Rottman, C., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Turniansky, A., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Avnir, D., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Turniansky, A., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Avnir, D., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
We report the results of a comparative study of the properties of three azo dyes from the methyl red indicator family, which were coentrapped with the surfactant cetyltrimethylammonium bromide within tetramethoxysilane-derived silica sol-gel matrices. Characteristic parameters studied were spectral shifts, shifts in indicating ranges and in pK i values, isosbestic-point behavior, changes in the titration curves and stability to leaching. Physical entrapment of methyl red and para-methyl red (pMR) is compared to the covalent entrapment of a trialkoxysilane derivative of methyl red. High stability for leaching was found for all three entrapped indicators. The pK i change in entrapped pMR is interpreted in terms of intracage motion induced by pH changes.
