Dual binding mode of methylmethanetriacetic Acid to tripodal amidopyridine receptors.
A series of tripodal amidopyridine receptors capable of selective recognition of methylmethanetriacetic acid (MMTA) in organic solvents is described. Intramolecular hydrogen-bonding groups, built into some of the receptors, were designed as preorganization devices. Binding was studied by NMR titration, variable temperature NMR experiments, 2D-NMR, isothermal titration calorimetry, and single-crystal X-ray crystallography. The results reveal that a balancing act between inter- and intramolecular hydrogen-bonding interactions in the complexes governs both the dynamics and the geometry of binding. Receptor 1b (without intramolecular hydrogen-bonding groups) features a simple symmetric MMTA binding geometry with optimal enthalpic interactions. In sharp contrast, receptor 1a (with intramolecular hydrogen-bonding groups) reveals a temperature-dependent dual binding mode where MMTA can bind in two completely different geometries. The two solution binding geometries of 1a.MMTA were unraveled by NMR experiments and correlated to the X-ray structures.
Ballester
Pablo
P
Departament de Química, Universitat de les Illes Balears, 07071 Palma de Mallorca, Spain. paub@scripps.edu
Capó
Magdalena
M
Costa
Antoni
A
Deyà
Pere M
PM
Gomila
Rosa
R
Decken
Andreas
A
Deslongchamps
Ghislain
G