SummaryA chiral macrocyclic crown ether exhibits an enantiomer-selectivity of 2.6 for u -phenylethylammonium ion when incorporated in solvent polymeric membranes. The sequence of selectivity of these membranes clearly differs from that of lipophilicity for the different biogenic ammonium ions studied, indicating a significant structural contribution.Chiral macrocyclic polyethers which bind chiral ammonium ions with high enantiomer-selectivity and behave as ionophores have been described [ 1-31. The enantiomer-selectivity of such ligands can easily be determined quantitatively by using an electrochemical procedure described earlier [4] [ 5 ] . Here we report on such studies using the ion carrier 1 (Scheme) [6] in solvent polymeric membranes and phenylethylammonium ions as substrates in aqueous solutions contacting the membrane. Scheme 3The selectivities KF&, presented in Figure 1 indicate the preference of the ions J relative to the (k )-u-phenylethylammonium ion by the membrane. In contrast to other ionophores described (see 2 and 3 in Fig. I), 1 induces a rather high selectivity for PEA+ over ephedronium (EPH+) and pseudo-ephedronium 0018-019X/81/3/0657-05$01.00/0 0 1981 Schweizerische Chernische Gesellschaft

Self‐diffusion in cobalt is investigated from 896 to 1745 K by means of the standard radio‐tracer method using lathe sectioning in the paramagnetic and sputter sectioning in the ferromagnetic region. The diffusion coefficients vary between about 10−17 cm2 s−1 and 10−9 cm2 s−1; their temperature dependence can be described by DT = 0.55 exp (−2.99 eV/kT) cm2 s−1. In contrast to iron no influence of the magnetic order−disorder transition on the diffusivity is observed within the experimental accuracy. The isotope effect for self‐diffusion is measured at seven temperatures in the range 1451 to 1745 K. Its magnitude and its decrease with increasing temperature indicate that diffusion occurs mainly via monovacancies with an increasing but small contribution of divacancies with increasing temperature.

A cell assembly with two membranes containing each one enantiomer of the ionophor N,-tetracarboxamide is used for the direct potentiometric determination of the enantiomeric excess ee of 1-phenylethylammonium ions in aqueous solutions. The preference for the ( R ) -over the (S)-1-phenylethylammonium ion by the (2R,3R,11 R,12R)ionophor of 2.7 allows a reliable determination of ee even in the presence of known concentrations of the heavy interferent KC1. Einleitung. ~ Kurzlich haben wir uber eine Messkette berichtet [I], die es grundsatzlich erlaubt, den Enantiomerenuberschuss von Ephedrinium-Ionen in wasserigen Losungen direktpotentiometrisch zu erfassen. Es fand dabei eine ionenselektive Halbzelle rnit einer den Weichmacher (+)-(R,R)-Weinsauredi(5-nonyl)ester [2] enthaltenden PVC-Membran Venvendung, die gegen die enantiomorphe Halbzelle rnit (-)-(S,S)-Weinsauredi(5-nony1)ester in der Membran geschaltet wurde. Obwohl die Halbzelle rnit dem (R,R)-Ester das (+)-( 1 S,2R)-Ephedrinium-Ion lediglich um einen Faktor von 1,5 gegenuber dem (-)-( 1 R,2S)-Enantiomeren vorzuziehen vermag, konnte der Enantiomerenuberschuss in storionenarmem Messgut erstaunlich gut bestimmt werden [ 11. Es sind jedoch bereits wesentlich hohere Enantiomerenselektivitaten in Membranen erzielt worden. So konnten rnit einem Binaphthyl-Kronenather aus dem Arbeitskreis von Cram (vgl. 8 in [3]) bzw. rnit (+)-(2R,3R,

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A cell assembly with two membranes each containing one enantiomer of a chiral ionophore is described. It is suitable for the direct potentiometric determination of the enantiomeric excess of ions. The method is used to determine the enantiomeric excess of ephedronium ions in aqueous solutions.