Density functional theory study on hydrogen‐bonded complexes of adenine with polyformamide molecules

The structures of hydrogen‐bonded complexes A–F_n (n = 2–7) of adenine with polyformamide molecules have been fully optimized at B3LYP/6‐31G(d) basis set level. All the formamide molecules prefer to be N? H proton donor rather than C? H proton donor and are favorably bound to the five‐numbered moiety of adenine. A displacement of formamide molecules to one side of adenine mean plane has happened with an increasing number of formamide molecules. An obvious effect of hydrogen‐bonding cooperativity can be seen during the complex process. The most interesting geometrical change of adenine upon the complex is the shortening of the bond C4? N6 resulting from the strengthening of the conjugation between the π system of the adenine ring and the lone pair of the nitrogen atom. An existence of weak N? H···π bonding interaction between the π system of adenine and N? H bond of F7 is found and further conformed by an natural bond orbital analysis specially carried out on A–F₇. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008