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Preparation of drug-montmorillonite UV-radiation protection compounds by gas-solid adsorption

C. del HOYO^1,2, M. A. VICENTE^2,3, and V. RIVES^1,2,*

¹ Departamento de Química Inorgánica, Universidad de Salamanca, 37008-Salamanca, Spain, ² Unidad Asociada IRNASA(CSIC)-Universidad de Salamanca, c/Cordel de Merinas, s/n, 37008-Salamanca, Spain, and ³ Instituto de Recursos Naturales y Agrobiología, Consejo Superior de Investigaciones Científicas,c/Cordel de Merinas, s/n, 37008-Salamanca, Spain

^* E-mail: vrives{at}gugu.usal.es

(Received 15 June 2000; revised 12 February 2001)

Ethyl cinnamate/montmorillonite intercalation complexes were obtained by gaseous adsorption of the drug on the clay surface. They were characterized by powder X-ray diffraction, differential thermal and thermogravimetric analyses and by visible-UV and IR spectroscopies. It was found that after 1 day of adsorption, most of the drug enters the interlayer space of the clay by substitution of water molecules, and is removed only after heating at high temperature. In addition, a portion is physisorbed on the external surface of the crystallites, being removed easily below 100°C. The interlayer complex improves the protecting ability of the pure clay or the pure drug against ultraviolet radiation, specially in the so-called ‘C’ range (290–190 nm).

KEYWORDS: montmorillonite, ethyl cinnamate, drug-clay interaction, gas-solid adsorption, UV radiation protection