Manipulation of intraparticle charge delocalization by selective complexation of transition-metal ions with histidine moieties.

Ruthenium nanoparticles were cofunctionalized with pyrene and histidine moieties through Ru═carbene π bonds. The selective complexation of the histidine moiety with transition-metal ions led to a marked diminishment of the emission peak at 490 nm which arose from the nanoparticle-bridged pyrene moieties that behaved analogously to pyrene dimers with a conjugated spacer. This is accounted for by the polarization of the core electrons by the added positive charge that impacted the intraparticle charge delocalization between the particle-bound pyrene moieties. This electronic interaction was likely facilitated by the π interactions between the metal ions and the imidazole ring as well as by the conjugated molecular backbone that linked the imidazole ring to the nanoparticle cores. Within the present experimental context, of all the metal ions tested, the impacts were much more drastic with Pb(2+), Co(2+), and Hg(2+) than with Li(+), K(+), Rb(+), Mg(2+), Ca(2+), and Zn(2+) ions, with the most sensitive variation observed with Pb(2+). This is ascribed to the enhanced π interactions of the histidine moiety with the Pb(2+), Co(2+), and Hg(2+) ions because of their capability of donating d electrons, a behavior consistent with prior studies based on conventional histidine-metal ion complexes.