Silica imprinted materials containing pharmaceuticals as a template: textural aspects
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ORIGINAL PAPER
Silica imprinted materials containing pharmaceuticals as a template: textural aspects Everton C. Morais • Gabriel G. Correa • Rodrigo Brambilla • Paolo R. Livotto • Joa˜o Henrique Z. dos Santos • Mateus Borba Cardoso
Received: 25 May 2012 / Accepted: 4 August 2012 / Published online: 17 August 2012 Ó Springer Science+Business Media, LLC 2012
Abstract Silica-based materials were prepared by the acid catalyzed sol–gel method using different pharmaceuticals as a template. The template molecules investigated were fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol and tetracycline. The resulting hybrid silicas underwent ultrasound extraction in the presence of several solvents and were characterized by elemental analysis, porosimetry by adsorption/desorption of nitrogen (BET method), small-angle X-ray scattering and X-ray diffraction. Drug extraction was carried out by the combination of solvent and ultra-sound. The textural characteristics of the hybrid xerogels and resulting imprinted materials were shown to be highly dependent on the molecular weight and molecular volume of the drug template. Increasing the molecular weight of the template results in a decrease in the encapsulation content of the resulting material. In the case of paracetamol and fluoxetine, the dimensions of the surface area are not sufficient to guarantee the adsorption of the smaller molecule. Instead, the shape generated through encapsulation and extraction during the production of the imprinted silica dictates the adsorption behavior. Keywords Molecular imprinting Pharmaceuticals Silica Sol–gel Adsorption
E. C. Morais G. G. Correa R. Brambilla P. R. Livotto J. H. Z. dos Santos (&) Instituto de Quı´mica, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc¸alves, 9500, Porto Alegre 91501-970, Brazil e-mail: [email protected] M. B. Cardoso Laborato´rio Nacional de Luz Sı´ncrotron, Caixa Postal 6192, Campinas, SP CEP 13083-970, Brazil
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1 Introduction The development of molecular imprinted materials is an area of intense research. Materials with tailor-made pore sizes and shapes can potentially be used for molecular recognition in processes such as adsorption [1], chemical sensing [2], pre-concentration [3], electroanalytical measurements [4], catalysis [5], and drug delivery [6]. The majority of systems developed by molecular imprinting have been based on organic polymers. Fewer studies have been devoted to inorganic polymers, which are usually produced by the sol–gel technique [7]. One example of an inorganic system that has been studied is a titanate sol–gel layered system with mid-chain carbonic acids. This system was shown to be effective in the selective incorporation of oxidized base oil components [8]. Templated silica-based materials prepared by the sol– gel technique have also been described in the literature using either immobilized peptides [9] or ibuprofen [10] as a template. Drug imprinted systems are an important class of molecular imprinted materials. Recent examples of suc
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