A series of polynuclear coordination cages has been prepared which are based on bis(pyrazolyl-pyridine) bridging ligands (L) and transition-metal dications (M). Of these an octanuclear cage family M8L12, with a metal ion at each vertex of a cube and a bridging ligand spanning every edge, show size- and shape-selective binding of a range of organic guests. In organic solvents a major contribution to binding is hydrogen-bonding of the guest to specific sites on the interior surface of the host. In water, binding is dominated by the hydrophobic effect and ?G scales linearly with hydrophobic surface area of guest over a wide range of guests with aliphatic ketones such as adamantanone and cycloundecanone binding particularly strongly (up to 106 M-1); a model of the cycloundecanone complex is in Figure 1.Guests with ionisable groups (amines, pyridines, carboxylic acids) generally bind strongly in their hydrophobic neutral form but not in their hydrophilic ionised (protonated or deprotonated) form, thus allowing a pH swing to be used as the basis of uptake and release of several guests including a range of drug molecules. Guests such as 1-aminoadamantane ('amantidine'), aspirin and nicotine show a change in binding constant of 2 - 3 orders of magnitude between the neutral and ionised forms.

Host-guest chemistry of a cubic coordination cage: pH dependent uptake and release of drug molecules

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.