Critical appraisal of electronic structure of metmyoglobin. 14N and 57Fe hyperfine interactions

Mun, Seong Ki; Chang, Jane C.; Das, T. P.

doi:10.1016/0005-2795(77)90126-x

Cited by 9 publications

(4 citation statements)

References 28 publications

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“…The positive sign of A iso has been attributed to the direct transfer of electron spin from the metal d z 2 to the ligand nitrogen σ orbitals, which is consistent with our d z 2 orbital spin population. The nitrogen isotropic coupling constants are similar to those measured for metmyoglobin, which also include anisotropic coupling, indicating that the interaction of the high-spin ferric heme's unpaired electrons with ligand nitrogen atoms is largely isotropic, as in the doublet heme.…”

Section: Resultssupporting

confidence: 65%

Characterization of Electronic Structure and Properties of a Bis(histidine) Heme Model Complex

et al. 2003

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Ferric and ferrous hemes, such as those present in electron transfer proteins, often have low-lying spin states that are very close in energy. To explore the relationship between spin state, geometry, and cytochrome electron transfer, we investigate, using density functional theory, the relative energies, electronic structure, and optimized geometries for a high- and low-spin ferric and ferrous heme model complex. Our model consists of an iron-porphyrin axially ligated by two imidazoles, which model the interaction of a heme with histidine residues. Using the B3LYP hybrid functional, we found that, in the ferric model heme complex, the doublet is lower in energy than the sextet by 8.4 kcal/mol and the singlet ferrous heme is 6.7 kcal/mol more stable than the quintet. The difference between the high-spin ferric and ferrous model heme energies yields an adiabatic electron affinity (AEA) of 5.24 eV, and the low-spin AEA is 5.17 eV. Both values are large enough to ensure electron trapping, and electronic structure analysis indicates that the iron d(pi) orbital is involved in the electron transfer between hemes. Mössbauer parameters calculated to verify the B3LYP electronic structure correlate very well with experimental values. Isotropic hyperfine coupling constants for the ligand nitrogen atoms were also evaluated. The optimized geometries of the ferric and ferrous hemes are consistent with structures from X-ray crystallography and reveal that the iron-imidazole distances are significantly longer in the high-spin hemes, which suggests that the protein environment, modeled here by the imidazoles, plays an important role in regulating the spin state. Iron-imidazole dissociation energies, force constants, and harmonic frequencies were calculated for the ferric and ferrous low-spin and high-spin hemes. In both the ferric and the ferrous cases, a single imidazole ligand is more easily dissociated from the high-spin hemes.

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Section: Resultssupporting

confidence: 65%

Characterization of Electronic Structure and Properties of a Bis(histidine) Heme Model Complex

et al. 2003

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“…4. This expectation has been found to be borne out through overall satisfactory agreement (22,23) between theory and experiment for spectroscopic data in a number of metal-porphyrins and a number of properties related explicitly to the electronic wave functions such as hyperfine constants of iron (22) and other nuclei such as '4N (22) and halogen (24) nuclei, electron spectroscopy for chemical analysis (ESCA) (25), and isomer shift (26) data in a number of high-spin five-liganded and six-liganded heme systems. We have carried out calculations for both the five-liganded system with NO as the fifth ligand and the six-liganded systems with the Im of the proximal histidine as the sixth ligand.…”

Section: Methodsmentioning

confidence: 65%

Origin of observed changes in ¹⁴ N hyperfine interaction accompanying R → T transition in nitrosylhemoglobin

Mun

Chang

Das

1979

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

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Theoretical investigations of electronic distributions in eight different structural forms of nitrosylhemoglobin were carried out to study the changes in 14N hyperfine interaction observed with the transition from R to T structures under the influence of inositol hexaphosphate or changing pH. Four of the eight forms studied consisted of protonated and deprotonated N ros in the proximal imidazole ligand with linear and bent Fe-N-0 structures. Two other forms had a straight Fe-N-O structure and Fe-Im bond stretched by 0.5 and 1.0 .A. The other two systems we have studied are five-liganded NO-heme with bent and straight Fe-N-O structures. Our investigations show that arrangements of energy levels did not differ significantly among all the structures, the unpaired electron always occupying an antibonding orbital with d.2 symmetry. The protonated and deprotonated systems with either linear or bent Fe-N-O structure showed substantial hyperfine interaction of the 14N nuclei of the NO group and the Nf atom of the proximal imidazole, indicating that a 9-line electron spin resonance hyperfine pattern (R structure) would be expected in all four cases. On the other hand, the extensions of the Fe-Im bond produce a sizeable decrease in the 14Nf hyperfine interaction, indicating that an extension beyond 1.0 A\ would provide a 3-line hyperfine pattern close to that found for the five-liganded NO-heme system. Our results thus provide quantitative support for the model of severe extension or cleavage of the Fe-N, bond proposed in the literature for explaining the R-to-T transition of the a-chain of nitrosylhemoglobin.The study of the properties of nitrosylhemoglobin (NO-Hb) has assumed major importance (1-4) in recent years for two main reasons. First, it is a six-liganded hemoglobin derivative that is paramagnetic with spin 1/2, which makes it amenable for electron paramagnetic resonance (EPR) studies (2-10). Such studies allow one to follow the changes in the electron distribution over the molecule associated with transitions between R and T states, considered to be of crucial importance in the explanation of cooperativity (11) in the oxygen-binding properties of hemoglobin. The second reason is that, in contrast to oxyhemoglobin and carbonmonoxyhemoglobin, NO-Hb shows a pronounced R-to-T transition (12,13) in the presence of inositol hexaphosphate, this transition being also rather sensitive to changes (5, 9, 10) in pH of the surrounding environment. One of the properties of NO-Hb that is a sensitive indicator of changes of structure under the influence of inositol hexaphosphate or changes in pH is the splitting produced (3-10) in EPR spectra by 14N hyperfine interactions. Thus, in NO-Hb A, in the presence of inositol hexaphosphate or at low pH one finds for the aY chain a 3-line hyperfine pattern associated with the hyperfine interaction of the '4N nucleus of NO. On increasing the pH beyond 8.0, even in the presence of inositol hexaphosphate one sees a change (5) from the 3-line to a 9-line pattern, indicating that th...

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“…In recent years, hyperfine interaction data for 14N and *H nuclei have become available in ferricytochrome c through electron nuclear double resonance (ENDOR)1 measurements.2•3 456789It is therefore of interest to examine if one can explain these data through ab initio investigations of the electronic structures of this molecule, as has been possible in earlier work on other lowand high-spin heme systems. [4][5][6] The understanding of the electronic structure of ferricytochrome c is of particular interest because of the important role7-9 it plays in electron transfer processes in a number of biological systems. In particular, in explaining the mechanism by which the ferricytochrome molecule gets reduced to the ferrous state, it has been proposed10 that the unpaired spin orbital is in a ir-like (dxz or dra) state and that the sulfur of the methionine group carries a small positive charge that interacts electrostatically with the negative charge of an oxygen on the tyrosine molecule of the protein chain, this interaction providing a constraint on the orientation of the methionine group.…”

mentioning

confidence: 99%

“…Calculation of Hyperfine Constants. The nuclear spin Hamiltonian, 77spin, for an electronic system with spin S and a nucleus with spin 7 in the presence of a magnetic field along the Z direction is given by13 77, pin = SzzUbHS2 + AZZ1ZSZ "F Pzz[¡z2 -¡(J + 1)] -µ<^ 1 (5) where gzz, Azz, and Pzz represent the ZZ components respectively of the electronic g tensor and magnetic hyperfine and quadrupole coupling tensors, µ and µ representing the Bohr magneton and nuclear magnetic moment. The Azz and Pzz in eq 5 can be obtained from the expectation value of the electron nuclear hyperfine interaction Hamiltonian, eN, over the many-electron wave function,14 with (12) (a) M. Zerner, M. Gouterman, and H. Kobayashi, Theo.…”

mentioning

confidence: 99%

Electronic structure of ferricytochrome c and associated hyperfine interactions

Mishra¹,

Mishra²,

Das³

1983

J. Am. Chem. Soc.

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Critical appraisal of electronic structure of metmyoglobin. 14N and 57Fe hyperfine interactions

Cited by 9 publications

References 28 publications

Characterization of Electronic Structure and Properties of a Bis(histidine) Heme Model Complex

Characterization of Electronic Structure and Properties of a Bis(histidine) Heme Model Complex

Origin of observed changes in ¹⁴ N hyperfine interaction accompanying R → T transition in nitrosylhemoglobin

Electronic structure of ferricytochrome c and associated hyperfine interactions

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Critical appraisal of electronic structure of metmyoglobin. 14N and 57Fe hyperfine interactions

Cited by 9 publications

References 28 publications

Characterization of Electronic Structure and Properties of a Bis(histidine) Heme Model Complex

Characterization of Electronic Structure and Properties of a Bis(histidine) Heme Model Complex

Origin of observed changes in 14 N hyperfine interaction accompanying R → T transition in nitrosylhemoglobin

Electronic structure of ferricytochrome c and associated hyperfine interactions

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Origin of observed changes in ¹⁴ N hyperfine interaction accompanying R → T transition in nitrosylhemoglobin