A model for the chromophoric site of purple acid phosphatases

Yan, Shi‐Ping; Que, Lawrence; Taylor, Lucille F.; Anderson, Oren P.

doi:10.1021/ja00223a068

Cited by 65 publications

(55 citation statements)

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“…The formation of several dimer iron(III) species have been observed earlier with tetra-or pentadentate ligands [42][43][44][45][46], generally in non-aqueous medium. However, to our knowledge, the bhbdpa-iron(III) system is the first example when a pentadentate ligand is able to hold two iron(III) in aqueous solution by forming a dinuclear structure.…”

Section: Iron(iii) Complexes Of Bhbdpasupporting

confidence: 54%

“…One has to mention that the formation of a dimer of above dinuclear complex, with a composition of Fe 4 (bhbdpa) 2 (OH) 6 , can not be ruled out based on our data. However, the formation of l-oxo-bridges would result in a significantly increased CT transition around 500 nm [42][43][44]. The molar extinction coefficient determined for Fe 2 (bhbdpa)(OH) 3 is only 2952 M À1 cm À1 , which falls in the range expected for two iron(III)-phenolate bonds [33].…”

Section: Iron(iii) Complexes Of Bhbdpamentioning

confidence: 84%

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Iron(III)- and copper(II) complexes of an asymmetric, pentadentate salen-like ligand bearing a pendant carboxylate group

Jancsó

Paksi

Mikkola

et al. 2005

Journal of Inorganic Biochemistry

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Section: Iron(iii) Complexes Of Bhbdpasupporting

confidence: 54%

Section: Iron(iii) Complexes Of Bhbdpamentioning

confidence: 84%

Iron(III)- and copper(II) complexes of an asymmetric, pentadentate salen-like ligand bearing a pendant carboxylate group

Jancsó

Paksi

Mikkola

et al. 2005

Journal of Inorganic Biochemistry

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“…Also, the angle is higher than the average Fe-O-C bond angle of ∼128.5°observed in other octahedral iron(III)-phenolate complexes. 20,21,23, [39][40][41][42][43][44][45] A comparison of the structural parameters of 2 with those of 1‚CH 3 CN reveals remarkable differences in their structures. The replacement of one of the pyridine pendants in 1‚CH 3 CN by the sterically demanding -NMe 2 group to obtain 2 results in shortening of Fe-N but elongation of Fe-Cl bonds.…”

Section: Resultsmentioning

confidence: 99%

Iron(III) Complexes of Sterically Hindered Tetradentate Monophenolate Ligands as Functional Models for Catechol 1,2-Dioxygenases: The Role of Ligand Stereoelectronic Properties

2004

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The iron(III) complexes of the monophenolate ligands 2-(bis(pyrid-2-ylmethyl)aminomethyl)-4-nitrophenol [H(L1)], N,N-dimethyl-N'-(pyrid-2-ylmethyl)-N'-(2-hydroxy-4-nitrobenzyl)ethylenediamine [H(L2)], N,N-dimethyl-N'-(6-methyl-pyrid-2-ylmethyl)-N'-(2-hydroxy-4-nitrobenzyl)ethylenediamine [H(L3)], and N,N-dimethyl-N'-(1-methylimidazole-2-ylmethyl)-N'-(2-hydroxy-4-nitrobenzyl)ethylenediamine [H(L4)] have been obtained and studied as structural and functional models for the intradiol-cleaving catechol dioxygenase enzymes. The complexes [Fe(L1)Cl(2)].CH(3)CN (1), [Fe(L2)Cl(2)] (2), [Fe(L3)Cl(2)] (3), and [Fe(L4)Cl(2)] (4) have been characterized using absorption spectral and electrochemical methods. The single crystal X-ray crystal structures of 1 and 2 have been successfully determined. Both the complexes possess a rhombically distorted octahedral coordination geometry for the FeN(3)OCl(2) chromophore. In 2, the phenolate oxygen, the pyridine nitrogen, an amine nitrogen, and a chloride ion are located on the corners of a square plane with the nitrogen atom of a -NMe(2) group and the other chloride ion occupying the axial positions. In 1, also the equatorial plane is constituted by the phenolate oxygen, the pyridine nitrogen, an amine nitrogen atom, and a chloride ion; however, the axial positions are occupied by the second pyridine nitrogen and the second chloride ion. Interestingly, the Fe-O-C angle of 136.1 degrees observed for 2 is higher than that (128.5 degrees ) in 1; however, the Fe-O(phenolate) bond distances in both the complexes are the same (1.929 A). This illustrates the importance of the nearby sterically demanding coordinated -NMe(2) group and implies similar stereochemical constraints from the other ligated amino acid moieties in the 3,4-PCD enzymes, the enzyme activity of which is traced to the difference in the equatorial and axial Fe-O(tyrosinate) bonds (Fe-O-C, 133 degrees, 148 degrees ). The nature of heterocyclic rings of the ligands and the methyl substituents on them regulates the electronic spectral features, Fe(III)/Fe(II) redox potentials, and catechol cleavage activity of the complexes. Upon interacting the complexes with catecholate anions, two catecholate to iron(III) charge transfer bands appear, and the low energy band is similar to that of catechol dioxygenase-substrate complex. Complexes 1 and 3 fail to catalyze the oxidative intradiol cleavage of 3,5-di-tert-butylcatechol (H(2)DBC). However, interestingly, the replacement of pyridine pendant in 1 by the -NMe(2) group to obtain 2 restores the dioxygenase activity, which is consistent with its higher Fe-O-C bond angle. Remarkably, the more basic N-methylimidazole ring in 4 facilitates the rate-determining product releasing phase of the catalytic reaction, leading to enhancement in reaction rate and efficient conversion (77.1%) of the substrate to intradiol cleavage products as well. All these observations provide support to the novel substrate activation mechanism proposed for the intradiol-cleavage pathway.

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“…Both HL 1 [9] and HL 2 [10] have been described before and used for bioinorganic model studies [9] [10] [11] [12] [13] . The coordination chemistry of ligands like L 1 with varying "arm lengths" was developed extensively by D. E. Fenton [13] [14] [15] [16] including the modelling of the structure and reactivity of zinc enzymes [15] [16] and the preparation of dinuclear copper and zinc complexes of L [18] .…”

mentioning

confidence: 99%