Exploring the dynamics of calix[4]pyrrole: effect of solvent and fluorine substitution.
Molecular dynamics simulations show that calix[4]pyrrole (CP) and octafluorocalix[4]pyrrole (8F-CP) are extremely flexible molecules. CP mainly adopts the 1,3-alternate conformation in all the solvents, although the percentage of alternative conformations increases in polar solvents, especially those with good hydrogen-bonding acceptor properties. However, in the case of 8F-CP, the cone conformation is the most populated in some solvents. Transitions between conformers are common and fast, and both CP and 8F-CP can adopt the cone conformation needed for optimum interaction with anions more easily than would be predicted on the basis of previous gas-phase calculations. Furthermore, the present studies show that when a fluoride anion is specifically placed initially in close proximity to CP and 8F-CP in their respective 1,3-alternate conformations, an extremely fast change to the cone conformation is observed in both cases. The results suggest that preorganization does not represent a major impediment to anion-binding for either CP or 8F-CP, and that ion-induced conformational changes can follow different mechanisms depending on the solvent and the chemical substituents present on the calix[4]pyrrole beta-pyrrolic positions.
Blas
J Ramón
JR
Molecular Modeling and Bioinformatics Unit, Institut de Recerca Biomèdica, Parc Científic de Barcelona, Josep Samitier 1-5, Barcelona 08028, Spain.
López-Bes
Jose Maria
JM
Márquez
Manuel
M
Sessler
Jonathan L
JL
Luque
F Javier
FJ
Orozco
Modesto
M
D047250:Calixarenes / Q000737:chemistry*; D005461:Fluorine / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry*
D011166:Porphyrins; D012997:Solvents; C469811:calix(4)pyrrole; D047250:Calixarenes; D005461:Fluorine