Unsymmetrical Fe(III)Co(II) and Ga(III)Co(II) complexes as chemical hydrolases: biomimetic models for purple acid phosphatases (PAPs).
The design and development of suitable biomimetic catalytic systems capable of mimicking the functional properties of enzymes continues to be a challenge for bioinorganic chemists. In this study, we report on the synthesis, X-ray structures, and physicochemical characterization of the novel isostructural [Fe(III)Co(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (1) and [Ga(III)Co(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (2) complexes with the unsymmetrical dinucleating ligand H(2)BPBPMP (2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol). The previously reported complex [Fe(III)Zn(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (3) was investigated here by electron paramagnetic resonance for comparison with such studies on 1 and 2. A magneto-structural correlation between the exchange parameter J (cm(-1)) and the average bond lengh d (A) of the [Fe(III)-O-M(II)] structural unit for 1 and for related isostructural Fe(III)M(II) complexes using the correlation J = -10(7) exp(-6.8d) reveals that this parameter is the major factor that determines the degree of antiferromagnetic coupling in the series [(BPBPMP)Fe(III)(mu-OAc)(2)M(II)](+) (M(II) = Mn, Fe, Co, Ni) of complexes. Potentiometric and spectrophotometric titrations along with electronic absorption studies show that, in aqueous solution, complexes 1 and 2 generate the [(HO)M(III)(mu-OH)Co(II)(H(2)O)] complex as the catalytically active species in diester hydrolysis reactions. Kinetic studies on the hydrolysis of the model substrate bis(2,4-dinitrophenyl)phosphate by 1 and 2 show Michaelis-Menten behavior, with 2 being 35% more active than 1. In combination with k(H)/k(D) isotope effects, the kinetic studies suggest a mechanism in which a terminal M(III)-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst. In addition, the complexes show maximum catalytic activity in DNA hydrolysis near physiological pH. The modest reactivity difference between 1 and 2 is consistent with the slightly increased nucleophilic character of the Ga(III)-OH terminal group in comparison to Fe(III)-OH in the dinuclear M(III)Co(II) species.
Xavier
Fernando R
FR
Departamento de Química, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil.
Neves
Ademir
A
Casellato
Annelise
A
Peralta
Rosely A
RA
Bortoluzzi
Adailton J
AJ
Szpoganicz
Bruno
B
Severino
Patricia C
PC
Terenzi
Hernán
H
Tomkowicz
Zbigniew
Z
Ostrovsky
Sergei
S
Haase
Wolfgang
W
Ozarowski
Andrew
A
Krzystek
Jerzy
J
Telser
Joshua
J
Schenk
Gerhard
G
Gahan
Lawrence R
LR
D000042:Absorption; D000135:Acid Phosphatase / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D055162:Biocatalysis; D032701:Biomimetics; D002417:Cattle; D002942:Circular Dichroism; D003035:Cobalt / Q000737:chemistry*; D004247:DNA / Q000378:metabolism; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D005708:Gallium / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008280:Magnetics; D011199:Potentiometry; D017186:Titrimetry
D005290:Ferric Compounds; D006023:Glycoproteins; D003035:Cobalt; D004247:DNA; D005708:Gallium; C091137:purple acid phosphatase; D000135:Acid Phosphatase