Artificial receptors involved in enolization and pK(a) shifts.

Abiotic receptors used to enolize carbonyl compounds or to shift substrate pK(a) values are reviewed. These systems exhibit disparate frameworks and several approaches to binding and anion stabilization. Detailed emphasis is placed on a bicyclic cyclophane that induces pK(a) shifts in active methylene compounds through NH-pi hydrogen bonding with the resultant enolates.

Anion recognition: synthetic receptors for anions and their application in sensors.

Important contributions to the field of anion sensing include electrochemical lipophilic uranyl salophene receptors incorporated into membranes that act as fluoride-selective potentiometric microsensors. A promising optical-based sensor, selective for cyclic AMP, involves a preorganized, molecularly imprinted polymer employing an intrinsic fluorophore. Competition methods using ensembles of recognition units and external indicators have been used to sense citrate in highly competitive media and micromolar concentrations of inositol(tris)phosphate in water. In addition, DNA dendrimers immobilized on a quartz-crystal microbalance acted as an elegant biosensor for Cryptosporidium DNA. These designs display the varied methods of anion detection currently being pursued.