Structural Chemistry最新文献

The three dinaphthylketone constitutional isomers, 1,1′-NA₂CO, 1,2′-NA₂CO, and 2,2′-NA₂CO, have been subjected to Friedel–Crafts Acylation (polyphosphoric acid (PPA), 90–300°C, 12 h) and Scholl reaction (AlCl₃/NaCl, 120–300°C, 4 h). The resulting product mixtures are analyzed by NMR and separated by column chromatography. The starting ketones and the products have been calculated with DFT, B3LYP/6-311G**, to support analysis of the reaction mechanisms. The three dinaphthyl ketones have three, four, and three E,Z-conformations, which may potentially give ten Scholl reaction products by ortho-ortho, ortho-peri, and peri-peri couplings. In PPA, the products formed at relatively low temperatures are due to Scholl reactions of the starting ketones. At higher temperatures, naphthalene is formed and Friedel Crafts acyl rearrangements (FCAcRs) 1,1′-NA₂CO → 1,2′-NA₂CO → 2,2′-NA₂CO are observed. At high temperatures, additional Scholl products show that complex multi-step reactions occur including FCAcRs in both directions and cyclic FCAcRs of Scholl products. The reactions in AlCl₃/NaCl are highly selective, giving only the 6-ring Scholl cyclization products 13H-dibenzo[a,i]fluoren-13-one and 7H-benzo[hi]chrysen-7-one (BhiCO) and 7H-benzo[de]naphthacen-7-one (BdeNCO). Up to 240°C 1,1′-NA₂CO forms BhiCO and up to 220°C 1,2′-NA₂CO forms BdeNCO. At higher temperatures, both polycyclic aromatic ketones are formed from each of the three dinaphthyl ketones indicating FCAcRs. The detailed analysis of the experimental data in combination with the DFT calculations shows that FCAcRs are reactions in both directions in PPA and AlCl₃/NaCl, substantiating Gore’s 1955 proposition that the Friedel–Crafts acylation reaction of reactive aromatic hydrocarbons is a reversible process. The lower onset temperatures and selectivity of cyclization products suggest lower activation energies for Scholl reactions as compared to FCAcRs in PPA and even more pronounced in AlCl₃/NaCl. The common network of reaction pathways underlying the reactions in both media highlights the linkage between Friedel–Crafts acyl rearrangements and Scholl reactions.

Graphical Abstract

The Nobel Prize 2024 in Physiology or Medicine has been awarded for the discovery of miRNA and its role in post-transcriptional gene regulation. Firstly, the results were thought to be irrelevant to humans, but nowadays, at least 30% of the known miRNAs could be used as novel biomarkers for screening human diseases and therapeutic purposes targeting manipulation of cell functions under examinations.

In this work, we present and test a procedure for generating a chemical virtual library and its subsequent use to select molecular systems with desired properties. The library consists of molecular structures generated from a set of chemical fragments. As an example, we consider two tasks. The first one involves identifying structures with specific spectral properties, particularly concerning the UV–Vis region of the spectrum. To address this, the thiophene cycles with typical donor (dimethylamino) and acceptor (nitro) substituents are chosen as the molecular building blocks. First, the molecules from the derived virtual library are subject to computational screening using the semi-empirical tight binding density-functional method. The primary objective of the screening is to identify molecular structures that exhibit desired spectral properties, especially absorption in the long-wavelength region. Second, for the most promising structures identified in the initial screening, more accurate TD-DFT (B3LYP/cc-pVDZ) calculations are performed. Additionally, the advantage of the developed approach for library generation, aimed at further investigation of biological activity, is illustrated using an example involving papain-like protease (PLpro) inhibitors of the SARS-CoV-2 virus. The calculation scheme used in the considered examples is implemented in the Python program suite QUASAR.

The paper deals with the synthesis of a series of cationic [Rh(ppz)₂(N^N)]⁺ complexes containing deprotonated 1-phenyl-1H-pyrazole as cyclometallating (C^N) ligands and α-diimines (2,2’-bipyridine, 1,10-phenanthroline and its derivatives) as ancillary (N^N) ligands in the form of salts with PF₆ ⁻ counter ions. These complexes were obtained from [(ppz)₂Rh-μ-Cl]₂ precursor through cleaving the μ-dichloro-bridged dimer with N^N ancillary ligands. The complexes were identified by means of NMR spectroscopy and MS spectrometry and their molecular structures were finally confirmed by X-ray crystallography. These complexes showed strong luminescence in MeOH/EtOH 1:1 glasses at 77 K but were very week or almost non-emitting species in MeCN solutions at room temperature. Their emission properties were compared to analogues Ir(III) complexes.

Diaryl disulfides are important in chemistry and materials science, yet their conformational equilibria often remain experimentally unexplored due to conformer predominance or indistinguishable signals. High-level DFT calculations for 4,4’-dibromodiphenyl disulfide (1) reveal a preference for conformer B, characterized by sliding ring planes during S–S rotation, over conformer A, where the planes approach or distance themselves. Bromine substituents enhance π-π interactions, stabilizing conformer B, unlike in diphenyl disulfide (2). Notably, only conformer A appears in the solid state. NBO analysis attributes conformer B’s stability to weaker steric effects, while AIM analysis confirms an attractive interaction between the C2 atoms of both rings. These findings highlight the role of substituents in conformational behavior and provide insights for designing materials with optimized properties.

Substituent effect (SE) significantly influences the electronic structure of molecules. This study focuses on analyzing SEs in the 2,4-diaryl-4H-1,4-thiazine, with a specific emphasis on their impact on aromaticity and reactivity. The density functional theory (DFT) calculations, the harmonic oscillator model of aromaticity (HOMA) index, and frontier molecular orbital analysis are employed to compare SEs at two selected positions, R¹ and R², which correspond to the para positions of two phenyl rings in the parent 2,4-disubstituted-4H-1,4-thiazine. Our investigation reveals that the presence of any substituent (electron-withdrawing or electron-donating) at the R¹ position induces more significant changes in the molecule. The correlation between the Hammett constant (R) and HOMA suggests that electron-donating groups at the R¹ position activate the heterocyclic ring, leading to decreased aromaticity. These findings offer valuable insights into designing synthesis pathways for thiazine derivatives and other related physical and chemical properties.

Arthur Greenberg’s career is an unusual one by many measures. A “late bloomer,” he entered the academic job market in 1972 with complications due to an ROTC commitment. Starting at a non-research institution, having the good fortune to collaborate with friend and fellow graduate student Joel Liebman, Greenberg moved to progressively higher-level research departments. Not intending to follow an administrative pathway, he became a department chair and subsequently a dean. The pathway was certainly an unconventional one and may offer insights to those starting academic careers.

The volumes of atoms and molecules obtained by means of quantum theory of atoms in molecules (V_AM) in previously reported π and σ complexes were compared with those revealed from the Hirshfeld surfaces (V_HS) and the Voronoi tessellation (V_VD). For metal atoms, V_HS and V_VD are close to V_AM values. The Voronoi tessellation underestimates volumes of heavy and low-coordinated metal atoms by 27% in average, while for s- and d-metal ions in σ-complexes V_VD deviates from V_AM by 6% in average only. The Hirshfeld surfaces underestimate volumes of metal atoms in π-complexes by 17% and overestimate those in σ-complexes by 30% in average. Any correlation between atomic volumes of non-metals is absent; however, V_HS and V_VD values for polyatomic (even diatomic) molecules deviated from V_AM by 11% in average. All three methods indicate constancy of molecular volumes in crystals. Sensitivity of three methods to detect trends in atomic and molecular volumes over different datasets was discussed.