Single-crystal-to-single-crystal (SCSC) reactions are discussed as a specific case of solid-state reactions. Some shortcomings in the contemporary use of the term are revealed, and directions for ...research and interpretation of results are suggested.
Solid-state milling has emerged as an alternative, sustainable approach for preparing virtually all classes of compounds and materials. In situ reaction monitoring is essential to understanding the ...kinetics and mechanisms of these reactions, but it has proved difficult to use standard analytical techniques to analyze the contents of the closed, rapidly moving reaction chamber (jar). Monitoring by Raman spectroscopy is an attractive choice, because it allows uninterrupted data collection from the outside of a translucent milling jar. It complements the already established in situ monitoring based on powder X-ray diffraction, which has limited accessibility to the wider research community, because it requires a synchrotron X-ray source. The Raman spectroscopy monitoring setup used in this protocol consists of an affordable, small portable spectrometer, a laser source and a Raman probe. Translucent reaction jars, most commonly made from a plastic material, enable interaction of the laser beam with the solid sample residing inside the closed reaction jar and collection of Raman-scattered photons while the ball mill is in operation. Acquired Raman spectra are analyzed using commercial or open-source software for data analysis (e.g., MATLAB, Octave, Python, R). Plotting the Raman spectra versus time enables qualitative analysis of reaction paths. This is demonstrated for an example reaction: the formation in the solid state of a cocrystal between nicotinamide and salicylic acid. A more rigorous data analysis can be achieved using multivariate analysis.
The article concentrates on the image and reception of Slovak literature in specialised Hungarian-language texts from the period of Austro-Hungarian Compromise. In the history of Slovak-Hungarian ...relations, this period was one of the most complicated: the middle classes were being speedily assimilated and the Slovak culture was under intense pressure of the state and Hungarian culture. The first comprehensive publication on Slovak literature in this period was written by Imre Gáspár as early as 1879, but it remained without much feedback. Subsequent articles and encyclopaedic entries were penned by Slovak authors who either worked in Budapest as civil servants (Samo Czambel, Adolf Pechány) or were based directly in Martin, Slovakia (Jozef Škultéty). Škultéty was invited to write on Slovak literature by the Budapest-based professor Oszkár Asbóth who also authored a journal article on Svetozár Hurban Vajanský. Despite differences in authors’ social and cultural backgrounds, the narrative texts share several similarities: in the introduction, they provide a general overview of the history of the Slovak language and literature and then deal with outer-literary aspects in the works of a few authors and look for similarities. The works of Ján Hollý and Andrej Sládkovič were held in especially high esteem.
Mechanistic understanding of mechanochemical reactions is sparse and has been acquired mostly by stepwise ex situ analysis. We describe herein an unprecedented laboratory technique to monitor the ...course of mechanochemical transformations at the molecular level in situ and in real time by using Raman spectroscopy. The technique, in which translucent milling vessels are used that enable the collection of a Raman scattering signal from the sample as it is being milled, was validated on mechanochemical reactions to form coordination polymers and organic cocrystals. The technique enabled the assessment of the reaction dynamics and course under different reaction conditions as well as, for the first time, direct insight into the behavior of liquid additives during liquid‐assisted grinding.
Out of the dark: Mechanochemical reaction mechanisms were studied by a laboratory Raman spectroscopy technique developed for in situ and real‐time monitoring of milling reactions (see picture). The technique enabled the course of mechanochemical transformations of coordination polymers and organic materials to be followed as well as the study of liquid additives.
Chemical and structural transformations have long been carried out by milling. Such mechanochemical steps are now ubiquitous in a number of industries (such as the pharmaceutical, chemical and ...metallurgical industries), and are emerging as excellent environmentally friendly alternatives to solution-based syntheses. However, mechanochemical transformations are typically difficult to monitor in real time, which leaves a large gap in the mechanistic understanding required for their development. We now report the real-time study of mechanochemical transformations in a ball mill by means of in situ diffraction of high-energy synchrotron X-rays. Focusing on the mechanosynthesis of metal-organic frameworks, we have directly monitored reaction profiles, the formation of intermediates, and interconversions of framework topologies. Our results reveal that mechanochemistry is highly dynamic, with reaction rates comparable to or greater than those in solution. The technique also enabled us to probe directly how catalytic additives recently introduced in the mechanosynthesis of metal-organic frameworks, such as organic liquids or ionic species, change the reactivity pathways and kinetics.
Chemical and physical transformations by milling are attracting enormous interest for their ability to access new materials and clean reactivity, and are central to a number of core industries, from ...mineral processing to pharmaceutical manufacturing. While continuous mechanical stress during milling is thought to create an environment supporting nonconventional reactivity and exotic intermediates, such speculations have remained without proof. Here we use in situ, real-time powder X-ray diffraction monitoring to discover and capture a metastable, novel-topology intermediate of a mechanochemical transformation. Monitoring the mechanochemical synthesis of an archetypal metal-organic framework ZIF-8 by in situ powder X-ray diffraction reveals unexpected amorphization, and on further milling recrystallization into a non-porous material via a metastable intermediate based on a previously unreported topology, herein named katsenite (kat). The discovery of this phase and topology provides direct evidence that milling transformations can involve short-lived, structurally unusual phases not yet accessed by conventional chemistry.
Recent progress in the field of mechanochemistry has expanded the discovery of mechanically induced chemical transformations to several areas of science. However, a general fundamental understanding ...of how mechanochemical reactions by ball milling occur has remained unreached. For this, we have now implemented in situ monitoring of a mechanochemically induced molecular rearrangement by synchrotron X‐ray powder diffraction, Raman spectroscopy, and real‐time temperature sensing. The results of this study demonstrate that molecular rearrangements can be accomplished in the solid state by ball milling and how in situ monitoring techniques enable the visualization of changes occurring at the exact instant of a molecular migration. The mechanochemical benzil–benzilic acid rearrangement is the focal point of the study.
Forcing a rearrangement: In situ monitoring of the mechanochemical 1,2‐intramolecular phenyl migration in benzil was accomplished by a combination of real‐time analytical techniques and temperature sensing. The mechanochemical rearrangement occurs suddenly after an induction time, without detectable intermediates.
Just a pinch of salt: Small amounts of salts accelerate and direct the mechanochemical construction of metal–organic frameworks (MOFs) from a metal oxide (see scheme; ILAG= ion‐ and liquid‐assisted ...grinding). The resulting rapid and room‐temperature synthesis demonstrates the ability to control mechanosynthesis of metal–organic compounds by templating, as well as the ability to use mechanochemistry to include ionic guests within neutral MOFs.
The paper deals with two items (entry) of the interwar Hungarian lexicon for literature: the first item focused on the Slovak literature, the second item focused on the Hungarian literature in ...Czechoslovakia. The editor of lexicon was wellknown Hungarian historian of literature, Marcell Benedek. The author of Slovak item was Juraj Podhradský, who was the civil servant of Hungarian public administration with Slovak origin. Inspite of the old terminology, from the item about the Slovak literature are missing the Hungarian stereotypes about the Slovaks and Slovak literature.
The fidelity of protein synthesis depends on the capacity of aminoacyl‐tRNA synthetases (AARSs) to couple only cognate amino acid‐tRNA pairs. If amino acid selectivity is compromised, fidelity can be ...ensured by an inherent AARS editing activity that hydrolyses mischarged tRNAs. Here, we show that the editing activity of Escherichia coli leucyl‐tRNA synthetase (EcLeuRS) is not required to prevent incorrect isoleucine incorporation. Rather, as shown by kinetic, structural and in vivo approaches, the prime biological function of LeuRS editing is to prevent mis‐incorporation of the non‐standard amino acid norvaline. This conclusion follows from a reassessment of the discriminatory power of LeuRS against isoleucine and the demonstration that a LeuRS editing‐deficient E. coli strain grows normally in high concentrations of isoleucine but not under oxygen deprivation conditions when norvaline accumulates to substantial levels. Thus, AARS‐based translational quality control is a key feature for bacterial adaptive response to oxygen deprivation. The non‐essential role for editing under normal bacterial growth has important implications for the development of resistance to antimicrobial agents targeting the LeuRS editing site.
Synopsis
Aminoacyl‐tRNA‐synthetase (AARS) editing hydrolyses mischarged tRNAs. LeuRS editing is not a response to poor selectivity between Leu and Ile, as previously suggested, but targets the non‐standard amino acid norvaline during hypoxic growth.
LeuRS discriminates against isoleucine with more than 104‐fold specificity arising from weak ground state binding and decreased rate of the chemical step.
The major threat for the accuracy of Leu‐tRNALeu synthesis is posed by a non‐standard amino acid norvaline.
The prime role of the LeuRS post‐transfer editing domain is to prevent participation of norvaline in protein synthesis.
LeuRS post‐transfer editing is not required under normal or isoleucine‐rich growth conditions, but rescues Escherichia coli growth under norvaline‐rich conditions.
Low oxygen levels trigger accumulation of norvaline in Escherichia coli, providing a biological rationale for evolution of efficient LeuRS editing.
Aminoacyl‐tRNA‐synthetase (AARS) editing hydrolyses mischarged tRNAs. LeuRS editing is not a response to poor selectivity between Leu and Ile, as previously suggested, but targets the non‐standard amino acid norvaline during hypoxic growth.
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