Colloids and Surfaces B: Biointerfaces 76 (2010) 421–426 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces journal homepage: www.elsevier.com/locate/colsurfb Adsolubilization of drugs onto natural clinoptilolite modified by adsorption of cationic surfactants Tania Farías a , Louis Charles de Ménorval b , Jerzy Zajac b , Aramis Rivera a,∗ a Zeolites Engineering Laboratory, Institute of Science and Technology of Materials (IMRE), University of Havana, Zapata y G s/n, 10400 Havana, Cuba b Institut Charles Gerhardt Montpellier, UMR-5253 CNRS-UM2, Equipe Agrégats, Interface, et Matériaux pour l’Energie (AIME), Université Montpellier 2, C.C. 1502 Place Eugène Bataillon, 34095 Montpellier Cedex 5, France article info Article history: Received 8 August 2009 Received in revised form 20 November 2009 Accepted 23 November 2009 Available online 27 November 2009 Keywords: Zeolitic support Clinoptilolite Cationic surfactant Drug adsolubilization abstract The combined adsorption onto purified natural clinoptilolite (NZ) of the cationic surfactant benzalko- nium chloride (BC) and the model drugs metronidazole and sulfamethoxazole has been studied in order to design systems for the storage and release of drugs. The equilibrium adsorption of benzyldimethy- lalkylammonium chloride surfactants with hydrocarbon chain lengths corresponding to 12, 14 and 16 carbon atoms (BC12, BC14 and BC16) onto NZ from aqueous solutions was compared to that of BC. The effect of exchangeable cations on the NZ structure and that of acid–base pre-treatment of NZ on the adsorption capacity of BC was evaluated. It was shown that the nature of the exchangeable cations had little influence on the adsorption of BC onto NZ, and that acid–base treatments of NZ led to a decrease in the amount of surfactant adsorbed. The results indicated that the adsorption of the less polar drug, sul- famethoxazole, was enhanced by the presence of BC12 at the solid–liquid interface, whereas the uptake of metronidazole was independent of the surfactant adsorption. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Zeolites have emerged as exciting materials for biomedical applications due to their adsorptive, ion-exchange, and catalytic properties [1]. In particular, natural clinoptilolite has been widely used for such purposes due to its physicochemical stability in biological environment [2]. The use of clinoptilolite as food sup- plement in animal nutrition was demonstrated as effective in decreasing the uptake of radionuclei [3] and reducing the nega- tive effect of aflatoxin [4,5]. Evidences for anti-tumor activity of clinoptilolite as well as its possible action mechanism have been also reported [6,7]. The results of Grce and Pavelic [8] showed the possibility of therapeutic application of micronized clinoptilolite, either locally against herpes virus infections of the skin or orally in the case of adenovirus or enterovirus infections. Purified natural clinoptilolite, NZ, from Tasajeras deposit (Cuba), was proven to keep its structural integrity during its passage through the stomach, and the pharmacological and clinical stud- ies evidenced no biological damage to humans in contact with this material [9–11]. The original zeolitic material and its various modified forms were tested as gastric antacids, anti-diarrheic, anti- microbial, anti-hyperglycemic and hypocholesterolemic products, ∗ Corresponding author. Tel.: +53 7 8327349; fax: +53 7 8794651/88956. E-mail address: aramis@fisica.uh.cu (A. Rivera). as well as matrices for the release of ions and organic molecules of pharmaceutical interest [9,11–18]. The adsorption of surfactants at the solid–liquid interface may modify the properties of the solid surface and favors the uptake from solution of molecules which do not adsorb onto the solid in the absence of surfactants. This phenomenon, known in the literature as surface solubilization, adsolubilization or co-adsorption, is a sur- face analogue of micelle solubilization [19–22]. Some researchers have already studied the modification of solid surfaces by surfac- tants in the context of their use for drug delivery. The modification of silica surface for the adsorption of propantheline, acetylsalicylic acid and codeine is worth mentioning here [23–25]. Alumina [26], polystyrene latex particles [27], and polymers [28,29] were also considered as potential substrates for the co-adsorption of surfac- tants and drugs. Nevertheless, only few papers could be found in the literature that explore the possibility of using zeolite-surfactant composites as drug carriers [21,30]. A novel potential application of NZ modified with surfactants as a drug delivery system was reported previously [16]. The adsorption of surfactants of different natures (cationic, anionic and nonionic) onto NZ, and the adsorption of two model drugs (metron- idazole and sulfamethoxazole) on the resulting NZ–surfactant composites were evaluated. This study gave strong indications that NZ adsorbs preferentially the cationic surfactant benzalkonium chloride (BC) and that the NZ–BC composites retain a considerable amount of drugs, in particular the one which is hardly soluble in water. Consequently, the NZ–BC composites were selected as good 0927-7765/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2009.11.018