A Sodium Ion Selective Electrode Based on a Highly Lipophilic Monensin Derivative and Its Application to the Measurement of Sodium Ion Concentrations in Serum

Abstract

Five kinds of monensin derivatives were synthesized by chemical modifications of the natural carboxylic polyether antibiotic monensin. Their usefulness as active compounds (Na+-ionophores) for Nat-selective poly(vinyl chloride)(PVC)-matrix membrane electrodes was examined. The electrodes based on monensin ester derivatives exhibited high Nat-selectivity. Among them, the electrode based on the highly Lipophilic monensin dodecyl ester (log K° (partition constant)=8.7) had enough Nat-selectivity to determine the Nat-concentration in serum (log KNaK=-1.1, log Kv°aMg-4.0 and log KNaca-3.6); the electrode gave a Nernstian response (59.0 mV/pNa) ranging from 5X10-6 to 1 M Nat. The response potential of this electrode to a 0.1 M Na+ solution drifted within ±0.01 mV/ h. The values of the Nat-concentration in artificial and real serum samples were successfully determined with the monensin dodecyl ester-based electrode using diisodecylphthalate as the electrode membrane solvent.

Conductance Change in Phospholipid Bilayer Membrane by an Electroneutral Ionophore, Monensin

“…We found that G(0) values for methylmonensin were about 100 times greater than that obtained by monensin. Because the partition coefficient of methylmonensin to organic solvents is reported to be almost equal to that of monensin (Tohda et al, 1990), and because transmembrane rate constants of methyl-monensin and ordinary monensin seem not to be greatly different, the 100- Solutions separated by bilayer were 200 mM NaCl, buffered with 50 mM Hepes-Tris (pH 7.0). Temperature was 20 °C.…”

“…We found that G(0) values for methylmonensin were about 100 times greater than that obtained by monensin. Because the partition coefficient of methylmonensin to organic solvents is reported to be almost equal to that of monensin (Tohda et al, 1990), and because transmembrane rate constants of methyl-monensin and ordinary monensin seem not to be greatly different, the 100- fold increase in G(0) can be interpreted as the change in the concentration of the univalent ionic form of monensin which contributes to the electrogenic transport. In addition, we could not find any current when KC1 was used instead of NaC1.…”

Carrier-Based Ion-Selective Electrodes and Bulk Optodes. 2. Ionophores for Potentiometric and Optical Sensors

“…The interference from H + was found to depend particularly strongly on the site concentration. A rather high interference from Ba 2+ was observed (log (SSM): Ba 2+ , −0.9 (pH = 6.0), +1.0 (pH = 8); dibenzyl ether). ,, Note, however, that variaton of the sample solution pH confirmed that in the presence of anionic sites and at pH 7.0 monensin is a charged carrier for Ba 2+ (see section II.12) …”

Reaction of monensin silver salt with methyl iodide: smooth alkylation of a tightly hydrogen-bonded carboxylate

“…In the search for more efficient and selective cation-binding substances, the ionophoric properties of monensin derivatives, including esters and amides, have been investigated (2 -12). The ionophoric properties of monensin esters have been studied in ion-selective electrodes (13,14), and the methyl ester 2 has been employed in a clinical system for the quantitative analysis of sodium cations in human blood (15 -17). For this purpose, the methyl ester 2 must be free from contamination by sodium cations.…”