Synthèse d'oxaphénalènes substitués en position 2 par un groupement électro-attractif

Up to now, little is known about naphtho[1,8-bc]pyran (oxaphenalene) derivatives, although some of them have been detected in the vegetable kingdom. However, very recently [6], 2-nitronaphtho[1,8-bc]pyran and 6-methoxy-2-nitronaphtho[1,8-bc]pyran proved to be powerful mutagenic agents (the most efficient on mammal cells in culture hitherto known). This fact prompted us to investigate further this class of products by studying compounds bearing an electron-withdrawing group in the 2-position. We report in the present paper that, in certain cases, this synthesis can be achieved by the yet unattempted péri-heterocyclization of 8-hydroxy-1-naphthaldehydes with an halogenated active methylene compound in acetone in the presence of potassium carbonate. Thus, among others, 2-acetyl, 2-benzoyl and (4-methoxybenzoyl)naphtho[1,8-bc]pyrans, as well as the corresponding derivatives bearing a methoxy group in the 6-position have been prepared. Nevertheless, such a condensation according to Rap [1] cannot be carried out in certain cases, particularly with acetonitrile.     

Synthesis and NMR characterization of a dioxa-analog of benzo[a]pyrene: The 1-benzopyrano[6,5,4-mna]-xanthene (1,6-dioxabenzo[a]pyrene)

1,6-Dioxabenzo[a]pyrene, the first dioxa-analog of benzo[a]pyrene, was synthesized from 5-methoxy-1-naphthol in an eight-step reaction involving two peri-heterocyclizations.     

Synthesis of novel 8-(het)aryl-6H-pyrano[4′,3′:4,5]thieno[3,2-b]pyridines by 6-endo-dig cyclization of Sonogashira products and halolactonizations with Cu salts/NXS. Preliminary antitumor evaluation

Novel 8-(het)aryl-6H-pyrano[4′,3′:4,5]thieno[3,2-b]pyridines were prepared in good to high yields by a tandem one-pot procedure of Sonogashira coupling and 6-endo-dig lactonization from 3-bromothieno[3,2-b]pyridine-2-carboxylic acid and (het)arylalkynes. Sonogashira coupling products were also prepared from the corresponding methyl ester giving in the same reaction the corresponding 6-endo-dig compounds as minor products. The Sonogashira phenyl ester product gave cyclization with electrophiles only in low to moderate yields. Nevertheless, halolactonizations using Cu(I) or (II) salts/N-halosuccinimides (NXS) from either the phenyl ester or the carboxylic acid derivatives occurred in good to high yields. The growth inhibition potential of the compounds was evaluated using human tumor cell lines, HCT-15 (colorectal adenocarcinoma) and NCI-H460 (non-small cell lung cancer) and studies of apoptosis induction were performed for the three most promising compounds in HCT-15?cells. Two of them caused almost 40% of cell death by apoptosis when tested at their 1.5?×?GI₅₀ concentrations. The tricyclic lactone with a F atom in the meta position showed to be the most promising one.     

Metal Linkage Effects on Ultrafast Energy Transfer

We report the preparation of several new porphyrin homodimers bridged by a platinum(II) ion in which very intense electronic communication through the coordination link occurs. Moreover, the synthesis of a new porphyrin dyad and its photophysical properties are reported. This dyad exhibits the fastest singlet energy transfer ever reported for synthetic systems between a zinc(II) porphyrin and a porphyrin free base. This extremely fast transfer (～100 femtoseconds) is in the same range as the fastest one measured in natural systems. This feature is due to the platinum(II) linker, which allows for strong MO couplings between the two porphyrin units as experimentally supported by electrochemistry and corroborated by DFT computations.     

Das Atomgewicht des Nebuliums

Ohne Zusammenfassung     

About some properties of new poly(phenylene vinylene) derivatives: PPV-ether and C1-4PPV-ether

Although, the presence of the substituted groups induce a difference in physical and chemical properties of the co-polymer, it does not affect its symmetry group. We deduce from IR and RRS analyses of C_1-4PPV-ether, compared to those of PPV-ether, that the geometrical structural modifications with a decrease in the planarity of the chain and the vibrational features are possibly ascribed to conformational effects. The molecular packing effect is also outlined. Moreover, the decrease of the optical gap and the higher energy shifted transition could be assigned to the different lattice relaxations and vibrational behaviors shown by this co-polymer. Added to IR, RRS and optical density results, the PL measurements prove a great delocalization of π-electron system with a red shifted emission.     

Protonation thermochemistry of alpha-aminoacids bearing a basic residue

The proton affinity, PA, and protonation entropy, Delta(p)S degree, of glycine (Gly), 1, aspartic acid (Asp), 2, asparagine (Asn), 3, histidine (His), 4, lysine (Lys), 5, glutamic acid (Glu), 6, and glutamine (Gln), 7, have been reinvestigated by the extended kinetic method, using the "isothermal point" method and the orthogonal distance regression, ODR, technique. The proton affinity values of a-aminoacids bearing a basic residue (PA = 926.8; 965.2; 996.0; 993.9; 981.8 and 988.1 kJ.mol(-1) for 2-7, respectively) show significant deviation from the tabulated values. As expected from the effect of a strong intramolecular hydrogen bond in the protonated forms of these peculiar aminoacids, negative protonation entropies are detected (Delta(p)S degree = 36; 43; 37; 29; 95 and 55 J mol(-1) K(-1) for for 27 respectively).     

The metal-nonmetal transition in NiS studied by the Mössbauer effect of 57Fe

Mössbauer spectra of ⁵⁷Fe impurities in α NiS show an abrupt collapse of the hyperfine splitting at T_t = 260 K, the nonmetal-metal transition; the extrapolated Néel point is ～420 K. Below T_t, it appears that iron adjacent to a vacancy is low-spin. There us evidence of substantial d-electrons delocalisation above T_t. β NiS does not order magnetically down to 4 K.