Magnetic circular dichroism of low symmetry cupric sites

Gerstman, Bernard S.; Brill, Arthur S.

doi:10.1063/1.448494

Cited by 34 publications

(44 citation statements)

References 20 publications

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“…At liquid helium temperatures, the MCD intensities of paramagnetic copper complexes are dominated by the C-term contribution (Piepho and Schatz, 1983). In the case of a paramagnetic ion with a ground state electron spin S = 1/2 and g-values close to 2.0, the MCD intensity depends on the magnitude of spin-orbit coupling in the excited state (Gerstman and Brill, 1985). Taking the expressions given in Piepho and Schatz (1983) the ratio At/& is equal to (CJ Do) .…”

Section: Discussionmentioning

confidence: 99%

Spectroscopic and Mutagenesis Studies on the Cu_A Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans

Farrar

Lappalainen

Zumft

et al. 1995

European Journal of Biochemistry

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Cytochrome-c oxidase contains an unusual copper centre (Cu,) located in subunit 11. This centre mediates one-electron transfer from cytochrome c to low-spin heme a. Recent spectroscopic and biochemical studies have shown that this centre is a valence delocalised dinuclear [Cu( + 1.5)-Cu( + 1 S)] centre.We have measured the absorption, EPR and variable-temperature magnetic circular dichroism spectra of the CUA-binding domain isolated from Paracoccus denitrificans cytochrome aa3. The EPR spectrum showed the following signals: gll = 2.18; g = 2.03. gll exhibited a seven-line hyperfine splitting pattern, with an intensity ratio showing that the single unpaired electron interacted equally with two copper nuclei. The magnetic circular dichroism spectrum was identical to those from Cu, in bovine heart cytochromec oxidase and centre A of nitrous-oxide reductase, showing the close structural similarity between the three centres. To identify the ligands of Cu,, all the conserved putative ligands in the l? denitrificans Cu, domain were substituted. Only five residues, Cys244, Cys248, His209, His252, and Met255, were required for correct assembly of the Cu, centre. Replacement of Met255 caused protein misfolding. Hence, methionine may have a structural role for the folding of the protein rather than being a CuA ligand. Given that both copper ions must have identical coordination geometries, the number of possible structures is limited. Two models are proposed: one involves the thiolate side-chains of Cys244 and Cys248 bridging a pair of copper ions with one histidine coordinating each copper ion, and the other has terminal ligation of each copper ion by one cysteine and one histidine residue. In both models, the metal-metal distance can be sufficiently short to permit direct d-orbital overlap of the copper ions. The magnetic circular dichroism transitions at 475 nm and 525 nm are assigned to thiolate-to-copper charge-transfer processes polarised perpendicular to one another, although the magnetic circular dichroism intensities show that the excited states were heavily mixed with copper &orbitals. These intensities can be interpreted in the thiolate bridged model in terms of transitions within a Cu2(SR), rhomb. In the model involving terminal cysteine ligation, exciton coupling of two thiolate-to-copper charge-transfer transitions of similar energy, polarised along the Cu-S bonds, would contribute two transitions perpendicular to one another. This requires that the cysteine ligands have a cis orientation relative to one another. The spectral properties of the H252N variant (histidine at position 252 replaced by asparagine) and the high-pH form of l? denitrzjicuns Cu, were similar, showing that one copper ion had lost one histidine ligand in the latter form. The dimer was converted into a valence trapped [Cu(+l)-Cu(+2)] state, which may retain the metal-metal interaction.

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Section: Discussionmentioning

confidence: 99%

Spectroscopic and Mutagenesis Studies on the Cu_A Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans

Farrar

Lappalainen

Zumft

et al. 1995

European Journal of Biochemistry

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“…the strong S(Cys) and 2 N(His) to Cu 3d x 2 −y 2 CT transitions) will be x,y polarized along their respective metal-ligand bonds. The C 0 -parameter for the MCD intensity for a spin-allowed transition between two non-degenerate states in this coordinate system is then given by [28][29][30]:…”

Section: Absorption and Magnetic Circular Dichroism Spectroscopymentioning

confidence: 99%

Recent advances in understanding blue copper proteins

Solomon¹,

Hadt²

2011

Coordination Chemistry Reviews

154

152

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“…If more excited states are mixed by spin-orbit coupling, this leads to the "sum rule" where the total positive and negative MCD intensity over the full spectrum sums to zero. 26 If there is a large deviation from this (i.e., more C-term intensity over the spectrum in one circular polarization), it likely reflects spin-orbit coupling of a lowlying excited state, though thermally inaccessible, with the ground state. An important point of the above discussion is that C-term MCD intensity requires spin-orbit coupling between excited states.…”

Section: Information Content Of C-termsmentioning

confidence: 99%

“…26 MO diagram for a high-spin d 5 ion in a T d ligand field with sulfur ligands. Right-hand side gives the wavefunctions.…”

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confidence: 99%

Inorganic and Bioinorganic Spectroscopy

Solomon

Bell

2010

Physical Inorganic Chemistry

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Spectroscopic methods have played a critical and symbiotic role in the development of our understanding of the electronic structure, physical properties, and reactivity of inorganic compounds and active sites in biological catalysis. 1,2 Ligand field theory 3 developed with our understanding of the photophysical and magnetic properties of transition metal complexes. Ligand-metal (L-M) bonding descriptions evolved through the connection of p-donor interactions with ligand to metal charge transfer (LMCT) transitions and p-backbonding with metal to ligand charge transfer (MLCT) transitions. 4 X-ray absorption (XAS) spectroscopy initially focused on the use of extended X-ray absorption fine structure 5 (EXAFS) to determine the geometric structure of a metal site in solution, but evolved in the analyses of pre-edges and edges to probe the electronic structure and thus covalency of ligand-metal bonds. 6 In bioinorganic chemistry, spectroscopy probes the geometric and electronic structure of a metallobiomolecule active site allowing the correlation of structure with function (Figure 1.1). 7 Spectroscopies are also used to experimentally probe transient species along a reaction coordinate, where often the sample has been rapidly freeze quenched to trap intermediates. An important theme in bioinorganic chemistry is that active sites often exhibit unique spectroscopic features, compared to small model complexes with the same metal ion. 8 These unusual spectroscopic features reflect novel geometric and electronic structures available to the metal ion in the protein environment. These unique spectral features are low-energy intense absorption bands and unusual spin Hamiltonian parameters. We have shown that these reflect highly covalent sites (i.e., where the metal d-orbitals have significant ligand character) that can activate the metal site for reactivity. 9 It is the goal of this chapter to provide an overview of the excited-state spectroscopic methods, including electronic absorption, circular dichroism (CD), magnetic Physical Inorganic Chemistry: Principles, Methods, and Models Edited by Andreja Bakac FIGURE 1.2 (a) The interaction of electromagnetic radiation with a metal center promotes an electron from the ground state (Y g ) to the excited state (Y e ) as dictated by the transition moment operator. This leads to the absorption band shape shown in (b). LIGAND FIELD (d ! d) EXCITED STATES

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Magnetic circular dichroism of low symmetry cupric sites

Cited by 34 publications

References 20 publications

Spectroscopic and Mutagenesis Studies on the Cu_A Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans

Spectroscopic and Mutagenesis Studies on the Cu_A Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans

Recent advances in understanding blue copper proteins

Inorganic and Bioinorganic Spectroscopy

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Magnetic circular dichroism of low symmetry cupric sites

Cited by 34 publications

References 20 publications

Spectroscopic and Mutagenesis Studies on the CuA Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans

Spectroscopic and Mutagenesis Studies on the CuA Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans

Recent advances in understanding blue copper proteins

Inorganic and Bioinorganic Spectroscopy

Contact Info

Product

Resources

About

Spectroscopic and Mutagenesis Studies on the Cu_A Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans

Spectroscopic and Mutagenesis Studies on the Cu_A Centre from The Cytochrome‐c Oxidase Complex of Paracoccus Denitrificans