Periodic first principle calculation correlates the role of metal substitution (Sr and Ba in place of Ca) on selective encaging of active O- radicals inside the microporous 12MO, 7Al(2)O(3) crystal structure. We have exchanged Ca by Sr and Ba and as well extracted electron stepwise to monitor selectivity of different anion encaging inside the same structure type. Ca favors O2- encaging and shows no electron transition when neutral, whereas Sr shows no transition in absence of unpaired electron and can successfully trap O-, Ba though less active than the other metal substituents shows oxygen encaging at its zero and mono-positive state. (C) 2004 Elsevier B.V. All rights reserved.