Antonio Papagni

A convenient procedure for the synthesis of tetrathia-[7]-helicene and the selective α-functionalisation of terminal thiophene ring

This paper describes a convenient preparation of tetrathia-[7]-helicene (TH[7]), the generation of the α-anion on the terminal thiophene ring, and the synthesis of the 2-formyl-tetrathia-[7]-helicene (2-CHO-TH[7]). The key intermediate trans-1,2-dibenzodithiophene-ethene, prepared in 97% yield by McMurry coupling of the 2-formyl-benzo[1,2-b;4,3-b′]dithiophene, was transformed into TH[7] using a known procedure. The described method affords TH[7] in 46% overall yield, which is more than four times the yield previously reported in the literature. The α-anion of TH[7], which is easily generated on the α-position of one of the terminal thiophene rings, reacts with electrophilic reagents such as D2O and DMF. The latter reaction proved to be the best way to prepare 2-CHO-TH[7], a key intermediate for the preparation of new substituted heterohelicenes.

Experimental study of the second-order non-linear optical properties of tetrathia-[7]-helicene

Abstract Femtosecond hyper-Rayleigh scattering (HRS) experiments as a function of amplitude modulation frequency have been performed on tetrathia-[7]-helicene. The apparent first hyperpolarizability β app ( ω ) is a decreasing function of increasing frequency ω , due to the two-photon fluorescence (2PF) contribution. We observe, however, for the first time, also a frequency-dependent HRS depolarization ratio ρ ( ω ). An accurate value for ρ is important, since it offers an indication for the symmetry of the chromophore (5, resp. 1.5, for dipoles, resp. octopoles, but also independent of frequency, since identical for HRS and 2PF). For helicoidal symmetry ρ ( ω ) is increasing for higher frequencies, in agreement with theory.

Synthesis and non-linear properties of conjugated poly-unsaturated amino carbene complexes

A series of poly-unsaturated pyrrolidino carbene complexes have been synthesized and their first β hyperpolarizabilities evaluated using the Hyper Rayleigh Scattering (HRS) technique. Some of these complexes have good to high β values (up to 543×10−30 esu). A comparison of the non-linear responses of the complexes with those of the corresponding amides (their isolobal organic analogues) highlighted the potential usefulness of the pentacarbonylchromium carbene moiety as an electron-accepting group in the design of second order non-linear optical (NLO) materials.

CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication

Phloem, a plant tissue responsible for long-distance molecular transport, harbours specific junctions, sieve areas, between the conducting cells. To date, little is known about the molecular framework related to the biogenesis of these sieve areas. Here we identify mutations at the CHER1/AtCTL1 locus of Arabidopsis thaliana. The mutations cause several phenotypic abnormalities, including reduced pore density and altered pore structure in the sieve areas associated with impaired phloem function. CHER1 encodes a member of a poorly characterized choline transporter-like protein family in plants and animals. We show that CHER1 facilitates choline transport, localizes to the trans-Golgi network, and during cytokinesis is associated with the phragmoplast. Consistent with its function in the elaboration of the sieve areas, CHER1 has a sustained, polar localization in the forming sieve plates. Our results indicate that the regulation of choline levels is crucial for phloem development and conductivity in plants.

Hyaluronic acid in hydrophilic contact lenses: spectroscopic investigation of the content and release in solution

Two experimental spectroscopic methods for the determination of the content of hyaluronic acid in solution are provided based on the formation of complexes between the hyaluronic acid and cationic dyes with sensitivity down to concentrations of either 0.25 or 2.5 microg/ml. These techniques were applied to commercial hydrophilic contact lenses and allowed (i) distinguishing among contact lenses either loaded or non-loaded with hyaluronic acid, (ii) determining, for the loaded ones, the content of hyaluronic acid, (iii) evaluating the release of hyaluronic acid by the lens in solution, and (iv) determining the role of the hyaluronic acid in preventing the adsorption and the successive release by the contact lens of other components which can be present, for example, in the conservation solutions and/or in the blisters of the lenses. The results represent new physical chemistry insights for the field of contact lenses with impact on the advancement of current technology.

Tricarbonyl(η6arene)Chromium(0) complexes as chiral auxiliaries: Asymmetric synthesis of β-aminoesters and β-lactams by Reformatsky condensation

Abstract Highly stereoselective syntheses (e.e. > 98%) of β-aminoesters and β-lactams were accomplished using enantiomerically pure tricarbonyl (η6benzaldimine)chromium complexes in a Reformatsky type reaction promoted by ultrasound. A correlation between the configuration of complexed imines and absolute configuration of β-lactam derivatives is reported.

The first chiral racemic Fischer-type aminocarbene complex bearing a C2 symmetry amine: stereochemical characteristics and application to Michael addition reactions

Abstract The synthesis of [ trans -methyl(2,6-dimethyl)morpholinocarbene]pentacarbonylchromium(0) complex ( 3 ) is reported, together with the stereoselective Michael addition of the conjugate base of complex 3 to enones.

Preparation of highly pure quaterthiophene and role of impurities on its photoluminescence properties

Highly pure quaterthiophene (4T) has been prepared from monobromobithiophene by a Ni0-mediated coupling reaction. The analysis of impurities produced by the synthetic procedure, performed by mass spectrometry and gas chromatography with a mass spectrometer detector, has allowed the identification of at least four contaminants, among them, α-bromoquaterthiophene (Br-4T). Studies of photoluminescence carried out at low temperatures (from 70 to 4 K) on 4T thin films grown by organic molecular beam deposition are demonstrated to be a powerful tool in detecting impurities that can act as traps for 4T emission. Indeed, it was possible to assign the anomalous emission observed in some 4T thin films to Br-4T. A protocol for removal of 4T contaminants is also proposed.

Amplified spontaneous emission in quaterthiophene single crystals

The authors demonstrate amplified spontaneous emission (ASE) from quaterthiophene single crystals and study its behavior at low temperature. The room temperature photoluminescence exhibits line narrowing (spectral width down to 10nm) at 553nm for excitation fluence larger than 1mJcm−2. At low temperature (10K), ASE is observed from two vibronic transitions at 510nm (0-1) and 553nm (0–2), with line narrowing down to 5A, for fluences larger than 100μJcm−2. The stimulated emission cross section is of the order of 10−15cm2, and the ASE is found to be strongly affected by thermally induced dynamic disorder. The emission stability under photopumping is also studied and discussed.

Tricarbonyl(η6arene)chromium(0) complexes as chiral auxiliaries. Homochiralβ-lactams synthesis “via” [2+2] cycloaddition reaction.

Abstract A highly enantioselective synthesis of β-lactams “via” a [2+2] cycloaddition reaction of homochiral tricarbonyl [ N -(2-methoxybenzylidene)aniline]chromium with ketenes is reported. Moreover the reaction of (+)-( 1 S)-tricarbonyl[4-methoxy- N -(2-methoxy cinnamylidene)aniline]chromium with acetoxy ketene gives the corresponding 4-styryl-β-lactam in good yield but with moderate stereoselection.