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

Inline monitoring of chemical processes using spectroscopy is a powerful approach to replace conventional sampling. Spectroscopic data can be used with regression models to determine the endpoint or the onset temperature of reactions and can thus improve the efficiency and economics of processes. Spectroscopic data recorded during reactor operation is often complex, but partial least squares (PLS) is well-suited for dealing with this complexity. Here, we employed in situ attenuated total reflectance infrared (ATR-IR) spectroscopy in the hydrogenation of levulinic acid (LA) into γ-valerolactone (GVL) and operando ATR-IR spectroscopy in the ring-opening of γ-stearolactone (GSL), at high temperatures and pressures. Using PLS, we constructed a model to predict the GVL concentrations from spectra recorded during LA hydrogenation and determined the onset temperature of GVL formation. During the hydrogenation of branched unsaturated fatty acids, we determined the concentrations of the dilute byproduct GSL. The onset temperature of GSL ring-opening could not be determined, due to excessive variance caused by temperature differences during reactor heating, compared to limited variance caused by GSL conversion. We believe that in the oleochemical industry, this methodology can be used as a quality control tool to ensure that the produced branched saturated fatty acid fall within the GSL concentration specification limits.

The Front Cover symbolizes, amid crystalline salt formations and glowing pools of molten salt, the atomic complexity of molten salt systems and the advanced tools used to study them. X-ray absorption fine structure (XAFS) spectroscopy under in-situ conditions is the focus of this Review by A. I. Frenkel and co-workers (DOI: 10.1002/cmtd.202400097), which highlights recent advances and emerging synergies with machine learning—depicted as two giant pyramid-shaped networks—alongside simulations and complementary experimental techniques that illuminate these dynamic materials.

The Cover Feature shows poly-N-isopropyl-acrylamide (PNIPAAm) microspheres on a glass slide in water. PNIPAAm is a temperature-sensitive polymer that undergoes a volume transition between 20 and 45 °C. The spheres were fluorescently labelled and imaged with confocal fluorescence microscopy at 22 °C (top left) and at 45 °C (bottom right). In their Research Article (DOI: 10.1002/cmtd.202400040), R. Sorkin, A. Lesman and co-workers explain how they used the volume transition of PNIPAAm microspheres to measure the temperature close to a powerful optical tweezers laser beam. Measuring the temperature directly by using PNIPAAm helps to conduct optical tweezers experiments, especially with biological samples, and provides an additional control variable.

The eChem project has been previously presented as an interactive platform for quantum and computational chemistry education [J. Chem. Educ. 100, 1664–1671]. However, education is only one side of the eChem project. Another aspect is that it highly accelerates method development by means of code prototyping in notebooks. Complex equations can be understood, and algorithms are examined before the actual software programming step is carried out. Here, the benefits of notebooks for code prototyping are illustrated using the example of vibrational spectroscopy—a type of spectroscopy which involves complex equations with a large number of terms.

Zinc orthostannate (ZTO) is a promising wide-bandgap (3.6 eV) n-type semiconductor material for various applications, and to develop efficient, facile, and relatively mild synthetic methods, we selected important advantages driving the high-temperature solid-state process and implemented them into mechanochemical reactions, and utilized the low-melting properties of metal acetates and the wetting abilities of Li-based dopants. Therefore, we report on two synthetic methods of undoped and Li-doped ZTO materials, prepared by the direct mechanochemical reactions from ZnO and SnO₂, and ZnO-SnO₂ blend, prepared at 480 °C from mechanochemically activated (500 rpm, 20 min) zinc(II) and tin(IV) acetates, are reported. The reactions’ progress is followed by ex situ powder X-ray diffractometry, Raman spectroscopy, and ultraviolet and visible light spectrometry after grinding within 20–200 min in an agate planetary ball mill at 500 rpm. The scanning electron microscopic morphological analysis uncovered the presence of monocrystalline ZTO cubes embedded in polycrystalline ZTO bodies obtained from ball milling of the Li₂O–ZnO–SnO₂ blend. These morphological changes significantly affect the bandgap from the commonly accepted 3.6 eV to about 4.0 eV. Moreover, the X-ray photoelectron spectroscopy studies showed the presence of a Zn-rich surface (Zn:Sn ratio: 5.85:1) on the starting material after thermal blending and decarbonization of precursors.

Heterohelicenes with multiple chiral axes are promising materials due to their unique electronic and chiroptical features. However, their synthesis becomes more challenging as their structural complexity increases with multi-helical frameworks and various heteroatoms. This complexity requires lengthy synthetic steps and purification processes, often resulting in low yields and limiting practical applications. This review explores recent advancements to tackle these challenges, focusing on innovative strategies for the short-step synthesis of double and triple heterohelicenes. These strategies are categorized, highlighting how they improve the synthesis of functionalized materials and offer valuable opportunities for achieving a balance between synthetic efficiency and tunable properties with enhanced functionality. Remaining challenges and future potential are discussed, providing a comprehensive reference for researchers working on these molecules for next-generation technologies.

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.