title: Adsorption and release of ampicillin antibiotic from ordered mesoporous silica.
abstract: In this work the adsorption and the release of ampicillin - a β-lactam penicillin-like antibiotic - from MCM-41, SBA-15, and (amino functionalized) SBA-15-NH2ordered mesoporous silica (OMS) materials were investigated. The silica matrices differ for their pore size (SBA-15 vs. MCM-41) mainly, and also for surface charge (SBA-15 and MCM-41, vs. SBA-15-NH2). OMS samples were characterized through small-angle X-rays scattering (SAXS), transmission electron microscopy (TEM), N2adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and potentiometric titrations. The quantification of immobilized and released ampicillin was monitored by mean of UV-Vis spectroscopy. Experimental adsorption isotherms evidenced that ampicillin's loading is not related to the pore size (dBJH) of the adsorbent. Indeed the maximal loadings were 237mg/g for SBA-15 (dBJH=6.5nm), 278mg/g for MCM-41 (dBJH=2.2nm), and 333mg/g for SBA-15-NH2(dBJH=5.6nm). Loading seems, instead, to be related to the surface charge density (σ) of the sorbent surface. Indeed, at pH 7.4 ampicillin drug is negatively charged and likely prefers to interact with SBA-15-NH2(σSBA-15-NH2=+0.223Cm-2) rather than the slightly negatively charged silicas (σSBA-15=-0.044Cm-2and σMCM-41=-0.033Cm-2). Similarly, ampicillin release is affected by interfacial interactions. Indeed, we found a burst release from pure silica samples (SBA-15 and MCM-41), whereas a sustained one from SBA-15-NH2sample. We explain this behavior as a result of an attractive interaction between the protonated amino group of SBA-15-NH2and the negatively charged carboxylate group of ampicillin. In summary, in order to obtain a sustained drug release, the chemical nature of the matrix's surface plays a role which is more important than its textural features. SBA-15-NH2matrix is hence a suitable candidate for local sustained release of antibiotic drugs.
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari-CSGI and CNBS, Cittadella Universitaria, S.S. 554 bivio Sestu, 09042 Monserrato, CA, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Nairi
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari-CSGI and CNBS, Cittadella Universitaria, S.S. 554 bivio Sestu, 09042 Monserrato, CA, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Medda
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari-CSGI and CNBS, Cittadella Universitaria, S.S. 554 bivio Sestu, 09042 Monserrato, CA, Italy. Electronic address: monduzzi@unica.it.
authors.forename: Maura
authors.initials: M
authors.lastname: Monduzzi
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari-CSGI and CNBS, Cittadella Universitaria, S.S. 554 bivio Sestu, 09042 Monserrato, CA, Italy. Electronic address: asalis@unica.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Salis
mesh_terms: D000327:Adsorption; D000667:Ampicillin / Q000032:analysis / Q000737:chemistry*; D000900:Anti-Bacterial Agents / Q000032:analysis / Q000737:chemistry*; D065546:Drug Liberation; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D012822:Silicon Dioxide; D000667:Ampicillin
keywords: Adsorption; Ampicillin; Drug delivery; Functionalization; Ordered mesoporous silica