UNRAVELLING THE CONFORMATIONAL LANDSCAPE OF NICOTINOIDS: THE STRUCTURE OF COTININE BY BROADBAND ROTATIONAL SPECTROSCOPY

begin{wrapfigure}{i}{0pt} includegraphics[scale=0.2]{conf2_conf4.eps} end{wrapfigure} Alkaloids such as nicotine, cotinine or anabasine share a common floppy structural motif consisting of a two-ring assembly with a 3-pyridil methylamine skeleton. In order to investigate the structure-activity relationship of these biomolecules, structural studies with rotational resolution have been carried out for nicotinefootnote{J.-U. Grabow, S. Mata, J. L. Alonso, I. Pe�a, S. Blanco, J. C. L�pez, C. Cabezas, textit{Phys. Chem. Chem. Phys.} 2011, textbf{13}, 21063.} and anabasinefootnote{A. Lesarri, E. J. Cocinero, L. Evangelisti, R. D. Suenram, W. Caminati, J.-U. Grabow, textit{Chem. Eur. J.} 2010, textbf{16}, 10214.} in the gas phase, where these molecules can be probed in an �interaction-free� environment (no solvent or crystal-packing interactions). We hereby present a structural investigation of cotinine in a jet expansion using the chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer recently built at the University of the Basque Country (UPV-EHU). The rotational spectrum (6-18 GHz) reveals the presence of two different conformations. The conformational preferences of cotinine originate from the internal rotation of the two ring moieties, the detected species differing in a near $180^{circ}$ rotation of pyridine. The final structure is modulated by steric effects