Structure of a (μ-Oxo)(dihydroxo)diiron(III) Complex and Its Reactivity toward Phosphodiesters

Abstract

The first (μ-oxo)diiron(III) complex with one terminal hydroxide ligand at each iron has been structurally characterized, thus providing new information on Fe−OH bonds. Acid/base equilibria were observed in aqueous solution, and the conjugate acid of the title complex was found to be a catalyst for hydrolysis of phosphodiesters at 50 °C, reinforcing the general idea about a synergistic effect in a dinuclear unit of a substrate binding site and a site containing a nucleophile. This effect has been proposed in the mechanism of purple acid phosphatase and other bimetallic hydrolases.

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

“…In both cases loss of the bridging acetates would be anticipated under the conditions of catalysis [9, 10, 12-14, 23, 25] (Fig. 8) [17][18][19]21]. Some support for the assignment of the catalytically active entity being a dimer arises from the investigation of the dependence of the complex concentration on [15] the hydrolysis reaction.…”

“…For the Fe(III)Fe(III) form of uteroferrin an upper limit of less than 1% of the activity of the heterovalent form has been determined [16], the release of the ultimate reaction product (phosphate) being proposed as the likely candidate for the rate-limiting step in the PAP-catalyzed reaction [1,18,25,40]. This hypothesis finds support in the relative water exchange rates of Fe(III) and Fe(II) (10 2 and 10 6 s -1 , respectively) [41][42][43].…”

“…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].…”

Mechanistic Studies on the Oxidation of Nitrite by a μ‐Oxodiiron(III,III) Complex in Aqueous Acidic Media

“…1) selected for the present investigation, is an attractive Raman-spectroscopy model for the binuclear iron site in the RNR and metHr, the oxidized form of the oxygen-transport protein hemerythrin [7]. Its conjugate base, [Fe 2 3+ (2) is also a possible functional model for the purple acid phosphatase [2a] [8]. The dinuclear complex 1 is soluble in H 2 O, and the solution is fairly stable towards self-decomposition in a wide pH range (3.0 -7.0) in presence of added 1,10-…”

The impact of the second coordination sphere in phosphatase model complexes

“…114 As discussed above, the trend of a higher activity of the heterovalent diiron form compared to the homovalent Fe III 2 form was also detected for the native PAP enzyme and ascribed to an increased ligand exchange rate of Fe II compared to Fe III . 278 The release of the reaction product was proposed to be most likely the rate-limiting step in the catalytic mechanism, 21,66,266,295 Table 23 lists these values and compares them to data for other diiron complexes. centers.…”