Flexibility at the Fringes: Conformations of the Steroid Hormone β‐Estradiol

Abstract

We present the accurate experimental structure of the steroid hormone β-estradiol obtained with high-resolution rotational spectroscopy under the solvent free, isolated, and cold conditions of a molecular jet. This is the first time that the rotational signature of a steroid hormone is reported. β-Estradiol is a primary female sex hormone and features a rigid steroidal ring system. Three conformers could be identified in the cold environment of a supersonic molecular jet, which only differ in the orientation of the two hydroxy groups attached to the steroidal backbone. The conformers are almost isoenergetic and have very similar rotational constants but still could be clearly resolved and assigned. The high sensitivity of the technique allowed us to record and identify all singly substituted C isotopologues in natural abundance for the dominant conformer. The additional spectroscopic constants led to an accurate determination of its experimental molecular structure. Along with a previous comparison of β-estradiol structures in the solid state and the liquid phase, this study completes the investigations in all three main phases by providing the interaction free gas-phase structure.

Assessing the performance of rotational spectroscopy in chiral analysis

“…In the simplest case of a rigid-rotor molecule, the rotational spectrum of a molecule is characterised by the rotational constants, A, B, and C. These rotational constants are inversely proportional to the moments of inertia of the molecules so that a rotational spectrum strongly depends on the structure of the molecule. Different orientations of a particular side group with respect to the rest of the molecule, as in the case of b-estradiol, 31 for example, or the exchange of a 12 C by a 13 C isotope, result in different moments of inertia and thus in different rotational constants and spectra. The latter is routinely employed to obtain accurate experimental structures of molecules and molecular complexes via isotopic substitution.…”

Unexpected discovery of estrone in the rotational spectrum of estradiol: a systematic investigation of a CP-FTMW spectrum

“…Precise information on the structure and conformational landscape can be obtained from molecular spectroscopy in the gas phase, under isolated conditions and free of packing or solvent effects. In the gas phase, estradiol-17b has been studied by laser-spectroscopy methods 13,14 and rotational spectroscopy, 15 both coupled with supersonic expansion. Using laser spectroscopy, four conformers were detected out of the six possible forms arising from the rotation of both -OH groups.…”

“…The observed spectral features were tentatively assigned to specific conformers based on the comparison of the electronic transition energies and IR spectra of the position of the -OH stretching bands with the calculated ones. 13,14 In the rotational spectroscopy work three conformers were unambiguously identified, 15 since even small structural changes lead to clear differences in the rotational spectrum. For estrone, two bands were observed in the experiment performed in the gas phase using laser spectroscopy.…”

Shape of Testosterone

“…Its rotational spectrum has been recently reported, and three conformers have been characterized. 11 In a first attempt, we tried to measure the rotational spectrum of testosterone through heating, but no spectral signature was obtained. This problem can be overcome by using laser ablation techniques, which have proven to be successful for many biomolecules.…”