Geometric and Electronic Structure Contributions to Function in Bioinorganic Chemistry:  Active Sites in Non-Heme Iron Enzymes

Solomon, Edward I.

doi:10.1021/ic010348a

Cited by 91 publications

(97 citation statements)

References 89 publications

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“…68,78,[82][83][84][85][86] MCD measures the differential absorption of left and right circular polarised light, similar to circular dichroism (CD), but in the presence of a magnetic field. 84 Application of a magnetic field parallel to the direction of light causes all matter to exhibit MCD activity so it is not restricted to paramagnetic materials.…”

Section: Catalytic Mechanism Of Gpdqmentioning

confidence: 99%

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

et al. 2014

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An enhanced understanding of the metal ion binding and active site structural features of phosphoesterases such as the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ), and the organophosphate degrading agent from Agrobacterium radiobacter (OpdA) have important consequences for potential applications. Coupled with investigations of the metalloenzymes, programs of study to synthesise and characterise model complexes based on these metalloenzymes can add to our understanding of structure and function of the enzymes themselves. This review summarises some of our work and illustrates the significance and contributions of model studies to knowledge in the area.

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Section: Catalytic Mechanism Of Gpdqmentioning

confidence: 99%

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

et al. 2014

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“…The analysis of VTVH MCD data from non-Kramers-type systems has been reviewed previously 8,11,22,23 and is illustrated in brief for a ferrous system (S ¼ 2) with negative ZFS ( Figure 5, right panel). The VTVH MCD behavior of S ¼ 2 systems with positive ZFS qualitatively resembles negative ZFS systems with a large and is thus not further discussed here.…”

Section: Non-kramers Ionsmentioning

confidence: 99%

Magnetic Circular Dichroism of Paramagnetic Species

Solomon

Neidig

Schenk

2003

Comprehensive Coordination Chemistry II

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MCD spectroscopy combines the CD experiment with a longitudinal magnetic field, where the application of the magnetic field induces optical activity in any material so that all substances exhibit MCD activity. MCD probes the Zeeman splittings in the ground and excited states and the field-induced mixing between states. MCD intensity for a transition from a ground state |Ai to an excited state |Ji is given by Equation (1):for broadband transitions when the MCD intensity is linear with field. Here, ÁA is the fielddependent difference between left-and right-circularly polarized light (lcp and rcp, respectively) absorption, E ¼ h#, is the electric permeability, C is the concentration, l is the path length, n is 339

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“…Nevertheless, the results described here, together with those of Carver et al, 12 suggest a commonality in electronic structure of HS Fe(II) complexes with N 6 coordination and, more generally, that HFEPR, at least in certain propitious cases such as complex 1B, can and should be added to the armamentarium of techniques for investigating HS Fe(II) complexes side-by-side with well-established methods. 1,[7][8][9] JA048336M Figure 1. HFEPR spectra of polymorph B of 1 at 610 GHz and 10 K using optical modulation (black trace), and magnetic modulation (blue trace).…”

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High-Frequency and -Field EPR of a Pseudo-octahedral Complex of High-Spin Fe(II): Bis(2,2‘-bi-2-thiazoline)bis(isothiocyanato)iron(II)

et al. 2004

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Iron is ubiquitous in metalloproteins, in a wide range of coordination environments. A large and important class of Fe proteins consists of the non-heme Fe proteins, in which Fe is often six-coordinate and generally has two or more endogenous histidine ligands. 1,2 HS 3 Fe(II) (3d 6 , S ) 2) is an important state in nonheme Fe proteins; however, this state is relatively difficult to investigate by EPR, normally a technique of choice for paramagnetic transition metal systems. HS Fe(II) is a non-Kramers (integer spin) ion of typically large zfs, on the order of 5-20 cm -1 . 4,5 The allowed EPR transitions thus generally appear at high frequencies, and/or at high magnetic fields. 6 Among spectroscopic methods generally applied to HS Fe(II) systems, Mössbauer spectroscopy 7,8 and MCD 1,9 are most informative, as are magnetic susceptibility measurements. 10 Far-infrared (FIR) spectroscopy 11 and, more recently, INS 12 have also been employed to detect transitions among the HS Fe(II) quintet-state zero-field levels and consequently provide information on its electronic structure. Another approach is to employ EPR, but at frequencies and fields sufficiently high to observe the allowed transitions. 13 12 The HFEPR results in the latter report were, however, secondary to highly informative INS results. Very few HFEPR transitions were observed, and the S/N ratio of reported EPR spectra was relatively low. 12 We demonstrate here that it is indeed possible to observe multiple HFEPR transitions for HS Fe(II) with high S/N ratio, in this case for a cis-FeN′ 2 N 4 chromophore complex: bis(2,2′-bi-2-thiazoline)-bis(isothiocyanato)iron(II) (1). Complex 1 can be considered as an approximate model for six-coordinate active sites in non-heme Fe proteins, wherein their histidine ligands are represented in 1 by the imino N-donor thiazoline ligands. We show that it is possible by HFEPR to accurately determine spin Hamiltonian parameters in this complex, and relate them to the electronic structure.Complex 1 exists as two polymorphs, A 15-18 and B. 18 It was polymorph A that drew initial attention since it undergoes a temperature-driven spin-crossover transition to a diamagnetic (LS, S ) 0) state. [15][16][17][18] Polymorph B remains paramagnetic (HS, S ) 2) to 4.2 K but is "silent" at conventional EPR frequencies. Crystals of each polymorph can be independently prepared, and their structures have been determined. 18 The structure of polymorph B (1B) is shown in Chart 1. Crystals of 1B were ground to a fine powder for HFEPR experiments. The HFEPR apparatus and the tunable-frequency EPR methodology as employed here have been previously described. 19 We have also performed Mössbauer spectroscopy measurements at 77 and 293 K, and DC SQUID magnetometry between 1.8 and 293 K for 1B. Figure 1 shows typical HFEPR spectra of 1B using two different modulation techniques: chopping the sub-THz wave beam, which results in an absorptive shape (black trace), and standard modulation of magnetic field (blue trace). The red trace is a derivative simulat...

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Geometric and Electronic Structure Contributions to Function in Bioinorganic Chemistry: Active Sites in Non-Heme Iron Enzymes

Cited by 91 publications

References 89 publications

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

Magnetic Circular Dichroism of Paramagnetic Species

High-Frequency and -Field EPR of a Pseudo-octahedral Complex of High-Spin Fe(II): Bis(2,2‘-bi-2-thiazoline)bis(isothiocyanato)iron(II)

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