The structures of estrogens (estrone, β-estradiol, estriol) and their 1:1 hydrogen-bonded (hydrated) clusters with water formed in supersonic jets have been investigated by various laser spectroscopic methods and quantum chemical calculations. In the S1-S0 electronic spectra, all the three species exhibit the band origin in the 35050－35200 cm-1 region. By applying ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy, two conformers, four conformers and eight conformers, arising from different orientation of OH group(s) in the A-ring and D-ring, were are identified for estrone, β-estradiol, and estriol, respectively. The Infrared-ultraviolet double resonance (IR-UV DR) spectra in the OH stretching vibration were observed to discriminate different conformers of the D-ring OH for β-estradiol and estriol, and it is suggested that in estriol only the intramolecular hydrogen bonded conformer exists in the jet. For the 1:1 hydrated cluster of estrogens, the S1-S0 electronic transition energy is quite different depending on whether the water molecule is bound to A-ring OH or D-ring OH. It is found that the water molecule prefers to form an H-bond to the A-ring OH for estrone and β-estradiol due to the higher acidity of phenolic OH than that of the alcoholic OH. On the other hand, in estriol the water molecule prefers to be bound to the D-ring OH due to the formation of a stable ring-structure H-bonding network with two OH groups. From these results, we conclude that estriol has a hydrogen bonding ability quite different from that of β-estradiol although their difference is just only one substituent.

This is a preprint of an article published by American Chemical Society in Journal of Physical Chemistry A, 2013, available online: http://pubs.acs.org/doi/abs/10.1021/jp407438j.