Sequence-Dependent Guest Release Triggered by Orthogonal Chemical Signals.

Three Zn(II)4L4 coordination cages, assembled from trisiminopyridine ligands, exhibit differences in their guest-binding selectivities and reactivity with tris(2-aminoethyl)amine (tren), which enabled the design of a molecular network that responded in distinct ways to different chemical signals. When two of these cages were present in solution together, one of them was observed to selectively encapsulate chloroform, and the other was observed to selectively encapsulate cyclohexane. The two guests could be released sequentially, in a specified order defined by the input of two separate chemical signals: tren and perrhenate. Furthermore, the observed reactivity of tren with the initial cage mixture provided control over the uptake and release of perrhenate within the third cage formed in situ. One of these tetrahedral cages has been identified as a tight (K(a) > 10(7) M(-1)) and selective host for perrhenate, an anion of great physicochemical similarity to pertechnetate, both having uses in nuclear medicine.