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Issue 45, 2011
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Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins

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Noncovalent binding of fullerenes to bisporphyrins was studied in the gas phase by energy-dependent collision-induced dissociation (CID) with Xe under single-collision conditions. The electrospray ionization mass spectra of calix[4]arene-linked bisporphyrins show that bisporphyrins take up to 3–4 protons, depending on the type of meso-substituents. Of the protonated bisporphyrins, the diprotonated species form stable 1:1 complexes with fullerenes (C60 and C70). CID cracking patterns of the diprotonated bisporphyrins indicate that each monomeric porphyrin moiety is singly protonated. CID yield–energy curves obtained from the 1:1 diprotonated bisporphyrin–fullerene complexes suggest that a fullerene occupies the endo-binding site intercalated between the two singly protonated porphyrin moieties. In the cases of 1:2 diprotonated bisporphyrin–fullerene complexes, CID results show that one fullerene binds inside (endo-binding) and the other outside (exo-binding). The exo-binding mode is energetically almost identical to the binding of fullerenes to singly protonated porphyrin monomers. The endo-binding energy is at least twice the exo-binding energy. To gain insights into the binding mode, we optimized structures of diprotonated bisporphyrins and their 1:1 endo-complexes with fullerenes, and calculated the endo-binding energy for C60, C70 (end-on), and C70 (side-on). The endo-binding of fullerenes to diprotonated bisporphyrins nearly doubles the π–π interactions while reducing the electrostatic repulsion between the two singly protonated porphyrin moieties. The side-on binding of C70 is favored over the end-on binding because the former exerts less steric strain to the lower rim of calixarene.

Graphical abstract: Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins

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Publication details

The article was received on 27 Jun 2011, accepted on 14 Sep 2011 and first published on 12 Oct 2011

Article type: Paper
DOI: 10.1039/C1CP22091H
Citation: Phys. Chem. Chem. Phys., 2011,13, 20248-20254
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    Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins

    S. Jung, J. D. van Paauwe, P. D. W. Boyd and S. K. Shin, Phys. Chem. Chem. Phys., 2011, 13, 20248
    DOI: 10.1039/C1CP22091H

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