Base pair analogs in the gas phase

A rotationally resolved electronic spectrum of the gas-phase dimer 2-aminopyridine-2-pyridone, an analog of the adenine-thymine base pair, has been observed and assigned, leading to precise measurements of its moments of inertia and preliminary determinations of its structure. A Watson-Crick configuration results, with N...H-N and N-H...O hydrogen bond lengths of 2.898 and 2.81o Angstrom, respectively. The two bases are found not to be coplanar; a dihedral angle of 6.1degrees between the base planes is also estimated from the measured moments of inertia. Possible chemical and biological implications of these results are discussed.