Inframolecular protonation process of norbadione A: influence of the ionic environment and stereochemical consequences.
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.
Kuad
Paul
P
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.
Borkovec
Michal
M
Desage-El Murr
Marine
M
Le Gall
Thierry
T
Mioskowski
Charles
C
Spiess
Bernard
B
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
D010648:Phenylacetates; D011522:Protons; C464564:norbadione A; D015107:4-Butyrolactone