Effect of surface properties of mesoporous silica on adsorption of mesoionic compound molsidomine
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Molsidomine is one of the sydnonimine class of antianginal drugs that due to its structure exhibits both dipolar nature and aromatic properties. To select efficient carrier for the drug, unmodified and modified mesoporous silica materials were synthesized using phenyltriethoxysilane and 3-aminopropyltriethoxysilane via cocondensation and grafting routes. Synthesis of the mesoporous silica materials via cocondensation was carried out in the presence of D-glucose as pore-forming agent. Equilibrium isotherms for the adsorption of mesoionic compound molsidomine on the mesoporous silica materials were analyzed by the Langmuir, Freundlich, Redlich-Peterson and Langmuir–Freundlich (Sips) models. Langmuir model is found to be the best to explain the equilibrium data. Comparative study of the adsorption properties of the unmodified and modified mesoporous silica materials demonstrated that the phenyl-modified silica materials are the most efficient adsorbents for molsidomine. They exhibit the highest adsorption capacity and affinity in relation to the mesoionic compound.
I. INTRODUCTION
Mesoporous silica materials have been extensive research subjects due to their potential applications in the fields where porosity plays an important role. One such field is the development of controlled drug delivery matrixes.1–3 Unique combination of useful properties of mesoporous silica materials (stable pore structure and high surface area, easy surface modification by functionalized molecules and adjustable pore size, biocompatibility, biological inertness, etc.) makes them suitable carriers for different therapeutic applications. Efficient drug delivery systems allow improvement of therapeutic index and consumer properties of the drugs. Molsidomine [N-(ethoxycarbonyl)-3-(4-morpholino) sydnonimine (Fig. 1)] is a drug possessing vasodilating and antiplatelet activity that is used clinically. We proposed that efficient silica carrier may improve its pharmacokinetic and consumer properties. The drug is a mesoionic compound containing five-member heterocycle and exhibits pseudoaromatic properties.4,5 Therefore, p-p interaction should play an important role in adsorption of molsidomine. Phenyl-modified silica was used for liquid chromatography determination of sydnonimines in human plasma.6 On the other hand, molsidomine molecules have a large dipole moment.4 So, their dipolar nature should favor strong hydrophilic interactions (e.g., electrostatic, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.329 2858
J. Mater. Res., Vol. 27, No. 22, Nov 28, 2012
http://journals.cambridge.org
Downloaded: 11 Mar 2015
ion-dipole, hydrogen bonding with participation of N and O atoms).7 The aim of this work was to elucidate the nature of interactions responsible for the adsorption process of molsidomine onto mesoporous silica particles to select optimal silica material for further development of the drug carrier. For this purpose, unmodified, aminopropylmodified and phenyl-modified silica materials were synthesized and charac
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