= Solution
The <molecule> combines three chemically different binding regions.
* \b[<sodium>: the oxygen-rich <calixarene>/<polyether> region], including the <ether> <oxygens> and suitably oriented <ester> <carbonyl> <oxygens>. <sodium> is a hard <Lewis acid> and favors multidentate coordination by hard <oxygen> donors. The scaffold holds several donors near one another and can reduce the conformational cost of binding.
* \b[<nitrate>: the two <urea> groups.] Their NH groups donate <hydrogen bonds> to <nitrate> <oxygens>. Several NH donors can cooperate around an <anion>; the <carbonyl> <oxygen> of a <urea> is an acceptor and is not the proposed nitrate-binding donor.
* \b[<silver>: the terminal bipyridyl nitrogen donors.] The <pyridine> lone pairs coordinate the softer <silver> <ion>. The actual coordination may involve donor sites on more than one arm or more than one receptor, depending on geometry and <concentration>.
These assignments identify the preferred local sites, rather than guaranteeing three independent binding constants: occupancy can alter <conformation>, electrostatics and the affinity of neighboring sites.
Back to article page
