Best dioctahedral smectite for nitrogen heterocyclics adsorption - A reactivity index study

The activity of nitrogen heterocyclics present in biomacromolecules and its suitable sorbent from the dioctahedral smectite family is investigated usi ng a range of reactivity index using density functional theory (DFT). For t he first time, a novel function A has been defined for quantitative descrip tion of weak adsorption cases, which was so far qualitative inside the doma in of DFT. From the values of the local softness, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics, which are of importance within the framework of the hard a nd soft acids and bases (HSAB) principle. We first rationalized an understa nding of the electronic structures of a range of nitrogen heterocyclics ran ging from indole, imidazole, pyrrole, and pyridine, followed by the local s oftness calculation to locate its active site. We compared its activity wit h that of the OH group of isomorphously substituted (Fe3+, Mg2+, Fe2+ and L i+) dioctahedral smectite family. Two types of interactions were identified between heterocyclics and smectite. The ordering for best sorption follows the order Mg2+ > Fe2+ > Fe3+ > Li+, whereas the order for best sorbent is imidazole > pyridine > pyrrole > indole. The results rationalize the experi mental observation.