Helvetica Chimica Acta最新文献

The synthesis and characterization of cross-shaped π-extended dibenzo[e,l]pyrene derivatives with combined fjord and armchair edge structures were reported. The target molecules were synthesized via Yamamoto coupling and Scholl reactions, and their structures were fully characterized by nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HR-MS), and single-crystal X-ray diffraction. Photophysical studies revealed a significant redshift in absorption and emission spectra compared to the parent dibenzo[e,l]pyrene, attributed to the extended π-conjugation system. Density functional theory (DFT) calculations provided insights into the molecular orbital distribution and reduced bandgap resulting from the elongated conjugation pathway. This work offers a versatile synthetic strategy for polycyclic aromatic hydrocarbons with tailored edge topologies and paves the way for their potential applications in optoelectronic materials.

I chose chemistry as a career because after participating in the Chemistry Olympiad, I was fascinated by everything chemists can do. My favorite quote is “Life is like riding a bicycle: to keep your balance, you must keep moving” by Albert Einstein. If I were not a scientist, I would be a teacher of either chemistry, music, or step aerobics.

A novel, cost-effective, and sustainable method for the synthesis of highly crosslinked methyl silicone resins by upcycling silicone oil, specifically linear polyorganylsiloxanes, was developed. Using mild reaction conditions, a high yield of DT resins (up to 80%) along with silicone oligomers as a byproduct was achieved. Solid state ²⁹Si NMR spectroscopy confirmed the structure of the synthesized resins, while gas chromatographic analysis of the reaction headspace revealed methane as the only byproduct. Electron paramagnetic resonance (EPR) spectroscopy revealed the intermediacy of radical species, providing a unique insight into the reaction mechanism, which contrasts with traditional nucleophilic substitution pathways. This approach not only provides an efficient route to resin production, but also contributes as an alternative for the sustainable valorization of silicone waste.

Nanopore technology is a powerful single-molecule platform for detecting and sequencing a wide range of biomolecules. Among nanopores, aerolysin has emerged as a particularly promising candidate for peptide sensing. However, its ability to capture long biopolymers is limited due to its lack of a vestibule structure. In this study, we engineered electrostatics at the entry of the aerolysin pore and observed an increase in event frequency – up to 2 times higher for DNA and for the peptide compared to wild-type aerolysin. Importantly, this modification did not affect the pore's current-voltage characteristics. When tested with DNA and α-synuclein peptides, the engineered pore (D209R) exhibited comparable dwell times and current blockages to the wild-type pore, while ion selectivity and electroosmotic flux show an increase. These findings highlight that fine-tuning the electrostatic properties at the pore entry can significantly enhance event frequency without compromising key transport properties such as current blockage or dwell time. This improvement expands the utility of aerolysin nanopores for sensing and sequencing applications and paves the way for more effective diagnostic tools and analytical methods in the field of proteomics and biomarker discovery.

Pairwise distance root mean square deviation defines a hyperspace where conformers with similar shape reside close to each other. The radius of gyration of protein ensembles in this abstract conformer space (ACS) converges at ensemble sizes between 50 and 500, depending on the extent of disorder. Upon further increase of ensemble size, the root mean square distance of conformers to their nearest neighbors decreases only slowly. Clustering in ACS can reveal distinct subensembles. For proteins that exist in two states, clustering in a common ACS reveals differences between the ensembles in the two states. The dimension of ACS can be reduced to 2D or 3D by multi-dimensional scaling or principal component analysis. Visualization in these lower-dimensional spaces also reveals differences between protein states or the existence of subensembles. The ratio between the gyration radius in ACS and its counterpart in real space is a global disorder parameter.

Gold(I)-catalyzed cross-coupling reactions with aryldiazonium salts are instrumental in forming C─C and C─N bonds. However, mechanistic details remain unclear, particularly the role of diazenyl intermediates. We employ stoichiometric reactions, NMR spectroscopy, electrospray ionization mass spectrometry, and infrared photodissociation spectroscopy to investigate the reactivity of gold-aryl complexes with aryldiazenyl radicals and aryldiazonium ions. Our results reveal that [(NHC)Au(Ar)] complexes form short-lived electron donor-acceptor (EDA) complexes [(NHC)Au(Ar)(Ar'N₂)]⁺ in solution, which undergo a C─N coupling reaction during the transfer to the gas phase to form gold(I) azoarene complexes. The rearrangements of the gold complexes during the transfer from the solution to the gas phase were studied by ion-mobility separation, IRPD spectra, and delayed reactant labeling experiments. We also show that gold-chloride complexes facilitate the oxidative addition of aryldiazonium ions to form [(NHC)Au^III(Cl)(Ar)(N₂)]⁺, suggesting an alternative non-radical mechanism initiating the C─C bond formation reactions. In solution-phase reactivity, ligand steric effects are crucial in steering the reaction selectivity: IMes ligands favor N₂ expulsion followed by the C─C coupling, while bulkier IPr and IPent ligands promote the C─N coupling. These findings refine our understanding of gold(I)-mediated cross-coupling reactions, and the observed solution-gas phase discrepancies highlight the need for careful interpretation of ESI-MS data in mechanistic studies.