title: Inframolecular protonation process of norbadione A: influence of the ionic environment and stereochemical consequences.
abstract: The microscopic protonation mechanism, at an inframolecular level, of norbadione A, a pigment extracted from mushrooms and known to complex cesium cations, was determined by using 1H NMR titrations and the cluster expansion method. This study revealed a pH dependent Z to E isomer switch that occurs in both pulvinic moieties. As a consequence, norbadione A can exist in solution in four stereomeric forms (E-E, E-Z, Z-E, and Z-Z), which can be of interest in the development of molecular-level devices. In the presence of 0.15 M NaCl, the calculated microconstants showed an unusual apparent cooperativity between the enol groups, which results from the release of the sodium cations upon protonation of norbadione A.
authors.affiliation: Laboratoire de Pharmacochimie de la Communication Cellulaire, UMR 7081 du CNRS, Université Louis Pasteur, Faculté de Pharmacie, 74, route du Rhin, 67401 Illkirch Cedex, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Kuad
authors.forename: Michal
authors.initials: M
authors.lastname: Borkovec
authors.forename: Marine
authors.initials: M
authors.lastname: Desage-El Murr
authors.forename: Thierry
authors.initials: T
authors.lastname: Le Gall
authors.forename: Charles
authors.initials: C
authors.lastname: Mioskowski
authors.forename: Bernard
authors.initials: B
authors.lastname: Spiess
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D010648:Phenylacetates / Q000737:chemistry*; D011199:Potentiometry; D011522:Protons; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
chemical_list: D010648:Phenylacetates; D011522:Protons; C464564:norbadione A; D015107:4-Butyrolactone