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

Electrochemical reactions are better understood by gaining insight into the molecular transformations at the electrodes. This paper introduces a straightforward experimental arrangement in which the voltammetry experiment in a standard electrochemical cell integrates with online electrospray-ionization mass-spectrometry. The procedure allows for monitoring of the ions produced at the working electrode. The ionic species sampling is facilitated by a silica capillary embedded in the working electrode and connected directly to the electrospray ionization source. This integration configures real-time monitoring of the ions produced at the working electrode, enhancing our knowledge of the electrochemical process. The methodology is thoroughly described and exemplified by monitoring the reactive intermediates and products that arise during the electrochemical oxidation of carbazole. This design provides an opportunity to study intermediates in electrochemical reactions with advanced mass spectrometry methods such as ion mobility separation or ion spectroscopy.

N-Nitrosamines acting as contaminants in our environment is a topic of increasing concern. Detection methods are required, necessitating analytical standards. Herein, we discuss some conventional methodologies to prepare N-nitrosamines and compare them with unconventional pathways towards their synthesis. These methods are often more environmentally benign and safer.

Renewed interest in advanced nuclear reactors, such as Molten Salt Reactors (MSRs), has spurred studies in actinide halide chemistry and property measurements. Several proposed research-scale and commercial MSR designs incorporate uranium trichloride (UCl₃) fuel. There are relatively few preparations for isolated actinide halides reported in the literature, therefore novel methods for the isolation of pure material are desired. This communication describes the thermal elimination of pyridine (py) from the coordination complex UCl₃py₂ to yield gram-scale quantities of UCl₃. The purity of the UCl₃ product was determined through powder X-ray Diffractometry (pXRD) and Elemental Analysis (EA).

Chemogenetic tools are genetically encoded systems regulated by user-defined chemicals. Their ability to temporally modulate protein functions in specific cell populations has facilitated in-depth understanding of dynamic biological systems. Many chemogenetic domains have been developed for regulating a wide range of biological processes, ranging from cellular events to animal behaviors. These tools share some common mechanisms, including proximity regulation, conformational change and allosteric control, as well as steric hinderance control. Here in this review, we aim to provide an overview of different chemogenetic tool designs that utilize the above three common mechanisms to control cellular events.

The design and commissioning of a cell suitable for operando studies using high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy in the tender X-ray regime is reported. The cell is optimized for measurements within the energy range of 1.5 keV to 4.5 keV. It has a plug-flow geometry and can be used for sieved powder samples, analogous to reactors employed for laboratory tests. The functionality of the spectroscopic cell is demonstrated in the area of emission control using CO oxidation as target reaction over 1 wt.% Rh/γ-Al₂O₃ as catalyst. We show how HERFD-XANES at the Rh L₃-edge captures variations in the noble metal structure resulting from the interaction with the support material and reactant molecules. Moreover, distinct structural changes were identified along the catalyst bed as a function of temperature and local gas mixture.

Polymer membrane electrolyzers benefit from high-pressure operation conditions and low gas cross-over and can either conduct protons (H⁺) or hydroxide ions (OH⁻). Both types of electrolyzers have a similar design, but differ in power density and the choice of catalysts. Despite the significant endeavor of their optimization, to date, there is no well-established impedance model for detailed analysis for either type of these devices. This complicates the in-situ characterization of electrolyzers, hindering the investigation of degradation mechanisms and electrocatalytic processes as a function of applied current density or time. Nevertheless, a detailed understanding of such individual processes and distinguishing the performance-limiting factors are the keystones for sophisticated device optimization. In this work, an impedance model based on electrode processes has been developed for an anion exchange membrane electrolyzer utilizing iridium oxide anode and platinum cathode electrocatalysts. This model allows to deconvolute the measured impedances into constituents related to the individual electrode processes and to estimate actual physico-chemical quantities such as the reaction kinetic parameters and double-layer capacitances. We discuss the meaning of the fitting parameters and show that this model enables, for the first time, the estimation of the electrochemically active surface area of the anode electrocatalysts under reaction conditions.

pH adjustment is crucial for many industrial products, yet this step is typically performed by manual trial-and-error. A particularly industrially relevant yet challenging titration is that of adjusting viscous liquid formulations using weak, polyprotic titrants (usually citric acid). Handling of viscous, non-Newtonian formulations, with such polyprotic acids preferred for their chelation and buffering effects make a robotic solution challenging. We present a self-driving pH robot integrated with physics-informed learning; this hybrid physical-ML model enables automated titration with weak-strong acid/base pairs. To deal with the high viscosities of these formulations, we developed specific automated mixing and cleaning protocols. We hit the target pH within two to five iterations over 250 distinct formulations in lab-scale small-batch (~10 mL and 12 samples) titrations. In the interest of scaling up to match industrial processes, we also demonstrate that our hybrid algorithm works at ~25× scale-up. The method is general, and we open-source our algorithm and designs.