Anion binding to a ferric porphyrin complexed with per-O-methylated beta-cyclodextrin in aqueous solution.
5,10,15,20-Tetrakis(4-sulfonatophenyl)porphinato iron(III) (Fe(III)TPPS) forms a very stable 1:2 complex with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMe-beta-CD), whose iron(III) center is located at a hydrophobic cleft formed by two face-to-face TMe-beta-CD molecules. Various inorganic anions (X(-)) such as F(-), Cl(-), Br(-), I(-), N(3)(-), and SCN(-) coordinate to Fe(III)TPPS(TMe-beta-CD)(2) to form five-coordinate high-spin Fe(III)TPPS(X)(TMe-beta-CD)(2), while no coordination occurs with ClO(4)(-), H(2)PO(4)(-), NO(3)(-), and HSO(4)(-). Except for F(-), none of the anions investigated coordinate to Fe(III)TPPS in the absence of TMe-beta-CD due to extensive hydration to the anions as well as to Fe(III)TPPS. The present system shows a high selectivity toward the N(3)(-) anion. The thermodynamics suggests that Lewis basicity, hydrophilicity, and shape of an X(-) anion are the main factors to determine the stability of the Fe(III)TPPS(X)(TMe-beta-CD)(2) complex.
Kano
Koji
K
Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan. kkano@mail.doshisha.ac.jp
Kitagishi
Hiroaki
H
Tamura
Shigeto
S
Yamada
Akihisa
A
D000838:Anions; D002151:Calorimetry; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D011166:Porphyrins / Q000737:chemistry*; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D047392:beta-Cyclodextrins / Q000737:chemistry*
D000838:Anions; D005290:Ferric Compounds; D011166:Porphyrins; D012996:Solutions; D047392:beta-Cyclodextrins; D014867:Water; C016136:tetraphenylporphine sulfonate