title: The exceptional hydrogen-bond properties of neutral and protonated lobeline.
abstract: The X-ray diffraction structure of (-)-lobeline, a high affinity nicotinic ligand, has been determined. A comparison with its hydrobromide and hydrochloride salts shows the great flexibility of the two lateral chains of the N-methylpiperidine ring. Infrared studies carried out on the same species, in the solid state and in solution, reveal the propensity of this molecular framework to accommodate very specific hydrogen bonds (HBs) depending on the state-neutral or protonated-of the molecule. In solution, a strong internal HB between the hydroxyl group and the piperidine nitrogen gives an exceptionally high HB affinity to the hydroxyl oxygen of the lobeline base. In the ionic form, both NH+ and OH groups of the molecule cooperate as HB donors to chelate the counterion. These interactions provide very stable structures and indicate that protonated lobeline can also act as a strong HB donor.
authors.affiliation: Laboratoire de Spectrochimie et Modélisation (EA 1149, FR 2465), Université de Nantes, Nantes Atlantique Universités, Faculté des Sciences et des Techniques de Nantes, 2, rue de la Houssinière, BP 92208, F-44322 Nantes Cedex 3, France.
authors.forename: Abel
authors.initials: A
authors.lastname: Locati
authors.forename: Michel
authors.initials: M
authors.lastname: Berthelot
authors.forename: Michel
authors.initials: M
authors.lastname: Evain
authors.forename: Jacques
authors.initials: J
authors.lastname: Lebreton
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Le Questel
authors.forename: Monique
authors.initials: M
authors.lastname: Mathé-Allainmat
authors.forename: Aurélien
authors.initials: A
authors.lastname: Planchat
authors.forename: Eric
authors.initials: E
authors.lastname: Renault
authors.forename: Jérôme
authors.initials: J
authors.lastname: Graton
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007536:Isomerism; D008024:Ligands; D008120:Lobeline / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D018722:Nicotinic Agonists / Q000737:chemistry*; D011522:Protons; D012996:Solutions
chemical_list: D008024:Ligands; D018722:Nicotinic Agonists; D011522:Protons; D012996:Solutions; D008120:Lobeline