Communication: Where does the first water molecule go in imidazole?

Supersonic jet FTIR spectroscopy supplemented by O-18 substitution shows unambiguously that water prefers to act as an O-H center dot center dot center dot N hydrogen bond donor towards imidazole, instead of acting as a N-H center dot center dot center dot O acceptor. Previous matrix isolation, helium droplet, and aromatic substitution experiments had remained ambiguous, as are standard quantum chemical calculations. The finding is supported by a study of the analogous methanol complexes and by higher level quantum chemical calculations. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624841]