Structure-reactivity Relationships Research Articles

Nitrobenzoate as a flotation depressant for arsenopyrite: A theoretical study of the structure-reactivity relationship

Nitrobenzoate can effectively depressor the flotation of arsenopyrite, making theoretical studies to elucidate the mechanism essential. This study investigates the structure-reactivity relationship of nitrobenzoate as a flotation depressant for arsenopyrite by density functional theory calculations. The results revealed that O/N heteroatoms participated in the formation of chemical bonds with the metal atoms on the mineral surface as o-nitrobenzoate, m-nitrobenzoate, and p-nitrobenzoate molecules and had significant chemical reactivities. The interaction of the flotation depressant with the mineral surface followed the order: m-nitrobenzoate > p-nitrobenzoate > o-nitrobenzoate, which was further confirmed by flotation experiments. Furthermore, the reactive sites of the three nitrobenzoate isomers were investigated, and the results revealed that all three isomers had the same reactive sites, but interacted differently with the metal atoms.

Synergetic Regulation of the Microstructure and Acidity of HZSM-5/MCM-41 for Efficient Catalytic Cracking of n-Decane.

Alkane catalytic cracking is regarded as one of the most significant processes for light olefin production; however, it suffers from serve catalyst deactivation due to coke formation. Herein, HZSM-5/MCM-41 composites with different Si/Al2 ratios were first prepared by the hydrothermal method. The physicochemical properties of the prepared catalysts were analyzed by a series of bulk and surface characterization methods, and the catalytic performance was tested in n-decane catalytic cracking. It was found that HZSM-5/MCM-41 showed a higher selectivity to light olefins and a lower deactivation rate compared with the parent HZSM-5 due to an enhanced diffusion rate and decreased acid density. Moreover, the structure-reactivity relationship revealed that conversion, light olefin selectivity, and the deactivation rate strongly depended on the total acid density. Furthermore, HZSM-5/MCM-41 was further extruded with γ-Al2O3 to obtain the catalyst pellet, which showed an even higher selectivity to light olefins (∼48%) resulting from the synergy effect of the fast diffusion rate and passivation of external acid density.

Spectroscopic identification of water splitting by neutral group 3 metals

Spectroscopic study of water splitting by neutral metal clusters is crucial to understanding the microscopic mechanism of catalytic processes but has been proven to be a challenging experimental target due to the difficulty in size selection. Here, we report a size-specific infrared spectroscopic study of the reactions between neutral group 3 metals and water molecules based on threshold photoionization using a vacuum ultraviolet laser. Quantum chemical calculations were carried out to identify the structures and to assign the experimental spectra. All the M2O4H4 (M = Sc, Y, La) products are found to have the intriguing M2(μ2-O)(μ2-H)(μ2-OH)(η1-OH)2 structures, indicating that the HOH bond breaking, the MO/MH/MOH bond formation, and hydrogen production proceed efficiently in the reactions between laser-vaporized metals and water molecules. The joint experimental and theoretical results on the atomic scale demonstrate that the water splitting by neutral group 3 metals is both thermodynamically exothermic and kinetically facile in the gas phase. These findings have important implications for unravelling the structure-reactivity relationship of catalysts with isolated metal atoms/clusters dispersed on supports.

Structure-reactivity relation in the oxidation of some aliphatic aldehydes by Tripropylammonium chlorochromate

The oxidation of six aliphatic aldehydes by tripropylammonium chlorochromate (TPACC) in dimethyl sulfoxide (DMSO) leads to the formation of corresponding carboxylic acids. The reaction is of first order each in TPACC. A Michaelis-Menten type of kinetics is observed with respect to the aldehydes. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: kobs = a + b[H+]. The oxidation of deuteriated acetaldehyde MeCDO exhibited a substantial primary kinetic isotope effect (kH/kD = 5.75 at 298 K). The oxidation of acetaldehyde has been studied in nineteen different organic solvents. The solvent effect has been analysed using Taft's and Swain's multiparametric equations. The rate constants correlate well with Taft’s * values, reaction constants being negative. A mechanism involving transfer of hydride ion has been suggested.

Unveiling the interaction mechanism between facet-dependent pyrite nanoparticles and Cr(VI) under anaerobic environment: adsorption, redox, and phase transformation

The environmental migration and bioavailability of Hexavalent chromium (Cr(VI)) could be affected by facet-dependent pyrite (FeS2) existing in soils and sediments. Conversely, the occurrence state of facet-dependent FeS2 might also be influenced by Cr(VI). However, the complex interactive mechanism at the solid–liquid interface between facet-dependent FeS2 and Cr(VI) still remained ambiguous. Herein, FeS2 nanobelts, FeS2 nanosheets, and FeS2 nanocubes with corresponding dominant facets of (−110), (001), (100)/(210) were prepared. The adsorption and reduction experimental results reflected that Cr(VI) species were predominantly adsorbed and a portion of them was reduced to Cr(III) at the FeS2 interfaces. In particular, the adsorption efficiency of Cr(VI) on (001) facet was 1.39 and 4.69 times than those on (−110) and (100)+(210) facets, respectively. The results of in situ Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) measurements and Density Functional Theory (DFT) calculations suggested that bidentate binuclear (BB) coordinated chromates were generated on the (001) facet while monodentate mononuclear (MM) coordinated chromates were formed on (−110), (100), and (210) facets. Due to the stronger adsorption energy and more stable coordination mode of BB for Cr(VI) species on (001) facet, FeS2 NS exhibited higher efficiency of Cr(VI) removal and reduction compared with FeS2 NB and FeS2 NC. In addition, partial FeS2 particles were proved to be transformed to goethite under the effect of Cr(VI). Owing to the stronger adsorption of Cr(VI) species on (001) facet, FeS2 NS also had a faster phase transformation rate than FeS2 NB and FeS2 NC. Above results all reflected the good structure–reactivity relationships between the FeS2 facets and the Cr(VI) removal efficiency as well as the phase transformation of FeS2 particles.

Pyrolysis of Methyl Formate and the Reaction of Methyl Formate with H Atoms: Shock Tube Experiments and Statistical Rate Theory.

Methyl formate (MF) is the smallest carboxylic ester and currently considered a promising alternative fuel. It can also serve as a model compound to study the combustion chemistry of the ester group, which is a typical structural feature in many biodiesel components. In the present work, the pyrolysis of MF was investigated behind reflected shock waves at temperatures between 1430 and 2070 K at a nominal pressure of 1.1 bar. Both time-resolved hydrogen atom resonance absorption spectroscopy (H-ARAS) and time-resolved time-of-flight mass spectrometry (TOF-MS) were used for species detection. Additionally, the reaction of MF and perdeuterated MF-d4 with H atoms was investigated at temperatures between 1000 and 1300 K at nominal pressures of 0.4 and 1.1 bar with H-ARAS. In the latter experiments, ethyl iodide served as precursor for H atoms. Rate coefficients of seven parallel unimolecular decomposition channels of MF and five parallel reaction channels of the MF + H reaction were calculated from statistical rate theory on the basis of molecular and transition state data from quantum chemical calculations. These calculated rate coefficients were implemented into an MF pyrolysis/oxidation mechanism from the literature, and the experimental concentration-time profiles of H (from ARAS) as well as MF, CH3OH, HCHO, and CO (from TOF-MS) were modeled. It turned out that the literature mechanism, which was originally validated against flow-reactor experiments, ignition delay times, and laminar burning velocities, was generally able to fit also the concentration-time profiles from the shock tube experiments reasonably well. The agreement could still be improved by substituting the original rate coefficients, which were estimated from structure-reactivity relationships, by the values calculated from statistical rate theory in the present work. Details of the channel branching are discussed, and the updated mechanism is given, also in machine-readable form.

Methanation reactions for chemical storage and purification of hydrogen: Overview and structure-reactivity correlations in supported metals

The drastic effects associated with climate changes, mainly induced by the increasing carbon emissions, challenge our modern society and mandate immediate solutions. This requires in the first place, accelerating the introduction of green alternatives for the standing carbon-based energy technologies, and simultaneously increasing the contribution of the carbon-free renewables to our energy sector. Among a few catalytic processes, the methanation of carbon oxides is currently envisaged as a cornerstone in the renewable energy concepts. On one hand, the methanation of CO is intensively studied for ultra-purification of reforming-generated hydrogen feed gases used in the low-temperature hydrogen fuel cells and in the production of ammonia. This involves the selective methanation of CO in CO2-rich H2 fuels to lower CO concentration from about 5000 ppm down to <5 ppm. The other major application involves the solo or the total methanation of CO and CO2. This involves the conversion of syngas or the methanation of air-captured CO2 using green hydrogen produced from renewable energies (power-to-gas). These aspects revive the importance of Sabatier reactions and presents them as an essential part of the cycle of renewable-energy applications. In this review, we will focus on the recent advancements of the methanation of CO and CO2 on oxide supported Ni and Ru catalysts in the frame of their use in the abovementioned applications. After an overview of different catalytic processes related to hydrogen production, we will basically concentrate on the structure-reactivity relationships of CO and CO2 methanation in different applications, highlighting limitations and advantages of different catalytic systems. Basically, we will map out the interplay of different electronic and structural features and correlate them to the catalytic performance for CO and CO2 methanation. This includes the discussion of metal particle size effect, nature of the support, and the effect of reaction gas atmospheres. Clarifying the interplay of these parameters will help us to further understand the metal-support interaction (MSI) based on structural (SMSIs) and electronic (EMSIs) aspects which is essential for steering the catalytic performance of these catalysts for a specific reaction pathway.

Exploring the structure–reactivity relationship of sn-Cr binary catalysts with XRD extrapolation method: The vital role of surface O2− and acidic sites for toluene combustion

To explore the structure–reactivity relationship of solid solutions and design effective catalysts for toluene combustion, Sn-Cr catalysts with varied Sn/Cr mole ratios have been fabricated by a co-precipitation method. With various techniques, the crystalline and surface features, and the Cr distributions have been investigated. By adopting XRD and XPS extrapolation methods, it is found that lattice capacity of Cr3+ in SnO2 matrix is 0.210 g Cr2O3 /g SnO2, being equal to a Sn/Cr mole ratio of 7/3. If the Cr content is above this capacity, Cr2O3 species/crystallites will be formed. The catalysts (SnCr7-3 and SnCr6-4) with Cr contents around the lattice capacity possess the largest quantities of surface active O2− anions and acidic sites, thus showing the highest intrinsic catalytic activity. The synergistic action between these surface two active sites determines the activity of Sn-Cr catalysts. It is proposed that the optimal catalyst can be prepared by doping the SnO2 matrix with capacity quantity of Cr3+, which can form the largest amount of pure sn-Cr solid solution phase in the structure.

Highly efficient electrochemical oxidation of hexafluoropropylene oxide homologues at a boron-doped diamond anode

As substitutes for perfluoroalkyl substances (PFASs), hexafluoropropylene oxide (HFPO) homologues are still environmentally problematic for their issues in toxicity, bioaccumulation, and long-distance mobility, which urges efficient removal technologies and in-depth mechanistic studies. Herein, we present the systematic optimizations on the electrochemical oxidation of 100 mg L−1 HFPO dimer acid (HFPO-DA) at a boron-doped diamond anode (3.6 V, 100 mM Na2SO4, pH 7.0), which exhibits a powerful mineralization capacity over 97% within 210 min of operation and is highly tolerant to various environmental factors. Under the optimized conditions, the structure-reactivity relationship has been analyzed by comparing six kinds of PFASs, proving that the increasing numbers of ether bonds in the HFPO homologues favor their removal and defluorination processes. Density functional theory (DFT) calculations further indicate that the facile, water-assisted cleavage of the ether bonds in the HFPO homologues can significantly reduce the energy barriers and shorten the "-CF2" unzipping degradation cycles, which is different from the conventionally proposed mechanism for degrading PFASs. Our findings demonstrate the promising application of electrochemical oxidation in the efficient removal of PFAS substitutes and offer new mechanistic insights for designing environment-friendly F-based chemicals.

Reactive oxygen nanobiocatalysts: activity-mechanism disclosures, catalytic center evolutions, and changing states.

Benefiting from low costs, structural diversities, tunable catalytic activities, feasible modifications, and high stability compared to the natural enzymes, reactive oxygen nanobiocatalysts (RONBCs) have become dominant materials in catalyzing and mediating reactive oxygen species (ROS) for diverse biomedical and biological applications. Decoding the catalytic mechanism and structure-reactivity relationship of RONBCs is critical to guide their future developments. Here, this timely review comprehensively summarizes the recent breakthroughs and future trends in creating and decoding RONBCs. First, the fundamental classification, activity, detection method, and reaction mechanism for biocatalytic ROS generation and elimination have been systematically disclosed. Then, the merits, modulation strategies, structure evolutions, and state-of-art characterisation techniques for designing RONBCs have been briefly outlined. Thereafter, we thoroughly discuss different RONBCs based on the reported major material species, including metal compounds, carbon nanostructures, and organic networks. In particular, we offer particular insights into the coordination microenvironments, bond interactions, reaction pathways, and performance comparisons to disclose the structure-reactivity relationships and mechanisms. In the end, the future challenge and perspectives for RONBCs are also carefully summarised. We envision that this review will provide a comprehensive understanding and guidance for designing ROS-catalytic materials and stimulate the wide utilisation of RONBCs in diverse biomedical and biological applications.

The quest for organo-alkali metal monomers: unscrambling the structure-reactivity relationship.

Organo-alkali metal reagents are essential tools in synthetic chemistry. Alkali metal organometallics aggregate in solution and solid-state forming clusters and polymers. The structure of these aggregates and their structure-reactivity relationship have been of great interest for many decades. This Perspective will look at the strategies that have been employed to isolate low aggregates and, in particular, monomeric complexes of the most common alkali metal alkyls (M = Li-Cs, R = methyl, trimethylsilylmethyl, bis/tris(trimethylsilylmethyl), butyls and benzyl) and the relationship between level of aggregation, structure and reactivity.

Formation of lignin alkyl-O-alkyl ether structures via 1,6-addition of aliphatic alcohols to β-O-4-aryl ether quinone methides.

Quinone methides (QMs) are formed as the intermediates during lignin biosynthesis and chemical transformation; the chemical structure of the resulting lignin can then be significantly modified via the corresponding aromatization. Herein, the structure-reactivity relationship of β-O-4-aryl ether QMs (GS-QM, GG-QM and GH-QM, which are 3-monomethoxylated QMs carrying syringyl, guaiacyl and p-hydroxyphenyl β-etherified aromatic rings, respectively) was investigated to clarify the formation of alkyl-O-alkyl ether structures in lignin. The structural features of these QMs were characterized by NMR spectroscopy, and their alcohol-addition experiment was well performed at 25 °C to generate alkyl-O-alkyl/β-O-4 products. The preferential conformation of GS-QM contains a stable directional intramolecular H-bond between γ-OH hydrogen and β-phenoxy oxygen, which makes the β-phenoxy group locate on the same side with γ-OH. In contrast, the β-phenoxy groups in both GG- and GH-QM conformations are distant from the γ-OH; thus, the stable intermolecular H-bond is associated with the γ-OH hydrogen. Based on UV spectroscopy, the addition of methanol and ethanol occurs in QMs with a half-life of 1.7-2.1 and 12.8-19.3 minutes, respectively. With the same nucleophile, these QMs react faster in the order GH-QM > GG-QM > GS-QM. However, the reaction rate appears to be more influenced by the type of nucleophile than by the β-etherified aromatic ring. Furthermore, the NMR spectra of products indicate that the steric bulkiness of both the β-etherified aromatic ring and nucleophile contributes to the erythro-preferential formation of adducts from QMs. Moreover, the effect is more pronounced for the β-etherified aromatic ring of QMs than the nucleophiles. The structure-reactivity relationship study demonstrates that the competition effect between H-bonds and steric hindrance determines the approaching direction and the accessibility of nucleophiles to planar QMs, resulting in stereo-differentiating formation of adducts. This model experiment may provide implications for the biosynthetic route and structural information of the alkyl-O-alkyl ether structure in lignin. Its results can also be further utilized to design innovative extraction methods of organosolv lignins for subsequent selective depolymerization or material preparation.

Thiophene-fused boron dipyrromethenes as energy efficient near-infrared photocatalysts for radical polymerizations

A series of thiophene-fused boron dipyrromethene (BODIPY) photoredox catalysts are systematically examined to identify structure–reactivity relationships that enable efficient near-infrared light-induced polymerizations.

Role of Substituents in the Removal of Emerging Fluorinated Liquid Crystal Monomer Pollutants under the UV/Peroxydisulfate Treatment

Fluorinated liquid crystal monomers (LCMs) have been identified as emerging persistent and bioaccumulative chemicals with non-negligible environmental concentrations. Herein, 12 fluorinated LCMs including highly detected 4-ethoxy-2,3-difluoro-4′-(trans-4-propylcyclohexyl)biphenyl (EDPB) were selected as target fluorinated LCMs to investigate their structure–reactivity relationships by the ultraviolet/peroxydisulfate (UV/PDS) treatment. EDPB with biphenyl and ethoxy showed the highest first-order degradation rate constant of 1.93 h–1, while that of fluorinated LCMs with ethoxy (1.10–1.26 h–1) and biphenyl (0.45–0.56 h–1) and without biphenyl or ethoxy (0.27–0.30 h–1) decreased sequentially. HO• and SO4•– were identified as the main oxidative species in the UV/PDS treatment. Theoretical calculation suggested that biphenyl and ethoxy can significantly alter the electron distribution of LCM molecules, providing more attackable sites for HO• and SO4•– on LCMs with biphenyl or ethoxy. Oxalic acid, cyclohexane, and bicyclohexane were the main degradation products of fluorinated LCMs even though their degradation pathways were determined by their different molecular structures. Toxicity estimation revealed that fluorinated LCMs with high acute toxicity and developmental toxicity could be decomposed into some final products with less toxicity. This study is expected to fill knowledge gaps in the structure–activity relationships of fluorinated LCMs by the UV/PDS treatment.

Structure-Reactivity Insights on the Alkaline Hydrolysis of Organophosphates: Non-Leaving and Leaving Group Effects in a Bilinear Brønsted-Like Relationship.

The high toxicity of organophosphates, along with its wide use as agrochemicals and chemical warfare, urges efficient degradation methods. Alkaline hydrolysis stands out, which is strongly structure-dependent. The alkaline hydrolysis of various organophosphates is described using a bilinear variation of the Brønsted equation, which evaluates concomitantly the effect of the leaving and non-leaving groups. Over 50 reactions were successfully correlated linearly and the contribution of the usually underestimated non-leaving group seems to be as important as the leaving group. The hetero atom effect (P=O and P=S) seems to vary the contribution of these groups. This concise understanding of the structure-reactivity relationship allows to predict optimal neutralization processes and is key for chemical security, saving time, resources and avoiding unnecessary manipulation of toxic chemicals.

Synthesis and computational investigation of N,N-dimethyl-4-[(Z)-(phenylimino)methyl]aniline derivatives: Biological and quantitative structural activity relationship studies

This study describes the synthesis, characterisation and biological activities of four Schiff base compounds, namely: N, N-dimethyl-4-(((4-nitrophenyl)imino)methyl)aniline (ABS1), 4-(((2-chlorophenyl)imino)methyl)-N,N-dimethylaniline (ABS2), 4‑bromo-2‑chloro-N-(4-dimethylamino)benzylidene) aniline (ABS3), and N,N-dimethyl-4-(((2-(trifluoromethyl)phenyl)imino)methyl)aniline (ABS4). These compounds were characterised by UV–Visible, FTIR, CHN-elemental analysis, PXRD, HRMS, and NMR (1H, 13C, DEPT, 1H1H– COSY, NOESY, HSQC, and HBMC) spectroscopic techniques. Furthermore, compounds ABS2–4 were suitable for single crystal X-ray diffraction analysis, and support the structures proposed. The antibacterial, antifungal and antioxidant activities of the compounds were investigated using both micro dilution and DPPH radical scavenging assays, showing a broad range of activity from high to moderate. Computational chemistry (molecular electrostatic potential maps, conceptual density functional theory calculations and non-covalent-interactions analysis) correlates with the experimental electronic properties as well as structure-reactivity relationship for the drug-likeness properties of the compounds. Molecular docking studies identified potential binding modes of the compounds, and the results corroborate with those obtained from MIC and MFC studies. The lead compounds (ABS1 and ABS3) exhibit outstanding drug-like properties.

Rapid hydrogel formation via tandem visible light photouncaging and bioorthogonal ligation

The formation of benign polymer scaffolds in water using green-light-reactive photocages is described. These efforts pave an avenue toward the fabrication of synthetic scaffolds that can facilitate the study of cellular events for disease diagnosis and treatment. First, a series of boron dipyrromethene (BODIPY) photocages with nitrogen-containing nucleophiles were examined to determine structure-reactivity relationships, which resulted in a >1,000× increase in uncaging yield. Subsequently, photoinduced hydrogel formation in 90 wt % water was accomplished via biorthogonal carbonyl condensation using hydrophilic polymer scaffolds separately containing BODIPY photocages and ortho-phthalaldehyde (OPA) moieties. Spatiotemporal control is demonstrated with light on/off experiments to modulate gel stiffness and masking to provide <100 μm features. Biocompatability of the method was shown through pre-/post-crosslinking cell viability studies. Short term, these studies are anticipated to guide translation to emergent additive manufacturing technology, which, longer term, will enable the development of 3D cell cultures for tissue engineering applications.

Cover Feature: Structure–Reactivity Relationship of Organozinc and Organozincate Reagents: Key Elements towards Molecular Understanding (Eur. J. Org. Chem. 44/2022)

Cover Feature: Structure–Reactivity Relationship of Organozinc and Organozincate Reagents: Key Elements towards Molecular Understanding (Eur. J. Org. Chem. 44/2022)

Structure-Reactivity Relationships of Buchwald-Type Phosphines in Nickel-Catalyzed Cross-Couplings.

The dialkyl-ortho-biaryl class of phosphines, commonly known as Buchwald-type ligands, are among the most important phosphines in Pd-catalyzed cross-coupling. These ligands have also been successfully applied to several synthetically valuable Ni-catalyzed cross-coupling methodologies and, as demonstrated in this work, are top performing ligands in Ni-catalyzed Suzuki Miyaura Coupling (SMC) and C-N coupling reactions, even outperforming commonly employed bisphosphines like dppf in many circumstances. However, little is known about their structure-reactivity relationships (SRRs) with Ni, and limited examples of well-defined, catalytically relevant Ni complexes with Buchwald-type ligands exist. In this work, we report the analysis of Buchwald-type phosphine SRRs in four representative Ni-catalyzed cross-coupling reactions. Our study was guided by data-driven classification analysis, which together with mechanistic organometallic studies of structurally characterized Ni(0), Ni(I), and Ni(II) complexes allowed us to rationalize reactivity patterns in catalysis. Overall, we expect that this study will serve as a platform for further exploration of this ligand class in organonickel chemistry as well as in the development of new Ni-catalyzed cross-coupling methodologies.

Structure–Reactivity Relationship of Organozinc and Organozincate Reagents: Key Elements towards Molecular Understanding

AbstractThe main parameters that influence the structure–reactivity relationship of organozinc and organozincate reagents are gathered in this perspective article. Influences of substituents, inorganic salts, and solvents are discussed and illustrated with examples from the literature. Based on the peculiarities of this chemical system, the perspective is enlarged by molecular modelling considerations to raise the comprehension at the molecular scale of structure–activity relationships of organozinc and organozincate reagents in solution.