Hydrogen bonding and charge interactions are both essential for molecular recognition and the self-assembly of biological macromolecules. They are also employed heavily in the design of new systems for fundamental, biological, and materials research. The influence of a charge-bearing functional group on pK a values [1] and chemical reactivity [2] has been well documented in the form of Hammett-type substituent constants in physical organic studies. Changes in the hydrogen-bonding behavior of ligands upon complexation with cationic transition metal centers have been indicated by theoretical calculations. [3] Such calculations also indicated that anions could induce a large cooperative effect in the hydrogen-bonding network of peptides. [4] Enhancement was observed experimentally in urea´carboxylate binding when the carbonyl group of the urea molecule was coordinated to a Lewis acid. [5] The optical property of [Ru(bpy) 3 ] 2 (bpy bipyridine) in a phosphodiester sensor was changed when the hydrogen-bonding sites were bound. [6] Although both hydrogen-bonding and charge-bearing sites are important in molecular recognition, interestingly, it is not common to find examples in supramolecular chemistry in which hydrogenbonding sites are designed to be controlled by a covalently bound charge-bearing substituent. Charge-assisted CÀH´´´X hydrogen bonds have been recognized in recent years [7] and metallocene complexes have been used to achieve redoxswitched binding. [8] Nevertheless, the binding sites are basically adjacent to the charged centers, and we felt that charge centers can have a more far-reaching influence on a binding site.If a charged group and a binding site can communicate with each other, one can use a three-component system (a charged group, a linker, and a binding site) as a signal transducer. The charge-bearing group can be viewed as a reaction site, whose charge state can be altered by reactions such as protonation, metalation, oxidation, reduction, or chemical transformation of a functional group. On the basis of this concept we designed test compounds 1 a ± d and 2 a ± d, and calculated the energies N X X N H H N X X N H H H n n 1a: X = CH, n = 1 1b: X = CH, n = 2 1c: X = CH, n = 3 1d: X = CH, n = 4 2a: X = CH, n = 1 2b: X = CH, n = 2 2c: X = CH, n = 3 2d: X = CH, n = 4 3a: X = N, n = 1 3b: X = N, n = 2 3c: X = N, n = 3 3d: X = N, n = 4 4a: X = N, n = 1 4b: X = N, n = 2 4c: X = N, n = 3 4d: X = N, n = 4of formation of a hydrogen bond (binding energies) to find out how efficiently the reaction and binding centers can communicate with each other. In these compounds the reaction center is an imine group and the binding center is pyrrole; compounds 1 a ± d are neutral imines and 2 a ± d are cationic iminium compounds. Ammonia was chosen as the hydrogen-bonding partner of the NÀH group of pyrrole for the sake of geometric simplicity, since it only has one lone pair of electrons. The ammonia binding energy of 2 a (À 13.17 kcal mol À1 ) at the HF/6-31G* level is double that of cationic 1 a (À 6.84 kcal mo...