Arlette Garnier

Electronic structure, electronic spectra and Mössbauer hyperfine interactions in ruthenium complexes

Self-consistent charge and configuration molecular orbital calculations have been performed for [Ru(CN)5− NO]−2 [RuCl5NO]−2 and [Ru(NH3)5NO]+. The empirical parameters required in the SCCC-MO calculations were derived from the fitting of calculated electronic transitions to those measured by optical absorption spectroscopy. The electronic populations obtained in this manner were used to interpret the isomer shifts and quadrupole splittings measured by Mossbauerspectroscopy with 99Ru complexes.

Ceruloplasmin-anion interaction a circular dichroism spectroscopic study

The effect of anion binding to ceruloplasmin has been studied using absorption and cirbular dichroism spectral data. At anion to ceruloplasmin molar ratios approaching infinite, OCN-, N3- and SCN- bind to ceruloplasmin giving rise to similar alterations in circular dichroism and absorption spectra. The positive bands at 610 and 520 nm in circular dichroism spectra disappear, a negative one apperars at 600 nm and the peak at 450 nm is only slightly modified. There is a new negative band at 410 nm well-defined in OCN- ceruloplasmin spectra. The decrease in absorption at 610 nm is ascribed to the disruption of one type I Cu-S(cysteine) bond owing presumably to the changes induced by anions in the protein secondary structure. The new band at 410 nm is assigned to a charge transfer transition from the ligand replacing cysteine at its binding site. Both absorption and circular dichroism spectra show isobestic points indicating that anion binding to the enzyme, disruption of one of the two type I Cu-S bonds and coordination of this Cu to another protein residue take place simultaneously.

The effect of laser radiations on human ceruloplasmin. Absorption, circular dichroism and electron paramagnetic resonance study.

Abstract Laser radiations at wavelengths ranging from 514.5 to 360.0 nm decolorize human ceruloplasmin. Kinetic behavior of the two chromophores absorbing at 610 nm, as measured by absorption and circular dichroism data, indicate different quantum yields of the two type I copper ions, whose maximum lies approximatively at 400 nm. Furthermore, as Electron Paramagnetic Resonance measurements demonstrate, the photochemical process involves reduction of the two type I copper ions leaving type II copper unchanged.

Formation and structure of Cu (II) — poly (L-arginine) complexes in aqueous solution

Abstract Cu (II) — poly (L-arginine) (PLA) complexes have been studied using potentiometric titrations, optical absorption and circular dichroism spectra. Three different complexes have been observed. The first one (complex I) is formed up to pH 8 and results from the coordination of two guanidinium groups to the metal ion. The second and third complexes (complexes IIA and IIB) are formed between pH 8 and 11, in different proportions which are dependent on PLA: Cu molar ratio. In these two complexes two guanidinium groups and two peptide nitrogens participate as ligands around the copper ion.

Ferroxidase II. The essential role of copper in enzymatic activity

Abstract One of the biological roles of ceruloplasmin is the oxidation of Fe(II) to Fe(III). It has therefore been called Ferroxidase I whereas a cuprilipoprotein has been called Ferroxidase II. It is shown that this protein can bind several Cu(II) but only one being essential for its enzymatic activity. The hypothesis that ferroxidase activity arises from lipo-hydroperoxides has been ruled out.

Circular dichroism and resonance Raman spectra of the Cu(II)-Cu(I) complex of D-Penicillamine. The CuS(CYS) stretching mode in blue copper proteins

Abstract Circular dichroism and resonance Raman spectra of the cluster anion: [Cu(II) 6 Cu(I) 8 (D-Penicillamine) 12 Cl] 5− enable the assignment of the S(mercaptide)→Cu(II) charge transfer transition to a band lying at 18250 cm −1 . The resonance Raman spectra compare with that of copper-diethyldithiocarbamate obtained previously. The implications of both series of data upon the resonance Raman spectra of blue copper proteins and the assignment of the CuS(cys) stretching mode are pointed out.

Cu(II)—(lAsp)n system. Spectroscopic evidence of hexatomic chelate ring formation

Abstract The study of the Cu(II)-(L Asp)n system using circular dichroism and potentiometric data has provided evidence indicating the formation of two complexes in a two step process. In the first (I) of these complexes, obtained at pH 4.5, two carboxyl residues are bound to the metal. This complex partially inhibits the transition from α helix to nonperiodic conformation. In the second complex (II) two peptide nitrogens and two carboxylate oxygens are bound to each Cu(II) ion forming two hexatomic chelate rings. The CD spectral pattern is then the opposite of what is obtained when a five-membered chelate ring is formed.

Ceruloplasmin–diethyldithiocarbamate (DTC) interaction Evidence of DTC chelation to two non enzymatic Cu(II)

Abstract Ceruloplasmin (Cp) is a plasma copper oxidase containing several copper ions. Among them five are essential to enzymatic activity and are classified into three types [1]: two cupric ions of type I (Ia and Ib [2]) or ‘blue’, one cupric ion of type II or ‘non blue’ and two cupric ions of type III which are not EPR detectable. In this communication we report evidence suggesting the presence of two extra cupric ions that can bind chelating agents such as diethyldithiocarbamate (DTC). The addition of DTC to Cp (pH 5.5) yields an absorption at 445 nm in the Cp spectrum. When increasing equivalents of DTC are reacted with the protein no further spectral changes are appreciable at DTC/Cp > 4 and the absorptivity at 445 nm indicates the chelation of two Cu(II) forming two Cu(DTC)2. The absorption at 610 nm is not modified and the circular dichroism (CD) spectrum exhibits only a slight decrease. On the other hand the band at 445 nm due to the DTC → Cu2+ charge transfer transition is not optically active indicating that the Cu(DTC)2 complex is not coordinated to the protein. Addition of an inhibitor, such as N−3, to a Cp–DTC solution gives rise to the absorption at 380 nm and to the CD spectrum characteristics of N−3 bound to type II Cu(II). Moreover, the Cp–DTC solution exhibits the same enzymatic activity as Cp free of DTC. From these results we can infer that the five cupric ions necessary to the enzymatic activity of Cp are not modified by the addition of DTC which instead chelates two extra cupric ions hereafter labeled X and Y. Both X and Y Cu(II) can be removed from Cp, by centrifugation, after addition of DTC, if this is performed within ten minutes following the addition of DTC. On the other hand, when Cp is incubated for several hours with DTC a very slight precipitate appears and the solution recovers the blue color of native Cp. If DTC is then added to the supernatant the absorption at 445 nm due to both DTC-bound X and Y reappears. These results suggest that as time elapses the Cu(DTC)2 complexes dissociate and that X and Y Cu(II) reenter the protein.

Resonance-Raman spectra of copper(II) and nickel(II) diethyldithiocarbamates

Copper(II) and nickel(II) diethyldithiocarbamates display a resonance-Raman spectrum when excited with laser lines at wavelengths approaching that of the first allowed charge-transfer (c.t.) transition. Both spectra show the preferential intensity enhancement of four bands in the M–S stretching and SCS, SCN, MSC, and SMS bending region at 157–367 cm–1. Except for one deformation mode, all the bands are polarized. Assignments of these bands have been made by comparison with normal-co-ordinate analysis data for dithiocarbamato-complexes. The experimental intensity dependence on Albrecht frequency factors suggests a Raman activity derived from mixing between one c.t. and one ligand transition. The two electronic transitions involved have been assigned by taking into account depolarization ratios and using polarized absorption data and molecular-orbital calculations from the literature.