Allosteric binding of an Ag+ Ion to cerium(IV) bis-porphyrinates enhances the rotational activity of porphyrin ligands

Masato Ikeda, Masayuki Takeuchi, Seiji Shinkai, Fumito Tani, Yoshinori Naruta, Shigeru Sakamoto, Kentaro Yamaguchi

Research output: Contribution to journalArticle

62 Citations (Scopus)

Abstract

Abstract: A series of cerium(IV) bis-porphyrinate double-deckers [Ce(bbpp)2] (BBPP = 5,15-bis(4-butoxyphenyl)porphyrin dianion), [Ce(tmpp)2] (TMPP = 5,10,15,20-tetrakis(4-methoxyphenyl)-porphyrin dianion), [Ce(tfpp)2] (TFPP = 5,10,15,20-tetrakis(4-fluorophenyl)porphyrin dianion), [Ce(tmcpp)2] (TMCPP = 5,10,15,20-tetrakis(4-methoxycarbonylphenyl)porphyrin dianion), and [Ce(tmpp)(tmcpp)] was prepared. They bind three Ag+ ions to their concave porphyrin π subunits (π-clefts) according to a positive homotropic allosteric mechanism with Hill coefficients (nH) of 1.7-2.7. The rotation rates of the porphyrin ligands in [Ce(bbpp)2] were evaluated to be 200s-1 at 20°C (ΔG293 = 14.1 kcalmol-1) and 220 s-1 at -40°C (ΔG233 = 11.0 kcalmol-1) without and with Ag+ ions, respectively. These results consistently support our unexpected finding that Ag+ binding can accelerate rotation of the porphyrin ligand. On the basis of UV-visible, IH NMR, and resonance Raman spectral measurements, the rate enhancement of the rotational speed of the porphyrin ligands is attributed to conformational changes of the porphyrin in cerium(IV) bis-porphyrinate induced by binding of Ag+ guest ions in the clefts. This novel concept of positive homotropic allosterism is applicable to the molecular design of various supramolecular and switch-functionalized systems.

Original languageEnglish
Pages (from-to)5541-5550
Number of pages10
JournalChemistry - A European Journal
Volume8
Issue number24
DOIs
Publication statusPublished - Dec 16 2002

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

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