Enhanced methylation rate within a foldable molecular receptor.

A N,N-(dimethylamino)pyridine monomer is incorporated into the backbone of a m-phenyleneethynylene oligomer such that the pyridine nitrogen is located on the interior surface of the binding cavity in the folded structure of the oligomer. For an oligomer having a chain length of 13 monomer units, competitive inhibition experiments reveal that methyl iodide binds weakly within the oligomer cavity with an association constant K(a) = 2 M(-1), and the oligomer-methyl iodide complex reacts with unimolecular rate constant k(u) = 0.082 s(-1) to provide the methylated product. The effective molarity is calculated to be 230 M by comparison of k(u) for the 13-mer with the second-order rate constant for a 3-mer that is too short to fold and thus unable to bind methyl iodide.