Cryogenic infrared ion spectroscopy for the structural elucidation of drug molecules: MDMA and its metabolites.

We present a cryogenic infrared spectroscopy study of protonated 3,4-methylenedioxymethampetamine (MDMA) and some of its metabolites. The IR spectra are sufficiently well resolved to give distinct vibrational signatures for each molecule, as well as indicate common functional groups in some of the variants. A more detailed analysis reveals that the spectral interpretation is more complex. The overly rich IR spectra already betray the existence of a number of conformers, which are assigned by comparison to quantum-chemical calculations. An attempt to quantify the various conformers for MDMA was not successful, strongly suggesting that the conformers can freely interconvert at these cryogenic temperatures. Image 1 • Cryogenic IR ion spectroscopy reveals common features held by MDMA metabolites. • Increased resolution at cryogenic temperatures disambiguates key spectral features. • Complexity of spectra indicates a number of trapped conformers. • Attempts at conformer quantitation provide evidence for rapid interconversion. [ABSTRACT FROM AUTHOR]