by the removal of two chlorine atoms. In the secondary pathway, the removal of one chlorine atom from 2,4-DCP to generate 2-CP or 4-CP as intermediate was the rate controlling step. The final dechlorination product (phenol) was obtained when the dechlorination rate accelerated with the progress of the reaction. This study contributes to the broad topic of organic pollutant treatment by the application of clay minerals.

Microwave-Assisted Base-Free Oxidation of Glucose with H2O2 on Gold- and Manganese-Containing SBA-15-Insight into Factors Affecting the Reaction Pathway

The aim of this work was to gain insights into the role of manganese in MnSBA-15 support for gold in the base-free glucose oxidation with H₂O₂ using a microwave reactor. MnSBA-15 (manganese-acidity source) and SBA-15 (for comparison) were modified with Au (2.2 wt. %) and Cu (for comparison). The physicochemical properties of the catalysts were investigated by XRD, N₂ ads/des, TEM, UV-vis, XPS, pyridine adsorption combined with FTIR, ATR-FTIR, and 2-propanol decomposition. The effects of the Mn presence in the support, Au NPs size that determines the number of active Au centers, and the Fermi energy (E_F), together with the effects of the pore size, reaction temperature, and time on the activity and selectivity of the applied catalysts were assessed and discussed. It has been demonstrated that the presence of Mn generated Lewis acid centers which did not participate in glucose and H₂O₂ adsorption, and thus, were not directly involved in the reaction pathway. Both reagents were adsorbed on gold nanoparticles. H₂O₂ was decomposed to molecular oxygen which oxidized glucose to gluconic acid (50-90% of glucose conversion depending on the reaction time and ~100% selectivity). The presence of manganese in MnSBA-15 was responsible for increased Au NPs size and only slightly influenced the negative charge on gold particles. To achieve effective activity a compromise between the number of active gold species and the level of E_F has to be reached (for 5.7 nm Au NPs).

Electrochemical degradation of vanillin using lead dioxide electrode: influencing factors and reaction pathways

In this study, a novel PbO₂-CeO₂ composite electrode was applied it to the electrocatalytic degradation of vanillin. The operating parameters such as applied current density, initial vanillin concentration, supporting electrolyte concentration and pH value were investigated and optimised. After 120 min, in a 0.10 mol L^-1 Na₂SO₄ solution with a current density of 50 mA cm^-2 and a pH value of 5.0 containing 30 mg L^-1 vanillin, the vanillin removal efficiency can reach 98.03%, the COD removal efficiency is up to 73.28%. The results indicate that electrochemical degradation has a high ability to remove vanillin in aqueous solution. The reaction follows a pseudo-first-order reaction kinetics model with rate constants of 0.03036 min^-1. In the process of electrochemical degradation, up to eight hydroxylated or polyhydroxylated oxidation by-products were identified through hydroxylation, dealkylation and substitution reactions. Furthermore, the degradation pathways were proposed, which eventually mineralised into inorganic water and carbon dioxide.

Real-Time Single-Molecule Studies of RNA Polymerase-Promoter Open Complex Formation Reveal Substantial Heterogeneity Along the Promoter-Opening Pathway

The expression of most bacterial genes commences with the binding of RNA polymerase (RNAP)-σ70 holoenzyme to the promoter DNA. This initial RNAP-promoter closed complex undergoes a series of conformational changes, including the formation of a transcription bubble on the promoter and the loading of template DNA strand into the RNAP active site; these changes lead to the catalytically active open complex (RPO) state. Recent cryo-electron microscopy studies have provided detailed structural insight on the RPO and putative intermediates on its formation pathway. Here, we employ single-molecule fluorescence microscopy to interrogate the conformational dynamics and reaction kinetics during real-time RPO formation on a consensus lac promoter. We find that the promoter opening may proceed rapidly from the closed to open conformation in a single apparent step, or may instead involve a significant intermediate between these states. The formed RPO complexes are also different with respect to their transcription bubble stability. The RNAP cleft loops, and especially the β' rudder, stabilise the transcription bubble. The RNAP interactions with the promoter upstream sequence (beyond -35) stimulate transcription bubble nucleation and tune the reaction path towards stable forms of the RPO.

Water Formation Reaction under Interfacial Confinement: Al0.25Si0.75O2 on O-Ru(0001)

Confined nanosized spaces at the interface between a metal and a seemingly inert material, such as a silicate, have recently been shown to influence the chemistry at the metal surface. In prior work, we observed that a bilayer (BL) silica on Ru(0001) can change the reaction pathway of the water formation reaction (WFR) near room temperature when compared to the bare metal. In this work, we looked at the effect of doping the silicate with Al, resulting in a stoichiometry of Al_0.25Si_0.75O₂. We investigated the kinetics of WFR at elevated H₂ pressures and various temperatures under interfacial confinement using ambient pressure X-ray photoelectron spectroscopy. The apparent activation energy was lower than that on bare Ru(0001) but higher than that on the BL-silica/Ru(0001). The apparent reaction order with respect to H₂ was also determined. The increased residence time of water at the surface, resulting from the presence of the BL-aluminosilicate (and its subsequent electrostatic stabilization), favors the so-called disproportionation reaction pathway (*H₂O + *O ↔ 2 *OH), but with a higher energy barrier than for pure BL-silica.

Density Functional Theory Calculations Decipher Complex Reaction Pathways of 6:2 Fluorotelomer Sulfonate to Perfluoroalkyl Carboxylates Initiated by Hydroxyl Radical

6:2 Fluorotelomer sulfonate (6:2 FTSA) is a ubiquitous environmental contaminant belonging to the family of per- and polyfluoroalkyl substances. Previous studies showed that hydroxyl radical (^•OH) efficiently transforms 6:2 FTSA into perfluoroalkyl carboxylates (PFCAs) of different chain lengths (C2-C7), yet the reaction mechanisms were not elucidated. This study used density functional theory (DFT) calculations to map the entire reaction path of 6:2 FTSA initiated by ^•OH and experimentally verified the theoretical results. Optimal reaction pathways were obtained by comparing the rate constants calculated from the transition-state theory. We found that 6:2 FTSA was first transformed to C7 PFCA and C₆F₁₃^•; C₆F₁₃^• was then further reacted to C2-C6 PFCAs. The parallel addition of ^•OH and O₂ to C_nF_2n+1^• was essential to producing C2-C6 PFCAs. The critical step is the generation of alkoxyl radicals, which withdraw electrons from the adjacent C-C groups to result in chain cleavage. The validity of the calculated optimal reaction pathways was further confirmed by the consistency with our experimental data in the aspects of O₂ involvement, identified intermediates, and the final PFCA profile. This study provides valuable insight into the transformation of polyfluoroalkyl substances containing aliphatic carbons in ^•OH-based oxidation processes.

Electrochemical Reduction of CO2 to HCOOH over Copper Catalysts

Although great progress has been made in the field of electrochemical CO₂ reduction reaction (eCO₂RR), inducing product selectivity is still difficult. We herein report that a thiocyanate ion (SCN^-) switched the product selectivity of copper catalysts for eCO₂RR in an H-cell. A cuprous thiocyanate-derived Cu catalyst was found to exhibit excellent HCOOH selectivity (faradaic efficiency = 70-88%) over a wide potential range (-0.66 to -0.95 V vs RHE). Furthermore, it was revealed that the formation of CO and C₂H₄ over commercial copper electrodes could be dramatically suppressed with the presence of SCN^-, switching to HCOOH. Density functional theory calculations disclosed that SCN^- made the formation of HCOO* easier than COOH* on Cu (211), facilitating the HCOOH generation. Our results provide a new insight into eCO₂RR and will be helpful in the development of cheap electrocatalysts for specific utilization.

Order from a Mess: The Growth of 5-Armchair Graphene Nanoribbons

The advent of on-surface chemistry under vacuum has vastly increased our capabilities to synthesize carbon nanomaterials with atomic precision. Among the types of target structures that have been synthesized by these means, graphene nanoribbons (GNRs) have probably attracted the most attention. In this context, the vast majority of GNRs have been synthesized from the same chemical reaction: Ullmann coupling followed by cyclodehydrogenation. Here, we provide a detailed study of the growth process of five-atom-wide armchair GNRs starting from dibromoperylene. Combining scanning probe microscopy with temperature-dependent XPS measurements and theoretical calculations, we show that the GNR growth departs from the conventional reaction scenario. Instead, precursor molecules couple by means of a concerted mechanism whereby two covalent bonds are formed simultaneously, along with a concomitant dehydrogenation. Indeed, this alternative reaction path is responsible for the straight GNR growth in spite of the initial mixture of reactant isomers with irregular metal-organic intermediates that we find. The provided insight will not only help understanding the reaction mechanisms of other reactants but also serve as a guide for the design of other precursor molecules.

A New Strategy to Regulate the Selectivity of Photo-Mediated Catalytic Reaction

Here we developed a new method for regulating the selectivity of photo-mediated catalytic reaction by manipulating the surface charge of Au/TiO₂ (gold/titanium dioxide) catalysts within chemical reaction timescales. Two kinds of photocatalytic reactions, hydrogenation of acetophenone and benzyl alcohol oxidation, have been applied to investigate the photocatalytic performance over Au/TiO₂ catalysts with tunable surface charges. We found that a suitable timescale of switching surface charge on Au would benefit for the enhanced quantum efficiency and play different roles in the selectivity of desired products in hydrogenation and oxidation reactions. Au/TiO₂ catalyst under 5 μs flashing light irradiation exhibits much higher selectivity of 1-phenylethanol in the hydrogenation of acetophenone than that under continuous light and 5 s flashing light irradiation; by contrast, Au/TiO₂ catalysts under both flashing light and continuous light irradiation exhibit a similar selectivity of benzaldehyde in benzyl alcohol oxidation. Our findings will benefit for a better understanding of electronic structure-mediated reaction mechanism and be helpful for achieving highly efficient photocatalytic systems.

[Long-term Storage and Rapid Activity Recovery of ANAMMOX Granular Sludge]

At 4℃ and with no substrate, the activity recovery of ANAMMOX granular sludge was examined after 230 days of storage, and the effect of adding two organic carbon sources (glucose and sodium propionate) on the recovery was explored. After 230 days of long-term storage, the activity of ANAMMOX bacteria was 0.013 g·(g·d)^-1, which was just 6.02% of the baseline, and the average particle size was 135.05 μm, which was 38.23% lower. The sludge disintegration, black in color. In the activity recovery stage, the R2 and R3 reactors added glucose and sodium propionate as organic carbon sources. The recovery results showed that after 15 days of recovery, the PN content of the R1, R2, and R3 reactors reached 126.30, 188.86, and 168.82 mg·g^-1, respectively, and the activity of the ANAMMOX bacteria was improved, reaching 0.145, 0.185, and 0.126 g·(g·d)^-1, respectively. The R2 reactor with glucose as the organic carbon source had the highest ANAMMOX bacteria activity, which recovered 85.65% before preservation, and the total nitrogen removal rate reached 81.61%. On the 20th day, the particle sizes of the ANAMMOX granular sludge in the R1, R2, and R3 reactors were 289.81, 359.66, and 314.37 μm, respectively, indicating that the long-term preservation of ANAMMOX granular sludge is not an insurmountable problem. Furthermore, adding glucose during the recovery phase can not only effectively increase the EPS content and promote particle growth and adhesion, but also enrich the reaction pathways of ANAMMOX, enhancing recovery rates.

New Insights into the N-S Bond Formation of a Sulfurized-Polyacrylonitrile Cathode Material for Lithium-Sulfur Batteries

Sulfurized polyacrylonitrile (S-cPAN) has been recognized as a particularly promising cathode material for lithium-sulfur (Li-S) batteries due to its ultra-stable cycling performance and high degree of sulfur utilization. Though the synthetic conditions and routes for modification of S-cPAN have been extensively studied, details of the molecular structure of S-cPAN remain yet unclear. Herein, a more reasonable molecular structure consisting of pyridinic/pyrrolic nitrogen (N_PD/N_PL) is proposed, based on the analysis of combined X-ray photoelectron spectroscopy, ¹³C/¹⁵N solid-state nuclear magnetic resonance, and density functional theory data. The coexistence of vicinal N_PD/N_PL entities plays a vital role in attracting S₂ molecules and facilitating N-S bond formation apart from the generally accepted C-S bond in S-cPAN, which could explain the extraordinary electrochemical features of S-cPAN among various nitrogen-containing sulfurized polymers. This study provides new insights and a better understanding of structural details and relevant bond formation mechanisms in S-cPAN, providing a foundation for the design of new types of sulfurized cathode materials suitable for application in next-generation high-performance Li-S batteries.

Influence of the Reaction Pathway on the Defect Formation in a Cu2ZnSnSe4 Thin Film

Point defect engineering in Cu₂ZnSnSe₄ (CZTSe) thin films is the main issue to improve its device performance. This study reveals the correlation between the reaction pathway and the point defects in the CZTSe film. The reaction pathway from a metallic precursor (Mo/Zn/Sn/Cu) to a kesterite CZTSe film is varied by changing the annealing process. The synthesized CZTSe films under different reaction pathways induce different device performances with different defect energy levels, although all CZTSe films have similar structural and optical properties (E_g ∼ 1.0 eV). The admittance spectroscopy demonstrates the correlations between point defect types (V_Zn, Zn_Sn, Zn_Cu, Cu_Zn, and V_Cu) and the reaction pathways for the formation of CZTSe films. The different growth rates of binary selenides, such as ZnSe and/or Sn-Se phases, during the annealing process are especially strongly related to the formation of point defects, leading to the different open-circuit voltages (396-451 mV) and fill factors (51-65%). The results of this study suggest that controlling the reaction pathway is an effective approach to adjust the formation of defects in the kesterite CZTSe film as well as to fabricate high-performance solar cell devices.

Mineralization of Diazinon with nanosized-photocatalyst TiO2 in water under sunlight irradiation: optimization of degradation conditions and reaction pathway

The photocatalytic degradation of Diazinon under sunlight irradiation is investigated by using the nanosized photocatalyst TiO₂. Eight intermediates are detected during the degradation, and the reaction pathway is proposed on the base of their intermediates. The degradation parameters, concerning photocatalyst concentration, temperature, pH, sunlight intensity and irradiation time are optimized. Under the optimal conditions, the photocatalytic degradation of Diazinon can be completed within 60 min. The photodegradation is found to follow the pseudo-first-order kinetic law at a rate constant of 0.068 min^-1. The activation energy is 14.7 kJ/mol. The formations of sulphate, phosphate, nitrate and ammonium ions during the degradation are observed. About 83% of the initial N is detected as ammonium and nitrate ions during 50 h of irradiation time.

Synthesis of Grafted Nanofibrillated Cellulose-Based Hydrogel and Study of Its Thermodynamic, Kinetic, and Electronic Properties

Hydrogels were synthesized by a copolymerization reaction of nanofibrillated cellulose (CNF) with acrylic acid (AA) and acrylamide (AM) and N,N-methylene-bis-acrylamide (MBA) as a cross-linker and their absorption performance as a function of composition was determined. Hydrogels with 4% by weight CNF had swelling of about 250 g/g and with 7% CNF about 200 g/g for water. Thermodynamic and kinetic studies of the reaction pathways and the electronic properties of the cellulose and monomers were investigated through density functional theory calculations. Thermodynamic investigations revealed that the radical formation of cellulose that initiates the hydrogel process can occur through the breaking of the homolytic covalent bonds C6-OH and C3-OH. The results show that the reaction of CNF with monomers is thermodynamically favorable in the decreasing order of AM, AA, and MBA. The kinetic study also indicates that the reaction kinetics of CNF with AM is faster than with AA which is much faster than with MBA. Overall, this study has elucidated some of the key chemical characteristics that impact the derivatization of nanocellulose structures to produce advanced renewable bioproducts.

Understanding Reaction Pathways in High Dielectric Electrolytes Using β-Mo2C as a Catalyst for Li-CO2 Batteries

The rechargeable Li-CO₂ battery has attracted considerable attention in recent years because of its carbon dioxide (CO₂) utilization and because it represents a practical Li-air battery. As with other battery systems such as the Li-ion, Li-O₂, and Li-S battery systems, understanding the reaction pathway is the first step to achieving high battery performance because the performance is strongly affected by reaction intermediates. Despite intensive efforts in this area, the effect of material parameters (e.g., the electrolyte, the cathode, and the catalyst) on the reaction pathway in Li-CO₂ batteries is not yet fully understood. Here, we show for the first time that the discharge reaction pathway of a Li-CO₂ battery composed of graphene nanoplatelets/beta phase of molybdenum carbide (GNPs/β-Mo₂C) is strongly influenced by the dielectric constant of its electrolyte. Calculations using the continuum solvents model show that the energy of adsorption of oxalate (C₂O₄^2-) onto Mo₂C under the low-dielectric electrolyte tetraethylene glycol dimethyl ether is lower than that under the high-dielectric electrolyte N,N-dimethylacetamide (DMA), indicating that the electrolyte plays a critical role in determining the reaction pathway. The experimental results show that under the high-dielectric DMA electrolyte, the formation of lithium carbonate (Li₂CO₃) as a discharge product is favorable because of the instability of the oxalate species, confirming that the dielectric properties of the electrolyte play an important role in the formation of the discharge product. The resulting Li-CO₂ battery exhibits improved battery performance, including a reduced overpotential and a remarkable discharge capacity as high as 14,000 mA h g^-1 because of its lower internal resistance. We believe that this work provides insights for the design of Li-CO₂ batteries with enhanced performance for practical Li-air battery applications.

Influence of the Catalyst Particle Size on the Aqueous Phase Reforming of n-Butanol Over Rh/ZrO2

Butanol is a by-product obtained from biomass that can be valorized through aqueous phase reforming. Rh/ZrO₂ catalysts were prepared and characterized, varying the size of the support particles. The results showed a relatively mild effect of internal mass transport on butanol conversion. However, the influence of internal transport limitations on the product distribution was much stronger, promoting consecutive reactions, i.e., dehydrogenation, hydrogenolysis, and reforming of propane and ethane. Hydrogen consuming reactions, i.e., hydrogenolysis, were more strongly enhanced than hydrogen producing reactions due to internal concentration gradients. Large support particles deactivated faster, attributed to high concentrations of butyraldehyde inside the catalyst particles, enhancing deposit formation via aldol condensation reactions. Consequently, also the local butyric acid concentration was high, decreasing the local pH, enhancing Rh leaching. The influence of internal transfer limitation on product distribution and stability is discussed based on a reaction scheme with three main stages, i.e., (1) formation of liquid intermediates via dehydrogenation, (2) formation of gas via decarbonylation/decarboxylation reactions, and (3) hydrocarbon hydrogenolysis/reforming/dehydrogenation.

Atmospheric Low-Temperature Plasma-Induced Changes in the Structure of the Lignin Macromolecule: An Experimental and Theoretical Investigation

Atmospheric low-temperature plasma has emerged as a promising pretreatment for lignocellulose to improve bio-refining. Herein, we investigated plasma-induced changes in the chemical structure of lignin to obtain a fundamental understanding of the plasma-lignocellulose interaction. Based on the results, plasma possesses a strong capacity to cleave C-C covalent bonds in the aliphatic region of lignin, accompanied by oxidation. Plasma treatment leads to the degradation and fragmentation of lignin. Pronounced deconstruction of β-O-4 aryl ether is observed in plasma. The relative content of β-O-4 aryl ether was reduced from the initial value of 65.1/100Ar to 58.7/100Ar for lignin from corncob and from the initial value of 72.5/100Ar to 63.8/100Ar for lignin from poplar after plasma treatment, respectively. According to the density functional theory analysis, the oxygen atom of β-O-4 aryl ether is the most likely potential reaction site and the C_β-O covalent bond exhibits the lowest decomposition free energy (50.5 kcal mol^-1), which will easily be cleaved in plasma. The dominant reaction pathway of lignin degradation is the cleavage of the C_β-O covalent bond followed by the cleavage of the C_β-C_α bond. We propose that this investigation is beneficial to optimize and expand the applications of plasma treatment in pretreatment of lignocellulose.

Elucidation of the Reaction Mechanism of C2 + N1 Aziridination from Tetracarbene Iron Catalysts

A combined computational and experimental study was undertaken to elucidate the mechanism of catalytic C₂ + N₁ aziridination supported by tetracarbene iron complexes. Three specific aspects of the catalytic cycle were addressed. First, how do organic azides react with different iron catalysts and why are alkyl azides ineffective for some catalysts? Computation of the catalytic pathway using density functional theory (DFT) revealed that an alkyl azide needs to overcome a higher activation barrier than an aryl azide to form an iron imide, and the activation barrier with the first-generation catalyst is higher than the activation barrier with the second-generation variant. Second, does the aziridination from the imide complex proceed through an open-chain radical intermediate that can change stereochemistry or, instead, via an azametallacyclobutane intermediate that retains stereochemistry? DFT calculations show that the formation of aziridine proceeds via the open-chain radical intermediate, which qualitatively explains the formation of both aziridine diastereomers as seen in experiments. Third, how can the formation of the side product, a metallotetrazene, be prevented, which would improve the yield of aziridine at lower alkene loading? DFT and experimental results demonstrate that sterically bulky organic azides prohibit formation of the metallotetrazene and, thus, allow lower alkene loading for effective catalysis. These multiple insights of different aspects of the catalytic cycle are critical for developing improved catalysts for C₂ + N₁ aziridination.

Synthesis of liquid fuel via direct hydrogenation of CO2

Synthesis of liquid fuels (C₅₊ hydrocarbons) via CO₂ hydrogenation is very promising. Hydrogenation of CO₂ to liquid hydrocarbons usually proceeds through tandem catalysis of reverse water gas shift (RWGS) reaction to produce CO, and subsequent CO hydrogenation to hydrocarbons via Fischer-Tropsch synthesis (FTS). CO₂ is a thermodynamically stable and chemically inert molecule, and RWGS reaction is endothermic and needs a higher temperature, whereas FTS reaction is exothermic and is thermodynamically favored at a lower temperature. Therefore, the reported technologies have some obvious drawbacks, such as high temperature, low selectivity, and use of complex catalysts. Herein we discovered that a simple Co₆/MnO_x nanocatalyst could efficiently catalyze CO₂ hydrogenation. The reaction proceeded at 200 °C, which is much lower than those reported so far. The selectivity of liquid hydrocarbon (C₅ to C₂₆, mostly n-paraffin) in total product could reach 53.2 C-mol%, which is among the highest reported to date. Interestingly, CO was hardly detectable during the reaction. The in situ Fourier transform infrared characterization and ¹³CO labeling test confirmed that the reaction was not via CO, accounting for the eminent catalytic results. This report represents significant progress in CO₂ chemistry and CO₂ transformation.

Catalytic methyl esterification of colophony over ZnO/SFCCR with subcritical CO2: catalytic performance, reaction pathway and kinetics

A heterogeneous catalyst (ZnO/SFCCR) composed of ZnO supported on spent fluid cracking catalyst by wet impregnation was synthesized and applied to the esterification of colophony acids with methanol under subcritical CO₂ conditions. The catalyst was characterized by SEM-EDS, BET, ICP, FTIR, XRD and Py-IR. An experimental set-up involving a new injection technique was designed to promote the heterogeneous methyl esterification, and the subcritical CO₂ played a role in auxiliary acid catalysis (a pH range of 3.54-3.91), increasing the lifespan of ZnO/SFCCR, reducing the viscosity of the system to promote gas-liquid mass transfer. A maximum conversion rate of 97.01% was obtained in a relatively short time of 5 h. Kinetic experiments were performed from 190 to 220°C using a special high-temperature sampling device and analysing aliquots with high-performance liquid chromatography. A new reaction pathway, involving methyl abietate, methyl dehydroabietate, methyl neoabietate and methyl palustrate along with other kinds of colophony acids, was developed. The kinetic parameters were obtained using the Levenberg-Marquardt nonlinear least-squares method, and the activation energies for the isomerizations of neoabietic and palustric acids and for the methyl esterification of neoabietic, abietic, palustric and dehydroabietic acids were found to be 107.09, 113.95, 68.99, 49.85, 75.43 and 59.20 kJ mol^-1, respectively. The results from the kinetic model were in good agreement with experimental values.

Oxidative degradation of pentachlorophenol by permanganate for ISCO application

Potassium permanganate (KMnO₄) has been an effective technology for the in situ chemical oxidation (ISCO) of many organic compounds including chlorinated alkanes and alkenes, but it has rarely been applied for oxidizing aromatic organochlorines. This study confirms the ability of permanganate to oxidize an aromatic chlorinated compound, pentachlorophenol (PCP), in an efficient manner at neutral pH. The rate of the reaction between KMnO₄ and PCP was calculated and the results indicated that the reaction between PCP and permanganate is relatively fast with a second-order rate constant k″ ∼ 30 M^-1 s^-1. Besides the kinetic aspect, the authors identified the main reaction by-products, and proposed a possible reaction mechanism scheme. The general pathway shows the formation of chlorinated intermediates, and ultimately, the complete mineralization to chloride, water, and CO₂ confirmed by total organic carbon and chloride measurement in solution. Flow-through column experiments, consisting of flushing a PCP-contaminated sandy or natural soil with oxidant, showed the good ability of permanganate to eliminate the pollutant. After 24 h of treatment, 77% and 56% of PCP abatement were obtained for sandy and natural soil, respectively. These findings show the high potential of permanganate for the in situ remediation of aromatic organochlorine contaminated soils.

Platinum catalyzed hydrodeoxygenation of guaiacol in illumination of cresol production: a density functional theory study

The unprocessed bio-oil obtained by the pyrolysis of lignocellulosic biomass comprises hundreds of oxy-components which vitiate its quality in terms of low heating value, low stability, low pH, etc. Therefore, it has to be upgraded prior to its use as transportation fuel. In this work, guaiacol, a promising compound of the phenolic fraction of unprocessed bio-oil, is considered as a model component for studying its hydrodeoxygenation over a Pt₃ catalyst cluster. The production of catechol, 3-methylcatechol, m-cresol and o-cresol from guaiacol over a Pt₃ cluster is numerically investigated using density functional theory. Further, the kinetic parameters are obtained over a wide range of temperature, i.e. 473-673 K at an interval of 50 K. Briefly, results indicate that O─H and C─H bond scissions determine the reaction rates of 'guaiacol to catechol' and 'catechol to 3-methylcatechol' reactions with activation energies of 30.32 and 41.3 kcal mol^-1, respectively. On the other hand, C─O bond scissions determine the rates of 3-methylcatechol to m- and o-cresol production reactions, respectively. The kinetics of all reactions indicate that ln k versus 1/T plots are linear over the entire range of temperature considered herein.

Deoxygenation of Palmitic and Lauric Acids over Pt/ZIF-67 Membrane/Zeolite 5A Bead Catalysts

The deoxygenation of palmitic and lauric acids over 0.5 wt % Pt/ZIF-67 membrane/zeolite 5A bead catalysts is demonstrated. Almost complete conversion (% deoxygenation of ≥95%) of these two fatty acids was observed over both fresh and recycled catalyst after a 2 h reaction time. The catalysts displayed high selectivity to pentadecane and undecane via decarboxylation reaction pathway even at low 0.5 wt % Pt loading. Selectivity to pentadecane and undecane as high as ∼92% and ∼94% was observed under CO₂ atmosphere when palmitic and lauric acids were used respectively as reactants. Depending on the reaction gas atmosphere, two distinctive reaction pathways were observed: decarboxylation and hydrodeoxygenation. Specifically, it was found that decarboxylation reaction pathway was more favorable in the presence of helium and CO₂, while hydrodeoxygenation pathway strongly competed against the decarboxylation pathway when hydrogen was employed during the deoxygenation reactions. Esters were identified as the key reaction intermediates leading to decarboxylation and hydrodeoxygenation pathways.

An effective method and pathways of acrylonitrile degradation to acrylic acid through an alkaline hydrothermal system

Degradation of pollution for specific chemicals represents an optimal approach to high-strength wastewater treatment. One-pot selective conversion of acrylonitrile to acrylic acid in a hydrothermal system with NaOH as a catalyst was carried out. The influence factors were evaluated, including initial acrylonitrile concentration, reaction temperature, reaction time and amount of alkali. Experimental results showed that the highest yield of acrylic acid (55%) was obtained at the initial acrylonitrile concentration of 3 × 10³ mg/L, 300°C for 90 s with 1.0 M NaOH. To determine the reaction path, intermediates analysis and calculation of carbon and nitrogen balance were carried out by means of HPLC, GC and TOC/TN methods. Two probable reaction pathways were proposed as follows: (1) Acrylonitrile was hydrolyzed into acrylamide, and acrylic acid was obtained via further hydrolysis. (2) Acrylonitrile was converted into 3-hydroxy-propionitrile via additive reaction, and this product was readily converted to 3-hydroxy-propionic acid through two steps of hydrolysis, followed by dehydration reaction to produce acrylic acid. This study offered not only an efficient method to transfer highly toxic pollutants into valuable chemical, but also a better understanding of hydrothermal alkali catalytic reaction.

Decomposition pathways of polytetrafluoroethylene by co-grinding with strontium/calcium oxides

Waste polytetrafluoroethylene (PTFE) could be easily decomposed by co-grinding with inorganic additive such as strontium oxide (SrO), strontium peroxide (SrO₂) and calcium oxide (CaO) by using a planetary ball mill, in which the fluorine was transformed into nontoxic inorganic fluoride salts such as strontium fluoride (SrF₂) or calcium fluoride (CaF₂). Depending on the kind of additive as well as the added molar ratio, however, the reaction mechanism of the decomposition was found to change, with different compositions of carbon compounds formed. CO gas, the mixture of strontium carbonate (SrCO₃) and carbon, only SrCO₃ were obtained as reaction products respectively with equimolar SrO, excess SrO and excess SrO₂ to the monomer unit CF₂ of PTFE were used. Excess amount of CaO was needed to effectively decompose PTFE because of its lower reactivity compared with strontium oxide, but it promised practical applications due to its low cost.

Imaging Successive Intermediate States of the On-Surface Ullmann Reaction on Cu(111): Role of the Metal Coordination

The in-depth knowledge about on-surface reaction mechanisms is crucial for the tailor-made design of covalently bonded organic frameworks, for applications such as nanoelectronic or -optical devices. Latest developments in atomic force microscopy, which rely on functionalizing the tip with single CO molecules at low temperatures, allow to image molecular systems with submolecular resolution. Here, we are using this technique to study the complete reaction pathway of the on-surface Ullmann-type coupling between bromotriphenylene molecules on a Cu(111) surface. All steps of the Ullmann reaction, i.e., bromotriphenylenes, triphenylene radicals, organometallic intermediates, and bistriphenylenes, were imaged with submolecular resolution. Together with density functional theory calculations with dispersion correction, our study allows to address the long-standing question of how the organometallic intermediates are coordinated via Cu surface or adatoms.

Crystal Structures of Diaryliodonium Fluorides and Their Implications for Fluorination Mechanisms

The radiofluorination of diaryliodonium salts is of value for producing radiotracers for positron emission tomography. We report crystal structures for two diaryliodonium fluorides. Whereas diphenyliodonium fluoride (1 a) exists as a tetramer bridged by four fluoride ions, 2-methylphenyl(phenyl)iodonium fluoride (2 a) forms a fluoride-bridged dimer that is further halogen bonded to two other monomers. We discuss the topological relationships between the two and their implications for fluorination in solution. Both radiofluorination and NMR spectroscopy show that thermolysis of 2 a gives 2-fluorotoluene and fluorobenzene in a 2 to 1 ratio that is in good agreement with the ratio observed from the radiofluorination of 2-methylphenyl(phenyl)iodonium chloride (2 b). The constancy of the product ratio affirms that the fluorinations occur via the same two rapidly interconverting transition states whose energy difference dictates chemoselectivity. From quantum chemical studies with density functional theory we attribute the "ortho-effect" to the favorable electrostatic interaction between the incoming fluoride and the o-methyl in the transition state. By utilizing the crystal structures of 1 a and 2 a, the mechanisms of fluoroarene formation from diaryliodonium fluorides in their monomeric, homodimeric, heterodimeric, and tetrameric states were also investigated. We propose that oligomerization energy dictates whether the fluorination occurs through a monomeric or an oligomeric pathway.

Coupling between ATP hydrolysis and protein conformational change in maltose transporter

As the intracellular part of maltose transporter, MalK dimer utilizes the energy of ATP hydrolysis to drive protein conformational change, which then facilitates substrate transport. Free energy evaluation of the complete conformational change before and after ATP hydrolysis is helpful to elucidate the mechanism of chemical-to-mechanical energy conversion in MalK dimer, but is lacking in previous studies. In this work, we used molecular dynamics simulations to investigate the structural transition of MalK dimer among closed, semi-open and open states. We observed spontaneous structural transition from closed to open state in the ADP-bound system and partial closure of MalK dimer from the semi-open state in the ATP-bound system. Subsequently, we calculated the reaction pathways connecting the closed and open states for the ATP- and ADP-bound systems and evaluated the free energy profiles along the paths. Our results suggested that the closed state is stable in the presence of ATP but is markedly destabilized when ATP is hydrolyzed to ADP, which thus explains the coupling between ATP hydrolysis and protein conformational change of MalK dimer in thermodynamics. Proteins 2017; 85:207-220. © 2016 Wiley Periodicals, Inc.

Trimeric cluster of lithium amidoborane-the smallest unit for the modeling of hydrogen release mechanism

A detailed first-principle DFT M06/6-311++G(d.p) study of dehydrogenation mechanism of trimeric cluster of lithium amidoborane is presented. The first step of the reaction is association of two LiNH2 BH3 molecules in the cluster. The dominant feature of the subsequent reaction pathway is activation of H atom of BH3 group by three Li atoms with formation of unique Li3 H moiety. This Li3 H moiety is destroyed prior to dehydrogenation in favor of formation of a triangular Li2 H moiety, which interacts with protic H atom of NH2 group. As a result of this interaction, Li2 H2 moiety is produced. It features N(-) H(+) H(-) group suited near the middle plane between two Li(+) in the transition state that leads to H2 release. The transition states of association and hydrogen release steps are similar in energy. It is concluded that the trimer, (LiNH2 BH3 )3 , is the smallest cluster that captures the essence of the hydrogen release reaction.

Crystal structures of five new substituted tetrahydro-1-benzazepines with potential antiparasitic activity

Tetrahydro-1-benzazepines have been described as potential antiparasitic drugs for the treatment of chagas disease and leishmaniasis, two of the most important so-called `forgotten tropical diseases' affecting South and Central America, caused by Trypanosoma cruzi and Leishmania chagasi parasites, respectively. Continuing our extensive work describing the structural characteristics of some related compounds with interesting biological properties, the crystallographic features of three epoxy-1-benzazepines, namely (2SR,4RS)-6,8-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (1), (2SR,4RS)-6,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (2), and (2SR,4RS)-8,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (3), all C22H21NO, and two 1-benzazepin-4-ols, namely 7-fluoro-cis-2-[(E)-styryl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C18H18FNO, (4), and 7-fluoro-cis-2-[(E)-pent-1-enyl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C15H20FNO, (5), are described. Some peculiarities in the crystallization behaviour were found, involving significant variations in the crystalline structures as a result of modest changes in the peripheral substituents in (1)-(3) and the occurrence of discrete disorder due to the molecular overlay of enantiomers with more than one conformation in (5). In particular, an interesting phase change on cooling was observed for compound (5), accompanied by an approximate fourfold increase of the unit-cell volume and a change of the Z' value from 1 to 4. This transition is a consequence of the partial ordering of the pentenyl chains in half of the molecules breaking half of the -3 symmetry axes observed in the room-temperature structure of (5). The structural assembly in all the title compounds is characterized by not only (N,O)-H...(O,N) hydrogen bonds, but also by unconventional C-H...O contacts, resulting in a wide diversity of packing.

Unprecedented Carbonato Intermediates in Cyclic Carbonate Synthesis Catalysed by Bimetallic Aluminium(Salen) Complexes

The mechanism by which [Al(salen)]2 O complexes catalyse the synthesis of cyclic carbonates from epoxides and carbon dioxide in the absence of a halide cocatalyst has been investigated. Density functional theory (DFT) studies, mass spectrometry and (1) H NMR, (13) C NMR and infrared spectroscopies provide evidence for the formation of an unprecedented carbonato bridged bimetallic aluminium complex which is shown to be a key intermediate for the halide-free synthesis of cyclic carbonates from epoxides and carbon dioxide. Deuterated and enantiomerically-pure epoxides were used to study the reaction pathway. Based on the experimental and theoretical results, a catalytic cycle is proposed.

Four related benzazepine derivatives in a reaction pathway leading to a benzazepine carboxylic acid: hydrogen-bonded assembly in zero, one, two and three dimensions

(2R*,4S*)-Methyl 2,3,4,5-tetrahydro-1,4-epoxy-1H-benz[b]azepine-2-carboxylate, C12H13NO3, (I), and its reduction product (2R*,4S*)-methyl 4-hydroxy-2,3,4,5-tetrahydro-1H-benz[b]azepine-2-carboxylate, C12H15NO3, (II), both crystallize as single enantiomers in the space group P212121, while the hydrolysis product (2RS,4SR)-4-hydroxy-2,3,4,5-tetrahydro-1H-benz[b]azepine-2-carboxylic acid, C11H13NO3, (III), and the lactone (2RS,5SR)-8-(trifluoromethoxy)-5,6-dihydro-1H-2,5-methanobenz[e][1,4]oxazocin-3(2H)-one, C12H10F3NO3, (IV), both crystallize as racemic mixtures in the space group P21/c. The molecules of compound (IV) are linked into centrosymmetric R2(2)(10) dimers by N-H···O hydrogen bonds, and those of compound (I) are linked into chains by C-H···π(arene) hydrogen bonds. A combination of O-H···O and O-H···N hydrogen bonds links the molecules of compound (III) into sheets containing equal numbers of R4(4)(14) and R4(4)(26) rings, and a combination of C-H···π(arene) hydrogen bonds and three-centre O-H···(N,O) hydrogen bonds links the molecules of compound (II) into a three-dimensional framework structure. Comparisons are made with some related compounds.

Electrolytic synthesis of aqueous aluminum nanoclusters and in situ characterization by femtosecond Raman spectroscopy and computations

The selective synthesis and in situ characterization of aqueous Al-containing clusters is a long-standing challenge. We report a newly developed integrated platform that combines (i) a selective, atom-economical, step-economical, scalable synthesis of Al-containing nanoclusters in water via precision electrolysis with strict pH control and (ii) an improved femtosecond stimulated Raman spectroscopic method covering a broad spectral range of ca. 350-1,400 cm(-1) with high sensitivity, aided by ab initio computations, to elucidate Al aqueous cluster structures and formation mechanisms in real time. Using this platform, a unique view of flat [Al13(μ3-OH)6(μ2-OH)18(H2O)24](NO3)15 nanocluster formation is observed in water, in which three distinct reaction stages are identified. The initial stage involves the formation of an [Al7(μ3-OH)6(μ2-OH)6(H2O)12](9+) cluster core as an important intermediate toward the flat Al13 aqueous cluster.