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1.D.212.  The Self-Assembled Anion Channel (SAAC) Family 

The figure below shows eleven synthetic compounds that transport anions across lipid membranes. Each of these compounds has been proposed to form self-assembled ion channels. With the exception of lipopeptide 65 and thiophene 66, these molecules are too small to bridge the bilayer membrane by themselves. To form a functional channel, they must self-assemble into larger structures.

Monomers used to form self-assembled ion channels.

These eleven compounds have much in common. They typically have molecular weights <1000 amu and are straightforward to synthesise. The monomers often have alkyl tails and/or hydrophobic amino acid sidechains, which help them partition into the membrane. Except for thiophene 66, all have secondary amides, which enable intermolecular hydrogen-bonding. Little is known about supramolecular structures in the membrane, but crystal structures and/or computational models informed many of the studies. The table below presents transport properties for these compounds, namely EC50 values measured in liposomes and specific conductance values in planar bilayers. This table is intended to summarize information and not meant to compare transporters with each other, since experimental conditions vary so much from laboratory to laboratory.


  Transport activities in LUVs, expressed as EC50 (μM) and single-channel conductance values (pS) for compounds 56–66

Compound Mol. wt EC50a Conductanceb Ref.
56 fumaramide 278 3.5 60.8 60
57 trimesic amide 820 3.0 (I/OH) 0.396 61
58 triazolium 296 4.47% (+Val)c Multipled 62
59 isophthalamide 604 0.48 (KCl) 100 63
60 monopeptide 368 0.32 (NO3/OH) 0.559 64
61 halogen bBonder 560 0.39 0.586 65
62 tripeptide 609 0.0016 (I/OH) 0.687 66
63 sugar peptide 970 2.14 nd 67
64 sugar peptide 561 15.83 nd 68
65 SCMTR 1230 nd 15.5, 27.8 69
66 thiophene 944 0.28