Affinity capillary electrophoretic study of K+/Na+ selectivity of hexaarylbenzene-based polyaromatic receptor

Affinity capillary electrophoretic (ACE) study has proved the selectivity of hexaarylbenzene-based polyaromatic receptor (R) for K⁺ ion over Na⁺ ion. The apparent binding constants of the R complexes with K⁺ and Na⁺ ions were determined from the dependence of effective electrophoretic mobility of R on the concentration of the above alkali metal ions in the background electrolyte using a non-linear regression analysis. The apparent binding constants (K_b) of the K-R⁺ and Na–R⁺ complexes in methanolic medium were evaluated as log K_b = 3.20 ± 0.22 for the K–R⁺ complex, and log K_b??0.7 for the Na–R⁺ complex.     

ACE applied to the quantitative characterization of benzo‐18‐crown‐6‐ether binding with alkali metal ions in a methanol–water solvent system

ACE was applied to the quantitative evaluation of noncovalent binding interactions between benzo‐18‐crown‐6‐ether (B18C6) and several alkali metal ions, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in a mixed binary solvent system, methanol–water (50/50 v/v). The apparent binding (stability) constants (K_b) of B18C6–alkali metal ion complexes in the hydro‐organic medium above were determined from the dependence of the effective electrophoretic mobility of B18C6 on the concentration of alkali metal ions in the BGE using a nonlinear regression analysis. Before regression analysis, the mobilities measured by ACE at ambient temperature and variable ionic strength of the BGE were corrected by a new procedure to the reference temperature, 25°C, and the constant ionic strength, 10 mM . In the 50% v/v methanol–water solvent system, like in pure methanol, B18C6 formed the strongest complex with potassium ion (log K_b=2.89±0.17), the weakest complex with cesium ion (log K_b=2.04±0.20), and no complexation was observed between B18C6 and the lithium ion. In the mixed methanol–water solvent system, the binding constants of the complexes above were found to be about two orders lower than in methanol and about one order higher than in water.     

Affinity capillary electrophoresis and density functional theory employed for the characterization of hexaarylbenzene-based receptor complexation with alkali metal ions

In this study, affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations were combined to investigate non-covalent binding interactions between the hexaarylbenzene-based receptor (R) and alkali metal ions, Rb(+) and Cs(+) , in methanol. The apparent binding (stability) constants (K(b) ) of the complexes of receptor R with alkali metal ions in the methanolic medium were determined by ACE from the dependence of effective electrophoretic mobility of the receptor R on the concentration of Rb(+) and Cs(+) ions in the BGE using a non-linear regression analysis. The receptor R formed relatively strong complexes both with rubidium (log K(b) =4.04±0.21) and cesium ions (log K(b) =3.72±0.22). The structural characteristics of the above alkali metal ion complexes with the receptor R were described by ab initio density functional theory calculations. These calculations have shown that the studied cations bind to the receptor R because they synergistically interact with the polar ethereal fence and with the central benzene ring via cation-π interaction.     

On-line atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry

A new technique is presented for the coupling of atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) mass spectrometry with liquid delivery systems. Mass measurements of polymers and peptides are demonstrated using a co-dissolved matrix, e.g. alpha-cyano-4-hydroxycinnamic acid (HCCA). Improvements in terms of sensitivity are achieved by optimizing the shape und control of the exit capillary and by using a laser (355 nm) at a 1 kHz repetition rate. Two calibration experiments promise a good applicability of the presented coupling method for quantitative measurements. The limit of detection achieved so far is 500 nM for peptides in methanol solution containing 25 mM HCCA.     

Trimethymetall-urotropinaddukte des aluminiums,galliums, indiums und thalliums

Reactions of urotropine (C₆H₁₂N₄) with trimethylmetal derivatives of Al, Ga, In und Tl in various ($\text{1}\text{1}$$\text{1}\text{4}$) molar ratios lead to stable and monomeric $\text{1}\text{1}$, $\text{1}\text{2}$ or $\text{1}\text{3}$ adducts in good yields, but no $\text{1}\text{4}$ addition product could be isolated. The vibrational spectra (IR and Raman) of all compounds are recorded and partly assigned. Some characteristic frequencies of the C₆N₄-skeletons clearly show the symmetry changes in the series of the $\text{1}\text{1}$ → $\text{1}\text{2}$ → $\text{1}\text{3}$ adducts (C_3ν → C_2ν → C_3ν). The X-ray structure determinations of C₆H₁₂N₄·.GaMe₃ (MeCH₃) and C₆H₁₂N₄·.2GaMe₃, are in good agreement with the vibrational spectra. Both compounds crystallize in monoclinic space groups (P2₁ and C2/c). The GaN distances are around 214 pm, and the values for the C₆N₄-skeletons are not significantly different from those for free urotropine.     

Darstellung, eigenschaften und kristallstruktur von methylgalliumdiacetat CH3Ga(OOCCH3)2

Trimethylgallium reacts with acetic acid in a $\text{1}\text{2}$ molar ratio yielding methylgallium diacetate, CH₃Ga(OOCCH₃)_2? The structure is determined by vibrational spectroscopy and the crystal structure is described. Methylgallium diacetate crystallizes in the monoclinic space group P2₁/c with lattice constants a 776.5, b 1428.9, c 1406.3 pm, β 91.87° and eight formula units per cell. The monomers are linked together by acetate groups forming polymeric, waved layers. Besides the bridging acetate there are also “free” acetate groups coordinated at the distorted trigonal-bipyramidal coordinated Ga(1) atom. A second gallium atom Ga(2) is coordinated distorted tetrahedrally, the acetate groups bonded to Ga(2) being all bridging. The mean intermolecular distances are: GaC 194.6 pm, Ga(1)O_apical 215.3 pm, Ga(1)O_eq(bridge) 194.3 pm, Ga(1)O_eq(free) 187.3 pm, Ga(2)O 191.3 pm, CC 151.5 pm, CO 119.4 pm, CO 131.1 pm, CO 127.3 pm.     

Determination of impurities and counterions of pharmaceuticals by capillary electromigration methods

The review presents a survey of recent applications of high‐performance capillary electromigration methods—capillary zone electrophoresis, nonaqueous capillary electrophoresis, capillary isotachophoresis, micellar electrokinetic chromatography, microemulsion electrokinetic chromatography and capillary electrochromatography—for the determination of impurities of pharmaceuticals, including chiral impurities, for the period 2007–2013. In addition, due to the missing evaluation of the determination of counterions of pharmaceuticals by capillary electromigration methods in the last 20 years, the publications dealing with this topic since 1995 are included in this review. General aspects of both these types of applications of capillary electromigration methods in pharmaceutical analysis are discussed, and detailed experimental conditions used for determination of various chemical impurities and counterions of many particular drugs are described.     

Recent developments and applications of capillary and microchip electrophoresis in proteomics and peptidomics (mid-2018–2022)

This review gives a wide overview of recent advances and applications of capillary electrophoresis and microchip capillary electrophoresis methods in the fields of proteomics and peptidomics in the period from mid-2018 up to the end of 2022. The methodological topics covering sample preparation and concentration techniques, hyphenation of capillary electrophoresis methods with mass spectrometry, and multidimensional separations by on-line or off-line coupled different capillary electrophoresis and liquid chromatography techniques are described and new developments in both bottom-up and top-down approaches in proteomics are presented. In addition, various applications of capillary electrophoresis methods in proteomic and peptidomic studies are demonstrated. They include monitoring of protein posttranslational modifications and applications in biological and biochemical research, clinical peptidomics and proteomics, and food analysis.     

Application of bare gold nanoparticles in open-tubular CEC separations of polyaromatic hydrocarbons and peptides

In this study, bare gold nanoparticles (GNPs) immobilized in the sol-gel-pretreated fused-silica (FS) capillary as a stationary phase for open-tubular capillary electrochromatography (OT-CEC) are for the first time shown to be able to separate both hydrophobic polyaromatic hydrocarbons (PAHs) as well as hydrophilic cationic antimicrobial peptides. Model mixture of four PAHs, naphthalene, fluorene, phenanthrene, and anthracene, was resolved by OT-CEC in the GNP-modified FS capillaries using the hydro-organic background electrolyte (BGE) composed of 20 mmol/L sodium phosphate buffer, pH 7, modified with ACN at 8:2 v/v ratio. On the other hand, three synthetic analogues of an antimicrobial peptide mastoparan PDD-B, basic tetradecapeptides INWKKLGKKILGAL-NH(2), INSLKLGKKILGAL-NH(2) and NWLRLGRRILGAL-NH(2), were separated in aqueous acidic BGEs, pH 2.1-3.1, composed of weak acids (formic and acetic) or amphoteric amino or imino acids (aspartic or iminodiacetic), utilizing the advantage of a slow reversed (anodic) EOF and slightly positive charge of the GNP-modified FS capillary suppressing the adsorption of cationic peptides on the inner capillary wall and improving their resolution.