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Phosphatidylcholine - Mg2+ equilibria in a monolayer at the air/water interface

100%
Petelska A., Figaszewski Z.
Open Chemistry
|
2013
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vol. 11
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issue 3
424-429
EN
Abstract The interaction between Mg2+ and a phosphatidylcholine (lecithin, L) monolayer at the air/water interface was investigated. Surface tension measurements (Langmuir method) of phosphatidylcholine monolayers as a function of Mg2+ concentration were carried out at 22°C using a Teflon trough and a Nima 9000 tensiometer. Interactions between phosphatidylcholine and Mg2+ result in significant deviations from additivity. An equilibrium theory was developed to obtain the stability constants and areas occupied by one molecule of LMg+ and L2Mg. The stability constants were K 1 = 9.95×102 m2 mol−1 and K 2 = 3.87×104 m2 mol−1. The area occupied by LMg+ is 77 Å2 molecule−1, while that occupied by L2Mg is 109 Å2 molecule−1. The Gibbs free energies of complexation for LMg+ and L2Mg are −16.91 ± 0.51 and −25.88 ± 0.76 kJ mol−1. Graphical abstract [...]
2
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Altered membrane amino acids composition in human colorectal cancer tissue

81%
Szachowicz-Petelska B., Sulkowski S., Figaszewski Z.
Open Chemistry
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2012
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vol. 10
|
issue 4
1245-1252
EN
Cancer transformation is characterized by changes in cell metabolism, which can alter the structure and function of cell membrane components, including integral membrane proteins. Qualitative and quantitative estimations of integral membrane protein are necessary for studies aimed at understanding their modifications under pathological conditions. Herein, we used a high-performance liquid chromatography (HPLC)-based approach that involved selective hydrolysis of isolated tissue cell membrane proteins to peptides, resolution by chromatography and determination of the amino acid content (phenylalanine (Phe), tyrosine (Tyr), cysteine (Cys) and lysine (Lys)) in individual peptides. The results demonstrate decrease in peptide levels and their amino acids content in integral membrane proteins in human colorectal cancer tissue. Therefore, cancer transformation causes a decrease in the levels of integral membrane proteins, which may in turn lead to an increase in the levels of other charged molecules on the cell surface, such as phospholipids. It might lead to the reconstruction and functional rearrangement of the cell membrane, for example: the permeability, electric properties, fluidity etc. [...]
3
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Analytical applications of electrode sensitive to labetalol in pharmaceuticals

81%
Gorodkiewicz E., Falkowski P., Sankiewicz A., Figaszewski Z.
Open Chemistry
|
2003
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vol. 1
|
issue 3
242-259
EN
The analytical properties of an ion-selective electrode sensitive to labetalol with a liquid membrane, based on ion-pair complexes with sodium tetraphenylborate (TPB-Na+) are described. The studied electrode can be used for the determination of labetalol hydrochloride as a protonated form of labetalol in pharmaceuticals. The calibration curve, e.g. EMF=f(pCLabHCl) is linear in the range from 10−5 to 10−2 mol L−1 with a correlation coefficient of 0.9992 and slope of 61.13 mV/decade, which is close to the Nernstian slope. The detection limit of the examined electrode is 7.20×10−6 mol L−1. The influence of pH of the tested solutions on the formulation of the electrode is not as considerable since the electrode works correctly in the pH range 3.0–8.0. The main attributes of the developed electrode are: stability, good reproducibility of EMF and short response time, close to 30 seconds depending on labetalol concentration in the solution. The electrode shows good selectivity for many inorganic ions. The selectivity for drug cations is weaker due to the structural similarity of the interfering cations to labetalol. The results of labetalol determination using direct potentiometry in drugs such as Pressocard (Polpharma) and Trandate (GlaxoWellcome) were compatible with the quantity of labetalol declared by the manufacturer, and with parallel UV spectrophotometric and HPLC determinations.
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