The resonance Raman spectra of intermediate-spin ferrous porphyrin

Kitagawa, Teizo; Teraoka, Junji

doi:10.1016/0009-2614(79)80685-5

Cited by 92 publications

(121 citation statements)

References 15 publications

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“…2), thereby mitigating against four-coordination for deoxy-Mb under these conditions. Resonance Raman data have also been obtained on model compounds in which the strength of the axial ligand was varied (19). It was observed that characteristic five-coordinate high-spin spectra were obtained from model compounds in which either the moderately strong-field ligand imidazole or the weak-field ligand tetrahydrofuran was coordinated to the heme.…”

Section: Discussionmentioning

confidence: 97%

“…To understand the consequences of the results reported here, we turn to model compound data. The resonance Raman spectra of four-coordinate hemes are different from those of five-coordinate hemes (18)(19)(20)(21)(22). The spectra of four-coordinate ferrous hemes are similar to those oflow-spin ferric hemes, having 14 at z1375 cm-1, vlo at -1640 cm-t, and v2 at 1585 cm-'.…”

Section: Discussionmentioning

confidence: 99%

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Metastable intermediates in myoglobin at low pH.

Han

Rousseau

Giacometti

et al. 1990

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

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Resonance Raman and optical absorption spectra of ligand-free (deoxy) myoglobin and CO-bound myoglobin (MbCO) at pH 2.6 have been measured by using continuous-flow/rapid-mixing techniques. The spectra of deoxy myoglobin at low pH within 6 ms of the pH drop demonstrate that the iron-histidine bond has been ruptured but that the heme is still five-coordinate. Comparison with data from model complexes indicates that a weak-field ligand, such as a water molecule, is coordinated at the fifth position. The Raman spectrum of MbCO at low pH has an Fe-CO stretching mode that is characteristic of a six-coordinate heme with an unhindered Fe-CO moiety. Immediately following the pH drop in this case, there is no indication that the iron-proximal histidine bond is broken. Three different structural changes are detected at low pH: (i) the iron-proximal histidine (F8) bond in ligandfree myoglobin is broken and replaced by a weak-field ligand, (ih) the distal pocket in MbCO is opened, and (iii) protein constraints on the heme group in MbCO are relaxed. Previous conclusions that the kinetics of CO-binding in hemoproteins at low pH is modified by rupturing the iron-proximal histidine bond are supported by these new results which, however, demand a more complete reevaluation of the phenomenon.Since heme proteins carry out diverse biological functions, a great deal of effort has gone into determining the molecular basis for their properties. Myoglobin (Mb) is one of the simplest heme proteins and has been extensively studied in order to understand the factors that control the binding and release of oxygen, its physiological ligand, as well as CO, which is a convenient oxygen substitute for laboratory studies (1, 2). In several reports, the binding of CO to Mb (3,4) and other heme proteins (5, 6) has been monitored after a rapid drop in pH. For most Mbs and monomeric hemoglobins (Hbs) (3, 4) and for human tetrameric Hb (5), it was found that at low pH (-2.5) a large increase in the CO-binding rate occurs. This was interpreted as a consequence of protonation of the proximal histidine and the associated rupture of the iron-histidine bond, thereby allowing the iron atom to adopt an in-plane position and thus lower the barrier for CO binding. The rupture of the iron-histidine bond was supported by the absorption spectra, which, in the case of the ferrous ligand-free protein at low pH, are similar to those of fourcoordinate model compounds (4).Resonance Raman scattering is a well-suited technique to determine ligand coordination and the structure of the active site in heme proteins. Modes in the high-frequency region are known to be sensitive to axial coordination, porphyrin macrocycle core size, and heme doming (7). Axial ligand modes are often present in the resonance Raman spectrum and may be used to determine the heme coordination and the structure of the ligands (8,9). In addition, the properties of the iron-histidine bond may be monitored, since the ironhistidine stretching mode is present in five-coordinate ferrous hemes (1...

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Metastable intermediates in myoglobin at low pH.

Han

Rousseau

Giacometti

et al. 1990

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

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“…• [74]. Therefore, a computational calculation was important to predict the reason for those results.…”

Section: Spin-crossover (Sco)mentioning

confidence: 99%

The DFT+U: Approaches, Accuracy, and Applications

Tolba¹,

Gameel²,

Ali³

et al. 2018

Density Functional Calculations - Recent Progresses of Theory and Application

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This chapter introduces the Hubbard model and its applicability as a corrective tool for accurate modeling of the electronic properties of various classes of systems. The attainment of a correct description of electronic structure is critical for predicting further electronic-related properties, including intermolecular interactions and formation energies. The chapter begins with an introduction to the formulation of density functional theory (DFT) functionals, while addressing the origin of bandgap problem with correlated materials. Then, the corrective approaches proposed to solve the DFT bandgap problem are reviewed, while comparing them in terms of accuracy and computational cost. The Hubbard model will then offer a simple approach to correctly describe the behavior of highly correlated materials, known as the Mott insulators. Based on Hubbard model, DFT+U scheme is built, which is computationally convenient for accurate calculations of electronic structures. Later in this chapter, the computational and semiempirical methods of optimizing the value of the Coulomb interaction potential (U) are discussed, while evaluating the conditions under which it can be most predictive. The chapter focuses on highlighting the use of U to correct the description of the physical properties, by reviewing the results of case studies presented in literature for various classes of materials.

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“…1 , suggested on the basis resonance Raman spectroscopy [5]. It is difficult to say in this stage of the study which one of the above factors is dominant.…”

Section: Iron(ii) Derivativesmentioning

confidence: 99%

“…Depending on a solvent used in the reduction process, kind of the reduction process (chemical or electrochemical), and the molecular structure of porphyrin ligands, Fe(II) ions can exist in all the possible spin states (S = 0, S = 1 and S = 2) [2]. Results obtained from different experimental methods, even for the same Fe(II)-octaethylporphyrin complex, generated by reduction in the tetrahydrofuran (THF) solvent were interpreted ambiguously [3][4][5]. In the case of Fe(I)-porphyrins their electronic structure is more uncertainly explained than the Fe(II) analogs.…”

Section: Introductionmentioning

confidence: 99%