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.

13C longitudinal relaxation time measurements and DFT-GIAO NMR computations for two ammonium ions of a tetraazamacrocyclic scorpiand system

“…On the other hand, one could discuss about two other events affecting the protonated states of amine 1 , namely, (i) supporting H-bonding of type C–H⋯O − –N found in some crystal structures [49 and refs therein] as an equivalent of interactions C–H⋯O − –X (where X = C or P) known from NMR pH-titrations of some biomolecules in aqueous media [50, 51 and refs therein]. Its presence causes ‘wrong-way’ changes in the δ H and δ P data upon protonation to a higher and lower magnetic field, respectively.…”

Conformational and Cs+complexation properties of norbadione-A: a molecular modeling study

“…25 This contrasts with the high sensitivity of d(H 8 ) to changes of the protonation state in some cases, following experimental observations. 7 7 The QM calculations on the pulvinic Pulv2 and Pulv3 species predict that in their neutral states they should prefer the E form. There is no experimental evidence in solution, but the X-ray structure of Pulv3 has been solved, 29 showing that the molecule is also in the E form with an internal hydrogenbond, and the corresponding O enol Á Á ÁO COOMe distance (2.507 Å ) is close to our optimized value (2.587 Å ).…”

“…These results are consistent with the NMR titration results which indicate that the norbadione must be tetradeprotonated to complex two Cs + cations. 7 The remaining Cs + cation coordinates to NBA 2À either via the carboxylate group of one arm (E/E conformer of the NBA enol 2À ), the enol group of one arm and the ketone group (Z/Z conformers of NBA enol 2À and NBA COOH 2À ), or the acid group of one arm and the enolate group of the other arm (E/E isomer of NBA COOH 2À ) (see Fig. 5).…”

“…markedly deshielded (by Dd E 1 ppm), H 9 /H 9 0 and H 11 /H 11 0 protons are somewhat shielded (Dd E À0.3 ppm), whereas H 8 0 and the CH 3 anisole protons are quasi-unchanged. We thus mainly focus on the H 8 protons for which Kuad et al7 observed a marked downfield shift Dd in both Pulv2 (Dd E 0.6 ppm) and Pulv3 (Dd E 0.25 ppm) molecules upon full deprotonation of their OH groups, at pH values above 9.5 and 5 respectively.As seen inTables 1 and 3, d(H 8 ) is very sensitive to the protonation state, but not to the Z 2 E isomerisation if one considers the most stable forms 25. For Pulv2, at low pH (Pulv2 0 form), d(H 8 ) is about 7.8 ppm for both Z and E isomers.…”

scyllo‐Inositol Pentakisphosphate as an Analogue of myo‐Inositol 1,3,4,5,6‐Pentakisphosphate: Chemical Synthesis, Physicochemistry and Biological Applications

“…More details of the fitting procedure are provided elsewhere. [25,33,34] Cloning of human Ins(1,3,4,5,6)P 5 2-kinase: The gene encoding human Ins(1,3,4,5,6)P 5 2-kinase was amplified by PCR by using a TrueClone human full-length cDNA clone (OriGene) as template. The upstream primer was 5'-GGGGACAAGTAGTTTGTACAAAAAAG-CAGGCACCATGGAAGAGGGGAAGATGGACG-3', and the downstream primer was 5'-GGGGACCACTTTGTACAAGAAAGCTGGTTA-GACCTTGTGGAGAACTAATG-3'.…”