Artículo de revista
Thermodynamic and geometric study of diasteroisomeric complexes formed by racemic flavanones and three cyclodextrins through NMR
Fecha
2013Registro en:
J Incl Phenom Macrocycl Chem (2013) 75:119–136
DOI 10.1007/s10847-012-0153-5
Autor
Acuña Rougier, C.
Olea Azar, Claudio
Institución
Resumen
The main purpose of this work was to study the
chiral recognition thermodynamics of inclusion complexes
formed by flavanones and b-cyclodextrins, and its relation
with the inclusion geometries, through NMR experiments.
By using the racemic mixtures of (±)-flavanone (FL) and
(±)-20-hydroxyflavanone (20OHFL), diasteroisomeric complexes
were formed employing b-cyclodextrin (bCD), (2-
hydroxypropil)-b-cyclodextrin (HPbCD) and heptakis-(2,
6-O-dimethyl)-b-cyclodextrin (DMbCD). 1H NMR experiments
of the complexes showed enantiodifferentiation for
FL/bCD, FL/HPbCD, FL/DMbCD, 20OHFL/HPbCD and
20OHFL/DMbCDcomplexes, so they were able to be studied
by obtaining the stoichiometry (1:1 for each complex),
association constants (Ka), Ka ratios, and thermodynamics
(DH, DS and DG). The results show that Ka values decrease
with increasing temperature and that Ka ratio values
removed from 1 not always reflect better enantiodiscrimination
by NMR. Thermodynamics (DH and DG) show an
exothermic and spontaneous formation of the complexes.
Since the results were established for each couple of diasteroisomeric
complexes separately, comparison of thermodynamics
between them was possible, concluding that one
half of the couples of diasteroisomeric complexes present
chiral recognition due to enthalpic phenomena and the other
half due to entropic phenomena. Additionally, ROESY
experiments were performed to estimate the inclusion
geometry of the complexes, which are in good agreement
with the thermodynamic and Ka results.