Helvetica Chimica Acta最新文献

A recurring misconception in some textbooks and research papers has led to an abandonment of fundamental physical laws when describing a subset of acid-base equilibria, especially regarding the role of the solvent. In the specific case of the autoprotolysis of water, experiments and theoretical calculations prove that the K_w of water at 25 °C, 1.00×10⁻¹⁴, is identical to its acid ionization constant, K_a. Nevertheless, several articles have been published erroneously purporting to give theoretical proof that the K_a of water is 10^−15.743 (1.81×10⁻¹⁶) and that the K_a of the aqueous proton (hydronium ion) is 55.3 rather than 1.00. Here we argue that using the incorrect numbers has pedagogical implications beyond those of a simple error. Arguments for the incorrect K_a and pK_a values require a misapplication of Henry's law and violate long-standing methods that use Raoult's law and the conservation of matter to describe the behavior of solutions. As a result, chemistry students may be asked to accept one set of physical principles in one course and another set in another course. Here we argue for adherence to fundamental physical laws governing solution equilibria as applied to the autoprotolysis of water and all aqueous acid base equilibria.

Herein, we detail an extension of our research on the synthesis of a small library of furanoheliangolides and the characterization of the covalent interaction between goyazensolide and IPO5. Using a build-couple-pair strategy, we assembled a small library of germacrene-type lactones and diversified them into eight groups of structurally different analogues. The germacrene lactones were synthesized using Sonogashira coupling and Barbier-type macrocyclization, while the furanoheliangolides were further elaborated through gold-catalyzed transannulation followed by esterification. This synthetic approach enabled the generation of a goyazensolide alkyne-tagged cellular probe, which was used to identify the selective binding between goyazensolide and the oncoprotein importin-5 (IPO5). Mass spectrometry analysis of the proteolytic digest from the reaction between the goyazensolide probe and a recombinant IPO5 indicated a covalent engagement at Cys560 of IPO5, which was confirmed by site-directed mutagenesis.

Imido ligand is a ubiquitous motif in organometallic chemistry, serving roles spanning from ancillary ligands to reactive sites. The nature of M=N bond is highly depended on the metal centres and their d-electron configuration, with late transition metal (TM) imido complexes exhibiting contrasting features when compared to their early TM analogues. Envisioning to uncover general electronic descriptor for the nature of imido ligands, we computationally investigate the solid-state ¹⁵N NMR signatures of late TM imido complexes with various central metals, geometries and d-electron counts, and compare them against these of the corresponding early TM systems. The spectroscopic signatures are mostly driven by the presence of filled, π-symmetry orbitals in late TM imido complexes, suggesting the development of high-lying π(M=N) and low-lying σ/σ^*(M=N) orbitals. This contrasts with what is observed for the reported early TM systems, for which high-lying σ-type orbitals determine the NMR signature. Noteworthily, Ni- and Pd-imido complexes with formal d¹⁰ configurations exhibit highly asymmetric nitrogen-15 NMR signature with extremely deshielded principal components, because of the presence of filled, high-lying antibonding π^*(M=N) orbitals, consistent with their high reactivity. The sensitive response of ¹⁵N NMR signature to the nature of metal sites further highlights that chemical shift is a useful reactivity descriptor.

Multi-resonant thermally activated delayed fluorescence (MR-TADF) helicenes show great potential as chiral emitters due to their typically high photoluminescence quantum yield and that they emit circularly polarized luminescence. Here, a new propeller-shaped chiral MR-TADF helicene DiKTa3, integrating three DiKTa moieties, was designed and synthesized aiming to achieve co-parallel electronic and magnitude transition dipole moments that would lead to a high dissymmetry factor, g. It emits at λ_PL of 491 nm, with a full width at half maximum of 52 nm and has a moderate ΔE_ST value of 0.24 eV in toluene. The separated (P,P,P) enantiomer shows an absorption dissymmetry factor |g_abs| of 6.8×10⁻⁴ at 450 nm, which results from a lower symmetry conformation adopted by the compound in solution than the C₃-symmetric optimized structure. This work highlights the strong influence that geometry can have on the chiroptical properties of the emitter.

Synthesis of a series of indolo[1,2-a]quinoxaline derivatives substituted with phthalazinones/isoindolinones/carbonyl benzoylesters at C-4 position have been accomplished under open air rt/heating conditions following ANRORC (Addition of Nucleophile, Ring Opening and Ring Closure) mechanism. Initially condensation of 2-(1-indolyl)-aniline and ninhydrin generates a spirocyclic intermediate 5′H-spiro[indene-2,6′-indolo[1,2-a]quinoxaline]-1,3-dione, which upon reaction with various nucleophiles like hydrazine/phenylhydrazine, amines and alcohols affords C-4 substituted indolo[1,2-a]quinoxalines in high yield (up to ~88 %) via ANRORC. The photophysical investigation shows that the quinoxaline derivatives possess significant fluorescence property with high quantum yield (QY~11.0–17.0). The N-phenylphthalazinone substituted indolo[1,2-a]quinoxaline, a molecule structurally similar to 2,2′-bipyridine system, can efficiently and selectively detect Fe²⁺ through fluorescence turn off sensing.

Herein, a selective protocol for the complete removal of acetyl protecting groups from carbohydrate derivatives based on copper nanoparticles supported on activated carbon is presented. The deacetylation procedure occurs under neutral conditions, is applicable to a wide range of substrates and tolerates a variety of functional groups (e. g. azido, allyl and silyl groups). Quantitative yields of the deacetylated product were obtained for all evaluated derivatives using catalyst amounts between 1 and 10 mol%. As a special highlight, the dual behavior of the nanocatalyst in both deacetylation and click reactions is reported.

Young people should study chemistry because it's both fun and useful. I chose my field of research because I love to be able to make precision tools using chemistry to gain understanding of, and control over, a biological system. My valuable advice from a more senior colleague at the beginning of my career was ‘a scientific path is not linear, even though it may appear to be so when the story is told afterwards'

Fluorine's high electronegativity, lipophilicity, and metabolic stability make it a valuable element for drug design and development. Consequently, significant synthetic efforts have focused on introducing fluorine and fluorinated motifs into organic molecules, with the synthesis of trifluoromethyl ketones (TFMKs) recently attracting considerable attention. Building on our ongoing research on radical organofluorine chemistry, we present herein the divergent synthesis of trifluoromethyl ketones directly from olefins using readily available chloro- and bromotrifluoroacetone as synthetic precursors of the trifluoroacetonyl radical under photoredox catalysis. Mechanistic studies revealed that the divergence is attained through radical polar crossover (RPC) and hydrogen atom transfer (HAT) mechanisms.