Preparation and solid state NMR characterization of phosphonates encapsulated in raw and organically modified SBA-15
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1227-JJ04-06
Preparation and solid state NMR characterization of phosphonates encapsulated in raw and organically modified SBA-15 Thierry Azais1, Daniela Aiello2, Flaviano Testa2, Guillaume Laurent1, and Florence Babonneau1 Laboratoire Chimie de la Matière Condensée de Paris, Université Paris 6 – CNRS, UMR 7574 Collège de France, Paris, 75005, France. 2 Department of Chemical Engineering and Materials, CR-INSTM, University of Calabria, 87036 Arcavacata di Rende (CS), Italy. 1
ABSTRACT We present in this communication the preparation and the solid state NMR characterization of phenyl phosphonic acid encapsulated both in pure and aminopropyl-modified SBA-15 mesoporous silica materials. The 31P and 1H MAS studies revealed two radically different behaviors of the confined molecules. The included phosphonic acid in SBA-15 is submitted to a confinement effect that implies a weak interaction with the SiO2 surface and a relative mobility at room temperature. On the contrary, phenyl phosphonic acid molecules in the aminopropyl modified sample possess a strong interaction with the hybrid surface of the material. This finding is supported by a two dimensional double-quantum 1H experiment that revealed the close proximity between phenyl phosphonic acid and aminopropyl surface groups. INTRODUCTION Ordered mesoporous silica matrices are a class of materials highly attractive in reason of a high porous volume associated to a high specific area (up to 1000 m2.g-1). Since 2001, their textural characteristics are widely used in order to store and release drug molecules [1].Up to now many studies have been done on different micelles templated silica materials such as MCM41 or SBA-15 [2]. In particular, it has been shown that a functionalization of the pore surface can provide a control of the drug release kinetic [3]. Recently, similar drug delivery systems have been designed with alendronate, a drug that belongs to the class of bisphosphonates that inhibit bone resorption and consequently help fight osteoporosis. It has been shown that the modification of the siliceous pore surface with aminopropyl groups allows to optimize the amount of the encapsulated drug and to tune drug release kinetic [4]. The kinetic properties of these drug release systems seem to be linked to the physical state of the confined molecules and its chemical interaction with the pore surface [5]. Nevertheless, the relationship between release properties and chemical properties is still not well understood and for this reason we choose to study phenyl phosphonic acid as a model-molecule for bisphosphonates, confined in pure and aminopropyl-modified SBA-15. We characterized these materials by means of solid state NMR which is a perfect tool to differentiate different physical state of a drug and also to probe hostguest interactions [6]. In particular we studied in details the inclusion of phenyl phosphonic acid through 31P and 1H MAS NMR experiments that revealed different physical behavior for the guest molecules depending on the chemical nature of the porous s
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