We report a comparative study of the leadage of hydrophilic molecules from vesicles of egg lecithin (EL) and of dipalmitoyllecithin (DPL). The effect of osmotic pressure differences a leakage is consistent with a model for statistical pore nucleation process. The major difference in osmotic pressure induced leakage from DPL and EL is that the number of pore creation sites is much greater in DPL. We suggest that the difference in number of these sites also accounts for other differences in the properties of DPL and EL, namely for differences in vesicle fusion and apparent rate of "flip-flop".

Molecular wires, which would allow electron flow to take place between different components, are important elements in the design of molecular devices. An approach to such species would be molecules possessing an electron-conducting conjugated chain, terminal electroactive polar groups, and a length sufficient to span a lipid membrane. To this end, bispyridinium polyenes of different lengths have been synthesized and their incorporation into the bilayer membrane of sodium dihexadecyl phosphate vesicles has been studied. Since they combine the features of carotenoids and of viologens, they may be termed caroviologens. Vesicles containing the caroviologen whose length approximately corresponds to the thickness of the sodium dihexadecyl phosphate bilayer display temperature-dependent changes of its absorption spectrum reflecting the gel --liquidcrystal phase transition of the membrane. The data agree with a structural model in which the caroviologens of sufficient length span the bilayer membrane, the pyridinium sites being close to the negatively charged outer and inner surfaces of the sodium dihexadecyl phosphate vesicles and the polyene chain crossing the lipidic interior of the membrane. These membranes may now be tested in processes in which the caroviologen would function as a continuous, transmembrane electron channel-i.e., as a molecular wire. Various further developments may be envisaged along these lines.Molecular devices may be defined as structurally organized and functionally integrated chemical systems built into supramolecular architectures. The development of such devices requires the design of molecular components performing a given function (e.g., photoactive, electroactive, ionoactive, thermoactive, or chemoactive) and suitable for assembly into an organized array. A major requirement is that these components and the devices that they build up should perform their function(s) at the molecular and supramolecular (1) levels, as distinct from the level of the bulk material.

temperature-independent in the temperature range shown. The iron complex 2 displays a change in the thermal conductivity by a factor of two at the spin transition.

Articles you may be interested inSmall-angle neutron-scattering study on a structure of microemulsion mixed with polymer networks Small angle neutron scattering near the wetting transition: Discrimination of microemulsions from weakly structured mixtures Small angle neutron scattering near Lifshitz lines: Transition from weakly structured mixtures to microemulsions Microemulsions are colloidal systems which are made by a dispersion of minute droplets (a few hundred A in diameter) of one component (e.g. water) in a continuous medium formed by another immiscible component (e.g. oil); the droplets are surrounded by a mixed film of surfactants. New information has been obtained about the distribution of the various components in the elementary droplet. The hydrodynamical interface is shown to contain an important amount of the continuous phase and a quantity of alcohol which increases with the amount of solubilized water. In contrast. the corresponding variation of the area per polar head of the surfactant molecule is relatively small. Small angle neutron scattering indicates that a portion of the interfacial film, 9 A thick, is not penetrated by the oily phase. The droplets are weakly correlated.