Structure of a dioxygen adduct of (1-methylimidazole)-meso-tetrakis(.alpha.,.alpha.,.alpha.,.alpha.,-o-pivalamidophenyl)porphinatoiron(II). An iron dioxygen model for the heme component of oxymyoglobin

Jameson, G. B.; Rodley, G. A.; Robinson, Ward T.; Gagné, Robert R.; Reed, Aisha; Collman, James P.

doi:10.1021/ic50182a012

Cited by 154 publications

(81 citation statements)

References 7 publications

(10 reference statements)

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“…This difference could result from a significantly lower energy barrier for 02 approaching Fe on trajectories of large angle between the 02 axis and the heme plane, agreeing with Szabo's suggestions (44). Oxygen bonds to the heme at an angle to the normal, even in unstrained model compounds for which the CO is upright (45)(46)(47).…”

Section: Methodsmentioning

confidence: 99%

Iron-carbonyl bond geometries of carboxymyoglobin and carboxyhemoglobin in solution determined by picosecond time-resolved infrared spectroscopy.

Moore

Hansen

Hochstrasser

1988

Proc. Natl. Acad. Sci. U.S.A.

110

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The iron-carbonyl geometries in carboxymyoglobin (MbCO) and carboxyhemoglobin (HbCO) in ambient temperature solution have been investigated using picosecond time-resolved infrared spectroscopy. Polarized infrared and visible beams were used to monitor the change in infrared absorbance of the bound CO stretch bands on photodissociation of the ligand. The ratio of the change in absorbance for perpendicular and parallel relative polarizations of the photolysis and infrared probe beams is directly related to the angle between the ligand bond axis and the normal to the heme plane. Ratios, and hence the angles, have been obtained for the configurations giving rise to the principal CO We have recently suggested a new method of determining IR spectra with ps time resolution (2). In this measurement the sample is first pumped by a ps pulse of visible or UV light and the IR spectrum of the sample consisting of both photoproducts and unphotolyzed material can be recorded at variable ps delay times. The experiment can be done with polarized IR and visible beams, so that the magnitude and decay of the orientational correlation function for photoproducts and unphotolyzed material can be evaluated. For heme proteins-where the overall molecular rotation is slow-the magnitude of the polarization anisotropy is directly related to the angle between the transition dipoles for the IR and visible absorptions. In this paper we present results from a significantly improved version of the original experimental design, applied to the photodissociation of carboxymyoglobin (MbCO) and carboxyhemoglobin (HbCO). The measurements are used to define the heme-CO geometry for these heme proteins in solution. The preliminary results (2) for MbCO involved an uncertainty in the polarization anisotropy of >50%. In this study the error is reduced to -10% and allows a sharp definition of the ligand geometry of this heme protein in solution. MATERIALS AND METHODSSpectroscopic Method. The transient IR spectra were recorded using the same principles as previously described (2 The polarization experiment was carried out as follows. The upconversion signal intensity was measured both with the photolyzing beam blocked and with the photolyzing beam incident on the sample. The A/2 plate in the photolyzing beam was then rotated such that the polarization of that beam was rotated by 900, and the signal measurements were repeated.In this way, the change in IR absorbance could be measured for both parallel and perpendicular IR/photolysis laser polarizations. Measurements were taken using a time delay of 40 ps between the pump and probe lasers. A correction factor of ==5% was required to compensate for the difference in reflectance for the two polarizations of the dichroic beam Abbreviations: MbCO, carboxymyoglobin; HbCO, carboxyhemoglobin. 5062The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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Section: Methodsmentioning

confidence: 99%

Iron-carbonyl bond geometries of carboxymyoglobin and carboxyhemoglobin in solution determined by picosecond time-resolved infrared spectroscopy.

Moore

Hansen

Hochstrasser

1988

Proc. Natl. Acad. Sci. U.S.A.

110

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“…Earlier studies on Cu-O 2 C À species [4b] and reactivity patterns associated with hemoglobin also reveal that the M-O-O angle is strongly correlated to its reactivity. [22] Since the angle alters the magnetic coupling significantly this in turn affects the reactivity. This relationship can be substantiated if the magnitudes of the spin density on the metal atoms are analyzed.…”

Section: Fementioning

confidence: 99%

CH Bond Activation by Metal–Superoxo Species: What Drives High Reactivity?

Ansari¹,

Jayapal²,

Rajaraman³

2014

Angewandte Chemie

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Metal-superoxo species are ubiquitous in metalloenzymes and bioinorganic chemistry and are known for their high reactivity and their ability to activate inert CÀH bonds. The comparative oxidative abilities of M-O 2 C À species (M = Cr III , Mn III , Fe III , and Cu II ) towards CÀH bond activation reaction are presented. These superoxo species generated by oxygen activation are found to be aggressive oxidants compared to their high-valent metal-oxo counterparts generated by O···O bond cleavage. Our calculations illustrate the superior oxidative abilities of Fe III -and Mn III -superoxo species compared to the others and suggest that the reactivity may be correlated to the magnetic exchange parameter.Mononuclear metalloenzymes with coordinated oxygen at the metal center have applications in biology, industry, and the laboratory.[1] Oxygenated metal intermediates like oxo, peroxo, hydroperoxo, and superoxo species play a vital role in catalytic reactions such as hydrogenation, halogenation, hydroxylation, olefin epoxidation, and C À H bond activation.[2] In the last decade many high-valent metal-oxygen species have been studied to understand the fundamental structural, functional, and mechanistic aspects of their enzymes and their counterparts. [2a,d, 3] Apart from the metaloxo species, oxidation of CÀH bonds by several superoxometal complexes is also reported.[4] Unlike the metal-oxo species, the reactivity of M-O 2 C À species and their competing oxidative abilities are relatively less explored, although nature utilizes both species to carry out efficient catalysis. [5] Among other factors, the nature of the transition metals in M-O 2 C À species is also important, as it determines the electronic structure and the reactivity of these species. Over the years, the synthesis, structure, and reactivity of superoxo species containing copper, [6] iron, [5,7] and manganese [8] have been reported along with other metals.[9] An important addition to this class is the report of the crystal structure of the end-on Cr-O 2 C À species and kinetic studies to probe its ability to perform C À H bond activation in hydrocarbons. [10] Metal-superoxo species are generally transient in nature and are generated at the first step of the oxygen activation both in enzyme catalysis and in biomimetic chemistry. [7c, 10b] As these species are key intermediates in iron and copper catalysis, it suggests that the M-O 2 C À species perhaps play a larger role as an oxidant in enzyme catalysis. [6,11] In the M-O 2 C À species the unpaired electrons on the metal and the radical center are strongly coupled and the electronic configuration of the metal ions dictates the nature of the magnetic coupling (J) and this may in turn correlate to the CÀH bond activation. Here we have undertaken a detailed theoretical study to specifically address the following questions 1) probing the mechanism of C À H bond activation by Cr-O 2 C À and its comparative oxidative ability to high-valent metal-oxo species, 2) establishing the comparative oxidativ...

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“…6A will be discussed below.) The radius of porphyrin used for the calculation is 7.4 Å, estimated from the effective molecular volume calculated from x-ray crystallographic data for oxygenated Fe(II) picket-fence porphyrin by assuming the molecule is spherical (16). A radius of 1.47 Å, derived from van der Waals constants (17), was used for O 2 .…”

Section: ϫ3mentioning

confidence: 99%

“…In most of these models, the reactive sites are assumed to be on the surface of the molecules (22)(23)(24). In the present case O 2 is known to bind, from the encumbered side, to the cobalt center in the pocket formed by the four pickets (16). To a first-order approximation, an encounter formed by O 2 colliding with porphyrin at the area defined by the four pickets can be assumed to be the effective encounter leading to the association.…”

mentioning

confidence: 99%

Molecular recognition of oxygen by protein mimics: Dynamics on the femtosecond to microsecond time scale

Zou

Baskin²,

Zewail³

2002

Proc. Natl. Acad. Sci. U.S.A.

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Molecular recognition by biological macromolecules involves many elementary steps, usually convoluted by diffusion processes. Here we report studies of the dynamics, from the femtosecond to the microsecond time scale, of the different elementary processes involved in the bimolecular recognition of a protein mimic, cobalt picket-fence porphyrin, with varying oxygen concentration at controlled temperatures. Electron transfer, bond breakage, and thermal ''on'' (recombination) and ''off'' (dissociation) reactions are the different processes involved. The reaction on-rate is 30 to 60 times smaller than that calculated from standard Smoluchowski theory. Introducing a two-step recognition model, with reversibility being part of both steps, removes the discrepancy and provides consistency for the reported thermodynamics, kinetics, and dynamics. The transient intermediates are configurations defined by the contact between oxygen (diatomic) and the picket-fence porphyrin (macromolecule). This intermediate is critical in the description of the potential energy landscape but, as shown here, both enthalpic and entropic contributions to the free energy are important. In the recognition process, the net entropy decrease is ؊33 cal mol ؊1 K ؊1 ; ⌬H is ؊13.4 kcal mol ؊1 . U nderstanding the process of O 2 binding to hemoglobin and myoglobin is of importance in biological science because these molecules are responsible for the oxygen transportation and storage in mammalian cells. It has been shown by various kinetic studies that the binding process involves movement of oxygen through multiple energy barriers, facilitated by fluctuations in protein structure (1, 2). However, details regarding the origin of each barrier are difficult to determine because of the complex nature of the protein structure. Synthetic model porphyrins are used to mimic the structure and function of the proteins to obtain insights into the correlation between structure and function (3). Picket-fence porphyrin is one of these synthetic models (4). One side of the porphyrin plane is a cage formed by four pivalamido pickets. An attractive property of the picket fence is its high O 2 affinity at room temperature when there is a base attached to its unencumbered side, and the oxygen binding is reversible (4).Recently, our laboratory reported femtosecond dynamics of cobalt picket-fence porphyrin in benzene (5). From the transient absorption responses, the excited oxygenated picket-fence porphyrin was found to undergo energy relaxation within the porphyrin ring and porphyrin-to-metal electron transfer on the femtosecond scale, followed by reverse electron transfer and release of O 2 within 2 ps. No substantial recombination of O 2 to porphyrin occurred on a time scale up to 20 ns after the excitation, indicating the insignificance of geminate recombination. Because of the limitation of the maximum delay time available with the femtosecond system, the recombination process on longer time scales could not be observed.Here we report our detailed study, using transie...

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Structure of a dioxygen adduct of (1-methylimidazole)-meso-tetrakis(.alpha.,.alpha.,.alpha.,.alpha.,-o-pivalamidophenyl)porphinatoiron(II). An iron dioxygen model for the heme component of oxymyoglobin

Cited by 154 publications

References 7 publications

Iron-carbonyl bond geometries of carboxymyoglobin and carboxyhemoglobin in solution determined by picosecond time-resolved infrared spectroscopy.

Iron-carbonyl bond geometries of carboxymyoglobin and carboxyhemoglobin in solution determined by picosecond time-resolved infrared spectroscopy.

CH Bond Activation by Metal–Superoxo Species: What Drives High Reactivity?

Molecular recognition of oxygen by protein mimics: Dynamics on the femtosecond to microsecond time scale

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