Synthèse photochimique de biaryles et hétérobiaryles à partir d'aryl-et hétéroarylamines,d'un nitrite d'alkyle et d'un substrat aromatique ou hétéroaromatique

Photochemical synthesis of biaryls and heterobiaryls from aryl and heteroarylamines, alkylnitrite and aromatic or heteromatic substrates The photochemical reaction of aromatic and heteroaromatic amines with excess t-butyl nitrite in aromatic solvents (benzene, p-xylene, mesitylene) and in hetero-aromatic solvents (furan, thiophene) leads to biaryls or heterobiaryls. t-Butyl nitrite is more convenient than isopentyl nitrite which gives by-products. This new method has been used to synthesize 28 compounds in 17 to 60% yield.     

High-stability reference setup for photoacoustic spectroscopy

2 laser at 9.676 μm. Received: 2 December 1996/Revised version: 2 April 1997     

Ultrafast excited-state dynamics of DNA fluorescent intercalators: new insight into the fluorescence enhancement mechanism

The excited-state dynamics of the DNA bisintercalator YOYO-1 and of two derivatives has been investigated using ultrafast fluorescence up-conversion and time-correlated single photon counting. The free dyes in water exist in two forms: nonaggregated dyes and intramolecular H-type aggregates, the latter form being only very weakly fluorescent because of excitonic interaction. The excited-state dynamics of the nonaggregated dyes is dominated by a nonradiative decay with a time constant of the order of 5 ps associated with large amplitude motion around the monomethine bridge of the cyanine chromophores. The strong fluorescence enhancement observed upon binding of the dyes to DNA is due to both the inhibition of this nonradiative deactivation of the nonaggregated dyes and the dissociation of the aggregates and thus to the disruption of the excitonic interaction. However, the interaction between the two chromophoric moieties in DNA is sufficient to enable ultrafast hopping of the excitation energy as revealed by the decay of the fluorescence anisotropy. Finally, these dyes act as solvation probes since a dynamic fluorescence Stokes shift was observed both in bulk water and in DNA. Very similar time scales were found in bulk water and in DNA.     

The photochemical behaviour of bis aryl-1,3 triazenes

The photolysis of bis aryl-1,3 triazenes carried out in non-aromatic solvents gives products whose structures are consistent with a cage recombination process of homolytically formed radicals and the subsequent abstraction of hydrogen from the solvent molecules by these arylamino radicals.In aromatic solvents, a free-radical chain process leads to the formation of products resulting from the homolytic substitution on the solvent.     

Photodynamic activities of silicon phthalocyanines against achromic M6 melanoma cells and healthy human melanocytes and keratinocytes

Dichlorosilicon phthalocyanine (Cl2SiPc) and bis(tri-n-hexylsiloxy) silicon phthalocyanine (HexSiPc) have been evaluated in vitro as potential photosensitizers for photodynamic therapy (PDT) against the human amelanotic melanoma cell line M6. Each photosensitizer is dissolved in a solvent-PBS mixture, or entrapped in egg-yolk lecithin liposomes or in Cremophor EL micelles. The cells are incubated for 1 h with the sensitizer and then irradiated for 20 min, 1 h or 2 h (lambda > 480 nm, 10 mW cm-2). The photocytotoxic effect is dependent on the photosensitizer concentration and the light dose. Higher phototoxicity is observed after an irradiation of 2 h: treatment with a solution of photosensitizer (2 x 10(-9) M) leads to 10% (HexSiPc in egg-yolk lecithin liposomes) or 20% (Cl2SiPc in DMF-PBS solution) cell viability. After 1 h incubation and 20 min of light exposure, the photodynamic effect is connected with the type of delivery system used. For HexSiPc, lower cell viability is found when this photosensitizer is entrapped in egg-yolk lecithin instead of solvent-PBS or for Cremophor EL micelles with Cl2SiPc. Liposome-delivered HexSiPc leads to lipid damage in M6 cells, illustrated by an increase of thiobarbituric acid-reacting substances (TBARs), but the change is not significant with Cremophor EL. The same is observed for the antioxidative defences after photodynamic stress. The cells irradiated with HexSiPc entrapped in liposomes display an increase of superoxide dismutase (SOD) activity and a decrease of glutathione (GSH) level, glutathione peroxidase (GSHPx) and catalase (Cat) activities.     

Meromorphic Parametric Non-Integrability;?the Inverse Square Potential

We let H(X,Y,α) be a Hamiltonian depending meromorphically on positions X, inertial momenta Y and parameters α. In Theorem 1 we give conditions for the “meromorphic parametric” non-integrability of H. Theorem 2 proves the meromorphic non-integrability of the 4-body problem on a line with given masses (1,m,m,1) with m≠ 1, and of the 3-body problem in ℝ ^p with p≥ 2 and given masses (1,1,m), for the inverse square potential. Those are the simplest cases left open after the integrability results of Jacobi (3 bodies on a line with arbitrary masses) and Calogero-Moser (n bodies on a line with equal masses). Taking the masses as parameters and using both Theorems 1 and 2, we prove Theorem 3, which shows meromorphic parametric non-integrability results for the inverse square potential. Accepted: August 18, 1999