C O M M U N I C A T I O N S
five- or six-membered ring interacts most directly with Na+ or K+
is determined by structural as well as electronic factors. In nature,
indole is not attached to a constraining macroring, and it seems
likely that either aromatic subunit of indole may be available for
cation complexation. The abundance of Na+ and K+ ions in all
living systems makes interactions such as those modeled here
probable if not imperative.
Acknowledgment. We thank the NIH (GM-36262) and the PRF
(PRF 37197-AC4) for grants that supported this work.
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