Lucia Tosi

Spectroscopic studies of metal complexes containing π-delocalized sulfur ligands. The resonance raman spectra of the iron(II) and iron (III) complexes of the antitumor agent 2-formylpyridin thiosemicarbozone

Abstract The resonance Raman spectra of the Fe(II) and Fe(III) complexes of 2-formylpyridine thiosemicarbazone have been measured in acid (pH 3.94.2) and alkaline (pH 7.4) aqueous media. In the spectra of both compounds the bands most strongly enhanced are due to skeletal modes (primarily CN and CS stretches) and ring deformations. On the basis of these results the strong visible absorption of these complexes is attributed to a pπ(s) → σ *(Fe) ligand to metal charge transfer transition. Moreover, the excitation profiles of the Fe(II) complex show a progression of peaks with regular spacing, which are interpreted as arising from successive vibrational levels involving the CS stretching mode. CN vibrations are very sensitive both to metal charge and protonation of the ligand whereas the CS vibrational frequencies are only dependent on metal charge. These results suggest appreciable dππ metalsulfur back bonding in the Fe(II) complex.

Kinetic and mechanism of vesicle lipoperoxide decomposition by Fe(II)

Abstract Small unilamellar vesicles of l -α-phosphatidylcholine have been subjected to peroxidation and the initial kinetic rate of decomposition of these peroxides (ROOH) induced by the presence of Fe(II) or alternatively the oxidation of Fe(II) to Fe(III) by these peroxides has been determined. The oxidation of Fe(II) exhibits saturation kinetics. A mechanism is then proposed involving, as a first step, the fixation of Fe(II) to the membrane, and then the decomposition of the peroxide by the complex thus formed. The disruption of the RO-OH bond follows a second-order rate law with k 2 = 1500 ± 500 M −1 · s −1 at 25°C. Moreover, these data suggest that the ROOH groups are localized at the aqueous interface.

Ceruloplasmin-anion interaction a resonance Raman spectroscopic study

Summary Resonance Raman spectra of ceruloplasmin using the 632.8 nm He-Ne radiation show bands at 415, 402 (shoulder), 382, 360 and 340 cm−1 which can be assigned to the metal-ligand stretching modes of the two “blue” Cu(II) ions present in the enzyme. After addition of N3− and SCN− to ceruloplasmin the Cu(II)-ligand bonds of one of the two “blue” copper sites are disrupted and three bands in the RR spectra disappear, namely, at 415, 382 and 340 cm−1. RR data enable the assignment of the metal-ligand stretching vibrations of each “blue” cupric ion, give evidence of subtle conformational changes around the non disrupted one, and confirm previous results indicating the non equivalency of the two “blue” copper sites.

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.

Circular dichroism investigation of the (L Lysine)n-Cu(II) (I:I) System with n = 4 and n = 25

The study of the (L Lys)n-Cu(II) (1:1) system with n = 4 and n = 25 using circular dichroism (CD) data has provided evidence indicating the formation of two complexes in a two-step process. In the first of these complexes, obtained at pH 6.6, the alpha-amino terminal group and the adjacent deprotonated amide nitrogen are bound to the metal. In the second, additional amino nitrogens of side chains lie at the other two corners of the coordination square. A comprehensive investigation of changes occuring in spectral patterns when coordination takes place enables the assignment of three bands that are characteristic to each type of nitrogen coordination.

Iron·bleomycin·DNA·system evidence of a long-lived bleomycin·iron·oxygen intermediate

Abstract When Fe(II) is added to a bleomycin. DNA mixture in the presence of air a long-lived ( t 1 2 = 45 minutes ) EPR silent species (I′) is formed; the circular dichroism and absorption spectra of which have been characterized. This complex slowly decays yielding a ferric complex (III′) analogous to the well known low spin Fe(III). BLM species.

Spectrophotometric studies of the copper(II)–D-o-tyrosine complex. Assignment of the 330-nm dichroic band in copper(II) and iron(III) transferrins

The separation of both enantiomers of racemic o-tyrosine by means of binapthylphosphoric acid has been undertaken. Copper(II) interacts with D-o-tyrosine to form two complexes. The first, obtained at pH 6, displays a circular-dichroism (c.d.) spectral pattern characteristic of metal co-ordination through amino-nitrogens and carboxylate oxygens. The second complex starts to form at pH 8 and is fully defined at pH 10.5. Its c.d. spectrum, in the region below 400 nm, is very similar to those of iron(III) and copper(II) transferrins and displays two well defined bands at ca. 400 and 330 nm. So far, only the origin of the higher-frequency peak has been well established as arising from a phenolate-oxygen-to-metal charge-transfer transition, whereas that of the lower-frequency peak remains uncertain. Resonance-Raman measurements upon excitation into the envelope of the two absorptions at 400 and 330 nm clearly indicate a common origin to both bands, namely: phenolate oxygen → CuII charge-transfer transition.

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.

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.

The effects of neutral salts on the conformational transition of ceruloplasmin

Neutral salts inhibit the activity of ceruloplasmin in an order of increasing effectiveness for anions as follows: ClO4− < Br− < Cl− < F− < SCN− < OCN− < N3− < CN−. Circular dichroism measurements show that, save CN−, this order parallels that of increasing effectiveness in inducing α-helix structure.