title: Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins.
abstract: 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 (C(60) and C(70)). 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 C(60), C(70) (end-on), and C(70) (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 C(70) is favored over the end-on binding because the former exerts less steric strain to the lower rim of calixarene.
authors: Bio-Nanotechnology Center, Department of Chemistry, Pohang University of Science and Technology, San31 Hyoja-dong Nam-gu, Pohang, Kyungbuk 790-784, Korea.
authors: Sunghan
authors: S
authors: Jung
authors: John D
authors: JD
authors: van Paauwe
authors: Peter D W
authors: PD
authors: Boyd
authors: Seung Koo
authors: SK
authors: Shin
mesh_terms: D001665:Binding Sites; D047250:Calixarenes / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry*; D008958:Models, Molecular; D010636:Phenols / Q000737:chemistry; D011166:Porphyrins / Q000737:chemistry*; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D037741:Fullerenes; D010636:Phenols; D011166:Porphyrins; D011522:Protons; C121325:calix(4)arene; D047250:Calixarenes