Helvetica Chimica Acta最新文献

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.

A simple method for the electrochemical allylic oxidation of olefins to enones based on peroxide-mediated C–H activation is presented. t-Butyl hydroperoxide serves a dual role as mediator and oxygen source, avoiding the utilization of expensive transition metal catalysts, potentially explosive supporting electrolytes such as perchlorates, or additional environmentally harmful mediators. This elegant methodology allows for an operationally simple and sustainable late-stage transformation of delicate natural compounds such as terpenes or steroids into highly value-added building blocks. Such an approach provides a greener alternative to conventional oxidation methods used for industrial applications. In total, 25 examples are demonstrated with isolated yields up to 80%. The robust scalability of the method was also demonstrated, and chromatography could be avoided in scale-up simply by using recrystallization, which decreases the cost of downstream processing.

The integration of boron into π-conjugated systems is a reliable approach to enhance photophysical properties. In this context, boramidines have emerged as a promising class of fluorophores. In this work, the design, synthesis, and chiroptical properties of novel axially chiral isoquinoline-derived boramidines are reported. Thanks to metal-catalyzed cross-coupling allied with atroposelective C─H arylation strategies or chiral stationary phase HPLC resolution, enantioenriched boramidines 1 and 2 are afforded (ee 90%–99%). Comparing with more classical boramidines, investigations reveal (i) bathochromic absorption shifts in the UV–vis region (>50 nm) and (ii) emission maxima now in the green and cyan domains, along with fluorescence quantum yields reaching 70% in N₂-saturated environments. Chiroptical measurements demonstrate well-defined electronic circular dichroism (ECD) spectra and circularly polarized luminescence (CPL) signals with |g_lum| values up to 2 × 10⁻³.

Extreme ultraviolet (XUV) radiation is highly efficient for functionalization of solid materials by means of pronounced radical formation. To prevent collective effects, and study single photon effects, a low-fluence XUV source with 200 μJ/cm² was used to irradiate polymers such as poly-methyl methacrylate (PMMA) and poly-tetrafluoroethylene (PTFE). The unexposed and XUV-exposed sample domains were analyzed with time-of-flight secondary ion mass spectrometry (TOF-SIMS), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The findings show that XUV photons drive photochemical modification of the surface, fragmentation, and ionization of the desorbed products. Besides a theoretical analysis, the XUV-induced surface modification of PTFE is discussed a new application for surface functionalization.

A detailed picture of the reactivity of metallacyclobutanes is key to the understanding and development of new reactions relying on these reactive intermediates, including olefin metathesis and cyclopropanation. More than 40 years ago, Miyashita and Grubbs reported experimental studies on the thermal decomposition pathways of a phosphine-supported nickelacyclobutane (NiCB) suggesting that nickel may be amenable to both cyclopropanation and olefin metathesis. Here we report a computational investigation of this system that shows that cyclopropane reductive elimination is the primary decomposition pathway for monometallic NiCBs, independently of the number of coordinated phosphine ligands. Further calculations suggest that bimetallic species may be responsible for the olefinic products of apparent [2+2] cycloreversion.