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Molybdenum disulfide (MoS2 ) is at the forefront of materials research. It shows great promise for electrochemical applications, especially for hydrogen evolution reaction (HER) catalysis. There is a significant discrepancy in the literature on the reported catalytic activity for HER catalysis on MoS2 . Here we test the electrochemical performance of MoS2 obtained from seven sources and we show that these sources provide MoS2 of various phase purity (2H and 3R, and their mixtures) and composition, which is responsible for their different electrochemical properties. The overpotentials for HER at -10 mA cm-2 for MoS2 from seven different sources range from -0.59 V to -0.78 V vs. reversible hydrogen electrode (RHE). This is of very high importance as with much interest in 2D-MoS2 , the use of the top-down approach would usually involve the application of commercially available MoS2 . These commercially available MoS2 are rarely characterized for composition and phase purity. These key parameters are responsible for large variance of reported catalytic properties of MoS2 .
- Klíčová slova
- electrocatalysis, hydrogen evolution reaction, molybdenum disulfide, phase purity, transition metal dichalcogenides,
- Publikační typ
- časopisecké články MeSH
This article deals with the evaluation of the chemical purity of iodine-filled absorption cells and the optical frequency references used for the frequency locking of laser standards. We summarize the recent trends and progress in absorption cell technology and we focus on methods for iodine cell purity testing. We compare two independent experimental systems based on the laser-induced fluorescence method, showing an improvement of measurement uncertainty by introducing a compensation system reducing unwanted influences. We show the advantages of this technique, which is relatively simple and does not require extensive hardware equipment. As an alternative to the traditionally used methods we propose an approach of hyperfine transitions' spectral linewidth measurement. The key characteristic of this method is demonstrated on a set of testing iodine cells. The relationship between laser-induced fluorescence and transition linewidth methods will be presented as well as a summary of the advantages and disadvantages of the proposed technique (in comparison with traditional measurement approaches).
- Klíčová slova
- absorption spectroscopy, frequency stability, iodine cells, laser spectroscopy, laser standards,
- Publikační typ
- časopisecké články MeSH
A new approach for the evaluation of chiral purity of serine esterification products bearing long-chain alkyl substituents was developed. The compounds were simply converted to aryl-substituted oxazolines which: (i) facilitates effective chromatographic enantioseparation and (ii) enables direct detection using ultraviolet absorption. The method employs a polysaccharide-based chiral stationary phase and allows enantioseparation of highly stable oxazoline products in less than 6 min using a simple binary mobile phase. As opposed to the previously used normal phase method the developed method was performed in the reversed-phase mode. Aside from the benefits of switching to less hazardous solvents with regard to the principles of Green Chemistry, this has also led to a reduction in the analysis time. In comparison with known serine chromophores, the best enantioseparation of aryloxazoline rigid structure may be achieved only based on non-polar interactions with the chiral stationary phase. In contrast, the substitution of the chromophore moiety with hydroxyl substituent affected intra and intermolecular interactions that caused enantioseparation differences. Concurrently, we found high chirality retention of (R)- and (S)-configuration oxazoline standards (≥99% enantiomeric excess) during the introduction of the ultraviolet label. The method is suitable for rapid injection of the mixture containing the ultraviolet absorption marker without prior purification.
- Klíčová slova
- chiral purity, enantioselective chromatography, enantioseparation, esterification, oxazoline,
- MeSH
- polysacharidy * MeSH
- rozpouštědla MeSH
- serin * MeSH
- stereoizomerie MeSH
- vysokoúčinná kapalinová chromatografie metody MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- polysacharidy * MeSH
- rozpouštědla MeSH
- serin * MeSH
Understanding the mechanisms regulating the development of cereal seeds is essential for plant breeding and increasing yield. However, the analysis of cereal seeds is challenging owing to the minute size, the liquid character of some tissues, and the tight inter-tissue connections. Here, we demonstrate a detailed protocol for dissection of the embryo, endosperm, and seed maternal tissues at early, middle, and late stages of barley seed development. The protocol is based on a manual tissue dissection using fine-pointed tools and a binocular microscope, followed by ploidy analysis-based purity control. Seed maternal tissues and embryos are diploid, while the endosperm is triploid tissue. This allows the monitoring of sample purity using flow cytometry. Additional measurements revealed the high quality of RNA isolated from such samples and their usability for high-sensitivity analysis. In conclusion, this protocol describes how to practically dissect pure tissues from developing grains of cultivated barley and potentially also other cereals.
Capillary isotachophoresis (ITP) was applied to the qualitative and quantitative analysis of both natural and synthetic oligo- and polypeptides. Based on the mathematical model of acid-base equilibria for a general ampholyte, a procedure and a computer program for the calculation of the pH dependence of the effective and specific charge and effective mobility of peptides with known amino acid sequence were developed which allow the selection of electrolyte systems for peptide isotachophoretic analysis to be rationalized. Basic peptides (bovine pancreatic trypsin inhibitor, bull seminal isoinhibitors of trypsin, arginine vasopressin and adamantylamide-alanylisoglutamine) were analysed with a cationic ITP system at acidic pH. Neutral and acidic peptides (insulin, proinsulin, bull seminal isoinhibitors of trypsin, cow colostrum isoinhibitors of trypsin) were analysed with an anionic ITP system, mostly at alkaline pH. Peptide purity (electrophoretic homogeneity) was determined from the ITP degree of purity defined by a peptide itself and the zone length ratio of its admixtures. Enrichment of peptide in the sample during the purification procedure was measured by its zone length relative to unit mass of the amount of sample analysed.
- MeSH
- amfolytové směsi MeSH
- elektroforéza metody MeSH
- hemopexin analýza MeSH
- inhibitory trypsinu analýza MeSH
- inzulin analýza MeSH
- koncentrace vodíkových iontů MeSH
- lidé MeSH
- peptidy analýza MeSH
- prasata MeSH
- skot MeSH
- spektrofotometrie ultrafialová MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- skot MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- amfolytové směsi MeSH
- hemopexin MeSH
- inhibitory trypsinu MeSH
- inzulin MeSH
- peptidy MeSH
A method for purity control of newly synthesized lactic acid-based liquid crystals has been developed. The electrokinetic chromatography proved to be suitable for the separation of these electroneutral substances from their impurities. The separations were performed in an acidic acetonitrile-based background electrolyte (BGE) with a pseudostationary phase formed by a cationic surfactant. During the optimization step, appropriate concentrations of cetyltrimethylammonium bromide, acetic acid, and water were seeked. In the optimized method, separations were carried out in acetonitrile with 1-mol/L acetic acid, 80-mmol/L cetyltrimethylammonium bromide, and 6% (v/v) water. Interesting positive effects of a small water content in the BGE on electroosmotic flow and resolution of liquid crystal substances from their impurities were observed and discussed. Samples of five liquid crystal substances, both pure and containing impurities from synthesis, were analyzed. The identification of analytes was based on a comparison of relative migration times related to the migration time of mesityl oxide. For all five samples, impurities were separated from the liquid crystals and the method thus showed its viability. To the best of our knowledge, this method is used for the first time for the purity control of newly synthesized liquid crystals. This method can be used to confirm or complement the results obtained by commonly used high-performance liquid chromatography and supercritical fluid chromatography methods. Furthermore, the electrokinetic chromatography method requires very small amounts of sample, solvents, and buffer constituents. Overall, its operational costs are significantly lower.
- Klíčová slova
- capillary electrophoresis, electrokinetic chromatography, liquid crystals, nonaqueous,
- MeSH
- acetonitrily chemie MeSH
- cetrimonium MeSH
- chromatografie micelární elektrokinetická kapilární * metody MeSH
- elektrolyty MeSH
- kapalné krystaly * MeSH
- superkritická fluidní chromatografie * MeSH
- voda chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- acetonitrily MeSH
- cetrimonium MeSH
- elektrolyty MeSH
- voda MeSH
This research analyzes the adverse impact of white noise on collective quantum measurements and argues that such noise poses a significant obstacle for the otherwise straightforward deployment of collective measurements in quantum communications. Our findings then suggests addressing this issue by correlating outcomes of these measurements with quantum state purity. To test the concept, a support vector machine is employed to boost the performance of several collective entanglement witnesses by incorporating state purity into the classification task of distinguishing entangled states from separable ones. Furthermore, the application of machine learning allows to optimize specificity of entanglement detection given a target value of sensitivity. A response operating characteristic curve is reconstructed based on this optimization and the area under curve calculated to assess the efficacy of the proposed model. Finally, we test the presented approach on an experimental dataset of Werner states.
- Publikační typ
- časopisecké články MeSH
Liquid crystals (LCs) are among the most prominent materials of the current information age, mainly due to their well-known application in liquid crystal displays (LCDs). Their unique electro-optical properties stem from their ability to form organised structures (mesophases) on the transition from solid state to isotropic liquid. Molecules of LCs in a mesophase still maintain the anisotropy of solid crystals, while simultaneously exhibiting the fluidity of liquids, which gives the system the ability to react immediately to external stimuli such as electric or magnetic fields, light, mechanical stress, pressure and, of course, temperature. For the proper function of LC-based devices, not only chemical, but also optical purity of materials is strongly desirable, since any impurity could be detrimental to the self-assembly of the molecules. Therefore, in this study we aimed to verify synthetic methods published in the literature, which are used nowadays to prepare chiral building blocks based on lactic acid, for their enantioselectivity. Moreover, we have focused on the development of an analytical chiral separation method for target liquid crystalline materials. Using a chiral polysaccharide-based column operated in liquid chromatography mode, we show that not all published methods of LC synthesis are enantioselective, which could lead to significant differences in the properties of the resulting materials. We show that high-performance liquid chromatography with UV detection and supercritical fluid chromatography with UV and mass spectrometry detection enable full control over the chemical and optical purity of the target LCs and the corresponding chiral building blocks. For the first time, we utilise supercritical fluid chromatography with mass detection for the direct chiral analysis of liquid crystalline materials and impurities formed during the synthesis.
- Klíčová slova
- chiral liquid crystals, chiral separation, enantioseparation of liquid crystals, mass spectrometry detection, mesomorphic properties, optical purity, supercritical fluid chromatography,
- MeSH
- hmotnostní spektrometrie MeSH
- kapalné krystaly * MeSH
- kyselina mléčná chemie MeSH
- stereoizomerie MeSH
- superkritická fluidní chromatografie metody MeSH
- vysokoúčinná kapalinová chromatografie metody MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- kyselina mléčná MeSH
Capillary zone electrophoresis (CZE) and capillary isotachophoresis (CITP) were applied for the determination of peptide purity degree and counter-ion content in lecirelin, the synthetic analogue of luteinizing hormone-releasing hormone (LHRH). CZE analyses were carried out in acidic background electrolyte (100 mM H3PO4, 50 mM Tris, pH 2.25) in bare fused silica capillary using UV-absorption detection at 206 nm. CITP analyses were performed in the electrophoretic analyzer with column coupling, equipped with contactless conductivity detectors both in preseparation capillary and in analytical capillary, and with UV-absorption detector (220 and 254 nm) in analytical capillary. Determinations of peptide purity were carried out in cationic mode with leading electrolyte (LE), 10 mM KOH/AcOH, pH 4.5, and terminating electrolyte (TE), 10 mM beta-alanine (BALA)/AcOH, pH 4.4. Degree of peptide purity determined by both CZE and CITP was in the range 60.1-80.9% for crude preparations of lecirelin and in the range 96.4-99.9% for HPLC purified batches. Concentrations of contaminating counter-ions, the anions of trifluoromethanesulfonic acid (TFMSA), trifluoroacetic acid (TFA) and acetic acid (AcOH), were determined by CITP analyses in anionic mode with LE 10 mM HCl/His, pH 6.0, and TE 10 mM 2-(N-morpholino)-ethanesulfonic acid (MES), pH 4.0, by the calibration curve method. Mass percentages of the counterion contents in the analyzed lecirelin batches varied from zero to ca. 9% (TFMSA), 3% (TFA) and 11% (AcOH), respectively.
- MeSH
- anionty analýza MeSH
- elektroforéza kapilární metody MeSH
- hormon uvolňující gonadotropiny analogy a deriváty chemie izolace a purifikace MeSH
- kyselina trifluoroctová chemie MeSH
- methansulfonáty chemie MeSH
- reprodukovatelnost výsledků MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- anionty MeSH
- hormon uvolňující gonadotropiny MeSH
- kyselina trifluoroctová MeSH
- methansulfonáty MeSH
- trifluoromethanesulfonic acid MeSH Prohlížeč
Trace amounts of lead were determined in high purity aluminium salts (especially in ammonium aluminium sulfate) using inductively coupled plasma-optical emission spectrometry (ICP-OES) after extractive pre-concentration and matrix separation. Metals were extracted from the aluminium matrix in the form of chelates with ammonium pyrolidine dithoocarbamate into methyl isobutyketone. The organic extract was digested with nitric acid and hydrogen peroxide. The limit of detection for the determination of lead in crystalline ammonium aluminium sulfate was ca. 0.044 mug g(-1). The relative expanded uncertainty of the lead determination was ca. 23% at the level of 0.2 mug g(-1) and ca. 16% at the level of 1.0 mug g(-1). The main uncertainty contribution was associated with repeatability of the whole analytical procedure.
- Publikační typ
- časopisecké články MeSH
