Electron capture by oxyhaemoglobin: an e. s. r. study

Symons, Martyn C. R.; Petersen, Richard

doi:10.1098/rspb.1978.0046

Cited by 56 publications

(35 citation statements)

References 26 publications

(29 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The diamagnetic 4a and 4b complexes do not exhibit EPR signals. Therefore, to use 4a as a calibration standard to establish correlations between the known crystal structure and MCD and EPR spectra, 4a was cryoreduced by shedding the γ-radiation onto the sample dissolved in butyronitrile (PrCN) and kept frozen in liquid N 2 . Unlike chemically reduced species that undergo geometric structural relaxation upon reduction, the paramagnetic Ni III version of 4a generated from cryoreduction has the geometric structure frozen at the original Ni IV state.…”

Section: Resultsmentioning

confidence: 96%

Correlation between the C–C Cross-Coupling Activity and C-to-Ni Charge Transfer Transition of High-Valent Ni Complexes

et al. 2020

View full text Add to dashboard Cite

High-valent Ni complexes have proven to be good platforms for diverse cross-coupling reactions that are otherwise difficult to be achieved with conventional low-valent catalysts. However, their reductive elimination (RE) activities are still significantly variable by up to 5 orders of magnitude, depending on the supporting ligand and oxidation state of the Ni center. To elucidate frontier molecular orbitals (FMOs) that determine the RE activity of the Ni center, the electronic structures of cycloneophyl (CH2C(CH3)2-o-C6H4) NiIII and NiIV complexes have been characterized by utilizing various transition metal-based spectroscopic techniques such as electronic absorption, magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopies. In combination with density functional theory computations, the spectroscopic analyses have shown that the energies of the C-to-Ni charge-transfer (CT) electronic transitions are strongly correlated to the rates of C–C bond-forming RE reaction. This correlation suggests that the kinetic barrier of the RE reaction is determined by energy cost for internal CT (ICT) from the coordinated carbon moiety to the Ni center, and that FMOs involved in the RE reaction and the C-to-Ni CT electronic transitions are essentially identical. This FMO determination has led us to discover that photoexcitation to the C-to-Ni CT excited states accelerates the C–C cross-coupling reaction by up to 105 times, as the CT electronic transition can substitute for the rate-determining ICT step of the RE reaction at the ground electronic state.

show abstract

Section: Resultsmentioning

confidence: 96%

Correlation between the C–C Cross-Coupling Activity and C-to-Ni Charge Transfer Transition of High-Valent Ni Complexes

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Exposing of aqueous glasses containing MbO 2 or HbO 2 to γ-rays at 77 K resulted in efficient electron capture at the Fe–O 2 centers. , The initial products observed upon 77 K cryoreduction of MbO 2 and HbO 2 were characterized as [FeO 2 ] end-on “ferric peroxo” species (Fe 3+ –O 2 2– ). This assignment was based on the observation of EPR spectra of a low-spin ferriheme species ( g ≈ [2.22, 2.11, 1.96]) (Figure ).…”

Section: Application Of Pulse Radiolysis To Biological Systemsmentioning

confidence: 99%

Pulse Radiolysis Studies for Mechanism in Biochemical Redox Reactions

Kobayashi

2019

Chem. Rev.

View full text Add to dashboard Cite

Pulse radiolysis is a powerful method for generating highly reduced or oxidized species and free radicals. Combined with fast time-resolved spectroscopic measurement, we can monitor the reactions of intermediate species on time scales ranging from picoseconds to seconds. The application of pulse radiolysis to water generates hydrated electrons (eaq –) and specific radicals, rendering this technique useful for investigating a number of biological redox processes. The first pulse radiolysis redox investigations explored in this review involved intramolecular electron transfer processes in protein with multiple electron-accepting sites. Pulse radiolysis enabled direct monitoring of the internal electron transfer rates and the distribution of electrons within proteins. Structural information from X-ray data has allowed analysis of the rate constants and their activation parameters in relation to the mechanisms with current theoretical treatments. The second set of pulse radiolysis redox investigations explored here concerned the intermediates of enzyme reactions after redox reactions. Pulse radiolysis allowed the extremely rapid donation of electrons to a redox center in a protein. It makes it possible to observe the unstable intermediates after the reduction and the following subsequent steps. For example, the intermediates generated through the one-electron reduction of oxygenated hemoproteins, such as cytochrome P450 and nitric oxide synthase, were characterized. Interestingly, ligand exchange can occur upon the reduction of heme iron, in which different amino acid residues bind to heme in the ferrous and ferric states, respectively. We directly observed the ligand-switching intermediates of bacterial CooA, a CO sensor, and bacterial iron response regulator protein. These ligand exchange processes are physiologically important for regulating the electrode potential and effective formation of superoxide anion or HO•. The third set of pulse radiolysis redox investigations explored in this review concerns free-radical processes in biological systems. Free radicals are produced in cells and organisms in a variety of processes. The cell has developed special and very effective machinery for controlling and detoxifying reactive radicals. Radiation-generated radicals allow studies of the reactions between specific radicals and solutes, often revealing the mechanisms underlying the initial and subsequent reactions. The crucial contribution was made using pulse radiolysis techniques and knowledge of the identities, properties, and reactions of radicals. These radicals include superoxide (O2 •–), nitric monoxide (NO•), ascorbate, urate, and protein radicals. This review focuses on the reactions of these radicals and their physiological functions.

show abstract

“…50−68 In particular, cryoreduction of oxy-ferrous heme proteins to yield EPR-active peroxo-and hydroperoxo-ferric heme states, which retain the conformation of the oxy heme precursor, has been extremely successful in probing the interactions of oxygen with its active site environment in oxygen-activating proteins. [50][51][52][53][54][55][56][57][58]65 Moreover, EPR of subsequently annealed cryoreduced samples yields additional valuable information about the protonation environment of the distal heme pocket. As mentioned above, this technique was used to understand the structural features responsible for F33Y-Cu B Mb reactivity.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The EPR parameters of the first species, with g 1 = 2.24 in both proteins, suggest that it is a ferric peroxo state in which the peroxo ligand engages in a hydrogen bond with the distal His64. [50][51][52][53]61 The somewhat broadened g 1 feature in F33Y-Cu B Mb indicates a slight conformational distribution. The second species with g 1 = 2.29 in both proteins is in the range characteristic of ferrichydroperoxo intermediates.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…To improve our understanding of how the introduced Glu residue tunes the reactivity of Cu B Mb and F33Y-Cu B Mb, we sought to probe the interactions of the oxygen-bound intermediate. We and others have previously shown that EPR is a valuable tool for probing the interactions within the active sites of heme and non-heme iron proteins. − In particular, cryoreduction of oxy-ferrous heme proteins to yield EPR-active peroxo- and hydroperoxo-ferric heme states, which retain the conformation of the oxy heme precursor, has been extremely successful in probing the interactions of oxygen with its active site environment in oxygen-activating proteins. − , Moreover, EPR of subsequently annealed cryoreduced samples yields additional valuable information about the protonation environment of the distal heme pocket. As mentioned above, this technique was used to understand the structural features responsible for F33Y-Cu B Mb reactivity .…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

An Engineered Glutamate in Biosynthetic Models of Heme-Copper Oxidases Drives Complete Product Selectivity by Tuning the Hydrogen-Bonding Network

et al. 2021

View full text Add to dashboard Cite

Efficiently carrying out the oxygen reduction reaction (ORR) is critical for many applications in biology and chemistry, such as bioenergetics and fuel cells, respectively. In biology, this reaction is carried out by large, transmembrane oxidases such as heme-copper oxidases (HCOs) and cytochrome bd oxidases. Common to these oxidases is the presence of a glutamate residue next to the active site, but its precise role in regulating the oxidase activity remains unclear. To gain insight into its role, we herein report that incorporation of glutamate next to a designed heme-copper center in two biosynthetic models of HCOs improves O2 binding affinity, facilitates protonation of reaction intermediates, and eliminates release of reactive oxygen species. High-resolution crystal structures of the models revealed extended, water-mediated hydrogen-bonding networks involving the glutamate. Electron paramagnetic resonance of the cryoreduced oxy-ferrous centers at cryogenic temperature followed by thermal annealing allowed observation of the key hydroperoxo intermediate that can be attributed to the hydrogen-bonding network. By demonstrating these important roles of glutamate in oxygen reduction biochemistry, this work offers deeper insights into its role in native oxidases, which may guide the design of more efficient artificial ORR enzymes or catalysts for applications such as fuel cells.

show abstract

Electron capture by oxyhaemoglobin: an e. s. r. study

Cited by 56 publications

References 26 publications

Correlation between the C–C Cross-Coupling Activity and C-to-Ni Charge Transfer Transition of High-Valent Ni Complexes

Correlation between the C–C Cross-Coupling Activity and C-to-Ni Charge Transfer Transition of High-Valent Ni Complexes

Pulse Radiolysis Studies for Mechanism in Biochemical Redox Reactions

An Engineered Glutamate in Biosynthetic Models of Heme-Copper Oxidases Drives Complete Product Selectivity by Tuning the Hydrogen-Bonding Network

Contact Info

Product

Resources

About