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

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).

Porous hybrid glasses-based on metal-organic frameworks (MOFs) have garnered significant interest in gas separation, due to their excellent processing ability, porosity, and grain boundary-free properties. Melt-quenching and mechanical vitrification are the currently used methods to transform crystalline MOFs into glasses. However, research is still ongoing to make the formation process of MOFs-based porous glasses easier, scalable, and energy efficient. A simple and scalable process overcoming the limitations of the existing methods to form glass of an extensively studied MOF, i.e., zeolitic imidazolate framework-62 (ZIF-62) is reported. Ball milling and melt-quenching are widely explored methods for ZIF-62 glass formation. ZIF-62 undergoes reversible amorphization (nonglassy phase) at very high hydrostatic pressure at ambient temperature. The present study demonstrates that successive nonhydrostatic compression at lower pressures irreversibly transforms crystalline ZIF-62 into an amorphous phase having glassy characteristics. The pore network characteristics and local structure of the compression-induced phase are compared with the melt-quenched ZIF-62. X-ray absorption spectroscopy confirms an identical local structure of both the glasses. Positron annihilation lifetime spectroscopy measurements show that the compression-induced glassy phase exhibits a higher number density of smaller pores compared to the melt-quenched glass which exhibits lower number density of larger pores.

Cluster research plays an important role in chemistry. To explore the cluster configuration space, it is usually necessary to run a large-scale search. Yet for some instances, the desired cluster configuration may be counterintuitive, making it challenging to provide a reasonable initial guess to search for the corresponding minimum. There exist several routes to generate cluster configuration. However, they may suffer from the dimension problem or need some other prerequisite. In this work, generative adversarial networks (GANs) are employed to efficiently generate cluster configurations based on small-sized datasets. A dynamic clamp function is introduced during the training. The size of the dataset is controlled to be on the order of magnitude of dozens to hundreds of samples. Furthermore, the convex hull volume and area are established to assist in identifying unique structures. It is found that the proposed GAN architecture is not sensitive to network structures and can be used effectively to generate novel cluster configurations. The introduced dynamic clamp function significantly alleviates the mode collapse problem. Compared to the previous studies, the dataset size is much reduced to avoid large-scale training. Datasets containing fewer than 200 samples already yield satisfactory results. This method performs better than the genetic algorithm and is expected to have a wide range of chemical application scenarios.

Optical tweezers have numerous applications in biochemistry and biophysics research. Many optical tweezers experiments require the use of high laser powers, having a substantial heating side effect that can influence experimental results. The degree of heating and its spatial profile, however, depends on experimental conditions and requires direct measurement. Various methods for local temperature measurement have been proposed, each with its advantages and drawbacks. Herein, the use of the temperature-sensitive poly(N-isopropyl-acrylamide) (PNIPAAm) microspheres to measure the local heating caused by optical tweezers is demonstrated and the temperature profile around the laser focus at varying laser powers is characterized. The main advantage of this method is its applicability to virtually any setup and experiment. Using simple image analysis, the temperature within the biologically relevant range can be determined with 1°–2° accuracy. Possible applications and limitations of this method are discussed.

The Front Cover illustrates a new method (cSPRING) to study the interaction of a target molecule exposed to a continuous titration of a small ligand inside a flow capillary. The fluorescence emission of the target is detected in two separate spectral bands. A ratiometric measurement allows to extract the binding affinity (K_d) from a single measurement. Requiring only two samples and less than a minute, this method is well-suited for high-throughput screening applications. For more details, see the Research Article by Henrik Jensen and co-workers (10.1002/cmtd.202400059).

Benchtop nuclear magneic resonance (NMR) spectrometers are more affordable and accessible than high-field NMR instruments but suffer from higher limits of detection (LOD) and lower chemical shift resolution due to their moderate magnetic fields. Herein, reductions in the single-scan LOD values for ¹⁹F benchtop (1 T) NMR of 3,5-difluoropyridine (DFP) and 2,4,6-trifluorobenzylamine (TFBA) to (6.84 ± 0.45) μM and (162 ± 28) μM are demonstrated via signal amplification by reversible exchange (SABRE) hyperpolarization. Further reductions in LOD to (600 ± 20) nM and (17.5 ± 2.0) μM are achieved by combining SABRE with sensitive, homogeneous, and resolved peaks in real time detection. Quantification is demonstrated over the micromolar concentration range using linear external calibration. The effects of polarization transfer to the solvent via proton exchange in the case of TFBA are shown to be minimized in methanol-d₄; however, ¹⁹F detection and quantification are also achieved in protio methanol, with a LOD of (42.6 ± 3.6) μM.

It has long been known that paramagnetic materials are weakly attracted by external magnetic fields but this attraction has been little studied for porous paramagnetic materials whose composition depends on adsorption processes. In this work, how paramagnetic metal–organic frameworks (MOF) particles can be displaced and even kept stationary by strong external magnetic fields without falling down while immersed in a liquid medium is shown. The magnetic field required for this behavior is specific to each MOF but it also changes with each adsorption process in which the composition, and hence, the mass accumulation in the pores, varies. Therefore, the threshold at which this stasis phenomenon occurs can be correlated to the mass of adsorbate trapped by the porous paramagnetic MOFs. Based on this phenomenon, a simple device has been constructed that allows the determination of the amount of mass trapped, modulating the magnetic field with the variation of the distance between the sample holder containing the paramagnetic MOF particles and a permanent magnet.

The galvanic replacement reaction triggered by the electrochemical potential difference between two metals enables the design of multifunctional nanostructures for catalysis, sensing, and energy. However, there is still limited knowledge of the dynamics in the nonequilibrium and equilibrium realms to maximize material access or prevent structure damage. A methodology is reported to capture galvanic exchange events between atoms of electrodeposited bare Ag particles and aqueous Au^(III)Cl₄ ⁻ species. As the population of Au^(III)Cl₄ ⁻ species increases from the stoichiometric value to two orders of magnitude, the open-circuit potential parameter that determines galvanic exchanges in the nonequilibrium and equilibrium domains follows a quasi-sigmoidal shape. An autocatalytic reaction network mechanism is postulated. The galvanic reaction can be interrupted whenever required to yield stable, separable intermediates that increase the rate of their own formation. The knowledge of the Au^(III)Cl₄ ⁻ concentration-dependent potential-time curves permits to drastically reduce the reaction duration, from 85 to 13 min, while maintaining the material structure and properties, which will undoubtedly inspire new insights into other galvanic exchange processes.

Among the order-sensitive (anisotropic) nuclear magnetic resonance (NMR) interactions, the residual ²H quadrupolar couplings measured at the level of natural abundance or on deuterated compounds dissolved in (chiral) oriented solvents, is a unique and relevant source of molecular information (isotopy, chirality, structure, configuration, etc.). Until now, the aligned media used as NMR solvents (lyotropic or not) have generally been monophasic, although isotropic-anisotropic biphasic systems have recently been exploited. As a promising possibility, herein, the potential of lyotropic bimesophasic samples is examined based on a mixture of immiscible helical polymers, which result in two demixed chiral nematic domains (stable over time), each with its own orientation properties. The extraction of two independent and nonlinearly related sets of anisotropic NMR data is achieved with spatially resolved ²H nD experiments. First applied to small achiral, prochiral and chiral deuterated compounds, the approach is extended to investigate nonenriched molecules by natural abundance deuterium 2D NMR. Here lyotropic bimesophasic chiral systems combining a polypeptide (PBLG) and a polyacetylene polymer (PLA or l-MSP) in organic solvents are examined in depth, in relation with several applications. The dynamic behavior of these systems (polymer demixing and exchange process) is studied by analyzing ²H EXSY, ²H relaxation and ²H DOSY data.