Review: Sample Concentration Based on Inclusion of Organic Solvents in Capillary Zone Electrophoresis
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Capillary electrophoresis, as an analytical tool for drugs, offers several advantages for pharmaceuticals and clinical applications; however, it suffers from poor detection limits. Concentration on the capillary (stacking) improves greatly this problem and is very easy to perform. One of the simple and practical methods to perform stacking is dissolving the sample in organic solvents and injecting a large volume of sample on the capillary. This leads to concentration of the sample 10-30 folds directly on the capillary, removes the excess of proteins found in biological fluids and overcomes the deleterious effects of salts. The stacking can be performed in both the hydrodynamic and electroinjection. This stacking brings the detection limits of the CE closer to that of the HPLC. The mechanism, practical applications, different factors, and optimum conditions for this type of stacking are reviewed and discussed. Keywords: Stacking, Organic solvents, Concentration, Drug analysis, Capillary electrophoresis, Transient pseudoisotachophoresisThe stacking of layers forming three-dimensional periodic structures is explored in the general case, where neither the layers nor the stacking need to be close-packed, and the connectivity number for the system may be either two or four. Procedures are described whereby all possible stacking variants can be systematically derived for a given number of layers, and for a given number of possible stacking positions. The latter depends on the structure of the layer and on the stacking vector.
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As an extension of Table 7.1.5B of International Tables for X-ray Crystallography [(1967), Vol. II. Birmingham: Kynoch Press], the possible stacking variants up to ten layers are arranged according to the percentage of hexagonal stacking. A method is given which allows one to calculate the number of possible stacking variants for any number of layers.
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The Stacking-capillary Method is widely used in the fabrication of the Micro-structure Fiber (MSF). We describe an improved stacking-capillary method, which can fabricate the MSF without interstitial holes. The method includes several steps. Firstly, the MSF preform is made by the stacking-capillary method; secondly, the MSF preform is put into the high temperature furnace to heat at 1600°, then the positive pressure is produced into the capillaries by adding air, every three adjacent capillary holes are expanded in the preform, and the interstitial holes are eliminated, all the capillaries are fused together, although the round capillary have changed to hexagon, the size of the prefrom does not change, and still keeps very good structure. The step of eliminating the interstitial hole can help to keep the MSF structure during drawing fiber. We get well results by the Improved Stacking-capillary Method.
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Modulating the Interlayer Stacking of Covalent Organic Frameworks for Efficient Acetylene Separation
Controllable modulation of the stacking modes of 2D (two-dimensional) materials can significantly influence their properties and functionalities but remains a formidable synthetic challenge. Here, an effective strategy is proposed to control the layer stacking of imide-linked 2D covalent organic frameworks (COFs) by altering the synthetic methods. Specifically, a modulator-assisted method can afford a COF with rare ABC stacking without the need for any additives, while solvothermal synthesis leads to AA stacking. The variation of interlayer stacking significantly influences their chemical and physical properties, including morphology, porosity, and gas adsorption performance. The resultant COF with ABC stacking shows much higher C2 H2 capacity and selectivity over CO2 and C2 H4 than the COF with AA stacking, which is not demonstrated in the COF field yet. Furthermore, the outstanding practical separation ability of ABC stacking COF is confirmed by breakthrough experiments of C2 H2 /CO2 (50/50, v/v) and C2 H2 /C2 H4 (1/99, v/v), which can selectively remove C2 H2 with good recyclability. This work provides a new direction to produce COFs with controllable interlayer stacking modes.
Acetylene
Covalent organic framework
Separation (statistics)
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Capillary electrophoresis, as an analytical tool for drugs, offers several advantages for pharmaceuticals and clinical applications; however, it suffers from poor detection limits. Concentration on the capillary (stacking) improves greatly this problem and is very easy to perform. One of the simple and practical methods to perform stacking is dissolving the sample in organic solvents and injecting a large volume of sample on the capillary. This leads to concentration of the sample 10-30 folds directly on the capillary, removes the excess of proteins found in biological fluids and overcomes the deleterious effects of salts. The stacking can be performed in both the hydrodynamic and electroinjection. This stacking brings the detection limits of the CE closer to that of the HPLC. The mechanism, practical applications, different factors, and optimum conditions for this type of stacking are reviewed and discussed. Keywords: Stacking, Organic solvents, Concentration, Drug analysis, Capillary electrophoresis, Transient pseudoisotachophoresis
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Predicting the strength of stacking interactions involving heterocycles is vital for several fields, including structure-based drug design. While quantum chemical computations can provide accurate stacking interaction energies, these come at a steep computational cost. To address this challenge, we recently developed quantitative predictive models of stacking interactions between drug-like heterocycles and the aromatic amino acids Phe, Tyr, and Trp (DOI: 10.26434/chemrxiv.7628939.v4). These models depend on heterocycle descriptors derived from electrostatic potentials (ESPs) computed using density functional theory and provide accurate stacking interactions without the need for expensive computations on stacked dimers. Herein, we show that these ESP-based descriptors can be reliably evaluated directly from the atom connectivity of the heterocycle, providing a means of predicting both the descriptors and the potential for a given heterocycle to engage in stacking interactions without resorting to any quantum chemical computations. This enables the conversion of simple molecular representations ( e.g . SMILES) directly into accurate stacking interaction energies using a freely-available online tool, thereby providing a way to rapidly rank the stacking abilities of large sets of heterocycles.
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Quantum chemical
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<p>Predicting the strength of stacking interactions involving heterocycles is vital for several fields, including structure-based drug design. While quantum chemical computations can provide accurate stacking interaction energies, these come at a steep computational cost. To address this challenge, we recently developed quantitative predictive models of stacking interactions between drug-like heterocycles and the aromatic amino acids Phe, Tyr, and Trp (DOI: 10.26434/chemrxiv.7628939.v4). These models depend on heterocycle descriptors derived from electrostatic potentials (ESPs) computed using density functional theory and provide accurate stacking interactions without the need for expensive computations on stacked dimers. Herein, we show that these ESP-based descriptors can be reliably evaluated directly from the atom connectivity of the heterocycle, providing a means of predicting both the descriptors and the potential for a given heterocycle to engage in stacking interactions without resorting to any quantum chemical computations. This enables the conversion of simple molecular representations (<i>e.g</i>. SMILES) directly into accurate<i> </i>stacking interaction energies using a freely-available online tool, thereby providing a way to rapidly rank the stacking abilities of large sets of heterocycles.</p> <p> </p>
Quantum chemical
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The interplay of π-stacking and inter-stacking interactions in two-component organic crystals without conventional hydrogen bonds.
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Stacking vs thickness: Stacking between the metal–organic layers (MOLs) of MOFs determines their thickness: the higher the stacking, the higher the thickness. This thickness plays an important role in controlling the function of the material, hence, regulating the stacking in 2D nano-MOFs might be very important. We tuned the stacking by modulating the chemical structure of the organic linkers in a series of isostructural MOFs. AFM, XRPD, FESEM, etc. showed the chemical functionality of the linkers to play a pivotal role in modulating stacking efficiency. Such an approach might open a new avenue in controlling the thickness of 2D materials. More information can be found in the Research Article by B. Manna, S. Ida et al. (DOI: 10.1002/chem.202201665).
Isostructural
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Predicting the strength of stacking interactions involving heterocycles is vital for several fields, including structure-based drug design. While quantum chemical computations can provide accurate stacking interaction energies, these come at a steep computational cost. To address this challenge, we recently developed quantitative predictive models of stacking interactions between druglike heterocycles and the aromatic amino acids Phe, Tyr, and Trp (DOI: 10.1021/jacs.9b00936 ). These models depend on heterocycle descriptors derived from electrostatic potentials (ESPs) computed using density functional theory and provide accurate stacking interactions without the need for expensive computations on stacked dimers. Herein, we show that these ESP-based descriptors can be reliably evaluated directly from the atom connectivity of the heterocycle, providing a means of predicting both the descriptors and the potential for a given heterocycle to engage in stacking interactions without resorting to any quantum chemical computations. This enables the rapid conversion of simple molecular representations (e.g., SMILES) directly into accurate stacking interaction energies using a freely available online tool, thereby providing a way to rank the stacking abilities of large sets of heterocycles.
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