New Fe^IIIZn^II Complex Containing a Single Terminal Fe−O_phenolate Bond as a Structural and Functional Model for the Active Site of Red Kidney Bean Purple Acid Phosphatase

Abstract

The new heterodinuclear complex [Fe(III)Zn(II)(BPBPMP)(OAc)(2)]ClO(4) (1) with the unsymmetrical N(5)O(2) donor ligand 2-bis[((2-pyridylmethyl)-aminomethyl)-6-[(2-hydroxybenzyl)(2-pyridylmethyl)]-aminomethyl]-4-methylphenol (H(2)BPBPMP) has been synthesized and characterized by X-ray crystallography, which reveals that the complex cation has an Fe(III)Zn(II)(mu-phenoxo)-bis(mu-carboxylato) core. Solution studies of 1 indicate that a pH-induced change of the bridging acetate occurs, and the formation of an active [(OH)Fe(III)Zn(II)(OH(2))] species as a highly efficient catalyst under weakly acidic conditions for phosphate diesters hydrolysis is proposed.

Phosphate ester cleavage promoted by a tetrameric iron(III) complex

“…(x = 1 or 2), with the fully deprotonated form responsible for the low but significant activity above pH * 9.5 ( Fig. 6) [14]. The model predicts that at high pH the active species retains sufficient coordination flexibility to permit coordination of BDNPP, but the low rate is likely to be due to the slow exchange rate of hydroxide at the substrate binding site.…”

“…Here, L is BPBPMP 2-and M B is Zn (pK a1 4.86, pK a2 6.00, pK a3 7.22), Ni (pK a1 5.3, pK a2 6.80, pK a3 8.61), Cu (pK a1 5.25, pK a2 6.20, pK a3 7.82) or Co (pK a1 5.00, pK a2 6.58, pK a3 8.31) [9,11,13,14]. In these cases the bellshaped pH-rate profiles were fitted such that only pK a1 and pK a3 (the low-pH and high-pH extrema) were included in the analysis but not pK a2 , representing an intermediate species.…”

“…Phosphatase activities of the Fe(III)-M(II) (M is Mn, Co, Ni, Cu or Zn) complexes of BPBPMP 2-have been measured with the activated substrate 2,4-bis(dinitrophenyl) phosphate (BDNPP) [9][10][11]. These reactions are strongly dependent on pH, giving rise to bell-shaped pH versus rate profiles and pH optima in the range 6.0-7.0 [10][11][12][13][14]. In each case the catalytically active species is proposed to be of the type [(OH)Fe(III)(l-OH)M(II)(OH 2 )] [1].…”

“…Although it is believed that PAPs are only active in the heterovalent state [16], phosphatase activity has been reported for a number of diferric model complexes [17][18][19][20][21][22][23] [8,9,[17][18][19][20][21][22][23][24][25], particularly those for which more than two deprotonation equilibria are considered as part of the profile [9,13,14].…”

Synthesis, molecular structure and spectroscopic, electrochemical and magnetic properties of a new dinuclear iron complex containing µ-sulfate-di-µ-alkoxo bridges: evaluating the influence of the sulfate bridge on the physicochemical properties of the di-µ-alkoxo-diiron unit

“…[2][3][4][5][6][7][16][17][18][19] This is due to the high ε values observed in electronic spectra of PAPs, which are attributed to a tyrosine→Fe III charge transfer transition. Thus, such dinucleating ligands hold the two metal centers in close proximity and provide phenolate coordinating groups, allowing the study of the influence of such groups on the properties exhibited by the metal centers in the complexes as well as in the enzyme.…”