ORIGINAL PAPER B 12 -induced formation of stishovite in sol–gel produced amorphous SiO 2 matrices E. Espericueta • J. R. Martı ´nez • A. L. Guerrero-Serrano • G. Ortega-Zarzosa • J. Gonza ´lez-Herna ´ndez Received: 7 September 2010 / Accepted: 7 May 2011 Ó Springer Science+Business Media, LLC 2011 Abstract Composites containing vitamin B 12 (cyanoco- balamin) dispersed in amorphous silica xerogel were studied structurally as a function of annealing temperature. Silica xerogel samples were prepared by the sol–gel method using an ethanol:H 2 O:TEOS molar ratio of 4:11.6:1 and loaded with cyanocobalamin. We found that the structure of the cobalamin is unaltered, although dec- oordination of the benzimidazole nucleobase of B 12 , whereas the amorphous quartz structure of the matrix is maintained under heat-treatment without low-cristobalite phase transformation, typically of this kind of materials. We found in our samples partial crystallization of the glass matrix in form of stishovite obtained at very lower pressure than those specified by the phase diagram, and tempera- tures about 400 °C due to the presence of vitamin B 12 . The presence of stishovite is corroborated by the Rietveld refinement method. Keywords Stishovite Á Sol–gel Á Cyanocobalamin Á Rietveld refinement Á Structure 1 Introduction Metal porphyrins are molecules present in nature, such chlorophyll and heme systems. Cobalt (III) porphyrin is present in vitamin B 12 . Among the use in drug released systems, these kinds of porphyrins have numerous optical, electrical and catalytic properties. Porphyrins are naturally occurring organic tetrapyrrole macrocycles composed of four pyrrole-type rings joined by methylidene bridges. Metal complexed porphyrins and other biological porphyrin-type molecules like vitamin B 12 have several properties that make them very appealing for the treatment of persistent organic pollutants. Much recent work has established that encapsulation of biofunctional molecules and porphyrins in sol–gel glasses are highly effective in the development of biocatalyst and biosensors [1–5]. In order to fully exploit the interesting properties in some cases it is necessary to implant them in appropriate solid supports. The sol–gel method has the ability to incorporate organic molecules in inorganic metal oxide matrices at low temperature [6–8]. The incorporation of the organic molecules is done in the starting solutions before it gels. Few works have been realized with cyanocobalamine dispersed in silica xerogel matrix, mainly focused to utilize as biomimetic catalyst system with the manufacture of an inorganic–organic hybrid nanocomposite, via a sol–gel reaction in the presence of porphyrin, for the dechlorination of chloro-organic compound. Besides their practical applications, these kinds of nanocomposites are very E. Espericueta Facultad de Ingenierı ´a, Universidad Auto ´noma de San Luis Potosı ´, 78000 San Luis Potosı ´, Me ´xico E. Espericueta Á A. L. Guerrero-Serrano Á J. Gonza ´lez-Herna ´ndez Centro de Investigacio ´n en Materiales Avanzados, Chihuahua, Chih, Me ´xico J. R. Martı ´nez Á A. L. Guerrero-Serrano Á G. Ortega-Zarzosa Facultad de Ciencias, Universidad Auto ´ noma de San Luis Potosı ´, 78000 San Luis Potosı ´, Me ´xico J. R. Martı ´nez (&) Departamento de Fı ´sico-Matema ´ticas, Universidad Auto ´ noma de San Luis Potosı ´, 78000 San Luis Potosı ´, Me ´xico e-mail: flash@fciencias.uaslp.mx 123 J Sol-Gel Sci Technol DOI 10.1007/s10971-011-2486-8