Silvia Cauteruccio

Phosphathiahelicenes: Synthesis and Uses in Enantioselective Gold Catalysis

Enantiomerically pure thiahelicenes displaying a terminal phosphole unit and a stereogenic phosphorus center have been prepared by oxidative photocyclization of a diaryl-olefin precursor. Starting from one of these phosphathiahelicene oxides, the corresponding trivalent phosphine-Au(I) complex is obtained with complete diastereoselectivity. It affords a new, excellent precatalyst for the enantioselective cycloisomerization of N-tethered enynes (up to 96 % ee).

Gold(I) complexes of tetrathiaheterohelicene phosphanes.

New tetrathia[7]helicene-based (7-TH-based) gold(I) complexes 6 and 7 have been readily prepared by reaction of the respective phosphine ligands 2 and 3 with Au(tht)Cl in a 1:1 and 1:2 molar ratio, respectively. These complexes have been fully characterized by analytical and spectroscopic techniques as well as quantum chemical calculations. The molecular structure of dinuclear complex 7 has been determined by single-crystal X-ray diffraction, showing a gold-gold interaction of 3.1825(3) Å and a significant contraction of the 7-TH total dihedral angle. Au(I) complex 7 displays luminescence emission at room and low temperature in diluted solution and in the solid state. Quantum chemical calculations show that the luminescence emission at room temperature is primarily due to slightly perturbed fluorescence emission from purely ππ* excited states of the conjugated helicene scaffold. At 77 K phosphorescence emission is displayed as well. Preliminary studies on the use of 6 and 7 as catalysts in typical Au(I)-catalyzed cycloisomerizations have demonstrated the reactivity of these systems in the intramolecular allene hydroarylations and the hydroxycarboxylation of allene-carboxylates.

Superparamagnetic iron oxide nanoparticles functionalized by peptide nucleic acids

A novel efficient method has been developed for covalently linking Peptide Nucleic Acid (PNA) oligomers and superparamagnetic iron oxide nanoparticles (SPION), to produce water soluble hybrid nanomaterials that can act as MRI contrast agents, as hyperthermia promoters and as PNA carriers. The multistep procedure involves: (i) preparation of oleate-stabilized SPION by using the thermal decomposition method, to control the size of the magnetic core (here 17 ± 2 nm, by TEM measurement); (ii) exchange of the oleate layer by dimercaptosuccinic acid (DMSA), to impart water solubility and to provide functional groups for PNA grafting; (iii) functionalization of a PNA oligomer with a terminal maleimide moiety, to allow SPION–PNA conjugation by thiol-maleimide Michael addition reaction, exploiting the SH groups of DMSA on the SPION surface. The method was tested using a model PNA decamer containing all four nucleobases (–CTAGATCACT–). SPION–PNA conjugation by SH addition was found more efficient than conjugation through amide bond between the COOH groups of DMSA and the terminal NH2 groups of PNA. Elemental analysis, UV-Vis and IR spectra, and ζ-potential measures confirmed the PNA binding (a loading of ca. 400 PNA strands per SPION was estimated, molar ratio ca. 1 : 15 with respect to DMSA). A detailed characterization of the morphology, relaxivity and magnetic properties of the SPION used for PNA binding is reported, and compared to the one relative to the SPION–PNA conjugate. The analysis of the magnetic behaviour showed that the nanoparticles are in the superparamagnetic regime at room temperature, and have a considerably high saturation magnetization (85 emu g−1). Magnetic hyperthermia measurements gave a remarkable value of the heat released (SAR = 65 W g−1), which makes these SPION suitable for magnetic hyperthermia treatments. The SPION were also able to effectively shorten both longitudinal and transverse relaxation times of water, with r1 and r2 values higher with respect to routinely used commercial contrast agents, at the typical fields of clinical instrumentation.

Chiral Thiahelicene-Based Alkyl Phosphine–Borane Complexes: Synthesis, X-ray Characterization, and Theoretical and Experimental Investigations of Optical Properties

Chiral helical-based phosphanes are challenging and promising ligands, with a great potential for the generation of both organic and organometallic catalysts. We report here the preparation of novel chiral thiahelicene-based alkyl phosphanes, isolated and characterized as air-stable borane adducts, and the investigation of their experimental and theoretical (chir)optical properties. X-ray characterization of a mono- and a disubstituted derivative as a racemic mixture has been performed, which confirms the influence of the number and nature of substituents on the flexibility of the helix. In addition, the absolute configuration inferred from CD spectra of the two enantiomers of a diborane complex has been established from X-ray analysis. State-of-the-art quantum chemical calculations of vibrationally resolved spectra allow, for the first time, for an unambiguous assignment of the experimentally observed peaks in linear absorption and circular dichroism spectra to excited electronic states of this class of thiahelicene phosphorus derivatives.

Magnetic Iron Oxide Nanoparticle Functionalization : Isocyanate Moiety as a Suitable Monodentate Anchoring Group

A new strategy for anchoring organic molecules onto superparamagnetic iron oxide nanoparticles (SPIONs) using isocyanate containing linkers has been realized. This functional group easily and efficiently reacts with the hydroxyl residues of the nanoparticle surface, leading to the formation of a stable carbamate bond, as confirmed by means of spectroscopic and analytical data.

A non-photochemical route to synthesize simple benzo[1,2-b:4,3-b′]dithiophenes: FeCl3-mediated cyclization of dithienyl ethenes

The FeCl3-mediated cyclization of α,α′-disubstituted Z-alkenes 1 is reported as a general and non-photochemical route to synthesize benzo[1,2-b:4,3-b′]dithiophene (BDT) derivatives 2, achievable in good yields starting from cheap and easily available materials. The influence of the temperature and the nature of the substituents on the scope and limitations of this methodology is also reported.

Dirhenium Coordination Complex Endowed with an Intrinsically Chiral Helical-Shaped Diphosphine Oxide

A one-pot, multicomponent strategy was used to synthesize the first example of the dirhenium carbonyl coordination complex 2, in which the two metal atoms are connected through a chiral helical-shaped diphosphine oxide. Thanks to the flexibility of the helix of helicene 1, complex 2 was isolated in quite a good yield as a stable compound. It was characterized by analytical and spectroscopic techniques as well as by single-crystal X-ray analysis, which confirmed the chemical structure and the peculiar architecture of 2. In addition, computational studies were in agreement with the transitions observed in the experimental UV–vis spectrum, revealing the presence of two bands with maxima at about 520 (metal-to-ligand charge transfer) and 400 nm (IL).