Iron(III) complexes with a tripodal N3O ligand containing an internal base as a model for catechol intradiol-cleaving dioxygenases.
A bis(mu-alkoxo)-bridged dinuclear iron(III) complex [Fe(L)(NO3)]2(NO3)2 [1; HL = N,N-bis(2-pyridylmethyl)-N-(2-hydroxyethyl)amine] of the tripodal N3O ligand was prepared as a biomimetic model for the intradiol-cleaving dioxygenase enzymes. The reaction of 1 and catechol in the presence of excess triethylamine gave the catecholate (CAT) chelate bis(mu-alkoxo)-bridged dinuclear iron(III) complex [Fe(L)(CAT)]2 (2). The molecular structures of complexes 1 and 2 were determined by X-ray crystallography. Diiron complexes 1 and 2 contain the same bis(mu-alkoxo)diiron diamond core. All heteroatoms (N3O) of the ligand are coordinated to the iron center in complex 1 with two pyridine nitrogen atoms on the axial bonds, while one of the pyridyl arms of the ligand is left uncoordinated in complex 2. The interaction of the diiron complex 1 and 3,5-di-tert-butylcatechol (H2DBC) was investigated by electronic and mass spectroscopy. Complex 1 displays the intradiol-cleaving dioxygenase activity, and the coordinate ethoxyl arm of the ligand is capable of accepting the proton from catechol, which mimics the function of Tyr447 in the protocatechuate 3,4-dioxygenase as an internal base. The spectrophotometric titration experiment indicates the relatively low demand of the external base (0.8 equiv based on Fe(3+)) for attaining the highest dioxygenase activity of complex 1. The reaction rate of the reactive intermediate [Fe(HL)(DBC)]+ with dioxygen is 0.38 M(-1) s(-1) determined by kinetic studies.
Li
Fei
F
State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian 116012, China.
Wang
Mei
M
Li
Ping
P
Zhang
Tingting
T
Sun
Licheng
L
D002396:Catechols / Q000378:metabolism*; D018360:Crystallography, X-Ray; D049308:Dioxygenases / Q000378:metabolism*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009589:Nitrogen Oxides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet
D002396:Catechols; D008024:Ligands; D009589:Nitrogen Oxides; D007501:Iron; D049308:Dioxygenases; C034221:catechol