Structure-reactivity Relationships Research Articles

Structure-reactivity relationships of novel α-hydroxyketone-functionalized cyclopolymerizable and cyclopolymeric photoinitiators

Three novel monomeric photoinitiators (I2959-NTBDA, I2959-NDAA and I2959-NAA) with 1,6-heptadiene structure and based on 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) and the photoinitiating cyclocopolymer of the first (Mn = 28000 D has six-membered rings in the backbone) are synthesized and characterized by NMR, FTIR, UV–Vis spectrometry and thermogravimetry. I2959-NTBDA is synthesized from reaction of tert-butyl α-bromomethacrylate with amine functionalized I2959; cleavage of tert-butyl groups gives I2959-NDAA. Synthesis of I2959-NAA involves reaction of allylamine derivative of I2959 and acryloyl chloride. These photoinitiators have λmax (269–280 nm) and ε values (13700–17300 M−1 cm−1) similar to I2959. The chemical mechanism investigated by electron spin resonance (ESR) and steady state photolysis confirms generation of isopropyl ketyl radicals. Structure-reactivity relationships of the monomeric photoinitiators studied during polymerizations of 2-hydroxyethyl methacrylate (HEMA), poly(ethylene glycol) diacrylate (PEGDA, Mn = 575 D) and trimethylol propane triacrylate (TMPTA) show the order of reactivity I2959-NDAA > I2959-NTBDA > I2959-NAA, indicating that both electronic and steric effects of PI structures are effective. The migration stability of the residual I2959-NTBDA in the cured film is much higher than that of I2959 due to incorporation into the network structure, indicating their potential for producing environmentally friendly materials.

Synthetic Approaches to Novel Human Carbonic Anhydrase Isoform Inhibitors Based on Pyrrol-2-one Moiety.

New dihydro-pyrrol-2-one compounds, featuring dual sulfonamide groups, were synthesized through a one-pot, three-component approach utilizing trifluoroacetic acid as a catalyst. Computational analysis using density functional theory (DFT) and condensed Fukui function explored the structure-reactivity relationship. Evaluation against human carbonic anhydrase isoforms (hCA I, II, IX, XII) revealed potent inhibition. The widely expressed cytosolic hCA I was inhibited across a range of concentrations (KI 3.9-870.9 nM). hCA II, also cytosolic, exhibited good inhibition as well. Notably, all compounds effectively inhibited tumor-associated hCA IX (KI 1.9-211.2 nM) and hCA XII (low nanomolar). Biological assessments on MCF7 cancer cells highlighted the compounds' ability, in conjunction with doxorubicin, to significantly impact tumor cell viability. These findings underscore the potential therapeutic relevance of the synthesized compounds in cancer treatment.

Layered Quasi-Nevskite Metastable-Phase Cobalt Oxide Accelerates Alkaline Oxygen Evolution Reaction Kinetics.

Clarifying the structure-reactivity relationship of non-noble-metal electrocatalysts is one of the decisive factors for the practical application of water electrolysis. In this field, the anodic oxygen evolution reaction (OER) with a sluggish kinetic process has become a huge challenge for large-scale production of high-purity hydrogen. Here we synthesize a layered quasi-nevskite metastable-phase cobalt oxide (LQNMP-Co2O3) nanosheet via a simple molten alkali synthesis strategy. The unit-cell parameters of LQNMP-Co2O3 are determined to be a = b = 2.81 Å and c = 6.89 Å with a space group of P3̅m1 (No. 164). The electrochemical results show that the LQNMP-Co2O3 electrocatalyst enables delivering an ultralow overpotential of 266 mV at a current density of 10 mA cmgeo-2 with excellent durability. The operando XANES and EXAFS analyses clearly reveal the origin of the OER activity and the electrochemical stability of the LQNMP-Co2O3 electrocatalyst. Density functional theory (DFT) simulations show that the energy barrier of the rate-determining step (RDS) (from *O to *OOH) is significantly reduced on the LQNMP-Co2O3 electrocatalyst by comparing with simulated monolayered CoO2 (M-CoO2).

Lignin Carboxymethylation: Probing Fundamental Insights into Structure–Reactivity Relationships

Lignin Carboxymethylation: Probing Fundamental Insights into Structure–Reactivity Relationships

CO Oxidation Promoted by NO Adsorption on RhMn2O3- Cluster Anions.

CO oxidation represents an important model reaction in the gas phase to provide a clear structure-reactivity relationship in related heterogeneous catalysis. Herein, in combination with mass spectrometry experiments and quantum-chemical calculations, we identified that the RhMn2O3- cluster cannot oxidize CO into gas-phase CO2 at room temperature, while the NO preadsorbed products RhMn2O3-[(NO)1,2] are highly reactive in CO oxidation. This discovery is helpful to get a fundamental understanding on the reaction behavior in real-world three-way catalytic conditions where different kinds of reactants coexist. Theoretical calculations were performed to rationalize the crucial roles of preadsorbed NO where the strongly attached NO on the Rh atom can greatly stabilize the products RhMn2O2-[(NO)1,2] during CO oxidation and at the same time works together with the Rh atom to store electrons that stay originally in the attached CO2- unit. The leading result is that the desorption of CO2, which is the rate-determining step of CO oxidation by RhMn2O3-, can be greatly facilitated on the reactions of RhMn2O3-[(NO)1,2] with CO.

Structure-reactivity relations in Cu/ZrO2 catalysed glycerol dehydration to acetol in continuous flow system

The selective dehydration of glycerol to hydroxyacetone (acetol) was studied in a continuous flow fixed-bed reactor with CuO supported on monoclinic (m-) or tetragonal (t-) ZrO2 nanoparticles. Catalysts were characterised...

Exploration of structure sensitivity of gold nanoparticles in low-temperature CO oxidation

A theoretical investigation of the dynamic structure–reactivity relation of Au nanoparticles in CO oxidation.

Cooperative small molecule activation by apolar and weakly polar bonds through the lens of a suitable computational protocol.

Small molecule activation processes are central in chemical research and cooperativity is a valuable tool for the fine-tuning of the efficiency of these reactions. In this contribution, we discuss recent and remarkable examples in which activation processes are mediated by bimetallic compounds featuring apolar or weakly polar metal-metal bonds. Relevant experimental breakthroughs are thoroughly analyzed from a computational perspective. We highlight how the rational and non-trivial application of selected computational approaches not only allows rationalization of the observed reactivities but also inferring of general principles applicable to activation processes, such as the breakdown of the structure-reactivity relationship in carbon dioxide activation in a cooperative framework. We finally provide a simple yet unbiased computational protocol to study these reactions, which can support experimental advances aimed at expanding the range of applications of apolar and weakly polar bonds as catalysts for small molecule activation.

Spectroscopic characterization of carbon monoxide activation by neutral chromium carbides.

Spectroscopic characterization of carbon monoxide activation by neutral metal carbides is of essential importance for understanding the structure-reactivity relationships of catalytic sites, but has been proven to be very challenging owing to the difficulty in size selection. Here, we report a size-specific infrared-vacuum ultraviolet spectroscopic study of the reactions between carbon monoxide with neutral chromium carbides. Quantum chemical calculations were carried out to identify the low-lying structures and to interpret the experimental features. The results reveal that the most stable structure of CrC3(CO)2 consists of a CCO ketenylidene unit and that of CrC4(CO)2 has a semi-bridging CO with a very low CO stretching vibrational frequency at 1821 cm-1. The electron structure analyses show that this semi-bridging CO is highly activated through the delocalized Cr-C-C three-center two-electron (3c-2e) interaction between the antibonding orbitals of CO and the metal carbide skeleton. The formation of these metal carbide carbonyls is found to be both thermodynamically exothermic and kinetically facile in the gas phase. The present findings have important implications for the mechanical understanding of the catalytic processes with isolated metal atoms/clusters dispersed on supports.

Construction of Cu–Ru bimetallic catalyst for the selective catalytic transfer hydrogenation of carbonyl (C[dbnd]O) in biomass-derived compounds

The catalytic transfer hydrogenation (CTH) of levulinate ester to γ-valerolactone is one of the important reactions for production of renewable fuels from biomass. An efficient and robust bimetallic Cu–Ru catalyst were developed for the hydrogenation of biomass-derived ethyl levulinate to γ-valerolactone. A series of bimetallic catalysts were prepared and characterized in detail. Subsequently, the as-prepared catalysts were evaluated in the hydrogenation system of ethyl levulinate. The results showed that Cu–Ru/ZrO2–SO3–SiO2-450 catalyst provided 100 % GVL yield in 12 h at 180 °C. Meanwhile, it also exhibited high catalytic hydrogenation activity for the various biomass-derived carbonyl compounds. The structure-reactivity relationship of catalysts was investigated in detail, and the results show the interaction between support and metal sites played an important role in the hydrogenation activity. The sulfur species could tune the electronic states of metallic sites to gain optimal activity. Besides, the Cu–Ru/ZrO2–SO3–SiO2-450 catalyst performed excellent recyclability in five reaction runs without an obvious loss of activity.

(Invited) Photoactive Inorganic Nanosystems for Environmental and Energy-Related Applications

Nowadays, one of the main technological challenges that we are facing is the ability to provide a sustainable supply of clean energy and, among all renewable sources, solar energy displays the greatest potential. Recently, the development of novel synthetic strategies has led to the preparation of nanostructured materials displaying unique properties compared to the bulk counterpart systems, with controlled and tunable morphologies able to enhance the activity and selectivity of a heterogenous process.This talk will focus on the importance of tuning the morphological features of a catalyst as a strategy to improve its photoactivity, focusing on how rationally designing inorganic materials at the nanoscale can lead to shapes and structures suitable to enhance the performance of industrially and environmentally important processes. The talk will discuss some energy and environmental applications that can be addressed by multi-component systems synthesized via the bottom–up approach, highlighting their structure-reactivity relationship. Photocatalytic H2 production and purification and drugs degradation will be presented as successful cases history [1-3].[1] E. Moretti, L. Storaro, A. Talon, P. Riello, A. Infantes Molina, E. Rodríguez-Castellón, Appl. Catal. B: Environmental 168 (2015) 385.[2] M. Telkhozhayeva, B. Hirsch, R. Konar, E. Teblum, R. Lavi, M. Weitman, B. Malik, E. Moretti, G.D. Nessim, Appl. Catal. B: Environmental 318 (2022) 121872.[3] L. Liccardo, M. Bordin, P.M. Sheverdyaeva, M. Belli, P. Moras, A. Vomiero, E. Moretti, Adv. Funct. Mater. (2023) in press.

Direct Electrochemical Regeneration of NADH and Its Biomimetics

Enzyme-catalyzed redox transformations are an attractive approach for conversion of unactivated alkanes into value-added products under mild reaction conditions. This is especially true since advancements in the area of enzyme engineering has led to a dramatic expansion in the use of modified oxidoreductases for selective functionalization of commodity petrochemicals in non-aqueous media. Despite their appeal, many redox enzymes rely on stoichiometric quantities of expensive coenzymes, such as nicotinamide adenine dinucleotide (NADH), that are not easily regenerated. The use of direct electrochemistry to catalytically regenerate NADH has long been an aspiration of chemists as a convenient and straightforward method that would enable use of the expensive cofactor in enzyme-catalyzed synthesis on an industrial scale. Unfortunately, direct electrochemical reduction of the oxidized form of nicotinamide adenine dinucleotide (NAD+) results in unstable radical intermediates that rapidly form biologically inactive byproducts. Recent progress has been made towards the development of inexpensive artificial NADH biomimetics as replacements for the natural coenzyme, but the strategies to regenerate these biomimetic coenzymes is equally limiting. A primary focus of our research is to design synthetic analogues of NAD+ and NADH that are both enzymatically active and electrochemically regenerable. We will present our recent progress in understanding the structure-reactivity relationships that lead to dimerization over the preferred formation of 1,4-dihydronicotinamide in NAD+ and its biomimetics, and we will describe strategies to prevent dimerization of electrochemically reduced NAD+.

(Invited) Structure-Reactivity Relationship for Pt-Rare Earth Electrocatalysts for Oxygen Reduction Reaction

Alloys of Pt with rare-earth metals (REM) have been demonstrated as one of the most promising candidates with high activity towards oxygen reduction reaction and durability with respect to pure Pt and Pt-alloys with late transition metals1,2. However, due to very low reduction potentials and high oxygen affinity of such elements, the synthesis of Pt-REM nanoalloys by conventional chemical methods is not trivial.Our group prepared and characterized a series of carbon supported Pt-REM nanocatalysts using a solid-state route3. A systematic investigation of the influence of the type of rare earth metal (Y, Gd, Nd), of the Pt:REM ratio4, and of the post-synthesis treatment5, on the structural, morphological and electrochemical properties of the prepared electrocatalysts was performed. Operando techniques were used to investigate the evolution of the nanoalloys during the electrochemical experiments, providing evidence for the structural transitions and strain dynamics that govern the electrocatalytic activity towards the ORR. For instance, the evolution of the structural, morphological and compositional properties of Pt-Nd nanoalloys occurring during electrochemical activation was studied by online ICP-MS6.In this presentation an overview of the results obtained on these carbon-supported Pt-REM nanostructured electrocatalysts will be given and the challenges for their application at the PEMFC cathode presented. J. Greeley et al., Nat. Chem., 1, 552–6 (2009).C. A. Campos-Roldán, D. J. Jones, J. Rozière, and S. Cavaliere, ChemCatChem, 14 (2022)Y. Hu, J. O. Jensen, L. N. Cleemann, B. A. Brandes, and Q. Li, J. Am. Chem. Soc., 142, 953–961 (2020)C. A. Campos-Roldán et al., ACS Catal., 11, 13519–13529 (2021).C. A. Campos-Roldán et al., Nanoscale Adv., 4, 26–29 (2022)C. A. Campos-Roldán et al., sumbitted. The research leading to these results has received funding from the IMMORTAL project, which receives funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under Grant Agreement No. 101006641. This Joint Undertaking receives support from the European Union's Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research.

Operando Surface X-Ray Diffraction Studies of Co Oxide Catalyst Films for Electrochemical Water Splitting

The need for environmental friendly and sustainable energy conversion has triggered renewed interest into the electrochemical and photoelectrochemical splitting of water. A key challenge in this field is the development of economically viable electrocatalyst materials for the oxygen evolution reaction (OER). Transition-metal oxide catalysts, in particular the cobalt (hydr)oxide materials, have been found as promising candidates, since they are earth-abundant, efficient and scalable over a wide range of electrochemical conditions [1]. They present good catalytic properties and stability in alkaline solution under ambient conditions. Although a wide variety of different catalysts with rather diverse nanoscale morphologies have been synthesized and studied, the atomic scale surface structure usually is still unknown or poorly defined. This makes it difficult to compare their electrocatalytic activity and correlate it with ab initio theoretical studies, which hinders the development of clear structure-reactivity relationships and unambiguous determination of the OER reaction mechanism.We presentsystematic comparative studiesof structurally well-defined, 18-35nm thick Co3O4 films, prepared by electrodeposition or physical vapor deposition (PVD) on Au(111), Au(100) and Ir(100) single crystals. In all cases a well ordered epitaxial Co3O4(111) arrangement results, but the film morphology differs substantially, as shown by AFM and surface X-ray diffraction (SXRD). In order to elucidate the quantitative relationship between the catalyst surface structure and the OER reactivity, synchrotron-based operando SXRD and electrochemical measurements were performed simultaneously under reaction conditions, using a dedicated operando cell which allows massive gas evolution and current densities of up to 150 mA/cm2 [2,3].We find that the Co3O4(111) layers prepared by PVD on Ir(100) stay perfectly stable in the pre-OER and OER potential regime, whereas all electrodeposited films exhibit reversible changes in the oxide structure and oxidation state, in agreement with a previous study of Co3O4 catalysts [2]. Specifically, we observe the reverse formation of an ultrathin X-ray-amorphous CoOx(OH)y skin layer above 1 V vs. RHE and the gradual buildup of tensile lattice strain in the underneath, remaining Co3O4 layer with increasing potential. These structural changes occur for all electrodeposited samples, albeit to a different extent, depending on the film morphology [3]. Studying the relationship between the effective thickness of this skin layer and the OER reactivity, we found clear evidence that the entire skin layer is a three dimensional OER zone, which strongly exceeds one monolayer.Our results suggest that even subtle changes of the surface morphology have large influence on the OER activity of the Co3O4 catalyst, which may be expected also for other spinel-type transition metal oxides. On the one hand, this reveals that great care as to be taken in comparing the OER activity of differently prepared catalysts. On the other hand, these observations may provide a base for targeted preparation of highly reactive oxide catalysts.[1] C. C. L. McCrory et al., Journal of the American Chemical Society 2015, 137, 4347.[2] F. Reikowski, et al., ACS Catalysis, 2019, 9, 3811.[3] T. Wiegmann, et al., ACS Catalysis, 2022, 12, 256.

Quantitative Structure-Reactivity Relationships for Synthesis Planning: The Benzhydrylium Case.

Selective and feasible reactions are among the top targets in synthesis planning. Mayr's approach to quantifying chemical reactivity has greatly facilitated the planning process, but reactivity parameters for new compounds require time-consuming experiments. In the past decade, data-driven modeling has been gaining momentum in the field, as it shows promise in terms of efficient reactivity prediction. However, state-of-the-art models use quantum chemical data as input, which prevent access to real-time planning in organic synthesis. Here, we present a novel data-driven workflow for predicting reactivity parameters of molecules that takes only structural information as input, enabling de facto real-time reactivity predictions. We use the well-understood chemical space of benzhydrylium ions as an example to demonstrate the functionality of our approach and the performance of the resulting quantitative structure-reactivity relationships (QSRRs). Our results suggest that it is straightforward to build low-cost QSRR models that are accurate, interpretable, and transferable to unexplored systems within a given scope of application. Moreover, our QSRR approach suggests that Hammett σ parameters are only approximately additive.

Dynamic tracking of photocatalytic oxidation of organic micropollutant by Raman spectroscopy over Aurivillius Bi3.4La0.6Ti3O12 nanocatalyst

The need to develop an approach to gather detailed molecular information occurring on catalytic surfaces and gain deeper understanding of the structure-reactivity relationship of nanocatalysts for rational design and improved performance is essential in catalysis. In this study, we report the dynamic tracking of the degradation of a recalcitrant diazenyl-based micropollutant over Aurivillius lanthanum-doped bismuth titanate nanoparticles (BLT NPs) by Raman spectroscopy. By leveraging this powerful analytical technique, rich structural information can be retrieved, including the adsorbed species, which can provide profound insight of the degradation mechanism. Our observations show significant asymmetrical broadening in the vibrational spectra particularly within the range of 1300 cm−1 to 1400 cm−1, which can be attributed to the photo-oxidation of diazenyl derivatives within their specific chemical environment at ambient condition. The results, supported by high-performance liquid chromatography and mass spectrometry, demonstrate the selective cleavage of the pollutant's C-N and N = N bonds, likely resulting in the formation of 4-nitroazobenzene as the predominant intermediate product.

Boosting the Release of Leaving Group from Blebbistatin Derivative Photocages via Enhancing Intramolecular Charge Transfer and Stabilizing Cationic Intermediate.

Blebbistatin (Bleb) derivatives are a visible light photocage platform. During the photocleavage process, intramolecular charge transfer (ICT) and cationic intermediates play a decisive role. However, slow photolysis rate and low photolysis quantum yield are the main problems for Bleb's derivatives. Herein, by introducing a substituted OCH3 group at the para-position of the D ring, Bleb and Bleb derivatives with various leaving groups were synthesized and studied, and the photolysis performance was unveiled by steady-state spectra, photolysis rate experiments, photolysis quantum yield, and density functional theory calculations. Substituted OCH3 derivatives of Bleb may enhance the photolysis rate and increase the photolysis quantum yield because the electron-donating group can promote the ICT process and stabilize the cationic intermediate during the photolytic reaction. More generally, the insights gained from this structure-reactivity relationship may provide theoretical guidance and aid in the development of new highly efficient photoreactions.

Electrophilicity, mechanism and structure–reactivity relationships of cyclic secondary amines addition to 2-methoxy-3,5-dinitropyridine

The second-order rate constants (k) for the nucleophilic aromatic substitution reactions of 2‑methoxy-3,5-dinitropyridine 1 with secondary cyclic amines 2a-c in acetonitrile solution at 20 °C are reported. The logarithms of these rate constants are particularly significant as possible measures of the electrophilicity parameters E for 2‑methoxy-3,5-dinitropyridine 1 according to the linear free energy relationship log k (20 °C) = sN(N + E). Additional kinetic data for reactions of 2-methoxy-3,5-dinitropyridine 1 with a series of nitroalkyl anions in DMSO solution are also measured and found to agree with those calculated by Mayr's approach from the known two solvent-dependent parameters N and sN of nitroalkyl anions and the electrophilicity parameter E measured in this work. A Single Electron Transfer (SET) mechanism is proposed for the SNAr reactions, on the basis of the linear Brönsted plot with the βnuc value of 0.94. The validity of this mechanism is confirmed by the agreement between the rate constants, k, and the oxidation potentials E° of these series of secondary cyclic amines. Also, reactivity descriptors such as the electronic chemical potential (μ), and the chemical hardness (η) for a series of pyridine derivatives were calculated by Density Functional Theory (DFT), and it is shown that the global electrophilicity index (ω = μ2/2η) is significantly correlated with the electrophilicity parameters E.

Chemical Kinetic Method for Active-Site Quantification in Fe-N-C Catalysts and Correlation with Molecular Probe and Spectroscopic Site-Counting Methods.

Mononuclear Fe ions ligated by nitrogen (FeNx) dispersed on nitrogen-doped carbon (Fe-N-C) serve as active centers for electrocatalytic O2 reduction and thermocatalytic aerobic oxidations. Despite their promise as replacements for precious metals in a variety of practical applications, such as fuel cells, the discovery of new Fe-N-C catalysts has relied primarily on empirical approaches. In this context, the development of quantitative structure-reactivity relationships and benchmarking of catalysts prepared by different synthetic routes and by different laboratories would be facilitated by the broader adoption of methods to quantify atomically dispersed FeNx active centers. In this study, we develop a kinetic probe reaction method that uses the aerobic oxidation of a model hydroquinone substrate to quantify the density of FeNx centers in Fe-N-C catalysts. The kinetic method is compared with low-temperature Mössbauer spectroscopy, CO pulse chemisorption, and electrochemical reductive stripping of NO derived from NO2- on a suite of Fe-N-C catalysts prepared by diverse routes and featuring either the exclusive presence of Fe as FeNx sites or the coexistence of aggregated Fe species in addition to FeNx. The FeNx site densities derived from the kinetic method correlate well with those obtained from CO pulse chemisorption and Mössbauer spectroscopy. The broad survey of Fe-N-C materials also reveals the presence of outliers and challenges associated with each site quantification approach. The kinetic method developed here does not require pretreatments that may alter active-site distributions or specialized equipment beyond reaction vessels and standard analytical instrumentation.

Relationship between molecular structure and pyrolysis performance for high-energy-density fuels

High-energy-density endothermic hydrocarbon fuels (HDEHFs) are the ideal on-board coolants for the thermal management of advanced aircrafts. However, the pyrolysis performace of high-energy-density (HED) fuels with different molecular structures remains ambiguous. Herein, we investigated the pyrolysis performance of five HED fuels with different cyclic structures, i.e., bicyclohexyl (BCH), perhydrofluorene (PHF), decahydronaphthalene (DHN), exo-tetrahydrodicyclopentadiene (exo-THD) and cyclopropyl-tetrahydrodicyclopentadiene (CTHD), to reveal the molecular structure-reactivity relationship. The pyrolysis conversion (650 °C, 4 MPa) of the tested fuels is in the order of CTHD > PHF > BCH > DHN > exo-THD, which is highly associated with their C + H atom numbers, nH+C (except for CTHD with high-tension ring). With the analysis of product distribution as well as DFT calculation, the decomposition reaction pathways of the fuels were proposed. The heat sink of the fuels follows the order of BCH > PHF > DHN > exo-THD > CTHD, which is closely correlated with nH/C6.9 × nH+C3.8. Meanwhile, the fitting results between molecular structures and physicochemical properties of the fuels were also demonstrated. This study could provide a guidance on the design and development of HDEHFs fuels for the high-performance aerospace vehicles with long flight distance and hypersonic speed.