The exceptional hydrogen-bond properties of neutral and protonated lobeline.
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.
Locati
Abel
A
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.
Berthelot
Michel
M
Evain
Michel
M
Lebreton
Jacques
J
Le Questel
Jean-Yves
JY
Mathé-Allainmat
Monique
M
Planchat
Aurélien
A
Renault
Eric
E
Graton
Jérôme
J
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
D008024:Ligands; D018722:Nicotinic Agonists; D011522:Protons; D012996:Solutions; D008120:Lobeline