Vibrational spectrum of solid picene (C22H14).

Recently, Mitsuhashi et al observed superconductivity with a transition temperature up to 18 K in potassium doped picene (C(22)H(14)), a polycyclic aromatic hydrocarbon compound (Mitsuhashi et al 2010 Nature 464 76). Theoretical analysis indicates the importance of electron-phonon coupling in the superconducting mechanisms of these systems, with different emphasis on inter- and intra-molecular vibrations, depending on the approximations used. Here we present a combined experimental and ab initio study of the Raman and infrared spectrum of undoped solid picene, which allows us to unambiguously assign the vibrational modes. This combined study enables the identification of the modes which couple strongly to electrons and hence can play an important role in the superconducting properties of the doped samples.

Hydrocarbon activation. Synthesis of beta-cycloalkyl (di)nitriles through photosensitized conjugate radical addition.

Photoinduced hydrogen abstraction from aliphatic cyclic hydrocarbons (C(5) to C(7), C(12), as well as adamantane) by triplet aromatic ketones in the presence of alpha,beta-unsaturated (di)nitriles offers a straightforward entry to the corresponding alkylated (di)nitriles via the alkyl radicals. Yields are moderate to good depending on the olefins structure (substitution in beta slows down the addition to mononitriles, but with alpha,alpha-dinitriles electronic activation allows efficient alkylation also of beta,beta-disubstituted substrates). A tandem alkylation-cyclization process has been obtained with (1-methylpent-4-enylidene)malononitrile.

Photoinduced, ionic Meerwein arylation of olefins.

Irradiation of 4-chloroaniline or of its N,N-dimethyl derivative in polar solvents generates the corresponding triplet phenyl cations. These are trapped by alkenes yielding arylated products in medium to good yields. B3LYP calculations show that the triplet cation slides with negligible activation energy to a bonded adduct with ethylene, whereas it forms only a marginally stabilized CT complex with water (chosen as a representative sigma nucleophile). The structure of the final products depends on the preferred path from the adduct cation with the alkene. In the case of aryl olefins, this deprotonates to stilbene derivatives, while, from 2,3-dimethyl-2-butene and allytrimethylsilane, allylanilines are obtained by elimination of an electrofugal group in gamma. In the case of mono- and disubstituted alkenes the cation adds chloride rather than eliminating and beta-chloroalkylanilines are obtained. The regio- and sterochemistry of the addition across the alkene are best understood with a phenonium ion structure for the adduct. The nucleophile entering in beta can be varied under conditions in which the adduct cation is trapped more efficiently than the starting phenyl cation. Thus, beta-methoxyalkylanilines are formed when the irradiation is carried out in methanol. beta-Iodoalkylanilines are obtained in acetonitrile containing iodide and unsubstituted alkylanilines in the presence of sodium borohydride. A case of intramolecular nucleophilic trapping is found with 4-pentenoic acid. The reaction is a wide-scope ionic analogue of the radicalic Meerwin arylation of olefins.

Generation and reactivity of the 4-aminophenyl cation by photolysis of 4-chloroaniline.

4-Chloroaniline and its N,N-dimethyl derivative are photostable in cyclohexane but undergo efficient photoheterolysis in polar media via the triplet state and give the corresponding triplet phenyl cations. CASSCF and UB3LYP calculations show that the 4-aminophenyl triplet cation has a planar geometry and is stabilized by >10 kcal mol(-1) with respect to the slightly bent singlet. The triplet has a mixed carbene-diradical character at the divalent carbon. This species either adds to the starting substrate forming 5-chloro-2,4'-diaminodiphenyls (via an intermediate cyclohexadienyl cation) or is reduced to the aniline (via the aniline radical cation) in a ratio depending on the hydrogen-donating properties of the solvent. Transients attributable to the triplet aminophenyl cation as well as to the ensuing intermediates are detected. Chemical evidence for the generation of the phenyl cation is given by trapping via electrophilic substitution with benzene, mesitylene, and hexamethylbenzene (in the last case the main product is a 6-aryl-3-methylene-1,4-cyclohexadiene). Relative rates of electrophilic attack to benzene and to some alkenes and five-membered heterocycles are measured and span over a factor of 15 or 30 for the two cations. The triplet cation formed under these conditions is trapped by iodide more efficiently than by the best pi nucleophiles. However, in contrast to the singlet cation, it does not form ethers with alcohols, by which it is rather reduced.

Synthesis and anti-aggregatory activity of linear retro-inverso RGD peptides.

Six retro-inverso tri- and tetrapeptide analogues of RGD were prepared and their anti-aggregatory activity was determined by platelet aggregation tests in comparison with the corresponding parent peptides. An efficient method for the introduction of a malonyl-aspartic residue into a peptide chain is described for the first time. A 2-3-fold decrease in potency or total loss of bioactivity was observed with the new peptides; structure-activity relationships are discussed.

Photochemical alkylation of ketene dithioacetal S,S-dioxides. An example of captodative olefin functionalization

Radical alkylation of some ketene dithioacetal S,S-dioxides failed through the tin hydride promoted chain process but was successfully performed through stoichiometric photochemical initiation, either by electron transfer or hydrogen abstraction. In the first case, alkyl radicals were produced from tetralkylstannanes (t-Bu-, i-Pr-, n-Bu-SnR(3)) via radical cation fragmentation, while in the second case these were produced from alkanes (cyclohexane, adamantane) by benzophenone triplet. When bulky radicals (t-Bu, adamantyl) were involved, the addition occurred with complete diastereoselectivity.

[Radiological changes after mitral valvuloplasty]. / Modificazioni radiologiche dopo valvuloplastica mitralica.

The results of a radiological study carried out on a limited number of patients undergoing mitral valvuloplasty are reported. The good results achieved with this technique are confirmed objectively.