CrossRef enabled

PAC Archives

Archive →

Pure Appl. Chem., 2009, Vol. 81, No. 8, pp. 1345-1355

Published online 2009-07-19

Solid-state NMR characterization of drug-model molecules encapsulated in MCM-41 silica

Thierry Azaïs1, Geoffrey Hartmeyer1, Sandrine Quignard1, Guillaume Laurent1, Corine Tourné-Péteilh2, Jean-Marie Devoisselle2 and Florence Babonneau1*

1 Université Pierre et Marie Curie-Paris6 and CNRS, UMR 7574, Laboratoire Chimie de la Matière Condensée de Paris, Paris, F-75005, France
2 UMR 5253 CNRS/ENSCM/UM2/UM1, Institut Charles Gerhardt Montpellier, 8 rue de l'Ecole Normale, 34296 Montpellier Cedex 5, France

Abstract: In this contribution, we present a solid-state NMR approach to characterize drug-model molecules as ibuprofen, benzoic acid and lauric acid, encapsulated in MCM-41 silica and submitted to strong confinement effects. In particular, we show that by a careful choice of the solid-state NMR sequences, it is possible to efficiently characterize these highly mobile molecules and their interactions with the pore surface. Thus, we demonstrate that 13C NMR spectroscopy is a powerful tool to characterize and even quantify entrapped and non-entrapped species by using either single-pulse excitation (SPE) or cross-polarization (CP). Whereas the standard {1H}-13C CP experiment is of poor efficiency for mobile species, we show that 13C signal-to-noise (S/N) ratio can be significantly improved through 1H-13C cross-relaxation (namely, nuclear Overhauser effect, nOe) by using a 1H power-gated technique. The long transversal relaxation times [T2(1H) up to 22 ms] observed allow the set-up of J-coupling based experiments such as 2D {1H}-13C heteronuclear multiple-quantum coherence (HMQC) in order to fully characterize the encapsulated molecules. Thus, we demonstrate that the use of sequences derived from solution-state NMR such as these two latter experiments is highly efficient to characterize highly mobile organic molecules trapped in mesopores. Finally, we show that 1H spin diffusion-based experiments can give useful informations on the proximities between trapped molecules and the silica surface.