Infrared ion dip spectroscopy of a noradrenaline analogue: Hydrogen bonding in 2-amino-1-phenylethanol and its singly hydrated complex

The conformational landscapes of 2-amino-1-phenylethanol and its 1:1 water complexes have been investigated by UV band contour, UV-W hole-burning, and IR-UV ion dip spectroscopy, coupled with ab initio computation. The two mo lecular conformers observed are both stabilized by an intramolecular hydrog en bond, located in the folded(gauche) OCCN side chain, which links the pro ton donor OH group to the terminal amino group and leads to a significant c onstriction of the side chain. In the dominant 1:1 water complex, the intra molecular hydrogen bond is disrupted by the first water molecule, which ins erts between the OH group and the nitrogen atom, to forms cyclic H-bonded s tructure. The side chain expands significantly in order to accommodate the water molecule within the neighborhood of both the hydroxyl and amino group s.