A Heterobimetallic Fe^IIIMn^II Complex of an Unsymmetrical Dinucleating Ligand: A Structural and Functional Model Complex for the Active Site of Purple Acid Phosphatase of Sweet Potato

Abstract

The heterodinuclear mixed-valence complex [FeMn(ICIMP)-(OAc) 2 Cl] (1) {H 2 ICIMP = 2unsymmetrical N 4 O 2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the Mn II ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mössbauer spectroscopy shows that the iron ion in 1 is high-spin Fe III . Two quasi-reversible redox reactions for the complex, attributed to the Fe III Mn II / [a]2204 Fe II Mn II (at -0.67 V versus Fc/Fc + ) and Fe III Mn II /Fe III Mn III (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an Fe III -Mn II distance of 3.58 Å, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the Mn II ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the Fe III ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group.

An Unsymmetric Ligand with a N5O2 Donor Set and Its Corresponding Dizinc Complex: A Structural and Functional Phosphoesterase Model

“…Similarly to the previous studies,, , the rate‐determining barrier for the overall process is calculated by considering two catalytic cycles. In this case it is calculated to be 24.1 kcal/mol, which is very similar to the value obtained for the dizinc complex of DPCPMP (25.0 kcal/mol) .…”

“…The design and synthesis of small (biocompatible) molecular catalysts that can effectively hydrolyze phosphoester bonds is of interest . Such molecules may, in principle, be used as artificial metallonucleases and may also shed light on aspects of the enzymatic mechanisms.…”

“…Phosphoester linkages in the phosphate backbones of DNA and RNA play key roles in the significant stability of these nucleic acids under normal (pseudo)physiological conditions The hydrolysis of phosphoester bonds in nucleic acids and kinases is essential for energy production, cell signaling, biosynthesis, and the regulation of protein function . The phosphoesterase enzymes that catalyze phosphoester hydrolysis have therefore been the subject of intense investigations . These studies have been directed towards understanding the specific mechanisms of the enzymes, the structure‐function relationship and also the design of more efficient catalysts .…”

Di- and Tetrairon(III) μ-Oxido Complexes of an N3S-Donor Ligand: Catalyst Precursors for Alkene Oxidations

“…IR characterization of 2 shows characteristic asymmetric (ν asym ) and symmetric (ν sym ) C = O stretching bands as a broad peak at 1,614 cm −1 and two very sharp peaks for ν sym at 1,490 and 1,453 cm −1 , consistent with the presence of two bridging formates (Deacon and Phillips, 1980; Kurtz, 1990; Das et al, 2014a,b, 2018). In addition, the presence of a very sharp band at 1,080 cm −1 confirms the presence of perchlorate anions; the bands at 744 and 620 cm −1 correspond to the asymmetric and symmetric stretching modes of the Fe-O-Fe units (Kurtz, 1990; Norman et al, 1990).…”

Structural characterization of ferromagnetic bridged-acetato and -dichlorido copper(II) complexes based on bicompartmental 4-t-butylphenol

“…Metal(II) complexes of binucleating phenolic compounds containing pendant pyridyl groups have been used to mimic the spectroscopic structures and the mechanism of metalloenzymes, particularly in hydrolytic reactions of phosphodiesters, DNA cleavage and carbonic hydratase [1][2][3][4]. The phenolic group in this class of binucleating compounds has the capability of bridging metal ions through the deprotonated (phenoxido group) or neutral phenolate [5].…”