Membranelektrode zur selektiven, potentiometrischen Erfassung organischer Kationen

Scholer, R.; Simon, W.

doi:10.1002/hlca.19720550539

Cited by 71 publications

(22 citation statements)

References 17 publications

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“…The selectivity sequence of membranes with 8 roughly corresponds to that which is typical for cation exchange membranes (see column 1 in Fig. 2 ) [14]. This is somewhat surprising since 8 does not seem to be present in the deprotonated form in substantial concentration in the membrane phase.…”

mentioning

confidence: 84%

Lipophilic Di‐ and Triamides as Ionophores for Alkaline Earth Metal Cations

Erne

Stojanac

Ammann

et al. 1980

Helvetica Chimica Acta

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SummaryDifferent electrically neutral lipophilic di-and triamides were prepared and their ion selectivity in membranes studied. In membranes the ionophore N, N'-diheptyl-N, N'-dimethyl-succinamide prefers Ca2+ over Mg2+ by a factor of 20 but rejects Na+ and K+ in respect to Mg2+ by a factor of 100 and 10, respectively. This selectivity suffices to perform useful intracellular Mg2+ activity studies.Introduction. -The monocarboxylic polyether antibiotic-60 16 has been reported to be a Mg2+ selective ionophore which displays preferential extraction from an aqueous into an organic phase of Mg2+ over Ca2+ and Ba2+ [ 11. We were, however, unable to detect potentiometrically such selectivities when the antibiotic was incorporated in solvent polymeric membranes. In these membranes Ca2+ was clearly favoured over Mg2+. Similar results were obtained for the antibiotic A23187 which was claimed to be Ca2+ selective in extraction [2] as well as in transport systems [3]. The potentiometrically determined selectivity sequence is, however, Ba2+ > Ca2+ > Mg2+ [4j1).Despite major efforts it has so far been impossible to prepare a single membrane system showing a high selectivity for Mg2+ over Ca2+. According to model calculations such a preference for Mg2+ might be achieved by an octahedral coordination of the cation with the 0-atoms present in the high-dipole-moment ligand groups [8]. A number of 3-oxapentane diamides were prepared and tested in membranes [9] to see whether the suspected 1 : 2 catiodligand complexes were formed by a hexadentate coordination. Although N, N, N , N'-tetracyclohexyl-3-oxapentane diamide does indeed form 1 : 2 Mg2+/ligand complexes [9] [lo], in membranes it induces a selectivity of about lo4 for Ca2+ over Mg2+. This can be explained by the observed formation of highly lipophilic 1 : 3 Ca2+/ligand complexes [9].

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mentioning

confidence: 84%

Lipophilic Di‐ and Triamides as Ionophores for Alkaline Earth Metal Cations

Erne

Stojanac

Ammann

et al. 1980

Helvetica Chimica Acta

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“…For cations a logical choice of sensor is a liquid membrane incorporating tetraphenylborate, since this compound is highly selective for tetraalkylammonium ions (Scholer & Simon, 1972;Baum, 1972;Dionne, 1976). This sensor is available from Corning, designated as a potassium ion exchanger.…”

Section: Choice Of Ionsmentioning

confidence: 99%

Ion diffusion modified by tortuosity and volume fraction in the extracellular microenvironment of the rat cerebellum.

Nicholson¹,

Phillips²

1981

The Journal of Physiology

752

685

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SUMMARY1. The validity of the macroscopic laws of ion diffusion was critically examined within the microenvironment of the extracellular space in the rat cerebellum using ion-selective micropipettes and ionophoretic point sources.2. The concepts of volume averaging, volume fraction (a) and tortuosity (A) were defined and shown to be theoretically appropriate for quantifying diffusion in a complex medium such as the brain.3. Diffusion studies were made with the cations tetramethylammonium and tetraethylammonium and the anions a-naphthalene sulphonate and hexafluoroarsenate, all of which remained essentially extracellular during the measurements. Diffusion parameters were measured for a period of 50 s and over distances of the order of 0-1 mm. 4. Measurements ofthe diffusion coefficients of the ions in agar gel gave values that were very close to those derivable from the literature, thus confirming the validity of the method.5. Measurements in the cerebellum did not reveal any systematic influences of ionophoretic current strength, electrode separation, anisotropy, inhomogeneity, charge discrimination or uptake, within the limits tested. 6. The pooled data from measurements with all the ions gave a = 0-21 +002 (mean+s.E. of mean) and A = 1-55+0-05 (mean+S.E. of mean).7. These results show that the extracellular space occupies about 20 % of the rat cerebellum and that the diffusion coefficient for small monovalent extracellular ions is reduced by a factor of 2-4 (i.e. A2) without regard to charge sign. The over-all effect of this is to increase the apparent strength of any ionic source in the cerebellum by a factor of A2/a, about 12-fold in the present case, and to modify the time course of diffusion.8. These conclusions confirm that the laws of macroscopic diffusion are closely obeyed in the cerebellum for small ions in the extracellular space, provided that volume fraction and tortuosity are explicitly taken into account. It is likely that these conclusions are generally applicable to other brain regions and other diffusing substances. PHY 321C. NICHOLSON AND J. M. PHILLIPS

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“…It is known that ion-exchanger electrodes (unlike valinomycin electrodes) can respond not only to K+, but also to quaternary ammonium compounds in micromolar concentrations, particularly if the tip diameter exceeds 1 tm (e.g. Scholer & Simon, 1972;. To compare our results with the earlier values, we made measurements using an ion-exchanger resin ofknown composition, thought to be that of Corning 477317 (Baum & Wise, 1971), and known to have very similar selectivity properties (Oehme & Simon, 1976;Coles, 1988 Fig.…”

Section: Baseline [K+]0 In the Hypothalamusmentioning

confidence: 99%

Extracellular K+ in the supraoptic nucleus of the rat during reflex bursting activity by oxytocin neurones.

Coles

Poulain

1991

The Journal of Physiology

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SUMMARY1. We have investigated changes in extracellular potassium concentration [K+]o in the supraoptic nucleus of lactating rats and in particular those that occur during the intense burst of firing by the oxytocin neurones involved in the milk ejection reflex.2. Double-barrelled K+-selective microelectrodes containing a highly selective sensor based on valinomycin were lowered through the exposed cortex towards the supraoptic nucleus (SON) of female rats anaesthetized with urethane. The mean resting [K+]o in the hypothalami of five rats was 2-4 mM, S.D. = 0-3 mM.

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Membranelektrode zur selektiven, potentiometrischen Erfassung organischer Kationen

Cited by 71 publications

References 17 publications

Lipophilic Di‐ and Triamides as Ionophores for Alkaline Earth Metal Cations

Lipophilic Di‐ and Triamides as Ionophores for Alkaline Earth Metal Cations

Ion diffusion modified by tortuosity and volume fraction in the extracellular microenvironment of the rat cerebellum.

Extracellular K+ in the supraoptic nucleus of the rat during reflex bursting activity by oxytocin neurones.

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