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CHELATION OF COPPER(II) IONS BY DOXORUBICIN AND 4'-EPIDOXORUBICIN - ELECTRON-SPIN-RESONANCE EVIDENCE FOR A NEW COMPLEX AT HIGH ANTHRACYCLINE COPPER MOLAR RATIOS
No full textDoxorubicin and 4′-epidoxorubicin form chelate complexes with Cu(II), the structures of which are dependent on the drug-to-metal ratio r. The complex stoichiometry is defined by the structure of the drug, the pH and the r values. The cupric ion is able to evidence minor structural differences (doxorubicin versus 4′-epidoxorubicin), the substitution pattern of the antraquinone moiety and the self-association of the anthracycline ligand
Electron spin resonance of some paramagnetic compounds of iridium(II)
No full textThis paper deals with some electronic problems suggested by Malatesta. Electron spin resonance with [IrBr3(NO)(PPh3)2] shows that the electronic configuration of the paramagnetic compound is described by that of the Ir-NO moiety. Specifically the three values of g tensor components demonstrate that the unpaired electron is located in a largely comprised π* (NO) orbital, so that the electronic state of NO is similar to that of gaseous trapped NO. The overlap between Ir and NO orbitals is through the dπ (dxz or dyz) metal orbitals, with consequent bent coordination of NO ligand. In conclusion the stability of d7 configuration of Ir in this monomeric compound is due to the easy electron transfer between metal and ligand, in agreement with that described in other monomeric Ir(II) compounds. © 1982
ANTHRACYCLINE COPPER(II) COMPLEXES - STRUCTURE-DEPENDENT COORDINATION PATTERN AS EVIDENCED BY ELECTRON-SPIN-RESONANCE
No full textThe copper(II) coordination properties of different anthracycline antitumor agents were studied by ESR spectroscopy. Three classes of drugs have been identified: (i) adria-like, which contains adriamycin, daunomycin, 4′-deoxydaunomycin, 4′-deoxy- 4′-iododaunomycin and 4-demethoxydaunomycin; (ii) 4′-epiadria-like, which contains 4′-epiadriamycin, 4′-epidaunomycin, 4-demethoxy-6-deoxydaunomycin and 4-demethoxy-11-deoxydaunomycin; and (iii) border-line type, which contains carminomycin, 6-O- methylcarminomycin, 11-deoxycarminomycin and 6- deoxycarminomycin. They have been characterized by their different Cu(II) chelation properties. The adria-like class members give rise to multi- nuclear complexes, where both the CO and COH functionalities of both sides of the hydroxyanthra- quinone system are involved in the coordination. By contrast, the 4′-epiadria-like drugs form monomeric Cu(II) complexes because of the unavailability of the C(6)OH group. The border-line type compounds yield more than one monomeric Cu(II)adduct because of the presence of OH at the C(4) position. All Cu(II) derivatives are characterized by a very strong ligand field, the unpaired electron lying in the dx2-y2 orbital. The onset of comptexation is oxygen dependent and this is related to the σ and π bond properties of the anthracycline ligand
ESR investigation of paramagnetic carbonyl-metal clusters of high nuclearity
No full textAn ESR study has been made of the high nuclearity paramagnetic metal cluster anions [Rh12(CO)13(μ2-CO)10(C)2]3-, [Co13(CO)12(μ2-CO)12(C)2]4- and [Co6(CO)8(μ2-CO)6C]-. The assignment of the HOMO is based on a mixed valence model which relates the g tensor components of cluster systems to those of an appropriate conventional paramagnetic center. With this model the HOMOs of [Rh12(CO)13(μ2-CO)10(C)2]3- and of [Co13(CO)12(μ2-CO)12(C)2]4- are found to be mainly comprised of metal dz2 atomic orbitals, while for [Co6(CO)8(μ2-CO)6C]- a large overlap between d atomic orbitals and ligand orbitals is suggested. The occupation of the valence molecular orbitals deduced from the ESR data is consistent with the variations in MM bond distance observed by X-ray analysis. © 1982
ON THE USE OF ELECTRON-SPIN-RESONANCE IN INVESTIGATING DISPERSED METAL SYSTEMS - A CONTRIBUTION TO RELATIONSHIPS BETWEEN CLUSTERS AND METAL-SURFACES
No full textOxygen chemisorption on γ-Al2O3·phthalocyaninato·-cobalt(II): Coordination of O2 by complexed cobalt centers; Tumbling of molecular oxygen on surface cobalt centers
No full textThe system phthalocyaninatocobalt(II)·Al2O3, ([Co(pc)]·γ-Al2O3), if contacted with air at high temperatures (70 - 150 °C), has been found to be active to oxygen chemisorption. ESR measurements revealed that the chemisorption is a reversible process, leading to the formation of [Co(pc)O2]·γ-Al2O3 as a paramagnetic intermediate. ESR spectroscopy has also been used to investigate the rate of angular reorientation of O2 absorbed on the [Co(pc)]·γ-Al2O3 surface at a variety of temperatures. Computer simulations of the ESR spectra were compared with spectra obtained experimentally, and correlation times for reorientation and anisotropic g values were calculated. The fitting of the anisotropic g values to a model based on second-order perturbation theory suggests that the ground state of [Co(pc)O2]·γ-Al2O3 is (x2 - y2)2(z2)2(xz or yz)2(yz or xz), with the unpaired electron localized mainly on cobalt. According to this finding, oxygen interacts with cobalt mainly through a π overlap. © 1982
Defect chemistry in ruthenium-supported tin dioxide: a spectromagnetic approach
No full textThe reactivity towards CO and air of SnO2 defects, singly and doubly ionized oxygen vacancies (V(o)/· V(o)/··), bivalent tin centers, was studied in ruthenium-supported tin oxide (Ru/SnO2), and compared with that in pure SnO2. Electron paramagnetic resonance and X-ray photoelectron spectroscopy studies demonstrated that CO treatment produces V(o)/· and V(o)/·· defects in SnO2, some V(o)/· transferring their electrons to Sn4+ centers; instead in Ru/SnO2, some V(o)/· defects transferred their electrons to Ru(n+) centers (n=0,1,2,3) and no one bivalent tin center was observed. When contacted with air, pure SnO2 transferred a part of the electrons of V(o)/· and of bivalent tin centers to O2, instead Ru/SnO2 emptied all V(o)/· defects transferring the electrons from V(o)/· to ruthenium and to O2. The via ruthenium transfer increases the number of electrons exchanged between SnO2 and the surrounding atmosphere and gave a rationale for the higher sensitivity towards CO displayed by transition metal-doped SnO2 with respect to pure SnO2
Chromium(III) complexes of L(+)-cysteine, DL-penicillamine and L(-)-cystine. Synthesis and spectromagnetic characterization
No full textChromium(III) chloro-complexes with L(+)-cysteine, dl-penicillamine and l(-)-cystine were isolated and characterized by their vibrational, electronic and spectromagnetic properties. The coordination of sulphur containing amino acids involves amino and/or carboxylato groups; only in the case of penicillamine the mercapto group shows bonding with metal. The difference in the relative strength of binding sites, in the compounds here reported, is related to the σ -donor and π -acceptor properties of sulphur containing amino acids; specifically coordination of mercapto group becomes possible if amino and carboxylato groups supply to chromium the electronic charge required for the back-donation to dπ sulphur orbitals
3,6-BIS(2'-PYRIDYL)PYRIDAZINE DINUCLEAR COMPLEXES - PALLADIUM(II), PLATINUM(II) AND 1ST ROW TRANSITION METAL(II) MIXED COMPLEXES
No full textNew Pd(II) and Pt(II) 3,6-bis(2′-pyridyl)pyridazine (dppn) mononuclear complexes of the type M(dppn)Cl2 were prepared and characterized. From M(dppn)Cl2, the bimetallic homonuclear complexes M(dppn)MCl4 were prepared by reaction with Pd(PhCN)2Cl2 or K2PtCl4. Bimetallic heteronuclear species of the type M(dppn)M′Cl4, were prepared reacting the mononuclear complexes with the stoichiometric amount of M′Cl2 (M′ = Cu, Co, Ni). All the described reaction give product in high yield. The isolated compounds, almost completely insoluble in most organic solvents, were characterized by elemental analysis, IR, ESR, reflectance spectra, and magnetic moment measurements. On the basis of these data the geometries around the metals are discussed
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