A photosensitizer dinuclear ruthenium complex: intramolecular energy transfer to a covalently linked fullerene acceptor.

A fullerene derivative (5) in which a dinuclear ruthenium complex is covalently linked to a fulleropyrrolidine (FP) through a rigid spacer has been prepared through azomethine ylide cycloaddition to C60. Electrochemical and photophysical studies revealed that ground-state electronic interactions between the bimetallic ruthenium chromophore and the FP moiety are small. The absorption spectrum of 5 displays a metal-to-ligand charge transfer (MLCT) transition at about 620 nm in CH2Cl2 which is shifted by nearly 160 nm relative to that of a previously reported mononuclear dyad (8). The photophysical investigations have also shown that both in dichloromethane and acetonitrile the photoexcited MLCT state of dyad 5 transforms into the fullerene triplet excited state with a quantum yield of 0.19 and that, contrary to mononuclear dyad 8, electron transfer, if any under the applied conditions, is negligible relative to energy transfer.

Photoinduction of fast, reversible translational motion in a hydrogen-bonded molecular shuttle.

A rotaxane is described in which a macrocycle moves reversibly between two hydrogen-bonding stations after a nanosecond laser pulse. Observation of transient changes in the optical absorption spectrum after photoexcitation allows direct quantitative monitoring of the submolecular translational process. The rate of shuttling was determined and the influence of the surrounding medium was studied: At room temperature in acetonitrile, the photoinduced movement of the macrocycle to the second station takes about 1 microsecond and, after charge recombination (about 100 microseconds), the macrocycle shuttles back to its original position. The process is reversible and cyclable and has properties characteristic of an energy-driven piston.

Cytotoxicity and probable mechanism of action of sulphimidazole.

Sulphimidazole (1-methyl-2((4-aminophenyl)-sulphonyl)-amino-5-nitroimidazole) is a new compound in which a p-aminobenzenesulphonamide radical has been attached at position 2 of the 5-nitroimidazole ring. It possesses a useful spectrum of activity in vitro against various anaerobic microorganisms and its action against aerobic and facultative bacteria is synergically enhanced in association with trimethoprim. In the present study, we determined the cytotoxicity in vitro of sulphimidazole and trimethoprim, both alone and in combination, and analysed the viability of Vero cells and the protein content of their cell lysate in the presence of increasing concentrations of these drugs. Also, in order to verify the hypothesis that the action of sulphimidazole against aerobic and facultative bacteria is mediated by the sulphonamide component of the molecule, while that against anaerobic bacteria depends on the action of the nitro group of the 5-nitroimidazole ring, we studied the mechanism of action of the new compound both indirectly, by means of microbiological techniques, and directly, by determining its oxidoreduction potential with respect to that of metronidazole. The results show that sulphimidazole is only slightly toxic in vitro for Vero cells, either alone or in association with trimethoprim, and that the combination of the two functional groups in a single molecule not only maintains its structure-activity relationship intact but also broadens its antibacterial spectrum.

Medium effects on the antioxidant activity of dipyridamole.

Very strong medium effects have been observed when testing the antioxidant activity of dipyridamole (DP) in different media such as benzene, tert-butanol, methanol solutions and egg yolk lecithin unilamellar and multilamellar vesicles. Actually, dipyridamole behaves as a very poor antioxidant in benzene while its ability to inhibit the lipid peroxidation reaction increases with increasing solvent polarity, being the highest in lipid vesicles. This behavior can not be rationalized on the basis of the classical chain breaking mechanism which operates in the case of phenolic and amine antioxidants and involving the transfer of a hydrogen atom to peroxyl radicals. An explanation is instead given in terms of an electron transfer reaction which leads to the oxidation of DP by the chain carrying peroxyl radical to give the dipyridamole cation radical, DP+*, and the peroxyl anion LOO-, and whose rate constant is expected to increase in strongly polar media. EPR and electrochemical data supporting this interpretation have been collected.

In-vitro studies of two 5-nitroimidazole derivatives.

This paper reports the findings obtained using two new compounds belonging to the 5-nitroimidazole family: sulphuridazole (V1) and sulphonidazole (V2). We first assessed their antimicrobial activity on Clostridia spp. and then extended the study to Gram-positive and Gram-negative aerobic microorganisms and to Candida albicans. Their MICs were compared with those of metronidazole. The findings show that the antibacterial and antimycotic activity of sulphonidazole is greater than that of sulphuridazole, while metronidazole is not active against any aerobic organism. It also emerges that the NO2 group is indispensable for all the microorganisms assayed and that sulphuridazole and sulphonidazole are the first two 5-nitroimidazoles active against C. albicans. The redox potentials of the 5-nitroimidozoles studied suggest that their action mechanism is mainly based on redox processes.