Hydrogen-Bond Cooperativity in Formamide2–Water: A Model for Water-Mediated Interactions

Abstract

The rotational spectrum of formamide2-H2O formed in a supersonic jet has been characterized by Fourier transform microwave spectroscopy. This adduct provides a simple model of water mediated interaction involving the amide linkages, as occur in protein folding or amide association processes, showing the interplay between self-association and solvation. Mono-substituted 13C, 15N, 18O and 2H isotopologues have been observed to investigate the structure. The adduct forms an almost planar three body sequential cycle. The two formamide molecules link on one side through an N-H···O hydrogen bond and on the other side through a water-mediated interaction with the formation of C=O···H-O and O···H-N hydrogen bonds. The analysis of the quadrupole coupling effects due to the presence of two 14N-nuclei reveal the subtle inductive forces associated to cooperative hydrogen bonding. These forces are involved in the changes detected in the C=O and C-N bond distances with respect to bare formamide.