Silvana Sostero

Detection of xanthine oxidase activity products by EPR and HPLC in bronchoalveolar lavage fluid from patients with chronic obstructive pulmonary disease

Xanthine oxidase (xanthine: oxygen oxidoreductase, EC 1.1.3.22), a molybdenum-containing hydroxylase that produces superoxide and uric acid from purine substrates and molecular oxygen, is involved in the oxidative stress underlying several human pathologies including lung diseases. An enzymatic activity similar to xanthine oxidase was previously reported in bronchoalveolar lavage fluid of patients with chronic obstructive pulmonary disease (COPD-BAL), by fluorometric analysis of DNA unwinding and cytochrome c reduction kinetics. Here we report the detection of xanthine oxidase activity products by electron paramagnetic resonance (EPR) in presence of the spin-trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and reversed-phase high-performance liquid chromatography (RP-HPLC) in COPD-BAL (n = 14, average age of patients 65 years, range 38-81) and BAL from healthy nonsmoker controls (n = 6, average age 64 years, range 44-73). Superoxide DMPO adducts were detected in COPD-BAL and in an in vitro system containing xanthine and xanthine oxidase (XA/XO), but not in BAL controls and when superoxide dismutase (SOD, 1000 I.U./ml) was added to COPD-BAL. The HPLC analyses after addition of xanthine showed production of uric acid in COPD-BAL and in the XA/XO system but not in BAL controls. These results support the involvement of xanthine oxidase in the mechanisms of superoxide production by BAL supernatant, which increases oxidative stress in chronic obstructive pulmonary disease.

Ligand and medium controlled photochemistry of iron and ruthenium mixed-ligand complexes: prospecting for versatile systems

Abstract Selected Fe and Ru systems, whose photochemical behaviour is sensitive to numerous parameters, are presented. These systems, containing multiple species in equilibrium, are versatile enough to be adapted to special tasks and may also be used to model the phenomena and mechanisms occurring in nature. The role of various parameters is analysed and principal emphasis is given to the ligand sphere influence on the nature of the excited state and thereby on the photochemical mode. This is crucial in the case of Fe(II) complexes of the type [Fe(CN) 5 L] n − , whereas in the carbolyl–cyclopentadienyl complexes, represented by [cpRu(CO) 2 ] 2 , the nature of the excited state is of less importance than for pentacyanoferrates(II). The photochemistry of the carbonyl–cyclopentadienyl complexes is more susceptible to the impact of the medium and the role of the secondary processes is more significant.

Photodeposition of uranium oxides onto TiO2 from aqueous uranyl solutions

The photoreduction of uranyl solutions on illuminated TiO2 suspensions and electrodes has been investigated. The photoreduction leads to the formation, on TiO2, of an uranium oxide having a stoichiometry close to U3O8.Adsorption of uranyl species in the dark was examined. It was found that the degree of adsorption depended on pH and on the formation of uranyl complexes in solution.Initial rates of photoreduction are given for the cases when propan-2-ol, sodium acetate or sodium formate are used as scavengers of the photogenerated holes.With the use of microelectrode theory, it was possible to calculate the photoreduction rates from photoelectrochemical data obtained with TiO2 electrodes. The reduction rates calculated in this way were from 3.5 to 4 times lower with the electrode than with the suspension, in agreement with the larger area available in the latter case.

Influence of hydroxypropyl‐β‐cyclodextrin on photo‐induced free radical production by the sunscreen agent, butyl‐methoxydibenzoylmethane

The aim of the study was to investigate the effect of hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) on the photo‐induced production of free radicals by the sunscreen agent, butyl‐methoxydibenzoylmethane (BMDBM). Spin‐trapping/electron paramagnetic resonance spectroscopy was used to evaluate the formation of radicals and the extent of BMDBM photodegradation was measured by high‐performance liquid chromatography. The stable 2,2,6,6‐tetramethylpiperidine‐1‐oxyl, nitroxide radical (TEMPO) was used as spin‐trap. Any free radicals generated during irradiation of the sunscreen agent will couple with the TEMPO radicals giving diamagnetic species and thus a decrease of the signal intensity in the electron paramagnetic resonance spectrum. Following 2‐h illumination with simulated sunlight, the solution containing free BMDBM exhibited a 93.9% decrease of the intensity of the TEMPO signal. Under the same irradiation conditions, only a 12.2% reduction of the TEMPO concentration was measured in the sample containing BMDBM complexed with HP‐β‐CD. Moreover, the decrease of the spin‐trap level observed for the HP‐β‐CD/BMDBM complex was not significantly different from that produced when solutions containing TEMPO only or TEMPO in the presence of HP‐ β‐CD alone were subjected to irradiation. In addition, the photodegradation of the sunscreen agent was reduced by complexation with HP‐β‐CD (the extent of degradation was 27.6% for the complex compared with 63.1% for free BMDBM). The results obtained indicate that the free radicals generated by BMDBM when exposed to simulated sunlight are effectively scavenged by inclusion complexation of the sunscreen agent with HP‐β‐CD.

Photochemistry of ethylene-bis(triphenylphosphine)platinum

Abstract When [(Ph3P)2Pt(C2H4)] was irradiated in several solvents and at various wavelengths, the results differ with the conditions used. In particular irradiation at 254 nm gives a new alkylplatinum(II) complex by an insertion reaction.

Photochemistry of the [Fe(CN)5N(O)SR]3- complex : A mechanistic study

Photochemical behaviour of the title complex (RS − = mercaptosuccinate) was defined as photodissociation and photooxidation–

Photochemistry of [(η5-C5H5)Ru(CO)2]2 in polar and non-polar solvents

Abstract The photochemistry of bridged and non-bridged isomers of the title complex was studied in various solvents by flash photolysis and continuous irradiation at different wavelength regions. Reactive decay of the excited non-bridged isomer produced either a polymer (in neat non-polar solvents) or monomeric [CpRu(CO)2Cl] complex (in non-polar solvents containing CCl4) via homolytic cleavage of the RuRu bond. Polymerization was preceded by generation of a transient species (IP1) with λ max ≈470 nm and τ 1 2 ≈4 ms , which was tentatively formulated as a trimer [CpRu(CO)2]3. Photolysis of the bridged isomer generated another transient species, IP2, characterized by the solvent-dependent absorption at 315–330 nm, assigned to the mono-bridged dimer with coordinated solvent L, [Cp(CO)2Ru(μ-CO)Ru(CO)LCp]. The IP2 properties and reactivity led to conclusion that photocleavage of the CO-bridge is the mode for the bridged isomer.

Spin trapping and some reactions of ruthenium-centred radicals

The generation of ruthenium-centred radicals by photolysis of dimeric ruthenium complex [Ru(CO)2Cp]2 (Cp=η5-C5H5) has been studied by EPR and spin trapping. Mechanistic studies reveal that in toluene homolytic cleavage of both the RuRu and RuCO bonds takes place yielding ·Ru(CO)2Cp radicals and an intermediate dinuclear ruthenium complex which is CO-bridged. This reacts with P[OCH(CH3)2]3 yielding the monosubstituted dinuclear compound {Cp2Ru2(CO)3P[COH(CH3)2]3}. The ruthenium-centred radicals react with dioxygen to form peroxyl radicals which may abstract hydrogen from CH bonds. The reactivity of the photogenerated ruthenium species with various substrates is reported.

Spin trapping of radicals formed during the photolysis of the dimeric iron carbonyl complexes [η5-C5H5)Fe(CO)2]2 and [(η5-C5Me5)Fe(CO)2]2

Abstract The generation of free radicals by photolysis of dimeric iron complexes [(η 5 -C 5 H 5 )Fe(CO) 2 ] 2 and [(η 5 -C 5 Me 5 )Fe(CO) 2 ] 2 has been studied by EPR and spin trapping. Unlike [(η 5 -C 5 H 5 )Fe(CO) 2 ] 2 , no evidence for homolytic C 5 Me 5 Fe cleavage was found for [(η 5 -C 5 Me 5 )Fe(CO) 2 ] 2 . Photolytic scission of the FeFe bond appears to be the dominating free radical process in both complexes. The resulting iron-centered free radicals react readily with dioxygen to form iron peroxyl radicals which may abstract hydrogen from CH bonds. In addition, electron transfer has been observed between photoexcited [(η 5 -C 5 Me 5 )Fe(CO) 2 ] 2 and the spin trap 2-methyl-2-nitrosopropane, which leads to a variety of secondary radicals. Unlike the situation with monohalocarbons, no carbon-centered radicals were detected when the photolysis was carried out in CCl 4 and CFCl 3 , respectively.

Radical-forming electron-transfer; photoreactions involving iron group metallocenes

Abstract Iron group metallocenes Cp2M (Cp = C5H5, M = Fe, Ru, Os) and chlorocarbon solvents RCl (CCl4, CHCl3, CH2Cl2, C2Cl4) form electron donor-acceptor (EDA) complexes. During irradiation of EDA complexes in the presence of spin traps, nitroxide radical adducts of chlorocarbon radicals ·R have been detected, and on this basis a mechanism for the photolysis of EDA complexes is suggested. The ability of metallocenes, particularly Cp2Fe, to trap transient radicals ·R in electron transfer processes has been demonstrated.