Folding-promoted methylation of a helical DMAP analogue.

The methylation rate for a series of pyridine-containing phenylene ethynylene oligomers shows a nonlinear dependence on chain length, with a significant rate enhancement observed for oligomers that adopt a folded, helical conformation. The folded structure provides a microenvironment that lowers the energy barrier for the methylation reaction. Of these noncovalent interactions, the largest stabilization may arise from binding of methyl iodide in the hydrophobic cavity of the folded oligomer, in close proximity to the pyridine nucleophile.