Experimental and Theoretical Studies on the Rearrangement of 2‐Oxoazepane α,α‐Amino Acids into 2′‐Oxopiperidine β2,3,3‐Amino Acids: An Example of Intramolecular Catalysis

Enantiopure β‐amino acids represent interesting scaffolds for peptidomimetics, foldamers and bioactive compounds. However, the synthesis of highly substituted analogues is still a major challenge. Herein, we describe the spontaneous rearrangement of 4‐carboxy‐2‐oxoazepane α,α‐amino acids to lead to 2′‐oxopiperidine‐containing β^2,3,3‐amino acids, upon basic or acid hydrolysis of the 2‐oxoazepane α,α‐amino acid ester. Under acidic conditions, a totally stereoselective synthetic route has been developed. The reordering process involved the spontaneous breakdown of an amide bond, which typically requires strong conditions, and the formation of a new bond leading to the six‐membered heterocycle. A quantum mechanical study was carried out to obtain insight into the remarkable ease of this rearrangement, which occurs at room temperature, either in solution or upon storage of the 4‐carboxylic acid substituted 2‐oxoazepane derivatives. This theoretical study suggests that the rearrangement process occurs through a concerted mechanism, in which the energy of the transition states can be lowered by the participation of a catalytic water molecule. Interestingly, it also suggested a role for the carboxylic acid at position 4 of the 2‐oxoazepane ring, which facilitates this rearrangement, participating directly in the intramolecular catalysis.     

Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2

The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO₂ revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO₂ co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion.     

Microstructural stability and age-hardening behavior of Re-added dual two-phase Ni3Al and Ni3V intermetallic alloys

The effect of Re addition on the microstructure and hardening behaviour of the dual two-phase Ni₃Al (L1₂) and Ni₃V (D0₂₂) intermetallic alloy was investigated by scanning electron microscopy, transmission electron microscopy and Vickers hardness test. The two-phase eutectoid microstructure accompanying the Re-rich precipitates were observed in the channel region of the alloys in which Re substituted for Ni but not in those in which Re substituted for Al and V. The concomitant addition of Nb (or Ta) with Re more stabilized the two-phase eutectoid microstructure and consequently more induced the fine precipitates in the channel region. The annealing at temperatures below the eutectoid temperature was necessary to induce the fine precipitates in the channel region and thereby result in the precipitation hardening. The fine precipitation in the channel region and related hardening was attributed to the alloying feature so that Re is soluble in the A1 (fcc) phase at high temperatures and becomes less soluble in the two intermetallic phases decomposed from the A1 phase at low temperatures.     

Comparison of Ferroptosis-Inhibitory Mechanisms between Ferrostatin-1 and Dietary Stilbenes (Piceatannol and Astringin)

Synthetic arylamines and dietary phytophenolics could inhibit ferroptosis, a recently discovered regulated cell death process. However, no study indicates whether their inhibitory mechanisms are inherently different. Herein, the ferroptosis-inhibitory mechanisms of selected ferrostatin-1 (Fer-1) and two dietary stilbenes (piceatannol and astringin) were compared. Cellular assays suggested that the ferroptosis-inhibitory and electron-transfer potential levels decreased as follows: Fer-1 >> piceatannol > astringin; however, the hydrogen-donating potential had an order different from that observed by the antioxidant experiments and quantum chemistry calculations. Quantum calculations suggested that Fer-1 has a much lower ionization potential than the two stilbenes, and the aromatic N-atoms were surrounded by the largest electron clouds. By comparison, the C4′O-H groups in the two stilbenes exhibited the lowest bond disassociation enthalpies. Finally, the three were found to produce corresponding dimer peaks through ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry analysis. In conclusion, Fer-1 mainly depends on the electron transfer of aromatic N-atoms to construct a redox recycle. However, piceatannol and astringin preferentially donate hydrogen atoms at the 4′-OH position to mediate the conventional antioxidant mechanism that inhibits ferroptosis, and to ultimately form dimers. These results suggest that dietary phytophenols may be safer ferroptosis inhibitors for balancing normal and ferroptotic cells than arylamines with high electron-transfer potential.     

Experimental and Theoretical Mechanistic Study on the Thermal Decomposition of 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline

The present paper is a continuation of comprehensive study regarding to synthesis and properties of pyrazoles and their derivatives. In its framework an experimental and theoretical studies of thermal decomposition of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline were performed. It was found, that the decompositions of the mentioned pyrazoline system in the solution and at the melted state proceed via completely different molecular mechanisms. These mechanisms have been explained in the framework of the Molecular Electron Density Theory (MEDT) with the computational level of B3LYP/6-31G(d). A Bonding Evolution Theory (BET) examination of dehydrochlorination of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline permits elucidation of the molecular mechanism. It was found, that on the contrary for most known HCl extrusion processes in solution, this reaction is realised via single-step mechanism.     

Cyanide Bridged Platinum-Iron Complexes as Cisplatin Prodrug Systems: Design and Computational Study

The potential role of cyanide-bridged platinum-iron complexes as an anti-cancer Pt(IV) prodrug is studied. We present design principles of a dual-function prodrug that can upon reduction dissociate and release concurrently six cisplatin units and a ferricyanide anion per prodrug unit. The prodrug molecule is a unique complex of hepta metal centers consisting of a ferricyanide core with six Pt(IV) centers each bonded to the Fe(III) core through a cyano ligand. The functionality of the prodrug is addressed through density functional theory (DFT) calculations.     

Effects of Ionic Liquids on the Thermodynamics of Hydrogen Activation by Frustrated Lewis Pairs: A Density Functional Theory Study**

Nowadays, hydrogen activation by frustrated Lewis pairs (FLPs) and their applications are one of the emerging research topics in the field of catalysis. Previous studies have shown that the thermodynamics of this reaction is determined by electronic structures of FLPs and solvents. Herein, we investigated systems consisting of typical FLPs and ionic liquids (ILs), which are well known by their large number of types and excellent solvent effects. The density functional theory (DFT) calculations were performed to study the thermodynamics for H₂ activation by both inter- and intra-molecular FLPs, as well as the individual components. The results show that the computed overall Gibbs free energies in ILs are more negative than that computed in toluene. Through the thermodynamics partitioning, we find that ILs favor the H−H cleavage elemental step over the elemental steps of proton attachment, hydride attachment and zwitterionic stabilization. Moreover, the results show that these effects are strongly dependent on the type of FLPs, where intra-molecular FLPs are more affected compared to the inter-molecular FLPs.     

A New Metric for Evaluating DFT Calculated Proton and Carbon Chemical Shifts of Natural Products and Organic Compounds

The calculation of DFT (density functional theory) chemical shifts have become an important technique for the verification of a proposed structure. An easily calculated metric developed for proton and carbon chemical shifts of natural products and organic compounds, the calculated chemical shift index (CCSI), has been developed, which uses the deviation of each pair of calculated and experimental chemical shifts. The mean absolute deviation (MAD), which is commonly used as the goodness of fit metric for DFT calculated chemical shifts, can conceal large deviations in the calculated data. A classification strategy is also proposed for the CCSI to highlight when further assessment of the NMR data is required.     

Impact of Imine Bond Orientations on the Geometric and Electronic Structures of Imine-based Covalent Organic Frameworks

Many efforts are currently devoted to improving the stability and crystallinity of imine-based two-dimensional (2D) covalent organic frameworks (COFs) given their wide range of potential applications. The variation in the relative orientations of the imine bonds has been found to be a critical factor that impacts the stacking of the 2D COF layers, leads to the formation of isomer structures, and influences the crystallinity of the final product. Most investigations to date have focused only on the structural properties, while the role of the imine orientations on the electronic properties has not been studied systematically. Here, we explore this effect by examining how the electronic band structures, electronic couplings, and effective masses evolve when considering four isomeric structures of an imine-linked tetraphenyl-pyrene naphthalene-diimide COF. Our results provide an understanding of the impact of the imine orientations and how they need to be controlled to realize COF inter-layer stackings that can lead to efficient cross-plane electron transport. They can be used to guide the design and synthesis of imine-based COFs for applications where charge transport needs to be optimized.     

On modeling of MPS‐based multiphase fluid flow with low density ratios

A divergence‐free moving particle semi‐implicit framework has been formulated for modeling of multiple miscible fluids having small density ratios (≤ 1.10) in the presence of free surface. A density‐weighted pressure gradient along with a hybrid free‐surface treatment is specifically adopted to incorporate the effect of marginal density difference through a higher‐order kernel. The hybrid free‐surface treatment reduces error in velocity divergence and resulting spurious velocity fluctuation in the vicinity of free surface for low‐velocity system. Scalar transport equation is resolved to update density associated with the particles at every time step. A total of 9 cases of lock‐exchange flow with different lock positions and density ratios have been utilized to validate the proposed framework. The model performs satisfactorily irrespective of lock positions and low density variations (3%‐9%).