Laser Spectroscopic Study of β‑Estradiol and Its Monohydrated Clusters in a Supersonic Jet

Abstract

The structures of 17β-estradiol (estradiol) and its 1:1 cluster with water have been investigated in supersonic jets. The S₁–S₀ electronic spectrum of estradiol monomer shows four strong sharp bands in the 35050–35200 cm^–1 region. Ultraviolet–ultraviolet hole-burning (UV–UV HB) and infrared-ultraviolet double-resonance (IR-UV DR) spectra of these bands indicate that they are due to four different conformers of estradiol originating from the different orientation of the OH groups in the <i>A</i>- and <i>D</i>-rings. The addition of water vapor to the sample gas generates four new bands in the 34700–34800 cm^–1 region, which are assigned to the estradiol–H₂O 1:1 cluster with the <i>A</i>-ring (phenyl ring) OH acting as a hydrogen­(H)-bond donor. In addition, we found very weak bands near the origin bands of bare estradiol upon the addition of water vapor. These bands are assigned to the isomers of estradiol–H₂O 1:1 cluster having an H-bond at the <i>D</i>-ring OH. We determine the conformation of bare estradiol and the structures of its monohydrated clusters with the aid of density functional theory calculation and discuss the relationship between the stability of hydrated clusters and the conformation of estradiol