The magnitude of [C-H center dot center dot center dot O] hydrogen bondingin molecular and supramolecular assemblies

Ab initio calculations at the MP2/6-311++G** level on model systems (N-meth ylpyridinium complexes of dimethyl ether and dimethyl phosphate anion) prov ide quantitative measures of the large stabilization energies that arise fr om [C-H . . .O] contacts in charged systems. These attractive interactions control (i) the self-assembly of bipyridinium-based catenanes and rotaxanes in solution, (ii) the self-organization of left-handed Z-DNA with alternat ing [dC-dG] sequences in the solid state, and (iii) the binding of pyridini um derivatives with single- and double-stranded DNA. Slightly attractive in teractions occur between the donor ether and phosphate moieties and a neutr al pyridine molecule in the gas phase. Electrostatic potential and solvatio n calculations demonstrate that [C-H . . .O] interactions which involve a c ationic [C-H] donor are dominated by electrostatic terms.