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The selectivity and the permeability of neutral-carrier-based membranes for substrate ions not only depend on the complexation behavior of the ionophores used, but also on their environment. In asymmetric membranes, ionophores may generally exhibit asymmetric transport properties. Such asymmetric bulk membranes were prepared from two PVC half-membranes incorporating synthetic cation-carriers in different plasticizers. The results of potentiometric and electrodialytic studies are discussed on the basis of a theoretical analysis of the carrier-mediated electrical properties of asymmetric bulk and bilayer membranes.Introduction. -Virtually, all experimental and theoretical studies concerning the ion transport behavior of ionophores in artificial membranes were restricted either to lipid bilayers of uniform compositions or to homogeneous bulk membrane phases. It is clear that these model membranes behave as symmetric barriers, i.e., the ion permeabilities should be the same in both directions perpendicular to the membrane plane. On the other hand, biological membranes probably show partial asymmetries in composition, as indicated by the preferential location or action of certain membrane proteins (e.g. enzymes) on one side. It is, therefore, conceivable that carriers or channels in such asymmetric membranes may generate an anisotropic permeability behavior in the sense that the flux or even the kind of transferred species will depend on the direction of transport. Although the studies by Liiuger and coworkers [l] [2] and others [3-71 indicate certain asymmetry effects for channels in bilayer membranes (e.g. rectification phenomena), there is still no clear evidence for the existence of biological or artificial membranes having an asymmetric permeability selectivity based on ion carriers.Here, we report on a bulk membrane in which one given ionophore, an electrically neutral carrier ligand, transports cations in the two directions with different selectivity. This asymmetric permeability has been realized for a two-segmented solvent polymeric membrane which offers the ionophore different environments at both membrane/solution interfaces. The asymmetric selectivity behavior observable in potentiometric and electrodialytic studies on such membranes is corroborated by the results of a theoretical analysis.

SummaryInvestigation of the formation of complex products in the gas-phase ozonolysis of cis-2-butene by linear-reactor-infrared-matrix and linear-reactor-microwave spectroscopy is reported. The following species have been unequivocally detected: secondary 2-butene ozonide, acetic acid, peracetic acid, glycolaldehyde, dimethyl ketene, the simple and mixed anhydrides of formic and acetic acid, 2,3-epoxybutane and 2-butanone, besides polyatomic products already known. In contrast, the primary ozonide has been detectable neither by LR.-MW. nor by LR.-IR. Observation of both stereoisomeric epoxides and kinetic modelling are used to support the intermediate formation of the O'Neal-Blumstein radical CH3CH (02)CH (0)CH3 and the existence of a reaction channel in which the two carbon atoms of the C , C double bond of the olefin remain connected. As the dominant reaction path a mechanism with a Criegee type split into methyldioxirane (ethylidene peroxide) and acetaldehyde is considered and subsequently proposed to explain formation of many complex products by either unimolecular or bimolecular processes of the peroxide. For the reactions considered, thermochemical estimates of reaction enthalpies and activation data are included. Kinetic modelling for a partial reaction mechanism involving at least two different paths of decay of the O'Neal-Blumstein biradical into Criegee-type intermediates and the 2,3-epoxybutanes is discussed.

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