Transition State Structures Research Articles

Overcoming the Pitfalls of Computing Reaction Selectivity from Ensembles of Transition States.

The prediction of reaction selectivity is a challenging task for computational chemistry, not only because many molecules adopt multiple conformations but also due to the exponential relationship between effective activation energies and rate constants. To account for molecular flexibility, an increasing number of methods exist that generate conformational ensembles of transition state (TS) structures. Typically, these TS ensembles are Boltzmann weighted and used to compute selectivity assuming Curtin-Hammett conditions. This strategy, however, can lead to erroneous predictions if the appropriate filtering of the conformer ensembles is not conducted. Here, we demonstrate how any possible selectivity can be obtained by processing the same sets of TS ensembles for a model reaction. To address the burdensome filtering task in a consistent and automated way, we introduce marc, a tool for the modular analysis of representative conformers that aids in avoiding human errors while minimizing the number of reoptimization computations needed to obtain correct reaction selectivity.

Steric Effect and Intrinsic Electrophilicity and Nucleophilicity from Conceptual Density Functional Theory and Information-Theoretic Approach as Quantitative Probes of Chemical Reactions.

Appreciating reactivity in terms of physicochemical effects for chemical processes is one of the most important undertakings in chemistry. While transition state (TS) theory provides the framework enabling the reliable calculation of the barrier height for a given elementary step, analytical tools are necessary to gain insight into key factors governing the different processes during chemical reactions. In this contribution, we partition the potential energy surface of an elementary step along the intrinsic coordinate into three segments, the so-called Pre-TS, TS, and Post-TS regions, and then determine the most important factors dictating each segment. This analysis is based on the use of both reactivity descriptors from conceptual density functional theory and concepts from the information-theoretic approach in density functional theory. We found that in both Pre-TS and Post-TS regions, steric effects are the dominant factors, whereas in the TS region, it is the intrinsic electrophilic and nucleophilic propensity of the transition state structure that governs the reactivity. The wide applicability of our approach is shown by a validation for a total of 37 organic and inorganic reactions. Different partition approaches from density functional theory, energy decomposition analysis and wavefunction-based resonance theory are employed to support our main conclusions.

Calculation of the Structure and Reaction Potential Barrier of the Decomposition Products of SF6/N2 Mixed Gases

Abstract The greenhouse effect caused by SF6 gas in the power system cannot be ignored, and N2 has enormous industrial potential to replace pure SF6 by mixing with SF6 due to its advantages of low environmental pollution, low price, and stable chemical performance. This article combines density functional theory (DFT) and transition state theory (TST) to calculate the molecular structure and vibrational frequency information of various reactants, products, and transition states involved in SF6/N2 gas mixtures containing water and oxygen. The single point energy of each component is calculated using the CCSD (T)/cc pvtz theory level, and all reaction barrier energies are obtained. The calculated molecular structure and vibration frequency results are in good agreement with the experimental data of NIST, proving the reliability of the calculation method in this paper. The difficulty of the reaction can be determined by obtaining all the reaction barrier energies. It was found that SF5 molecules are unstable and prone to decomposition. SF4 is very important in the SF6/N2 reaction system, and further decomposition will produce a large number of stable by-products. The calculation method in this article helps to deeply understand the decomposition reaction mechanism of SF6/N2 mixed gas, and is of great significance for the research of decomposition experiments.

Experimental and Quantum Chemical Calculations on the High-Efficiency Transesterification of Dimethyl Carbonate with Alcohol Catalyzed by Calcium Oxide.

Typical catalysts used in dimethyl carbonate (DMC) transesterification encounter challenges in terms of environmental sustainability and economic viability. Calcium oxide (CaO), being an environmentally friendly and cost-effective catalyst, exhibits favorable compatibility with the criteria above. It has been conclusively demonstrated that CaO performs high efficiency as a catalyst for the transesterification between alcohols and DMC. The optimal conditions for the CaO-catalyzed transesterification of DMC and 1-octanol were determined (90 °C, 17 h, and CaO/1-octanol/DMC molar ratio = 0.3:1.0:40.0), under which the conversion of 1-octanol reaches 98.3%, while the yield and selectivity of methyl octyl carbonate are 98.1 and 99.9%, and CaO has been proven to have the efficient ability to be recycled three times. Meanwhile, the CaO-catalyzed reaction mechanism of the transesterification of DMC with alcohol is illustrated in the quantum chemical method based on the M06-2X functional, and the structures of the corresponding transition states are simultaneously derived. The activation energy barrier is proven to be effectively decreased by the catalytic effect of CaO. In addition, the electrostatic potential diagram verifies the proposed reaction sites. This research constructs the theoretical basis for CaO-based DMC chemistry and expands the green catalysts available for the synthesis of dialkyl carbonates.

Effect of different substituent on the ESIPT process and fluorescence features of 2-(2-hydroxyphenyl)benzoxazole derivatives: A DFT/TD-DFT study

In this contribution, four derivatives of 5′-(para-R-Phenylene) vinyl-2-(2′-hydroxyphenyl) benzoxazole (PVHBO) were ingeniously designed by introducing two electron-withdrawing substituents and two electron-donating substituents, aiming to investigate the influence of different substituents on the photophysical properties of PVHBO and the excited state intramolecular proton transfer (ESIPT) process via the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. By utilizing the geometric parameters and the simulated infrared (IR) spectra, we compared the intramolecular hydrogen bonds (IHBs) strengths in the S0 and S1 states of the molecules. Via conducting the hole-electron analysis, the reduction in fluorescence intensity for the enol and keto forms of PVHBO, PVHBO-MeO, and PVHBO-NH2 were also well explicated. Besides, the potential energy curves (PECs) and corresponding transition state (TS) structures for both S0 and S1 states were also constructed to accurately obtain energy barriers of forward and reversed proton transfer processes. The calculated absorption and fluorescence spectra also show that PVHBO-NH2 has the largest Stokes shifts of 158 nm and 219 nm in both the enol and keto states, with a significant increase in fluorescence intensity observed upon the induction of electron-withdrawing groups. Through this work, it can provide the theoretical basis for the design of novel luminescent materials.

Theoretical study on the insertion reaction of the stannylenoid H2SnLiF with X-H bonds (X = N, O, F).

The insertion reactions of p-complex (RP) and three-membered ring configuration (RS) of stannylenoid H2SnLiF with NH3, H2O and HF have been studied theoretically by quantum chemical calculation. The structures of reactants, precursors, transition states, intermediates and products have been fully optimized at the M06-2X/def2-TZVP level. The single point energy of all fixed points were calculated using the QCISD method. The calculation results show that the three-membered ring configuration is easier to conduct the insertion reaction. Comparing the reaction energy barriers of RP, RS to NH3, H2O and HF, we found that the difficulty of the insertion reaction is NH3 > H2O > HF. The solvent corrected calculation results show that in THF, the reaction energy barrier of RP is lower than that in vacuum, while the reaction energy barrier of RS is higher. This work provides theoretical support for the reaction properties of stannylenoid.

Frustrated Lewis pair-mediated hydro-dehalogenation: crucial role of non-covalent interactions.

Organic halides stand as invaluable reagents with diverse applications in synthetic chemistry and various industrial processes. Despite their utility, concerns arise due to their inherent toxicity. Addressing these apprehensions, hydro-dehalogenation has emerged as a promising strategy involving the replacement of halogen atoms with hydrogen atoms to transform toxic organic halides into hydrocarbons. This study delves into the computational exploration of hydro-dehalogenation reactions of benzyl halide, mediated by frustrated Lewis pairs (FLPs), using density functional theory (DFT). The reactions entail the formation of FLP1 or FLP2 in the presence of TMP or lutidine with B(C6F5)3, respectively. This is followed by heterolytic cleavage of dihydrogen and subsequent reaction with benzyl halides. Non-covalent interaction analysis underscores the significance of π-π stacking and CH-π interactions in stabilizing transition states. Additionally, the activation strain model (ASM) dissects activation energies, revealing the substantial impact of strain energy on reaction barriers. Energy decomposition analysis (EDA) offers insights into the contributions of electrostatic, orbital, and dispersion energies to the overall attractive interaction energy. The investigation extends to hydro-dehalogenation reactions of ethyl halides, uncovering distinct mechanisms and activation barriers. This comprehensive analysis illuminates the intricacies of hydro-dehalogenation reactions, providing valuable insights into their mechanisms and paving the way for future studies in this field. Geometry optimizations were carried out at the M06-2X/def2-SVP level of theory, which was performed using the Gaussian 16 program. Solvent-corrected single-point energies were also calculated using the polarizable continuum model (PCM) at the PCM(chloroform)-M06-2X/def2-TZVP//M06-2X/def2-SVP level of theory. The Gibbs free energy correction was determined from computations performed at the M06-2X/def2-SVP level of theory. Principal interacting orbital (PIO) analysis was conducted using the NBO 6.0 software. The nature of bonding in the respective transition state (TS) structures was analyzed using atoms-in-molecules (AIM) analyses. Additionally, the presence of non-covalent interactions (NCI) was exemplified using Multiwfn software.

Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether.

We combine in situ laser spectroscopy, quantum chemistry, and kinetic calculations to study the reaction of a singlet oxygen atom with dimethyl ether. Infrared laser absorption spectroscopy and Faraday rotation spectroscopy are used for the detection and quantification of the reaction products OH, H2O, HO2, and CH2O on submillisecond time scales. Fitting temporal profiles of products with simulations using an in-house reaction mechanism allows product branching to be quantified at 30, 60, and 150 Torr. The experimentally determined product branching agrees well with master equation calculations based on electronic structure data and transition state theory. The calculations demonstrate that the dimethyl peroxide (CH3OOCH3) generated via O-insertion into the C-O bond undergoes subsequent dissociation to CH3O + CH3O through energetically favored reactions without an intrinsic barrier. This O-insertion mechanism can be important for understanding the fate of biofuels leaking into the atmosphere and for plasma-based biofuel processing technologies.

N2 dissociation on AuCoFeMoRu high-entropy alloys: Circumventing scaling relations and step dependencies

Finding a better catalyst for the reduction of nitrogen to ammonia would be of considerable use to the chemical industry, allowing for cheaper and possibly decentralized ammonia production. One approach to find a better catalyst is to explore the element component space continuously via the use of high-entropy alloys, uncovering as of yet untested multi-element catalysts and reaction sites to optimize reaction activity. Utilizing DFT calculations and microkinetic modeling, we use the AuCoFeMoRu high-entropy alloy as a discovery platform for N2 reduction catalysts. Testing both terrace and step sites, we find that high-entropy alloy terraces can reach as high activities as steps for the N2 reduction reaction, due to their heterogeneous surface structure. We also find that high-entropy alloys are able to circumvent the scaling relations to an extent, due to the decoupling of the transition state and final state structure of the reaction. We discover several promising high-entropy alloy reaction sites, with a roughly twofold improvement in activity over the best monometallic surface. However, significantly larger gains in activity seem to still be fundamentally limited by the scaling relations.

Unveiling [3 + 2] cycloaddition reactions of diphenyl diazomethane to thiobenzophenone and cycloaliphatic thioketones in the light of molecular electron density theory

The reactivity, regiochemistry and substituent effects observed in the [3 + 2] cycloaddition (32CA) reactions of diphenyldiazomethane (PDM) with thiobenzophenone and a series of cycloaliphatic thioketones (TKs) have been studied within the molecular electron density theory at the ωB97XD/6-311G(d,p) computational level. The cycloaliphatic TK series shows remarkable substituent effects, changing from a non-polar 32CA reaction to a highly polar one, with the electron density flowing from PDM to the corresponding TK in a reaction classified as a forward electron density flux (FEDF). These 32CA reactions follow a one-step mechanism through earlier asynchronous transition state structures in which the formation of the two new single bonds has not yet begun, and the energetically predicted regiochemistry towards the generation of 1,3,4-thiadiazole is in complete agreement with the experimental outcome.

Kinetics and mechanism of the gas-phase reaction of the hydroxyl radical with meta-aminotoluene compound.

An ab initio investigation into the potential energy landscape of the meta-aminotoluene + •OHreaction has been conducted in this study. The calculated results reveal that the reaction channel leading to the product (NHC6H4CH3 + H2O) prevails under the 300-1700K temperature range, while the reaction path forming the product (NH2C6H4CH2 + H2O) dominates in the higher-temperature region (T ≥ 1800K). Within the specified temperature range, the product branching ratio for the former declines from 48 to 30%, while the latter shows an increase, reaching 29%. The overall second-order rate constants of the titled reaction obtained at the pressure 760Torr (N2) can be illustrated by the modified Arrhenius expression of ktotal = 1.46 × 10-13 T0.58 exp[(-0.759kcal.mol-1)/RT] cm3 molecule-1s-1 and ktotal = 1.86 × 10-22 T3.24 exp[(-5.086kcal.mol-1)/RT] cm3 molecule-1s-1, covering the temperature range of T = 300-600K and T > 600K, respectively. The total rate constant at the ambient conditions in this work, 1.43 × 10-11 cm3 molecule-1s-1, has been found to be roughly one order of magnitude lower than the available experimental data, ~ 1.2 × 10-10 cm3 molecule-1s-1, measured by Atkinson et al., Rinke et al., and Witte et al., or the theoretical value, 4.4 × 10-10 cm3 molecule-1s-1, and calculated by Abdel-Rahman and co-workers for the aniline + •OH reaction. The structures of reactants, transition states, intermediate states, and products of the meta-aminotoluene + •OHreaction are calculated with the aug-cc-pVTZ basis set and the methods DFT/B3LYP and CCSD(T). The rate constants and branching ratios in the 300-2000K temperature range are calculated with the statistical theoretical TST and RRKM master equation computations including tunneling corrections, with potential energy surface constructed by the CCSD(T)//B3LYP/aug-cc-pVTZ approach.

Darobactin Substrate Engineering and Computation Show Radical Stability Governs Ether versus C-C Bond Formation.

The Gram-negative selective antibiotic darobactin A has attracted interest owing to its intriguing fused bicyclic structure and unique targeting of the outer membrane protein BamA. Darobactin, a ribosomally synthesized and post-translationally modified peptide (RiPP), is produced by a radical S-adenosyl methionine (rSAM)-dependent enzyme (DarE) and contains one ether and one C-C cross-link. Herein, we analyze the substrate tolerance of DarE and describe an underlying catalytic principle of the enzyme. These efforts produced 51 enzymatically modified darobactin variants, revealing that DarE can install the ether and C-C cross-links independently and in different locations on the substrate. Notable variants with fused bicyclic structures were characterized, including darobactin W3Y, with a non-Trp residue at the twice-modified central position, and darobactin K5F, which displays a fused diether ring pattern. While lacking antibiotic activity, quantum mechanical modeling of darobactins W3Y and K5F aided in the elucidation of the requisite features for high-affinity BamA engagement. We also provide experimental evidence for β-oxo modification, which adds support for a proposed DarE mechanism. Based on these results, ether and C-C cross-link formation was investigated computationally, and it was determined that more stable and longer-lived aromatic Cβ radicals correlated with ether formation. Further, molecular docking and transition state structures based on high-level quantum mechanical calculations support the different indole connectivity observed for ether (Trp-C7) and C-C (Trp-C6) cross-links. Finally, mutational analysis and protein structural predictions identified substrate residues that govern engagement to DarE. Our work informs on darobactin scaffold engineering and further unveils the underlying principles of rSAM catalysis.

Physical Prior Mean Function-Driven Gaussian Processes Search for Minimum-Energy Reaction Paths with a Climbing-Image Nudged Elastic Band: A General Method for Gas-Phase, Interfacial, and Bulk-Phase Reactions.

The climbing-image nudged elastic band (CI-NEB) method serves as an indispensable tool for computational chemists, offering insight into minimum-energy reaction paths (MEPs) by delineating both transition states (TSs) and intermediate nonstationary structures along reaction coordinates. However, executing CI-NEB calculations for reactions with extensive reaction coordinate spans necessitates a large number of images to ensure a reliable convergence of the MEPs and TS structures, presenting a computationally demanding optimization challenge, even with mildly costly electronic-structure methods. In this study, we advocate for the utilization of physically inspired prior mean function-based Gaussian processes (GPs) to expedite MEP exploration and TS optimization via the CI-NEB method. By incorporating reliable prior physical approximations into potential energy surface (PES) modeling, we demonstrate enhanced efficiency in multidimensional CI-NEB optimization with surrogate-based optimizers. Our physically informed GP approach not only outperforms traditional nonsurrogate-based optimizers in optimization efficiency but also on-the-fly learns the reaction path valley during optimization, culminating in significant advancements. The surrogate PES derived from our optimization exhibits high accuracy compared to true PES references, aligning with our emphasis on leveraging reliable physical priors for robust and efficient posterior mean learning in GPs. Through a systematic benchmark study encompassing various reaction pathways, including gas-phase, bulk-phase, and interfacial/surface reactions, our physical GPs consistently demonstrate superior efficiency and reliability. For instance, they outperform the popular fast inertial relaxation engine optimizer by approximately a factor of 10, showcasing their versatility and efficacy in exploring reaction mechanisms and surface reaction PESs.

Unveiling the mechanism and selectivity of the [3 + 2] cycloaddition reactions of nitrone with acetylene derivatives leading to anticancer 4-isoxazoline derivatives from the MEDT perspective

The [3 + 2] cycloaddition reactions of N-methyl-C-(2-furyl) nitrone (a) with a series of acetylene derivatives (4b), (5b), and (6b) have been studied at the B3LYP-D3/6-31G(d) computational level within the framework of Molecular Electron Density Theory. Topological analysis allows classifying the nitrone (a) as a zwitterionic (zw-) three-atom component (TAC) associated with high energy barrier. These 32CA reactions follow a one-step mechanism under kinetic control with highly asynchronous bond formation. Bonding Evolution Theory (BET) analysis indicates that no new covalent CO and CC bonds form at the transition states (TSs). Interestingly, the global electron density transfer (GEDT) between 0.08 and 0.18 e predicts low polar character of forward electron density transfer (FEDF) type with the electronic flux from the nitrone (a) to the acetylene derivatives. Electron localization function (ELF) and atom-in-molecules (AIM) topological analysis of the electron density at the TS structures characterize the non-concerted nature of these one-step zw-type 32CA reactions.

Influence of atomic electronegativity on ESIPT behaviour for the BTDI and its derivatives: Theoretical exploration

In this work, we theoretically explored the influence of atomic electronegativity on excited-state intramolecular proton transfer (ESIPT) behavior among novel fluorescent probes BTDI and its derivatives (BODI and BSeDI). A thorough examination of the optimized structural parameters and infrared vibrational spectra reveals an enhancement in intramolecular hydrogen bonding within BTDI and its derivatives upon light excitation. This finding is further reinforced by topological analysis and interaction region indicator scatter plots, which underscores the sensitivity of atomic electronegativity to variations in hydrogen bonding strength. With regards to absorption and fluorescence spectra, the decrease in atomic electronegativity leads to a pronounced redshift, primarily attributed to the narrowing of the energy gap. Additionally, an analysis of potential energy curves and the exploration of intrinsic reaction coordinate paths based on transition state structures afford a deeper understanding of the mechanism underlying ESIPT and being modulated through the manipulation of atomic electronegativity. We anticipate that this work on atomic electronegativity regulating ESIPT behavior will serve as a catalyst for novel fluorescent probes in the future, offering fresh perspectives and insights.

Atomic‐Scale Study of Intercrystalline (Mg,Fe)O in Planetary Mantles: Mechanics and Thermodynamics of Grain Boundaries Under Pressure

AbstractPolycrystalline (Mg,Fe)O ferropericlase is the second most abundant mantle constituent of the Earth and possibly of super‐Earth exoplanets. Its mechanical behavior is expected to accommodate substantial plastic deformation in Earth's lower mantle. While bulk properties of ferropericlase have been extensively studied, the thermodynamics of grain boundaries and their role on mechanical response remain largely unexplored. Here, we use density functional theory calculations to investigate mechanical behavior and thermodynamics of the {310}[001] grain boundary—a representative proxy for high‐angle {hk0}[001] tilt grain boundaries—at relevant mantle pressures of the Earth and super‐Earth exoplanets. Our results provide evidence that shear‐coupled migration and grain boundary sliding are the dominant mechanisms of (Mg,Fe)O grain boundary mobility. We show that pressure‐induced structural transformations of grain boundaries can trigger a change in the mechanism and direction of grain boundary motion. Significant mechanical weakening of the grain boundary is observed under multi‐megabar pressures, caused by a change in the grain boundary transition state structure during motion. Our results identify grain boundary weakening in periclase as a potential mechanism for viscosity reductions in the mantle of super‐Earths. We further demonstrate that structural grain boundary transitions control the spin crossover of Fe2+ in the grain boundaries. We model iron partitioning behavior between bulk and grain boundaries and predict equipartitioning to occur in μm size ferropericlase grains. Our findings suggest that the iron spin crossover pressure in ferropericlase may increase several tens of GPa by pressure‐induced structural grain boundary transitions in dynamically active fine‐grained lower mantle regions.

Thermal rate constants and kinetic isotope effects of the H + H2O2 reactions: barrier height and reaction energy from single- and multireference methods.

One of the more significant sub-mechanisms of H2/O2 combustion involves the reaction of hydrogen peroxide with hydrogen atoms (H + H2O2), resulting in the production of OH + H2O (R1) and H2 + HO2 (R2) paths. Previous experimental and ab initio calculations reveal some variations in the barrier height for (R1). To improve the energetics of both (R1) and (R2), single reference and multireference ab initio methods are employed, and the rate constants and H/D kinetic isotope effects (KIEs) are calculated as a function of temperature. For (R1), the best results for the barrier height and reaction energies computed with the CASPT2(15,11)/aug-cc-pV6Z are 5.2 and - 70.3kcal.mol-1, respectively. CCSD(T)/aug-cc-pV5Z + CV (core-valence) calculations for (R2) give 9.7 and - 15.6kcal.mol-1 to those parameters. The CVT/SCT rate constants of both paths agree well with the fitted rate constants from uncertainty-weighted statistical analysis of the 14-mechanism of H2/O2. The kinetic isotopic effect (kH/kD) for the reaction D + H2O2 → DH + HO2 was found to be 0.47, which is in excellent agreement with the experimental value of 0.43. The structures of reactants, transition state, and products of (R1) and (R2) are calculated with the aug-cc-pVTZ basis set and M062X DFT, CCSD(T), and CASSCF methods. The barrier heights and reaction energies of (R1) and (R2) are computed using the M06-2X, CCSD(T), MRCI, and CASPT2 methods and various basis sets. The rate constants are calculated with the variational transition state theory including multidimensional tunneling corrections (VTST-MT), with potential energy surfaces built by the M06-2X/aug-cc-pVTZ approach.

Revealing the Critical Role of Global Electron Density Transfer in the Reaction Rate of Polar Organic Reactions within Molecular Electron Density Theory.

The critical role of global electron density transfer (GEDT) in increasing the reaction rate of polar organic reactions has been studied within the framework of Molecular Electron Density Theory (MEDT). To this end, the series of the polar Diels-Alder (P-DA) reactions of cyclopentadiene with cyanoethylene derivatives, for which experimental kinetic data are available, have been chosen. A complete linear correlation between the computed activation Gibbs free energies and the GEDT taking place at the polar transition state structures (TSs) is found; the higher the GEDT at the TS, the lower the activation Gibbs free energy. An interacting quantum atoms energy partitioning analysis allows for establishing a complete linear correlation between the electronic stabilization of the electrophilic ethylene frameworks and the GEDT taking place at the polar TSs. This finding supports Parr's proposal for the definition of the electrophilicity ω index. The present MEDT study establishes the critical role of the GEDT in the acceleration of polar reactions, since the electronic stabilization of the electrophilic framework with the electron density gain is greater than the destabilization of the nucleophilic one, making a net favorable electronic contribution to the decrease in the activation energy.

Activation of p53 signaling and regression of breast and prostate carcinoma cells by spirooxindole-benzimidazole small molecules.

This study discusses the synthesis and use of a new library of spirooxindole-benzimidazole compounds as inhibitors of the signal transducer and activator of p53, a protein involved in regulating cell growth and cancer prevention. The text includes the scientific details of the [3 + 2] cycloaddition (32CA) reaction between azomethine ylide 7a and ethylene 3a within the framework of Molecular Electron Density Theory. The mechanism of the 32CA reaction proceeds through a two-stage one-step process, with emphasis on the highly asynchronous transition state structure. The anti-cancer properties of the synthesized compounds, particularly 6a and 6d, were evaluated. The inhibitory effects of these compounds on the growth of tumor cells (MDA-MB 231 and PC-3) were quantified using IC50 values. This study highlights activation of the p53 pathway by compounds 6a and 6d, leading to upregulation of p53 expression and downregulation of cyclin D and NF-κB in treated cells. Additionally, we explored the binding affinity of spirooxindole analogs, particularly compound 6d, to MDM2, a protein involved in regulation of p53. The binding mode and position of compound 6d were compared with those of a co-crystallized standard ligand, suggesting its potential as a lead compound for further preclinical research.

Transition-state defect structure: A new strategy for TiO2-based porous materials to enhance photodegradation of pollutants

The aim of this paper is to investigate the derived structure and properties of Zeolitic Imidazolate Framework-8 (ZIF-8), and the effect of residual structural on the catalytic properties after loading with Titanium Dioxide (TiO2). For this purpose, we ingeniously prepare C-ZIF-8@TiO2 with a transition-state defect structure and apply it for efficiently degrading organic dye wastewater represented by Rhodamine B (Rh–B). Thanks to the transition-state defect structure loaded with TiO2 and ZIF-8 self-derived Carbon (C) and Zinc Oxide (ZnO), the catalytic performance of C-ZIF-8@TiO2 is superior to that of TiO2 and normal TiO2/ZIF-8 composites, and it is effective in degrading a variety of antibiotics and dyes. The related characterization also shows good photovoltaic properties and long-term durability for C-ZIF-8@TiO2. The mechanism on free radical action is elucidated and the possible degradation pathway for Rh–B is speculated. Therefore, C-ZIF-8@TiO2 provides a new strategy for the degradation of organic pollutants in water bodies.