Channel compounds

Tabushi I, Kuroda Y, Yokata K (1982) A,B,D,F-Tetrasubstituted beta-cyclodextrin as artificial channel compound. Tetrahedron Lett 23 4601 1604... 

The ability of compounds 21, 22, 23, 25, and 28-32 to conduct cations was examined in planar bilayers composed of phosphatidylethanolamine (PE) painted across a 200 pm diameter aperture in a septum between two aqueous compartments filled with 600 mM KC1 (10 mM HEPES pH 7.2) (Figure 13). Bilayer quiescence was confirmed at 148 mV and bilayer stability was observed to be unaffected by the addition of up to 5 pL of DMSO. Stock solutions of the channel compounds (10 pM) were prepared immediately prior to use, and 0.1-5 pL (i.e. 1-50 pmol of substance) in DMSO was added to the stirred solution in the cis chamber. Typically, channel insertion into the bilayer occurred between 30 s and 30 min. 

I. Tabushi, Y. Kuroda, K. Yokota, A,B,D,F-Tetrasubstituted 8-Cyclodextrin as Artificial Channel Compound , Tetrahedron Lett, 23,4601 (1982)... 

The aminoisobutyric acid containing peptide alamethi-cinl6] IS a naturally occurring ion-channel compound that... 

Unimolecular channel compounds have also been formed using an o(-helical peptide scaffold to support an assay of 21-crown-7 moieties, 4. Models suggest that the stmcture formed is about 3.2 nm long, and that the crown ethers stack to form the chaimel. Compound 4 showed transport ability similar to that of gramicidin and displayed bilayer-dependent single-chaimel features. 

Attempts to mimic naturally occuning channels yielded a wide range of compounds of many shapes, sizes, and stmctures. Each group of compounds synthesized has a basic stmcture, which appears in every case to be subject to stmcture-activity control. Clearly, a wide range of basic stmctural types will support channel formation, making it unlikely that stmcturally specific interactions between the channel compound and the transient ion are essential. 

There are also many uses for nonenzymatic polymeric catalysts. For instance, polymer-bound crown ethers, cryptates, and channel compounds behave as polymeric phase-transfer catalysts. The catalytic activity is based on selective complex formation. An example is the use of polystyrene-attached oxygen heterocycles [18]-crown-6 or a cryptand[222] to catalyze replacements of bromine in n-octyl bromide by an iodine or by a cyanide groups... 

The definition of a co-crystal is still matter of debate [74,75]. The definition initially put forward by Aakeroy focused on the aggregation state co-crystals are made from reactants that are solids at ambient conditions [76] and has also been taken up by others [71,77]. This definition, however, is not without ambiguity (see below). We prefer to take up Dunitz more liberal view of co-crystals as encompassing molecular compounds, molecular complexes, solvates, inclusion compounds, channel compounds, clathrates, and other types of multi-component crystals. This view has been echoed recently by Stahly [78] who wrote that co-crystals consist of two or more components that form a unique crystalline structure having unique properties. At the bottom line, these multicomponent systems ought to be looked at as crystals of supermolecules whereby the component units interacting via non-covalent interactions generate collective physico-chemical properties that are different from those of the homo-molecular crystals formed by the components. 

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