Hydrogen bonding between amino acid backbone and side chain analogues: A high-level ab initio study

We have carried out calculations of hydrogen-bonding structures and energies, using the pseudospectral local MP2 methodology and a high-quality triple zeta basis set for a large set of amino acid side chain analogues. Both neutral and charged amino acid analogues are examined, and interactions between donors and the pi electron acceptor moiety in a benzene ring are considered. A total of > 140 structures have been studied, representing all possible hydrogen-bonding interactions between a set of 11 amino acid side chain analogues. The effects of electron correlation, basis set size, and basis set superposition error are analyzed in detail for this data set. A particular focus of the paper in terms of chemically interesting effects is the influence of resonance interactions upon hydrogen-bonding strength, which is elucidated quantitatively for a significant number of donor-acceptor pairs. Finally, it is observed that donors and accepters fall into "strong" and "weak" categories, with the weak species severely damping the variation in hydrogen-bonding strength as the partner donor or acceptor is varied.