Chemistry methods : new approaches to solving problems in chemistry最新文献

Raman optical activity (ROA) provides unique chiroptical insights into biomolecular structure but suffers from inherently weak signals. A substantial enhancement in the low-wavenumber/THz region (50–250 cm⁻¹/1.5–7.5 THz) of ROA spectra upon the formation of mononucleotide G-quadruplexes (mG4) from guanosine-5′-monophosphate (5′rGMP) is reported. Using concentration-dependent Raman and ROA measurements, a nearly 100-fold increase in ROA intensity upon aggregation is identified, with spectral features highly sensitive to cation-mediated structural variations. These effects can be traced to long-range chiral interactions and distinct stacking arrangements within mG4. While strong terahertz Raman optical activity (THz-ROA) signals have previously been observed in globular proteins and α-helical polypeptides, the findings of this study represent the first evidence of this phenomenon in nucleotides, demonstrating that noncovalent self-assembly into supramolecular helices can give rise to intense low-frequency chiroptical responses. This establishes THz-ROA as a powerful background-free tool for studying supramolecular chirality and nucleotide self-assembly, with potential applications in characterizing biologically relevant G-quadruplex structures.

The homologation of esters—in the presence of a lithium carbenoid—to thioesters, amides, and carboxylic acid is reported. By controlling the tetrahedral intermediate collapsing and promoting a series of rearrangements ultimately leading to a high electrophilic ketene, the subsequent incorporation of S-, N-, and O-nucleophilic elements furnishes the title compounds. Despite the coexistence of multiple (concomitant) equilibria and short-living entities, the protocol features remarkable chemocontrol and flexibility. Notably, the formal oxidation state of the final compounds is retained.

A gas rapid injection nuclear magnetic resonance (GRI-NMR) system has been constructed to investigate reactions requiring the use of gas reagents. The system allows for the accurate delivery of gases under inert conditions to a standard NMR glass tube inside the spectrometer permitting in situ reaction monitoring to be conducted which mimics reactions performed at the bench. The system provides a unique avenue to investigate reaction systems that require a continuous and/or precise delivery of gas reagents. To showcase the newly constructed GRI-NMR system, the reaction of carbon dioxide binding with phosphine-ligated nickel zero complexes is monitored in real time providing detailed kinetic data.

Levoglucosenone is a fascinating carbohydrate-based building block obtained from renewable sources, and its use in organic synthesis for the obtainment of highly added-value compounds is particularly encouraged from a circular economy point of view. Herein, the allyl cyanate–isocyanate metal-free rearrangement is reported on the allyl carbamate derived from levoglucosenone. In the presence of O-, N-, and S-nucleophiles this rearrangement forms (4S)-carbamates, ureas, and carbamothioates in a regio- and stereoselective manner. The elaboration of the unsaturated adducts through dihydroxylation of the double bond after the rearrangement allows access to new, unique d-allo configured 4-deoxy-4-aminosugar derivatives.

This study develops a novel heterogeneous palladium catalyst immobilized on etched silicon powder, demonstrating high efficiency and long-term stability under continuous flow conditions. Characterization reveals that the Pd⁰ species are generated via in situ reduction of the Pd^II precursor by terminal hydrogens preloaded on the etched silicon surface. The catalyst readily integrates into packed-bed column reactors, facilitating efficient hydrogenation and reductive alkylation. The practical applicability of this system is demonstrated through the continuous synthesis of several valuable chemical compounds, including key fragrance and pharmaceuticals. A long-term durability test confirms sustained catalytic performance over 30 days without noticeable deactivation. Remarkably, the catalyst retains its activity even after 2 years of storage without protective measures. The system enables the flexible synthesis of diverse products by changing the starting materials, all within the same reactor setup. This study represents a significant advancement in green and sustainable chemistry, offering a robust and adaptable catalytic platform for scalable and resource-efficient chemical production.

The application of Design of Experiments (DoE) significantly accelerates the optimization of reaction conditions for previously unreported transformations. DoE achieves this by focusing experimental efforts, enabling efficient exploration of the so-called experimental space. In this study, two DoE paradigms are used to determine the optimal parameters for converting the model substrate, N-methylindole, into its C-3 phenylselenylated analogue. The DoE approaches include the widely recognized face-centered central composite design and the less familiar D-optimal design, implemented using the freeware Chemometric Agile Tool (CAT) for experimental plan development and data analysis. A comparison of the two designs reveals that the D-optimal design, requiring 25% fewer reactions, provided equivalent results in terms of experimental space exploration and information retrieved. This highlights its efficiency and potential advantages. One aim of this report is to raise awareness within the organic chemistry community about the capabilities of the D-optimal design. Reaction kinetics are studied using an online FlowNMR device, which allows real-time reaction monitoring without the need for stopping the reaction or performing work-up procedures that might introduce errors or yield misleading results. Finally, the scope of the reaction is briefly explored.

The investigation of epoxide ring opening of (R)-glycidol with phosphorylcholine in water leads to the development of an effective synthesis of L-α-glycerophosphorylcholine (L-α-GPC), a commercially available drug. The precise control of reaction pH with an automatic titrator proves to be crucial for achieving conversions of up to 98% and limiting byproduct formation. Additionally, an effective method for the synthesis of phosphocholine as inner salt is reported for the first time, which is also essential for achieving the described results.

The detection of ammonia in aqueous solutions using solid-phase microextraction (SPME)-GC-MS (gas chromatography-mass spectrometry) is described. This technique enables the direct detection of ammonia without the need for derivatization or the use of colorimetric methods, which can be prone to interference from transition metal ions or organic cosolvents typically used in nitrogen reduction catalysis. The use of a fused-silica SPME fiber coated with polydimethylsiloxane/divinylbenzene is found to allow fast and direct quantification of ammonia with a limit of detection = 0.17 ppm and a limit of quantification = 0.5 ppm in water. The method is straightforward to implement and can be readily automated using commercial instrumentation. It is also capable of detecting isotopically labeled ¹⁵NH₃ as well as simple alkylamines such as methylamine or ethylamine which may be produced or released during the course of a reaction.

2D MXenes have garnered significant attention in energy storage due to their high volumetric capacitance. However, their practical application is hindered by the restacking of MXene layers. Herein, a novel strategy to address this challenge by constructing a multilayered sandwich-structured MXene/biomass pristine carbon (PC)/biomass cellulose (BC) composite film with a hierarchical network architecture is reported. The 1D BC nanofibers act as mechanical bridges, interlinking MXene sheets and PC particles to form a robust, flexible network, thereby improving mechanical flexibility and creating interconnected ion-transport channels. This architecture not only prevents MXene restacking but also facilitates electrolyte infiltration and ion diffusion, owing to expanded interlayer spacing (14.5 Å) and a substantially increasing specific surface area (526.4 m² g⁻¹). The optimized MXene/PC/BC-1 film exhibits an ultrahigh volumetric capacitance of 1225.1 F cm⁻³ at 1 A g⁻¹, three times higher than that of pure MXene (407.0 F cm⁻³).  A symmetric flexible soft-pack supercapacitor fabricated with this composite film achieves 83.8 mWh cm⁻³ energy density at 5.3 W cm⁻³ and retains 98% of its initial capacitance after 10 000 cycles. This work demonstrates the synergistic combination of biomass-derived materials with MXene, offering a sustainable, scalable strategy for flexible energy storage devices.

The Front Cover offers Chemistry-Methods readers a futuristic view of the analytical interest of lyotropic chiral bimesophasic systems consisting of two immiscible helical polymers and, using modern NMR tools such as tailored spatially resolved 1D/2D experiments, to collect two sets of anisotropic data. Crossing new frontiers with innovative NMR spectroscopies in the space of chirality, prochirality, or 3D configurational analysis remains an exciting challenge for Chemistry. For more details, see the Research Article by Michael Reggelin, Philippe Lesot, and co-workers (10.1002/cmtd.202500011).