Quercetin 2,3-dioxygenase mimicking ring cleavage of the flavonolate ligand assisted by copper. Synthesis and characterization of copper(I) complexes [Cu(PPh3)2(fla)] (fla = flavonolate) and [Cu(PPh3)2(O-bs)] (O-bs = O-benzoylsalicylate)

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Abstract

Cu(PPh3)2(fla) has been prepared by reacting copper(I) chloride with sodium flavonolate in tetrahydrofuran solution. Crystallographic characterization of the complex (orthorhombic, P212121, a = 9.588(1) Å, b= 17.364(3) Å, c = 24.378(3) Å, V = 4058.6(10) Å3, Z = 4, R = 0.049) has shown that the coordination geometry of the molecule is tetrahedral. Oxygenation of Cu(PPh3)2(fla) in a methylene chloride solution at ambient conditions gives the O-benzoylsalicylato copper complex Cu(PPh3)2(O-bs) and carbon monoxide. Labeling experiments with an 18O216O2 mixture (1:4) evidenced the incorporation of both 18O atoms of 18O2 into the O-bs ligand. IR and MS studies of labeled O-bs confirmed the incorporation of 18O2 while the released CO remained unlabeled. Crystallographic characterization of Cu(PPh3)2(O-bs) on crystals obtained as the acetone solvate (triclinic, P1̄, a = 13.154(1) Å, b = 17.991(1) Å, c = 20.495(1) Å, a = 80.01(1)°, β= 88.02(1)°, γ = 71.83(1)°, V = 4537.5(5) Å3, Z = 4, R = 0.0403) shows that the molecule has a distorted tetrahedral structure. The oxygenolysis was followed by spectrophotometry, and the rate constants were determined according to the rate law - d[Cu(PPh3)2(fla)]/dt = fa[Cu(PPh3)2(fla)][O2]. The rate constant, activation enthalpy, and entropy at 363.16 K are as follows: k2/M-1 s-1 = 4.16 ± 0.48, ΔH/kJ mol-1 = 102 ±7, ΔS/J mol-1 K-1 = -13.0 ± 21. The reaction fits a Hammett linear free energy relationship for 4′-substituted flavonolates, and an increase of the electron density on copper makes the oxygenation reaction faster.

Original languageEnglish
Pages (from-to)3787-3795
Number of pages9
JournalInorganic Chemistry
Volume38
Issue number17
Publication statusPublished - Dec 1 1999

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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