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 molecular conformers observed are both stabilized by an intramolecular hydrogen bond, located in the folded(gauche) OCCN side chain, which links the proton donor OH group to the terminal amino group and leads to a significant constriction of the side chain. In the dominant 1:1 water complex, the intramolecular hydrogen bond is disrupted by the first water molecule, which inserts between the OH group and the nitrogen atom, to forms cyclic H-bonded structure. The side chain expands significantly in order to accommodate the water molecule within the neighborhood of both the hydroxyl and amino groups.