202199-30-2Relevant academic research and scientific papers
Iron(III) Complexes as Superoxide Dismutase Mimics: Synthesis, Characterization, Crystal Structure, and Superoxide Dismutase (SOD) Activity of Iron(III) Complexes Containing Pentaaza Macrocyclic Ligands
Zhang, DeLong,Busch, Daryle H.,Lennon, Patrick L.,Weiss, Randy H.,Neumann, William L.,Riley, Dennis P.
, p. 956 - 963 (1998)
Iron(III) complexes with four pentaaza macrocylic ligands, [Fe (L)Cl2](PF6), have been synthesized, where the ligand L is 1,4,7,10,13-pentaazacyclopentadecane (L1), 2R,3R,8S,9S-dicyclohexano-1,4,7,10,13-pentaazacyclopentadecane (L2), 2R,3R,8R,9R -dicyclohexano-1,4,7,10,13-pentaazacyclopentadecane (L3), or 2S,5R,8S,11R,14S-pentamethyl-1,4,7,10,13-pentaazacyclopentadecane (L4), respectively. Conductivity measurements in acetonitrile are consistent with two chloro anions coordinated to iron(III). In acetonitrile solution, all four iron complexes exhibit a reversible or quasi-reversible redox couple in the experimental range -1.5 to +1.5 V vs EAg/Ag+ and the redox potentials for those four complexes are similar (from -0.15 to -0.19 V vs NHE). In aqueous solutions, the electrochemical properties of those complexes are different from those in acetonitrile solution; the redox peaks shift more than 0.5 V more positive. The complexes with L1, L2, and L3 display a reversible redox at 0.35, 0.45, and 0.43 V vs NHE, respectively, while [Fe(L4)Cl2](PF6) shows a cathodic peak at 0.44 V and two anodic peaks at 0.31 and 0.14 V vs NHE, respectively. The base titration results reveal that two water molecules are coordinated to the iron(III) in these complexes, pKa1 and pKa2: 3.46(7) and 7.31(7) for [Fe(L1)Cl2](PF6); 3.7(1) and 7.50(2) for [Fe(L2)Cl2](PF6); 4.1(1) and 7.73(2) for [Fe(L3)Cl2](PF6); 3.6(7) and 7.4(2) for [Fe(L4)Cl2](PF6). The Superoxide dismutase (SOD) activity, assessed by stopped-flow experiments, reveals that all four metal complexes catalyze the fast disproportionation of Superoxide in aqueous solution: at pH = 7.8, the catalyic rate constants for the complexes were 0.81 × 107, 1.42 × 107, 1.41 × 107, and 0.29 × 107 M-1 s-1 for [Fe(L1)Cl2]-(PF6), [Fe(L2)Cl2](PF6), [Fe(L3)Cl2](PF6), and [Fe(L4)Cl2](PF6), respectively. The crystal structure of [Fe(L2)-Cl2](PF6) was determined. Crystal data: triclinic, P?1 a = 7.367(2), b = 10.707(2), c = 17.632(2) A?; α = 81.27(2), β = 79.74(2), γ = 83.38(2)°; R = 0.0465 for observed data (I > 2σ (I)). The iron is seven-coordinate with five nitrogen atoms from the pentaaza macrocylic ligand and trans-chloro anions in a pentagonal bipyramidal arrangement. The average bond lengths for Fe-N and Fe-Cl are 2.271 and 2.339 A?, respectively.
