Giuseppe Condorelli

Molecular mechanism of photosensitization. XI. Membrane damage and DNA cleavage photoinduced by enoxacin.

The photosensitizing activity of enoxacin, 1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐(1‐piperazinyl)‐1,8‐naphthyridine‐3‐carboxilic acid (ENX), toward membranes and DNA has been studied, taking into account human erythrocyte photohemolysis, unilamellar liposome alterations and plasmid pBR322 DNA photocleavage. Hydroxyl radicals and an aromatic carbene generated from ENX photode‐fluorination seem to be the active intermediates involved in the photosensitization process. The steady‐state photolysis products do not participate in the process. The mechanism of photosensitization responsible for the membrane damage depends on the oxygen concentration and follows a different path with respect to that operative for DNA cleavage. Between oxygenated radicals, the hydroxyl seems the species mainly responsible for membrane damage, whereas DNA cleavage is mainly produced by the carbene intermediate. A molecular mechanism of the photosensitization induced by ENX is proposed.

Complexes between fluoroquinolones and calf thymus DNA: binding mode and photochemical reactivity

The binding of the highly photocarcinogenic and phototoxic fluoroquinolones (FQs) lomefloxacin (LOM) and enoxacin (ENX) to calf thymus DNA (ct-DNA), as well as the photoreactivity of the FQs-ct-DNA complexes, have been investigated at neutral pH through the combination of several spectroscopic techniques. Both the nature and efficiency of the binding are markedly dependent on the buffer concentration. In 10−3 M phosphate buffer the interaction with ct-DNA seems to involve mainly the cationic form of both FQs, which bind to the helix with different efficiency. The overall results are consistent with a binding mode characterized by a close proximity of the chromophores to the DNA bases. An increase of one order of magnitude of the buffer concentration induces a displacement of the molecules from the DNA interior, leading to significant decrease of the association constants. The formation of external complexes involving mainly the zwitterionic forms and characterized by similar binding efficiency for both FQs appears highly probable under these experimental conditions. In this overall scenario, the positively charged piperazinyl ring of both molecules is thought to act as a pivot, going from one binding mode to another. The FQs-DNA complexes reveal a remarkably different photoreactivity. The LOM-ct-DNA complex is characterized by a photodefluorination yield similar to that observed for the free molecule whereas the ENX-ct-DNA complex is basically unphotoreactive. A rationale for these effects is provided. The relation of the overall results to the adverse side reaction photoinduced by these drugs is also commented upon briefly.

Inhibition of photohemolysis by copper(II) complexes with Sod-like activity

Red blood cell lysis photosensitized by Ketoprofen, 2-(3-benzoxyphenyl)propionic acid (KPF), was investigated in the presence of some copper(II) complexes with linear and cyclic dipeptides as well as functionalized beta-cyclodextrins with SOD-like activity with the aim of ascertaining their protective activity towards the photoinduced cell damage. The comparison between the decrease of photolytic activity caused by these complexes and their superoxide dismutase activity showed an appreciable correlation. The correct determination of species existing in experimental conditions was obtained through a simulation approach based on the knowledge of the stability constants of the complexes.

Antioxidant effect of inorganic ions on UVC and UVB induced lipid peroxidation.

Phosphate buffer suspensions of unilamellar liposomes of phosphatidylcholine were irradiated with UVC (254 nm) and UVB (300 nm) light. The irradiation provoked lipid peroxidation and liposome lysis with release of entrapped glucose-6-phosphate. At the same intensity of absorbed light, the photochemical effect at 254 nm is higher than at 300 nm. The addition of copper(II) and manganese(II) reduced both the peroxidation and the lysis. The copper showed an inhibitory effect only on the process provoked by the 254 nm irradiation, whereas the manganese was efficient both at 254 and 300 nm. The results are interpreted with a mechanism of peroxidation and quenching, involving photoformation of peroxyl radicals that are scavenged by manganese(II) and copper(I), with consequent breaking of the radical chain and reduction of the peroxidation rate. The copper(I), which is the active species, can be formed only at 254 nm by electron capture. The experimental data fit the kinetic equations obtained by the proposed mechanism by means of computer software.

Synthesis, characterization and application of Ni(tta)2.tmeda to MOCVD of nickel oxide thin films.

A novel nickel beta-diketonate adduct, Ni(tta)2.tmeda, has been synthesized using 2-thenoyltrifluoroacetone as the beta-diketonate and N,N,N,N-tetramethylethylendiamine as the Lewis base. It has been characterized by elemental analyses, IR, 1H NMR, 13C NMR spectroscopy and single-crystal X-ray diffraction studies. Physical and thermal properties of Ni(tta)2.tmeda precursor have been also extensively investigated. Its efficacy as a metal-organic chemical vapour deposition (MOCVD) precursor for the growth of nickel oxide films has been fully tested by applying it to the deposition of NiO films on quartz substrate. NiO thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy and UV spectroscopy.

Photoelectron spectroscopy of actinide organometallic compounds I. Bis(cyclooctatetraene)actinide(IV) complexes

Abstract The He(I) photoelectron spectra of the antinocene species Th(cot) 2 and U(cot) 2 (cot = cyclooctatetraene) have been determined. The 5 f metal ionization has been detected at the onset of the uranocene spectrum. The low ionization energy region of both spectra is discussed in terms of simple qualitative molecular orbital scheme.

MOLECULAR MECHANISM OF DRUG PHOTOSENSITIZATION. IX. EFFECT OF INORGANIC IONS ON DNA CLEAVAGE PHOTOSENSITIZED BY NAPROXEN

Abstract— Photocleavage of DNA induced by naproxen and the correlated protective effect by some inorganic ions have been considered. The presence of a DNA complex is suggested and only associated naproxen seems to be responsible for the cleavage, for which the quantum yield of single strand breaks was calculated. The inorganic ions I‐, Mn2+, Co2+ and Cu2+ decrease naproxen‐photoin‐duced DNA cleavage. Iodide acts by a heavy atom mechanism, thus inhibiting naproxen photolysis and decreasing the amount of free radicals responsible for the photocleavage both in aerobic and anaerobic conditions. Metallic ions protect only within a range of concentrations, as for higher amounts damaging processes are observed. The protective efficiency of cations decreases with the increase of free drug concentration in the bulk of the solution, due to their involvement in the scavenging of naproxen radicals generated by photolysis of the free drug. In the presence of EDTA the cations show a better protective action. The most likely hypothesis is an inhibiting effect on the damaging processes via a redox cycle. The different behaviors of copper and of the two other cations can be justified by the influence of redox potentials of free and complexed metals and by the superoxide dis‐mutase‐like activity of copper.

Effect ofβ-cyclodextrin complexation on the photohaemolitic activity induced by Ketoprofen and Naproxen sensitization

Red blood cell lysis photosensitized by two non-steroidal anti-inflammatory drugs Naproxen (NAP) and Ketoprofen (KPF) was investigated in the presence of β-cyclodextrin (β-Cyd). The photohaemolysis was inhibited by the addition of β-Cyd both for NAP and, to a lesser extent, for KPF. The protective action was found only in a restricted range of concentration of β-Cyd. Higher amounts of β-Cyd interfered with the resistance of the cell to the osmotic shock induced by the photosensitization process. The complexing action of β-Cyd was ascertained through UV-vis absorption spectroscopy, induced circular dichroism and emission spectroscopy.The isolated complexes Naproxen-β-Cyd (NAP-β-Cyd) and Ketoprofen-β-Cyd (KPF-β-Cyd) were found to protect from the photosensitized membrane damage induced by the two drugs, even if it occurred only in a limited range of concentration. This suggests a valid tool in alleviating thein vitro phototoxic consequences caused by these compounds, even if care has to be taken in therapeutic administration due to the presence of the uncomplexed β-Cyd.

Molecular mechanism of drug photosensitization: VIII. Effect of inorganic ions on membrane damage photosensitized by naproxen.

The inhibitory effect of Cu2+, Mn2+, Co2+, and I- on naproxen-induced photohemolysis was investigated. In order to better understand this effect, these ions were also tested for lipid peroxidation and protein crosslinking, which are among the main processes involved in erythrocyte membrane damage. The overall results support the hypothesis that metal cations act via a redox scavenging of the radicals which are produced on the lipid component of the membrane. This process occurs through hydrogen abstraction operated by photogenerated naproxen radicals. Moreover, copper can also act as a superoxide anion scavenger: its decay is noxious in photohemolysis, whereas it is not in lipid peroxidation. Metal cations, besides, are not able to scavenge protein crosslinking. On the other hand, iodide is able to reduce both processes because it acts as a heavy atom, favoring intersystem crossing to the unreactive triplet state of the drug, thus reducing naproxen photolysis and, as a consequence, the amount of the damaging species produced. This mechanism was supported by luminescence experiments performed in the absence and in the presence of iodide.

Synthesis and characterization of La2−xBaxCuO4+δ thin film through a simple MOCVD approach

Superconducting La2−xBaxCuO4+δ n (LBCO) films have been deposited on 10 × 10 mm2 n (100) LaAlO3 substrates using an in-situ MOCVD process and adopting the multi-component single source approach. Highly c-axis oriented films are fabricated and X-ray diffraction (XRD) n (103) pole figures point to the epitaxial nature of the LBCO films. Scanning electron and atomic force microscopy images show highly homogeneous surfaces. Energy dispersive (EDX) and wavelength dispersive X-ray (WDX) analyses show a good homogeneity over all the 10 × 10 mm2 substrate and the absence of any F or C contaminations.